JP2882230B2 - Air-fuel ratio control device for lean burn engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control device for a lean burn engine.

[0002]

2. Description of the Related Art The following conditions are used for controlling fuel supplied to an engine: (a) cooling water temperature is 80 ° C. or higher; (a) throttle valve opening is a predetermined value or less; When all of the above conditions are satisfied, feedback correction to the stoichiometric air-fuel ratio is stopped, and the air-fuel ratio is switched to the target air-fuel ratio on the lean side (see JP-A-63-50641). In the lean air-fuel ratio, the same torque is generated as the stoichiometric air-fuel ratio, but the air flow increases and the pumping loss decreases, and the specific heat ratio of the combustion gas increases. It improves.

In this apparatus, the auxiliary air flow rate is increased at the time of switching to the lean air-fuel ratio so that the torque does not change before and after the switching of the air-fuel ratio. Therefore, as shown in FIG. 21 is provided with a flow control valve 22 capable of duty control.
Then, the on-duty Bα0 given to the control valve, Bα0 = AAC _TW + AAC _ABV + AAC _FB ... where AAC _TW ; basic characteristic value according to cooling water temperature AAC _ABV ; deceleration air increase AAC _FB ; feedback correction Flow area ABα0 of control valve 22
32 is obtained from the target air-fuel ratio KMR with reference to a table containing the contents of FIG. 32, and the required correction area ABα1 of the control valve 22 is calculated from these values as follows: ABα1 = ABα0 + (Aα + ABα0) × KBA where Aα It is determined by the flow path area of the throttle valve.

Now, when the throttle valve opening is equal, the target air-fuel ratio on the lean side (for example, 2
0) (when the water temperature is substantially the same before and after the switching for the sake of simplicity), the difference between the air correction factors before and after the switching at the time of switching is multiplied by the total flow area (Aα + ABα0). The control valve 22 is opened further, thereby trying to prevent a decrease in torque when the air-fuel ratio is made lean.

On the other hand, in the injector 23 located immediately upstream of the throttle valve 5, Qcyl = Qa / N... Tp = Qcyl / KMR... Qa; intake air flow rate measured by an air flow meter N; engine speed Qcyl The basic injection pulse width Tp equivalent to cylinder intake is calculated from the intake air flow rate per unit rotation KMR; the target air-fuel ratio. From this, Ti = Tp × α × K _ACC + Ts..., Where α: Air-fuel ratio feedback correction coefficient K _ACC ; The fuel injection pulse width Ti calculated by the transient correction coefficient Ts; invalid pulse width is given.

Here, the target air-fuel ratio KMR in the equation is: KMR = K _TW × (NKMR × n + KMR × (1-n)) where K _TW ; water temperature increase correction coefficient n; time constant equivalent value (less than 1) NKMR; calculated from the map value of the target air-fuel ratio obtained from N and Tp. When switching from the stoichiometric air-fuel ratio to the lean air-fuel ratio, the target air-fuel ratio KMR changes with a first-order delay as shown in FIG. The reason why the target air-fuel ratio is given with the first-order lag is to smooth the change of the air-fuel ratio at the time of switching and reduce the torque shock at the time of switching.

However, the actual air-fuel ratio is further delayed from the solid target air-fuel ratio KMR as shown by the dashed line in FIG. 33 when switching to the lean air-fuel ratio.
By calculating the required correction area ABα1 from the equation
The air increase is too fast, and the difference causes a temporary increase in torque before and after switching. This is because even if the auxiliary air flow rate is responsively increased in accordance with the target air-fuel ratio, the wall flow fuel amount does not immediately decrease to an equilibrium value. This is because a mixture richer than the target is inhaled until the value is settled.

Therefore, in order to provide a response delay even when the auxiliary air flow rate is increased so that the wall flow fuel amount and the auxiliary air flow rate are supplied in phase, | NKBA-KBA _OLD |
H is compared, and when | NKBA−KBA _OLD |> LH, KBA = NKBA × n1 + KBA _OLD × (1-n1) where NKBA; map value of the air correction factor obtained from KMR KBA _OLD ; previous KBA n1 ; NKBA−KBA _OLD | ≦ LH, KBA = NKBA × n2 + KBA _OLD × (1-n2) where n2: Time constant equivalent value (n2 <n1) ) Is used to determine the air correction factor KBA.

When the target air-fuel ratio KMR changes suddenly, the change of the actual air-fuel ratio does not become a delay waveform having a fixed time constant, but the change is fast in the initial stage and slow in the latter stage. NKBA-KBA _OLD |, depending on the value) by changing the degree of delay, it is possible to suppress the torque step before and after switching as a dashed line in FIG. 33 into smaller ones.

[0010]

By the way, in order to suppress NOx which frequently occurs during the switching of the air-fuel ratio, the switching of the air-fuel ratio must be made faster. Theoretical air-fuel ratio ($ 1
In 4.5), NOx emissions are suppressed by the three-way catalyst,
Also, when the air-fuel ratio becomes lean (for example, 22), N
This is because NOx is emitted most at an air-fuel ratio in the middle of switching, such as 17 to 18, because the amount of Ox emission is small.

However, when switching to the lean target air-fuel ratio is performed in a region where the intake air flow rate is large, even if the differential pressure across the control valve 22 is small or if it is desired to increase the auxiliary air flow rate, Since it is not possible to increase the flow rate beyond the maximum flow rate of the control valve 22, even if the switching speed of the target air-fuel ratio is increased, a torque level difference actually occurs due to insufficient increase in the auxiliary air flow rate.

In order to eliminate the influence of the torque step on the driving performance, the switching speed of the air-fuel ratio may be reduced. However, in such a case, the emission of NOx during the switching of the air-fuel ratio cannot be suppressed.

It is conceivable to increase the maximum flow rate of the control valve 22 in order to speed up the switching of the air-fuel ratio.
When a large control valve flow rate is used, on the other hand, when the control valve 22 is shared for idle speed control, it becomes difficult to finely adjust the control valve flow rate in idle speed control. Doing so is not an appropriate measure.

Therefore, the present invention increases the switching speed of the air-fuel ratio until the calculation result of the auxiliary air flow rate exceeds the maximum flow rate of the control valve, and reduces the switching speed after the calculation result exceeds the maximum flow rate. It is an object to suppress the emission of NOx during the switching of the air-fuel ratio in the flow rate range.

[0015]

According to a first aspect of the present invention, as shown in FIG. 1, means 31 for judging whether or not an operating condition signal is a lean condition is provided. Means 32 for calculating the target air-fuel ratio according to the operating condition signal when a condition other than the lean condition is satisfied, and a target air-fuel ratio corresponding to the condition other than the lean condition. Means 33 for calculating the switching speed, means 34 for calculating the basic injection amount from the switching speed of the target air-fuel ratio and the operating condition signal, and device 35 for supplying the fuel calculated based on the basic injection amount to the intake pipe 35 An air control valve 37 that adjusts an auxiliary air flow rate that bypasses the intake throttle valve 36; and a switchover of the target air-fuel ratio (that is, a target air-fuel ratio according to the lean condition and an airflow control according to conditions other than the lean condition). Means 38 for calculating the amount of increase in the auxiliary air flow rate using the target air-fuel ratio switching speed and the operating condition signal so that the torque becomes the same before and after the switching (at the time of switching to the air-fuel ratio); Means 39 for driving the air control valve 37 in accordance with the increased amount; means 40 for determining whether or not the auxiliary air flow rate exceeds the maximum flow rate of the air control valve 37; Means 41 are provided for setting the switching speed of the target air-fuel ratio high until the maximum flow rate of the control valve 37 is exceeded, and for decreasing the switching speed of the target air-fuel ratio when the maximum flow rate is exceeded.

According to a second aspect of the present invention, as shown in FIG. 34, means 3 for determining whether the operating condition signal is a lean condition or not.
A means for calculating a target air-fuel ratio according to the lean condition from the determination result, and a target air-fuel ratio according to the condition other than the lean condition when a condition other than the lean condition is satisfied. 32, means 33 for calculating the air-fuel ratio switching speed until switching to the target air-fuel ratio, means 34 for calculating the basic injection amount from the target air-fuel ratio switching speed and the operating condition signal, A device 35 for supplying the calculated fuel to the intake pipe, an air control valve 51 for reducing the intake according to the control amount without mechanically interlocking with the accelerator pedal, and before and after switching when the target air-fuel ratio is switched. Means 52 for calculating the amount of change in the intake air flow rate using the target air-fuel ratio switching speed and the operating condition signal so that the torque is the same; Means 53 for driving 51; means 54 for determining whether or not the intake air flow rate exceeds the maximum flow rate of the air control valve 51; and, based on the determination result, the intake air flow rate exceeds the maximum flow rate for the air control valve 51. Means 55 for setting the switching speed of the target air-fuel ratio fast until the maximum flow rate is exceeded, and setting the switching speed of the target air-fuel ratio low when the flow rate exceeds the maximum flow rate.

[0017]

When switching to the target air-fuel ratio on the lean side is performed in the high intake air flow rate range, the differential pressure before and after the air control valve is small, and even if it is desired to increase the auxiliary air flow rate, the maximum value of the air control valve can be maintained. Since the flow rate cannot be increased beyond the flow rate, even if the switching speed of the target air-fuel ratio is uniformly increased, a torque step may actually occur due to insufficient increase in the auxiliary air flow rate.

On the other hand, in the first invention, it is determined whether or not the auxiliary air flow exceeds the maximum flow of the air control valve.
If the switching speed of the target air-fuel ratio is reduced only when the maximum flow rate is exceeded, and the switching speed of the target air-fuel ratio is increased at other times, even if the air-fuel ratio is switched in the high intake air flow rate range, the target air-fuel ratio will be increased halfway. Is switched, so that the air-fuel ratio in the middle of the switching can be reduced for a short period of time, and NOx
Emissions are reduced. A second aspect of the present invention is directed to a configuration in which, instead of an intake throttle valve mechanically linked to an accelerator pedal, an air control valve that is not linked mechanically to an accelerator pedal but throttles intake according to a control amount is provided. In the present invention, similarly to the first invention, the emission of NOx during switching of the target air-fuel ratio is suppressed.

[0019]

In FIG. 2, air sucked from an air cleaner 11 is temporarily stored in a collector portion 12a having a fixed volume, and then flows into a cylinder of each cylinder via a branch pipe. An injector 3 is provided in an intake port 12b of each cylinder, and fuel is intermittently injected from the injector 3 in synchronization with engine rotation.

When a certain condition is satisfied, the air-fuel ratio target value is switched from the stoichiometric air-fuel ratio to the lean air-fuel ratio. At this time, the auxiliary air flow rate is increased (when the air-fuel ratio is switched to the stoichiometric air-fuel ratio, the auxiliary air flow is reduced). ), The torque is controlled so that the torque is the same before and after the switching.

For this reason, a flow control valve 22 having a relatively large flow rate is provided in the auxiliary air passage 21 which bypasses the intake throttle valve 5. The control valve 22 is of a proportional solenoid type, and as the on-duty from the control unit 2 (the ON time ratio in a certain cycle) increases, the flow rate of auxiliary air flowing through the passage 21 increases.

The reason why the control valve 22 has a relatively large flow rate is to ensure that the torque control at the time of switching the fuel-air ratio is performed with a margin and reliably. However, when the control valve flow rate is increased, a torque exceeding the driver's request may be generated due to a malfunction of the control valve 22, so that a fail-safe function is provided as described later. The control valve 22 is commonly used for idling speed control as well.

In order to suppress CO and HC which increase due to combustion instability in the lean air-fuel ratio range, the intake port 12b is provided so that swirl is given to the intake air flowing into the combustion chamber.
, A swirl control valve 13 partially provided with a notch (not shown) is provided. By setting the swirl control valve 13 to the fully closed position in the lean air-fuel ratio range and restricting the intake air, the flow velocity of the intake air is increased to generate swirl in the combustion chamber. Exhaust pipe 1 in stoichiometric air-fuel ratio range
NOx is purified by the three-way catalyst 19 provided in the fuel cell 8.

In order to control the amount of fuel supplied from the injector 3 and the amount of auxiliary air flowing through the flow control valve 22, the control unit 2 sends signals from various sensors for detecting engine operating conditions required for control. Is entered. Reference numeral 4 denotes a hot-wire type air flow meter for detecting the flow rate of air sucked from the air cleaner 11, reference numeral 6 denotes a throttle sensor for detecting the opening of the intake throttle valve 5, reference numeral 7 denotes a signal for each unit crank angle and a ref signal (reference for crank angle). 8 is a water temperature sensor, and 9 is a wide-range air-fuel ratio sensor capable of widely detecting an actual air-fuel ratio from a stoichiometric air-fuel ratio to a lean air-fuel ratio.

When switching to the lean target air-fuel ratio is performed in the high intake air flow rate range, the control valve 22 does not need to have a small differential pressure across the control valve 22 or to increase the auxiliary air flow rate. Since it cannot be increased beyond the maximum flow rate of
Even if the switching speed of the target air-fuel ratio is increased, a torque step actually occurs due to insufficient increase of the auxiliary air flow rate. In order to eliminate the influence on the operability due to the torque step, the switching speed of the air-fuel ratio should be reduced, but in such a case,
The emission of NOx during switching of the air-fuel ratio cannot be suppressed.

In order to cope with this, in this example, the switching speed of the target air-fuel ratio is changed until the calculation result of the control valve passage area that determines the increase amount of the auxiliary air flow exceeds the control valve passage area at the maximum flow rate. If the speed is increased and the control valve flow area at the maximum flow rate is exceeded, the switching speed of the target air-fuel ratio is set to be slow.
Before describing this, the overall control will be described using the flowcharts shown in FIGS. 3 to 29 and the characteristic diagrams showing the contents of tables and maps used for this control.
, Flow rate control, <2> setting of target air-fuel ratio, and <3> injection amount control.

Considering that the fuel control is performed with the aim of the target air-fuel ratio, and finally the supplied fuel amount is obtained from the detected value of the air flow, (air flow) × (fuel-air ratio) = (supply Since the relationship (fuel amount) holds, the fuel-air ratio is easier to handle than the air-fuel ratio.

<1> Flow control of control valve 22 <1-1> Relationship with idle speed control As shown in FIG. 15, the torque control duty Tcvdty is set separately from the on-duty ISCONP for idle speed control. Calculation (Step 7 in FIG. 15)
2) When the closed condition of the idle speed control is not satisfied, the torque control duty Tcv is substituted for ISCONP.
dty is output (steps 73 and 74 in FIG. 15).

Here, the on-duty ISCONP for controlling the idle speed is, for example, ISCONP = Areg + ISCi + ISCp + ISCtr + ISCat + ISCa + ISCrfn (1) where Areg; warm-up duty (corresponding to air regulator) ISCi; Differential amount of correction ISCtr; Air increase at deceleration (equivalent to dashpot) ISCat; N / D range correction of A / T car (large in D range) ISCa; Correction when air conditioner is ON ISCrfn; Radiator fan ON (Step 71 in FIG. 15).

The warm-up duty Ar of the equation (1)
For the first time after starting the engine, the value (table value) obtained by referring to the table according to the cooling water temperature at that time is used as it is in the Areg as a variable, and thereafter used at a constant cycle (for example, every 1 sec). To compare the table value corresponding to the cooling water temperature with the previous value to increase or decrease the value of Areg (for example, Table value> Are by previous Areg
g = Areg + 1, table value <Ar in previous Areg
eg = Areg-1) A value that works until the warm-up is completed. For this reason, no air regulator is provided in the intake pipe. A
Values other than reg are the same as in the prior art.

<1-2> Torque Control Duty Tcvdty This is calculated by a subroutine as shown in FIGS.

First, the throttle valve passage area Atvo is referred to from the throttle valve opening TVO with reference to the table containing FIG. 18, and the basic duty Iscdt to be given to the control valve 22 is referred to with the table containing FIG. Control valve flow area A
isc0 is obtained, and the sum of these is entered into the variable Aa0 as the basic channel area (steps 81 and 82 in FIG. 16). In addition, since all table references (also for map references) are provided with interpolation calculations, they are hereinafter simply referred to as table references (map references).

Here, the basic duty Iscdt is: Iscdt = (Iscdty−Tcvofs) × Tcvgin (2) where Iscdty; reduction basic duty Tcvofs; control valve rise duty Tcvgin; duty correction rate.

The basic reduction duty Iscdt of the formula (2)
y is the feedback correction amount ISCcl (= ISCi + I) held at the end of the previous feedback correction condition.
SCp) is corrected for weight loss, and Iscdty = ISCcl × Gistv (21) where Gistv: weight loss correction rate (0 or more and 1 or less). This reduction correction reduces the maximum flow rate of the control valve 22 by enlarging the range in which the control valve 22 can be moved for torque control at the time of switching the air-fuel ratio, and performs a feedback correction that performs a minute flow control aiming at a target value. This is because the valve accuracy under the condition is not reduced.

The control valve rise duty Tc of the equation (2)
The vofs and the duty correction rate Tcvgin are corrections when the battery voltage drops, and will be described later.

From the basic flow passage area Aa0, the equilibrium required area Tatcvh of the control valve is calculated as follows: Tatcvh = Aa0 × Kqh0 × (1 / (Dml × LTCGIN #) − 1) (3) where Kqh0: differential pressure correction rate LTCGIN # The torque control gain Dml is obtained from the ramp response value of the target fuel-air ratio (step 84 in FIG. 16).

To make the formula (3) easier to understand, Tatcvh = Aa0 × (1 / Tdml-1) (3-1) where Tdml is a map value of the target fuel-air ratio. Is an expression similar to the second term of the expression.

In the equation (3-1), (1 / Tdml-
Since 1) is equivalent to the air-fuel ratio difference from the stoichiometric air-fuel ratio, a value obtained by multiplying the air-fuel ratio by Aa0 as the total flow area indicates an increasing area (a decreasing area when switching to the stoichiometric air-fuel ratio). It is.

For example, at the stoichiometric air-fuel ratio (14.5), the target fuel-air ratio map value Tdml is 1, and the air-fuel ratio is 20 on the lean side.
And Tdml is a value such as approximately 0.66. Note that T
The reason that dml is 1 or 0.66 is that the fuel-air ratio (target fuel-air ratio) is not the reciprocal of the air-fuel ratio itself, but a relative value that sets the theoretical fuel-air ratio to 1, as described later. Because it is.

Here, if Tdml in equation (3-1) is set to 1, Tatcvh = 0, and if Tdml is set to 0.66, Tatcvh = 1 / 0.66-1 ≒ 0.52, and (0. 52-0) × Aa0 is the increased area when switching from the stoichiometric air-fuel ratio to the lean air-fuel ratio.

Returning to the equation (3), the differential pressure correction rate Kqh0 is
Throttle valve 5 and control valve 2 as the load increases with the same flow passage area
Since the pressure difference between before and after 2 becomes small and the flow rate becomes small, the correction is performed to make the flow rate the same even if the pressure difference between before and after is different.
For this reason, the difference from Qh0 as a load (which is a known linearized flow rate and is determined from the throttle valve opening TVO, the engine speed N, and the cylinder volume V) is referred to by referring to the table shown in FIG. Pressure correction rate Kqh
0 is obtained (step 83 in FIG. 16). The torque control gain LTCGIN # in the equation (3) is a value required for matching.

The upper limit of the required equilibrium area Tatcvh is determined by subtracting the control valve flow area Aisc0 from the flow area TCVMAX # of the control valve 22 at the maximum flow rate (TCC).
VMAX # -Aisc0) (step 85 in FIG. 16). This is because the value of Aisc0 is a value that has already been used in idle speed control, and the remainder obtained by subtracting this value is in a range in which the control valve 22 can be moved for torque control during air-fuel ratio switching.

Tatcvh> TCVMAX # -Aisc
When it reaches 0 (that is, when it reaches the upper limit), FA
It is assumed that ACOF = 1 (steps 86 and 88 in FIG. 16).
This flag FAACOF is a flag for changing the switching speed of the target air-fuel ratio, which will be described later.

For the required equilibrium area Tatcvh, Tatcv0 = Tatcvo + (Tatcvh-Tatcvo) × Tcvtc (4) where Tatcvo; the previous value of Tatcvh Tcvtc; The advance compensation area is obtained by the following equation (Step 91 in FIG. 16). When the intake pipe volume downstream of the control valve 22 is large in the MPI method, the air delay in the intake pipe is relatively larger than the fuel delay, so that the air is advanced in accordance with the responsive fuel. That is, the phases of both the air flow rate and the fuel supply to the cylinder are matched.

In the SPI system, when the intake pipe volume downstream of the control valve is small, the fuel flows into the cylinder with a delay later than the air. Therefore, the flow of air into the cylinder is delayed in accordance with the fuel. Tatcv0 _n-1 + (Tatcvh-Tatcv0 _n-1 ) × Tcvtc (5) where Tatcv0 _n-1 ; the previous value of Tatcv0 Tcvtc; a delay compensation time constant equivalent value (a value less than 1), and a first-order lag equation. (Step 92 in FIG. 16), the phase of supply of air and fuel to the cylinder is made to coincide.

The flow charts of FIGS.
In order to be able to share the two types of engines, i.e., the engine having a large intake pipe volume in the I system and the engine having a small intake pipe volume in the SPI system, it is determined whether Tcvtc ≧ 1.0. When it is 0, it is determined that the engine has a large intake pipe volume, and the above equation (4) is calculated as follows:
If Tcvtc <1.0, equation (5) is adopted (steps 90 and 91 and step 9 in FIG. 16).
0,92).

The lead compensation or delay compensation time constant equivalent value Tcvtc in the equations (4) and (5) is obtained from the engine speed N with reference to a table containing FIG. 21 (step 89 in FIG. 16). FIG. 21 shows characteristics of both a large intake pipe volume and a small intake pipe volume, but the engine shown in FIG. 2 does not need the characteristic of a small intake pipe volume. The lead compensation or lag compensation area Tat thus obtained
From cv0, the required correction area Tatcv is obtained from Tatcv = Tatcv0n _-DLYIS + Aisc0 + Aokuri (6) where Aokuri; postponed (step 93 in FIG. 17).

Here, the required correction area Tatcv has a lower limit of 0 and an upper limit of the required flow area TCVMAX # when the control valve has the maximum flow rate.
And a value obtained by adding a margin MXOS # for advance compensation (TC
VMAX # + MXOS #). Due to this limitation, these limits are set to the required correction area T in the equation (6).
atcv may protrude. In order to reflect the protruding portion in the next time (after 10 ms), if Tatcv <0, the value of Tatcv that underflows is put into the variable Aokuri as a postponed portion (step 94, FIG. 17).
95), also when Tatcv> TCVMAX # + MXOS #, the overflow value of Tatcv− (TCVMAX # + MXOS #) is put into the variable Aokuri as a postponement (steps 96 and 97 in FIG. 17). This Aoku
The value of ri is calculated next time by using the equation (6) to obtain the required correction area Ta.
It is used when calculating tcv.

Tatcv0 _{n-DLYIS in the} equation (6) is a _value of the lead compensation or delay compensation area Tatcv0 a predetermined number of times (for example, DLYIS #). This takes into account the dead time from when the valve opening signal is sent to the injector 3 to when the injector 3 actually starts to open.

The required correction area Tatcv is converted into an on-duty Dtytc with reference to the table containing FIG. 22 (step 99 in FIG. 17), and the torque control duty Tcvdty is calculated as Tcvdty = Dtytc / Tcvgin + Tcvovs (7) where Tcvgin Duty correction rate Tcvofs; Calculate based on control valve rise duty (Steps 100 and 101 in FIG. 17).
This expression is equivalent to the expression (2) obtained with respect to Iscdty.

The control valve rise duty Tc of the equation (7)
Until the on-duty reaches a certain value, vofs is obtained by referring to the table containing FIG. 24 from the battery voltage Vb because the control valve 22 does not substantially operate as shown in FIG. As shown in FIG. 25, in the proportional solenoid type control valve 22, it is considered that the control valve rise duty Tcvofs increases as the battery voltage Vb decreases.

The duty correction rate Tcvgin is shown in FIG.
Is obtained by referring to a table containing This is shown in FIG.
In the flow characteristic of the control valve 22 of No. 5, since the slope of the straight line rising obliquely becomes smaller as the battery voltage Vb decreases, the correction is performed to make the control valve flow the same even when the battery voltage Vb decreases.

<2> Setting of target fuel-air ratio The target fuel-air ratio is calculated from a map value Tdml → a ramp response value Dml →
It is determined in the order of the damper value Kmr.

<2-1> Map Value Tdml of Target Fuel-Air Ratio As shown in FIG. 6, if the condition is lean, the target fuel-air ratio MDMLL is calculated by referring to the lean map shown in FIG.
If the condition is not the lean condition, the target fuel-air ratio MDMLS is obtained by referring to the non-lean map of FIG. 8 (steps 31, 32, 31 and 33 of FIG. 6). Put in Tdml (step 34 in FIG. 6).

Here, the MDM which becomes the target fuel-air ratio map value
The values of LL and MDMLS are not the values of the fuel-air ratio itself as shown in FIGS. 7 and 8, but are relative values with the stoichiometric fuel-air ratio being 1.0.

<2-2> Ramp Response Value Dml of Target Fuel-Air Ratio As the name implies, the waveform of the ramp response value Dml is, as shown in FIG. Specifically, as shown in FIG. 9, if the change speed of the fuel-air ratio in the lean direction is Dmll and the change speed of the fuel-air ratio in the rich direction is Dmlr, as shown in FIG. (Previous Dml) and T
Since the comparison in dml indicates which direction the change is, if Dmlold <Tdml, it is determined that the switching is to the rich direction, and Tdml and (Dmlold + D
mlr) into Dml and vice versa
When old ≧ Tdml, it is determined that the switching is in the lean direction, and the larger one of Tdml and (Dmlold−Dmll) is put in Dml (steps 44 and 4 in FIG. 9).
5, steps 44 and 46), and a ramp response value (variable speed response value) is obtained. Considering NOx, the degree of activity of the catalyst is better when switching from the stoichiometric air-fuel ratio to the lean air-fuel ratio, so that Dmll can be smaller than Dmlr.

On the other hand, if any of the following conditions is satisfied: (a) the start switch is ON, and (a) when Tdml ≧ upper limit value TDMLR #, Dml = Tdml (steps 41 and 42 in FIG. 9). , 43).

The ramp response value Dml is obtained in synchronization with the engine rotation (in synchronization with the ref signal). The reason for the determination in synchronization with the engine rotation is that the exhaust performance changes in synchronization with the engine rotation.

<2-3> Damper value Kmr of target fuel-air ratio As shown in FIG. 12, for the lamp response value Dml, Dmlo = Dml × Fbyatc + Dmlon _-1 × (1-Fbyatc) (9) , Fbyatc; a delay time constant equivalent value (a value less than 1) to add a first-order delay (step 65 in FIG. 12).

This is because when the volume of the intake pipe downstream of the control valve is large in the MPI system, the fuel supply is performed according to the equation (9) in accordance with the increase in the auxiliary air flow rate with a delay from the control valve 22 to the cylinder. By delaying the delay (if the target air-fuel ratio is delayed by the equation (9), the supply of fuel will eventually be delayed), the phases of the supply of fuel and air to the cylinders at the time of switching the air-fuel ratio are matched. Therefore,
The equation (9) is equivalent to the equation of the conventional example in that it is an averaging process (the equation of the conventional example is equivalent to FIGS. 9 and 10 of the present invention aiming at smoothing the torque change). .

As the damper value Dmlo of the equation (9), the value up to three times before is stored, and the damper value Dmlo is stored a predetermined number of times before (eg, DLYF).
The value of (BA # times before) is entered in the variable Kmr (step 66 in FIG. 12). The value before DLYFBA # times is shown in FIG.
As shown in FIG. 4, the delay of the control valve 22 (dead time)
Is considered.

However, if any of the following conditions are satisfied: <a> Start switch is ON, <A>Dml> 1.0, <C> | ΔTVO | ≧ predetermined value DTVOTR # Does not perform the delay processing (steps 61, 62, 63, 67 in FIG. 12).

The delay time constant equivalent value Fbyatc in equation (9)
Is obtained by referring to the large intake pipe volume in the table having the contents shown in FIG. 13 (step 64 in FIG. 12). The delay of the increase or decrease of the air flow rate at the time of switching the air-fuel ratio increases as the engine speed N decreases.
3, the value of Fbyatc is set (for an engine having a small intake pipe volume only in a low rotation range).

FIG. 13 also shows the characteristics of a small intake pipe volume downstream of the control valve in a superimposed manner. In an SPI type engine having a small intake pipe volume downstream of the control valve, air responds better than fuel. Fbyatc = 1.0 because it is good and there is no need to delay the fuel. That is, FIG.
FIG. 1 becomes unnecessary according to the size of the intake pipe volume downstream of the control valve of the engine in which the table containing the contents is actually mounted.
By deleting one of the three characteristics, the flowchart of FIG. 12 can be shared with the SPI method.

In the MPI system, when the volume of the intake pipe downstream of the control valve is large, in order to make the phases of the increase in the auxiliary air flow rate and the supply of the fuel quantity coincide when switching the air-fuel ratio,
There are two embodiments of (a) delaying the fuel amount in accordance with the increasing amount of the auxiliary air flow, and (b) increasing the increasing amount of the auxiliary air flow in accordance with the fuel amount. Is a flow chart incorporating two embodiments (a total of four embodiments including the SPI system). Therefore, in order to select one at the embodiment level, the embodiment shown in FIG.
Steps 90, 91, and 92 of FIG. 6 must be deleted, and steps 64 and 65 of FIG. 12 must be deleted in another embodiment of (b).

<2-4> Target fuel-air ratio Tfbya This is as shown in FIG. 6, Tfbya = Kmr + Kas + Ktw (8) where Kmr; damper value of target fuel-air ratio Kas; post-start increase correction coefficient Ktw; water temperature increase The calculation is performed using the correction coefficient (step 38 in FIG. 6).

Here, the post-start increase correction coefficient Kas is determined according to the cooling water temperature during cranking, and gradually decreases with time immediately after the start of the engine. The water temperature increase correction coefficient Ktw is calculated from the cooling water temperature based on the table. (Steps 37 and 36 in FIG. 6), both of which are known.

<3> Injection amount control <3-1> Fail safe of control valve 22 As shown in FIG.
A is converted into an air flow rate unit by referring to a table after A / D conversion (steps 21 and 22 in FIG. 5), but the air flow rate Q obtained by this conversion is limited to an upper limit Fqmax (step 23 in FIG. 5). , 24). This is to prevent an erroneous operation of the control valve 22 having a relatively large flow rate from causing the auxiliary air having a large flow rate to flow into the cylinder and generating a torque exceeding the driver's demand.

FIG. 26 is a flowchart for obtaining the upper limit Fqmax. In FIG. 26, the throttle valve flow path area Fatvo is referred to a table containing FIG. 27, and the predicted value Aisc of the control valve flow path area when the control valve 22 is normally operated is shown in FIG. 26, respectively, by referring to the table (step 111, FIG.
112).

In FIG. 27, Tvoabs on the horizontal axis is a value obtained by subtracting TVO when fully closed from throttle valve opening TVO, and AOA
FST # is an offset amount for making the throttle valve opening TVO correspond to the actual air flow rate. Aacdt on the horizontal axis in FIG. 28
y is a value of either ISCONP (idling speed control on-duty) or Tcvdty (torque control duty).

The total flow area (Fatvo + A) of the throttle valve flow area Fatvo and the predicted value Aisc of the control valve flow area.
isc) is Pqmax = (Fatvo + Aisc) × KAQGIN # (10) where KAQGIN #; constant is converted into an air flow unit (step 11 in FIG. 26).
3). Pqmax in the equation (10) is a predicted value of the total intake air flow rate when the control valve 22 operates normally. From this predicted value Pqmax, the upper limit value Fqmax is obtained by Fqmax = Pqmax × Qmxg (11) where Qmxg; gain (step 115 in FIG. 26).

The gain Qmxg is a ratio (Q / Pqma) between the air flow rate Q obtained from the air flow meter 4 and the predicted value Pqmax.
x) with reference to the table having the contents shown in FIG. 29 (step 114 in FIG. 26). In FIG. 29, Q / P
In a region where qmax is small, the value of the gain Qmxg is constant, but in a region where Q / Pqmax is large, the gain Qmxg is constant.
The value of mxg is increased. This is to prevent the lean misfire because, for example, when the control valve 22 is fully opened and fixed in the region where the throttle valve opening TVO is small, the fuel-air ratio is excessively shifted to the lean side, causing a lean misfire and the rotation becomes too low. is there. Since Q / Pqmax indicates the degree of malfunction of the control valve 22, when the degree is large, the upper limit Fqmax for the predicted value Pqmax is set so as not to cause lean misfire.
The ratio of x is increased.

<3-2> Basic Injection Pulse Width Tp Corresponding to Cylinder Intake In FIG. 5, when Q> Fqmax, the upper limit value Fqma
The basic injection pulse width Tp equivalent to the cylinder intake is calculated from x (= Q) and otherwise using Q as it is, by a known formula Tp0 = (Q / Ne) × KCONST # × Ktrm (12) Tp = Tp0 × Flood + Tp × (1-Fload) (13) where Tp0: Basic injection pulse width corresponding to the throttle valve portion KCONST #; Constant for giving the base air-fuel ratio Ktrm; Trimming coefficient Fload: Intake pipe air delay coefficient (FIG. 5) Step 25).

The equation (13) takes into account the response delay of the air in the intake pipe at the time of transition (related to a change in operating conditions and not related to switching of the air-fuel ratio).

<3-3> Fuel Injection Pulse Width Ti FIG. 3 is a flowchart for calculating the fuel injection pulse width Ti to the injector 3 provided in the intake port 12b. This is calculated as Ti = Tp × Tfbya × (α + αm ) × Ktr + Ts (14) where α: air-fuel ratio feedback correction coefficient αm; air-fuel ratio learning control coefficient Ktr; transient correction coefficient Ts: invalid pulse width corresponding to the battery voltage (step 2 in FIG. 3). Is output at the injection timing as shown in FIG. 4 (step 11 in FIG. 4).

[0076] (14) transition correction coefficient Ktr of, corrects the transport delay in the intake pipe of the fuel is the same value as the K _ACC of formula in the conventional example. For example, the initial value is determined according to | ΔTVO | when the absolute value | ΔTVO | of the amount of change in the throttle valve opening exceeds a predetermined value (that is, when acceleration or deceleration is determined) and decreases with time. .

The outline is completed above. When the switching to the lean air-fuel ratio is performed by moving the control valve 22 to increase the auxiliary air flow rate, the higher the increase amount of the auxiliary air flow rate, the higher the target air-fuel ratio switching speed. It cannot be increased beyond the maximum flow rate of 22.

Therefore, if the required equilibrium area Tatcvh of the control valve 22 that determines the amount of increase in the auxiliary air flow rate is compared with the control valve flow path area TCVMAX # at the maximum flow rate, the auxiliary air flow rate indicates that the maximum flow rate of the control valve 22 is You can know if it has been exceeded.

However, the portion (Aisc0) of the control valve passage area used for idle speed control cannot be used for torque control at the time of air-fuel ratio switching. If the area is TCVMAX #,
The value obtained by subtracting the control valve passage area Aisc0 from this value (T
CVMAX # -Aisc0) is the required equilibrium area Tatcv
h (step 85 in FIG. 16).

For this reason, Tatcvh ≦ TCVMAX #
-FAACOF = 0 at Aisc0, Tatcvh> TC
When VMAX # −Aisc0 (that is, when the upper limit is reached), FAACOF = 1 is set (steps 86, 87, 86, 88 in FIG. 16). FAACOF
Is a flag for making the speed of the ramp response value of the target air-fuel ratio variable.

Using the value of the flag FAACOF, as shown in FIG. 11, when FAACOF = 0, the large predetermined values DDMLH # and DDMLRH # are changed to a variable Dml.
1, Dmlr (steps 51 and 52 in FIG. 11)
When FAACOF = 1, DDMLH #, DDML
A value smaller than RH # is stored in variables Dmll and Dmlr.

As shown in FIG. 10, the variables Dmll and Dmlr determine the rate of change of the ramp response value Dml (fuel-air ratio change per control).
When a large value is set in the ramp response value Dml changes at a high speed when the air-fuel ratio is switched, and the variables Dmll and Dml
By setting a small value for r, the lamp response value Dml
Changes at a slow rate.

Further, when FAACOF = 1, the variable Dm
11 and Dmlr are not fixed values but values having magnitudes corresponding to the absolute value | ΔTVO | of the throttle valve opening change amount are selected and entered (steps 51 and 53 in FIG. 11). For example, when represented by one variable Dmll, | ΔTVO
│ <DTVO1 # and the predetermined value DDMLL0 #
1 # ≦ | ΔTVO | <DTVO2 # and predetermined value DDMLL
1 #, DTVO2 # ≦ | ΔTVO | <DTVO3 #, and a predetermined value DDMLL2 #, and DTVO3 # ≦ | ΔTVO |
Select the predetermined value DDMLL3 #. However,
DDMLL0 # <DDMLL1 # <DDMLL2 # <D
DMLL3 # <DDMLH #.

Here, the operation of this example in the high intake air flow rate region will be described with reference to FIG. 30. The left half of FIG. 30 shows the operation waveform at the time of switching to the lean air-fuel ratio. The required equilibrium area Tatcvh that determines the amount is the upper limit (T
After reaching (CVMAX # -Aisc0), the speed of the target fuel-air ratio ramp response value Dml is switched from a sharp value to a slow value. Even during the switching of the target air-fuel ratio, the rate of change of the ramp response value Dml is reduced only when the required equilibrium area Tatcvh reaches the upper limit value. Therefore, even during the switching of the air-fuel ratio in the high intake air flow rate region as shown in FIG. Up to this time, the target air-fuel ratio can be switched at a high speed, so that the air-fuel ratio in the middle of the switching can be reduced for a short period of time, so that the NOx emission can be reduced.

Similarly, at the time of switching to the stoichiometric air-fuel ratio shown in the right half, the rate of change of the lamp response value Dml becomes faster during the switching, thereby suppressing the amount of NOx emission.

On the other hand, if the characteristics of NOx when the target air-fuel ratio is slowly changed from the beginning are superimposed by broken lines in FIG. 30, the time at the midway air-fuel ratio becomes longer.
NOx emissions are increasing.

As described above, in this example, the required equilibrium area Tatcvh of the control valve 22 which determines the amount of increase of the auxiliary air flow rate is directly observed, and only when this exceeds the upper limit value, the changing speed of the target fuel-air ratio ramp response value Dml is slowed down. By doing so, the switching speed of the target air-fuel ratio can be increased in most of the intake air flow rate range. In regions other than the high intake air flow region, the required equilibrium area T
In many cases, the atcvh does not reach the upper limit value. In this case, the target fuel-to-air ratio ramp response value changes at a high speed until the end of the switching, and the emission of NOx during the air-fuel ratio switching can be suppressed. .

Further, the rate of change of the lamp response value after the required equilibrium area Tatcvh reaches the upper limit value is not a constant speed but a value corresponding to the absolute value | ΔTVO | Selected and put. | ΔTVO | is a value for observing the degree of change in the operating conditions, and during a rapid acceleration / deceleration, even if the torque change at the time of switching the target air-fuel ratio is large, it is difficult for the driver to sense as a shock as in a steady state. By increasing the rate of change of the ramp response value Dml as the degree of acceleration / deceleration is increased, it is possible to minimize the emission of NOx during switching of the air-fuel ratio while maintaining a balance with drivability.

In the embodiment, the case where the control valve 22 is shared for idle speed control has been described. However, when the control valve 22 is not shared for idle speed control, the upper limit value (TCV
MAX # -Aisc0), but the flow area TCVMAX # of the control valve 22 at the maximum flow rate. In the embodiment, the comparison is made based on the flow path area of the control valve (Tatcvh and TC
Although VMAX # -Aisc0 is compared), the flow rate of the control valve itself may be compared (comparison of the control valve flow rate obtained from Tatcvh with the control valve flow rate obtained from TCVMAX # -Aisc0).

In the embodiment, the case where the auxiliary air flow rate is increased has been described. However, the air control valve for restricting the intake according to the control amount is not mechanically linked with the accelerator pedal. The present invention can also be applied to a device provided in place of the intake throttle valve linked to the above.

[0091]

According to the first aspect of the present invention, it is determined whether or not the operating condition signal is a lean condition. Based on the result of the determination, a target air-fuel ratio corresponding to the lean condition is determined under the lean condition. A target air-fuel ratio corresponding to a condition other than the lean condition is calculated according to the operating condition signal, an air-fuel ratio switching speed until switching to the target air-fuel ratio is calculated, and the target air-fuel ratio switching speed and the operating condition signal are calculated. Calculating the basic injection amount from the base injection amount and supplying the fuel calculated on the basis of the basic injection amount to the intake pipe, while providing an air control valve for adjusting the auxiliary air flow rate bypassing the intake throttle valve. The amount of increase in the auxiliary air flow rate is calculated using the switching speed of the target air-fuel ratio and the operating condition signal so that the torque becomes the same before and after the switching at the time of switching, and the air control is performed according to the increase amount of the auxiliary air flow rate. And determines whether or not the auxiliary air flow exceeds the maximum flow rate of the air control valve. Based on the determination result, the switching speed of the target air-fuel ratio is maintained until the auxiliary air flow exceeds the maximum flow rate of the air control valve. And the switching speed of the target air-fuel ratio is set to be slower when the maximum flow rate is exceeded. Therefore, the switching speed of the target air-fuel ratio can be increased in most of the intake air flow rate range, and the emission of NOx during switching is suppressed. be able to.

In the second invention, it is determined whether or not the operating condition signal is a lean condition. Based on the result of the determination, the target air-fuel ratio corresponding to the lean condition is determined. A target air-fuel ratio corresponding to a condition other than the conditions is calculated in accordance with the operating condition signal, an air-fuel ratio switching speed until switching to the target air-fuel ratio is calculated, and a basic air-fuel ratio switching speed and an operating condition signal are calculated from the target air-fuel ratio switching speed and the operating condition signal. Calculating an injection amount, supplying the fuel calculated based on the basic injection amount to the intake pipe, and providing an air control valve that throttles intake according to the control amount without mechanically interlocking with the accelerator pedal, At the time of switching the target air-fuel ratio, the change amount of the intake air flow rate is calculated using the target air-fuel ratio switching speed and the operating condition signal so that the torque becomes the same before and after the switching, and according to the change amount of the intake air flow rate. While driving the air control valve, it is determined whether or not the intake air flow rate exceeds the maximum flow rate of the air control valve.From the determination result, the target air flow rate exceeds the target flow rate until the intake air flow rate exceeds the maximum flow rate of the air control valve. Since the switching speed of the air-fuel ratio is set to be high and the switching speed of the target air-fuel ratio is set to be low when the maximum flow rate is exceeded,
The same effects as those of the first invention are obtained.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to a claim of the first invention.

FIG. 2 is a system diagram of one embodiment.

FIG. 3 is a flowchart for explaining calculation of a fuel injection pulse width Ti.

FIG. 4 is a flowchart for explaining an output of a fuel injection pulse width Ti.

FIG. 5 is a flowchart for explaining calculation of a basic injection pulse width Tp corresponding to cylinder intake;

FIG. 6 is a flowchart for explaining calculation of a target fuel-air ratio Tfbya.

FIG. 7 is a characteristic diagram for explaining the contents of a lean map.

FIG. 8 is a characteristic diagram for explaining the contents of a non-lean map.

FIG. 9 is a flowchart for explaining calculation of a ramp response value Dml of a target fuel-air ratio.

FIG. 10 is a waveform diagram of a ramp response value Dml of a target fuel-air ratio.

FIG. 11 is a flowchart for explaining the calculation of the change speeds Ddmrr and Ddmll.

FIG. 12 is a flowchart for explaining calculation of a damper value Kmr of a target fuel-air ratio.

FIG. 13 shows a delay time constant equivalent value Fbyat of the two embodiments.
It is a characteristic diagram which overlaps and shows the table content of c.

14 is a waveform chart for explaining a dead time of the control valve 22. FIG.

FIG. 15 is a flowchart for explaining the calculation of the on-duty for the control valve 22;

FIG. 16 is a flowchart for explaining calculation of a torque control duty Tcvdty shared by two embodiments different from the two embodiments.

FIG. 17 is a flowchart for explaining calculation of a torque control duty Tcvdty.

FIG. 18 is a characteristic diagram showing a table of a throttle valve passage area Atvo.

FIG. 19 is a characteristic diagram showing a table content of a control valve passage area Aisc0.

FIG. 20 is a characteristic diagram showing the contents of a table of a differential pressure correction rate Kgh0.

FIG. 21 is a characteristic diagram showing the table contents of the delay-advance compensation time constant equivalent value Tcvtc of the two embodiments different from the above-described two embodiments in a superimposed manner.

FIG. 22 is a characteristic diagram showing table contents of a basic duty Dtytc.

FIG. 23 is a characteristic diagram showing the contents of a table of a duty correction rate Tcvgin.

FIG. 24 is a characteristic diagram showing a table content of a control valve rising duty Tcvofs.

FIG. 25 is a flow rate characteristic diagram of the control valve 22;

FIG. 26 is a flowchart for explaining calculation of an upper limit Fqmax.

FIG. 27 is a characteristic diagram showing a table of a throttle valve passage area Fatvo.

FIG. 28 is a characteristic diagram showing a table content of a predicted value Aisc of a control valve passage area.

FIG. 29 is a characteristic diagram showing the contents of a table of gains Qmxg.

FIG. 30 is a waveform diagram for explaining an operation at the time of switching the target fuel-air ratio in a high intake air flow rate region.

FIG. 31 is a system diagram of a conventional example.

FIG. 32 is a characteristic diagram showing the contents of a table of a conventional air correction rate KBA.

FIG. 33 is a waveform chart for explaining the operation of the conventional example.

FIG. 34 is a diagram corresponding to a claim of the second invention.

[Explanation of symbols]

 Reference Signs List 2 control unit 3 injector (fuel supply device) 4 air flow meter 5 intake throttle valve 6 throttle sensor 7 crank angle sensor (rotation speed sensor) 12a collector section 12b intake port 21 auxiliary air passage 22 flow control valve (air control valve) 31 lean Condition determining means 32 target air-fuel ratio calculating means 33 switching speed calculating means 34 basic injection amount calculating means 35 fuel supply device 36 intake throttle valve 37 air control valve 38 auxiliary air flow rate increasing amount calculating means 39 driving means 40 determining means 41 switching speed setting Means 51 Air control valve 52 Intake air flow rate change amount calculation means 53 Driving means 54 Judgment means 55 Switching speed setting means

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F02D 41/04 305 F02D 41/04 310 F02D 41/04 315 F02D 45/00 301

Claims (2)

(57) [Claims] A means for judging whether the operating condition signal is a lean condition, a target air-fuel ratio corresponding to the lean condition based on a result of the determination, and a condition other than the lean condition when the condition other than the lean condition is satisfied. Means for calculating a target air-fuel ratio according to the operating condition signal in accordance with the conditions of the above, a means for calculating a switching speed of the air-fuel ratio until switching to the target air-fuel ratio, a switching speed of the target air-fuel ratio and an operating condition signal Means for calculating a basic injection amount from the fuel injection device, a device for supplying fuel calculated based on the basic injection amount to the intake pipe, an air control valve for adjusting an auxiliary air flow rate bypassing the intake throttle valve, and the target air amount. Means for calculating the amount of increase in the auxiliary air flow rate using the target air-fuel ratio switching speed and the operating condition signal so that the torque becomes the same before and after the change in the fuel ratio, and the amount of increase in the auxiliary air flow rate Means for driving the air control valve in accordance with the above, means for determining whether the auxiliary air flow rate exceeds the maximum flow rate of the air control valve, the auxiliary air flow rate from the determination result the maximum flow rate of the air control valve Means for setting the switching speed of the target air-fuel ratio to be high until the engine speed exceeds the maximum flow rate, and to decrease the switching speed of the target air-fuel ratio when the flow rate exceeds the maximum flow rate. 2. A means for determining whether the operating condition signal is a lean condition, a target air-fuel ratio corresponding to the lean condition based on the determination result, and a condition other than the lean condition when the condition is other than the lean condition. Means for calculating a target air-fuel ratio according to the operating condition signal in accordance with the conditions of the above, a means for calculating a switching speed of the air-fuel ratio until switching to the target air-fuel ratio, a switching speed of the target air-fuel ratio and an operating condition signal Means for calculating a basic injection amount from a fuel injection device, a device for supplying fuel calculated based on the basic injection amount to an intake pipe, and air control for restricting intake air according to a control amount without mechanically interlocking with an accelerator pedal. Means for calculating the amount of change in the intake air flow rate using the target air-fuel ratio switching speed and the operating condition signal so that the torque becomes the same before and after the switching at the time of switching the target air-fuel ratio. Means for driving the air control valve in accordance with the amount of change in the incoming air flow rate, means for determining whether the intake air flow rate exceeds the maximum flow rate of the air control valve, and determining whether the intake air flow rate is Means for setting the target air-fuel ratio switching speed high until the maximum flow rate of the air control valve is exceeded, and slowing down the target air-fuel ratio switching speed when the maximum flow rate is exceeded. Air-fuel ratio control device.