JPH0849582A - Intake control system for lean burn engine - Google Patents

Abstract

(57) [Summary] [Purpose] To improve the accuracy of torque fluctuation prevention. [Structure] Means 107 for increasing the intake air amount so as to suppress torque fluctuations when switching from the vicinity of the stoichiometric air-fuel ratio to lean air-fuel ratio, and means 105 for detecting the load of the engine.
And means for detecting the engine speed, and means for correcting the increase rate of the intake air amount when the load and the engine speed are low, and correcting the increase rate to be small when the engine load and the engine speed are high.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to switching of an air-fuel ratio in a lean burn engine, and more particularly to control of an intake air amount when switching the air-fuel ratio.

[0002]

2. Description of the Related Art A lean-burn engine for the purpose of improving fuel economy has been receiving attention in recent years. This is configured such that the air-fuel mixture is switched between an air-fuel ratio near the stoichiometric air-fuel ratio and an air-fuel ratio leaner than the stoichiometric air-fuel ratio, depending on engine operating conditions. When the engine is operated in the lean environment, the throttle opening is relatively large because a large amount of air is sucked in compared with the operation in the stoichiometric air-fuel ratio, and as a result, the energy required for air intake is reduced. Further, the heat loss is reduced due to the decrease in the combustion gas temperature. In this way, lean combustion improves fuel efficiency because the energy loss associated with operation is small.

However, when the stoichiometric air-fuel ratio is switched to the lean air-fuel ratio only by reducing the fuel injection amount, the torque generated by the engine is reduced.
No. 7340 proposes to reduce the fuel injection amount and increase the intake air amount at the same time when the air-fuel ratio is switched from the stoichiometric air-fuel ratio to the lean air-fuel ratio. The fuel injection amount is basically determined by the ratio with the intake air amount, and even with a lean air-fuel ratio, the fuel injection amount increases by increasing the intake air amount. This increase amount and a part of the decrease amount of the fuel injection amount due to the air-fuel ratio switching are canceled out, and as a result, the fluctuation of the torque generated by the engine can be suppressed small.

[0004]

However, even if the air-fuel ratio is the same, the generated torque is different under different operating conditions. Therefore, the degree of torque fluctuation due to the switching of the air-fuel ratio is different depending on the operating conditions. Therefore, it is difficult to completely prevent the torque fluctuation by only mechanically increasing the intake air amount when switching to the lean air-fuel ratio.

The present invention has been made to solve the above problems, and prevents torque fluctuations by increasing or decreasing the amount of increase in the intake air amount when switching to the lean air-fuel ratio in accordance with the operating conditions of the engine. Increase accuracy.

[0006]

The invention according to claim 1 is based on FIG.
As shown in, means 101 for switching the target air-fuel ratio between the vicinity of the theoretical air-fuel ratio and the lean air-fuel ratio on the leaner side thereof.
A means 102 for detecting the intake air amount, a means 103 for calculating the fuel supply amount based on the switched air-fuel ratio and the detected intake air amount, a means 104 for supplying the calculated fuel supply amount, and a theoretical air-fuel ratio. In a lean-burn engine equipped with a means 107 for increasing the intake air amount to suppress torque fluctuations when switching from the vicinity of the air conditioner to a lean air-fuel ratio, means 105 for detecting the load of the engine and speed of the engine are detected. And a means 108 for correcting the increase rate of the intake air amount to be large when the load and the rotational speed are low, and for correcting the increase rate to be small when the load and the rotational speed are high.

[0007]

According to the invention of claim 1, the switching means 101
When the air-fuel ratio is switched to the lean air-fuel ratio by the air intake air amount increasing means 107, the intake air amount detecting means 102 increases the intake air amount by increasing the intake air amount.
Along with this, the fuel supply amount calculated by the calculation means 103 increases as compared with the case where the intake air amount is not increased, so that the decrease in torque due to switching to the lean air-fuel ratio is compensated.

Further, since the correction means 108 corrects the increase rate of the intake air amount to a small value in accordance with the increase in the engine load and the rotation speed detected by the detection means 105 and 106, the lean air-fuel ratio which differs depending on the rotation speed and the load. The intake air amount is controlled in response to the torque decrease when switching to the control mode, and the torque decrease can be accurately prevented.

[0009]

2 to 21 show an embodiment of the present invention.

The multi-cylinder engine 1 shown in FIG. 2 has an intake passage 1
The air is sucked from the exhaust gas 2 and the combustion gas is discharged from the exhaust passage 18.

The intake passage 12 is provided with an air cleaner 11 and a throttle 5 for adjusting the intake amount. Intake passage 1
The air absorbed by 2 is branched for each cylinder in the collector portion 12A, and the injector 3 provided in the intake port 12 injects fuel into the flow of this air to supply it to each cylinder of the engine 1 as a mixture.

An intake throttle 5 is provided in the middle of the intake passage 12.
An auxiliary air passage 21 that bypasses the auxiliary air passage is provided, and a flow control valve 22 is provided in the middle of this auxiliary air passage. The flow rate control valve 22 is of a proportional solenoid type and allows a larger amount of air to flow as the on-duty of the input signal increases.

Reference numeral 13 is a swirl control valve. This is to give swirl to the intake air flowing into the combustion chamber in order to suppress the generation of CO and HC in the lean air-fuel ratio range. That is, in the lean air-fuel ratio range, the swirl control valve 1 is fully closed to allow the intake air to flow only through the notches, thereby increasing the flow velocity of the intake air and causing swirl in the combustion chamber.

On the other hand, the exhaust passage 18 contains HC, N in the exhaust gas.
A three-way catalytic converter 19 that purifies Ox and CO by oxidation or reduction is provided.

A control unit 2 is provided to control the fuel injection amount of the injector 3 and the auxiliary air flow rate flowing through the flow rate control valve 22. Control unit 2
Signals are input to the sensor from various sensors that detect the operating conditions of the engine necessary for these controls. That is, a hot-wire type air flow meter 4 for detecting the flow rate of air taken in from the air cleaner 11, a throttle sensor 6 for detecting the opening of the intake throttle 5, a signal for each unit crank angle and a ref signal (for each crank angle reference position). Signal) and a crank angle sensor 7, a water temperature sensor 8 that detects the cooling water temperature, a wide range air-fuel ratio sensor 9 that can widely detect the actual air-fuel ratio from the theoretical air-fuel ratio to the lean side air-fuel ratio, and the vehicle speed A vehicle speed sensor 10 for detecting and a gear position sensor 14 for detecting a gear position. In addition, battery voltage signal and starter switch ON / O
The FF signal and the FF signal are input to the control unit 2.

Control unit 2 Based on these input signals, the target air-fuel ratio is switched between the stoichiometric air-fuel ratio and the lean air-fuel ratio leaner than the stoichiometric air-fuel ratio according to operating conditions, and the switched target air-fuel ratio is realized. First, the fuel injection amount is feedback-controlled based on the air-fuel ratio signal of the wide-range air-fuel ratio sensor 9. Further, the intake flow rate is controlled via the flow control valve 22 of the auxiliary air passage 21 in accordance with the operating conditions so that the generated torque does not fluctuate when the air-fuel ratio is switched.

The contents of this control executed by the control unit 2 will be described with reference to the following flow chart.

(1) Control of intake air amount The torque control duty Tcvdty is calculated according to the flowcharts of FIGS. 9 and 10.

First, referring to the table having the contents of FIG. 11 from the throttle opening TVO, the throttle valve passage area Atvo
And the basic duty Isc to be applied to the flow rate control valve 22.
The control valve passage area Aisc0 is obtained from dt by referring to the table having the contents of FIG. 12, and the sum of these is put into the variable Aa0 as the basic passage area (steps 81 and 8 in FIG. 9).
2). It should be noted that since all table references (also for map references) have interpolation calculation, they are simply referred to as table references (map references) below.

Here, the basic duty Iscdt is Iscdt = (Iscdty−Tcvofs) × Tcvgin (1) where Isddty: reduction basic duty Tcvofs; control valve rising duty Tcvgin; duty correction rate.

The reduced basic duty Iscdty is the feedback correction amount ISCcl (= ISCi + ISCp) held at the end of the previous feedback correction condition, which is reduced and corrected, and Iscdty = ISCcl × Gistv (2). This reduction correction reduces the maximum flow rate of the control valve 22 by expanding the range in which the control valve 22 can be moved for torque control when switching the air-fuel ratio, and is a feedback correction that performs a minute flow rate control aiming at a target value. This is to prevent the valve precision from being reduced under the conditions.

The control valve rising duty Tcvofs 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 increased equilibrium area T
Atcvh is calculated by Tatcvh = Aa0 × Kqh0 × {1 / (Dml × LTCGIN #)-1} (3) where Kqh0; differential pressure correction rate LTCGIN #; torque control gain Dml; target fuel-air ratio ramp response value (Step 84 in FIG. 9).

In order to make the above equation easy to understand, Tatcvh = Aa0 × (1 / Tdml-1) (4) However, if Tdml is the map value of the target fuel-air ratio, (1 / Tdml-1) is Since it corresponds to the air-fuel ratio difference from the stoichiometric air-fuel ratio, Aa
It can be seen that the value multiplied by 0 represents the increased area (the decreased area when switching to the stoichiometric air-fuel ratio).

For example, at the theoretical air-fuel ratio (14.5), the map value Tdml of the target fuel-air ratio is 1, and the air-fuel ratio is 2 on the lean side.
At 0, Tdml has a value of about 0.66. In addition,
The value of Tdml is 1 or 0.66 because the fuel-air ratio (target fuel-air ratio) is not the reciprocal of the air-fuel ratio itself, but a relative value with the theoretical fuel-air ratio being 1, as will be described later. This is because

When 1 is added to Tdml, Tatc
vh = 0, and if Tdml is 0.66, Tatc
vh = (1 / 0.66) -1≈0.52, and (0.
52-0) × Aa0 corresponds to the increased area when the stoichiometric air-fuel ratio is switched to the lean air-fuel ratio.

Torque control gain LTCGIN of equation (3)
Is a value required for matching, which is obtained from the flowchart shown in FIG. 19 and the map shown in FIG.

That is, in step 101, the operating condition (engine speed Ne and load Tp) is read, and step 1
At 02, it is determined whether the lean condition is satisfied. The load Tp
Is applied to the value of the basic injection amount described in the section of the switching of the air-fuel ratio and the feedback control of the fuel injection amount.

In the case of the lean condition, in step 103, the torque control gain LTCGIN is searched from the map of FIG. 20 based on the engine speed Ne and the load Tp. In the map, the engine speed Ne is high and the load Tp
The torque control gain LTCGIN is set to a larger value as becomes larger. But in any case 1
The following numerical values are obtained. This torque control gain LTCGIN
May be given as a table for the intake air amount. Under lean conditions, LTCGIN is a number between 0 and 1.

If the lean condition is not satisfied, the routine proceeds to step 104, where the torque control gain LTCGIN = 1.

The differential pressure correction factor Kqh0 in the equation (3) is calculated from Qh0 as a load (a known linearized flow rate, which is determined from the throttle valve opening TVO, the engine speed N and the exhaust amount V). It is obtained by referring to the table having the contents of 13 (step 83 in FIG. 10).

As shown in FIG. 13, Kqh0 is close to 1 in the low load region where Qh0 is small, but the value of Kqh0 becomes larger than 1 as the load becomes higher, which increases the equilibrium area of the formula (3). The value of Tatcvh is increased.

This is because the opening of the flow control valve 22 is proportional to the flow rate in the sonic region shown in FIG. 13, but the flow rate becomes insufficient as the load becomes higher than this.

Returning to the flow of FIG. 9, the increased equilibrium area Ta
tcvh is the upper limit of the control valve passage area Aisc from the passage area TCVMAX # at the maximum flow rate of the control valve 22.
It is limited to a value (TCVMAX # -Aisc0) minus 0 (step 85). This is because the value of Aisc0 is a value that has already been used in idle speed control, and the remainder after subtracting this is the 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 the upper limit is exceeded, FAACO
F = 1 is set (steps 86 and 88). This flag FA
ACOF is a flag for changing the changing speed of the lamp response value Dml. When FAACOF = 1, the changing speed of Dml is slowed down. This is because even if the control valve 22 can be moved at a fast changing speed until the upper limit value is exceeded, the changing speed is not increased after the upper limit value is exceeded and abrupt torque change is prevented.

Tatcv0 = Tatcvo + (Tatcvh-Tatcvo) * Tcvtvc (5) where Tatcv0 = previous value of Tatcvo; Tcvvc; advance compensation time constant equivalent value (value of 1 or more) to the increased equilibrium area Tatcvh Then, the compensation area is obtained by the following equation (step 91). When the volume of the intake pipe downstream of the control valve 22 in the MPI system is large, the delay of the air in the intake pipe is relatively larger than the delay of the fuel, so that the air can be advanced in accordance with the fuel with good response. , The phases of the air flow rate and the fuel supply to the cylinder are matched.

Further, when the intake pipe volume downstream of the control valve is small in the SPI system, the fuel flows into the cylinder later than the air, so that the flow of air into the cylinder is delayed in accordance with the fuel, so that Tatcv0 = Tatcv0 _n-1 + (Tatcvh-Tatcv0 _n-1 ) × Tcvtc (6) where Tatcv0 _n-1 ; previous value of Tatcv0 Tcvtc; delay compensation time constant equivalent value (value less than 1) By calculating the delay compensation area (step 92), the phases of air and fuel supply to the cylinders are matched.

The flow charts of FIGS. 19 and 10 are MP
In order to be able to use both of the two types of the engine, the intake system having a large intake pipe volume and the SPI system having a small intake pipe volume, whether Tcvtc ≧ 1.0, Tcvtc ≧ 1. When it is 0, it is judged that the engine has a large intake pipe volume and the above equation (7) is changed to
If Tcvtc <1.0, the equation (8) is adopted (steps 90 and 91, steps 90 and 9).
2).

The lead compensation or delay compensation time constant equivalent value Tcvtc in the equations (5) and (6) is determined from the engine speed Ne by referring to a table having the contents of FIG. 14 (FIG. 10).
Step 89). FIG. 14 shows two types of characteristics for a large-volume intake pipe and a small-volume intake pipe, but the engine shown in FIG. 2 does not require the characteristic for a small intake pipe volume.

From the lead compensation or lag compensation area Tatcv0 thus obtained, the target flow passage area Tatcv is obtained by Tatcv = Tatcv0 _n-DLYIS + Aisc0 + Aokuri (7), where Aokuri: advance feed (step 93 in FIG. 10).

Here, the target flow passage area Tatcv has a lower limit of 0 and an upper limit of the flow passage area TCVMAX # at the maximum flow rate of the control valve.
And a value added with MXOS #, which is an allowance for compensation (TC
VMAX # + MXOS #), but the target flow passage area Tatcv of the equation (9) may be out of these limit values. This protrusion is the next time (10ms
If Tatcv <0, the value of the underflowed Tatcv is used as the advance amount for the variable A to be reflected in the latter).
Put in okuri (step 94, 95), Tatcv
> When TCVMAX # + MXOS #, Tatcv-
The overflow value of (TCVMAX # + MXOS #) is put into the variable Aokuri as the advance amount (step 9).
6,97). This value of Aokuri is used next time when the target flow passage area Tatcv is calculated using the equation (7).

Tatcv0 _{n -DLYIS in the} equation (7) is a value before the lead-compensation or delay-compensation area Tatcv0 by a predetermined number (for example, DLYIS #). This takes into account the dead time from when the valve opening signal is sent to the injector 3 until the injector 3 actually starts opening.

The target flow passage area Tatcv is converted into the basic duty Dtytc by referring to the table having the contents shown in FIG. 15 (step 99 in FIG. 17), and the torque control duty Tcvdty is Tcvdty = Dtytc / Tcvgin + Tcvofs (8) Tcvgin: Duty correction rate Tcvofs: Control valve rising duty is calculated (steps 100 and 101).

Control valve rising duty Tcvofs
Is the amount by which the control valve 22 does not substantially work as in FIG. 18 until the on-duty reaches a certain value, and is obtained from the battery voltage Vb by referring to the table having the content of FIG. As shown in FIG. 18, in the proportional solenoid type control valve 22, the control valve rising duty Tcvofs increases as the battery voltage Vb decreases.

The duty correction rate Tcvgin is shown in FIG.
The table is obtained by referring to the table. This is
In the flow rate characteristic of the control valve 22 of No. 8, since the slope of the straight line that rises diagonally becomes smaller as the battery voltage Vb decreases, this is a correction for making the control valve flow rate the same even if the battery voltage Vb decreases.

The torque control gain LTCCGIN is set to a larger value as the load increases and the rotation speed increases, but LTCGI in the formula (3) for calculating the increased equilibrium area Tatcvh is calculated.
Since N is on the denominator side, as a result, Tatcvh and the torque control duty Tcvdt calculated based on it
The gain with respect to y is set to be smaller at high load and high rotation, and larger at low load and low rotation.

(2) Switching of air-fuel ratio and feedback control of fuel injection amount FIG. 3 shows a damper operation for correcting the fuel-air ratio (reciprocal of the air-fuel ratio) when switching the air-fuel ratio of the engine 1. It is executed every time.

First, at step 11, the target fuel-air ratio Tdml
This target fuel-air ratio is set by searching the fuel-air ratio Mdml set in the map of FIG. 7 or FIG. 8 according to the engine speed and load. One of the maps is selected depending on whether it is the lean operation condition.

The determination as to whether or not the lean operation condition is made is performed as a background job according to the flowcharts of FIGS.

First, in step 21 of FIG. 4, the lean condition is judged. The specific content of this determination is performed by checking the content of steps 31 to 36 one by one, as shown in FIG. 5, and when all of the items are satisfied, the lean operation is permitted, and even one is contrary to the situation. In some cases, lean driving is prohibited.

That is, A) The air-fuel ratio (oxygen) sensor is activated.

B) The warm-up of the engine is completed.

C) The load (Tp) is in a predetermined lean region.

D) The rotation speed (Ne) is in a predetermined lean region.

E) The gear position is in the second speed or higher.

F) The vehicle speed is within a predetermined range.

At this time, the lean operation is permitted at step 37, and if not, the routine proceeds to step 38 to prohibit the lean operation. Of the above, steps 31 to 36 are conditions for performing stable lean operation without impairing operating performance.

When the lean condition is determined in this way,
Returning to step 22 in FIG. 4, when the lean condition is not satisfied,
In step 23, the theoretical fuel-air ratio or a map fuel-air ratio that is thicker than the theoretical fuel-air ratio is calculated.
In contrast, when the lean condition is satisfied, the map fuel-air ratio Mdml which is thinner than the theoretical fuel-air ratio by a predetermined range is similarly searched according to the map of FIG. To do.

The numerical value shown in this map is actually a value obtained by dividing the fuel-air ratio by the theoretical fuel-air ratio. Therefore, the numerical value of 10 corresponds to the theoretical fuel-air ratio, and the numerical value is smaller than this. Larger indicates rich, smaller indicates lean.

After determining the lean operation in this way, the damper operation at the time of switching the fuel-air ratio is performed after step 12 of the flow chart of FIG. That is,
When the air-fuel ratio is changed, the change is gently performed to prevent a sudden change in torque and to ensure the stability of operating performance.

In step 12, the held fuel-air ratio correction coefficient Dml is compared with the Tdml calculated above,
If Dml ≧ Tdml, that is, if the calculated target fuel-air ratio is larger than the held fuel-air ratio correction coefficient Dml, the previous correction coefficient is changed in step 13 in order to shift the air-fuel ratio to the rich side. A new Dml is obtained by adding Ddmlr corresponding to the air-fuel ratio change speed to the rich side to Dml. Then, in step 14, Dml is restricted so that the fuel-air ratio correction coefficient Dml does not exceed the calculated target fuel-air ratio Tdml.

On the other hand, if Dml ≧ Tdml,
At steps 15 and 16, a new fuel-air ratio correction coefficient Dml shifted to the lean side is obtained by subtracting Ddmll corresponding to the lean-side air-fuel ratio change speed from the held Dml, and further Dml is less than Tdml. Limit the Dml so that it does not occur.

The flowchart of FIG. 6 shows the contents of the control operation for calculating and outputting the fuel injection amount using the fuel-air ratio correction coefficient Dml thus obtained. First, at step 41, the fuel-air ratio correction coefficient Dml is calculated. Using Dml, the target fuel-air ratio Tf
Bya is calculated by the following formula.

Tfbya = Dml + Ktw + Kas (9) Here, Ktw is the fuel increase amount according to the cooling water temperature, and Kas
Is the amount of fuel increase immediately after starting. Next, at step 42, the output of the air flow meter is A / D converted and linearized to calculate the intake air amount Q. Then, in step 43, the basic fuel injection amount Tp is obtained from the intake air amount Q and the engine speed N as Tp = K × Q / N. K is a constant. The basic injection amount Tp obtained here is also used as a value representing the load of the engine as described above.

Then, in step 44, based on this Tp, the fuel injection amount Ti for one time is calculated according to the following equation.

Ti = Tp × Tfbya × Ktr × (α + αm) + Ts (10) where Ktr is a transient correction coefficient, α is an air-fuel ratio feedback correction coefficient, αm is an air-fuel ratio learning correction coefficient, and Ts is an invalid pulse. Width. However, under lean conditions,
These Ktr, α, αm, etc. are fixed to predetermined values.

Next, in steps 45 and 46, it is determined whether or not the fuel is cut, and in steps 47 and 48, if the fuel cut condition is satisfied, the invalid pulse width Ts is stored in the output register. Prepare for injection at a predetermined injection timing according to the output of.

Next, the operation will be described.

When the operating condition changes from the stoichiometric air-fuel ratio to the lean air-fuel ratio, the ramp response value Dml of the target fuel-air ratio changes to a value of 1 or less. In addition, the torque control gain LTCCGINS
Changes from 1 to a value between 1 and 0 depending on operating conditions.

As a result, the increased equilibrium area Tatcvh calculated by the equation (3) and the torque control duty Tcvdty calculated by the equations (4) to (7) based on this increase, but the degree of increase is Torque control gain LTCGI
It depends on the value of NS.

That is, the value of the torque control gain LTCGINS increases as the load increases and the rotation speed increases, and as a result, the increase rate of the torque control duty Tcvdty decreases.
That is, the rate of increase in the opening degree of the flow control valve 22 decreases, and the rate of increase in the intake air amount Q also decreases.

On the contrary, the value of the torque control gain LTCGINS is smaller as the load is lower and the rotation speed is smaller, and as a result, the increase rate of the torque control duty Tcvdty is larger. That is, the increase rate of the opening degree of the flow rate control valve 22 increases, and the increase rate of the intake air amount Q also increases.

The basic injection amount Tp, which is the basis of the calculation of the fuel injection amount Ti, increases in accordance with the increase of the intake air amount Q. Therefore, due to this increase, the torque decrease accompanying the switching from the stoichiometric air-fuel ratio to the lean air-fuel ratio. Thus, it is possible to prevent the deterioration of the driving performance due to the air-fuel ratio switching.

By the way, as shown in FIG. 21, the ratio between the stoichiometric air-fuel ratio generated torque and the lean air-fuel ratio generated torque becomes higher as the load increases and the rotational speed increases.
That is, the torque reduction ratio between the stoichiometric air-fuel ratio and the lean air-fuel ratio is smaller at high rotation and high load than at low load and low rotation.

As described above, this control device increases the gain in the calculation of the torque control duty Tcvdty when the load is low and the rotation is low, and the gain is small when the load is high and the rotation is high, so that the lean air-fuel ratio is changed. It is possible to prevent a decrease in torque regardless of operating conditions.

Further, in the high load / high speed region, in the past, operation was performed at the stoichiometric air-fuel ratio in order to secure the torque. By thus preventing the torque from decreasing, even in the high load / high speed region. It becomes possible to apply the air-fuel ratio.

In the above embodiment, the maps of steps 23 and 24 and FIGS. 7 and 8 of FIG. 4 are the air-fuel ratio switching means, the air flow meter 4 is the intake air amount detecting means, and FIGS. And the injector 3 constitute the fuel supply amount calculation means. Also,
The crank angle sensor 7 is an engine speed detecting means, step 43 of FIG. 4 is load detecting means, the flows of FIGS. 8 and 9 are intake air increasing means, and steps 103 and 10 of FIG.
4 and the map of FIG. 20 respectively constitute the correction means.

[0078]

As described above, according to the first aspect of the present invention, the increase rate of the intake air amount at the time of switching to the lean air-fuel ratio of the lean burn engine is larger at low load and low rotation and smaller at high load and high rotation. Therefore, it is possible to accurately prevent the torque decrease when switching to the lean air-fuel ratio regardless of the operating conditions.

Further, by preventing the torque fluctuation at the time of switching to the lean air-fuel ratio in this way, it becomes possible to perform the lean operation even in the high load and high rotation range, and the lean operation range is expanded.

[Brief description of drawings]

FIG. 1 is a claim correspondence diagram showing a configuration of the present invention.

FIG. 2 is a configuration diagram of an embodiment of the present invention.

FIG. 3 is a flowchart showing a calculation process of a fuel-air ratio correction coefficient Dml.

FIG. 4 is a flowchart showing a switching process between a stoichiometric air-fuel ratio and a lean air-fuel ratio.

FIG. 5 is a flowchart showing a lean condition determination process.

FIG. 6 is a flowchart showing a control process to a target air-fuel ratio and a fuel injection amount calculation process.

FIG. 7 is a map of lean air-fuel ratio.

FIG. 8 is a map of an air-fuel ratio near the stoichiometric air-fuel ratio.

FIG. 9 is the first half of a flowchart illustrating a process of calculating a torque control duty Tcvdty.

FIG. 10 is the second half of the flowchart for explaining the process of calculating the torque control duty Tcvdty.

FIG. 11 is a graph showing the contents of a table of throttle channel area Atvo.

FIG. 12 is a graph showing the table contents of the control valve passage area Aisc0.

FIG. 13 is a graph showing the table contents of the differential pressure correction rate Kqh0.

FIG. 14 is a graph showing the table contents of a delay / advance compensation time constant equivalent value Tcvtc.

FIG. 15 is a graph showing the table contents of the control valve basic duty Dtytc.

FIG. 16 is a graph showing the table contents of a duty correction rate Tcvgin.

FIG. 17 is a graph showing the table contents of the control valve rising duty Tcvofs.

FIG. 18 is a flow rate characteristic diagram of the flow rate control valve.

FIG. 19 is a flowchart showing a calculation process of a torque control gain LTCGIN.

FIG. 20 is a map of a torque control gain LTCGIN.

FIG. 21 is a graph comparing generated torques at a stoichiometric air-fuel ratio and a lean air-fuel ratio.

[Explanation of symbols]

 1 Engine 2 Control Unit 3 Injector 4 Air Flow Meter 5 Throttle 7 Crank Angle Sensor 22 Flow Control Valve

Claims (1)

[Claims] 1. A means for switching a target air-fuel ratio between the vicinity of a stoichiometric air-fuel ratio and a lean air-fuel ratio on a leaner side thereof, a means for detecting an intake air amount, a switched air-fuel ratio and a detected intake air amount. Means for calculating the fuel supply based on
In a lean burn engine provided with a means for supplying the calculated fuel supply amount and a means for increasing the intake air amount in order to suppress torque fluctuation at the time of switching from the vicinity of the theoretical air-fuel ratio to the lean air-fuel ratio, Means for detecting load, means for detecting the number of revolutions of the engine, means for increasing the rate of increase of the intake air amount when the load and the number of revolutions are low, and means for correcting the same rate of increase when the load and the number of revolutions are high. An intake air amount control device for a lean burn engine, comprising: