JP3319192B2 - Engine air-fuel ratio control device - 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 operating an engine lean (lean mixture).

[0002]

2. Description of the Related Art At the same time as improving fuel efficiency of an engine, NO
In order to reduce x, the fuel supply amount is controlled so that the air-fuel ratio, which is the ratio of air and fuel, becomes a lean air-fuel ratio leaner than the stoichiometric air-fuel ratio. An operating method of an engine in which the fuel ratio is corrected to a rich side to ensure combustion stability is disclosed in
It has been proposed in Japanese Patent Application Laid-Open No. 8-217732 and Japanese Patent Application Laid-Open No. 6-272591.

[0003]

However, according to the above apparatus, lean combustion becomes unstable when engine performance is deteriorated, for example, due to contamination of a spark plug, bite of a deposit in a valve seat, or wear of a piston ring. The air-fuel ratio is being corrected to the rich side,
For this reason, even if the air-fuel ratio itself is leaner than the stoichiometric air-fuel ratio, NOx increases with the shift to the rich side, and the engine is operated in the air-fuel ratio range where the amount of NOx emission becomes extremely large. May be controlled.

In order to cope with this, a correction amount of a set air-fuel ratio in a lean operation region (a stabilized fuel-air ratio correction coefficient Lldml in an embodiment to be described later) is set to a rich side limit value LLDMM.
X # is determined in advance, and when the correction coefficient Lldml is equal to or larger than the rich side limit value, by limiting to the rich side limit value LLDMMX #, the NOx emission amount is prevented from increasing due to deterioration of engine performance. ing.

[0005] Moreover, also predetermined lean-side limit value, to Rutoki the air-fuel ratio to the lean side correction amount setting an air-fuel ratio in the lean operation area is disengaged the lean-side limit value, the lean side Limited to the limit value.

In this case, since the limit air-fuel ratio for NOx emission and the limit air-fuel ratio for stability change depending on the set air-fuel ratio in the lean operation region, the control air-fuel ratio in the lean operation region under all operating conditions. Out of the limit air-fuel ratio of NOx emission
Of setting certain rich side limit value so as not to the rich side, since its value is a value for setting the air-fuel ratio when the come leanest side rich side limit value,
At other set air-fuel ratios, the correction range on the rich side is unnecessarily narrowed. Similarly, if the lean limit value is set at a constant value so that the lean air limit does not deviate from the limit air-fuel ratio for stability, the set value when the rich limit value is closest to the lean side is set. Since the value is based on the fuel ratio, the correction range on the lean side is unnecessarily narrowed at other set air-fuel ratios.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an appropriate margin from the limit air-fuel ratio under all operating conditions in the lean operation region to ensure the maximum correction range in the lean operation region.

[0008] The first invention, as shown in FIG. 15, the rotation
Means 51 for determining whether or not the engine is in a predetermined lean operation region based on a detection signal of an operating condition determined from the number and the load, and a target having a leaner air-fuel ratio than the stoichiometric air-fuel ratio when the lean operation region is determined. Means 52 for setting the value to a value, means 53 for detecting the stability of the engine, and means for calculating the correction coefficient Lldml of the set air-fuel ratio in the lean operation region in accordance with the output of the stability detection means 53 during lean operation. 54, means 55 for correcting the set air-fuel ratio in the lean operation region based on the correction coefficient Lldml, and means 56 for performing fuel control based on the corrected set air-fuel ratio.
And NOx emission that is a predetermined rich-side limit value for the correction coefficient Lldml and changes according to operating conditions.
Means 57 for setting a value for determining a margin from the limit air-fuel ratio of the amount in accordance with the detection signal of the operating condition, and setting the correction coefficient Lldml outside the rich-side limit value to make the air-fuel ratio rich. In some cases, means 58 for limiting the correction coefficient Lldml to the rich side limit value is provided.

[0009] The second invention, as shown in FIG. 16, the rotation
Means 51 for determining whether or not the engine is in a predetermined lean operation region based on a detection signal of an operating condition determined from the number and the load, and a target having a leaner air-fuel ratio than the stoichiometric air-fuel ratio when the lean operation region is determined. Means 52 for setting the value to a value, means 53 for detecting the stability of the engine, and means for calculating the correction coefficient Lldml of the set air-fuel ratio in the lean operation region in accordance with the output of the stability detection means 53 during lean operation. 54, means 55 for correcting the set air-fuel ratio in the lean operation region based on the correction coefficient Lldml, and means 56 for performing fuel control based on the corrected set air-fuel ratio.
And a predetermined lean limit value for the correction coefficient Lldml , which is a stability limit that varies according to operating conditions.
Means 61 for setting a value for determining a margin from the field air-fuel ratio in accordance with the detection signal of the operating condition, and when the correction coefficient Lldml is out of the lean-side limit value and the air-fuel ratio is set to the lean side. Means 62 for limiting the correction coefficient Lldml to the lean limit value.

A third aspect of the present invention, as shown in FIG. 17, the rotation
Means 51 for determining whether or not the engine is in a predetermined lean operation region based on a detection signal of an operating condition determined from the number and the load, and a target having a leaner air-fuel ratio than the stoichiometric air-fuel ratio when the lean operation region is determined. Means 52 for setting the value to a value, means 53 for detecting the stability of the engine, and means for calculating the correction coefficient Lldml of the set air-fuel ratio in the lean operation region in accordance with the output of the stability detection means 53 during lean operation. 54, means 55 for correcting the set air-fuel ratio in the lean operation region based on the correction coefficient Lldml, and means 56 for performing fuel control based on the corrected set air-fuel ratio.
And NOx emission that is a predetermined rich-side limit value for the correction coefficient Lldml and changes according to operating conditions.
A value for determining the allowance from the limit air-fuel ratio of the amount and a lean side limit value , and the stability that changes according to the operating conditions
Means 71 for setting a value for determining a margin from the limit air-fuel ratio in accordance with the detection signal of the operating condition and so that the limit width on the lean side is smaller than the limit width on the rich side, When the correction coefficient Lldml deviates from the rich side limit value to make the air-fuel ratio rich, the correction coefficient Lldml is deviated from the rich side limit value, and the correction coefficient Lldml deviates from the lean side limit value. Means for limiting the correction coefficient Lldml to the lean-side limit value.

[0011]

The limit air-fuel ratio of the NOx emission varies in accordance with the air-fuel ratio set in the lean operation range. Therefore, the rich side limit value is set so that the limit air-fuel ratio of the NOx emission does not deviate from the limit air-fuel ratio under all operating conditions. If you set a constant value,
Since this value is a value for the set air-fuel ratio when the rich side limit value is closest to the lean side, the correction range to the rich side is unnecessarily narrowed at other set air-fuel ratios. At this time, in the first invention, the rich-side limit value is set in accordance with the operating conditions, that is, is set in all operating conditions with an appropriate margin from the limit air-fuel ratio of the NOx emission amount that changes according to the operating conditions. , Under any operating condition in the lean operating range, N varies according to the operating condition.
The rich-side correction range is secured to the maximum corresponding to the limit air-fuel ratio of the Ox emission amount . Using the maximum rich-side correction range where the NOx emission does not exceed the limit at any operating condition in the lean operating range at the time of engine performance deterioration,
The set air-fuel ratio can be corrected to the rich side.

Since the limit air-fuel ratio of the stability changes depending on the air-fuel ratio set in the lean operation range, the lean-side limit value is set to a constant value so that the stability does not deviate from the limit air-fuel ratio under all operating conditions. When setting with, the value is the value for the set air-fuel ratio when the lean limit value is closest to the rich side.Therefore, at other set air-fuel ratios, the correction range to the lean side is unnecessarily increased. I will narrow it. At this time, in the second invention, the lean limit value is set in accordance with the operating conditions in the lean operating region, that is, set in all operating conditions with an appropriate margin from the stability limit air-fuel ratio that changes according to the operating conditions. Therefore, any operating condition in the lean operating range changes according to the operating condition.
The maximum lean-side correction range is ensured corresponding to the stability air-fuel ratio limit . Under any operating conditions in the lean operation range, the set air-fuel ratio can be corrected to the lean side using the maximum lean-side correction range in which the stability does not exceed the limit at that time.

In order to widen the rich-side correction range, the margin from the NOx emission limit air-fuel ratio at the rich-side limit value is narrowed, and accordingly, the margin from the stability limit air-fuel ratio at the lean-side limit value is reduced. When the air-fuel ratio is also narrowed, the stability near the stability limit air-fuel ratio rapidly deteriorates with respect to a change in the control air-fuel ratio. At this time, in the third invention, the limit width toward the lean side is smaller than the limit width toward the rich side.
Rich side limit value, lean side limit
Since the value is set, the margin from the stability limit increases, and the stability does not greatly deteriorate.

[0014]

1, an engine body 1 is provided with a fuel injection valve 7 located downstream of an intake throttle valve 5 in an intake passage 8 thereof. Fuel is injected and supplied into the intake air so that a predetermined air-fuel ratio is obtained. The control unit 2 receives a rotation speed signal from a crank angle sensor 4, an intake air amount signal from an air flow meter 6, an air-fuel ratio (oxygen concentration) signal from an oxygen sensor 3 installed in an exhaust passage 8, and a water temperature sensor 11. The engine cooling water temperature signal, the gear position signal from the gear position sensor 12 of the transmission, and the like are input, and the lean air-fuel ratio and the stoichiometric air-fuel ratio are controlled according to the conditions while determining the operating state based on these.

A three-way catalyst 10 is provided in the exhaust passage 8,
During operation at the stoichiometric air-fuel ratio, reduction of NOx in exhaust gas and oxidation of HC and CO are performed with maximum conversion efficiency. When the three-way catalyst 10 has a lean air-fuel ratio, HC and CO are oxidized, but NOx reduction efficiency is low.

However, the more the air-fuel ratio shifts to the lean side, the smaller the amount of NOx generated. If the air-fuel ratio is higher than a predetermined air-fuel ratio, it can be reduced to the same level as that obtained by purifying with the three-way catalyst 10. Fuel efficiency is improved as the lean air-fuel ratio is reached. On the other hand, when operating at a lean air-fuel ratio, combustion tends to be unstable depending on operating conditions.

Accordingly, in this example, in a predetermined operating region where the load is not so large, the operation is performed with the lean air-fuel ratio, the engine stability is detected at the same time, and if the engine stability deteriorates during the lean operation, the air-fuel ratio Is shifted to the rich side to ensure stability, that is, to perform stability feedback control at a lean air-fuel ratio to maintain good fuel economy characteristics without impairing engine stability.

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

First, FIG. 2 calculates a fuel-air ratio correction coefficient Dml for performing feedback control to an air-fuel ratio necessary for stabilizing the engine while detecting rotation fluctuation of the engine during operation with a lean air-fuel ratio. , Every 180 crank angles.

First, in step A), the inter-REF cycle Ref is read from the reference signal REF at every 180 degrees of the crank angle sensor 4, and in step B), the rotation fluctuation of the engine is calculated based on this Ref. The operation of calculating the rotation fluctuation is shown in the flowchart of FIG.

In step A) of FIG. 3, the period Refrv of one revolution section of the engine is calculated by the following formula: Refrv = Ref + Ref _n-1 (1) where Ref _n-1 is obtained by the previous equation of Ref. The old value of the rotation speed Nrv is shifted, and the previous data is stored in the RAM twice.
And 3 times before to 4 times before.

Next, in step C), Nrv = KN # / Refrv (2) where KN # is converted into an engine speed Nrev using Refrv in accordance with the equation of conversion constant from period to speed.

In step D), the rotational speed change amount D for each cylinder
The shift of the old value of nerv is performed in the same manner as the shift of nerv, and the new Dnerv is calculated as follows: Dnerv = Nerv-Nerv _n-4 (3) where Nerv _n-4 ; Is calculated by

In this case, a four-cylinder engine is taken as an example, and the rotational speed change amount Dnerv is the change amount of the current one rotation cycle with respect to one rotation cycle at the time of the previous combustion of the own cylinder (fourth previous combustion cylinder). Become. It should be noted that the variation is taken for each cylinder in order to prevent the variation between cylinders from being mistaken as a variation.

In step F), Llj, which is the amount of change in the number of revolutions, is calculated by the following formula: Llj = Dnerv-Dnervn _-1 (4) where Dnervn _-1 ;

Here, Llj is the amount of change from the immediately preceding Dnerv to the current Dnerv, and corresponds to a pseudo torque variation accompanying combustion. Then, in step G), the amount of change L
By performing a band-pass filter process on lj and storing the result as a stability signal (rotation fluctuation amount) Lljd, the operation of this flowchart ends.

It should be noted that the band pass filter processing is performed by the EC
U software is available, using the equation converted from continuous system to discrete system,
The frequency may be about 3 to 7 Hz, which is easily felt by the driver of the vehicle as a surge.

The flow of FIG. 3 constitutes means for detecting the stability of the engine.

After calculating the rotation fluctuation amount in this way,
Returning to FIG. 2, it is determined in step C) whether feedback (F / B) control with a lean air-fuel ratio is performed while monitoring the stability of the engine. This will be described with reference to the flowchart of FIG.

In step A) of FIG. 4, it is determined whether the condition is a lean condition. The lean operation conditions will be described in detail with reference to the flowcharts of FIGS. 7 and 8 described later, which are performed as a background job. Basically, the engine speed and load, and furthermore, the gear position and the vehicle speed are within predetermined ranges, respectively. Done if done. When the lean condition is reached, the control jumps to F / B control inhibition in step L).

However, even under the lean condition, the F / B control is not always performed in order to secure the stability of the control. Therefore, the following items are checked.

In step B), it is determined whether or not the air-fuel ratio is being switched. If Dml obtained in steps G) to K) in FIG. 2 described later is the same as Tdml, it is determined that switching is not being performed. If the switching is being performed, the process jumps to step L) as described above, and the F / B control is prohibited.

Next, it is determined in step C) whether or not the area is in the F / B control area. This is performed by checking a permission flag set according to the rotation speed Ne and the load Tp for the entire operating range of the engine as shown in FIG.
If it is not in the permitted F / B control area, the process jumps to F / B control prohibition. Note that, in this embodiment, the F / B control is performed except in a high rotation range.

In step D), the gear position is checked. If the gear position is less than the predetermined low-speed gear LLGR #, F /
Jump to B control prohibition. This is to inhibit the F / B control when the transmission is in a low-speed gear, because the rotation changes rapidly, for example, at the first speed. Also, when neutral, the F / B control is similarly prohibited. In step F), it is determined whether or not the gear position is being changed by comparing the previous gear position with the current gear position. If it is determined that a gear change has been made, the process also jumps to F / B control inhibition.

Next, in steps G) to I), a determination is made to inhibit the F / B control during the transient operation. The change in the throttle valve opening Tvo, the change in the basic pulse width Tp,
The change amount of the engine speed Ne is set to the set value LLD.
If any of the change amounts exceeds the set value compared to TVO #, LLDNE #, LLDTP #, it is determined that the state is a transient state and the F / B control is prohibited in the same manner as described above.

If all the conditions have been satisfied so far,
In step J), a process of giving a delay of the F / B control is performed. Here, it is checked whether or not a predetermined time TMLLC # has elapsed after all of the steps D) to I) have become the F / B control conditions, and the F / B control is prohibited until the predetermined time has elapsed. For the first time, it is determined that the region is the F / B control region.

The delay is given by the stability signal Llj.
d is passed through a filter, and when it is affected by disturbance, the output is not stabilized immediately, and the rotation fluctuation generated by gear change etc. does not disappear instantaneously due to the vibration system of the vehicle. Yes, more stable F /
In order to perform the B control, it is better to provide a predetermined delay.

After the determination of the F / B control is performed in this manner, the flow returns to FIG. 2 again. In step D), it is checked whether or not the stability F / B control is performed. E) according to the flowchart of FIG.
Correction rate of F / B control, that is, stabilized fuel-air ratio correction coefficient Ll
Update and calculate dml.

Here, a stabilized fuel-air ratio correction coefficient for performing the F / B control is calculated based on the rotation fluctuation amount calculated as described above. First, in step A), the above-mentioned stability signal Lljd is calculated. Sample and count this number of samples.

In step B), the number of samples is set. The number of samples is set as shown in FIG.
e, the set value of the long L, which varies with
In this case, the detection accuracy increases as the number of samples increases, but on the other hand, the control speed decreases (the smaller the number, the higher the detection speed).

Next, in step C), it is determined whether or not the number of samples is L. If so, step D)
The sample data total is divided by L to obtain an average value, and a value obtained by subtracting the stability determination comparison value SLL # from the average value is used to obtain the update amount Lldml (+/−) of Lldml from the characteristic map shown in FIG. Is calculated. In this characteristic diagram, in order to prevent torque fluctuation (shock) caused by changing the fuel-air ratio by this control, the dead zone where Dlldml = 0 is defined by the boundary between the region where the update amount is positive and the region where the update amount is negative. And a predetermined width around the center.

Then, in step F), the stabilized fuel-air ratio correction coefficient Lldml is updated by the following equation: Lldml = Lldml _n-1 + Dldml (5) where Lldml _n-1 ; Lldml one time before.

Therefore, the stabilized fuel-air ratio correction coefficient Lldm
l becomes a larger value as the rotation fluctuation amount increases, that is, as the stability of the engine deteriorates.

Step A) in the above flow of FIG.
To F) constitute means for calculating a correction coefficient of the set air-fuel ratio in the lean operation region.

Step G) and subsequent steps will be described later in detail.

Next, returning to FIG. 2, the F /
After completing the calculation of the correction rate of the B control, the process proceeds to step F) in FIG. 2 to calculate the target fuel-air ratio Tdml.
This target fuel-air ratio is calculated by searching for the fuel-air ratio Mdml set in the characteristic map shown in FIG. 9 or FIG. 10, and correcting this by the stabilized fuel-air ratio correction coefficient Lldml during F / B control. In this case, one of the maps is selected depending on whether or not the vehicle is in the lean operation condition.

Here, the determination of the lean operation condition will be described with reference to the flowcharts of FIGS.

These operations are performed as a background job. Lean conditions are determined in step A) of FIG. 7, and specific contents for this are shown in FIG.
The lean condition is determined by checking the contents of steps A) to F) of FIG. 8 one by one. When all of the items are satisfied, lean operation is permitted. Ban.

That is, Step A): The air-fuel ratio (oxygen) sensor is activated, Step B): The warm-up of the engine is completed, Step C): The load (Tp) is in a predetermined lean region. Step D): The rotational speed (Ne) is in a predetermined lean region. Step E): The gear position is in the second speed or higher. Step F): The vehicle speed is in a predetermined range. The lean operation is permitted, and if not, the process proceeds to step I) to prohibit the lean operation.
The above steps A) to F) are conditions for stably performing the lean operation without impairing the operation performance.

The above-described flow of FIG. 8 constitutes means for determining the lean operation region.

When the lean condition is determined in this way,
Returning to steps C) and D) in FIG. 7, when the condition is not the lean condition, the stoichiometric fuel-air ratio or a map fuel-air ratio deeper than the stoichiometric fuel-air ratio is determined in step C), and the characteristic map shown in FIG. Calculated by searching with Tp,
On the other hand, under the lean condition, the map fuel-air ratio Mdml that is thinner by a predetermined range than the stoichiometric air-fuel ratio in step D)
Is similarly searched according to the characteristic map shown in FIG.

The numerical values shown in these maps are relative values when the stoichiometric air-fuel ratio is 1.0, so that a larger value indicates richer and a smaller value indicates leaner. The above-described flow of FIG. 7 and the map of FIG. 9 constitute means for setting the air-fuel ratio target value in the lean operation region.

Here, returning to step F) of FIG. 2 again,
Of the map fuel-air ratio Mdml calculated in this way, for Mdml under the lean condition, based on the stabilized fuel-air ratio correction coefficient Lldml, Tdml = Mdml × Lldml (7) where Mdml: target fuel-air The target fuel-air ratio Tdml is calculated by correcting with the equation of the map value of the ratio.

The target fuel-air ratio Tdml is such that Lldml increases as the engine rotation fluctuation increases.
As the degree of stability deteriorates, the value increases, that is, the target air-fuel ratio shifts to the rich side.

The following step G) is to gradually change the air-fuel ratio in the damper operation process at the time of switching the fuel-air ratio, thereby preventing a sudden change in the torque and ensuring the stability of the driving performance. .

In step G), the fuel-air ratio correction coefficient Dml is compared with the previously calculated Tdml.
If not ≧ Tdml, that is, if the calculated target fuel-air ratio is larger than the held fuel-air ratio correction coefficient Dml, in order to shift the air-fuel ratio to the rich side in steps H) and I), Dmlr corresponding to the air-fuel ratio change speed to the rich side is added to the correction coefficient Dmln _-1 to obtain a new D
Obtain ml. Then, Dml is limited 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,
In steps J) and K), by subtracting the air-fuel ratio change speed Ddmll toward the lean side from the held Dml,
A new fuel-air ratio correction coefficient Dml shifted to the lean side is obtained, and Dm is adjusted so that Dml does not become less than Tdml.
l is restricted.

The flow of FIG. 2 constitutes means for correcting the set air-fuel ratio in the lean operation region.

It should be noted that there is no lean condition, and based on the characteristic map shown in FIG.
When dml is calculated, although not shown, the map fuel-air ratio Mdml in step F) is not corrected by the stabilized fuel-air ratio correction coefficient Lldml, and this Md
The fuel-air ratio correction coefficient Dml may be calculated by directly replacing ml with the target fuel-air ratio Tdml in step G).

Based on the fuel-air ratio correction coefficient Dml calculated in this way, the following calculation of the fuel injection amount is performed.

The flowchart of FIG. 6 shows the control operation for calculating and outputting the fuel injection pulse width using the fuel-air ratio correction coefficient Dml obtained in this manner. Using the coefficient Dml, the target fuel-air ratio Tfbya is calculated by the following equation: Tfbya = Dml + Ktw + Kas (8) where Ktw: water temperature increase correction coefficient Kas;

Here, Ktw is a fuel increase according to the cooling water temperature, and Kas is a fuel increase immediately after starting. Next, in step B), the output of the air flow meter is A / D converted and linearized to calculate the intake air flow rate Q. In step C), based on the intake air flow rate Q and the engine speed Ne, the basic pulse width Tp to be given to the fuel injection valve is calculated as Tp =
It is obtained as K × Q / N. K is a constant.

Then, in step D), based on this Tp, one fuel injection pulse width Ti is calculated as follows: Ti = Tp × Tfbya × Ktr × (α + αm) + Ts (9) where Ktr; Correction coefficient α; air-fuel ratio feedback correction coefficient αm; air-fuel ratio learning correction coefficient Ts; invalid pulse width

However, under the lean condition, these K
tr, α, αm, etc. are fixed at predetermined values.

Next, the fuel cut is determined in step F), and the invalid pulse width Ts is stored in the output register if the fuel cut condition is satisfied in steps G) and H), and Ti is stored in the output register otherwise. In preparation for injection at a predetermined injection timing according to the output of

The above-described flow of FIG. 6 constitutes means for performing fuel control based on the corrected set air-fuel ratio.

The fuel injection pulse width Ti is calculated in this manner. Therefore, when the stability is deteriorated during the stability feedback control in the lean operation, the set air-fuel ratio is shifted to the rich side accordingly, and Of fuel consumption and NOx without sacrificing drivability
To reduce

By the way, as shown in FIG. 14, in the operation with a lean air-fuel ratio, the leaner the air-fuel ratio, the lower the NOx emission level, but the worse the engine stability. Therefore, if the air-fuel ratio is maintained such that the NOx emission level is lower than the allowable limit and the engine stability is also at the allowable limit, it is possible to sufficiently reduce NOx without impairing the stability of the engine. Becomes
Deterioration of stability can be dealt with by shifting the air-fuel ratio to the rich side.
NOx emission levels exceed acceptable limits. Also,
If the air-fuel ratio blindly shifts to the lean side just because NOx decreases, combustion deteriorates, and stable operation of the engine cannot be maintained.

The A characteristic and the B characteristic in FIG.
The relationship between the NOx emission amount and the engine stability when the air-fuel ratio is changed under the A operating condition (load and rotation) and the B operating condition is shown. Even at the air-fuel ratio of NOx, the NOx emission characteristics and the stability characteristics are different.

Therefore, the map air-fuel ratio set as the target air-fuel ratio at the time of the lean operation as shown in FIG. 9 is used to determine the limit of the rich-side air-fuel ratio and the stability of the stability from the NOx emission amount while considering these operating conditions. If the predetermined value is set within a range from the limit to the limit of the lean air-fuel ratio, the lean operation can be performed under the condition that the NOx and the stability are always in a constant range. In this case, the stabilized fuel-air ratio correction coefficient Ll
Since the dml and the NOx emission amount substantially correspond to each other, the NOx emission amount can always be suppressed within the allowable limit without measuring the NOx emission amount.

The target air-fuel ratio is set, for example, by NO
The air-fuel ratio value is lean from the air-fuel ratio at the emission limit of x by a certain value, the air-fuel ratio value on the rich side by a certain value from the air-fuel ratio at the stability limit, the air-fuel ratio value approximately halfway between both limit air-fuel ratios, and both The limit air-fuel ratio can be set as an air-fuel ratio value that internally divides by a fixed ratio.

When lean combustion becomes unstable due to deterioration of engine performance, the air-fuel ratio is corrected to the rich side more and more. Therefore, even if the air-fuel ratio itself is leaner than the stoichiometric air-fuel ratio, it becomes richer. With the shift of NOx
, The engine may be controlled in the range of the air-fuel ratio where the amount of NOx emission becomes very large. In order to cope with this, a rich side limit value LLDMMMX # is predetermined for the stabilized fuel-air ratio correction coefficient Lldml,
When the correction coefficient Lldml is equal to or larger than the rich side limit value, by limiting to the rich side limit value,
It is possible to prevent the emission amount of NOx from increasing due to the deterioration of the engine performance.

Further, a lean limit value is also determined in advance, and when the correction coefficient Lldml is lower than the lean limit value, the control air-fuel ratio during lean operation is stabilized by limiting to the lean limit value. Leaning can be prevented from exceeding the temperature limit.

However, since the limit air-fuel ratio for NOx emission and the limit air-fuel ratio for stability change depending on the set air-fuel ratio during lean operation, the control air-fuel ratio during lean operation becomes lower under all operating conditions. Rich beyond the limit air-fuel ratio
If a constant rich side limit value is set so as not to be on the side, the value will be a value with respect to the set air-fuel ratio when the rich side limit value is closest to the lean side. Sometimes, the correction width on the rich side is unnecessarily narrowed. Similarly, deviate from the stability air-fuel ratio.
If the lean limit value is set at a constant value so that it does not become lean, the value will be the value for the set air-fuel ratio when the rich limit value is closest to the lean side. At the time of the air-fuel ratio, the correction range on the lean side is unnecessarily narrowed.

To cope with this, the control unit 2 sets the rich side limit value in order to provide an appropriate margin from each of the rich side and lean side limit air-fuel ratios under all the operating conditions in the lean operation region. And the limit value on the lean side are set according to the operating conditions.

Specifically, in FIG. 5, after the stabilized fuel-air ratio correction coefficient Lldml is updated in step F) as described above, the process proceeds to step G), where the rich side limit value and lean side limit value for Lldml are determined. Is set according to the rotation speed Ne at that time and the basic pulse width Tp as a load. For example, the limit width on the rich side is LDMLR (> 0) and the limit width on the lean side is L around 1.0.
LDMLL (≧ 0), these limited widths LLDML
A map using R and LLDMLL as parameters of Ne and Tp is created in advance, and LL is obtained from Ne and Tp at that time.
Search each map of DMLR and LLDMLL.

At this time, since 1.0 + LLDMLR is the limit value on the rich side and 1.0-LLDMLL is the limit value on the lean side, in step H), Lldml is compared with the rich side limit value, and Lldml is set to the rich side limit value. Is exceeded, Lldml is limited to the rich-side limit value in step I), and the routine of FIG. 5 ends. Similarly, in step J), Lldml is compared with the lean limit value. When Lldml is lower than the lean limit value, Lldml is limited to the lean limit value in step K). Note that Lldml is stored in the memory and is constantly updated during F / B control.

The characteristics of the LLDMLR and LLDMLL tend to be different for Ne and Tp. This is because the limit air-fuel ratio of the NOx emission and the limit air-fuel ratio of the stability are basically determined by the combustion characteristics during lean operation with the engine hardware configuration such as the combustion chamber shape, intake pipe shape, and swirl control valve. Depending on the set air-fuel ratio (that is, the lean map characteristic),
This is because the values of LLDMLR and LLDMLL are determined in relation to the different limit air-fuel ratio of the NOx emission amount and the limit air-fuel ratio of the stability. Therefore, after determining the engine hardware configuration and the set air-fuel ratio at the time of the lean operation, the characteristics of LLDMLR and LLDMLL are determined by matching.

For example, in FIG. 14, when the set air-fuel ratio (more precisely, Mdml) is 0.7, β is the maximum limit width on the rich side up to the limit air-fuel ratio of NOx emission, and γ is the limit air-fuel ratio of the stability. Therefore, a value that is slightly smaller than the rich-side maximum limit width in consideration of the margin of NOx emission is set as LDMLR, and the lean-side maximum limit is considered in consideration of the margin of stability. A value slightly smaller than the width is defined as LDMLL. Similarly, when the set air-fuel ratio becomes 0.66, δ becomes the rich-side maximum limit width up to the limit air-fuel ratio of NOx emission, and ε becomes the lean-side maximum limit width up to the limit air-fuel ratio of stability. At this time, the value of LLDMLR is also taken into consideration in consideration of the allowance for NOx emission,
Also, the value of LDMLL is determined in consideration of the margin of stability. In other words, the sizes of the rich-side maximum limit widths (β and δ) and the lean-side maximum limit widths (γ and ε) change depending on the set air-fuel ratio during the lean operation. Becomes smaller as the set air-fuel ratio becomes smaller,
The value of LLDMLL decreases.

As described above, if the set air-fuel ratio during the lean operation is made different and the data of the LLDMLR and the LLDMLL are collected, the characteristics of the LLDMLR and the LLDMLL using the set air-fuel ratio during the lean operation as a parameter are obtained. Since the set air-fuel ratio at the time of the lean operation is determined using Ne and Tp as parameters, the characteristics of LLDMLR and LLDMLL using the set air-fuel ratio at the time of lean operation as parameters, and LLDMLR and LL using Ne and Tp as parameters, respectively.
If the characteristics of DMLL are changed, LLDMLR and LL
Each map of DMLL can be created.

In order to give priority to the stability of the engine, LLDMLR is made larger than LDMLL under all conditions of Ne and Tp. This is because, as shown in FIG. 14, the stability rises sharply in the vicinity of the stability limit air-fuel ratio (that is, the drivability at the stability limit deteriorates sharply with a change in the air-fuel ratio). This is because we want to make the side limit value as small as possible.

In step G) of the flow of FIG. 5, the predetermined rich-side limit value and lean-side limit value for the correction coefficient Lldml are set in accordance with the detection signal of the operating condition, and the lean-side limit value is more than the rich-side limit value. Steps H), I) and
J) and K) denote the correction coefficient Lldml at the rich side limit value when the correction coefficient Lldml exceeds the rich side limit value, and the correction coefficient Lldml at the lean side limit value when the correction coefficient Lldml is below the lean side limit value. The means for restricting the number is constituted.

Here, the operation of this example will be described.

Since the limit air-fuel ratio of NOx emission varies depending on the set air-fuel ratio during lean operation, the rich side limit value is set so that the limit air-fuel ratio does not deviate from the limit air-fuel ratio of NOx emission under all operating conditions. If you set a constant value,
This value is a value for the set air-fuel ratio when the rich side limit value is closest to the lean side, and the correction range to the rich side is unnecessarily narrowed at other set air-fuel ratios.

On the other hand, in this example, the rich-side limit value is set in accordance with the operating conditions, that is, is set in all operating conditions with an appropriate margin from the limit air-fuel ratio of the NOx emission amount that changes according to the operating conditions. Then, the correction range on the rich side is maximized under any operating conditions during the lean operation. The set air-fuel ratio can be corrected to the rich side by using the maximum rich-side correction range in which the NOx emission amount does not exceed the limit under any operating conditions during the lean operation when the performance of the engine is deteriorated.

Also, since the limit air-fuel ratio of stability changes depending on the set air-fuel ratio at the time of lean operation, the lean limit value is set so that the stability does not deviate from the limit air-fuel ratio under all operating conditions. When setting at a constant value, the value is the value for the set air-fuel ratio when the lean limit value is closest to the rich side, and the correction range to the lean side is unnecessarily set at other set air-fuel ratios. I will narrow it.

At this time, in this example, the lean limit value is set in accordance with the operating conditions during the lean operation, that is, set in all operating conditions with an appropriate margin from the stability limit air-fuel ratio that changes depending on the operating conditions. Therefore, the lean correction range is maximized under any operating conditions during the lean operation. Under any operating conditions during the lean operation, the set air-fuel ratio can be corrected to the lean side by using the maximum lean-side correction range in which the stability does not exceed the limit at that time.

On the other hand, in order to widen the correction range on the rich side, the margin from the NOx emission limit air-fuel ratio at the rich side limit value is narrowed, and accordingly, the margin from the stability limit air-fuel ratio at the lean side limit value is reduced. When the margin is narrowed, the stability near the stability limit air-fuel ratio rapidly deteriorates with respect to the change in the control air-fuel ratio.

On the other hand, in this example, since the lean limit value is set smaller than the rich limit value, a margin from the stability limit is increased, and the stability is not greatly deteriorated.

In the embodiment, the example has been described in which the stabilized fuel-air ratio correction coefficient is calculated so that the stability becomes the target value. However, the stabilized fuel-air ratio correction coefficient is calculated such that the stability becomes the target value or less. It does not matter what you do. An example in which the stability is equal to or less than the target value is a case in which Lldml is not updated to the lean side in steps E) and F) of FIG. 5 (that is, Dlldml = 0 in a region where the average value -SLL # is negative in FIG. 13). )
It is.

[0091]

The first invention is based on the rotational speed and the load.
Means for determining whether the lean operation region on the basis of the detection signal is set in advance of operating conditions that, means for setting the air-fuel ratio to lean target value than the stoichiometric air-fuel ratio when it is determined the lean operation area Means for detecting the stability of the engine, means for calculating a correction coefficient for the set air-fuel ratio in the lean operation region in accordance with the output of the stability detection means during lean operation, and the lean control based on the correction coefficient. Means for correcting the set air-fuel ratio in the operation region, means for performing fuel control based on the corrected set air-fuel ratio, and a predetermined rich-side limit value for the correction coefficient ,
Allowance from the limit air-fuel ratio of NOx emission that changes according to
Means for setting a value for giving the operating condition according to the detection signal of the operating condition; and when the correction coefficient is outside the rich side limit value and the air-fuel ratio is on the rich side, the correction coefficient is set to the rich side limit value. since there is provided a means for limiting, the operating conditions in any operating condition of the lean operation area
Corresponding to the limit air-fuel ratio of NOx emission
As a result, the maximum rich-side correction range is ensured, and the maximum rich-side correction range in which the NOx emission does not exceed the limit at any time in any operating condition in the lean operation region when the performance of the engine is deteriorated, The set air-fuel ratio can be corrected to the rich side.

According to a second aspect of the present invention, a means for judging whether or not the engine is in a preset lean operation area based on a detection signal of an operating condition determined from the number of revolutions and the load, and judging the lean operation area. Means for setting the air-fuel ratio to a target value leaner than the stoichiometric air-fuel ratio, means for detecting the stability of the engine, and setting in the lean operation region corresponding to the output of the stability detection means during lean operation Means for calculating an air-fuel ratio correction coefficient, means for correcting the set air-fuel ratio in the lean operation region based on the correction coefficient, and performing fuel control based on the corrected set air-fuel ratio 56; response to the operating condition a predetermined lean-side limit value for the correction factor
Allowance from the limit air-fuel ratio of the continuously changing stability
Means for setting a value for the operating condition in accordance with the detection signal of the operating condition, and limiting the correction coefficient to the lean-side limit value when the correction coefficient deviates from the lean-side limit value and sets the air-fuel ratio to the lean side. Means to perform any operating conditions in the lean operating range according to the operating conditions.
The maximum lean-side correction range is ensured in response to the changing stability limit air-fuel ratio , so that the maximum lean-side correction at which the stability does not exceed the limit at any operating condition in the lean operation range Using the range, the set air-fuel ratio can be corrected to the lean side.

According to a third aspect of the present invention, there is provided a means for determining whether or not the engine is in a predetermined lean operation region based on a detection signal of an operating condition determined from the rotational speed and the load, and determining the lean operation region. Means for setting the air-fuel ratio to a target value leaner than the stoichiometric air-fuel ratio, means for detecting the stability of the engine, and setting in the lean operation region corresponding to the output of the stability detection means during lean operation Means for calculating an air-fuel ratio correction coefficient, means for correcting a set air-fuel ratio in the lean operation region based on the correction coefficient, means for performing fuel control based on the corrected set air-fuel ratio, response to the operating condition a predetermined rich-side limit value for the correction factor
Margin from the limit air-fuel ratio of NOx emissions
Value and the lean-side limit value and the operating conditions
Allowance from the limit air-fuel ratio of stability that changes according to
Means for setting a value for obtaining as limiting the width of the in accordance with the detection signal and the lean side of the limit width to the rich side of the operating conditions is reduced, the correction coefficient is the rich side limit value When the air-fuel ratio is deviated to the rich side, the correction coefficient is set to the rich side limit value. When the correction coefficient is deviated from the lean side limit value to make the air-fuel ratio lean, the correction coefficient is set to the lean side. Means for limiting to the side limit value, the set air-fuel ratio and NO
Correction according to the margins between the x limit air-fuel ratio and the stability limit air-fuel ratio can be performed, and the margin from the stability limit increases on the lean side, so that the stability does not greatly deteriorate.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a flowchart of a 180-degree job.

FIG. 3 is a flowchart for explaining calculation of rotation fluctuation.

FIG. 4 is a flowchart for explaining determination of a feedback control condition.

FIG. 5 is a flowchart for explaining calculation of a stabilized fuel-air ratio correction coefficient Lldml.

FIG. 6 is a flowchart of a 10 msec job.

FIG. 7 is a flowchart of a background job.

FIG. 8 is a flowchart illustrating the determination of a lean condition.

FIG. 9 is a characteristic diagram showing the contents of a lean map.

FIG. 10 is a characteristic diagram showing the contents of a non-lean map.

FIG. 11 is a region diagram showing both a region in which feedback control is performed and a region in which feedback control is prohibited.

FIG. 12 is a characteristic diagram showing a table content of a predetermined number L of samples.

FIG. 13 is an update amount D of the stabilized fuel-air ratio correction coefficient Lldml.
It is a characteristic diagram which shows the table content of lldml.

FIG. 14 is a characteristic diagram showing a relationship between an air-fuel ratio, a NOx emission amount, and stability.

FIG. 15 is a configuration diagram (claim correspondence diagram) of the first invention.

FIG. 16 is a configuration diagram (claim correspondence diagram) of the second invention.

FIG. 17 is a configuration diagram (claim correspondence diagram) of the third invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 2 Control unit 3 Oxygen sensor 4 Crank angle sensor 6 Air flow meter 7 Fuel injection valve 51 Lean operation region determination means 52 Air-fuel ratio target value setting means 53 Stability detection means 54 Correction coefficient calculation means 55 Set air-fuel ratio correction means 56 Fuel control means 57 Rich side limit value setting means 58 Limiting means 61 Lean side limit value setting means 62 Limiting means 71 Limit value setting means 72 Limiting means

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F02D 41/00-41/40 F02D 43/00-45/00

Claims (3)

(57) [Claims] A means for judging whether or not the engine is in a predetermined lean operation region based on a detection signal of an operation condition determined from a rotational speed and a load; Means for setting a leaner target value, means for detecting the stability of the engine, and a correction coefficient for the set air-fuel ratio in the lean operation region corresponding to the output of the stability detection means during lean operation. Means for correcting a set air-fuel ratio in the lean operation region based on the correction coefficient; means for performing fuel control based on the corrected set air-fuel ratio; and a predetermined rich limit for the correction coefficient. value met
Air-fuel ratio of NOx emission that varies depending on operating conditions
Means for setting a value for giving a margin from the operation condition according to the detection signal of the operating condition; and when the correction coefficient is outside the rich side limit value and the air-fuel ratio is on the rich side, the correction coefficient is An air-fuel ratio control device for an engine, comprising: means for restricting to a rich-side limit value. Means for determining whether or not the engine is in a predetermined lean operating region based on a detection signal of operating conditions determined from the rotational speed and the load; and determining the air-fuel ratio when the lean operating region is determined based on the stoichiometric air-fuel ratio. Means for setting a leaner target value, means for detecting the stability of the engine, and a correction coefficient for the set air-fuel ratio in the lean operation region corresponding to the output of the stability detection means during lean operation. Means for correcting the set air-fuel ratio in the lean operation region based on the correction coefficient; means for performing fuel control based on the corrected set air-fuel ratio; and a predetermined lean limit for the correction coefficient. value met
From the limit air-fuel ratio of the stability that changes according to the operating conditions
Means for setting a value for providing a margin according to the detection signal of the operating condition; and when the correction coefficient is outside the lean limit value and the air-fuel ratio is on the lean side, the correction coefficient is set to the lean side. An air-fuel ratio control device for an engine, comprising: means for restricting to a limit value. 3. A means for judging whether or not the engine is in a predetermined lean operation region based on a detection signal of an operation condition determined from a rotation speed and a load; Means for setting a leaner target value, means for detecting the stability of the engine, and a correction coefficient for the set air-fuel ratio in the lean operation region corresponding to the output of the stability detection means during lean operation. Means for correcting a set air-fuel ratio in the lean operation region based on the correction coefficient; means for performing fuel control based on the corrected set air-fuel ratio; and a predetermined rich limit for the correction coefficient. value met
Air-fuel ratio of NOx emission that varies depending on operating conditions
And the limit value on the lean side
Is the limit air-fuel ratio of stability that changes depending on operating conditions?
Means for setting a value for providing such a margin allowance in accordance with the detection signal of the operating condition and so that the limit width on the lean side is smaller than the limit width on the rich side, and the correction coefficient is The correction coefficient is set to the rich side limit value when the air-fuel ratio is deviated from the rich side limit value and the air-fuel ratio is deviated from the rich side limit value. Means for limiting a correction coefficient to the lean limit value.