JP3147689B2 - 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-mentioned apparatus, when the engine performance is significantly deteriorated (hereinafter referred to as "hard failure"), for example, the spark plug becomes dirty, the deposit gets stuck in the valve seat, the piston ring wears, and the like. When the lean combustion becomes unstable, the air-fuel ratio is corrected to the rich side more and more, so even if the air-fuel ratio itself is leaner than the stoichiometric air-fuel ratio, the air-fuel ratio becomes Since NOx increases, the engine may be controlled in a range of the air-fuel ratio in which the amount of NOx emission becomes extremely large.

To cope with this, when it is determined that a hardware failure has occurred, the lean operation is prohibited and the operation is switched to the operation at the stoichiometric air-fuel ratio so that the drivability does not deteriorate even in the case of the hardware failure. Has been proposed by the applicant at the same time as the present application.

However, in this prior application, the stability of the engine is detected from fluctuations in the rotation of the engine, and it is determined whether a hard failure has occurred based on the output of the stability detecting means during lean operation. There is a possibility that a malfunction is erroneously diagnosed as a hardware failure due to factors other than the hardware failure, such as when the state is rough or due to fine movement of the throttle valve, and thereafter, the lean operation is prohibited. For example, when the road surface condition is rough, the fluctuation of the road surface becomes the rotation fluctuation of the tire. When the engine and the driving system are directly connected, the rotation fluctuation of the tire adds to the fluctuation of the engine rotation. Even if the combustion of the engine is stable, the output of the stability detection means increases when the road surface condition is severely rough, so that a hard failure is diagnosed, and lean operation is prohibited even if it is not a hard failure. It will be.

The present invention is an improvement of the above-mentioned prior application. Even if lean operation is prohibited and the operation is returned to the operation at the stoichiometric air-fuel ratio when it is determined that a hardware failure has occurred, an erroneous diagnosis of a hardware failure is found thereafter. Then, the prohibition of the lean operation is released to increase the opportunities for the lean operation.

[0007] The present invention also relates to the problem of poor combustion due to a hardware failure.
Is very large during lean operation, but at stoichiometric air-fuel ratio
Hunting when driving is not very large
The purpose is to deal with the occurrence of.

[0008]

According to a first aspect of the present invention, as shown in FIG. 17, means 51 for judging whether or not a vehicle is in a preset lean operation region based on a detection signal of operation conditions.
Means 52 for setting the air-fuel ratio to a target value leaner than the stoichiometric air-fuel ratio when the lean operation region is determined, and means 53 for detecting the stability of the engine from fluctuations in engine rotation.
And a correction coefficient Lld of the set air-fuel ratio in the lean operation region corresponding to the output of the stability detecting means 53 during the lean operation.
ml calculating means 54, means 55 for correcting the set air-fuel ratio in the lean operation region based on the correction coefficient Lldml, means 56 for performing air-fuel ratio control based on the corrected set air-fuel ratio, Means 57 for determining whether a hard failure has occurred during lean operation, means 58 for inhibiting lean operation when it is determined that a hard failure has occurred, and stability detection in a state in which the lean operation is prohibited. A means 59 for judging whether or not the hard failure has been misdiagnosed by comparing the output of the means 53 with a judgment value for canceling the lean operation prohibition, and a lean operation by the lean operation prohibiting means 58 when the misdiagnosis is judged. The means 60 for canceling the prohibition of driving and the means 58
Count the number of times that lean operation is prohibited by this
As the number of times of prohibition of rotation increases, the
Means 61 for changing the determination value to a smaller value is provided.

In the second invention, as shown in FIG.
Lean operation set in advance based on the condition detection signal
Means 51 for determining whether or not the vehicle is in a turning region;
When the air-fuel ratio is determined to be leaner than the stoichiometric air-fuel ratio
Means 52 for setting the value of the
Means 53 for detecting from rotation fluctuations of the
The lean operation region corresponds to the output of the degree detection means 53.
For calculating the correction coefficient Lldml of the set air-fuel ratio in
4 and the correction coefficient Lldml.
Means 55 for correcting the set air-fuel ratio in the turning region;
Means 56 for performing air-fuel ratio control based on the set air-fuel ratio
And whether a hard failure has occurred during lean operation
Determining means 57 for determining that a hardware failure has occurred;
Means 58 for inhibiting the lean operation when the
The output of the stability detecting means 53 in the state where driving is prohibited and
Based on the comparison with the judgment value of the release of the prohibition of lean operation,
How to judge whether the judgment of hardware failure was misdiagnosis
Step 59 and the lean operation when it is determined that a misdiagnosis has occurred
Means 6 for releasing prohibition of lean operation by prohibition means 58
0 and means 62 for prohibiting the prohibition release of the lean operation by the prohibition releasing means 60 when the number of times of prohibition of the lean operation becomes equal to or more than a predetermined value.

[0010] In the third invention, as shown in FIG.
Lean operation set in advance based on the condition detection signal
Means 51 for determining whether or not the vehicle is in a turning region;
When the air-fuel ratio is determined to be leaner than the stoichiometric air-fuel ratio
Means 52 for setting the value of the
Means 53 for detecting from rotation fluctuations of the
The lean operation region corresponds to the output of the degree detection means 53.
For calculating the correction coefficient Lldml of the set air-fuel ratio in
4 and the correction coefficient Lldml.
Means 55 for correcting the set air-fuel ratio in the turning region;
Means 56 for performing air-fuel ratio control based on the set air-fuel ratio
And whether a hard failure has occurred during lean operation
Determining means 57 for determining that a hardware failure has occurred;
Means 58 for inhibiting the lean operation when the
The output of the stability detecting means 53 in the state where driving is prohibited and
Based on the comparison with the judgment value of the release of the prohibition of lean operation,
How to judge whether the judgment of hardware failure was misdiagnosis
Step 59 and the lean operation when it is determined that a misdiagnosis has occurred
Means 6 for releasing prohibition of lean operation by prohibition means 58
0 and provided with a said failure determining means 57, a means 71 for setting a predetermined rich-side limit value for the previous SL correction coefficient Lldml, the correction coefficient Lld when the correction coefficient Lldml exceeds the rich side limit value
a means 72 for limiting ml to the rich side limit value;
A means 73 for measuring a time during which the correction coefficient Lldml is continuously limited to the rich-side limit value, and a means 74 for determining that a hardware failure has occurred when the measured time exceeds a predetermined value. .

In a fourth aspect based on the third aspect , the rich-side limit value is set according to a detection signal of the operating condition.

[0012]

According to the first aspect of the invention, when it is determined that a hard failure has occurred from the output of the stability detection means or the correction coefficient Lldml of the set air-fuel ratio during the lean operation, the lean operation is prohibited, and the lean air-fuel ratio is determined. Since the operation is returned to the operation, the stability of the engine is ensured, and the drivability is not deteriorated even in the case of a hardware failure.

On the other hand, since the rotation of the engine becomes large even when the road surface is greatly roughened or due to slight movement of the throttle valve, the output of the stability detecting means becomes large and it is erroneously diagnosed as a hardware failure, whereby lean operation is prohibited. The operation may be switched to the operation at the stoichiometric air-fuel ratio.

[0014] In this case, the road surface will be rough
To return to a flat road surface, or
According to the first aspect, when the motion stops, the stability detecting means
Is below the judgment value, and the prohibition of lean operation is released.
After that, when it enters the lean operation range
Then, the lean operation is resumed. As a result, once
After diagnosing a card failure, continue to prohibit lean operation.
As compared with the case, the opportunity for lean driving is increased.

By the way, there is a case where the deterioration of the combustion due to the hardware failure is very large during the lean operation, but not so large during the operation at the stoichiometric air-fuel ratio. In this case,
During lean operation, it is determined that a hardware failure has occurred, and the lean operation is prohibited and the operation is returned to the stoichiometric air-fuel ratio.However, when operating at the stoichiometric air-fuel ratio, the deterioration of combustion due to the hardware failure is not so large, and stability is detected. The output of the means decreases, the prohibition of the lean operation is released, and the lean operation is restarted at the timing when the vehicle enters the lean operation region.

[0016] However, the deterioration of combustion due to hardware failure
It is very large during lean operation, so lean luck again
The rotation is prohibited, and the operation is switched to the operation at the stoichiometric air-fuel ratio.

As described above, when the deterioration of combustion due to the hardware failure is very large during the lean operation, but not so large during the operation at the stoichiometric air-fuel ratio, the inhibition of the lean operation and the release of the inhibition of the lean operation are repeated. That means
Although hunting occurs, in the first aspect, the output value of the stability detecting means is equal to or less than the determination value because the determination value of the release of the inhibition of the lean operation is changed to a smaller value as the number of times of the lean operation inhibition increases. Opportunities will be reduced,
Prevents the occurrence of hunting due to erroneous determination in the release cancellation of lean operation prohibition, such as hunting when the deterioration of combustion due to a hardware failure is very large during lean operation, but not so large during operation at stoichiometric air-fuel ratio. Is done.

According to the second aspect of the present invention, when the number of times of inhibition of the lean operation becomes equal to or more than the predetermined value, the determination of the release of the inhibition of the lean operation is inhibited. The occurrence is prevented.

According to the third aspect of the present invention, a hard failure is determined only when the limit to the rich-side limit value continues for a predetermined time or more. Until, it is not diagnosed as a hardware failure.

According to the fourth aspect, the rich-side limit value is set according to the operating condition, that is, N is varied according to the operating condition.
Since the setting is made under all operating conditions with an appropriate margin from the limit air-fuel ratio of the Ox emission, the correction range on the rich side is ensured to the maximum under any operating conditions during the lean operation.

[0021]

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.

Therefore, 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, and at the same time, the stability of the engine is detected. 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.

FIG. 2 is a diagram for calculating 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 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 cycle Refrv of one revolution section of the engine is calculated by the following equation: 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 to the engine speed Nrev using Refrv in accordance with the formula of conversion constant from cycle 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 (the combustion cylinder four times before). 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 ; the previous Dnerv formula.

Here, Llj is the amount of change from the immediately preceding Dnerv to the current Dnerv, and corresponds to a pseudo torque fluctuation 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.

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 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 reason why the delay is given is that 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 made 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 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, it is determined in step C) whether or not the number of samples is L. If they are, 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. In addition, Lldm
l is stored in the memory and is constantly updated during F / B control.

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 thereafter will be described later.

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, and the lean condition is determined in step A) of FIG. 7. The 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 part except the step G) in the flow of FIG. 8 constitutes means for determining the lean operation region. Step G), which was not described, will be described later.

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.

Since the numerical values shown in these maps are relative values with the stoichiometric air-fuel ratio being 1.0, a larger numerical value indicates richer and a smaller numerical 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 above 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.

FIG. 6 is a flow chart showing 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 the fuel increase according to the cooling water temperature, and Kas is the fuel increase immediately after the start. 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). 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 air-fuel ratio 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 in response to this, and during the lean operation, Of fuel consumption and NOx without sacrificing drivability
To reduce

By the way, as shown in FIG. 14, in the operation with the 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 of 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 taking these operating conditions into consideration. 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 a hardware failure, the air-fuel ratio is corrected to the rich side more and more, and there is a possibility that the engine is controlled in the range of the air-fuel ratio in which the NOx emission becomes extremely large. Therefore, the rich side limit value LLDMMX is added to the stabilized fuel-air ratio correction coefficient Lldml.
When the correction coefficient Lldml is equal to or greater than the rich side limit value, the NOx is limited to the rich side limit value, and NOx is reduced due to deterioration of engine performance.
Can be prevented from increasing.

However, since the limit air-fuel ratio for NOx emission varies depending on the set air-fuel ratio during lean operation, the control air-fuel ratio during lean operation does not exceed the limit air-fuel ratio for NOx emission under all operating conditions. Setting a constant rich-side limit value is a value for the set air-fuel ratio when the rich-side limit value is closest to the lean side. The correction width on the side is reduced.

Therefore, in the above-mentioned prior application, the rich side limit value is set according to the detection signal of the operating condition, and the correction coefficient of the set air-fuel ratio in the lean operation region is limited to the rich side limit value. In all the operating conditions in the lean operation region, an appropriate margin from the limit air-fuel ratio of the NOx emission is given to secure the maximum correction range in the lean operation region, and further, the rich side limit value is kept at a predetermined time or more. If the limit is continued, it is determined that a hardware failure has occurred, and lean operation is prohibited.After that, the operation is returned to the stoichiometric air-fuel ratio until the engine is stopped, so that drivability does not deteriorate even in the case of a hardware failure. I have to.

This will be described with reference to FIG. 5. In step F) of FIG. 5, the stabilized fuel-air ratio correction coefficient Lldm is calculated as described above.
After updating l, the process proceeds to step G), where the rich limit value and the lean limit value for Lldml are set according to the rotation speed Ne and the basic pulse width Tp as the load at that time. For example, assuming that the limit width toward the rich side is LDMLR (> 0) and the limit width toward the lean side is LDMLL (≧ 0) around 1.0, these limit widths L
A map using LDMLR and LLDMLL as parameters Ne and Tp is created in advance, and Ne and Tp at that time are created.
To retrieve the LLDMLR and LLDMLL maps. At this time, 1.0 + LLDMLL becomes the rich limit value, and 1.0-LLDMLL becomes the lean limit value.

Each characteristic of LLDMLR and LLDMLL is N
The tendency to e and Tp is not uniform. 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 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.

In this way, 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 FIG. 5, in step H), Lldm
1 is compared with the rich-side limit value 1.0 + LLDMLR. If Lldml exceeds the rich-side limit value, Lldml is limited to the rich-side limit value in step I).

Further, in step J), the timer value Tlmt
Is incremented. The timer value Tlmt is for measuring the time held at the rich side limit value, and the timer value Tlmt is compared with a predetermined value TFAIL in step K). If the process proceeds to step J) for the first time, Tlmt is less than TFAIL, and the routine of FIG. This flag Ffa
il resets when the engine starts.

Thereafter, as described above, the air-fuel ratio control is performed using the stabilized fuel-air ratio correction coefficient Lldml updated in FIG. 5, and the rotation fluctuation is calculated again. If the average value of the stability signal calculated from the rotation fluctuation is still equal to or larger than the rich side limit value in step H) of FIG.
Proceeding to step J), the timer value Tlmt is incremented. When the correction coefficient Lldml is held at the rich-side limit value, the timer Tlmt increases. When the timer Tlmt becomes TFAIL or more in step K), it is determined that a hardware failure has occurred, and the process proceeds to step L) to inhibit the lean operation. Set the flag Ffail. The set state of the flag Ffail is stored in the memory until the engine is stopped.

On the other hand, even when the correction coefficient Lldml temporarily exceeds the rich-side limit value, the correction coefficient Lldm does not change before the timer value Tlmt becomes equal to or more than TFAIL.
When 1 becomes smaller than the rich-side limit value, the timer value Tlmt is cleared in step M) (Tlmt =
0). The condition that Tlmt is equal to or more than the rich-side limit value and is maintained for a predetermined period of time is determined as a hardware failure because the correction coefficient L is determined only once, even though it is not a hardware failure.
Since ldml may be equal to or larger than the rich-side limit value, this case is excluded.

If the timer value Tlmt is less than TFAIL, the correction coefficient Lldml is compared with the lean limit value 1.0-LLDMLL in step N).
When ldml is lower than the lean limit value, in step O), Lldml is limited to the lean limit value.

On the other hand, the flag Ff stored in the memory
The aile is used in step G) of FIG. 8, and when the flag Ffail is set, the lean operation is prohibited. With this prohibition, the operation is switched to the operation at the stoichiometric air-fuel ratio.

Step G in the above flow of FIG.
Means for setting a predetermined rich-side limit value for the correction coefficient; steps H) and I) means for limiting the correction coefficient Lldml to the rich-side limit value when the correction coefficient exceeds the rich-side limit value; Step H),
J) and M) are means for measuring the time during which the correction coefficient is continuously limited to the rich-side limit value. If step G) in FIG. 8 determines that a hardware failure has occurred, lean operation is performed. Prohibition means are respectively configured.

As described above, in the prior application, the rich-side limit value is set according to the operating conditions, that is, all the operating conditions are set with an appropriate margin from the limit air-fuel ratio of the NOx emission amount that changes according to the operating conditions. Therefore, the maximum correction range on the rich side is ensured under any operating conditions during the lean operation. Under any operating conditions during lean operation at the time of hardware failure, NOx
The set air-fuel ratio can be corrected to the rich side using the maximum rich-side correction range in which the emission amount does not exceed the limit.

On the other hand, the time during which the correction coefficient Lldml is continuously limited to the rich side limit value of 1.0 + LLDMLR is measured by a timer, and the time is measured by the timer.
If the value exceeds AIL, it is diagnosed that a hardware failure has occurred, the flag Ffail is set, and the lean operation is prohibited. Since the operation is switched to the stoichiometric air-fuel ratio by the prohibition of the lean operation, the three-way catalyst 1
Thus, the stability of the engine is ensured while reducing NOx by making 0 effectively function.

As described above, by limiting the correction coefficient Lldml to the rich side limit value corresponding to the operating condition, the emission of NOx during the lean operation is maintained at a predetermined level or less, and the rich side limit value is kept at a predetermined level for a predetermined time or more. When it is maintained continuously, it is determined that a hardware failure has occurred, and the operation is returned to the operation at the stoichiometric air-fuel ratio, so that deterioration in drivability can be avoided.

Also, since a hard failure is hardly repaired during running and returns to a state without a hard failure,
If the operation is switched to the stoichiometric air-fuel ratio only when it is determined that a hardware failure has occurred, the lean operation and the stoichiometric air-fuel ratio operation may be repeated (so-called hunting may occur).

On the other hand, in this example, the flag Ffail is set at the timing when it is determined that a hardware failure has occurred, and the set state of the flag Ffail is maintained until the engine is stopped. In this state, the lean operation is prohibited. Therefore, once the flag Ffail is set, the lean operation is prohibited until the engine is stopped, so that the above-described hunting can be prevented.

However, in the above-mentioned prior application, there may be a case where a hardware failure is erroneously diagnosed due to factors other than a hardware failure such as a rough road surface condition or a slight movement of a throttle. Due to this erroneous diagnosis, the lean operation remains prohibited until the engine is stopped thereafter.

For example, when the road surface condition is rough,
The fluctuation of the road surface becomes the fluctuation of the rotation of the tire, and the fluctuation of the rotation of the tire is added to the fluctuation of the engine rotation when the engine and the driving system are directly connected. Even when the combustion of the engine is stable, the average value of the stabilization signal increases when the road surface condition is greatly rough, and at this time, the correction coefficient Lldml
Is updated on the increasing side to increase the stability, and is limited to the rich side limit value. Accordingly, if the road surface condition is largely roughened for a long time, the correction coefficient Lldml is continuously limited to the rich limit value for a predetermined time or more, and the lean operation is prohibited even though there is no hardware failure. It is. Also, when the throttle valve is finely moved, torque fluctuations occur while combustion is stable, so that also in this case, the average value of the stabilization signal becomes large, whereby it is erroneously diagnosed that a hardware failure has occurred. May be

In order to cope with this, in this example, the time during which the average value of the stabilization signal continuously becomes equal to or less than the predetermined value in a state where the lean operation is prohibited is measured, and the measured time exceeds the predetermined time. At that time, the prohibition of the lean operation is canceled because the misdiagnosis was determined to be a hardware failure.

More specifically, when the lean operation is prohibited by setting the flag Ffail and the operation is switched to the operation at the stoichiometric air-fuel ratio, the flow shown in FIG. 15 is executed.

In steps A) and B) of FIG. 15, the engine rotation fluctuation is calculated based on the inter-REF cycle Ref.
This is the same as steps A) and B) in FIG.

In step C), it is determined whether or not the prohibition of the lean operation is released while checking the stability of the engine. This will be described with reference to the flowchart of FIG.

The judgment conditions in FIG. 16 are the same as those in FIG. 4 except that step A) is deleted. If certain conditions are satisfied in steps B) to J) in FIG. The determination of the release of the prohibition of driving is permitted, and otherwise, the determination of the release of the prohibition of the lean operation is prohibited in step L).

In this manner, when the determination of the release of the lean operation prohibition is made, the process returns to FIG. 15, and it is checked in step D) whether or not the lean operation prohibition is released. If yes, go to step E).

In step E), the number of times of inhibition of the lean operation CNT so far is checked, and if this is equal to or larger than a predetermined value, the routine of FIG. The prohibition number CNT of the lean operation is the number of times Ffail is set, and is reset at the time of starting, and is counted up when Ffail is set (step P in FIG. 5).

If the number CNT of the prohibition of the lean operation is less than the predetermined value, the average value of the stability signal is obtained in steps F), G), H) and I). This part is the same as steps A), B), C) and D) in FIG.

In step J), the number of prohibitions C of the lean operation is set.
Determination comparison value SLok for release of inhibition of lean operation from NT
SLok = SLOK−Dsl × (CNT-1) (11) where SLOK is a positive constant and Dsl is a positive constant. Instead of using the calculation formula, the determination comparison value SLok may be obtained by searching a table using the number of times CNT of the lean operation is prohibited as a parameter.

From equation (11), SLok is a value that decreases as the number of times of prohibition of the lean operation increases. The reason why the value of SLok is reduced as the number of times of prohibition of the lean operation increases is as follows. It is considered that the stability determination during operation at the stoichiometric air-fuel ratio is extremely strict in terms of accuracy, and individual variation is also considered to be large.Therefore, if the prohibition of lean operation is canceled due to an erroneous determination, the lean The operation and the operation at the stoichiometric air-fuel ratio are repeated,
So-called hunting may occur. Therefore, it is determined that the greater the number of times the lean operation is prohibited, the greater the degree of erroneous determination is made, and the determination comparison value is reduced so that the average stability signal does not easily fall below the determination comparison value. Is reduced.

In the characteristics of the straight line shown in the equation (11), the value Dsl that determines the slope of the straight line is determined based on the accuracy of detecting the stability signal during operation at the stoichiometric air-fuel ratio.

In step K), the average value of the stability signal is compared with the judgment comparison value SLoc, and the average value of the stability signal is compared with SLock.
If not, the engine is determined to be stable, and the timer value Tok is incremented in step L. The timer value Tok is for measuring the time during which the engine is in a stable state, and the timer value Tok is compared with a predetermined value TOK in step M). If the process proceeds to step L) for the first time, Tok is less than TOK,
The routine of FIG. 15 ends as it is.

Thereafter, when the crank angle reaches 180 degrees, rotation fluctuations are calculated again in steps A) and B) in FIG. 15, and the average value of the stability signal calculated from the rotation fluctuations is calculated in step K) in FIG. If it is still equal to or less than SLoc, the process proceeds to step L) and the timer value Tok is incremented. When the stable state of the engine continues in this way, the timer value Tok increases. Eventually, when the timer value Tok becomes equal to or more than TOK in step M), it is determined that the determination of the hardware failure in FIG. 5 is a misdiagnosis, and the process proceeds to step N), in which the lean prohibition flag Ffail is returned to the reset state. This flag Ffai
The reset state of 1 is also stored in memory.

On the other hand, even when the average value of the stability signal becomes equal to or less than SLok at the same time, the timer value Tok is set to TO.
If the average value of the stability signal exceeds SLok before it becomes equal to or more than K, the timer value Tok is cleared in step O) (Tok = 0). On the condition that the average of the stability signal is equal to or less than SLok for a predetermined period of time, it is determined that an erroneous diagnosis is made.
This is to eliminate this case, since it may be less than or equal to Lo.

Step A) of the flow shown in FIG.
To M) and step O) constitute means for judging whether or not the determination of a hardware failure was a misdiagnosis, and also means for canceling the prohibition of lean operation when step N) judges that a misdiagnosis was made. ing.

On the other hand, the flag Ff stored in the memory
ail is used in step G of FIG.
When the "fail" is reset, the prohibition of the lean operation is released, and if all of the conditions in steps A) to F) in FIG. 8 are satisfied, the operation is switched to the lean operation again.

Now, the operation of this example will be described.

In this example, it is erroneously diagnosed as a hard failure due to a state in which the road surface is greatly rough or the fine movement of the throttle valve continues for a long time, whereby the lean operation is prohibited and the operation can be switched to the operation at the stoichiometric air-fuel ratio. Even after that, if the predetermined time has elapsed after returning to a flat road surface after passing through a greatly rough road surface, or if the predetermined time has passed after the fine movement of the throttle valve has stopped, the prohibition of the lean operation is released. Therefore, after that, the lean operation is restarted at the timing when the lean operation condition is satisfied. As a result, once a hard failure is diagnosed, the chances of lean operation are increased as compared with the case where the lean operation is prohibited until the engine stops.

Incidentally, there is a case where the deterioration of the combustion due to the hardware failure is very large during the lean operation, but not so large during the operation at the stoichiometric air-fuel ratio. In this case,
During lean operation, it is determined that a hardware failure has occurred, and the lean operation is prohibited and the operation is returned to the stoichiometric air-fuel ratio.However, when the operation is performed at the stoichiometric air-fuel ratio, the deterioration of combustion due to the hardware failure is not so large. The average value is reduced, the prohibition of the lean operation is released, and the lean operation is restarted at the timing when the lean condition is satisfied. However,
Since the deterioration of the combustion due to the hardware failure is extremely large during the lean operation, the lean operation is prohibited again, and the operation is switched to the operation at the stoichiometric air-fuel ratio.

As described above, when the deterioration of the combustion due to the hardware failure is very large during the lean operation, but not so large during the operation at the stoichiometric air-fuel ratio, the inhibition of the lean operation and the release of the inhibition of the lean operation are repeated. That means
Hunting occurs.

On the other hand, in this example, as the number CNT of lean operation prohibitions increases, the comparison value SLock for determining the release of the lean operation prohibition is changed to a smaller value. Hunting occurs due to erroneous release determination, such as when hunting occurs when the deterioration of combustion due to a hardware failure is very large during lean operation, but not so large during operation at stoichiometric air-fuel ratio. Can be prevented.

Similarly, the number of prohibitions of lean operation CNT
15 is equal to or greater than a predetermined value, the hunting due to an erroneous determination of the release determination is also prevented by not proceeding after step F in FIG. 15 (that is, the release determination of the lean operation is prohibited). I have.

In the embodiment, the diagnosis as to whether or not a hardware failure has occurred is made based on the correction coefficient Lldml. However, the diagnosis of the hardware failure can be made directly from the stability signal average value.

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.
The stabilized fuel / air ratio correction coefficient may be calculated so that the stability is equal to or less than the target value. An example in which the stability is equal to or less than the target value is Lldm in steps E) and F) in FIG.
1 is not updated to the lean side (that is, Dlldml = 0 in a region where the average value -SLL # is negative in FIG. 13).

[0125]

According to a first aspect of the present invention, there is provided a means for judging whether or not the engine is in a predetermined lean operation region based on a detection signal of an operating condition, and an air-fuel ratio which is determined from the stoichiometric air-fuel ratio when the lean operation region is judged. Means for setting a lean target value, means for detecting the stability of the engine from fluctuations in engine rotation, and correction of the set air-fuel ratio in the lean operation region corresponding to the output of the stability detection means during lean operation. Means for calculating a coefficient, means for correcting a set air-fuel ratio in the lean operation region based on the correction coefficient, means for performing air-fuel ratio control based on the corrected set air-fuel ratio, and Means for determining whether a failure has occurred;
When it is determined that a hardware failure has occurred, the means for inhibiting the lean operation and the output of the stability detecting means in the state where the lean operation is inhibited are compared with the determination value for releasing the inhibition of the lean operation. Means for determining whether the failure was determined to be a misdiagnosis and means for canceling the lean operation prohibition by the lean operation prohibiting means when it is determined to be a misdiagnosis are provided. In addition to preventing the road from becoming rough, even if the road surface is greatly rough or the output of the stability detection means becomes large due to slight movement of the throttle valve, etc. When returning to a flat surface or when the fine movement of the throttle valve stops, the prohibition of lean operation is released. As compared with the case to continue, it is possible to increase the opportunities for lean operation.

Further , the first invention counts the number of times the lean operation is prohibited by the lean operation prohibiting means, and changes the lean release prohibition release determination value to a smaller value as the number of times of the lean operation prohibition increases. In the case where the deterioration of the combustion due to the hardware failure is very large at the time of the lean operation, but is not so large at the time of the operation at the stoichiometric air-fuel ratio, the hunting occurs. Hunting due to an erroneous determination in the prohibition release determination can be prevented.

The second invention is based on a detection signal of an operating condition.
To determine if it is in the preset lean operation range
And the air-fuel ratio when the lean operation area is determined.
Means for setting a target value leaner than the stoichiometric air-fuel ratio;
Means for detecting gin stability from fluctuations in engine rotation
In response to the output of the stability detection means during lean operation.
Calculate the correction coefficient for the set air-fuel ratio in the lean operation range
Means in the lean operation region based on the correction coefficient.
Means for correcting the set air-fuel ratio, and the corrected set air-fuel ratio.
Means for performing air-fuel ratio control based on fuel ratio and during lean operation
Means for determining whether a hard failure has occurred in the
If it is determined that a hardware failure has occurred, perform lean operation.
Means of prohibition and this lean operation in a prohibited state
Output of stability detection means and judgment value of release of inhibition of lean operation
The determination of the hardware failure based on the comparison with
Means to determine whether or not the diagnosis has been made
The lean operation is prohibited by the lean operation prohibiting means.
Means for canceling, and when the number of prohibitions of the lean operation becomes equal to or more than a predetermined value, prohibition of the prohibition of the lean operation by the prohibition canceling means is prohibited. .

The third invention is based on the detection signal of the operating condition.
To determine if it is in the preset lean operation range
And the air-fuel ratio when the lean operation area is determined.
Means for setting a target value leaner than the stoichiometric air-fuel ratio;
Means for detecting gin stability from fluctuations in engine rotation
In response to the output of the stability detection means during lean operation.
Calculate the correction coefficient for the set air-fuel ratio in the lean operation range
Means in the lean operation region based on the correction coefficient.
Means for correcting the set air-fuel ratio, and the corrected set air-fuel ratio.
Means for performing air-fuel ratio control based on fuel ratio and during lean operation
Means for determining whether a hard failure has occurred in the
If it is determined that a hardware failure has occurred, perform lean operation.
Means of prohibition and this lean operation in a prohibited state
Output of stability detection means and judgment value of release of inhibition of lean operation
The determination of the hardware failure based on the comparison with
Means to determine whether or not the diagnosis has been made
The lean operation is prohibited by the lean operation prohibiting means.
Means for canceling, and the failure determination means,
Means for setting a predetermined rich side limit value for the correction coefficient; means for limiting the correction coefficient to the rich side limit value when the correction coefficient exceeds the rich side limit value; Means for measuring the time continuously limited to the side limit value, and means for determining that a hardware failure has occurred when the measured time exceeds a predetermined value. A hard failure is not diagnosed until it is not a limited hard failure.

According to a fourth aspect , in the third aspect , the rich-side limit value is set in accordance with the detection signal of the operating condition. Is maximized.

[0130]

[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 flowchart of a 180-degree job.

FIG. 16 is a flowchart for explaining determination of release of inhibition of lean operation.

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

FIG. 18 is a configuration diagram (claim correspondence diagram) of the second invention.

FIG. 19 is a configuration diagram (claim correspondence diagram) of the third invention.
You.

[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 area 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 Air-fuel ratio control means 57 Hard failure determination means 58 Lean operation prohibition means 59 Misdiagnosis determination means 60 Prohibition release means 71 Rich side limit value setting means 72 Limiting means 73 Measuring means 74 Hard failure determination means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-6-272591 (JP, A) JP-A-64-83434 (JP, A) JP-A-2-130255 (JP, A) JP-A 5- 296101 (JP, A) JP-A-58-217732 (JP, A) JP-A-4-136468 (JP, A) JP-A-3-52353 (JP, U) JP-A-2-37241 (JP, U) (58) Field surveyed (Int.Cl. ⁷ , DB name) F02D 41/04 305 F02D 41/14 310 F02D 41/22 305

Claims (4)

(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; and setting the air-fuel ratio to a target value leaner than the stoichiometric air-fuel ratio when the lean operation region is judged. Means for setting, means for detecting the stability of the engine from fluctuations in the rotation of the engine, means for calculating 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 air-fuel ratio control based on the corrected set air-fuel ratio; and whether a hard failure has occurred during the lean operation. Means for determining whether a failure has occurred, means for inhibiting lean operation when it is determined that a hardware failure has occurred, Means for determining whether or not the determination of the hardware failure was a misdiagnosis based on a comparison with a determination value for canceling the prohibition of driving, and canceling the prohibition of the lean operation by the lean driving prohibition means when the determination is a misdiagnosis. Means, counting means for counting the number of times the lean operation is prohibited by the lean operation prohibiting means, and means for changing the determination value for canceling the lean operation prohibition to a smaller value as the number of times the lean operation is prohibited is increased. Characteristic engine air-fuel ratio control device. 2. 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, and setting the air-fuel ratio to a target value leaner than the stoichiometric air-fuel ratio when the lean operation region is determined. Means for setting, means for detecting the stability of the engine from fluctuations in the rotation of the engine, means for calculating 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 air-fuel ratio control based on the corrected set air-fuel ratio; and whether a hard failure has occurred during the lean operation. Means for determining whether a failure has occurred, means for inhibiting lean operation when it is determined that a hardware failure has occurred, Means for determining whether or not the determination of the hardware failure was a misdiagnosis based on a comparison with a determination value for canceling the prohibition of driving, and canceling the prohibition of the lean operation by the lean driving prohibition means when the determination is a misdiagnosis. Means for prohibiting release of the lean operation prohibition by the prohibition releasing means when the number of times of prohibition of the lean operation becomes equal to or greater than a predetermined 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, and setting the air-fuel ratio to a target value leaner than the stoichiometric air-fuel ratio when the lean operation region is judged. Means for setting, means for detecting the stability of the engine from fluctuations in the rotation of the engine, means for calculating 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 air-fuel ratio control based on the corrected set air-fuel ratio; and whether a hard failure has occurred during the lean operation. Means for determining whether a failure has occurred, means for inhibiting lean operation when it is determined that a hardware failure has occurred, Means for determining whether or not the determination of the hardware failure was a misdiagnosis based on a comparison with a determination value for canceling the prohibition of driving, and canceling the prohibition of the lean operation by the lean driving prohibition means when the determination is a misdiagnosis. Means for setting a predetermined rich-side limit value for the correction coefficient, and when the correction coefficient exceeds the rich-side limit value, sets the correction coefficient to the rich-side limit value. Means for measuring the time during which the correction coefficient is continuously limited to the rich-side limit value, and means for determining that a hardware failure has occurred when the measured time exceeds a predetermined value. An air-fuel ratio control device for an engine, comprising: 4. The air-fuel ratio control device for an engine according to claim 3, wherein the rich-side limit value is set according to a detection signal of the operating condition.