JP3319191B2 - Engine air-fuel ratio control device and its failure diagnosis device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a failure diagnosis device for 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.

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] In this case, the limit air-fuel ratio of the NOx emission varies depending on the set air-fuel ratio in the lean operation region.
x To set a constant rich-side limit value so that it does not deviate from the limit air-fuel ratio of the emission amount to the rich side , the value is the value with respect to the set air-fuel ratio when the rich-side limit value is closest to the lean side. Therefore, at other set air-fuel ratios, the correction range on the rich side is unnecessarily narrowed.

Therefore, by setting the rich-side limit value according to the detection signal of the operating condition, an appropriate margin from the limit air-fuel ratio of the NOx emission amount is given in all the operating conditions in the lean operating region to perform the lean operation. At the same time as the present application, the present applicant has proposed a configuration that ensures the maximum correction range in the operating region.

However, according to this prior application, N
Although the emission amount of Ox is not deteriorated, poor stability (that is, poor operability) due to the hardware failure remains.

The present invention is an improvement on the above-mentioned prior application. In one aspect of the present invention, the correction coefficient of the set air-fuel ratio in the lean operation region is limited to a rich limit value corresponding to a detection signal of an operation condition. When the limit value is continuously limited to the rich side limit value for a predetermined time or more, the failure diagnosis is performed by determining that the hard failure has occurred, and in other inventions, when it is determined that the hardware failure has occurred based on the diagnosis result, the lean operation is performed. An object of the present invention is to prevent operability from being deteriorated even when a hardware failure occurs by prohibiting the operation.

[0009]

According to a first aspect of the present invention, as shown in FIG. 15, it is determined whether or not the engine is in a predetermined lean operation region based on a detection signal of an operating condition determined from a rotational speed and a load. Means 51, 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.
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.
means 54 for calculating a value for controlling the engine stability within a predetermined range, and a correction coefficient Lldml
55 for correcting the set air-fuel ratio in the lean operation region based on the above, a means 56 for performing air-fuel ratio control based on the corrected set air-fuel ratio, and a predetermined rich side limit value for the correction coefficient Lldml. NOx emissions
Of the means 57 is set in accordance with the values for providing a margin from limit Sakaisora ratio you vary the detection signal of the operating condition according to the operating condition, the correction coefficient Lldml said rich side limit value Means 58 for limiting the correction coefficient Lldml to the rich-side limit value, and measuring the time during which the correction coefficient Lldml is continuously limited to the rich-side limit value. Means 59 and means 60 for judging that a hardware failure has occurred when the time continuously limited beyond a predetermined time set in advance is measured.

A second invention, in the first aspect, when it is determined that hardware failure has occurred is provided a means to prohibit the lean operation. The third invention is directed to the first invention.
If it is determined that a hardware failure has occurred,
Provision of means to inhibit rotation and switch to operation at stoichiometric air-fuel ratio
Was.

In a fourth aspect based on the second aspect, the lean operation inhibiting means 61 sets a flag when it is determined that a hardware failure has occurred, and means for inhibiting the lean operation until the flag is reset. Consists of

[0012]

SUMMARY OF] According to the prior application device as described above, set according to the operating conditions of the rich-side limit value is determined from the load and rotational speed, i.e. the NOx emissions, change <br/> by the operating conditions since set in all operating conditions with a suitable margin from the limit Sakaisora ratio, whatever the operating conditions at the time of lean operation, the NOx emission amount, you change in accordance with the operating condition limit Sakaisora ratio Accordingly, the correction range on the rich side is maximized. 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 at any operating condition in the lean operation at the time of the hardware failure.

Meanwhile, the time correction factor Lldml is limited in succession to the rich side limit value is measured, beforehand
Time that is continuously limited beyond the specified time
Is measured, it is diagnosed that a hardware failure has occurred. The result of the diagnosis can be notified to the driver of a hardware failure by, for example, turning on a warning light provided in a driver's seat or sounding a warning buzzer.

According to the second and third aspects of the present invention, when it is determined that a hardware failure has occurred in the diagnosis result, the lean operation is prohibited and the operation is switched to the operation based on the stoichiometric air-fuel ratio. Nature is secured. By limiting the correction coefficient to the rich side limit value corresponding to the operating condition, the emission of NOx during lean operation is maintained below a predetermined reference, and when the rich side limit value is continuously held for a predetermined time or longer, Deterioration of drivability can be avoided by judging a hardware failure and returning to operation at the stoichiometric air-fuel ratio.

[0015] Since a hard failure is hardly recovered during driving and returns to a state without a hard failure, if it is determined that a hardware failure has occurred and the operation is switched to the operation at the stoichiometric air-fuel ratio only once, a lean operation and a theoretical operation are performed. There is a possibility that the operation with the air-fuel ratio may be repeated (so-called hunting may occur). However, in the fourth aspect , a flag is set when it is determined that a hardware failure has occurred, and lean operation is prohibited until the flag is reset. . For example, if the flag is reset when the engine is started, after the flag is set once, the lean operation is prohibited until the engine is stopped, so that the hunting described above is avoided.

[0016]

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, the amount of NOx can be reduced to the same level as that of the three-way catalyst 10, and at the same time, 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 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 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 cycle Refrv of one rotation 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 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 the 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 ; the previous Dnerv formula.

Here, Llj is an 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 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 way, the flow returns to FIG. 2 again, and it is checked in step D) 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, at step C), it is determined 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 expression: 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 subsequent steps will be described later in detail.

Next, returning to FIG. 2 again, 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 value indicates a richer value and a smaller value indicates a leaner value. 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.

This 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 process of damper operation 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 manner, 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, in step F), the fuel cut is determined. In steps G) and H), the invalid pulse width Ts is stored in the output register if the fuel cut condition is satisfied, 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 air-fuel ratio control based on the corrected set air-fuel ratio.

The fuel injection pulse width Ti is calculated in this manner. Therefore, if 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 the lean air-fuel ratio during the lean operation is reduced. Of fuel consumption and NOx without sacrificing drivability
To reduce

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 from the NOx emission amount and the stability 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 the lean combustion becomes unstable due to the hardware failure, the air-fuel ratio is corrected to the rich side more and more, and the engine may be controlled in the air-fuel ratio range 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 deviates from the limit air-fuel ratio for NOx emission under all operating conditions. If a constant rich side limit value is set so that it does not occur, the value will be a value for the set air-fuel ratio when the rich side limit value is closest to the lean side. Unnecessarily, the correction width on the rich side is narrowed.

Therefore, in the above-mentioned prior application, in order to give an appropriate margin from the limit air-fuel ratio of the NOx emission amount under all the operating conditions in the region of the lean operation, the rich side limit value is set in accordance with the operating conditions. NOx
Although the emission has not deteriorated, the poor stability due to the hardware failure still remains.

To cope with this, in the present application, the time continuously limited to the rich-side limit value is measured, and when the measured time exceeds a predetermined time, it is determined that a hardware failure has occurred, Even in the operation region, the lean operation is prohibited and the operation is switched to the operation at the stoichiometric air-fuel ratio.

More specifically, in FIG. 5, after updating the stabilized fuel-air ratio correction coefficient Lldml 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, 1.0 + LLDMLR becomes the rich limit value,
1.0-LLDMLL becomes the lean limit value.

When 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 rich-side maximum limit width of NOx emission up to the limit air-fuel ratio, 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.

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 can be 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, before the timer value Tlmt becomes equal to or more than TFAIL, the correction coefficient Lldm is obtained.
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 flow of FIG. 5)
Means for setting a predetermined rich-side limit value for the correction coefficient according to the detection signal of the operating condition, step H).
And I) are means for limiting the correction coefficient Lldml to the rich-side limit value when the correction coefficient exceeds the rich-side limit value. The step G) of FIG. 8 constitutes means for measuring the time limited by the above operation, and means for inhibiting the lean operation when it is determined that a hardware failure has occurred.

Here, the operation of this example will be described.

As described above, according to the prior application, the rich-side limit value is set according to the operating condition, 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 condition. Since the conditions are set, the correction range on the rich side is maximized 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 according to the operating condition, the NOx emission during the lean operation is maintained at or below a predetermined reference value, and the rich-side limit value is maintained at the rich-side limit value 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.

Further, since a hard failure is hardly repaired during traveling 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, the set state of the flag Ffail is maintained until the engine stops, and the state of the flag Ffail is checked. 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.

In this embodiment, the lean operation is prohibited when it is determined that a hardware failure has occurred. However, when it is determined that a hardware failure has occurred, a warning light provided on the operation panel is turned on or a warning buzzer sounds. Alternatively, the driver may be notified that a hardware failure has occurred. In the embodiment, the flag Ffail is reset at the time of starting the engine. However, it is backed up in a memory so that the value is not lost even after the engine is stopped, and at the time of the next operation,
It is also possible to prevent the lean operation from starting if the flag Ffail is set while looking at the memory.

Further, 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).

[0098]

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 determined from a rotation speed and a load. 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 the air-fuel ratio set in the lean operation region corresponding to the output of the stability detection means during lean operation. Means for calculating a correction coefficient for adjusting the stability of the engine within a predetermined range, 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 set air-fuel ratio, and a predetermined rich-side limit value NOx for the correction coefficient.
Emissions, means for setting in accordance with the values for providing a margin from limit Sakaisora ratio you change according to the operating condition of the detection signal of the operating condition, the correction factor is the rich side limit value Means for limiting the correction coefficient to the rich-side limit value when the air-fuel ratio is shifted to the rich side by deviating from
A means for measuring a time during which the correction coefficient is continuously limited to the rich-side limit value, and a hardware failure occurs when the time continuously limited for more than a predetermined time is measured. Means for determining that there is no
of x emissions, the rich-side correction range corresponding to the limit Sakaisora ratio you change in accordance with the operating conditions are ensured to the maximum, whereby the time at any operating conditions in the lean operation area when a hardware failure In addition, the set air-fuel ratio can be corrected to the rich side using the maximum rich-side correction range in which the NOx emission amount does not exceed the limit, and the driver can be notified of the hardware failure.

The second and third inventions are directed to the first invention.
Te, since when it is determined that hardware failure has occurred is provided a means for inhibiting the lean operation, NOx emissions at that time in any operating condition of the lean operation region during hardware failure is maximum does not exceed the limit Using the rich correction range, the set air-fuel ratio can be corrected to the rich side, and the stability of the engine can be ensured.

In a fourth aspect based on the second aspect, the lean operation inhibiting means includes means for setting a flag when it is determined that a hardware failure has occurred, and means for inhibiting the lean operation until the flag is reset. Therefore, it is possible to avoid occurrence of so-called hunting in which the lean operation and the operation at the stoichiometric air-fuel ratio are repeated.

[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.

[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 Rich-side limit value setting means 58 Limiting means 59 Measuring means 60 Failure determining 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 (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 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 calculating a value for keeping the stability of the engine within a predetermined range; means for correcting the set air-fuel ratio in the lean operation region based on the correction coefficient; and means for performing an air-fuel ratio control Te, of the correction NOx emissions to a predetermined rich-side limit value for the coefficients, a value for providing a margin from limit Sakaisora ratio you change according to the operating conditions Means for setting according to the detection signal of the operating condition, means for limiting the correction coefficient to the rich side limit value when the correction coefficient deviates from the rich side limit value and makes the air-fuel ratio rich side, Means for measuring a time during which the correction coefficient is continuously limited to the rich-side limit value, and a hardware failure occurs when the time during which the correction coefficient is continuously limited beyond a predetermined time is measured. And a means for determining that there is a failure in the air-fuel ratio control device of the engine. 2. A failure diagnosis device for an air-fuel ratio control device for an engine according to claim 1, further comprising means for inhibiting lean operation when it is determined that a hardware failure has occurred. 3. The engine air-fuel ratio control system according to claim 1, further comprising means for inhibiting lean operation and switching to operation at a stoichiometric air-fuel ratio when it is determined that a hardware failure has occurred. Fault diagnosis device. 4. The system according to claim 2, wherein said lean operation inhibiting means comprises means for setting a flag when it is determined that a hardware failure has occurred, and means for inhibiting the lean operation until the flag is reset. A failure diagnosis device for an air-fuel ratio control device for an engine as described in the above.