JPH08177576A - Air-fuel ratio control device for engine - Google Patents

Abstract

PURPOSE: To relax torque shock generated in association with the switching of an air-fuel ratio at the time of a driver hardly operating an accelerator even entering an upward slope during lean operation. CONSTITUTION: A judging means 21 judges whether an operation area is a preset lean operation area on the basis of the detection signal of an operating condition. At the time of judging the lean operation area, a setting means 22 sets an air-fuel ratio to the target value leaner than a stoichiometric air-fuel ratio. At the time of switching from this lean target value to the stoichiometric air-fuel ratio, a means 24 brings the air-fuel ratio target value close to the stoichiometric air-fuel ratio gradually at the air-fuel ratio enriching change speed at a time. On the basis of the set air-fuel ratio gradually brought close to the stoichiometric air-fuel ratio, an air-fuel ratio control means 25 performs air-fuel ratio control. When a vehicle speed condition comes off a specified range in the case of the condition of the lean operation area including the vehicle speed being within the specified range, a decrease-correcting means 26 decrease-corrects the air-fuel ratio enriching change speed set by a setting means 23.

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 Prior Art Improving engine fuel economy and at the same time 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 leaner air-fuel ratio, which is leaner than the theoretical air-fuel ratio. Japanese Unexamined Patent Publication No. 60-50241 proposes a method of operating an engine that restores operation at an air-fuel ratio.

In this system, the switching speed of the air-fuel ratio is set in accordance with the changing speed of the throttle valve opening (change amount of the throttle valve opening per unit time) ΔTVO. For example, the accelerator pedal is quickly operated during lean operation. When the throttle valve opening changes rapidly, such as when the pedal is depressed, the air-fuel ratio switching speed is increased.

[0004]

By the way, if the condition that the vehicle speed is within a predetermined range is in the lean operation region, the driver can accelerate the vehicle even if he / she goes uphill in the middle of lean operation. When you do almost no operation,
Due to the decrease of the vehicle speed, the vehicle speed deviates from the predetermined range and is not in the lean operation region, and the operation is returned to the stoichiometric air-fuel ratio.

At this time, in the above device, Δx is set so that the amount of NOx emission during the air-fuel ratio switching is not increased as much as possible.
Even when TVO is small, the switching speed of the air-fuel ratio is set to a relatively large value, so the throttle valve opening hardly changes before and after switching to the stoichiometric air-fuel ratio operation, but the operation due to the torque step is performed. Shock occurs.

Therefore, according to the present invention, when the lean operation is switched to the operation at the stoichiometric air-fuel ratio due to the decrease in the vehicle speed, the air-fuel ratio switching speed is reduced and corrected so that the driver enters the uphill during lean operation and the accelerator pedal is operated. The purpose is to alleviate the torque shock associated with the air-fuel ratio switching when almost no operation is performed.

[0007]

According to the present invention, as shown in FIG. 11, a means 21 for judging whether a lean operation area is preset based on a detection signal of an operation condition and a lean operation area. Means 22 for setting the air-fuel ratio to a target value leaner than the stoichiometric air-fuel ratio, means 23 for setting the air-fuel ratio enrichment change speed at the time of switching from this lean target value to the theoretical air-fuel ratio, and this change The air-fuel ratio of the engine including means 24 for gradually approaching the air-fuel ratio target value to the stoichiometric air-fuel ratio at each speed, and means 25 for performing air-fuel ratio control based on the set air-fuel ratio gradually approaching the stoichiometric air-fuel ratio. In the fuel ratio control device, when the vehicle speed condition is out of the predetermined range when the condition that the vehicle speed is within the predetermined range is the lean operation range, the air-fuel ratio rich change speed is set. The means 26 for reducing correction was provided.

[0008]

[Operation] When the driver does not operate the accelerator while going uphill in the middle of lean operation, when the vehicle speed falls out of the predetermined range and is returned to the stoichiometric air-fuel ratio due to the decrease in vehicle speed, The air-fuel ratio enrichment change speed is reduced, and the air-fuel ratio is switched to the stoichiometric air-fuel ratio more slowly than when the operation is returned to the stoichiometric air-fuel ratio under conditions other than the vehicle speed. This allows the air-fuel ratio when the vehicle speed deviates from the specified range and is returned to the stoichiometric air-fuel ratio when the driver does not operate the accelerator while going uphill in the middle of lean operation. Torque shock associated with switching is reduced.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 1 is an engine body, a fuel injection valve 7 is provided in an intake passage 8 of the engine downstream of an intake throttle valve 5, and an injection signal from a control unit 2 responds to operating conditions. Fuel is injected and supplied into the intake air so that a predetermined air-fuel ratio is achieved. The control unit 2 includes a rotation speed signal from the crank angle sensor 4, an intake air amount signal from the air flow meter 6, an air-fuel ratio (oxygen concentration) signal from the oxygen sensor 3 installed in the exhaust passage 8, and a water temperature sensor 11. The engine cooling water temperature signal, the gear position signal from the transmission gear position sensor 12, the vehicle speed signal from a vehicle speed sensor (not shown), etc. are input, and the lean air-fuel ratio is determined according to the conditions while determining the operating state based on these. And the stoichiometric air-fuel ratio.

A three-way catalyst 10 is installed in the exhaust passage 8,
When operating at the theoretical air-fuel ratio, NOx in the exhaust gas is reduced and HC and CO are oxidized with maximum conversion efficiency. The three-way catalyst 10 oxidizes HC and CO at a lean air-fuel ratio, but has a low NOx reduction efficiency.

However, as the air-fuel ratio shifts to the lean side, the amount of NOx generated decreases, and at a predetermined air-fuel ratio or higher, the NOx generation amount can be reduced to the same level as purification by the three-way catalyst 10, and at the same time, The fuel efficiency is improved as the lean air-fuel ratio is achieved.

Therefore, the lean air-fuel ratio is used for operation in a predetermined operating range where the load is not so large, and the air-fuel ratio is controlled to be at or near the stoichiometric air-fuel ratio in other operating ranges.

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

The flowchart of FIG. 2 shows the contents of the control operation for calculating and outputting the fuel injection pulse width. First, in step A), the target fuel-air ratio Tfbya is calculated as follows: Tfbya = Dml + Ktw + Kas (1) where Dml; Air ratio correction coefficient Ktw; water temperature increase correction coefficient Kas;

The fuel-air ratio correction coefficient Dml of the equation (1) is shown in FIG.
Alternatively, the fuel-air ratio Mdml set in the characteristic map of FIG. 6 is searched, and a predetermined damper operation is performed at the time of switching the air-fuel ratio. In this case, one of the maps is selected depending on whether or not the lean operation condition is satisfied. To be done.

Here, the determination of the lean operating 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. 3, and the specific contents therefor are shown in FIG.
The lean condition is determined by checking the contents of steps A) to F) of FIG. 4 one by one. When all of the items are satisfied, the lean operation is permitted, and when any of them is not satisfied, the lean operation is performed. Prohibit

That is, step A): the air-fuel ratio (oxygen) sensor is activated, step B): the engine warm-up is completed, step C): the load (Tp) is within a predetermined lean range. , Step D): The rotation speed (Ne) is in a predetermined lean range, Step E): The gear position is in the second speed or higher, Step F): The vehicle speed is in a predetermined range, and sometimes, in Step H). If lean operation is permitted, otherwise go to step I) and prohibit lean operation.
The above steps A) to F) are conditions for performing stable lean operation without impairing the operation performance.

The above flow of FIG. 4 constitutes means for determining the lean operation region.

When the lean condition is determined in this way,
Returning to steps C) and D) of FIG. 3, when the lean condition is not satisfied, the stoichiometric fuel air ratio or a map fuel air ratio that is denser than that is used in step C), and the characteristic map shown in FIG. It is calculated by searching with Tp. On the other hand, when the lean condition is satisfied, the map fuel-air ratio Mdml which is thinner than the stoichiometric air-fuel ratio by a predetermined range in step D) is the same according to the characteristic map shown in FIG. To search.

Since the numerical values shown in these maps are relative values with the stoichiometric air-fuel ratio being 1.0, richer values and lean values are indicated. The above-described flow of FIG. 3 and the map of FIG. 5 constitute means for setting the air-fuel ratio target value in the lean operation region.

Next, FIG. 7 is a flow chart showing the damper operation at the time of switching the air-fuel ratio. This is for ensuring a stable operation performance by gently switching the air-fuel ratio to prevent a sudden change in torque. is there.

In steps A) and B), the start switch and the map fuel-air ratio Mdml obtained above are checked, and when the start switch is ON or Mdml is the upper limit value TDML.
When R # or more, Mdml is set as the fuel-air ratio correction coefficient Dml in step C).

The start switch is not ON and Mdm
When l is less than TDMLR #, the previous fuel-air ratio correction coefficient Dmlold and Mdml are compared in step D), and when Dmlold ≧ Mdml is not established, it is time to switch to operation at the stoichiometric air-fuel ratio. In step E), the fuel-air ratio enrichment change speed Ddmlr is read, and in step H) Mdml and (Dmlold + Dd
The smaller one of mlr) is set as Dml. The skipped steps F) and G) will be described in detail later.

On the contrary, when Dmlold ≧ Mdml, it is judged that it is the time to switch to the lean operation, and in step I) the fuel-air ratio lean change rate Ddmll is read, and in step J) Mdml and ( Dmold-Dd
The larger of ml1) is set as Dml.

The above changing speeds Ddmrl and Ddmll
Is set to a faster value by setting a larger value as the throttle valve opening changes faster when switching the operating region. One Ddml
When represented by r, FIG. 8 is a flow chart for setting the changing speed. In steps A) to C), the change rate ΔTVO of the throttle valve opening and the determination values DTVO3 #, DTVO2 #, DT.
VO1 # is compared, and from the comparison result, step D) to
When ΔTVO ≧ DTVO3 # in G), a predetermined value DDMLR
0 # is a predetermined value DDTLR1 # when DTVO3 #> ΔTVO ≧ DTVO2 #, DTVO2 #> ΔTVO ≧ D
When TVO1 #, the predetermined value DDMLR2 # is set to DTVO1
When #> ΔTVO, the predetermined value DDMLR3 # is selected. However, DTVO3 #> DTVO2 #> DTV
O1 # and DDMLR0>DDMLR1> DDMLR
2> DDMLR3.

In this way, the change rate ΔTV of the throttle valve opening degree
By setting the change rate Ddmlr of the magnitude corresponding to O in four steps, the rise becomes steep when ΔTVO is large and becomes slow when ΔTVO is small, as shown in FIG. Is.

The above-described flow of FIGS. 7 and 8 constitutes means for gradually approaching the air-fuel ratio target value to the stoichiometric air-fuel ratio at each air-fuel ratio enrichment change speed.

Returning to FIG. 2, in step B) the output of the air flow meter is A / D converted and linearized to calculate the intake air flow rate Q. Then, in step C), the basic pulse width Tp given to the fuel injection valve is obtained from the intake air flow rate Q and the engine speed Ne as Tp = K × Q / N. Note that K is a constant.

Then, in step D), based on this Tp, the one-time fuel injection pulse width Ti is Ti = Tp × Tfbya × Ktr × (α + αm) + Ts (2) where Ktr; Correction coefficient α; air-fuel ratio feedback correction coefficient αm; air-fuel ratio learning correction coefficient Ts; invalid pulse width

However, under lean conditions, these K
tr, α, αm, etc. are fixed to predetermined values.

Next, in step F), the fuel cut is determined, and in steps G) and H), the invalid pulse width Ts is stored in the output register if the fuel cut condition is met, and if not, the crank angle sensor is stored in the output register. Prepare for injection at a predetermined injection timing according to the output of.

The above flow of FIG. 2 constitutes means for performing air-fuel ratio control based on the set air-fuel ratio.

Now, as described above, in the case where the condition that the vehicle speed is within the predetermined range is in the lean operation area (see step F in FIG. 4), the vehicle climbs uphill during the lean operation. If the driver hardly operates the accelerator even after entering, the vehicle speed deviates from the predetermined range due to the decrease in vehicle speed, and the vehicle is not in the lean operation region and is returned to the operation at the theoretical air-fuel ratio.

At this time, NO during switching of the air-fuel ratio
If the air-fuel ratio enrichment change speed (eg, DDMLR3 # of step G in FIG. 8) when ΔTVO is small is set to a relatively large value so that the emission amount of x does not increase as much as possible, the theoretical air-fuel ratio Although there is almost no change in the throttle valve opening before and after the switching to the driving mode, a driving shock occurs due to the torque difference.

To deal with this, in the control unit 2, when the lean operation is switched to the operation at the stoichiometric air-fuel ratio due to the vehicle speed falling out of the predetermined range during lean operation, the air-fuel ratio enrichment change speed Ddmlr is decreased. to correct.

In detail, when steps F) and G) are additionally provided in FIG. 7 and the flag Fdml is set, the air-fuel ratio enrichment change speed Ddmlr set by FIG. 8 is changed to Ddmlr = Ddmlr × A (3) However, A: A positive constant less than 1 is used to correct the weight reduction. The correction formula is not limited to the formula (3); Ddmlr = Ddmlr-B (4) However, the formula of B; a predetermined value may be used.

The setting operation of the flag Fdml is shown in FIG.
The flow is shown in.

When lean prohibition is prohibited in step A) and B) in FIG. 10 and whether lean operation was permitted last time, lean operation is prohibited and lean operation is permitted last time. (That is, when the lean operation is prohibited this time), proceed to step C). Otherwise, proceed to step E) and flag Fdml.
Reset. The flag Fdml is initially set to a reset state when the engine is started.

In step C), when the vehicle speed is viewed outside the predetermined range, the flag Fdml is set in step D). It is determined that the lean driving is prohibited because the vehicle speed deviates from the predetermined range. Therefore, even if the lean operation is switched to the prohibition this time, if the vehicle speed is within the predetermined range (that is, the lean operation is switched to the prohibition due to conditions other than the vehicle speed, such as when the load or rotation is no longer in the lean operation area). If it is given), the flow goes to step E) and the flag Fdml
Is reset.

Steps F) and G) of FIG. 7 and FIG.
When the vehicle speed condition deviates from a predetermined range.

In this way, when the driver does not operate the accelerator while going uphill in the middle of lean driving, the vehicle speed falls out of the predetermined range due to the decrease of the vehicle speed, and the operation is returned to the stoichiometric air-fuel ratio. When the air-fuel ratio is changed, the air-fuel ratio enrichment change speed Ddmlr is reduced and corrected, so that the air-fuel ratio is switched to the stoichiometric air-fuel ratio more slowly than when the operation is returned to the stoichiometric air-fuel ratio under conditions other than the vehicle speed. The driving shock associated with the step is alleviated.

When the operation is returned to the stoichiometric air-fuel ratio under conditions other than the vehicle speed, a relatively large value of the air-fuel ratio rich change speed is obtained even when the change rate ΔTVO of the throttle valve opening is small, as in the conventional case. It is needless to say that the increase in the NOx emission amount is suppressed because the above is set.

[0044]

According to the present invention, there is provided means for determining whether the lean operating region is preset based on the operating condition detection signal, and an air-fuel ratio leaner than the stoichiometric air-fuel ratio when the lean operating region is determined. Means for setting a desired target value, means for setting the air-fuel ratio enrichment change speed at the time of switching from this lean target value to the stoichiometric air-fuel ratio, and the air-fuel ratio target value is gradually changed to the theoretical air-fuel ratio at each change speed. And a means for performing air-fuel ratio control based on the set air-fuel ratio that gradually approaches the stoichiometric air-fuel ratio, in the engine air-fuel ratio control device, check that the vehicle speed is within a predetermined range. When the vehicle speed condition deviates from the predetermined range when it is set as the condition for the lean operation region, means for correcting the air-fuel ratio enrichment change speed by reducing the amount is provided. To reduce the torque shock caused by the air-fuel ratio switching when the vehicle speed deviates from the predetermined range and is returned to the stoichiometric air-fuel ratio due to the decrease in vehicle speed when the driver does not operate the accelerator on a slope. You can

[Brief description of drawings]

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

FIG. 2 is a flowchart of a 10 msec job.

FIG. 3 is a flowchart of a background job.

FIG. 4 is a flow chart for explaining a lean condition determination.

FIG. 5 is a characteristic diagram showing the contents of a lean map.

FIG. 6 is a characteristic diagram showing the content of a non-lean map.

FIG. 7 is a flow chart of a 180 degree job.

FIG. 8 is a flowchart for explaining setting of an air-fuel ratio enrichment change speed Ddmlr.

FIG. 9 is a waveform diagram for explaining a damper operation when switching the air-fuel ratio.

FIG. 10 is a flowchart for explaining setting of a flag Fdml.

FIG. 11 is a configuration diagram (claim correspondence diagram) of the present invention.

[Explanation of symbols]

 1 Engine Main Body 2 Control Unit 3 Oxygen Sensor 4 Crank Angle Sensor 6 Air Flow Meter 7 Fuel Injection Valve 21 Lean Operating Region Determination Means 22 Air-fuel Ratio Target Value Setting Means 23 Air-fuel Ratio Switching Speed Setting Means 24 Theoretical Air-fuel Ratio Approaching Means 25 Air-fuel Ratio Control Means 26 Weight loss correction means

Claims (1)

[Claims] Claim: What is claimed is: 1. Means for determining whether a lean operating range is preset based on an operating condition detection signal, and an air-fuel ratio set to a target value leaner than a theoretical air-fuel ratio when the lean operating range is determined. A means for setting, a means for setting the air-fuel ratio enrichment change speed at the time of switching from the lean target value to the stoichiometric air-fuel ratio, and a means for gradually approaching the air-fuel ratio target value to the stoichiometric air-fuel ratio by the change speed. In the air-fuel ratio control device for an engine, which comprises means for performing air-fuel ratio control based on the set air-fuel ratio that gradually approaches the stoichiometric air-fuel ratio, the lean operating range is that the vehicle speed is within a predetermined range. When the vehicle speed condition deviates from a predetermined range under the condition of, the means for reducing the air-fuel ratio enrichment change speed is provided to reduce the air-fuel ratio of the engine. Apparatus.