JP3075060B2 - Air-fuel ratio control device for internal combustion engine - 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 an internal combustion engine.

[0002]

2. Description of the Related Art In order to improve fuel efficiency and exhaust characteristics of an internal combustion engine, there is a lean combustion engine which controls a mixture supplied to the engine to be leaner than a stoichiometric air-fuel ratio. Driving at a lean air-fuel ratio improves fuel efficiency, but tends to cause problems in driving performance,
Therefore, the engine is temporarily returned to the stoichiometric air-fuel ratio during an operating condition in which the engine tends to be unstable, for example, during idling operation, to prevent engine stall and to ensure smooth operability (Japanese Patent Application Laid-Open No. 61-187552). Reference).

[0003]

In this case, the target air-fuel ratio is set according to the operating range on a map divided by the engine load and the number of revolutions, but the target air-fuel ratio under the operating conditions corresponding to the idling operation is set. If an attempt is made to set the fuel ratio to the stoichiometric air-fuel ratio, the area around the stoichiometric air-fuel ratio also becomes the stoichiometric air-fuel ratio, and accordingly, the lean air-fuel ratio area becomes narrower, and the fuel cost improvement margin is reduced.

On the other hand, the target air-fuel ratio is set to a lean air-fuel ratio in all the operation regions including the idling operation conditions, and only when the idle switch for detecting the fully closed state of the throttle is turned on. It is also conceivable to set the stoichiometric air-fuel ratio, but in this case, if the throttle is fully closed even during a gear change in which the accelerator pedal is temporarily released, the air-fuel ratio is switched to the stoichiometric air-fuel ratio, and unnecessary air-fuel ratio is changed. Fluctuations in fuel ratio deteriorate fuel efficiency and exhaust characteristics.

Further, as in the above-mentioned conventional example, a fixed delay time is set when the air-fuel ratio is switched, and during the gear change, the air-fuel ratio before the operating condition is changed is maintained during the delay time. Although there is one method, there are various states even in the case of a gear change, and depending on the setting of the delay time, it may not be possible to completely prevent engine stall or unnecessary fluctuation of the air-fuel ratio.

For example, in the case of a gear change at low rotation,
Although the engine speed immediately drops to the idle speed as soon as the accelerator is returned, if the set delay time is too long, the lean air-fuel ratio is maintained during that time, causing engine stall and deterioration in drivability. On the other hand, if the delay time is too short, as in the case of a gear change during high rotation, it takes a long time to return to the idle speed after returning the accelerator. Although it is not a number, the air-fuel ratio is unnecessarily switched to the stoichiometric air-fuel ratio. Thus, a fixed delay time cannot correctly cope with a gear change under different conditions.

The present invention solves such a problem, that is,
An object of the present invention is to extend the operating range of the lean air-fuel ratio as much as possible without impairing drivability.

[0008]

According to a first aspect of the present invention, as shown in FIG. 8, an operating condition detecting means 1 for detecting an engine operating condition is provided.
When a target air-fuel ratio setting means 2 for setting a target air-fuel ratio leaner than the stoichiometric air-fuel ratio according to the operating conditions, the high rotational speed
Limits the air-fuel ratio, which gradually changes to the lean side as it
The lean limit value setting means 3 for setting as a air-fuel ratio selecting means 4 for selecting the value of one rich side by comparing the set target air-fuel ratio and the limit value as the target air-fuel ratio, to the target air-fuel ratio A fuel supply amount calculating means 5 for calculating a fuel supply amount in response thereto, and a fuel supply means 6 for supplying fuel to the engine so as to attain the calculated fuel supply amount.

According to a second aspect of the present invention, in the first aspect, the lean limit setting means 3 comprises the limit value near an idle speed.
Is set to an air-fuel ratio near the stoichiometric air-fuel ratio .

As shown in FIG. 9, a third aspect of the present invention relates to an operating condition detecting means 1 for detecting an engine operating condition, and a target air-fuel ratio for setting a target air-fuel ratio leaner than a stoichiometric air-fuel ratio in accordance with the operating condition. Fuel ratio setting means 2 and lean limit value setting means 3 for setting a lean limit value of the air-fuel ratio in accordance with the engine speed
Determining means 7 for determining whether or not the throttle of the engine is in a fully-closed state;
Air-fuel ratio selecting means 8 for selecting the set target air-fuel ratio as it is, and comparing the target air-fuel ratio with a limit value in the fully closed state to select one of the richer values as the target air-fuel ratio; A fuel supply amount calculating means 5 for calculating a fuel supply amount in accordance with the selected target air-fuel ratio; and a fuel supply means 6 for supplying fuel to the engine so as to achieve the calculated fuel supply amount.

[0011]

According to the first invention, as the engine speed increases,
Set the air-fuel ratio that gradually changes to the lean side as the limit value
When the target air-fuel ratio is leaner than the limit value, the limit value is set as the target air-fuel ratio, so that the air-fuel ratio becomes leaner than the limit value in an operation (rotation) region where engine stall or the like becomes a problem. To prevent deterioration of driving performance,
In other regions, the target air-fuel ratio set according to the operating conditions is used so that the operating region of the lean air-fuel ratio is not unnecessarily reduced. Further lean limit
Since the threshold value changes according to the number of revolutions,
The air-fuel ratio is gradually reduced in response to the decrease in the rotation speed due to the full closure of the accelerator.
It can be controlled to the rich side in order to achieve the stoichiometric air-fuel ratio.
Sudden changes can be prevented to ensure smooth and stable operation.

[0012] In the second aspect of the present invention, before the idle rotation speed
The limit value is set to an air-fuel ratio near the stoichiometric air-fuel ratio.
Ensure that the air-fuel ratio is not leaner than the threshold
Deterioration of drivability such as a strike can be prevented .

In the third aspect of the present invention, the fully closed state of the throttle is determined, and when the throttle is fully closed, the air-fuel ratio on the rich side is selected from the limit value on the lean side and the target air-fuel ratio corresponding to the rotational speed. When the throttle is not fully closed, the air-fuel ratio is controlled so as to reach the target air-fuel ratio regardless of the limit value. For this reason, even when the rotation speed is close to the idle rotation speed, the lean air-fuel ratio can be maintained during low-speed operation in which the throttle is slightly opened, and the fuel consumption can be improved accordingly. When the accelerator pedal is depressed to some extent, such as when driving at low speed, the clutch is often engaged even when the rotational speed is low, and engine stall does not occur even if drivability is reduced by maintaining a lean air-fuel ratio.

[0014]

FIG. 1 shows an embodiment of the present invention, in which 11 is an engine, 12 is an intake passage, 13 is an exhaust passage, and an intake passage 12 is provided downstream of a throttle valve (hereinafter also simply referred to as a throttle) 14. The fuel injection valve 15 is installed at a position. The fuel injection valve 15 injects fuel in response to a signal from the control unit 16 and supplies the engine 11 with a lean air-fuel ratio leaner than the stoichiometric air-fuel ratio in principle.

For this reason, the control unit 16 includes:
Signals from an engine speed sensor 17 for detecting the engine speed, an air flow meter 18 for detecting the amount of intake air, and a throttle switch 19 for detecting the fully closed state of the throttle valve 14 are input, and based on these, according to operating conditions. The fuel injection amount is calculated so as to achieve the target lean air-fuel ratio set in the above. In an area where operating conditions deteriorate, such as during idling, the air-fuel ratio approaches the stoichiometric air-fuel ratio to maintain smooth drivability. The control unit 16 includes:
The air-fuel ratio is feedback-controlled to a target value based on a signal from a means for detecting an exhaust air-fuel ratio (not shown), and learning control is performed.

These control operations executed by the control unit 16 will be described with reference to the flowcharts of FIGS. In the following description, for the sake of convenience, the term air-fuel ratio, which is the reciprocal of the air-fuel ratio and the contrast value with the stoichiometric air-fuel ratio (corresponding to stoichiometric air-fuel ratio / air-fuel ratio), is used in the following description. .

FIG. 2 shows a routine which is processed as a background job in order to set a target fuel-air ratio in accordance with the operating conditions. First, in step 1, it is determined whether or not the engine is in a lean operating condition. Engine mileage, exhaust,
An operation region in which lean combustion is to be performed is set based on each requirement such as drivability, and it is determined whether the current operation condition is in the lean operation condition. Then, if it is under the lean operation condition, the lean fuel-air ratio map (MDMLL) is obtained in step 2.
, And otherwise, the map fuel-air ratio Mdml is searched from the non-lean fuel-air ratio map (MDMLS). As shown in FIG. 6, each fuel-air ratio map includes an engine load (fuel injection pulse width Tp) and a rotation speed N.
The target fuel-air ratio according to the operating condition is set for each of the lean fuel-air ratio and the non-lean fuel-air ratio.

In step 4, the retrieved map fuel-air ratio Mdml is replaced with the target fuel-air ratio Tdml, and the routine proceeds to the control routine of FIG. 3 or FIG.

FIGS. 3 and 4 show jobs executed in synchronization with a reference signal for each rotation range or cylinder for calculating a correction value of a target fuel-air ratio, respectively, showing another embodiment of the present invention. 3 will be described.

The target fuel-air ratio Tdml obtained in step 11
Is compared with the corrected fuel-air ratio Dml (corresponding to the current fuel-air ratio) in step 12. If Dml is greater than Tdml, the process proceeds to step 13, and assuming that the target fuel-air ratio has become larger (rich) than the current fuel-air ratio, the air-fuel ratio change speed Ddmrl is calculated as Dml _n-1 at the previous calculation. In addition, in step 15, the upper limit of Dml is limited to Tdml.

Meanwhile, when Dml is less than Tdml in step 12, as the target air-fuel ratio is smaller than the current fuel-air ratio (lean), air from Dml _n-1 of the previous operation in step 14 Subtract the fuel ratio change speed Ddmll,
Further, in step 16, the lower limit of Dml is limited to Tdml.

After the fuel-air ratio has been corrected in accordance with the target fuel-air ratio in this manner, the process proceeds to step 17, where the lower limit value (lean limit value) D of the fuel-air ratio defined according to the engine speed is set.
mllm is retrieved from the table of FIG. This Dm
When the engine speed is near idle,
It takes a value of 1.0 corresponding to the stoichiometric air-fuel ratio, gradually changes to the lean side as the rotation speed increases, and is set so as to take a constant lean value above a predetermined rotation speed. Is equivalent to the stability limit lean air-fuel ratio.

Then, at step 18, the corrected fuel-air ratio Dml
Is compared with the lower limit Dmlilm. If Dml is smaller, that is, if Dml is leaner than the lower limit, the lower limit Dml is determined in step 19.
ilm is set to the corrected air-fuel ratio Dml. If Dml is larger, the process is terminated.

As described above, Dml is a lean limit value Dmlil set according to the rotational speed at that time.
m, and if it is leaner than the lean limit value, this lean limit value is used as the fuel-air ratio to be controlled in order to stabilize drivability.

FIG. 4 is a flow chart of another embodiment, which is the same as that of FIG. 3 up to step 16. When the corrected fuel-air ratio Dml is obtained, it is determined in step 21 whether or not the throttle is fully closed based on the signal of the idle switch. If the throttle is in the idling state with the throttle fully closed, the process proceeds to step 22 and thereafter, otherwise, the process is terminated by using Dml as it is as the corrected fuel-air ratio.

When the throttle is fully closed, the lower limit value Dmli of the lean fuel-air ratio corresponding to the engine speed is determined in step 22.
lm is retrieved from the table as described above, and
In step 3, Dmlilm is compared with Dml. If Dml is leaner than the lower limit, the process proceeds to step 24, where Dml = Dmlilm.

When Dml is larger (rich side), the process is terminated with the corrected fuel-air ratio set to Dml as it is.

Therefore, in this embodiment, as compared with FIG. 3, comparison with the lean limit value for stable operation is performed only when the throttle is fully closed, and otherwise Dml is directly used as the corrected fuel-air ratio. I use it.

After calculating the corrected fuel-air ratio in this manner, the fuel injection amount is calculated according to the flowchart of FIG.

This is a job repeated every 10 ms. In step 31, the control target fuel-air ratio Tfbya is calculated using the corrected fuel-air ratio Dml, and Tfbya = Dml + Ktw.
Calculated as + Kas. Ktw indicates an increase in the water temperature, and Kas indicates an increase after the start. Ktw increases as the water temperature decreases, and Kas decreases according to the elapsed time after the start.
In step 32, the intake air amount Q output from the air flow meter is A / D converted and linearized. In step 33, the basic injection amount Tp is calculated from the intake air amount Q and the rotation speed N.
Is calculated as Tp = K × Q / N.
Ask for. K is a constant.

Then, at step 34, the fuel injection amount Ti is calculated as follows.

Ti = Avtp × Tfbya × Ktr × (α + αm) + Ts (1) where Ktr is a transient air-fuel ratio correction coefficient, α is an air-fuel ratio feedback correction coefficient, and αm is an air-fuel ratio learning correction. It is a coefficient. However, the above equation have already been presented in a number of application by the applicant, it is a known.

Next, at step 35, it is determined whether or not the operation condition is such that the fuel injection is cut off. If the condition is not the fuel cut condition, the calculated fuel injection amount Ti is stored in the output register. Pulse width T
s is stored in the output register to prepare for fuel injection at the next injection timing.

Therefore, in the first embodiment, the air-fuel ratio of the air-fuel mixture supplied to the engine is basically controlled to the target lean air-fuel ratio set according to the operating conditions. Is compared with the lean limit corresponding to the lean air-fuel ratio at the stability limit at that engine speed.If the lean limit is leaner than the lean limit, the lean limit is set as the target air-fuel ratio. Does not make the air-fuel ratio lean. For this reason, it is possible to reliably avoid deterioration in drivability while ensuring the maximum operating range at a lean air-fuel ratio.For example, during idling operation, it is necessary to achieve stable combustion according to the rotational speed. Even when the throttle is temporarily closed, such as when changing gears, the air-fuel ratio is set to an appropriate value according to the decrease in the number of rotations. It is possible to reliably prevent the air-fuel ratio from being unnecessarily increased from a high number, or to stall due to a delay in switching the air-fuel ratio during a gear change in a low rotation range.

The lean limit value is set in accordance with the rotational speed, and when the rotational speed gradually decreases, for example, during a gear change, the air-fuel ratio is gradually increased to the rich side, so that a sudden change in the air-fuel ratio is prevented and smooth. Rotation can be maintained.

In the second embodiment, the comparison between the target air-fuel ratio and the lean limit value is performed only when the throttle is fully closed, and in other operating ranges, the control is directly performed based on the target air-fuel ratio. Therefore, when the throttle is not fully closed, the lean air-fuel ratio is maintained as it is even if the air-fuel ratio at that rotational speed becomes leaner than the lean limit value. When the throttle is not fully closed, the driver often depresses the accelerator and the vehicle's clutch is often connected, and even if the air-fuel ratio is leaner than the lean limit value, the drivability will deteriorate. Since the lean air-fuel ratio is maintained in such a wider operating region without causing engine stall, the cost of improving fuel economy can be improved accordingly.

[0037]

According Effect of the Invention above therefore to the first invention, the machine
Sky gradually changes to lean side as Seki rotation speed increases
When the fuel ratio is set as a limit value on the lean side, and the target air-fuel ratio is on the lean side of the limit value, the limit value is set as the target air-fuel ratio. , To prevent the air-fuel ratio from becoming leaner than the limit value to prevent deterioration of drivability, and in other regions, gradually increase to the lean side as the engine speed increases.
By using the lean air-fuel ratio that is set to change, it is possible to prevent the operating range of the lean air-fuel ratio from being unnecessarily limited, and to improve the fuel efficiency while avoiding the deterioration of drivability. In addition, the limit value on the lean side
It changes depending on whether
The air-fuel ratio is gradually increased to the stoichiometric air-fuel ratio in response to the accompanying rotation speed decrease.
To prevent the air-fuel ratio from changing suddenly.
The smoothness and stability of rolling can be ensured.

According to the second aspect, the idle rotation
Set the limit value around the number to the air-fuel ratio near the stoichiometric air-fuel ratio.
Therefore, make sure that the air-fuel ratio is not leaner than the limit value.
As a result, it is possible to prevent the drivability such as engine stall from deteriorating .

According to the third aspect of the invention, the fully closed state of the throttle is determined, and when the throttle is fully closed, one of the lean limit value and the target air-fuel ratio corresponding to the rotation speed is selected. The air-fuel ratio is selected and controlled, but when the throttle is not fully closed, the air-fuel ratio is controlled so as to reach the target air-fuel ratio regardless of the limit value. By maintaining a lean air-fuel ratio, such as when driving at a low speed with the throttle slightly open, even when the drivability deteriorates a little and engine stall does not occur,
That can improve the fuel cost.

[Brief description of the drawings]

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

FIG. 2 is a flowchart showing the control operation.

FIG. 3 is also a flowchart.

FIG. 4 is also a flowchart.

FIG. 5 is also a flowchart.

FIG. 6 is an explanatory diagram showing a fuel-air ratio allocation map.

FIG. 7 is an explanatory diagram of a table in which a lean lower limit is set.

FIG. 8 is a configuration diagram of the first invention.

FIG. 9 is a configuration diagram of the second invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Operating condition detection means 2 Target air-fuel ratio setting means 3 Lean limit value setting means 4 Air-fuel ratio selection means 5 Fuel supply amount calculation means 6 Fuel supply means 7 Throttle fully closed state judgment means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-27748 (JP, A) JP-A-60-125739 (JP, A) JP-A-5-312081 (JP, A) JP-A-62 99644 (JP, A) JP-A-5-231210 (JP, A) JP-A-5-248281 (JP, A) JP-A-6-74079 (JP, A) JP-A-6-81699 (JP, A) JP-A-6-117291 (JP, A) JP-A-7-166938 (JP, A) JP-A-6-42384 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02D 41/00-41/40 F02D 45/00 301

Claims (3)

(57) [Claims] And operating condition detecting means for detecting as claimed in claim 1] engine operating conditions, and the target air-fuel ratio setting means for setting a target air-fuel ratio leaner than the stoichiometric air-fuel ratio according to the operating condition, gradually as the rotational speed increases Air fuel changing to lean side
Lean limit value setting means for setting the ratio as a limit value, air-fuel ratio selection means for comparing the set target air-fuel ratio with the limit value and selecting one of the richer values as the target air-fuel ratio, An air-fuel ratio of an internal combustion engine, comprising: a fuel supply amount calculation unit that calculates a fuel supply amount according to a fuel ratio; and a fuel supply unit that supplies fuel to the engine so as to achieve the calculated fuel supply amount. Control device. Wherein said lean limit setting means, idle speed
Set the limit value around the number to the air-fuel ratio near the stoichiometric air-fuel ratio.
Air-fuel ratio control system for an internal combustion engine according to claim 1 that. 3. An operating condition detecting means for detecting an engine operating condition; a target air-fuel ratio setting means for setting a target air-fuel ratio leaner than a stoichiometric air-fuel ratio in accordance with the operating condition; Lean limit value setting means for setting a limit value on the lean side of the fuel ratio; determining means for determining whether or not the engine throttle is in a fully closed state; Air-fuel ratio selecting means for directly selecting the air-fuel ratio and comparing the target air-fuel ratio with the limit value when the engine is in the fully closed state to select a value on one of the rich sides as the target air-fuel ratio; A fuel supply amount calculating means for calculating a fuel supply amount according to a target air-fuel ratio; and a fuel supply means for supplying fuel to the engine such that the calculated fuel supply amount is obtained. Fuel ratio control device.