JP3525447B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

Description: 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, and more particularly to an internal combustion engine capable of improving operating performance when an evaporative purge is turned on and off and when a cold start is performed. The present invention relates to an air-fuel ratio control device for an engine. 2. Description of the Related Art In an internal combustion engine of a vehicle, three major sources of vaporized fuel that diffuse into the atmosphere and pose a problem are a carburetor, an intake pipe, and a fuel tank. Although the evaporation loss during running is slight, immediately after the stop, the temperature of the engine room rises, and evaporation from the intake pipe and the carburetor becomes active. Since it is extremely difficult to prevent the fuel from evaporating, a method of using a canister to prevent the fuel from diffusing into the atmosphere is generally used. [0003] When the internal combustion engine is stopped, the evaporated fuel is directed toward the canister, which is a container filled with activated carbon, by utilizing the property that the evaporated fuel is loosely adsorbed on the surface of the activated carbon when it comes into contact with the activated carbon, and is released again when air flows therethrough. During operation, the air is taken in from the outside of the canister to supply the released fuel to the intake system. That is, in this evaporative fuel control system, the fuel tank and the intake passage downstream of the throttle valve in the intake system of the internal combustion engine communicate with each other through a ventilation passage. The generated evaporative fuel (evaporation) is adsorbed and held in the adsorbent, and during operation of the internal combustion engine, the evaporative fuel adsorbed and held by the introduction of fresh air from the air introduction passage is separated (purged) into the intake passage. A canister to be supplied is provided, that is, the canister is interposed between an evaporation passage and a purge passage which form a ventilation passage, and a purge valve is provided in the middle of the purge passage.
The operation of the purge valve is controlled by control means (not shown) for inputting each operation state of the internal combustion engine to adjust the purge amount. [0005] Such an evaporative fuel control system for an internal combustion engine is disclosed, for example, in Japanese Patent Application Laid-Open No. 1-190955. What is described in this publication is a purge valve control means for controlling the valve opening of the purge valve,
Canister temperature detecting means for detecting the temperature of the evaporative fuel collecting portion of the canister, engine operating state detecting means for detecting the high intake air amount operating state of the internal combustion engine, and opening correction for correcting the purge valve control opening of the purge valve control means Means is provided, and when it is detected that the temperature of the evaporative fuel collecting portion of the canister has shown a degree of decrease equal to or more than a predetermined value when it is detected that the purge valve opening degree is constant at a constant low intake operation state of the internal combustion engine, In addition, the control opening of the purge valve during the high intake operation by the purge valve control means is corrected by the purge valve opening correction means to increase the opening by a predetermined amount as compared with the normal operation. A conventional air-fuel ratio control device for an internal combustion engine equipped with an evaporative fuel control device controls the air-fuel ratio to a stoichiometric air-fuel ratio by an O ₂ sensor. As shown in the drawing, the correction amount necessary for setting the air-fuel ratio to the stoichiometric air-fuel ratio for each engine speed and engine load is stored in the learning divided area map in the air-fuel ratio feedback learning correction amount used for correcting the fuel supply amount (fuel injection amount) Is stored as the learning correction amount, and the fuel supply amount is corrected based on the learning correction amount. Further, when the evaporative purge is on, that is, when the purge valve is opened, as shown in FIG. 12, the evaporative guard control is applied to the learning correction amount (F _LAF ), which is the air-fuel ratio feedback learning correction amount, and the evaporative purge on state is performed. Sometimes, a correction range in which the learning correction amount (F _LAF ) can be controlled with respect to the base air-fuel ratio is set. In the evaporative guard control, as shown in FIG. 12, x% is defined as an evaporative guard with respect to a value obtained by connecting a straight line between the learning correction amount at the time of idling and the learning correction amount of 1.0 in the operating region Kn of the internal combustion engine. If the evaporative guard control is not performed, the previous learning correction is performed when the canister temperature is low and the amount of evaporation is small at the next cold start after the internal combustion engine is stopped, so that the air-fuel ratio becomes lean. Driving performance deteriorates. Further, in the conventional air-fuel ratio control device for an internal combustion engine, learning correction is not performed when the purge amount is equal to or more than a predetermined amount even when the purge amount of the evaporated fuel is large due to the evaporation guard control. For this reason, the air-fuel ratio becomes rich, and there is a disadvantage that the driving performance deteriorates. Furthermore, in the conventional air-fuel ratio learning control, for example, when operating in a state of K6 in FIG 11 corrects the value of / 2 (F _LAF + 〓F _LAF of K6) as F _LAF I have. For this reason, the guard is applied at a value lower than that of the evaporative guard, and the air-fuel ratio is enriched and the driving performance deteriorates. At this time, the ΔF _LAF is an average value of all the learning values in FIG. That is, 〓 _FLAF = (K1 + K2 +... Kn) / n. Further, as shown by reference numeral a in FIG. 13, when the evaporative purge changes from the OFF state to the ON state, the air-fuel ratio (A / F) suddenly becomes rich as shown by reference numeral b, and the operation is stopped. When the performance deteriorates and the evaporative purge changes from the on state to the off state as shown by the symbol c, the air-fuel ratio (A / F) rapidly becomes lean as shown by the symbol d. [0013] Then, due to the rapid change of the air-fuel ratio as described above, the engine speed is increased as shown by the symbol e in FIG.
There is a disadvantage that the operation becomes unstable and the driving performance deteriorates. SUMMARY OF THE INVENTION In order to eliminate the above-mentioned disadvantages, the present invention provides an internal combustion engine having an internal combustion engine which is provided in a fuel tank and an intake passage of an internal combustion engine. A canister that adsorbs and holds the evaporative fuel generated in the fuel tank during a stop and releases the evaporative fuel that is adsorbed and held by the introduction of fresh air during the operation of the internal combustion engine to supply the evaporative fuel to the intake passage; A purge valve is provided in the middle of the ventilation passage between the intake passages, and a learning correction of the air-fuel ratio is used for correcting the fuel supply amount by using a correction amount necessary to make the air-fuel ratio a stoichiometric air-fuel ratio for each engine speed and engine load. In order to set a correction range in which the learning correction amount can be controlled with respect to the base air-fuel ratio of the internal combustion engine when the evaporative purge on state is provided. In the air-fuel ratio control device for an internal combustion engine that controls an air-fuel ratio by performing an evaporative guard control on the learning correction amount to adjust a fuel supply amount to the internal combustion engine, the canister is provided with a temperature sensor that detects a canister temperature. When the learning correction amount reaches the evaporative guard even when the temperature is lower than the predetermined temperature, the purge reduction correction control is performed by the purge reduction correction amount set according to the canister temperature state, and the purge reduction correction amount is learned and purged. When storing in the learning region map, a learning value calculated by adding the coefficient set according to the canister temperature state to the purge reduction correction amount is stored in the purge learning region map, and based on this learning value, Control means for adjusting the fuel supply amount to the internal combustion engine to control the air-fuel ratio is provided. According to the structure of the present invention, when the learning correction amount of the air-fuel ratio reaches the evaporative guard even when the canister temperature is lower than the predetermined temperature, the control means sets the purge reduction amount according to the canister temperature state. When the purge reduction correction is controlled by the correction amount and the purge reduction correction amount is learned and stored in the purge learning region map, a learning value calculated by adding the coefficient set according to the canister temperature state to the purge reduction correction amount. Is stored in the purge learning region map, and the air-fuel ratio is controlled by adjusting the fuel supply amount to the internal combustion engine based on the learning value. As a result, the fuel supply amount is adjusted when the evaporative purge is turned on / off or after the cold start, so that the air-fuel ratio can be optimized and the driving performance can be improved, and the stability of exhaust harmful components at high altitudes can be improved. Can be done. Embodiments of the present invention will be described below in detail with reference to the drawings. 1 to 10 show an embodiment of the present invention. In FIG. 10, 2 is an intake passage, and 4 is a fuel tank. In the intake passage 2, an air cleaner (not shown) is provided on the upstream side, and an internal combustion engine (not shown) is provided on the downstream side. An intake throttle valve 6 is provided in the middle of the intake passage 2, and a surge tank 8 is formed downstream of the intake throttle valve 6. The surge tank 8 in the intake passage 2 and the fuel tank 4 are connected by an air passage 10. A canister 10 is provided in the middle of the ventilation path 10. Therefore, the ventilation path 10 includes the evaporation passage 10-1 between the fuel tank 4 and the canister 12, and the purge passage 10-2 between the canister 12 and the surge tank 8. A check valve 14 is provided in the middle of the evaporation passage 10-1. This check valve 14
Allows only the flow of evaporated fuel (evaporation) from the fuel tank 4 to the canister 12 side. A purge valve 16 is provided in the purge passage 10-2. This purge valve 16
Is opened / closed by a control means 20, which will be described later, and controls the amount of purge from the canister 12 to the surge tank 8. The canister 12 is provided with a temperature sensor 18 for detecting a canister temperature. This temperature sensor 18 is connected to control means 20. The control means 20 is a learning divided area map for storing a correction amount necessary for making the air-fuel ratio a stoichiometric air-fuel ratio for each engine speed and engine load as a learning correction amount of the air-fuel ratio (see FIG. 2). When the purge valve 16 is opened and the evaporative purge is on, the learning correction amount is set to a correction range in which the learning correction amount can be controlled with respect to the base air-fuel ratio of the internal combustion engine. The evaporative emission amount is set in accordance with the canister temperature (see FIG. 4). Even if the canister temperature is lower than the predetermined temperature (Ct), which is the canister purge correction execution determination temperature, the learning correction amount of FIG. Is reached, the purge reduction correction is controlled by the purge reduction correction set according to the canister temperature state (see FIG. 5), and this purge reduction correction is performed. Coefficient is in storing the learning is allowed to purge learning area map (see FIG. 7) is set according to the canister temperature state to the purge reduction correction amount (Tx) (FIG. 6
(See FIG. 7) is stored in a purge learning area map (see FIG. 7), and the air-fuel ratio is controlled by adjusting the fuel supply amount to the internal combustion engine based on the learning value. Next, the operation of this embodiment will be described with reference to the flowchart of FIG. When the internal combustion engine is started and the program of the control means 20 is started (step 102), first, the learning divided region is set according to the learning divided region map shown in FIG. 2, that is, for each engine speed and engine load. Identify (step 104). The value of the region identified in the learning divided region map shown in FIG. 2 is set as a learning correction amount (F _LAF ) for the air-fuel ratio feedback learning correction (step 106). Next, it is determined whether the evaporative purge condition is on (step 108). If NO in step 108, the learning correction amount (F
_It is determined whether or not _LAF is an evaporative guard (step 11).
0). On the other hand, if YES in step 108, the relationship between the canister temperature and the predetermined temperature (Ct) is
It is determined whether or not the canister temperature ≧ Ct (step 11).
2). If NO in step 112, the process proceeds to step 110 because the canister temperature is lower than the predetermined temperature (Ct). If NO in step 110, the learning control of the air-fuel ratio is performed with the learning correction amount (F _LAF ) as before, and this learning correction amount is set for each region of the learning divided region map shown in FIG. (F _LAF ) is stored (step 214),
Then, the process returns to step 104. If YES in step 112, or if the learning correction amount (F _LAF ) reaches the evaporation guard even if the canister temperature is lower than the predetermined temperature (Ct), and if YES in step 110, the normal learning is performed. Correction amount (F
_LAF ) control of the air-fuel ratio is stopped (step 11).
6) Then, the purge reduction correction amount (F
_KP ) to execute purge decrease correction control (step 118). In this step 118, the purge reduction correction amount in FIG. 5 is an initial value, and is used as a learning value after learning the purge reduction correction control as shown in the purge learning region map in FIG. Then, it is determined whether or not λ = 1 (step 120). That is, in this step 120,
For example, at the time of air-fuel ratio feedback control using an O ₂ sensor (not shown), it is determined whether the duty value of the air-fuel ratio feedback control is in the range of the hatched portion in FIG.
When the full-range air-fuel ratio sensor is used, it is determined whether or not the air-fuel ratio sensor is in a range indicated by a hatched portion in FIG. If NO in step 120, the air-fuel ratio is feedback-controlled so that the purge reduction correction amount (F _KP ) becomes λ = 1 (step 122).
Return to step 120. If YES in step 120,
That is, when λ = 1, the purge reduction correction amount (F _KP )
_Is replaced by a learning correction amount (F _LAF ) at the time of canister temperature ≧ Ct, and stored as a learning value in the purge learning region map shown in FIG. 7 for each engine speed and engine load (step 12).
4). That is, in this step 124, the purge reduction correction amount (F _KP ) is stored by replacing it with a numerical value 1.0 which is not affected by the canister temperature, as shown in FIG. That is, F _LKP , which is the learning correction amount when canister temperature ≧ Ct, is calculated by F _LKP = F _KP × Tx.
The learning value is stored in the purge learning area map of FIG. After the step 124, the process returns to the step 104. That is, in this embodiment, the canister temperature is the predetermined temperature (Ct) which is the purge correction execution determination temperature.
Even if it is lower, when the learning correction amount (F _LAF ) of the air-fuel ratio becomes the evaporation guard of the evaporation guard map shown in FIG. 3, the purge reduction correction control is executed in the same manner as when the canister temperature ≧ Ct. Further, by learning the purge decrease correction amount (F _KP ), learning correction at the time of canister temperature ≧ Ct as in the prior art can be performed.
In other words, in order to calculate F _LKP = (F _LKP old + F _KP ) / 2 and to more precisely control the effect of evaporation due to the canister temperature, the purge learning correction amount (F _LKP )
Is learned and stored, the coefficient (Tx) is calculated from FIG. 6 and replaced with the numerical value 1.0, which is a value that eliminates the influence of the canister temperature. More specifically, a purge decrease correction amount (F _KP ) corresponding to the canister temperature is obtained from FIG. 5, and after controlling the fuel supply amount by the purge decrease correction amount (F _KP ), it is actually set as a learning value. When storing in the purge learning area map in FIG. 7, the purge reduction correction amount (F _KP ) obtained in FIG. 5 is not entered as it is. That is,
When the purge reduction correction amount (F _KP ) in FIG.
After the restart, since the canister temperature is different, the learning value is not accurate, and the air-fuel ratio cannot be properly controlled. Therefore, a learning value is obtained by multiplying the purge reduction correction amount (F _KP ) of FIG. 5 by the coefficient (Tx) of FIG. 6, and after obtaining this learning value, the learning value is plotted for each engine speed and engine load. 7 is stored in the purge learning area map. Further, when executing the purge decrease correction control, on the contrary, the correction value corresponding to the canister temperature is changed by the coefficient (T
x) and is used for air-fuel ratio correction control. Further, as shown in FIGS. 8 and 9, it is determined whether the purge reduction correction amount (F _KP ) is λ = 1 or not, and more accurate control is performed. As a result, the fuel supply amount can be adjusted by the learning value stored in the purge learning region map of FIG. 7 when the evaporative purge is turned on / off or when the cold start is performed. Can be improved. Further, at high altitudes, gasoline as fuel evaporates more than in flat terrain, and exhaust harmful components become unstable. In this embodiment, the stability of exhaust harmful components can be improved. . Further, the same effect can be obtained without controlling the purge amount by the purge valve 16 which is a duty solenoid, so that the cost can be reduced. As is apparent from the above detailed description, according to the present invention, the canister is provided with the temperature sensor for detecting the canister temperature, and the learning correction amount reaches the evaporative guard even when the canister temperature is lower than the predetermined temperature. In this case, the purge reduction correction is controlled by the purge reduction correction amount set according to the canister temperature state, and when the purge reduction correction amount is learned and stored in the purge learning area map, the purge reduction correction amount is changed to the canister temperature state. The learning value calculated in consideration of the coefficient set according to the stored learning value in the purge learning area map,
By providing control means for controlling the air-fuel ratio by adjusting the fuel supply amount to the internal combustion engine based on the learning value, the fuel supply amount is adjusted by the learning value when the evaporative purge is turned on / off or after the cold start. Therefore, the driving performance can be improved by adjusting the air-fuel ratio appropriately, and the stability of exhaust harmful components at high altitude can be improved. The same effect can be obtained even if the purge amount is not controlled by the purge valve, so that the cost can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a flowchart of air-fuel ratio control. FIG. 2 is an explanatory diagram of a learning divided region map. FIG. 3 is an explanatory diagram of an evaporation guard map of a learning correction amount of an air-fuel ratio. FIG. 4 is a graph showing the relationship between the canister temperature and the evaporation amount. FIG. 5 is a relationship diagram between a canister temperature and a purge reduction correction amount. FIG. 6 is a relationship diagram between a canister temperature and a coefficient (Tx). FIG. 7 is an explanatory diagram of a purge learning area map. FIG. 8: λ = at the time of feedback control by an O ₂ sensor
It is explanatory drawing which shows the range of 1. FIG. 9 is an explanatory diagram showing a range of λ = 1 in the case of an all-area air-fuel ratio sensor. FIG. 10 is a system configuration diagram of an air-fuel ratio control device. FIG. 11 is an explanatory diagram of a conventional learning divided area map. FIG. 12 is an explanatory diagram of a conventional evaporation correction map of an air-fuel ratio learning correction amount. FIG. 13 is a time chart of a conventional evaporation purge, air-fuel ratio, learning correction amount, and engine speed. [Description of Signs] 2 Intake passage 4 Fuel tank 6 Intake throttle valve 8 Surge tank 10 Purge passage 12 Canister 16 Purge valve 18 Temperature sensor 20 Control means

Claims (1)

(57) [Claim 1] Adsorbed fuel vapor generated in the fuel tank during the stop of the internal combustion engine in the middle of an air passage communicating between the inside of the fuel tank and the intake passage of the intake system of the internal combustion engine. A canister is provided for holding and holding the evaporated fuel adsorbed and held by the introduction of fresh air during the operation of the internal combustion engine and supplying the evaporated fuel to the intake passage.A purge valve is provided in the middle of the ventilation passage between the canister and the intake passage. A learning division area map for storing a correction amount necessary for making the air-fuel ratio a stoichiometric air-fuel ratio for each engine speed and engine load as a learning correction amount of the air-fuel ratio used for correcting the fuel supply amount; In the Zeon state, the learning correction amount is subjected to evaporative guard control so as to set a correction range in which the learning correction amount can be controlled with respect to the base air-fuel ratio of the internal combustion engine. In the air-fuel ratio control device for an internal combustion engine that controls an air-fuel ratio by adjusting a fuel supply amount, a temperature sensor that detects a canister temperature is provided in the canister, and the learning correction amount reaches the evaporative guard even when the canister temperature is lower than a predetermined temperature. In this case, the purge reduction correction is controlled by the purge reduction correction amount set in accordance with the canister temperature state, and when the purge reduction correction amount is learned and stored in the purge learning region map, the purge reduction correction amount is set to the purge reduction correction amount. A learning value calculated in consideration of a coefficient set in accordance with the canister temperature state is stored in the purge learning region map, and an air-fuel ratio is adjusted by adjusting a fuel supply amount to the internal combustion engine based on the learning value. An air-fuel ratio control device for an internal combustion engine, further comprising control means for controlling.