JPH02245461A - Purge control unit for internal combustion engine - Google Patents

Abstract

PURPOSE:To dissolve a problem of a large quantity of purge gas flowing into an intake passage suddenly in the initial phase of starting of purge for preventing air fuel ratio from getting rich in transition by making the opening speed of a purge control valve slower as the fuel concentration in purge gas becomes higher. CONSTITUTION:A canister 16 connected to the upper space of a fuel tank 18 via a fuel vapor inductance passage 17 is connected to a surge tank 7 via a purge passage 19. And a purge control valve 21 is arranged in the purge passage 19. Still, the purge control valve 21 is open and close controlled by an electronic control unit 40 based on respective detected signals from various kinds of sensors 9, 30, 31, 33 for detecting running conditions of an internal combustion engine. On this occasion, fuel concentration in purge gas is calculated based on oxygen concentration in exhaust gas detected by O2 sensor 31, that is air fuel ratio of mixture, by means of the electronic control unit 40. And the higher fuel concentration in purge gas is the slower opening speed of the purge control valve 21 is made.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a purge control device for an internal combustion engine.

[Conventional technology]

JP-A No. 63-186955 discloses that a park control valve is disposed in a purge passage connecting a canister and an engine intake passage, and that the purge control valve is opened in a predetermined engine operating state to allow air to flow into the canister. It is equipped with a purge device that discharges the stored fuel vapor into the engine intake passage (hereinafter referred to as "purge"), and the basic fuel injection amount calculated according to the engine operating state is changed based on the output signal of the 02 sensor. An internal combustion engine is disclosed in which the air-fuel mixture supplied into the engine cylinder is controlled to have a stoichiometric air-fuel ratio by correcting it using a feedback correction coefficient FAF. In this internal combustion engine, the feedback correction coefficient FA during engine idling operation and during low load operation is
A control center value of F is calculated, and the fuel concentration of the purge gas is detected based on the difference between the control center values. I am trying to compensate by reducing the amount.

[Problem to be solved by the invention]

However, in this internal combustion engine, the purge control valve is opened from fully closed to fully open at any time when the purge execution conditions are met, so a large amount of purge gas suddenly flows into the intake passage from the canister, and the fuel concentration of the purge gas is particularly high. When is high, a large amount of fuel vapor is rapidly supplied into the intake passage. Correspondingly, the amount of fuel injected from the fuel injector is corrected to be reduced, but it is unable to follow the rapid fluctuations in the air-fuel ratio, and as a result, the air-fuel ratio transiently increases significantly at the beginning of the purge. There is a problem with getting rich.

[Means to solve the problem]

In order to solve the above problems, according to the present invention, a purge control valve is disposed in a purge passage connecting a fuel vapor storage container that temporarily stores fuel vapor and an engine intake passage, and a predetermined engine operation is performed. In the purge control device, the purge control valve is opened to introduce purge gas from the fuel vapor storage container into the engine intake passage when the purge control valve is opened, and the opening speed of the purge control valve is slowed down as the fuel concentration of the purge gas increases. ing.

[Operation] When the engine operating state is a predetermined engine operating state, the purge control valve is opened and purging is started. At this time, the purge control valve opens more slowly as the fuel concentration of the purge gas increases. Therefore, the flow rate of the purge gas flowing into the engine intake passage increases gradually, and the rate of increase becomes slower as the fuel concentration increases.

〔Example〕

Referring to FIG. 1, 1 is a cylinder block, 2 is a piston, 3 is a cylinder head, 4 is a combustion chamber, 5 is an intake manifold, and 6 is an exhaust manifold. The intake manifold 5 is connected to an air cleaner 10 via a surge tank 7, an intake duct 8, and an air flow meter 9. A throttle valve 11 is disposed in the intake duct 8 , and a fuel injection valve 12 is disposed in the intake manifold 5 so as to face an intake port 13 . An exhaust pipe 14 is connected to the exhaust manifold 6, and a three-way catalyst 15 is disposed in the middle of the exhaust pipe 14. A canister 16 filled with activated carbon is connected to the upper space of a fuel tank 18 via a fuel vapor introduction passage 17. Furthermore, the canister 16 is connected to the inside of the surge tank 7 via a purge passage v419, and the purge passage 19 is provided with a throttle 20 for adjusting the flow rate. Further, a purge control valve 21 is provided in the purge passage 19 between the canister 16 and the throttle 20. The purge control valve 21 is duty-controlled by the electronic control unit 40, and the relationship between the duty ratio and the opening degree of the purge control valve 21 is shown in FIG. 2, where the opening degree of the purge control valve 21 is proportional to the duty ratio. Fully closed at 0% duty ratio, 100% duty ratio
It becomes full throttle.

Referring again to FIG. 1, the electronic control unit 40 consists of digital combinations of ROMs (IJ-on memory) 42 interconnected by a bidirectional bus 41.
, RAM (random access memory) 43, CPU
(microprocessor) 44, a human power port 45, and an output port 46. An intake air temperature sensor 30 disposed within the air flow meter 9 detects the intake air temperature, and this output signal is input to the input port 45 via the AD converter 47 . The air flow meter 9 generates an output voltage proportional to the amount of intake air, and this output voltage is input to the input port 45 via the AD converter 48.

The 02 sensor 31 disposed inside the exhaust manifold 6 detects the oxygen concentration in the exhaust, and this output signal is sent to the AD converter 49.
The signal is input to the input port 45 via the input port 45. A crank angle sensor 33 built into the distributor 25 generates an output pulse indicative of the engine speed, and this output pulse is input to the manual power port 45 . On the other hand, the output port 46 is connected to the purge control valve 21 and the fuel injection valve 12 via corresponding drive circuits 50 and 51.

FIG. 3 shows a routine for calculating the fuel injection time TAU of the fuel injection valve 12. This routine is executed by an interrupt at every fixed crank angle. Referring to FIG. 3, first, in step 60, the intake air amount Q and the engine speed NE are read. Then, in step 61, Q
/NE is calculated. This Q/NE indicates the amount of intake air per engine revolution, and corresponds to the engine load. Step 62
Then, the basic fuel injection time TP is calculated from the two-dimensional map of the engine speed NE and Q/NE. In step 63, the fuel injection time TAU is calculated using the following equation.

TAU=TP-FAF- Here, FAF is a feedback correction coefficient that is changed based on the output signal of the 0□ sensor 31, and TP is corrected so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. however,
When feedback control is not executed, FAF is set to l. K is another correction coefficient.

FIG. 4 shows the FAF calculation method. Referring to FIG. 4, the 02 sensor 31 generates an output voltage of about 0.9 volts when the air-fuel mixture is rich, that is, when it is rich, and 0.1 volts when the air-fuel mixture is lean, that is, lean. Generates an output voltage of approximately 0. The output voltage V of the sensor 31 is a reference voltage V of about 0.45 volts at the electronic control unit 40.
If the output voltage V of the 02 sensor 31 is higher than Vr, it is determined to be rich, and if it is lower than Vr, it is determined to be lean. When it is determined that there has been a reversal from rich to lean, FAF suddenly increases by the set skip value and then gradually increases; when it is determined that there has been a reversal from lean to rich, FAF suddenly decreases by the set skip value and then gradually increases. Decrease.

FIG. 5 shows a lean determination routine.

This routine is executed by an interrupt every 3 ms, for example. Referring to FIG. 5, first, in step 70, it is determined whether the output voltage V of the 02 sensor 31 is equal to or higher than the reference voltage of 0.45 volts. (2) If ≧0.45 volts, that is, if the air-fuel ratio is rich, the routine proceeds to step 71, where the flag AF is set to 1, and this routine ends. V<0
．． If the voltage is 45 volts, that is, if the air-fuel ratio is lean, the process proceeds to step 72, where the flag AF is reset to 0, and this routine ends.

FIG. 6 shows a routine for executing purge control. This routine is executed by an interrupt every 100 m5, for example. Referring to FIG. 6, first in step 80 it is determined whether air-fuel ratio feedback control is being executed, and in step 81 it is determined whether the intake air temperature TA is 50° C. or higher.

In steps 80 and 81, it is determined whether the purge execution conditions are satisfied. If a negative determination is made in either step 80 or step 81, that is, if it is determined that the purge execution condition is not satisfied, the process proceeds to step 82 and the duty ratio is set to 0%. Next, in step 83, the purge control valve 21 is controlled based on the calculated duty ratio. As a result, the purge control valve 21 is fully closed and no purge is performed.

On the other hand, if an affirmative determination is made in both steps 80 and 81, that is, if it is determined that the purge execution condition is satisfied, the process proceeds to step 84 and the flag AF is set to 0.
In other words, it is determined whether the air-fuel ratio is lean or not. A
When F=1, that is, when the air-fuel ratio is rich, nothing is executed, that is, this routine ends with the purge control valve 21 maintained in the closed state. If AF=0 in the next processing cycle, that is, if the air-fuel ratio becomes lean, the process proceeds to step 85 and the duty ratio is increased by 2%. In step 86, it is determined whether the duty ratio exceeds 100%. In this case, since the duty ratio is 100% or less, the process proceeds to step 83, and the purge control valve 21 is controlled based on the calculated duty ratio.

As a result, the purge control valve 21 is opened by 2%. Therefore, a small amount of purge gas flows into the surge tank 7 and purge is started. In the subsequent processing cycle,
While AF=0, that is, the air-fuel ratio is lean, the purge control valve 21
The opening degree is increased by 2%. Therefore, the amount of purge gas is gradually increased while the air-fuel ratio is lean.

When the air-fuel ratio becomes rich due to the inflow of purge gas, AF=
1, so a negative determination is made in step 84 and the routine ends without executing anything. Therefore, the Denity ratio is not increased and the opening degree of the purge control valve 21 is maintained at the current opening degree. The opening process when the air-fuel ratio is rich is repeated, and the opening degree of the purge control valve 21 is maintained at the current opening degree. When the feedback correction coefficient FAF decreases and the air-fuel ratio becomes lean again, AF=0, and as described above, while the air-fuel ratio is lean, the duty ratio is increased by 2%, and therefore the opening degree of the purge control valve 21 is 2%. It is increased by %. The above-described process is repeated, and when the duty ratio exceeds 100%, an affirmative determination is made in step 86 and the process proceeds to step 87. In step 87, the duty ratio is set to 100%, and in step 83, the purge control valve 21 is fully opened.

As described above, in this embodiment, at the start of purge, the purge control valve 21 is opened step by step only while the air-fuel ratio is lean, so that a large amount of purge gas is released at the start of purge. Suddenly surge tank 7
This can prevent the air-fuel ratio from transiently becoming over-rimmed.

FIG. 7 shows an example of the operation of a conventional purge control device.

Referring to FIG. 7, the purge execution condition is not satisfied until time t1, so the purge is not executed, and the FAF is 1.0.
The air-fuel ratio is controlled to the stoichiometric air-fuel ratio.

When the purge condition is satisfied at time t1, the purge control valve is opened from fully open to fully open. Therefore, a large amount of purge gas from the canister 16 rapidly flows into the surge tank 7, and especially when the fuel concentration of the purge gas is high, a large amount of fuel vapor is supplied into the surge tank 7.

Correspondingly, the FAF gradually decreases, but it cannot follow the rapid fluctuations in the air-fuel ratio, and as a result, there is a problem that it becomes significantly rich transiently at the beginning of the purge.

8 and 9 are explanatory diagrams of the operation of this embodiment. FIG. 8 shows a case where the fuel concentration of the purge gas is low, and FIG. 9 shows a case where the fuel concentration of the purge gas is high.

Referring to FIG. 8, when the purge execution condition is satisfied at time t2, the opening degree of the purge control valve 21 is increased step by step, for example, every 100 m5 during the period when the air-fuel ratio is lean. As a result, the amount of purge gas flowing into the thermal tank 7 is gradually increased.

When the air-fuel ratio becomes rich due to the inflow of purge gas, the opening degree of the purge control valve 21 stops increasing during the rich period and is maintained at the current opening degree. When the air-fuel ratio becomes rich, FAF
decreases, so it becomes lean again. When the air-fuel ratio becomes lean, the opening degree of the purge control valve 21 is again increased little by little, and thereafter the purge control valve 21 is controlled in the same manner as described above and is fully opened.

Next, referring to FIG. 9, when the fuel concentration of the purge gas is high, compared to when the fuel concentration is low, the air-fuel ratio becomes rich by slightly increasing the opening degree of the purge control valve 21, and the time required for the air-fuel ratio to become rich is also determined. Therefore, the purge control valve 21 is opened more slowly (that is, the valve opening speed is slower) than when the fuel concentration is low, and it takes a relatively long time to fully open.

That is, according to this embodiment, it is detected whether the air-fuel ratio is lean or not, and only when the air-fuel ratio is lean, the opening degree of the purge control valve 21 is increased stepwise to adjust the purge gas amount so that the air-fuel ratio does not become overrich. Since it is increased in stages, it is possible to prevent the air-fuel ratio from becoming transiently overrich at the start of purge. Furthermore, in this embodiment, the higher the fuel concentration of the purge gas, the longer it takes for the purge control valve 21 to fully open. That is, the higher the fuel concentration of the purge gas, the slower the opening speed of the purge control valve 21 becomes. Therefore, regardless of the fuel concentration of the purge gas,
The opening degree of the purge control valve can be increased most quickly at each fuel concentration of the purge gas while preventing the air-fuel ratio from becoming significantly rich.

〔Effect of the invention〕

The higher the fuel concentration of the purge gas, the slower the opening speed of the purge control valve, so at the beginning of the purge,
A large amount of purge gas does not suddenly flow into the intake passage, and therefore, it is possible to prevent the air-fuel ratio from becoming transiently rich at the beginning of the purge.

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the relationship between duty ratio and purge control valve opening degree,
Figure 3 is a flowchart for calculating fuel injection time, Figure 4 is a diagram explaining how to calculate the feedback correction coefficient FAF, Figure 5 is a flowchart for determining whether the mixture is rich or lean, and Figure 6 is a flowchart for determining whether the mixture is rich or lean. A flowchart for executing the control, FIG. 7 is an explanatory diagram of the operation of the conventional purge control device, FIGS. 8 and 9 are explanatory diagrams of the operation of the purge control device of the present embodiment, and FIG. In the case of a purge gas having a low fuel concentration, FIG. 9 shows the case of a purge gas having a high fuel concentration. 7...Surge tank, 16...Canister, 1
9... Purge passage, 21... Purge control valve, 40
...Electronic control unit. Duty ratio 100°. Time 4th time

Claims (1)

[Claims] A purge control valve is disposed in a purge passage that connects a fuel vapor storage container that temporarily stores fuel vapor and an engine intake passage, and the purge control valve is opened in a predetermined engine operating state to remove the fuel. A purge control device for an internal combustion engine that introduces purge gas from a steam storage container into an engine intake passage, wherein the higher the fuel concentration of the purge gas, the slower the opening speed of the purge control valve.