JP3620151B2 - Evaporative fuel processing device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an evaporative fuel treatment apparatus for an internal combustion engine that prevents air pollution by burning evaporative fuel generated in a fuel tank or the like in a combustion chamber without releasing it to the outside.
[0002]
[Prior art]
Conventionally, an evaporative fuel treatment technique for preventing evaporative fuel from being discharged outside by purging evaporative fuel into a combustion chamber of an internal combustion engine is disclosed in Japanese Patent Application Laid-Open No. 62-153553.
[0003]
This technology collects the evaporated fuel generated in the fuel tank with a canister, and sucks the collected fuel into the intake passage by using the negative pressure generated on the downstream side of the throttle valve. The release to the outside is prevented.
[0004]
[Problems to be solved by the invention]
However, when negative pressure downstream of the throttle valve is used, negative pressure does not occur in a high-load operation state where the throttle valve is largely opened, and it becomes difficult to suck the collected fuel into the intake passage. There has been a problem that it may be assumed that the collection allowable value of the evaporated fuel collected by the canister is exceeded.
[0005]
The present invention has been made in view of such a problem. By controlling the opening of the throttle valve to forcibly generate a negative pressure in the intake passage, the evaporative fuel can be generated regardless of the operating state of the internal combustion engine. It is an object of the present invention to provide an evaporative fuel treatment device for an internal combustion engine that enables purging and prevents a decrease in the output of the internal combustion engine at that time .
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a canister for collecting evaporated fuel generated in a fuel tank or the like, and a canister connected to the canister via a purge passage that opens into an intake passage on the downstream side of the throttle valve. An evaporative fuel processing apparatus for an internal combustion engine that purges the fuel collected in step (b), comprising control means for reducing the opening of the throttle valve during the purge execution , wherein the control means opens the throttle valve. When the degree is decreased, the air-fuel ratio is corrected to the over-rich side .
[0007]
Further, the control means is configured to correct the air-fuel ratio to the rich side when reducing the opening of the throttle valve.
[0008]
Further, the control means is configured to increase the opening of the throttle valve in accordance with the amount of decrease in the opening of the throttle valve before or after the throttle valve opening is decreased.
[0009]
In addition, an exhaust gas purifying device having oxygen storage capacity is provided, and the control means corrects the air-fuel ratio to a lean side and then corrects to an excessively rich side.
[0010]
[Action]
In the first aspect of the invention, the negative pressure is generated in the intake passage by reducing the opening of the throttle valve at the time of purging, and the fuel collected in the canister is caused by this negative pressure. Inhale into the intake passage. Further, by correcting the air-fuel ratio to the rich side, purging is performed without causing a decrease in the output of the internal combustion engine due to a decrease in the opening of the throttle valve.
[0011]
According to the second aspect of the invention, the purge is executed without causing a decrease in the output of the internal combustion engine due to a decrease in the opening of the throttle valve by correcting the air-fuel ratio to the excessively rich side.
[0012]
In the invention according to claim 3, the substantial throttle valve opening at the time of purge execution corresponds to the operating state by increasing the opening corresponding to the amount of decrease in the throttle valve opening. Set the opening to Thereby, the purge is executed without causing a decrease in the output of the internal combustion engine.
[0013]
In the invention according to claim 4, the exhaust gas generated when the air-fuel ratio is corrected to the rich side at the time of purging by correcting the air-fuel ratio to the lean side before correcting the air-fuel ratio to the rich side. Increase gas purification efficiency. Thereby, purging is performed while preventing deterioration of emissions.
[0014]
Embodiment
(First embodiment)
An embodiment of a fuel vapor processing apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings. As an example, an evaporative fuel processing apparatus applied to an internal combustion engine having four cylinders will be described.
[0015]
In FIG. 1 showing the overall configuration of the internal combustion engine, fuel injection injectors 2a to 2d are provided at the intake ports of the cylinders of the engine body 2, and surge tanks are provided via intake manifolds 4a to 4d corresponding to the cylinders. 6, and an air cleaner 10 is connected to the surge tank 6 via an intake passage 8.
[0016]
An exhaust passage 14 is connected to an exhaust port of each cylinder of the engine body 2 via an exhaust manifold 12, and an air-fuel ratio sensor (O ₂ sensor) 16 and an exhaust gas purifying device having an oxygen storage capacity (O ₂ sensor) are connected to the exhaust passage 14. A three-way catalytic converter) 18 is interposed.
[0017]
A throttle valve (throttle valve) 22 driven by a step motor 20 is provided in the intake passage 8, and the opening degree θ of the throttle valve 22 is detected by an opening degree sensor 24 and provided in the surge tank 6. An absolute pressure Pb downstream of the throttle valve 22 is detected by the pressure sensor 26. Further, the engine speed Ne is detected by a crank angle sensor 28 provided in the engine body 2.
[0018]
The intake passage 8 downstream of the throttle valve 22 is provided with a purge system for purging the evaporated fuel generated in the fuel tank 32. This purge system is provided with a canister 34 that collects evaporated fuel with activated carbon, and is connected between the fuel tank 32 and the canister 34 by an evaporated fuel supply passage 38 having a bidirectional valve 36 interposed therebetween. A purge passage 42 interposing the valve 40 connects the downstream side of the throttle valve 22 in the intake passage 8 and the canister 34.
[0019]
When the purge control electromagnetic valve 40 is opened, the negative pressure generated in the intake passage 8 on the downstream side of the throttle valve 22 acts on the canister 34 and flows in through the air inlet provided at the lower end of the canister 34. The trapped fuel is released by the air, and a mixed gas of the collected fuel and air (hereinafter referred to as a purge gas) is generated in the intake tank 8 on the downstream side of the throttle valve 22 due to the negative pressure generated in the surge tank 6. Purged to the side.
[0020]
The detection signals of the air-fuel ratio sensor 16, the opening degree sensor 24, the pressure sensor 26 and the crank angle sensor 28 are supplied to a control unit 30 comprising a microcomputer system. The control unit 30 applies a so-called PID control law or the like to set the air-fuel ratio to the target air-fuel ratio (A / F), and based on these detection signals and the like, the opening degree of the throttle valve 22 and the injectors 2a to 2d. Feedback control of the fuel injection amount.
[0021]
In addition, the control unit 30 includes a control program for a purge process, which will be described later, and a data map for searching for an optimal purge state. When performing a purge, the control unit 30 controls opening / closing of the purge control electromagnetic valve 40 based on this control program. And the opening control of the throttle valve 22 and the fuel injection amount of the injectors 2a to 2d.
[0022]
The fuel vapor treatment apparatus for performing the purge process is realized by the purge system and the control unit 30 that controls the throttle valve 22 and the injectors 2a to 2d based on the detection signals of the various sensors 24, 26, and 28. ing.
[0023]
Next, the purge process in the internal combustion engine having such a configuration will be described with reference to the flowchart of FIG.
[0024]
In the flowchart of FIG. 2, in step S100, it is determined whether a normal purge process (S300) that only opens the purge control solenoid valve 40 should be executed or a compensated purge process (S110 to S180) should be executed. .
[0025]
That is, for each predetermined measurement period T, an integral value ΣNe of the engine speed Ne and an integral value ΣPb of the absolute pressure Pb in the surge tank 6 are obtained, and the predetermined threshold values N _THD and P _THD are obtained. Based on this, when the following expressions (1-a) and (1-b) are satisfied at the same time, the compensation purge process is started, and when not satisfied, the normal purge process is performed.
[0026]
ΣNe> N _THD (1-a)
ΣPb> P _THD (1-b)
Here, the threshold values N _THD and P _THD are used when the opening of the throttle valve 22 increases when the engine 2 is at a high speed and a high load, and the negative pressure in the intake passage 8 sucks the purge gas of the canister 34. It is set so that the operation state that becomes insufficient continues for the predetermined time T and the state where the evaporated fuel exceeds the allowable collection value of the canister 34 does not occur.
[0027]
In step S110, the engine torque TRQ _A of the engine 2 corresponding to the current target air-fuel ratio A / F _A (eg, 14.7) is retrieved by searching the first data map provided in the control unit 30. Ask. That is, as shown in FIG. 3, the air-fuel ratio vs. engine torque characteristic data of the internal combustion engine is provided in advance as a first data map, and the engine torque TRQ _A in the current operating state is retrieved by searching this data map. Ask for.
[0028]
In step S120, the first data map is searched again, and an estimated engine torque TRQ _B obtained when the target air-fuel ratio A / F _B is changed to a richer (over-rich) target air-fuel ratio is obtained. For example, the estimated engine torque TRQ _B corresponding to the air-fuel ratio (12.0) at which the maximum engine torque is obtained is searched.
[0029]
This target air-fuel ratio A / F _B is a value determined by the sum of the air-fuel ratio determined by the injected fuel of the injectors 4a to 4d and the mixture ratio of purge gas supplied when the purge control electromagnetic valve 40 is opened. It is measured by experiments.
[0030]
In step S130, a difference ΔTRQ _BA (= TRQ _B −TRQ _A ) between the engine torques TRQ _A and TRQ _B obtained in steps S110 and S120 is calculated, and in step S140, these target air-fuel ratio A / F _B and the difference ΔTRQ are calculated. Determine _BA .
[0031]
In step S150, a compensation purge is performed by searching a second data map stored in advance in the control unit 30 based on the current engine speed Ne, the current engine torque TRQ _A, and the torque difference ΔTRQ _BA. The opening degree θ _B of the throttle valve 22 to be set at the time of execution is obtained.
[0032]
As shown in FIG. 4, the second data map is characteristic data of the engine speed and the engine torque when the opening degree θ of the throttle valve 22 is used as a parameter, and is measured in advance through experiments or the like.
[0033]
First, an engine torque TRQ _B ′ lower than the current engine torque TRQ _A by a difference ΔTRQ _BA is determined, and an opening degree θ _B corresponding to the engine torque TRQ _B ′ and the current engine speed Ne is searched.
[0034]
In step S160, it is determined that the target air-fuel ratio should be A / F _B and the opening of the throttle valve 22 should be θ _B when the actual compensation purge is executed.
[0035]
In step S170, lean burn control is performed by setting the target air-fuel ratio to a lean air-fuel ratio A / F _L (for example, 16.7) during a predetermined period τ _L before executing the actual compensation purge. As a result, the exhaust gas concentration is reduced, and the catalyst O ₂ storage function of the exhaust gas purification device, which is a three-way catalyst device having oxygen storage capacity, is improved.
[0036]
Next, in step S180, the purge control electromagnetic valve 40 is opened and the target air-fuel ratio is set to A / F _B and the opening degree of the throttle valve 22 is set to θ _B in a predetermined compensation purge execution period τ _B. To execute the actual compensation purge.
[0037]
Since the opening degree θ _B of the throttle valve 22 is smaller than the opening degree when this compensation purge is performed, that is, at the time of high load or the like, the effective opening area by the throttle valve 22 becomes small, and the inside of the intake passage 8 downstream of the throttle valve 22 The negative pressure is forcibly generated, and the purge gas of the canister 34 can be sucked into the intake passage 8 by this negative pressure.
[0038]
Furthermore, merely reduced the degree of opening of the throttle valve 22, corresponding to it and thus to lead to deterioration of the drivability due to the reduction of the engine torque, to reduce the throttle valve 22 in opening theta _B since setting the target air-fuel ratio (rich air-fuel ratio) a / F _B and the purge is performed while preventing the reduction of the engine torque in advance.
[0039]
Moreover, since the improvement of the catalyst O ₂ storage function of the exhaust gas purification device 18 can be achieved by performing the lean burn before time compensation purge execution in step S170, be set to the rich air-fuel ratio A / F _B, emission Can be prevented in advance.
[0040]
Then, when the process of step S180 or S300 ends, the process from step S100 is repeated again.
[0041]
Thus, according to this embodiment, even when the opening of the throttle valve 22 becomes large and the purge becomes impossible when the engine 2 is in an operating state such as a high load and a high rotational speed, the throttle valve 22 is The purge is performed by reducing the pressure and generating a negative pressure in the intake passage 8 on the downstream side, so that the purge can be executed regardless of the operating state of the engine 2. Furthermore, it exhibits an excellent function of preventing a decrease in engine torque by appropriately controlling the air-fuel ratio in a state where the exhaust gas purification efficiency is increased.
[0042]
(Second Embodiment)
Next, another embodiment according to the present invention will be described with reference to FIGS. The internal combustion engine to which this embodiment is applied has the same configuration as that shown in FIG. 1, and the control unit 30 includes the first and second data maps corresponding to FIGS. 3 and 4 and purge processing. A control program is stored in advance.
[0043]
The operation of the purge process will be described based on the flowchart of FIG. 5. First, in steps S400 to S460, the same processes as those in steps S100 to S160 in FIG. 2 are performed.
[0044]
That is, by comparing the integral values ΣNe, ΣPb of the engine speed Ne at the predetermined time T and the pressure Pb in the surge tank 6 with the predetermined threshold values N _THD , P _THD , It is determined which of the compensation purge processing is performed (S400). When the compensation purge process is started, the engine torque TRQ _A corresponding to the current target air-fuel ratio A / F _A is searched based on the first data map (S410) and then set to the rich air-fuel ratio A / F _B The estimated engine torque TRQ _B is also searched based on the first data map (S420). _A difference ΔTRQ _BA between the engine torques TRQ _B and TRQ _A is obtained (S430), and the target air-fuel ratio A / F _B and the difference ΔTRQ _BA are determined (S440). Next, by searching the second data map using the current engine speed Ne, the engine torque TRQ _A, and the difference ΔTRQ _BA , the opening θ _B of the throttle valve 22 is obtained (S450), and this opening determining the first degree of opening of the throttle valve 22 should be set theta _B at compensating purge execution (S460).
[0045]
Next, processing specific to this embodiment is performed. First, in step S470, first by searching the data map, the estimated engine obtained when changed to the lean target air-fuel ratio A / F _C than the current target air fuel ratio A / F _A shown in FIG. 3 Torque TRQ _C is obtained. For example, as the average value of the rich air-fuel ratio A / _{F B} and the target air-fuel ratio A / _{F C} determined in step S440 becomes the current target air fuel ratio A / _{F A,} the target air-fuel ratio A / _{F C} decided to 17.4 to obtain the engine torque TRQ _C corresponding to the target air-fuel ratio a / _{F C.}
[0046]
In step S480, it calculates a difference? Trq _AC of the target air-fuel ratio A / _F engine torque TRQ corresponding to _{C C} and current engine torque _{TRQ A (= TRQ A -TRQ C} ).
[0047]
In step S490, the engine torque higher by the difference ΔTRQ _AC than the current engine torque TRQ _A is retrieved by searching the data map of FIG. 4 based on the current engine speed Ne, the current engine torque TRQ _A, and the difference ΔTRQ _AC . An opening degree θ _C corresponding to TRQ _C ′ and the current engine speed Ne is obtained, and in step S500, the opening degree θ _C is determined as the second opening degree when the compensation purge is executed.
[0048]
In step S510, among τ predetermined compensation purge execution period, opening the purge control solenoid valve 40 when set at the same time to the target air-fuel ratio (rich air-fuel ratio) A / F _B, as further shown in FIG. 6 (a), The throttle valve 22 is periodically switched and controlled to the first and second opening degrees θ _B and θ _C.
[0049]
In the period (period indicated by the slanted line) τ _B in which the throttle valve 22 decreases to the opening degree θ _B , the effective opening area by the throttle valve 22 becomes small, so that negative pressure is generated in the intake passage 8 downstream of the throttle valve 22. The negative pressure can effectively purge the purge gas of the canister 40 toward the surge tank 6. Since at the same time the target air-fuel ratio is set to the rich air-fuel ratio A / F _B, throttle valve 22 is also narrowed to opening theta _B, to prevent a decrease in engine torque.
[0050]
On the other hand, in the period τ _C in which the throttle valve 22 is expanded to the opening degree θ _C , the air-fuel ratio changes to the lean side compared to the period τ _B set to the opening degree θ _B , so that the exhaust gas concentration can be reduced. It is done. As a result, the exhaust gas concentration due to the rich air-fuel ratio in the period τ _B is diluted by the exhaust gas concentration due to the lean air-fuel ratio in the period τ _C , and emission deterioration can be prevented in advance. Further, since the opening degree of the throttle valve 22 is increased / decreased between θ _B and θ _C with the target air / fuel ratio set to the rich air / fuel ratio A / F _B , the air / fuel ratio alternately changes between the rich side and the lean side, since the air-fuel ratio moderated average (substantially) becomes closer to the target air-fuel ratio a / F _a to be originally set to prevent deterioration of drivability in advance to prevent the reduction of the engine torque.
[0051]
As described above, according to this embodiment, the opening degree of the throttle valve 22 is set to θ in the state where the target air / fuel ratio (rich air / fuel ratio) A / F _B is set to an appropriate value even in an operation state that cannot be purged. since _B and theta _C at decreasing control to generate a negative pressure in the intake passage 8, it is possible to perform the purge while skillfully prevented both reduction and emission deterioration of engine torque. Furthermore, it exhibits an excellent function of enabling a purge process regardless of the operating state of the engine 2.
[0052]
Note that the opening control of the throttle valve 22 shown in FIG. 6A is an example, and the present invention is not limited to this. For example, the as shown in FIG. (B), rather than the throttle valve 22 than to continuously and periodically varying at the opening theta _B and theta _C, opening theta period of time tau _B and opening theta _C of _B τ _C may be switched discontinuously. Further, as shown in FIG. (C), may change the time tau _B and duration tau _C cycle of opening theta _C opening theta _B. In short, in the compensation purge execution period τ determined in advance, and a time integral value of the air-fuel ratio when the time integral value of the air-fuel ratio and is set to the opening degree theta _C when it is set to an opening degree theta _B The present invention includes a case where the opening degree of the throttle valve 22 is controlled to be switched between θ _B and θ _C so that they are mutually offset and substantially the original target air-fuel ratio A / F _A is obtained.
[0053]
Further, in the present invention it does not necessarily need to be correct the air-fuel ratio so as to correspond to the control of the opening degree of the throttle valve 22, the air-fuel ratio remains the original target air-fuel ratio A / F _A, opening of the throttle valve 22 The degree may be switched and controlled by θ _B and θ _C. In this case, the engine torque is will vary in response to the opening theta _B and theta _C of the throttle valve 22, sufficiently short respectively the duration tau _C period tau _B and opening theta _C opening theta _B By setting the period, it is possible to prevent a change in the opening degree of the throttle valve 22 from θ _B and θ _C from appearing significantly as a change in the engine torque. The engine torque can be a torque substantially corresponding to an average value of θ _B and θ _C of the opening degree of the throttle valve 22. That is, the substantial opening degree of the throttle valve can be set to the target throttle valve opening degree that is set corresponding to the operating state.
[0054]
【The invention's effect】
As described above, according to the present invention, a negative pressure is forcibly generated by controlling the opening of the throttle valve, and the evaporated fuel is purged into the intake passage by this negative pressure. Regardless, the purge process can be performed, and problems such as the canister exceeding the permissible fuel vapor collection limit can be prevented.
[0055]
In addition, since the air-fuel ratio is controlled together with the opening degree control of the throttle valve, it is possible to prevent a decrease in the output of the internal combustion engine when the purge process is executed.
[0056]
In addition, the throttle valve opening is decreased in order to generate negative pressure, and the throttle valve opening is increased in response to the amount of decrease. It can be adapted to the target valve opening set. As a result, it is possible to prevent a decrease in the output of the internal combustion engine accompanying a decrease in the opening of the throttle valve.
[0057]
Further, since the air-fuel ratio is corrected to the lean side before the air-fuel ratio is corrected to the rich side, the catalyst O ₂ exhaust function of the exhaust gas purification device disposed in the exhaust port when the air-fuel ratio is lean is improved. Then, the exhaust gas generated when the air-fuel ratio is corrected to the rich side after that can be efficiently purified. As a result, it is possible to realize the purge process of the evaporated fuel while preventing the emission from being deteriorated.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an overall configuration of an internal combustion engine to which an embodiment according to an evaporated fuel processing apparatus of the present invention is applied.
FIG. 2 is a flowchart for explaining an operation of a purge process.
FIG. 3 is a characteristic diagram showing characteristics of air-fuel ratio versus engine torque in an internal combustion engine.
FIG. 4 is a characteristic diagram showing a characteristic of engine speed versus engine torque when the throttle valve opening is used as a parameter.
FIG. 5 is a flowchart for explaining an operation of a purge process according to another embodiment.
FIG. 6 is an explanatory diagram for explaining the control principle of the throttle valve opening according to another embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 2 ... Engine main body, 2a-2d ... Injector according to cylinder, 4a-4d ... Intake manifold, 6 ... Surge tank, 8 ... Intake passage, 18 ... Exhaust gas purification device, 20 ... Step motor, 22 ... Throttle valve, 24 ... Open Degree sensor 26 ... Pressure sensor 28 ... Crank angle sensor 30 ... Control unit 32 ... Fuel tank 34 ... Canister 36 ... Bidirectional valve 38 ... Evaporative fuel supply passage 40 ... Purge control solenoid valve 42 ... Purge passage.

Claims (1)

A canister for collecting evaporative fuel generated in a fuel tank or the like;
An evaporative fuel processing apparatus for an internal combustion engine that purges fuel collected by the canister via a purge passage that is connected to the canister and opens into an intake passage on the downstream side of the throttle valve,
Control means for reducing the opening of the throttle valve at the time of purging ,
The control means corrects the air-fuel ratio to an excessively rich side when reducing the opening of the throttle valve .

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