JPH0569987B2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to an evaporated fuel return system that temporarily stores evaporated fuel (vapor) in a fuel tank in a canister and returns (purges) the stored vapor to the engine when the engine is running. In particular, the present invention relates to a purge control device that adjusts the amount of purge depending on the driving state of an engine.

Prior Art Conventionally, in order to prevent vapors generated in the fuel tank due to atmospheric temperature when parking or vapors generated from the float chamber of the carburetor due to the rise in engine temperature after the engine is stopped from leaking to the outside, a ninth As shown in the figure, when fuel evaporates in a sealed fuel tank 1 and its internal pressure rises to a certain value, a two-way valve 2 opens and the vapor in the tank flows into a canister 3 containing activated carbon. The vapor temporarily stored in the canister 3 is sucked into the engine by opening the check valve 5 due to the negative pressure P _B in the inlet manifold 4 when the engine is started.

Recently, in order to prevent the large amount of vapor generated when fuel is supplied from the refueling gun into the fuel tank at high pressure to the outside, a separate on-board canister with a particularly large capacity has been installed. The canister is purged in the same manner as described above (see Japanese Patent Laid-Open No. 161952/1983).

However, in the case of vapor that evaporates naturally due to temperature rise, the amount is relatively small and there is no problem with the effect on the engine even if the amount of purge from the canister is not controlled, but especially in the case of an on-board canister. In this case, the amount of vapor accumulated is significantly large, so the amount of purge returned to the engine is also large, which greatly upsets the air-fuel ratio of the engine, adversely affecting the engine's emission characteristics and exhaust gas.

Therefore, in order to purge the onboard canister sufficiently and to eliminate any negative effects on the engine, it is necessary to return a purge amount proportional to the amount of intake air to the engine. There is a need to.

In particular, when using air-fuel ratio control that optimizes the engine's air-fuel ratio while detecting the oxygen concentration in exhaust gas, it is necessary to purge the canister in proportion to the engine's intake air amount. There is a high possibility that control will deviate.

In addition, if the purge amount is made to follow at the start of purge or when there is a sudden change in the intake air amount, a large deviation from the set air-fuel ratio will occur due to the response delay of the air-fuel ratio control system due to feedback, making it difficult to actually control the air-fuel ratio. There is a problem in that it takes a long time for the air-fuel ratio to settle to the set value.

Purpose The present invention was made in consideration of the above points, and
During the air-fuel ratio control period, the canister is purged in proportion to the intake air amount of the engine, and
In particular, it is an object of the present invention to provide a purge control device for an evaporative fuel reduction system that is capable of performing an optimal purge that matches the air-fuel ratio control state.

Configuration The purge control device according to the present invention includes an oxygen sensor that detects the oxygen concentration in the exhaust gas of an engine, an oxygen sensor state detection means that detects the active or inactive state of the oxygen sensor, and an oxygen sensor state detection means that detects the active or inactive state of the oxygen sensor. an air-fuel ratio feedback control for controlling the air-fuel ratio of the air-fuel mixture supplied to the engine based on the output signal of the oxygen sensor at that time in response to the fact that the oxygen sensor is detected to be in an active state by the means; a control means; an air-fuel ratio open-loop control means for controlling an air-fuel ratio in an open loop in response to the fact that the oxygen sensor is detected to be in an inactive state by the oxygen sensor state detection means; Purge adjustment is provided in a passage that communicates between the canister that stores fuel vapor and the engine intake system, and adjusts the amount of purge that introduces the fuel vapor stored in the canister into the engine intake system due to engine intake negative pressure. The purge adjustment means is characterized in that the purge amount is gradually changed when the purge amount is changed during the air-fuel ratio feedback.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows an example of the basic configuration of an evaporative fuel reduction system for carrying out the present invention, in which the onboard canister 3' is purged by ventilary negative pressure Pv, and
Opening of the valve under the control of the controller (ECU) 6,
A solenoid valve 7 for purge control is provided for closing and adjusting the opening degree of the valve.
The ventilate negative pressure is caused by the solenoid valve 7.
Pv is turned on and off to determine the timing of purge, and the ventilary negative pressure Pv that has been turned on is appropriately squeezed to adjust the amount of purge.

Here, the controller 6 outputs an output signal from an oxygen sensor that detects the oxygen concentration in the exhaust gas of the engine.
An air-fuel ratio control system 9 that maintains the air-fuel ratio of the engine at a predetermined optimum value in response to various engine status signals ES such as _O2 , engine cooling water temperature, engine speed, inlet manifold absolute pressure, and atmospheric pressure.
It also serves as a controller.

FIG. 2 shows an example of the configuration of the nozzle 11 portion of the fuel tank 1. When the cap 12 is removed and the fuel gun 13 is inserted into the nozzle 11 portion,
The shutter 14 is pushed down by the refueling gun 13, and a passage 15 to the canister 3' is opened, so that a large amount of vapor generated during refueling is guided toward the canister 3'. The shutter 14 is closed except when refueling to prevent vapor generated inside the tank from flowing into the passage 15 side.
Further, when the refueling gun 13 is inserted into the nozzle 11 portion, the nozzle seal 16 works to prevent vapor from leaking out from the inlet of the nozzle 11. In the figure, 17 indicates a breather pipe.

In the present invention, with this configuration, under the control of the controller 6, the solenoid valve 7 for purge control is opened during the air-fuel ratio control period to purge the canister 3, and the air-fuel ratio is controlled. A control means is used to adjust the opening degree of the solenoid valve 7 in proportion to the amount of intake air of the engine depending on the state.

Note that the controller 6 gives a full-open command to the solenoid valve 7 to completely open the valve, assuming that the disturbance caused by the purge can be tolerated during the period when the air-fuel ratio control is not performed, and thereby purges the canister 3. Do it to the maximum.

During the air-fuel ratio control period, the controller 6 issues an opening command to the solenoid valve 7 according to the intake air amount Qa of the engine at that time, as shown in FIG.
The purge amount Qp is adjusted by proportionally controlling the valve opening. At that time, when the intake air amount Qa is at a constant reference level L immediately after the start and end of the air-fuel ratio control, the controller 6 sends the first solenoid valve 7 to the
A stepwise opening command is given, and the canister 3' is made to let the valve reach the preset minimum opening.
purge. At this time, the purge amount Qp of the canister 3' becomes the minimum.

However, by causing the canister 3' to be purged during the engine air-fuel ratio control period under the control of the controller 6, the air-fuel ratio of the engine will not be significantly disturbed. In addition, while adjusting the purge amount Qp according to the air-fuel ratio control state of the engine, the vapor accumulated in the canister 3' is returned to the ventilate nozzle part of the carburetor based on the ventilary negative pressure Pv. It becomes possible to purge the canister 3' in proportion to the amount.

Further, in the present invention, when the controller 6 adjusts the opening degree of the solenoid valve 7 for purge control, as shown in FIG. 6 gradually opens the solenoid valve 7 using a predetermined PI control set in advance according to the response delay of the air-fuel ratio control system.
The rise of the valve opening is delayed by td1. Similarly, when adjusting the opening degree of the solenoid valve 7 according to an increase or decrease in the intake air amount Qa, the controller 6 controls the rise of the solenoid valve 7 using a predetermined PI control when the solenoid valve 7 is driven in the opening or closing direction. Only td2, its fall again
Only td3 and td4 are delayed.
At the end point t5 of the air-fuel ratio control, the response delay of the air-fuel ratio control system at that time does not pose any problem, so the solenoid valve 7 is fully closed without any delay time.

However, by adjusting the opening of the solenoid valve 7 by such PI control under the control of the controller 6, it is possible to prevent the actual air-fuel ratio from deviating significantly from the set value due to the response delay of the air-fuel ratio control system. It will be possible to prevent this from happening.

For example, as shown in FIG. 4a, if the purge is suddenly started at the air-fuel ratio control start point t1, the air-fuel ratio control will not be able to follow it and the actual air-fuel ratio A/F at the beginning of the purge will change. deviates significantly from the reference set value S, which is the control objective, and therefore air-fuel ratio control is executed according to the output signal _O2 of the oxygen sensor (the control status is shown in the A/F control characteristic in the figure). ) It takes a long time for the actual air-fuel ratio A/F to settle down to the standard setting value S.
This would require T4. Therefore, during this period, the air-fuel ratio of the engine becomes inappropriate, which adversely affects the engine's emission characteristics and exhaust gas. In the figure, tα indicates the response delay in the air-fuel ratio control system.

On the other hand, as shown in FIG. A/F
does not deviate significantly from the reference set value S, and therefore air-fuel ratio control is executed according to the output signal _O2 of the oxygen sensor (the control state is shown in the A/F control characteristics in the figure). The time T4' until the air-fuel ratio A/F reaches the reference setting value S becomes shorter. Therefore, it is effectively suppressed that the air-fuel ratio of the engine becomes inappropriate during that time and adversely affects the engine's emission characteristics and exhaust gas.

In the present invention, the purge amount is adjusted in accordance with the air-fuel ratio control of the engine according to the response delay of the air-fuel ratio control system, and in particular, when the air-fuel ratio control is started, O ₂ ( The present invention is characterized in that a control means is used to increase the term control at the time of purge startup until the activation of the oxygen sensor is completed.

In other words, for the air-fuel ratio control system,
Since the O ₂ sensor itself has poor sensitivity at low temperatures, the system is kept in an open loop to control the air-fuel ratio until it becomes hot and the O ₂ sensor is activated to operate normally. I try not to. In this case, when the air-fuel ratio control system is in an open-loop state immediately after the engine starts, the engine is still in a low temperature state, so the air-fuel ratio A/F at that time is set to the rich side in order to stabilize combustion. That's what I do.

Figure 5 shows the characteristics of the air-fuel ratio A/F with respect to the supplied fuel F, and when the air-fuel ratio A/F is on the rich R side, even if the supplied fuel F fluctuates by ΔF, the A/F remains unchanged.
The change in A/F is small, but as the air-fuel ratio A/F moves toward the lean L side by executing air-fuel ratio control, the change in A/F when the supplied fuel F fluctuates by ΔF becomes larger. .

Furthermore, Fig. 6 shows the characteristics of purge fuel G (grams) with respect to purge flow rate Q (litter) in canister 3'. In the early stage of purge, canister 3' purges when purge flow rate Q fluctuates by Δq. The change in fuel G Δg1 becomes very large, but as the purge progresses, the purge flow rate Q
Change amount Δg2 of purge fuel G with respect to change amount Δq
It has the characteristic that it becomes small.

However, when the air-fuel ratio control system is in an open loop state and the air-fuel ratio A/F is set to the rich side until the activation of the O ₂ sensor is completed,
Even if a large amount of purge is performed, the fluctuation rate of the air-fuel ratio A/F is small, and the engine will not be adversely affected.

Therefore, in the present invention, as shown in FIG.
During this time, the control at the time of purge startup is increased to quickly open the solenoid valve 7 and ensure the maximum purge amount at that time.

In this case, it goes without saying that a control means may be used to increase the P-term control at the start of purge until the activation of the O ₂ sensor is completed at the start of air-fuel ratio control.

FIG. 8 shows a specific configuration of the evaporative fuel reduction system when the present invention is implemented. Here, the check _valve (idle cutoff valve) is 5 is opened, and the magnitude of the negative pressure P _B passing through the check valve 5 is appropriately controlled via the solenoid valve 7 for purge control under the control of the controller 6 exactly as described above, and the controlled negative pressure is P _B adjusts the opening of the purge flow control valve 8,
The on-board canister 3' is purged through a flow rate control valve 8 whose opening degree is adjusted by the ventilator negative pressure Pv. Although not particularly shown, paper naturally generated in the fuel tank is purged to the engine side through a small-capacity canister 3 provided separately, as shown in FIG.

However, with this configuration, the on-board canister 3 can be operated with an optimal purge amount according to the air-fuel ratio control state, and with optimal responsiveness that meets the response delay of the air-fuel ratio control system. The vapor purged from the canister 3' is returned to the Pv port of the carburetor, and the canister 3' is eventually purged in proportion to the intake air amount of the engine.

Effects As described above, in the purge control device according to the present invention, when controlling the purge flow rate according to the operating state of the engine, the air-fuel ratio is adjusted by increasing or decreasing the purge amount at the start of purge or when adjusting the purge amount. In particular, when the air-fuel ratio is lean, the fluctuations in the air-fuel ratio due to increases and decreases in the purge amount are larger than when the air-fuel ratio is rich, and due to the delay in the air-fuel ratio control system, the air-fuel ratio setting Considering that it takes a long time for the air-fuel ratio to settle down, the purge amount is gradually changed when changing the purge amount during air-fuel ratio feedback.
It has the excellent advantage of preventing the air-fuel ratio from deviating significantly from the stoichiometric air-fuel ratio during air-fuel ratio feedback control and controlling the air-fuel ratio to an optimal air-fuel ratio.

[Brief explanation of the drawing]

FIG. 1 is a simplified diagram showing an example of the basic configuration of an evaporative fuel reduction system for implementing the present invention, FIG. 2 is a front sectional view showing an example of the configuration of a nozzle portion of a fuel tank in the same embodiment, The figure is a time chart showing the control contents of the controller in the same embodiment.
FIG. 4a is a time chart showing the purge state of the canister according to the conventional air-fuel ratio control, and FIG. 4b is a time chart showing the purge state of the canister according to the air-fuel ratio control when the present invention is applied. Figure 6 shows the air-fuel ratio characteristics for the fuel supplied to the engine, Figure 6 shows the purge characteristics of the onboard canister, and Figure 7 shows the characteristics at the start of purge.
A characteristic diagram showing the air-fuel ratio state according to PI term control, Fig. 8 is a simplified diagram showing the specific configuration of the evaporative fuel reduction system when the present invention is implemented, and Fig. 9 is a diagram showing the conventional evaporative fuel reduction system. FIG. 2 is a simplified diagram showing the configuration. 1...Fuel tank, 2...Two-way valve,
3, 3'...Canister, 4...Inlet manifold, 5...Check valve, 6...Controller, 7...Solenoid valve for purge control, 8...Flow control valve for purge.

Claims (1)

[Claims] 1 An oxygen sensor that detects the oxygen concentration in engine exhaust gas, an oxygen sensor state detection means that detects the active or inactive state of the oxygen sensor, and an oxygen sensor state detection means that detects the active state of the oxygen sensor. air-fuel ratio feedback control means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the engine based on the output signal of the oxygen sensor at that time;
an air-fuel ratio open-loop control means for controlling an air-fuel ratio in an open-loop manner in response to the oxygen sensor state detection means detecting that the oxygen sensor is in an inactive state; and a canister for storing fuel vapor. and a purge adjustment means, which is provided in a passage communicating between the canister and the engine intake system, and adjusts the purge amount of fuel vapor stored in the canister introduced into the engine intake system by the engine's intake negative pressure. , wherein the purge adjustment means gradually changes the purge amount when changing the purge amount during air-fuel ratio feedback.