JPH0569986B2 - - 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 (paper) 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 an increase in engine temperature after the engine is stopped, from leaking to the outside, a As shown in Figure 8, when fuel evaporates in the sealed fuel tank 1 and its internal pressure rises to a certain value, the two-way valve 2 opens and the vapor in the tank is transferred to the canister 3 containing activated carbon. When the engine is started, the check valve 5 is opened by the negative pressure P _B in the inlet manifold 4, and the vapor stored in the canister 3 is sucked into the engine side.

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 purging of the canister for use in the
(see publication).

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 much larger, so the amount of purge returned to the engine is also larger, which greatly upsets the air-fuel ratio of the engine, which has an adverse effect on the engine's emission characteristics and exhaust gas.

Generally, when the purge flow rate is controlled according to the engine operating state (engine load), the air-fuel ratio changes depending on the increase or decrease in the purge amount at the time of starting purge or adjusting the purge amount. That is,
At the start of purge, the purge amount is changed from zero to a purge amount depending on the operating state of the engine. Therefore, the introduction of evaporated fuel causes rapid fluctuations in the air-fuel ratio. Additionally, when the engine load changes, for example from low load to high load, the amount of purge changes from a small amount corresponding to a low load to a large amount corresponding to a high load, resulting in an increase in evaporated fuel. There is a problem in that this causes rapid fluctuations in the air-fuel ratio.

Purpose The present invention was made in consideration of the above points, and
A purge control device in an evaporative fuel reduction system that prevents sudden changes in the air-fuel ratio when changing the purge amount, and performs optimal purge that matches the air-fuel ratio control state according to the engine load. It provides:

Configuration The present invention provides a canister for storing fuel vapor generated in a fuel tank, an engine load detection means for detecting engine load, and a passageway that communicates the canister with an intake system of the engine. Purge amount change control that gradually changes the purge amount when changing the purge amount, in a purge control device that includes a purge control means that controls the amount of purge from a canister according to an engine load detected by a load detection means. It is characterized by having means.

Furthermore, the present invention is characterized in that the higher the engine load detected by the engine load detection means, the greater the degree of change in the purge amount.

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, which closes and adjusts the opening degree of the valve.
The solenoid valve 7 causes negative pressure in the enthule.
Pv is turned on and off to determine the timing of purge, and the conducted ventilium negative pressure Pv 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 road 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, under the control of the controller 6, as shown in FIG. 3, the solenoid valve 7 for the purge controller is opened during the air-fuel ratio control period T2 to purge the canister 3. At the same time, the control means is configured to adjust the opening degree of the solenoid valve 7 in proportion to the intake air amount of the engine according to the air-fuel ratio control state.

That is, as shown in FIG.
During step 3, a closing command is given to the solenoid valve 7 to completely close the valve, thereby cutting off the ventilary negative pressure Pv, which becomes the purge negative pressure, and preventing the canister 3 from being purged. . Also, during the air-fuel ratio control period T2, the controller 6 provides an opening command to the solenoid valve 7 according to the engine intake air amount Qa at that time to perform proportional control of the valve opening and adjust the purge amount Qp. have them do it. At that time, when the intake air amount Qa is at a constant reference level L immediately after the start and end of air-fuel ratio control, the first stage opening command is given from the controller 6 to the solenoid valve 7, and the opening command is given to the solenoid valve 7. The valve is opened to a preset minimum opening degree to purge the canister 3'. 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.

Furthermore, in the present invention, when the controller 6 adjusts the opening degree of the solenoid valve 7 for the purge controller, 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. td2 only, and its falling edge as td
3 and td4 are each 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 T for the actual air-fuel ratio A/F to settle down to the standard setting value S.
It would require 4. Therefore, during this time, 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, if the purge is started up gradually at the air-fuel ratio control start point t1 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 this way, when the purge amount is adjusted to follow the air-fuel ratio control of the engine, purge cut is performed depending on the engine driving condition, and when the purge amount suddenly decreases, the air-fuel ratio Control measures are taken to force the control back to the center value of its control range.

Normally, in the case of an air-fuel ratio control system, the control contents are set in advance to have characteristics that allow the optimum air-fuel ratio A/F to be obtained depending on the engine load condition, as shown in Fig. 5. There is. That is, when the engine is in the low load region A, the air-fuel ratio A/F is set to be rich R so that the engine can be driven smoothly, and when the engine is in the medium load region B, the combustion Because the internal pressure in the chamber is high enough and combustion is stable, the air-fuel ratio A/F
is set to be on the lean L side, and when the engine is in high load region C, a large engine output is required, and to protect the engine, the fuel supply is increased and the combustion temperature is lowered by fuel cooling. The air-fuel ratio A/F is preferably set to be on the rich R side.

Also, the air-fuel ratio A/ to the fuel F supplied to the engine
F has the characteristics shown in Fig. 6, and when the air-fuel ratio A/F is on the rich R side, the supplied fuel F
Even if the changes by ΔF, 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 amount of change in A/F when the supplied fuel ΔF changes increases.

However, when the engine is under high load and the air-fuel ratio A/F is set to the rich side,
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, the controller 6 detects the current load state of the engine according to various engine state signals ES, and when the detected load is in the high load region C side, the purge PI control is performed. By increasing the I-term control at the time, the rise and fall of the purge can be made rapid and the canister 3' can be purged efficiently.Also, the detected load is on the intermediate load area B side. In some cases, the I-term control during purge PI control is reduced, thereby slowing down the purge start-up and fall delays to prevent the air-fuel ratio A/F in the engine from becoming significantly distorted. .

At this time, when the engine load is very high, the effect on the engine's air-fuel ratio A/F can be almost ignored even if a large amount of purge is performed, so the solenoid valve 7 is fully opened and the canister is removed. Maximize the 3' purge amount.

Further, when the engine load is in the low load region A, the purge has a large influence on the air-fuel ratio A/F of the engine, so the solenoid valve 7 is fully closed to purge the canister 3'.

FIG. 7 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 the purge controller under the control of the controller 6 that is exactly the same 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, vapor naturally generated in the fuel tank is purged toward the engine via 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, the purge controller device according to the present invention can prevent sudden changes in the air-fuel ratio by gradually changing the purge amount, and can also reduce the engine load. The higher the load on the engine, the greater the degree of change in the purge amount, which makes it possible to reduce fluctuations in the air-fuel ratio due to changes in the purge amount, making it possible to perform the optimal purge that matches the operating conditions of the engine. It has excellent advantages.

[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 with respect to the engine load, Figure 6 shows the air-fuel ratio characteristics with respect to the fuel supplied to the engine, and Figure 7 shows the specific configuration of the evaporated fuel reduction system when the present invention is implemented. Simplified diagram, FIG. 8 is a simplified diagram showing the configuration of a conventional evaporative fuel reduction system. 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)

[Scope of Claims] 1. A canister for storing fuel vapor generated in a fuel tank, an engine load detection means for detecting engine load, and a passageway that communicates between the canister and the intake system of the engine; In a purge control device equipped with a purge control means that controls the purge amount from the canister according to the engine load detected by the engine load detection means, the purge amount is changed gradually when the purge amount is changed. A purge control device comprising a control means. 2. The purge control device according to item 1 above, wherein the degree of change in the purge amount is increased as the engine load detected by the engine load detection means becomes higher.