JPH01273864A - Evaporated fuel feeding device for engine - Google Patents

Abstract

PURPOSE:To prevent the deterioration of emission and drivability by carrying out the increase and decrease of the purge flow rate, in synchronization with the reversal of the feedback control of the air-fuel ratio. CONSTITUTION:A feeding means for feeding the evaporated fuel into the intake system of an engine, renewal means which renews the purge flow rate of the evaporated fuel by the feeding means into the gradually increasing or reducing direction in staircase form, and a synchronizing means for synchronizing the renewal timing of the purge flow rate to the reversal of the feedback signal are installed. Therefore, the self-complacent increase or reduction of the purge flow rate, disregarding the feedback control, is not carried out, and in the air-fuel ratio feedback control, the disturbance due to the increase or reduction of the purge flow rate can be sufficiently absorbed, and the deterioration of emission and drivability can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an apparatus for supplying evaporative fuel to an engine, and more specifically, to a device for supplying evaporative fuel to an engine, and more particularly, to a device for supplying evaporative fuel to an engine, and more particularly, to a device for supplying evaporative fuel to an engine, and more particularly, to a device for supplying evaporative fuel to an engine, and more particularly, to a device for supplying evaporative fuel to an engine, and more particularly, to a device for supplying evaporative fuel to an engine, and more specifically, to a device for supplying evaporative fuel to an engine, and more particularly, to It is related to the device.

(Prior Art) In order to prevent air pollution, engine systems are well known in which, for example, fuel evaporated in a fuel tank is trapped in a canister and the trapped fuel is returned to the air-fuel mixture. In this type of evaporative fuel supply system, the intake passage (generally
The surge tank) and the canister are in communication with each other through an orifice, and the vaporized fuel trapped in the canister is sucked into the tank by the negative pressure inside the surge tank. Therefore, it can be said that the purge flow rate itself is inevitably determined by the relationship between the negative pressure of the surge tank and the orifice diameter.

On the other hand, in order to improve exhaust gas emissions, the air-fuel mixture supplied to the engine combustion chamber is adjusted so that the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio based on the output of the air-fuel ratio sensor installed in the exhaust system. Those that perform feedback control of the air-fuel ratio are also common.

Now, the amount of evaporated fuel varies depending on factors such as temperature, and it is difficult to predict the exact amount. This is because the purge flow rate includes the vaporized fuel itself and the amount of air required to purge it. Therefore, if air-fuel ratio feedback control is combined with a system that supplies such vaporized fuel to the engine, the air-fuel ratio feedback control will not work properly for the following reasons, resulting in worsening of emissions and driving performance. problems are caused. That is, when the concentration of evaporated fuel in the purge flow m is high, the rich purge gas is sucked in uncontrollably and the air-fuel ratio feedback control cannot follow it.
The air-fuel ratio of the exhaust gas becomes rich, leading to an increase in the amount of Co and HC discharged. Conversely, when the concentration of evaporated fuel in the purge flow rate is low, the amount of air in the purge flow rate increases uncontrollably, leading to an increase in NOx components.

In an attempt to solve this problem, a technique called a so-called linear purge system, such as Japanese Patent Laid-Open No. 57-129247, has been proposed to control the purge flow rate.

This linear purge system is designed to actively control the purge flow rate by interposing a duty solenoid valve between the canister and the surge tank.

The purge flow rate control is shown in FIGS. 6 and 7, and its problems will be explained. As shown in Fig. 6, when the conditions for performing linear purge are satisfied, such as when the idle switch is turned off, the system waits for a certain period of time (1+ in Fig. 6) to elapse after the idle switch is turned off. After this time has elapsed, the solenoid valve is opened so that the purge flow rate remains at a predetermined initial value, and this state continues for a certain period of time (t). Thereafter, the solenoid valve is adjusted so that the purge flow rate changes stepwise with a constant slope as shown in FIG. 6, etc., and the purge flow rate is gradually increased. That is, the purge flow rate is gradually increased so as not to disturb the air-fuel ratio feedback control.

(Problem to be Solved by the Invention) Therefore, in the conventional linear purge system described above, the slope of the step-like gradual increase characteristic should be set so that the purge flow rate does not disturb the feedback control. Optimization of the above slope is difficult because the vaporized fuel concentration constantly changes as described above. Therefore, even in such a linear barge system, if the concentration of evaporated fuel is abnormally high, there may be a case where the feedback control cannot follow up as shown in FIG. This is because the linear purge system determines in advance the rate of increase in purge flow rate that will not disturb feedback control.
This is because the idea is to control the oven according to the purge flow rate based on this value. This is because since it is oven control, it does not take into consideration whether or not the air-fuel ratio feedback control is actually following up.

Therefore, the present invention was proposed in order to eliminate the drawbacks of the conventional example described above, and its purpose is to gradually increase or decrease the purge flow rate while confirming whether the air-fuel ratio feedback control can follow the purge gas supply. The present invention proposes an evaporative fuel supply system for an engine that prevents deterioration of exhaust gas emissions and deterioration of driving performance.

(Means and operations for solving the problems) As shown in FIG. 1, the configuration of the present invention for achieving the above problems is as follows: and a metering means for supplying an air-fuel mixture with a predetermined air-fuel ratio to the engine by mixing the metered fuel and the metered fuel, and generating a predetermined negative feedback signal according to the output of the sensor and the target air-fuel ratio,
Feedback control means for feedback controlling the air-fuel ratio of the air-fuel mixture supplied to the engine to the target value;
A supply means for supplying vaporized fuel to the intake system of the engine, an updating means for updating the purge flow rate of the vaporized fuel by the supply means so as to gradually increase or decrease in a stepwise manner, and a timing for updating the purge flow rate by the updating means. and synchronizing means for synchronizing the negative feedback signal with the inversion of the negative feedback signal.

(Example) Hereinafter, an example in which the present invention is applied to a fuel injection type engine will be described with reference to the accompanying drawings.

FIG. 2 is an overall view of this engine. In FIG. 0, 1 is an air cleaner, and 2 is a hot wire air flow meter. Also,
11 is an engine body, and 20 is an engine control unit (ECU) that controls the engine.

The air flow meter 2 measures the amount of intake air Q.

3 is a throttle valve, the opening degree of which is adjusted via an actuator 4 in response to a signal TV from the ECU 20. Further, the opening degree TVO of the throttle valve 3 is determined by the opening degree sensor 7.
When the throttle valve 3 is idling, the throttle valve 3 is fully open, and when the throttle valve 3 is fully closed, a switch (not shown) in the sensor 7 generates a signal IDLE.

The upstream and downstream sides of the throttle valve 3 are bypassed by a bypass passage 5. The amount of air passing through the passage 5 is controlled by the opening ratio of the duty solenoid valve 6 in accordance with the signal ISO from the ECU 20. During idling, etc., the engine speed during idling is controlled by the amount of air controlled by the solenoid valve 6 passing through this bypass passage.

8 is a surge tank, 9 is an injector that injects fuel, and the fuel injection amount is controlled by a pulse signal τ from the ECU 20. 11 is the engine body; 1
5 is a piston, and 16 is a cylinder. 10 is a temperature sensor that measures the temperature Tw of the cooling water flowing inside the cylinder 16.

13 is an air-fuel ratio sensor, and its output E is used for feedback control for exhaust gas purification. 21 is an ignition coil, 22 is a distributor, 24 is an engine speed sensor, and 23 is a spark plug.

Further, 27 is a fuel tank, 26 is a canister for trapping evaporated fuel, and 25 is a duty ratio control solenoid valve for controlling the amount of evaporated fuel trapped in the canister 26 to be supplied to the surge tank 8. This solenoid 25 is controlled by a signal PC from the ECU 20.

The air-fuel ratio control in the engine shown in FIG. This is done by controlling the purge flow rate to supply a purge gas containing purge gas into the surge tank 8. The former feedback control air-fuel ratio control determines whether the exhaust gas is currently rich or lean based on the output E of the air-fuel ratio sensor 13, and measures the air-fuel ratio of the mixture using the air flow meter 2. This is done by adjusting the amount of fuel injected from the injector 9 with respect to the intake air fiQ. In other words, the basic fuel injection amount. , the patent featuring a correction coefficient for air-fuel ratio feedback control is =τO(1+CF+1), while the latter purge flow rate is achieved by controlling the opening ratio of the valve 25. This opening ratio is determined by the duty ratio of the purge flow rate control signal PC output to the solenoid.

In the past, feedback control and purge flow rate control were not linked at all, so feedback control was disturbed by purge gas supply, but in this embodiment, purge flow control is performed by inverting the output of the air-fuel ratio sensor. Since the air-fuel ratio is controlled in synchronization with the air-fuel ratio, the air-fuel ratio can be controlled more appropriately.

Referring to FIG. 3, feedback control will first be explained. The program shown in FIG. 3 is an interrupt routine that is activated at predetermined time intervals. In step S2, the engine speed N and intake air ff1Q are read, and in step S4, the engine speed N and intake air f1Q are read.
With the basic fuel injection amount based on f1Q. Calculate.

Here, K is a predetermined constant. In step S6, the output E of the air-fuel ratio sensor 13 is read. In Stella 7'S8, this output value E is the slice level E.

It is checked whether or not it is equal to or greater than eEo. If it is equal to or greater than Eo, the process proceeds to step SIO, and the rich flag FR is set to "1" in order to memorize that the rich state is currently in place. And the air-fuel ratio correction coefficient C,! Integrate 1 in the negative direction.

That is.

CFQ=CFil-△I0, where △■. is a predetermined integral constant 6 Conversely, if the sensor output E is less than the threshold Eo in step S8, the flag FR is reset to "0" in step S14 to remember that the lean state is present. However, in step S16, integration in the positive direction is performed, that is, Cra=Cra+ΔI0.

Then, in step S18, the final fuel injection amount is calculated, and in step S20, fuel is injected from the injector.

Next, according to FIG. 4, purge flow rate control will be explained. The program shown in FIG. 4 is an interrupt routine that is started at predetermined time intervals and is started and executed in parallel with the feedback control program shown in FIG.

In step S30, step S10. Step S14
A flag FR that stores the current rich/lean state determined in step 1 is compared with a flag FRP that stores the rich/lean state one cycle ago. When the values of these flags differ from each other, it is when the air-fuel ratio of the exhaust gas changes from rich to lean or from lean to rich (reversal). When there is no reversal, the current purge flow fi (PC This is because the feedback control is in the process of following the air-fuel ratio fluctuation due to the purge gas supply while there is no 0 reversal without changing the PC and proceeding to step 846 in order to maintain the value (value). This step S
At step 46, the flag FRP that stores the previous state is updated with FR.

If a reversal is detected in the output of the air-fuel ratio sensor in step S30, the process proceeds to step 332 and subsequent steps. In steps S32 and subsequent steps, the control signal PC of the solenoid valve 25 is gradually increased - times in synchronization with this reversal. control.

That is, in step S32, the signal IDLE is read. If this signal is "1", that is, if it is currently in an idle state, there is no need to supply purge gas, and therefore, in step S44, the signal PC is set to "0". If it is not idling, the process advances to step S36, and the purge flow control signal P
Read the maximum value PCM of C from memory (not shown). This maximum value pc is a set value of the purge flow rate determined from the operating state of the engine (for example, the amount of intake air per revolution, etc.). In step S38, the current purge supply flow fiPc
is compared with this upper limit value PCMX, and if it is less than this upper limit value, that is, if PC is ≧PC, in step S42, the purge flow rate PC is
Limit with x. Further, when PC is less than PC-, that is, when PC&lx>PC, the purge flow rate PC is gradually increased in step S44.

pc=pc+△P0 Here, ΔP0 is a predetermined constant and is a gradual increase amount.

Thus, in this embodiment, the gradual increase in purge flow rate always occurs in synchronization with the reversal of the air-fuel ratio of the exhaust gas.

In other words, since air-fuel ratio reversal is evidence that the feedback control system is performing feedback control following the supply of purge gas, after confirming this fact, even if the purge flow rate is increased, the feedback control will not respond to this increase. This can be followed by feedback control.

FIG. 5 shows, in comparison with FIG. 7, the results of the purge flow rate control and air-fuel ratio feedback control according to this embodiment, i.e., as shown in FIG. After confirming that the feedback control can follow the flow, the purge flow M is increased. Therefore, the feedback control after the increase can also be followed, so that deterioration of emissions and deterioration of drivability due to over-rich 8 over-lean of the air-fuel mixture are also prevented.

In the above embodiment, the control to increase the purge flow rate at the time of starting the supply of evaporated fuel has been described, but it is also applicable to stopping the supply of evaporated fuel. That is, when the supply stop condition is satisfied, pc=pc-ΔP1 is performed in synchronization with the reversal of the air-fuel ratio sensor output E. Here, is this ΔP the same as ΔP0?
or a different constant value. By doing so, the feedback control can follow the transition period when the purge gas supply is stopped.

In addition, in the flowcharts of Figures 3 and 4, the purge flow rate is increased when the rich state or lean state is reversed based on the air-fuel ratio sensor output. Good, that is, the air-fuel ratio feedback control is performed not only by integral control but also by proportional control (P-control) to control the PI amount, and in addition, by detecting the rich state,
The purge flow rate is updated only when the correction coefficient CFa starts decreasing gradually (that is, when performing P control in the negative direction). In such a change, the P control in the negative direction (leaning direction) and the control to increase the amount of purge gas are harmonized, and disturbances in the feedback control due to the increase in the amount of purge gas are absorbed.

Further, although the control shown in FIGS. 3 and 4 is only integral control (I control), it may be changed as follows. That is, when a lean state is detected and the I control is changed from the previous control in the lean direction to the control in the rich direction, the purge flow rate is increased and the P control takes over. . Furthermore, in the above embodiment, the determination of reversal was based on the sensor output, but the air-fuel ratio correction coefficient Ct
It may be based on ts.

Furthermore, although the gradual increase characteristic in the above embodiment was step-like, it may be changed as follows. In other words, the dwell period in this step-like characteristic is a gradual increase characteristic with a relatively gentle slope,
The update characteristic is made to be a gradual increase characteristic with a relatively steep slope. In this case, a linear solenoid valve is suitable for controlling the purge flow rate.

Further, although the above embodiments have been described with respect to a fuel injection type engine, they can also be applied to an engine with a carburetor as long as an air-fuel ratio feedback control system is set.

It goes without saying that this invention is not limited to the configurations of the embodiments and modified examples described above, and can be modified in various ways without departing from the gist of the invention.

(Effects of the Invention) As detailed above, according to the engine vaporized fuel supply device according to the present invention, the purge flow rate is increased or decreased in m in synchronization with the reversal of the air-fuel ratio feedback control. There is no case where the purge flow rate is increased or decreased in one direction, ignoring feedback control. Therefore, air-fuel ratio feedback control can sufficiently absorb disturbances due to increase or decrease in purge flow rate, and J
.

Deterioration of transmission and drivability is prevented.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of the present invention, FIG. 2 is a diagram of an engine system according to an embodiment to which the present invention is applied, FIG. 3 is a flowchart of an air-fuel ratio feedback control program according to the embodiment, and FIG. FIG. 5 is a timing chart explaining the operation of the embodiment; FIG. 6 is a timing chart explaining the initial stage of purge flow control in the conventional example; FIG. is a timing chart illustrating problems in the conventional example. In the figure, 1... Air cleaner, 2... Hot wire air flow meter, 3... Throttle valve, 4... Throttle valve actuator, 5... Bypass passage, 6... ISO solenoid valve, 7... ...Throttle opening sensor, 8...
Surge tank, 9... Injector, lO... Water temperature sensor, 11... Engine body, 13... Air-fuel ratio sensor, ]4... Catalytic converter, 15... Piston, 16... Cylinder , 20... Engine control unit (ECU), 21... Ignition coil, 22...
... Distributor, 23 ... Spark plug, 24
... rotation speed sensor, 25 ... solenoid valve for purge flow rate, 26 ... canister, 27 ... fuel tank. Patent applicant Mazda Motor Corporation! - Child agent Patent attorney Yasunori Otsuka (and other names) Hi'', l:'
Expose 1-□ 1゜Figure 3Figure 7r'-doshi

Claims (1)

[Claims] (1) an air-fuel ratio sensor disposed in the exhaust system of the engine; and a metering means that mixes the intake air and metered fuel to supply an air-fuel mixture with a predetermined air-fuel ratio to the engine; feedback control means for generating a predetermined negative feedback signal according to the output of the sensor and a target air-fuel ratio, and feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the engine to the target value; supply means for supplying vaporized fuel; updating means for updating the purge flow rate of vaporized fuel by the supply means so as to gradually increase or decrease in a stepwise manner; and update timing of the purge flow rate by the updating means according to the negative feedback signal. 1. A evaporative fuel supply device for an engine, comprising a synchronizing means for synchronizing reversal.