JP2633618B2 - Engine fuel supply system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an apparatus for supplying fuel to an engine,
More specifically, the present invention relates to an evaporative fuel supply apparatus that appropriately suppresses the air-fuel ratio fluctuation due to the supply of the evaporative fuel.

2. Description of the Related Art There is a well-known engine system in which fuel evaporated in a fuel tank or the like is trapped on a canister to prevent air pollution, and the trapped fuel is returned to an air-fuel mixture.
In this type of evaporative fuel supply device, an intake path (generally, a surge tank) and a canister are communicated via an orifice, and the evaporative fuel trapped by the canister is sucked into the tank by a negative pressure in the surge tank. It is a structure that can be done. 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 the exhaust gas emission, the air-fuel mixture supplied to the engine combustion chamber is controlled based on the output of the air-fuel ratio sensor provided in the exhaust system so that the air-fuel ratio of the exhaust gas becomes the stoichiometric air-fuel ratio. The feedback control of the air-fuel ratio is also common.

The amount of fuel vapor itself varies depending on factors such as temperature, and it is difficult to predict an accurate value of the amount. The reason is that the purge flow rate is
This is because the amount of air required to purge it is included. Therefore, when the air-fuel ratio feedback control is coupled to such a system that supplies the fuel vapor to the engine, the air-fuel ratio feedback control becomes unsuccessful due to the following reasons, resulting in deterioration of the emission and running performance. Etc. are caused. In other words, when the evaporated fuel concentration during the purge flow rate is high, the rich purge gas is sucked without control, the air-fuel ratio feedback control cannot be followed, the exhaust gas air-fuel ratio becomes rich, and the CO and HC emissions are reduced. It leads to an increase. Conversely, when the fuel vapor concentration during the purge flow rate is low, the air amount during the purge flow rate increases without control, leading to an increase in the NOX component.

In order to solve such a problem, it has been proposed to control the purge flow rate with a technique called a so-called linear purge system, such as Japanese Patent Application Laid-Open No. 57-129247. In this linear purge system, a purge solenoid valve is interposed between a canister and a surge tank to actively control the purge flow rate.

The problem will be described with reference to FIGS. 6 and 7 showing the purge flow rate control. As shown in FIG. 6, when the condition for performing the linear purge is satisfied, for example, when the idle switch is turned off, it waits for a certain time (t _{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 maintains a predetermined initial value, and this state is continued for a fixed time (t ₂ ). Thereafter, the solenoid valve is adjusted so that the purge flow rate changes stepwise with a constant inclination as shown in FIG. 6 and the like, and the purge flow rate is gradually increased. That is, the purge flow rate is gradually increased so that the air-fuel ratio feedback control is not disturbed.

(Problems to be Solved by the Invention) Therefore, in the above-described conventional linear purge system, the gradient of the step-like gradually increasing characteristic should be set so that the purge flow rate does not disturb the feedback control. As described above, it is difficult to optimize the inclination because the concentration of the evaporated fuel constantly changes as described above. Therefore, even with such a linear purge system, when the fuel vapor concentration is abnormally high, as shown in FIG. 7, there may be a case where the feedback control cannot be followed. This is because the linear purge system is based on the idea that the purge flow rate is gradually increased so that the feedback control is not disturbed, and the purge flow rate is opened based on this value. This is because the open control is not considered whether the air-fuel ratio feedback control can actually follow.

Therefore, the present invention has been proposed to eliminate the above-mentioned disadvantages of the conventional example, and its purpose is to gradually increase or decrease the purge flow rate while confirming that the air-fuel ratio feedback control can follow the supply of the purge gas. By doing
It is an object of the present invention to provide an evaporative fuel supply device for an engine that prevents deterioration of exhaust gas emission and running performance.

(Means and Actions for Solving the Problems) As shown in FIG. 1, a configuration of the present invention for achieving the above-mentioned objects includes an air-fuel ratio sensor provided in an exhaust system of an engine, And the metered fuel
Metering means for supplying an air-fuel mixture of a predetermined air-fuel ratio to the engine; generating a predetermined negative feedback signal in accordance with the output of the sensor and a target air-fuel ratio to determine the air-fuel ratio of the air-fuel mixture supplied to the engine; Feedback control means for performing feedback control to a target value; supply means for supplying evaporated fuel to the intake system of the engine; and updating means for updating the purge flow rate of the evaporated fuel by the supply means so as to gradually increase or decrease in a stepwise manner. And a synchronizing means for synchronizing the update timing of the purge flow rate by the updating means with the inversion of the negative feedback signal.

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

FIG. 2 is an overall view of the engine. In the figure, reference numeral 1 denotes an air cleaner, and 2 denotes a hot wire air flow meter. Reference numeral 11 denotes an engine body, and reference numeral 20 denotes an engine control unit (ECU) that controls the engine.

By the air flow meter 2, the intake air amount Q _a is measured.
Reference numeral 3 denotes a throttle valve, the opening of which is a signal T from the ECU 20.
V adjusts through the actuator 4. The opening TVO of the throttle valve 3 is monitored by an opening sensor 7. At idle, the throttle valve 3 is in a fully closed state, and a signal IDLE is generated by a switch (not shown) in the sensor 7 according to the fully closed state.

The upstream and downstream 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 based on a signal ISC from the ECU 20. When idle,
The idling engine speed is controlled by the amount of air controlled by the solenoid valve 6 passing through the bypass passage.

8 is a surge tank, 9 is an injector for injecting fuel, and the fuel injection amount is a pulse signal τ from the ECU 20.
Is controlled by 11 is an engine body, 15 is a piston, and 16 is a cylinder. 10 is a temperature sensor for measuring the coolant temperature T _w flowing through the cylinder 16.

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

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

The air-fuel ratio control in the engine shown in FIG.
The air-fuel ratio of the air-fuel mixture supplied to the combustion chamber of the engine 11 is controlled based on negative feedback control performed based on the output signal E of the air-fuel ratio sensor 13, and the purge gas for supplying a purge gas containing evaporated fuel into the surge tank 8. This is done by controlling the flow rate. In the former air-fuel ratio control based on feedback control, it is determined whether the exhaust gas is presently rich or lean based on the output E of the air-fuel ratio sensor 13, and the air-fuel ratio of the air-fuel mixture is determined by the air flow meter 2. for connexion measured intake air amount Q _a, it made Te cowpea to meter a injection amount τ of the fuel injected from Injiekuta 9. That is,
Assuming that the basic fuel injection amount is τ ₀ and the correction coefficient of the air-fuel ratio feedback control is C _FB , τ = τ ₀ (1 + C _FB ). On the other hand, the latter purge flow rate is controlled by controlling the opening ratio of the valve 25. This opening ratio is determined by the date ratio of the purge flow control signal PC output to the solenoid. Conventionally, the feedback control has been disturbed by the supply of the purge gas because the feedback control and the purge flow rate control were not performed at all in association with each other. , The air-fuel ratio control is more appropriately performed.

First, the feedback control will be described with reference to FIG. The program in FIG. 3 is an interrupt routine started at predetermined time intervals. In step S2, it reads the engine speed N and the intake air amount Q _a. Then, at step S4, and calculates the basic fuel injection amount tau ₀ on the basis of the engine speed N and the intake air amount Q _a.

Here, K is a predetermined constant. In step S6, the output E of the air-fuel ratio sensor 13 is read. In step S8, the output value E checks whether a slice level E ₀ or more. If E ₀ or more, the process proceeds to step S10, the Ritsuchifuragu F _R to store that is currently in Ritsuchi state "1"
Set to Then, the air-fuel ratio correction coefficient _CFB is integrated in the minus direction. That is, C _FB = C _FB − △ I ₀ . Here, ΔI ₀ is a predetermined integration constant. In step S8 Conversely, if the sensor output E is less than the threshold value E _0, to store it in a lean state, step
In S14, the flag F _R is reset to "0", in step S16, performs the integral of the positive direction. That is, C _FB = C _FB + △ I ₀ .

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

Next, the purge flow rate control will be described with reference to FIG. The program shown in FIG. 4 is an interrupt routine which is started at a predetermined time interval and is started and executed in parallel with the feedback control program shown in FIG. At step S30, a flag storing the current rich / lean state determined at steps S10 and S14.
F _R is compared with a flag F _RP storing the rich / lean state one cycle before. The values of these flags differ from each other when the air-fuel ratio of the exhaust gas changes (reversed) from rich to lean or from lean to rich. When this reversal does not occur, the PC is not changed to maintain the current purge flow rate (the value of PC).
Proceed to 6. This is because the feedback control is trying to follow the air-fuel ratio fluctuation due to the supply of the purge gas while there is no reversal. In this step S46, the flag F _RP for storing the previous state is updated with F _R.

If an inversion is detected in the output of the air-fuel ratio sensor in step S30, the process proceeds to step S32. Step S32
The following is control for gradually increasing the control signal PC of the solenoid valve 25 only once in synchronization with the reversal. That is, in step S32, the signal IDLE is read. If this signal is "1", that is, if it is currently in the idle state, it is not necessary to supply the purge gas, so the signal PC is set to "0" in step S44. If not idle, the process proceeds to step S36, reads the maximum value PC _M of the purge flow control signal PC from a memory (not shown). The maximum value PC _M the operating state of the engine (e.g., intake air amount, the rotational speed, etc.) is a setting value of the purge flow rate obtained from. In step S38, the current purge supply flow rate PC is compared with the upper limit value PC _MX. If the current value is equal to or less than the upper limit value, that is, if PC _MX ≥ PC, the purge flow rate PC is set to PC _MX in step S42. Limit limit. When PC is less than PC _MX , that is, when PC _MX > PC, the purge flow rate PC is gradually increased in step S44.

PC = PC + ΔP ₀ Here, ΔP ₀ is a predetermined constant, and is a gradually increasing amount.

Thus, in this embodiment, the gradual increase of the purge flow rate is always performed in synchronization with the reversal of the air-fuel ratio of the exhaust gas. That is, since the air-fuel ratio reversal is evidence that the feedback control system can perform feedback control following the supply of purge gas, after confirming this fact, even if the purge flow rate is increased, the feedback control does not increase this amount. On the other hand, it can be followed by feedback control.

FIG. 5 shows the results of the purge flow rate control and the air-fuel ratio feedback control according to this embodiment in comparison with FIG. That is, as shown in FIG. 5 and as confirmed by the above-described flow chart control, after confirming that the feedback control can be followed, the purge flow rate is increased. For this reason, the feedback control after the increase can be followed, so that the deterioration of the emission, the deterioration of the driving performance due to the over-rich and over-lean of the air-fuel ratio of the air-fuel mixture, and the like can be prevented.

In the above embodiment, the control of increasing the purge flow rate at the start of the supply of the evaporative fuel has been described. That is, When the supply stop condition is satisfied, in synchronization with the inversion of the air-fuel ratio sensor output E, perform PC = PC- △ P _1. Wherein the △ P ₁ is the same as or the △ P _0, or a different constant values. By doing so, the feedback control can be followed even during the transition period of the stoppage of the purge gas supply.

In addition, in the flow charts of FIGS. 3 and 4, the purge flow rate is increased at the time of reversing the rich state and the lean state determined based on the output of the air-fuel ratio sensor. You may. That is, the air-fuel ratio feedback control is not only the integral control but also the PI control that takes into account the proportional control (P-control), and further detects the rich state.
The purge flow rate is updated only when the correction coefficient C _FB starts decreasing gradually (that is, when the P control in the minus direction is performed). In such a change, the P control in the minus direction (lean direction) and the control for increasing the purge gas are coordinated, and the disturbance of the feedback control due to the increase in the purge gas is absorbed.

Further, the control in FIGS. 3 and 4 is only the integral control (I control), but may be changed as follows. That is, when the lean state is detected and the I control is changed from the previous control in the leaning direction to the control in the rich direction, at the time of the change,
The purge flow rate is increased to substitute for P control. Further, in the above embodiment, the reversal was determined based on the sensor output, but the C _FB which is the air-fuel ratio correction coefficient is used.
May be based on

Furthermore, although the gradual increase characteristic in the above embodiment is step-like, it may be changed as follows. That is, the staying period in the step-like characteristic is set to a gradually increasing characteristic with a relatively gentle gradient, and the characteristic at the time of updating is set to a gradually increasing characteristic with a relatively steep gradient. In this case, a linear solenoid valve is suitable as a valve for controlling the purge flow rate.

Although the above-described embodiment has been described with respect to a fuel injection type engine, the present invention is applicable to an engine with a carburetor as long as an air-fuel ratio feedback control system is set.

It is needless to say that the present invention is not limited to the configurations of the above-described embodiments and modified examples, and can be variously modified without departing from the gist of the present invention.

(Effect of the Invention) As described in detail above, according to the evaporative fuel supply device for an engine according to the present invention, the purge flow rate is increased or decreased in synchronization with the reversal of the air-fuel ratio feedback control. Is not neglected, and the purge flow rate is not unilaterally increased or decreased. Therefore, the air-fuel ratio feedback control can sufficiently absorb the turbulence caused by increasing or decreasing the purge flow rate,
Emission and deterioration of drivability are prevented.

[Brief description of the drawings]

FIG. 1 is a diagram showing a 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, 4 is a flow chart according to a purge flow rate control program according to the embodiment, FIG. 5 is a timing chart illustrating operation of the embodiment, FIG. 6 is a timing chart illustrating an initial state of purge flow rate control in a conventional example, FIG. 7 is a timing chart for explaining a problem in the conventional example. In the figure, 1 ... air cleaner, 2 ... hot wire type air flow meter,
3 ... Throttle valve, 4 ... Throttle valve actuator, 5 ... Bypass passage, 6 ... ISC solenoid valve, 7
…… Throttle opening sensor, 8 …… Surge tank, 9…
... Injector, 10 ... Water temperature sensor, 11 ... Engine body, 13 ... Air-fuel ratio sensor, 14 ... Catalyst converter, 15 ...
... Piston, 16 ... Cylinder, 20 ... Engine control unit (ECU), 21 ... Ignition coil, 22 ... Distributor, 23 ... Spark plug, 24 ... Rotation sensor, 25 ... Purge flow rate Solenoid valve, 26 ... canister, 27 ... fuel tank.

Claims (1)

(57) [Claims] An air-fuel ratio sensor provided in an exhaust system of an engine, a metering means for mixing the air taken in and the metered fuel to supply an air-fuel mixture having a predetermined air-fuel ratio to the engine. A feedback control means for generating a predetermined negative feedback signal in accordance with the output of the sensor and a target air-fuel ratio to feedback-control the air-fuel ratio of the air-fuel mixture supplied to the engine to the target value; Supply means for supplying evaporative fuel to the system; updating means for updating the purge flow rate of the evaporative fuel by the supply means so as to gradually increase or decrease in a stepwise manner; An evaporative fuel supply device for an engine, comprising: synchronizing means for synchronizing signal inversion.