JPH0972254A - Evaporative emission controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent saturation caused by evaporative emissions in a canister by increasing a purge execution frequency in driving with a simple method. SOLUTION: A canister 10 is connected to an intake path 2 of an engine 1 via a purge control valve 15 and an ECU 20 controls the duty of the purge control valve 15 so as to purge the canister. Even if the control duty ratio of a purge control valve is lowered than a prescribed value, the ECU 20 executes purging in the case where intake/exhaust valve overlap quantity of the engine 1 is larger than the prescribed value. When the valve overlap quantity is large, the blow-back quantity of the burnt gas to the intake path increases and mixing between the canister purge gas and the intake air is improved so that the evaporated emission feeding quantity is eliminated from dispersing between cylinders even in operating the purge control valve in low duty ratio. Therefore, the purge can be performed under the conventional conditions of stopping the purge and the purge execution frequency is increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel evaporation controller, and more particularly to a fuel evaporation controller having a duty control purge valve for supplying evaporated fuel from an engine fuel tank to an engine intake passage.

[0002]

2. Description of the Related Art Evaporative fuel in a fuel tank of an internal combustion engine is adsorbed by an adsorbent such as activated carbon in a canister to prevent the evaporative fuel from being released into the atmosphere, and purge air is supplied to the canister while the engine is operating to supply the adsorbent. There is known a technique in which a mixture of evaporated fuel and purge air (purge gas) released from the adsorbent by purging the air is sucked into the engine intake passage and burned in the engine. Further, there is known a fuel evaporation control device in which a purge control valve driven by a solenoid is provided in a purge gas pipe that connects a canister and an engine intake passage, and the purge control valve is duty-controlled to control the purge gas supply amount to the engine. .

For example, an example of this type of fuel evaporation control device is disclosed in Japanese Patent Laid-Open No. 4-358755. In the device of the publication, a pipe having a large flow passage area and a pipe having a small flow passage area are provided in parallel in the pipe connecting the canister and the purge control valve, and only the pipe having a small flow passage area is operated during light load operation such as idle. The purge gas is supplied to the purge control valve through.

In the purge control valve for duty control,
When the pulse signal supplied to the drive solenoid is on, the purge control valve opens, and when the pulse signal is off, the purge control valve closes. Therefore, the flow rate of the purge gas passing through the purge control valve can be controlled by changing the duty ratio of the pulse signal (the ratio of the pulse signal ON time to the cycle of ON / OFF 1 cycle of the pulse signal).

On the other hand, since the flow rate of the purge gas supplied to the engine is normally reduced as the engine load is smaller, the duty ratio of the control valve is reduced in order to reduce the purge gas flow rate in the light load operation region (low intake air amount region) such as idle operation. Should be set small. However, in a solenoid-driven purge control valve, if the control duty ratio becomes small, the operation of the purge control valve may become unstable, and accurate control of the purge gas flow rate may not be possible. For this reason, when purging is performed while the engine is idling, rough idling, engine stall, and the like may occur due to fluctuations in the flow rate of the purge gas. Conventionally, purging was normally stopped in the light load operation region. However, when purging is stopped in the light load operation region, the chances of purging during engine operation decrease and the amount of evaporated fuel adsorbed by the adsorbent increases. There is a problem that the fuel vapor becomes saturated and is released into the atmosphere without being adsorbed by the adsorbent.

The device disclosed in the above publication is intended to solve this problem by supplying the purge gas to the purge control valve through a pipe having a small flow passage area during light load operation such as idling. That is, since the flow passage area of the pipe that supplies the purge gas to the purge control valve is set smaller than usual during light load operation, the amount of purge gas that passes through the purge control valve decreases even with the same duty ratio. . Therefore, the duty ratio of the purge control valve is relatively large even when a low purge gas flow rate is flowed during light load operation, the operation of the purge control valve is stable, and the purge gas flow rate can be accurately controlled. Therefore, according to the device of the publication, the canister purge can be performed even when the engine is idling, which has been considered difficult in the past, so that the purge execution area can be expanded and the adsorbent can be reliably prevented from being saturated with the evaporated fuel. Becomes

[0007]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
Japanese Patent No. 755 discloses that the operation of the control valve becomes unstable in a region where the duty ratio of the purge control valve is small, so that problems such as rough idle occur, but according to the research conducted by the applicant of the present application, the purge control is actually performed. It was found that problems such as rough idle at low duty ratios of the valve often occur not due to instability in the operation of the control valve itself, but rather due to non-uniform mixing of the purge gas supplied to the engine intake passage and intake air. are doing.

As described above, the purge control valve repeatedly opens and closes in response to ON / OFF of the pulse signal supplied, and the purge gas enters the intake passage when the pulse signal is ON, that is, when the purge control valve is opened. Supplied. Therefore, the purge gas containing a large amount of evaporated fuel is supplied to the intake passage in a pulsed manner, and the concentration of the evaporated fuel contained in the intake air supplied to the engine changes in a pulsed manner. If the duty ratio of the purge control valve is large and the opening time during the opening / closing cycle of the purge control valve 1 is long, this change in concentration does not pose a problem. However, when the duty ratio becomes smaller and the opening time of the purge control valve becomes shorter, the intake air supplied to the engine does not contain the evaporated fuel for most of the time, and the evaporated fuel concentration in the intake gas rapidly increases for a very short period of time. Like

In such a state, the amount of fuel supplied to each cylinder of the engine varies from cylinder to cylinder. That is, when the fuel vapor is supplied from the purge control valve, the cylinder in the intake stroke inhales intake air containing a large amount of the fuel vapor, and when the purge control valve is closed, the cylinder in the intake stroke evaporates. Only air that does not contain fuel will be inhaled. That is, the evaporated fuel supplied to each cylinder changes depending on the time when the purge control valve opening time and the cylinder intake stroke overlap, so that the amount of evaporated fuel supplied to each cylinder varies. become. On the other hand, the amount of fuel injected into each cylinder of the engine is usually controlled to be the same in each cylinder, so if the concentration of evaporated fuel in the intake air of each cylinder varies, the total amount of fuel supplied to each cylinder also varies. become,
The combustion air-fuel ratio in each cylinder becomes uneven. For this reason, the torque generated during the explosion stroke in each cylinder fluctuates, and in extreme cases, some cylinders have an air-fuel ratio that is too rich or misfiring due to excessive leaning, resulting in rough idle and other irregularities. This causes problems such as rotation and deterioration of exhaust properties.

According to the apparatus disclosed in Japanese Patent Laid-Open No. 4-358755 described above, it is possible to operate the purge control valve while keeping the control duty ratio of the purge control valve large at all times. It is also possible to prevent However, in the device of the publication, in order to solve this problem, two pipes having different flow passage areas are arranged in parallel between the canister and the purge control valve, and a light load is placed on the pipe having a larger flow passage area. It becomes necessary to provide a shutoff valve that closes during operation, which causes a problem that the configuration and control of the entire device becomes complicated.

On the other hand, if attention is paid to the fact that the above-mentioned problem at the time of controlling the low duty ratio of the purge control valve is caused by the non-uniformity of the evaporated fuel amount sucked into each cylinder, the control duty ratio of the purge control valve is always large. It should be possible to solve this problem without maintaining. Therefore, the present invention provides a fuel vaporization control device capable of expanding the purge execution region while preventing the above-described problems at the time of low duty ratio control of the purge control valve without inviting the overall configuration and control of the device to be complicated. It is intended to be provided.

[0012]

According to the invention as set forth in claim 1, a canister for adsorbing the evaporated fuel in the fuel tank of the internal combustion engine, and a purge passage for guiding the purge gas from the canister to the engine intake passage, A purge valve that opens and closes the purge passage according to the supplied pulse signal, and a control means that changes the duty ratio of the pulse signal supplied to the purge valve according to the engine load condition to control the flow rate of the purge gas passing through the purge passage. A purge inhibiting means for inhibiting the purge by keeping the purge valve fully closed when the duty ratio of the pulse signal becomes equal to or lower than a predetermined lower limit value, and the amount of evaporated fuel sucked into each cylinder of the engine. When the operating condition detecting means for detecting an engine operating condition parameter that affects the variation between cylinders, and the engine operating condition parameter is in a predetermined region, A purge execution means for stopping the purge inhibition operation by serial purge inhibition means, the fuel evaporative control system having a are provided.

That is, the purge inhibiting means inhibits the purge by holding the purge control valve fully closed when the duty ratio of the pulse signal supplied to the purge control valve becomes lower than a predetermined lower limit value. As a result, the problem due to the variation in the evaporated fuel supply amount between the cylinders when the purge control valve operates at a low duty ratio is prevented. On the other hand, the variation of the evaporated fuel supply amount to each cylinder is influenced by the engine operating state, so that the variation of the evaporated fuel supply amount between the cylinders does not occur even when the purge control valve is controlled at a low duty ratio. In some cases, purging need not be prohibited in such cases. When it is determined that the engine operating condition parameter is within the predetermined range and there is no variation in the evaporated fuel supply amount between the cylinders, the purge execution means performs the purge even when the purge control valve is operating at a low duty ratio. The purge prohibiting operation by the prohibiting means is stopped to execute the purge.

According to a second aspect of the present invention, the engine includes variable valve timing means for changing the valve overlap of the intake and exhaust valves according to engine operating conditions, and the engine operating state parameter is valve overlap. Quantity,
The fuel vaporization control device according to claim 1, wherein the purge execution means stops the purge prohibition operation by the purge prohibition means when the valve overlap amount is larger than a predetermined value.

The mixed state of the purge gas and the intake air changes depending on the valve overlap amount of the intake and exhaust valves. That is, as the valve overlap amount increases, the amount of burnt gas that flows back into the intake passage from the inside of the cylinder in the early stage of opening the intake valve increases, and the intake air in the intake passage is agitated by this burned gas, so that the purge gas and intake air Mixing is uniform. Therefore, when the valve overlap amount is large, the variation in the evaporated fuel supply amount between the cylinders is small even when the control duty ratio of the purge control valve is small. Therefore, in the invention of claim 2, the purge executing means stops the purge prohibiting operation by the purge inhibiting means to perform the purge when the valve overlap amount is large even when the purge control valve is operating at a low duty ratio. Run.

According to the third aspect of the present invention, the engine operating condition parameter is the concentration of evaporated fuel in the purge gas, and the purge execution means has the concentration of evaporated fuel in the purge gas equal to or lower than a predetermined upper limit value. The fuel evaporation control apparatus according to claim 1, wherein the purge prohibiting operation by the purge prohibiting means is stopped in a certain case. When the concentration of the evaporated fuel in the purge gas is low, the change in the concentration of the evaporated fuel in the intake air when the purge control valve is opened and closed is small, and the evaporated fuel supply between the cylinders is irrespective of the operating duty ratio of the purge control valve. The amount variation is small. Therefore, claim 3
In the invention described in (1), the purge execution means stops the purge prohibition operation by the purge prohibition means and executes the purge even when the purge control valve is operating at a low duty ratio and the evaporated fuel concentration is low.

According to the fourth aspect of the present invention, the purge execution means further sets the frequency of the pulse signal supplied to the purge valve when the concentration of the evaporated fuel in the purge gas is higher than the upper limit value. The fuel vaporization control device according to claim 3, wherein the fuel vaporization control device is set to be higher than when the fuel vapor concentration is equal to or lower than the upper limit value, and the purge prohibiting operation by the purge prohibiting means is stopped.

Even when the purge control valve is operating at a low duty ratio, if the control pulse signal frequency of the purge control valve (the number of times the pulse signal is turned on / off per unit time) is set high, the opening operation of the purge control valve is performed. Since the interval (the ON interval of the pulse signal) is shortened, the overlap time of the intake stroke of each cylinder and the opening time of the purge control valve becomes closer to uniform, and the fluctuation of the evaporated fuel supply amount between each cylinder is reduced. It Therefore, even when the evaporated fuel concentration is high and the operation duty ratio of the purge control valve is low, if the duty ratio of the control signal of the purge control valve is set high, the variation of the evaporated fuel supply amount between the cylinders does not occur. Therefore, in the invention of claim 4, the purge executing means executes the purge by setting the control pulse signal frequency of the purge control valve to be high even when the evaporated fuel concentration is high during the operation of the low duty ratio of the purge control valve. To do.

According to the fifth aspect of the present invention, the engine operating state parameters are the concentration of evaporated fuel in the purge gas and the engine speed, and the purge execution means determines the concentration of evaporated fuel in the purge gas in advance. If it is below the upper limit,
The fuel evaporation control device according to claim 1, wherein the purge prohibiting operation by the purge prohibiting means is stopped when the evaporated fuel concentration is higher than the upper limit value and the engine speed is equal to or higher than a predetermined lower limit value. .

When the engine speed is high, the flow velocity of the intake air in the intake passage becomes faster, so that the purge gas flowing into the passage and the intake air are uniformly mixed. Also, since the interval of the intake stroke of each cylinder is shortened, the number of cylinders that perform intake during the purge control valve opening increases compared to when the rotation speed is low, and even if the concentration of evaporated fuel in the purge gas is high, the purge control valve The variation of the evaporated fuel supply amount between the cylinders becomes small regardless of the operating duty ratio of. For this reason, in the invention according to claim 5, the purge execution means performs the purge prohibition operation by the purge prohibition means when the evaporated fuel concentration is low and when the engine speed is high even when the evaporated fuel concentration is high. When the purge control valve is stopped and the low duty ratio is activated, the purge is executed.

According to the sixth aspect of the present invention, the purge execution means further includes a purge valve when the fuel vapor concentration in the purge gas is equal to or higher than the upper limit value and the engine speed is lower than the lower limit value. The fuel vaporization control device according to claim 5, wherein the frequency of the pulse signal supplied is set higher than when the fuel vapor concentration is lower than the upper limit value, and the purge prohibiting operation by the purge prohibiting means is stopped. To be done.

As described above, if the control pulse signal frequency of the purge control valve is set to a high value, it is possible to reduce the problem of variations in the evaporated fuel supply amount between cylinders. Therefore, in the invention as set forth in claim 6, the purge execution means is most likely to cause variations in the evaporated fuel supply amount between the cylinders, and has a high duty of the purge control valve with a high evaporated fuel concentration and a low engine speed. When the specific operation is executed, the control pulse signal is set high to prevent the variation in the evaporated fuel supply amount between the cylinders, and then the purge prohibiting operation by the purge prohibiting means is stopped to execute the purge.

[0023]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram showing a schematic configuration of an embodiment when the present invention is applied to an automobile engine. In FIG. 1, reference numeral 1 denotes an automobile internal combustion engine. The internal combustion engine 1 of this embodiment is a multi-cylinder internal combustion engine, and only one cylinder is shown in FIG. Further, in FIG. 1, 2 is an intake passage connected to each cylinder intake port 2a of the engine 1, and 3 is an intake passage.
Is an exhaust passage connected to the exhaust port 3a of each cylinder, 2
Reference numerals b and 3b respectively indicate an intake valve and an exhaust valve of each cylinder. The intake passage 2 is provided with an air flow meter 4 that generates a voltage signal according to the intake air amount of the engine, and a throttle valve 6 that has an opening degree according to the operation amount of the accelerator pedal of the driver. Further, reference numeral 7 in FIG. 1 denotes a fuel injection valve for injecting pressurized fuel into the intake port 2a of each cylinder.

An air-fuel ratio sensor 31 that outputs a voltage signal according to the air-fuel ratio of the exhaust gas is provided at the exhaust gas merging portion from each cylinder in the exhaust passage 3 of the engine 1. In FIG. 1, 11 is a fuel tank for storing the fuel of the engine 1, and 10 is a canister for adsorbing the evaporated fuel in the fuel tank 11. The canister 10 contains an adsorbent 13 such as activated carbon, and is connected to the fuel upper space of the fuel tank 11 by a vapor pipe 12. The evaporated fuel in the fuel tank 11 flows into the canister 10 via the paper pipe 12. The vaporized fuel that has flowed into the canister 10 from the vapor pipe 12 is adsorbed by the adsorbent 13, and only the air from which the vaporized fuel has been removed is released to the atmosphere through the opening 16.

The inside of the canister 10 has a purge passage 1
4 is connected to the intake passage 2 downstream of the throttle valve 6. Therefore, during operation of the engine 1, the negative pressure in the canister is negative due to the negative intake pressure generated on the downstream side of the throttle valve 6, and the air is sucked through the opening 16. This air passes through the adsorbent 13 to release the fuel adsorbed by the adsorbent 13, and becomes a mixture (purge gas) of evaporated fuel and air and flows from the purge passage 14 into the engine intake passage. Therefore, in addition to the fuel supplied from the fuel injection valve 7, the evaporated fuel is supplied from the purge passage 14 to the engine.

Further, in this embodiment, the purge passage is provided with a purge control valve 15 which is an electromagnetic valve having a solenoid actuator. The purge control valve 15 repeats the opening / closing operation according to a pulse signal supplied from an electronic control unit (ECU) 20 described later. As will be described later, the flow rate of the purge gas passing through the purge control valve 15 is
It is controlled according to the duty ratio of the pulse signal supplied to the purge control valve 15.

Further, in this embodiment, the intake valve 2 of the engine 1
A variable valve timing device 40 for changing the intake valve opening / closing timing is provided in b. The variable valve timing device 40 will be described later. Electronic control unit (E
CU) 20 is a ROM (Read Only Memory), RAM
(Random access memory), CPU (Central processing unit), Input port, Output port are connected to each other by a bidirectional bus. Perform basic control. Further, in the present embodiment, in addition to the above control, the ECU 20 controls the duty ratio of the pulse signal supplied to the purge control valve 15 to purge the canister 10 and determine whether or not the purge can be performed. That is, in the present embodiment, the ECU 20 functions as each unit such as the control unit, the purge prohibiting unit, and the purge executing unit described in claim 1.

For each control described above, the input port of the ECU 20 has an intake air amount signal from the air flow meter 4 indicating the intake air amount of the engine, an air-fuel ratio sensor 31 indicating an air-fuel ratio signal indicating the exhaust air-fuel ratio, and an engine cooling water passage. The engine cooling water temperature is input from each of the temperature sensors (not shown) disposed in the engine converter through the AD converter 27, and the crankshaft speed is fixed from the rotation speed sensor 32 provided on the engine crankshaft (not shown). A pulse signal is input for each rotation angle. Also,
The ECU 20 for variable valve timing control described later
The input port of the intake camshaft (not shown)
A pulse signal is input from the cam rotation angle sensor 35 provided at each constant rotation angle of the intake camshaft. E
The CU 20 calculates the engine rotation speed based on the pulse signal frequency from the rotation speed sensor 32, and at the same time, based on the phase difference between the pulse signal of the rotation speed sensor 32 and the pulse signal of the cam rotation angle sensor 35, the intake valve Calculate valve timing.

The output port of the ECU 20 is connected to the fuel injection valve 7 and the hydraulic pressure switching valve (described later) of the variable valve timing device 40 via the drive circuit 28, and the fuel injection amount from the fuel injection valve 7 and In addition to controlling the valve timing of the intake valve 2b, it is connected to the purge control valve 15 and supplies a control pulse signal to the actuator of the purge control valve 15.

Next, the duty control of the purge control valve 15 will be described with reference to FIG. FIG. 2 is a diagram for explaining the control pulse signal supplied to the purge control valve 15 and the operation of the purge control valve 15. As shown in FIG. 2, in the present specification, the ratio of the pulse-on time (the time indicated by T ₁ in FIG. 2) to one cycle (the time indicated by T in FIG. 2) of the pulse signal (T
₁ / T) is defined as the duty ratio DR. The purge control valve 15 opens when the solenoid is energized (that is, when the pulse signal is on), and closes when it is off (see FIG. 2). Therefore, when the duty ratio of the pulse signal is large, the valve opening time of the purge control valve 15 becomes long and the valve opening interval (valve closing time) becomes short as shown in FIG. 2 (A). Therefore, the flow rate of the purge gas passing through the purge control valve 15 increases as the duty ratio increases. When the duty ratio is 100%, the purge control valve 15 is fixed in the open state, and the purge gas flow rate becomes maximum.

On the other hand, when the duty ratio of the pulse signal is small, on the contrary, as shown in FIG. 2 (B), the valve opening time becomes short and the valve opening interval becomes long. Therefore, the purge gas flow rate decreases as the duty ratio decreases, and when the duty ratio is 0%, the purge control valve 15 is kept closed and the purge gas flow rate becomes zero. Further, when the duty ratio is small, high-concentration evaporated fuel flows into the intake passage 2 from the purge passage 14 at a relatively long interval, and in a multi-cylinder engine, the evaporated fuel is evaporated in accordance with the intake stroke timing of each cylinder. The supply amount will vary.

For example, FIG. 2 (C) shows an example of the timing of the intake stroke of a 4-cylinder engine. In FIG. 2 (C),
Each of t ₁ , t ₂ , t ₃ , and t ₄ shows the timing of the intake stroke of the first to fourth cylinders in the case of a four-cylinder engine. When the duty ratio is large as shown in FIG. 2 (A), the intake stroke of each cylinder (t _{1 to} t _{4 in} FIG. 2 (C)) must always include the opening period of the purge control valve 15. Therefore, there is little variation in the evaporated fuel supply amount between the cylinders. On the other hand, when the duty ratio is low (FIG. 2 (B)), for example, in the first cylinder and the third cylinder, the intake stroke (FIG. 2 (C), t ₁ ,
Since the entire opening period of the purge control valve 15 is included in t ₃ ), a large amount of evaporated fuel is supplied to these cylinders as a whole, but in the second cylinder and the fourth cylinder, the intake stroke ( 2 (C), t ₂ and t ₄ ) and the opening period of the purge control valve 15 do not substantially overlap with each other, almost no evaporated fuel is supplied to these cylinders as a whole. The amount of supply will vary greatly. For this reason, when the duty ratio of the purge control valve 15 is small, misfiring and combustion failure are likely to occur due to variations in the air-fuel ratio among the cylinders, the engine speed becomes unstable, torque fluctuations, and exhaust properties deteriorate. May occur.

In this embodiment, the duty ratio of the control pulse of the purge control valve 15 is determined according to the engine load condition. As described above, the flow rate of the purge gas increases or decreases according to the duty ratio of the purge control valve 15. If the flow rate of the purge gas is large, the canister 10 can be purged in a short time. Therefore, it is preferable to set the duty ratio of the purge control valve 15 to a large value. However, if a certain amount or more of purge gas is supplied to the engine with respect to the engine intake air amount, problems such as deterioration of engine operability may occur. Therefore, in the present embodiment, the engine load condition (for example, engine intake air amount and The optimum purge flow rate is determined according to the engine speed. In this way, as a result of setting the duty ratio of the purge control valve 15 according to the engine load condition, the duty ratio of the purge control valve is set small depending on the engine load condition (for example, during light load operation). In some cases, it may be necessary to cause the problem of the above-mentioned variation of the evaporated fuel among the cylinders.

In order to prevent this problem, in the present embodiment, the ECU 20 keeps the purge control valve 15 in a fully closed state when the duty ratio setting value of the purge control valve 15 is below a certain lower limit value, and the purge Perform the operation to stop. Further, as described above, if the purging is always stopped when the duty ratio becomes equal to or lower than the lower limit value, the purge execution frequency decreases, so that the canister 10 is saturated with the evaporated fuel and cannot absorb the evaporated fuel. there is a possibility.

Therefore, in this embodiment, the engine 1 has the intake valve 2
When the valve overlaps between the valve b and the exhaust valve 3b is large, the purge is executed even when the duty ratio of the purge control valve 15 is small. Normally, the intake valve 2b starts opening at the end of the cylinder exhaust stroke. Therefore, there is a state (valve overlap) in which both the exhaust valve 3b and the intake valve 2b are simultaneously open at the end of the exhaust stroke. During the valve overlap period, the burnt gas in the cylinder flows back to the intake port. Therefore, when the amount of burnt gas that flows backward is large, the intake air in the intake passage is agitated by burnt gas, and the duty ratio of the purge control valve 15 is small, so that the purge gas is intermittently supplied as shown in FIG. 2 (C). In this case, the mixture of the intake gas and the purge gas is promoted, so that the purge gas is uniformly dispersed in the entire intake air. Further, the mixing promotion effect by the burned gas becomes better as the burned gas amount flowing back to the intake port is larger, that is, as the valve overlap period is longer (the valve overlap amount is larger).

Therefore, even if the duty ratio of the purge control valve 15 is small, if the valve overlap amount is large, the problem of variation in the evaporated fuel supply amount between the cylinders does not occur even if the purge is executed. . Therefore, in the present embodiment, if the duty ratio of the purge control valve 15 is smaller than the lower limit value and the valve overlap amount is larger than a predetermined constant value even if the purging should be stopped, the purging is executed. The purge execution frequency is increased.

Next, the variable valve timing device 40 used in this embodiment will be described with reference to FIG. As shown in FIG. 3, the variable valve timing device 40 includes a timing pulley 42 having a cylindrical sleeve 43, and a cover 44 that covers an end portion of the intake camshaft 2c, and the timing pulley 42 has the cylindrical sleeve 43. It is rotatably attached to the camshaft around the intake camshaft 2c via. Further, the cover 44 is fixed to the timing pulley 42 with bolts 45 so as to rotate integrally with the pulley 42.

A piston member 47 is provided inside the cover 44. The piston member 47 includes an annular piston portion 49 and a cylindrical portion 51 extending from the piston portion 49, and the outer peripheral surface and the inner peripheral surface of the piston portion 49 are
The inner peripheral surface of the cover 44 and the outer peripheral surface of the sleeve 43 of the pulley 42 are in sliding contact with each other. In addition, the piston member 47
An outer helical gear 51a and an inner helical gear 51b, each having a predetermined twist angle, are engraved on the outer peripheral surface and the inner peripheral surface of the cylindrical portion 51, and the outer helical gear 51a is formed on the inner peripheral surface of the cover 44. Inner tooth helical gear 52a and inner helical gear 51
b engages with a ring-shaped external tooth helical gear 52b integrally mounted on the end surface of the camshaft 2c.

Variable valve timing device 4 of this embodiment
At 0, the rotation of the crankshaft (not shown) of the engine is transmitted to the timing pulley 42 via the timing belt 42a. When the pulley 42 rotates, the cover 44 rotates integrally with the pulley 42, and the piston member 47 connected to the cover 44 via the helical gears 52a and 51a rotates integrally with the cover 44. The piston member 47 is connected to the camshaft 2c via the helical gears 51b and 52b, so that the camshaft 2c rotates integrally with the pulley 42.

That is, in the variable valve timing device 40 of this embodiment, the rotational driving force of the camshaft 2c is
It is transmitted from the crankshaft to the timing pulley 42 via the timing belt 42a, and the pulley 42 covers the cover 4
4, the helical gears 52a and 51a, the piston member 47, and the helical gears 51b and 52b, and then the camshaft 2c.
Is transmitted to

Variable valve timing device 4 of this embodiment
0 changes the valve timing of the intake valve by moving the piston member 47 in the axial direction of the camshaft 2c. That is, when the piston member 47 moves in the camshaft axial direction, the meshing positions of the helical gears 52a and 51a and 51b, 52b move in the axial direction along the respective tooth traces. For this reason, the cover 44 and the piston member 47, and the piston member 47 and the camshaft 2c respectively move in the circumferential direction along the tooth trace of the helical gear, and the cover 44, the piston member 47, and the piston member 47. And the cam shaft 2c rotate relative to each other. Therefore, the rotational phase of the timing pulley 42, that is, the rotational phase of the camshaft 2c with respect to the rotational phase of the crankshaft is advanced or retarded according to the moving direction of the piston member 47.
Therefore, the opening / closing timing of the intake valve driven by the valve is advanced or retarded.

As described above, since the variable valve timing device 40 of this embodiment changes only the rotational phase of the intake camshaft 2c, the valve opening timing and the valve closing timing of the intake valve are changed when the valve timing is changed. The timing always changes by the same amount, and the intake valve opening period itself is maintained constant.
In this embodiment, the valve timing of the intake valve is changed by moving the piston member 47 by hydraulic pressure during engine operation. As shown in FIG. 3, the camshaft 2
Two oil passages 62 and 63 are bored in c along the axial direction.

The oil passage 62 is provided at the center of the camshaft 2c, and the oil pressure chamber 65 is formed on the axial end side of the oil passage 62 between the inner surface of the cover 44 and the axial end side end surface of the piston 47 via the port 62a. Is in communication with. The other end of the oil passage 62 is connected to the hydraulic pressure switching valve 70 via a port 62b formed in the camshaft 2c in the radial direction. On the other hand, the end portion on the shaft end side of the oil passage 63 is closed by the above-mentioned ring-shaped external tooth helical gear 52b. Also,
The oil passage 63 communicates with a hydraulic chamber 68 defined by the end face of the piston 47, the timing pulley 42, and the cover 44 through a port 63a that is formed in the radial direction, and
It is connected to the hydraulic pressure switching valve 70 via the port 63b.

The hydraulic pressure switching valve 70 includes an engine lubricating oil pump 78.
Hydraulic oil from a hydraulic pressure supply source such as the above is supplied to the hydraulic passages 62 or 63 according to a signal from the ECU 20. Further, the hydraulic passage on the side not supplied with hydraulic oil is connected to the drain via the switching valve 70. When hydraulic fluid is supplied from the switching valve 70 to the hydraulic passage 62, the variable valve timing device 40
Lubricating oil flows into the hydraulic chamber 65 from a hydraulic pressure supply source 78 such as a lubricating oil pump of the engine via the hydraulic passage 62 and the port 62a, and presses the piston portion 49 to the right in FIG. At this time, the lubricating oil in the hydraulic chamber 68 is discharged from the port 63a to the drain through the oil passage 63, the port 63b and the hydraulic pressure switching valve 70. Therefore, the piston member 47 is shown in FIG.
Move to the right.

Further, in FIG. 3, when hydraulic oil is supplied from the hydraulic pressure switching valve 70 to the hydraulic passage 63, lubricating oil flows into the hydraulic chamber 8 through the oil passage 63 and from the hydraulic chamber 65 to the oil passage 62. Since the lubricating oil is discharged to the drain through the piston member 47, the piston member 47 moves leftward in FIG. During engine operation,
The ECU 20 calculates the optimum valve timing (target valve timing) from a predetermined relationship according to the engine load state, and at the same time, based on the pulse signals of the rotation speed sensor 32 and the cam rotation angle sensor 35, the current valve timing. Calculate VVT. Then, the actual valve timing VV is changed by switching the hydraulic pressure switching valve 70.
The position of the piston member 47, that is, the valve timing of the intake valve is feedback-controlled so that T coincides with the target valve timing. Therefore, the valve timing of the intake valve during engine operation is controlled according to the engine operating state. By the way, when the valve timing of the intake valve is advanced, the overlap amount of the intake and exhaust valves increases in accordance with the advance amount. As described above, in the present embodiment, the ECU 20 determines whether or not purging is possible based on the valve overlap amount, and the valve overlap amount is equal to or greater than the predetermined value even in the region where the operation duty ratio of the purge control valve 15 is small. In this case, control is performed to execute purging.

4 and 5 are flow charts showing the purge control operation according to the valve timing (valve overlap amount) of the intake valve described above. This routine is EC
It is executed by U20 at regular intervals. When the routine starts in FIG. 4, in step 401, the cooling water temperature THW and the engine intake air amount G are measured from the cooling water temperature sensor and the air flow meter 4, respectively, and the engine speed NE
Is read from the rotation speed sensor 35. Next, at step 403, it is judged if the preconditions for executing the purge are satisfied.

Here, the preconditions for purging at step 403 are that the engine temperature is sufficiently high (cooling water temperature THW is above a predetermined value (for example, 70 ° C.)), fuel during deceleration. That is, a predetermined time has elapsed since the cutting was completed, and so on. If these prerequisites are not satisfied, the routine proceeds to step 445, where the control duty ratio DR of the purge control valve 15 is set to D
R = 0 is set (that is, the purge control valve 15 is fully closed), the values of various control parameters and flags described later are set to 0 in step 447, and the routine ends.

If the precondition is satisfied, then the routine proceeds to step 405, where the control target value tDR of the duty ratio of the purge control valve 15 is calculated. In the present embodiment, the target duty ratio of the purge control valve 15 is determined according to the engine load condition, that is, in the present embodiment, the value of the target duty ratio tDR is previously set to the engine load condition (for example, intake air per engine revolution). It is stored in the ROM of the ECU 20 in the form of a numerical table as a function of the quantity G / NE and the engine speed NE). In step 405, the G / NE value is calculated based on the G and NE values read in step 401, and the target duty ratio tDR is calculated from the numerical table stored in the ROM using the NE and G / NE values. Perform the operation to read the value.

Next, at step 407, it is judged if the value of the target duty ratio tDR calculated above is smaller than a predetermined lower limit value A. Here, the value of A is set to the minimum duty ratio that can prevent the variation in the evaporated fuel distribution between the cylinders due to the low duty ratio operation of the purge control valve 15 (in the present embodiment, for example, the value of A is The duty ratio is set to about 10%).

In step 407, when tDR ≧ A, even if the control duty ratio DR of the purge control valve 15 is set to the target value tDR and the purge is executed, the vaporized fuel distribution does not vary. Therefore, in this case, the process proceeds to step 411 in FIG. 5 to execute the purge operation. on the other hand,
If tDR <A in step 407, the value of tDR is small. Therefore, when the control duty ratio DR of the purge control valve 15 is set to the target value tDR and purging is executed, variations in the evaporated fuel supply amount between the cylinders occur. Can occur.
For this reason, in principle, purging is not executed in this case.

However, as described above, when the valve overlap amount of the engine intake / exhaust valve is large, mixing of the intake air and the purge gas is promoted, so that the evaporated fuel supply amount between the cylinders is reduced even if the duty ratio is low. There is no variation. Therefore, in the present embodiment, if tDR <A in step 407, the process proceeds to step 409, it is determined whether or not the current valve overlap amount of the intake and exhaust valves is larger than a predetermined value, and the valve overlap amount is determined. If is larger than the predetermined value, the process proceeds to step 411 in FIG. 5 to execute the purge. That is, in step 409, the intake valve valve timing VV
It is determined whether T is larger than the predetermined value B, and only when VVT> B, the process proceeds to step 411 in FIG. Also, VVT ≦ B
If it is, steps 445 and 447 are executed, the purge control valve is fully closed, and the routine is ended. That is,
In this case, the purging operation is prohibited. Note that VVT in step 407 represents the value of the valve timing of the intake valve. In this embodiment, the larger the value of VVT, the larger the advance amount of the valve timing of the intake valve (that is, the larger the valve overlap amount of the intake and exhaust valves. )Become.

By executing steps 407 and 409, the precondition of step 403 is satisfied, and the purge control valve 1
When the operation duty ratio of No. 5 is equal to or more than the predetermined value, the purge operation is always executed, and even if the duty ratio of the purge control valve is smaller than the predetermined value, the valve overlap amount of the intake / exhaust valve is the predetermined amount. If it is larger, purge is executed. For this reason, the purge operation is prohibited only when the precondition of step 403 is satisfied only when the duty ratio of the purge control valve is smaller than a predetermined value and the valve overlap of the intake and exhaust valves is small. .
As a result, the frequency of execution of the purging operation during actual operation becomes high, and it becomes possible to effectively prevent the adsorbent 13 of the canister 10 from being saturated with the evaporated fuel. In step 409, the determination is made based on the actual valve timing detection value VVT instead of the target value of the valve timing of the intake valve, because the target value and the actual valve timing may differ due to the response delay of the variable valve timing device. This is because there may be a difference between them.

Next, the purging operation after step 411 in FIG. 5 will be described. In step 411 in FIG. 5, first, it is determined whether or not the value of the flag XDR is set to 0. The flag XDR is a flag indicating whether or not the transient control at the start of the purge operation is completed, and XDR = 0 indicates that the transient control is not completed.

If the transient control is not completed at step 411, the purge start control at steps 413 to 425 is executed. In the purge start control, first, step 413
Then, it is determined whether or not the value of the fuel injection rate K is smaller than a predetermined lower limit value. Here, the fuel injection rate K is a ratio between the current fuel injection amount TAU and a basic fuel injection amount TAUP described later, that is, a value defined by K = TAU / TAUP.

As will be described later, in this embodiment, the engine fuel injection amount TAU is feedback-controlled based on the output of the air-fuel ratio sensor 31 provided in the exhaust passage 3 so that the exhaust air-fuel ratio matches the theoretical air-fuel ratio. There is. Therefore, when the purge gas is supplied to the intake passage 2, the fuel injection amount from the fuel injection valve 7 is reduced by an amount corresponding to the amount of evaporated fuel in the purge gas, and the engine air-fuel ratio is maintained at the theoretical air-fuel ratio as a whole. It However, the fuel injection amount TA from the fuel injection valve 7
If U is excessively reduced, there is a problem that atomization of the injected fuel fails and combustion in the cylinder deteriorates. Therefore, in the present embodiment, a lower limit value is set for the fuel injection amount from the fuel injection valve 7, and the purge gas amount is adjusted so that the fuel injection amount does not become smaller than the lower limit value by performing the purge. The lower limit value changes according to the engine load state such as the negative pressure in the intake passage and the intake flow velocity. On the other hand, as will be described later, the basic fuel injection amount TAU P is an amount that is determined according to these engine load conditions, so in the present embodiment, the actual fuel injection amount TAU is used.
The fuel injection rate K defined by the ratio of the basic fuel injection amount TAUP to the basic fuel injection amount TAUP is used to define the lower limit of the fuel injection amount under each operating condition.

In this embodiment, the fuel injection amount TAU from the fuel injection valve 7 is calculated based on the following equation by a routine (not shown) which is separately executed by the ECU 20 at each constant crankshaft rotation angle. TAU = TAUP * (FAF-KP) Here, TAUP is the basic fuel injection amount, which is the fuel injection amount required to maintain the combustion air-fuel ratio of the engine at the theoretical air-fuel ratio. The value of TAUP is calculated, for example, as TAUP = (G / NE) × α (α is a predetermined constant) according to the engine load (for example, intake air amount G / NE per engine revolution). .

FAF is an air-fuel ratio correction coefficient determined by the output of the air-fuel ratio sensor 31, and is feedback-controlled so that the air-fuel ratio detected by the sensor 31 matches the theoretical air-fuel ratio. That is, the value of FAF is reduced when the exhaust air-fuel ratio detected by the air-fuel ratio sensor 31 is richer than the stoichiometric air-fuel ratio, and is increased when it is lean. As a result, the actual fuel injection amount TAU is corrected so that the exhaust air-fuel ratio matches the stoichiometric air-fuel ratio, so that the exhaust air-fuel ratio is accurately controlled to the stoichiometric air-fuel ratio regardless of the tolerance of the fuel injection valve 7. Like

Further, KP is a purge learning correction amount, and is provided for the purpose of preventing the value of FAF from greatly changing depending on whether or not purging is performed. The value of KP is set to 0 when purging is not executed, and is set to F during purging.
The increase / decrease is controlled so that the AF value becomes a value near 1.0. As a result, the fuel injection amount TAU is reduced by an amount corresponding to TAUP × KP when the purge is executed. That is, TAUP × KP corresponds to the amount of evaporated fuel supplied by purging.

As described above, since the fuel injection amount from the fuel injection valve 7 is reduced according to the amount of evaporated fuel in the purge gas, when the concentration of evaporated fuel in the purge gas is high or the target purge gas flow rate is large. In some cases, when the purge gas is rapidly increased at the start of purging, the fuel injection amount TAU is greatly reduced and falls below the lower limit value of the fuel injection amount, which may cause combustion failure or the like. Therefore, step 41 in FIG.
In Nos. 3 to 425, the purge start control is performed in which the purge gas amount is gradually increased while monitoring the value of the fuel injection rate K at the start of the purge, and the fuel injection rate K is prevented from becoming smaller than a predetermined lower limit value by the start of the purge. .

That is, at the start of purging, the ECU 20
In steps 413 to 425, the duty ratio of the purge control valve is gradually increased by a constant amount d every time the routine is executed to the target duty ratio tDR (steps 419 and 41).
The value of the fuel injection rate K is monitored together with 7), and if the value of K becomes equal to or less than the predetermined value C during the increase control of DR, the value of K is again set.
Until the value of exceeds the predetermined value C
The duty ratio DR is reduced one by one (steps 413, 4).
15, 417). The fuel injection rate K in step 413
The determination value C is set to a value having a certain margin with respect to the actual fuel injection rate lower limit value of the fuel injection valve 7, and the value of K may be equal to or lower than the fuel injection rate lower limit value during the purge control. It is supposed not to. Further, when DR reaches the target duty ratio tDR without the value of K becoming the predetermined value C or less (steps 421 and 423), the value of the flag XDR is set to 1 in step 425 to perform the purge start control. finish. As a result, from the next routine execution, the purge target value control of step 427 and subsequent steps of step 411 is executed.

Steps 427 to 441 correspond to step 4
Purge control valve 1 by the purge start control from 13 to 425
The control when the value of the target duty ratio tDR is changed after the duty ratio DR of 5 reaches the target duty ratio tDR or when the concentration of the evaporated fuel in the purge gas is changed is shown. That is, the duty ratio DR of the purge control valve
Even when the fuel injection rate is controlled to the target value tDR, the fuel injection rate K decreases as the evaporated fuel concentration in the purge gas increases,
There may be cases where it becomes less than the lower limit. Further, even when the fuel injection rate K is maintained at a value larger than the lower limit value C, if the target duty ratio tDR of the purge control valve is set to a large value due to changes in engine operating conditions, the fuel injection rate K will become the lower limit value. There may be a case where it becomes C or less.

In order to prevent this problem, in the purge target value control of steps 427 to 441, when the value of the fuel injection rate K becomes smaller than the lower limit value C when the purge control valve is controlled by the target duty ratio tDR (step 42
7) The value of the injection rate lower limit flag XK is set to 1 (step 431) and the purge control valve duty ratio DR is set to a constant value e every time the routine is executed until K becomes equal to or more than the lower limit value C.
(Step 429) The operation of gradually decreasing is performed (steps 429, 433). Further, once the duty ratio DR is changed to the target value tDR by the operations of steps 429 to 433.
When the value of the injection rate K becomes equal to or higher than the lower limit value C after being set to a smaller value (that is, after the value of the injection rate lower limit flag XK is set to 1), a constant value e is set for each routine execution.
Each time (step 437), the duty ratio DR is gradually increased so that DR matches the target value tDR (steps 439, 441, 433). As a result, even when the duty ratio target value tDR or the evaporated fuel concentration in the purge gas changes, the purge control valve is controlled near the target duty ratio while preventing the fuel injection rate K from falling below the lower limit value. .

Next, another embodiment of the present invention will be described with reference to FIG. In the embodiment of FIGS. 4 and 5, purging is focused on the fact that when the valve overlap amount of the intake / exhaust valve is large, intake air and purge gas are mixed well, and vaporized fuel distribution between cylinders does not vary. Even if the duty ratio of the control valve 15 is lower than the predetermined value, the purge is executed when the valve overlap amount is larger than the predetermined value.

However, as in the above embodiment, the application of the purge control based on the valve overlap amount is limited in the fixed valve timing engine having no variable valve timing device. On the other hand, the variation in fuel vapor distribution among cylinders is also affected by the fuel vapor concentration in the purge gas. That is, if the concentration of the evaporated fuel in the purge gas is low, the difference in the concentration of the evaporated fuel in the intake gas at the time of supplying the purge gas (when the purge control valve is opened) and at the time of the stop (when the purge control valve is closed) is small. Therefore, when the concentration of the evaporated fuel in the purge gas is low, the variation in the evaporated fuel supply amount between the cylinders becomes small even when the purge control valve operates at a low duty ratio.
Therefore, in the following embodiment, even when the duty ratio of the purge control valve is small, the purge is executed when the concentration of the evaporated fuel in the purge gas is low to increase the purge execution frequency.

FIG. 6 is a part of a flowchart showing the purge control routine of this embodiment. In this routine, the steps 409 and 601 of the routine of FIGS.
It is equivalent to the one replaced with. Therefore, in FIG. 6, only the portion related to the changed portion is shown, but other steps are the same as the steps in FIGS. 4 and 5. That is, FIG.
If the target duty ratio of the purge control valve is smaller than the predetermined lower limit value A (step 407: tDR
In <A), it is determined in step 601 whether or not the fuel injection rate K _i-1 at the time of executing the previous routine is equal to or larger than a predetermined upper limit value F,
When K _i−1 ≧ F, even if DR <A, the steps 411 and thereafter are executed to perform the purge. If K _i-1 <F in step 601, step 445.
Proceed to and prohibit the purge operation.

As described above, the fuel injection rate K (= TAU
The value of / TAUP) is set to a smaller value as the amount of evaporated fuel in the purge gas supplied to the engine increases. Therefore, if the value of the fuel injection K at the time of executing the previous routine is sufficiently small, it is considered that there is no variation in the evaporated fuel supply between the cylinders even if the duty ratio DR of the purge control valve this time is set smaller than the lower limit value. Therefore, in the present embodiment, the evaporated fuel concentration in the purge gas is estimated from the value of the fuel injection rate K, and when it is determined that the evaporated fuel concentration is small and the evaporated fuel supply amount between cylinders does not vary, the duty ratio is determined. Even if it is small, the purge is executed. The upper limit value F of K _{i-1 is} a value of the fuel injection rate corresponding to the evaporated fuel concentration that does not cause variations in the evaporated fuel supply amount between the cylinders, and is determined in detail by experiments or the like.

Next, another embodiment of the present invention will be described with reference to FIG. In the embodiment of FIGS. 4 to 6, the purge is prohibited when the duty ratio of the purge control valve is smaller than the lower limit and the valve overlap amount is small or when the evaporated fuel concentration in the purge gas is high. . For this reason, even if the precondition for purging (step 403 in FIG. 4) is satisfied during engine operation, purging may not be performed, and the frequency of purging may be reduced. Therefore, in the present embodiment, even when the purging is prohibited in the embodiment of FIGS. 4 to 6, the control duty ratio of the purge control valve is increased to prevent the variation in the evaporated fuel supply amount between the cylinders. To perform the purge.

As described above, the variation in the evaporated fuel supply amount between the cylinders when the purge control valve is operated at a low duty ratio varies between the purge control valve opening period and the intake air of each cylinder because the purge control valve opening interval becomes long. This occurs because the overlap time of the strokes varies greatly from cylinder to cylinder. Therefore, even if the duty ratio is low, the time T (see FIG. 2) of one cycle of the purge control valve opening / closing cycle is shortened without changing the duty ratio (that is, the pulse signal frequency supplied to the purge control valve is changed). (If set to a large value), the opening interval of the purge control valve becomes shorter, and the overlap time between the intake stroke of each cylinder and the purge control valve opening period is averaged, and the variation in the evaporated fuel supply amount between cylinders can be reduced. It will be possible. As is clear from FIG. 2, even if the frequency of the pulse signal changes, the flow rate of the purge gas passing through the purge control valve is kept the same if the duty ratio does not change.

On the other hand, if the frequency of the pulse signal is always set high, the number of times the purge control valve is opened / closed per unit time increases, so that the durability of the purge control valve deteriorates. Therefore, in the present embodiment, the deterioration of the durability of the purge control valve is prevented by increasing the frequency of the pulse signal and executing the purge only when the purge is prohibited in the embodiments of FIGS. 4 to 6. While increasing the purge frequency.

FIG. 7 shows a part of a flow chart when the above pulse frequency control is applied to the embodiment of FIG.
In FIG. 7 as well, parts not shown are the same as those in the flowcharts of FIGS. 4 and 5, so only the differences will be described here. In FIG. 7, when the target duty ratio tDR of the purge control valve is smaller than the lower limit value A in step 407, the evaporated fuel concentration in the purge gas at the time of executing the previous routine is determined in step 701 as in FIG. In the present embodiment, the evaporated fuel concentration is equal to or lower than a predetermined value (K _i-1 ≧
If it is F), the control pulse signal frequency DF of the purge control valve is set to a relatively low value N ₁ (for example, N ₁ = 10H).
z) and perform the purge. On the other hand, when the fuel vapor concentration is lower than the predetermined value (K _i-1 <F), from the N ₁ a pulse signal frequency DF in this embodiment for example G prohibit purging in the embodiment of FIG. 6 The purge is executed after setting the high frequency N ₂ (for example, N ₂ = 20 Hz). As a result, even if the duty ratio is low and the evaporated fuel concentration is high, the variation in the evaporated fuel supply amount between the cylinders is reduced, so that the purge can be executed. Further, the pulse signal frequency DF is increased because
Since it is only when both the conditions of steps 407 and 701 are satisfied, in the actual operation, the pulse signal frequency DF
Is increased relatively infrequently. Therefore, the durability of the purge control valve is not significantly reduced.

FIG. 8 shows a part of a flow chart when the pulse frequency control is applied to the embodiments of FIGS. 4 and 5. Since the flowchart of FIG. 8 is substantially the same as the flowchart of FIG. 7, detailed description thereof will be omitted. Next, FIG.
Another embodiment of the present invention will be described with reference to FIG. In the present embodiment, as in the embodiment of FIG. 6, even when the duty ratio of the purge control valve is small, the purge is executed when the concentration of the evaporated fuel in the purge gas is low. Even when the duty ratio is small and the evaporated fuel concentration is high, the purge is executed when the engine speed NE is high.
When the engine speed NE is high, the flow velocity of the intake air in the intake passage becomes high, so that the mixing of the purge gas injected into the intake passage and the intake air is promoted. Therefore, even when the duty ratio of the purge control valve is small and the evaporated fuel concentration in the purge gas is high, the variation in the evaporated fuel supply amount between the cylinders is small. Therefore, in the present embodiment, in addition to the embodiment of FIG. 6, even when the evaporated fuel concentration is high, the purge is executed when the engine speed is high, and the purge execution is performed as compared with the case of FIG. Increasing the frequency.

FIG. 9 is different only in that step 901 is added to the flowchart of FIG. That is,
In FIG. 9, when the evaporated fuel concentration is higher than the predetermined value in step 601 (K _i−1 ≧ F), next step 901
6 is different from FIG. 6 in that it is determined whether the engine speed NE is higher than a predetermined value G or not, and if NE> G, the process proceeds to step 411 and the purge is executed. Therefore, in the present embodiment, purging is prohibited only when NE ≦ G in step 901, that is, when the duty ratio is small, the evaporated fuel concentration is high, and the rotation speed is low. The purge execution frequency is further increased as compared with the embodiment.

FIG. 10 shows one modification of the embodiment shown in FIG. In this embodiment, step 9 in FIG.
Even if NE ≦ G in 01, the purge is not prohibited, and the pulse signal frequency DF of the purge control valve is set high before the purge is executed. As described above, by setting the pulse signal frequency DF high, the variation in the evaporated fuel supply amount between the cylinders is reduced. Therefore, in the present embodiment as well, if only the precondition (step 403 in FIG. 4) is satisfied, all Purging can be performed under operating conditions. Incidentally, N ₁ in step 1001, N ₂ in step 1003 is set to the same value as in FIG. Further, according to the present embodiment, the step of increasing the pulse signal frequency is step 407,
In addition to the condition of 601, the condition is further limited to the case where the condition of step 901 is satisfied. Therefore, the frequency of frequency increase is extremely low, and the deterioration of durability of the purge control valve is prevented.

[0074]

According to the invention described in each claim, when the engine operating state that affects the variation in the evaporated fuel supply amount between the cylinders is detected and it is determined that the variation is small,
By performing the purge even when the duty ratio of the control signal of the purge control valve is small, the purge execution frequency during operation can be greatly increased without complicating the device configuration and control. There is a common effect that it becomes possible.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of an embodiment of the present invention.

FIG. 2 is a diagram illustrating a duty ratio of a control pulse signal of a purge control valve.

FIG. 3 is a sectional view illustrating an example of the configuration of a variable valve timing device.

FIG. 4 is a part of a flowchart illustrating one embodiment of the purge control of the present invention.

FIG. 5 is a part of a flowchart illustrating one embodiment of the purge control of the present invention.

FIG. 6 is a part of a flow chart for explaining an embodiment of the purge control of the present invention different from that of FIGS. 4 and 5.

FIG. 7 is a part of a flow chart for explaining an embodiment of the purge control of the present invention different from that shown in FIGS. 4 and 5.

FIG. 8 is a part of a flowchart illustrating an embodiment of the purge control of the present invention, which is different from FIGS. 4 and 5.

FIG. 9 is a part of a flowchart illustrating an embodiment of the purge control of the present invention, which is different from FIGS. 4 and 5.

FIG. 10 is a part of a flowchart illustrating an embodiment of the purge control of the present invention, which is different from FIGS. 4 and 5.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Intake passage 10 ... Canister 11 ... Fuel tank 15 ... Purge control valve 20 ... ECU

Claims (6)

[Claims] 1. A canister for adsorbing evaporated fuel in a fuel tank of an internal combustion engine, a purge passage for introducing a purge gas from the canister to an engine intake passage, and a purge for opening and closing the purge passage according to a pulse signal supplied. A valve, control means for changing the duty ratio of the pulse signal supplied to the purge valve according to engine load conditions to control the flow rate of the purge gas passing through the purge passage, and the duty ratio of the pulse signal is lower than a predetermined lower limit value. Purge prohibition means for prohibiting purging by keeping the purge valve fully closed when it becomes low, and operation for detecting an engine operating state parameter that affects inter-cylinder variation in the amount of evaporated fuel sucked into each cylinder of the engine When the state detecting means and the engine operating state parameter are in a predetermined region, the purge inhibiting operation by the purge inhibiting means is performed. A fuel vaporization control device comprising: a purge execution unit that is stopped. 2. The engine includes variable valve timing means for changing the valve overlap of intake and exhaust valves according to engine operating conditions, the engine operating state parameter is a valve overlap amount, and the purge executing means is The purge prohibiting operation by the purge prohibiting means is stopped when the valve overlap amount is larger than a predetermined value.
The fuel evaporation control device as described in 1. 3. The engine operating condition parameter is a concentration of evaporated fuel in the purge gas, and the purge execution means purges by the purge prohibiting means when the concentration of evaporated fuel in the purge gas is equal to or lower than a predetermined upper limit value. The fuel evaporation control device according to claim 1, wherein the prohibited operation is stopped. 4. The purge execution means further sets the frequency of the pulse signal supplied to the purge valve when the vaporized fuel concentration in the purge gas is higher than the upper limit value when the vaporized fuel concentration is equal to or lower than the upper limit value. The fuel vaporization control device according to claim 3, wherein the fuel vaporization control device is set to a higher value than in a certain case, and the purge prohibiting operation by the purge prohibiting means is stopped. 5. The engine operating state parameter is a concentration of evaporated fuel in purge gas and an engine speed, and the purge execution means is used when the concentration of evaporated fuel in purge gas is equal to or lower than a predetermined upper limit value, and The fuel evaporation control device according to claim 1, wherein when the fuel concentration is higher than the upper limit value and the engine speed is equal to or higher than a predetermined lower limit value, the purge prohibiting operation by the purge prohibiting means is stopped. 6. The purge executing means further sets the frequency of the pulse signal supplied to the purge valve when the fuel vapor concentration in the purge gas is higher than the upper limit value and the engine speed is lower than the lower limit value, The fuel vaporization control device according to claim 5, wherein the vaporized fuel concentration is set to be higher than that when the vaporized fuel concentration is lower than the upper limit value, and the purge inhibiting operation by the purge inhibiting means is stopped.