JP4082004B2 - Canister purge system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a canister purge system, and more particularly to a canister purge system including a purge pump.
[0002]
[Prior art]
In order to prevent the vaporized fuel (fuel vapor) in the fuel tank of the internal combustion engine from being released into the atmosphere, an evaporation purge system is introduced in which the fuel vapor in the tank is guided to a canister containing an adsorbent such as activated carbon and once adsorbed on the adsorbent. Generally known. In such an evaporation purge system, in order to prevent the adsorbent in the canister from being saturated by the adsorbed fuel vapor, the canister and the engine intake passage are connected by the purge passage, and the air is sucked through the canister during engine operation. Inhalation into the passage. As a result, the fuel vapor adsorbed by the adsorbent is desorbed (purged) by the intake air, and is sucked into the engine together with the intake air to burn.
[0003]
That is, by connecting the canister to the atmosphere and the engine intake passage at the same time, the negative pressure in the intake passage causes the atmosphere to pass through the adsorbent in the canister and be sucked into the intake passage from the purge passage, and the air is removed from the adsorbent in the canister. When passing, the fuel vapor adsorbed by the adsorbent is desorbed from the adsorbent, and a mixture of air and fuel vapor (purge gas) flows into the intake passage from the purge passage. The fuel vapor that has flowed into the intake passage is sucked into the combustion chamber of the engine together with the engine intake air, so that the fuel vapor from the canister burns in the engine combustion chamber without being released to the atmosphere.
[0004]
However, since the purge gas is sucked from the canister by the negative pressure in the engine intake passage in the normal purge system, there is a problem that the canister cannot be purged in an engine having a small negative pressure generated in the intake passage.
For example, an in-cylinder fuel injection valve that directly injects fuel into the cylinder is provided, fuel is injected into the cylinder during the cylinder compression stroke, and an air-fuel ratio mixture in the combustible range is stratified only in the vicinity of the spark plug. In an engine or the like that performs lean combustion operation at an air / fuel ratio extremely higher than the stoichiometric air / fuel ratio, the intake air amount is not adjusted by the throttle valve in principle during lean combustion operation.
[0005]
For this reason, the throttle valve is almost fully opened during the lean combustion operation, and almost no negative pressure is generated in the intake passage.
In such an engine, a canister purge using intake negative pressure cannot be performed during lean combustion operation. For example, a purge pump that forcibly purges the fuel vapor in the canister into the intake passage is used.
An example of a canister purge system using a purge pump is described in, for example, Japanese Patent No. 2900704.
The purge system of the publication is configured such that a purge pump forcibly sucking fuel vapor in the canister and sending it to the intake passage is provided on a purge passage connecting the intake passage and the canister. The purge system disclosed in this publication suppresses fluctuations in fuel vapor concentration in the purge gas supplied to the intake passage by circulating a part of the purge gas discharged from the purge pump to the suction side of the purge pump. It is a thing.
[0006]
[Problems to be solved by the invention]
The apparatus of Japanese Patent No. 2900704 effectively prevents the fuel vapor from being released to the atmosphere without being adsorbed by the canister by purging the canister during engine operation.
However, although the apparatus of the above-mentioned Japanese Patent No. 2900704 can effectively purge the canister while the engine is operating, there is a problem that it is impossible to prevent the fuel vapor from being diffused from the intake passage after the engine is stopped.
[0007]
After the engine of the internal combustion engine is stopped, fuel paper is generated in the engine intake passage due to various causes. For example, when the fuel supplied to the cylinder combustion chamber during operation of the engine stays in the cylinder without being combusted when the engine is stopped, the fuel evaporates in the cylinder after the engine is stopped, and fuel paper is generated. Therefore, if there is a cylinder in which the intake valve is open when stopped, the fuel vapor flows out of the cylinder and the fuel vapor is filled in the intake passage. Further, if the fuel adhering to the intake port wall surface during operation of the engine remains in a liquid state when the engine is stopped, the fuel adhering to the wall surface evaporates after the engine stops and fuel vapor is formed in the intake passage. Furthermore, in an engine having a fuel injection valve, the fuel that has accumulated in the fuel injection valve after the engine has stopped may slightly leak into the intake passage and form fuel vapor in the intake passage.
[0008]
Thus, when fuel vapor is generated in the intake passage after the engine is stopped, the generated fuel vapor is filled in the intake passage, and further leaks into the atmosphere from the opening (intake port) of the intake passage. May cause air pollution due to hydrocarbons.
In view of the above problems, an object of the present invention is to provide a canister purge system capable of preventing fuel vapor from being released from the intake passage after the engine is stopped as well as during engine operation.
[0009]
[Means for Solving the Problems]
According to the first aspect of the present invention, a canister that adsorbs evaporated fuel in a fuel tank of an internal combustion engine, a vapor passage that connects a fuel liquid level upper space in the fuel tank to the canister, the canister and the engine Operates independently of the engine operation, supplying a purge passage connecting the intake passage, an atmospheric port communicating the canister and the atmosphere, and supplying gas in the intake passage to the canister via the purge passage And a purge pump control means for operating the purge pump and supplying fuel vapor staying in the engine intake passage into the canister after the engine is stopped. The purge pump is a pump capable of reverse rotation, and the purge pump control means operates the purge pump in the normal rotation direction during operation of the engine to move the fuel vapor in the canister through the purge passage. A canister purge system for operating the purge pump in the reverse direction when supplying fuel vapor to the engine intake passage and staying in the engine intake passage after the engine stops Is provided.
[0010]
That is, according to the first aspect of the present invention, a purge pump is provided for supplying the fuel vapor staying in the engine intake passage to the canister. The purge pump is driven by a drive source that can operate independently of the engine operation, such as an electric motor, and can operate even after the engine is stopped. Therefore, the fuel vapor generated in the intake passage after the engine is stopped is sent to the canister by operating the purge pump, and is adsorbed by the adsorbent in the canister. This prevents the fuel vapor from being diffused from the intake passage after the engine is stopped.
[0012]
In the invention of claim 1, The purge pump is a pump capable of both forward rotation operation and reverse rotation operation. When the purge pump is rotated forward during engine operation, the flow direction of the gas through the pump becomes the direction in which the fuel vapor in the canister flows into the intake passage, and the canister is purged. When the purge pump is operated in reverse after the engine is stopped, the gas flow through the pump is directed from the intake passage to the canister, and the fuel vapor staying in the intake passage is adsorbed by the canister. This makes it possible to prevent the fuel vapor from being released into the atmosphere not only during engine operation but also after the engine is stopped with a single purge pump.
[0013]
Claim 2 According to the invention described in (1), the purge pump is disposed on the purge passage. Claim 1 A canister purge system is provided.
[0014]
That is, Claim 2 In this invention, the purge pump is disposed on the purge passage connecting the intake passage and the canister. In this case, the fuel vapor in the canister is sent to the intake passage through the pump on the purge passage during the forward rotation of the pump, and the fuel vapor in the intake passage is reversed in the pump during the reverse rotation of the pump. And sent to the canister.
[0015]
Claim 3 The purge pump is connected to the atmospheric port of the canister, Claim 1 A canister purge system is provided.
[0016]
That is, Claim 3 In this invention, the purge pump is connected to the atmospheric port of the canister. In this case, during the forward rotation of the pump, the air is pumped into the canister by the purge pump, the fuel vapor adsorbed by the canister is desorbed, and flows into the intake passage from the purge passage. Further, when the pump is reversely operated, the air after the fuel vapor is removed by the canister is sucked from the canister and the inside of the canister becomes negative pressure. Thereby, the fuel vapor staying in the intake passage flows into the canister from the purge passage.
[0017]
Claim 4 According to the invention described in the above, the purge pump control means stops the operation of the purge pump when the engine temperature after engine stop is equal to or lower than a predetermined temperature. Claims 1 to 3 A canister purge system according to any one of the above is provided.
[0018]
That is, Claim 4 In this invention, the operation of the purge pump is stopped when the engine temperature after the engine stops is equal to or lower than a predetermined temperature. When the engine temperature is low, the intake passage wall surface temperature is also lowered accordingly. For this reason, when the engine temperature is low, the vapor pressure of the fuel in the intake passage also becomes low and the evaporation of the fuel remaining in the intake passage hardly occurs. In this state, almost no fuel vapor is discharged from the intake passage to the outside, so that the fuel vapor does not diffuse into the atmosphere even when the purge pump is stopped. Therefore, in the present invention, when the engine temperature is lowered to such an extent that the fuel vapor is not released into the atmosphere, it is possible to reduce the pump drive energy by stopping the purge pump. The engine temperature can be detected, for example, by directly measuring the intake passage wall surface temperature, but the cooling water temperature, the intake air temperature, the intake air temperature in the intake passage, or the like is any one of the engine temperature and the like. One or more may be detected and used as a parameter representing the engine temperature.
[0019]
Claim 5 According to the invention described above, the purge pump control means stops the purge pump after continuing the operation of the purge pump after stopping the engine for a predetermined time, and increases the engine temperature after stopping the engine for the predetermined operating time. Set it short, Claims 1 to 3 A canister purge system according to any one of the above is provided.
[0020]
That is, Claim 5 In this invention, the purge pump is operated only while fuel vapor is actually generated in the intake passage. The amount of fuel vapor generated in the intake passage increases as the engine temperature after the engine stops increases. For this reason, when the engine temperature after the stop is high, the fuel remaining in the intake passage evaporates in a relatively short time and becomes fuel vapor. For this reason, when the purge pump is operated after the engine is stopped, the higher the engine temperature, the shorter the total amount of fuel remaining in the intake passage is adsorbed to the canister in the form of fuel vapor, and thereafter the fuel in the intake passage. No vapor is generated. In the present invention, it is possible to reduce pump drive energy by operating the purge pump only while fuel vapor is generated in the intake passage.
[0021]
Claim 6 According to the invention described above, the purge pump control means starts the operation of the purge pump after a lapse of a predetermined delay time after the engine stop, and sets the predetermined delay time based on the engine temperature at the time of the engine stop. , Claims 1 to 3 A canister purge system according to any one of the above is provided.
[0022]
That is, Claim 6 In this invention, the purge pump is started at the timing when the fuel vapor generated in the intake passage actually reaches the connection portion between the purge passage and the intake passage. The purge pump sucks fuel vapor from the intake passage through the purge passage. However, while fuel vapor occurs mainly near the intake port of the intake passage, the connection (purge port) between the intake passage and purge passage is located away from the intake port, so it occurs near the intake port. There is a delay time until the fuel vapor reaches the purge port. This delay time is short, for example, when the engine temperature is high and fuel vapor is generated rapidly and in large quantities after the engine is stopped, and is long when the engine temperature is low and the amount of generated fuel vapor is small. In this embodiment, the purge pump operation delay time is set based on the engine temperature when the engine is stopped, so that the purge pump operation can be started at the timing when the fuel vapor actually reaches the purge port. As a result, the purge pump can be operated at a truly necessary timing, and the drive energy of the pump can be reduced.
[0023]
Claim 7 According to the invention described above, the purge pump control means further operates the purge pump in response to an increase in the engine temperature when the engine temperature has increased since the engine stopped after the engine stopped. Claims 1 to 6 A canister purge system according to any one of the above is provided.
[0024]
That is, Claim 7 In this invention, when the engine temperature rises after the engine is stopped, the purge pump is operated in the reverse direction. For example, when the engine temperature is low when the engine is stopped, most of the fuel remaining in the intake port does not evaporate and remains in the intake port. For this reason, even if the purge pump is operated when the engine is stopped, the fuel remaining in the intake port cannot be eliminated. However, the fuel remaining in the intake port at low temperatures also evaporates and becomes fuel vapor when the engine temperature (intake port temperature) becomes higher than when the engine is stopped, for example, due to a rise in temperature or radiant heat from direct sunlight. May leak. In the present invention, in order to prevent the fuel vapor from being released due to the engine temperature increase, the purge pump is operated in accordance with the temperature increase when the engine temperature has increased since the engine stopped. Here, “activate the purge pump in response to the temperature rise” not only starts the operation of the purge pump when the temperature rises by a certain rise width, but also, for example, It also includes changing the operation duration, or operating the purge pump each time the engine temperature rises by a predetermined increase after the engine is stopped. In the present invention, when the purge pump is operated according to the engine temperature rise from the time when the engine is stopped as described above, when the engine temperature is low and a relatively large amount of fuel remains in the intake port in the liquid state when the engine is stopped. However, it is possible to reliably prevent the fuel vapor from being released into the atmosphere.
[0025]
Claim 8 Further, after the engine is stopped, the purge pump control means performs the reverse operation of the purge pump, and the internal pressure of the purge system including the purge passage, the canister, and the fuel tank is set to the atmospheric pressure and a predetermined pressure. Adjusted to a value that causes a difference, and then sealed the purge system, and equipped with an abnormality diagnosis device for judging the presence or absence of leakage in the purge system based on the change in the purge system internal pressure after sealing, Claim 1 A canister purge system is provided.
[0026]
That is, Claim 8 In this invention, when the presence or absence of leakage in the purge system is determined after the engine is stopped, the pressure difference between the atmosphere and the purge system is generated by operating the purge pump in the reverse direction. For example, when detecting the presence or absence of leakage in the purge system, the purge system internal pressure is adjusted to a negative pressure or a positive pressure that generates a differential pressure from the atmospheric pressure and then sealed, and air enters the purge system through the leak. Alternatively, an abnormality diagnosis operation for measuring a change in the purge system internal pressure due to the outflow of gas from the inside to the atmosphere is performed. In this case, by operating the purge pump in the reverse direction to generate a differential pressure between the purge system and the atmosphere, fuel vapor in the purge system is prevented from entering the intake system due to abnormality diagnosis. For example, in the configuration in which the purge pump is arranged in the purge passage, the purge pump is operated in the reverse direction to suck air from the intake passage and pump it to the canister, so that the inside of the purge system becomes positive pressure. Further, in the configuration having the purge pump connected to the atmospheric port, the inside of the canister is made negative pressure by releasing the air in the canister to the atmosphere. Therefore, in either case, a flow from the intake passage toward the canister occurs during reverse operation of the purge pump, and the canister or the fuel vapor in the purge system does not enter the intake passage when the abnormality diagnosis is performed.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram showing a schematic configuration of an embodiment in which the present invention is applied to a purge system for an automobile internal combustion engine. In FIG. 1, reference numeral 100 denotes an internal combustion engine main body, 1 denotes an intake passage of the internal combustion engine 100, and 3 denotes an air cleaner disposed in the intake passage 1. The intake passage 1 is provided with a throttle valve 6 having an opening degree corresponding to the driver's operation of an accelerator pedal (not shown). In the present embodiment, the engine 100 is an engine capable of lean air-fuel ratio operation, and performs lean air-fuel ratio combustion in a specific operation region.
[0028]
During the lean air-fuel ratio operation, fuel is injected from the fuel injection valve 101 into the cylinder during the compression stroke, and a combustible air-fuel ratio mixture is stratified only in the vicinity of an ignition plug (not shown) in the cylinder. Ignition. As a result, combustion is possible in which the ratio (air-fuel ratio) between air and fuel supplied into the cylinder is extremely higher (lean) than the stoichiometric air-fuel ratio. During the lean air-fuel ratio operation of the engine 100, the throttle valve 6 is set to an opening that is almost fully open, and intake throttle loss is reduced. For this reason, almost no negative pressure is generated on the downstream side of the throttle valve 6 in the intake passage 1 during the lean air-fuel ratio operation.
[0029]
Reference numeral 11 in FIG. 1 denotes an engine fuel tank. The fuel oil in the tank 11 is boosted by the fuel pump 70 and is pumped to the fuel injection valve 101 of each cylinder of the engine 100 via the feed pipe 71.
The fuel tank 11 is provided with an oil supply pipe 111 for supplying oil into the tank. Further, a breather pipe 13 serving as a vapor passage that connects a space above the fuel oil level in the tank 11 to a canister 10 described later is connected to the upper portion of the tank 11.
[0030]
A vent valve 131, a COV (CUT OFF VALVE) 132 and a ROV (ROLL OVER VALVE) 133 each including a float valve are provided at a connection portion between the breather pipe 13 and the tank 11. The vent valve 131 is opened when the internal pressure of the fuel tank 11 becomes slightly higher than the internal pressure of the breather pipe 13, and allows the air containing the fuel vapor in the tank 11 to flow through the breather pipe 13 to the canister.
[0031]
Further, the ROV 133 is closed due to a rise in the liquid level during refueling, and disconnects the connection between the vent valve 131 and the fuel tank 11. The ROV 133 also has a function of closing a connection portion between the vent valve 131 and the tank 11 when the vehicle falls or the like and preventing a large amount of fuel oil from leaking to the outside through the breather pipe 13.
The COV 132 is arranged in parallel with the ROV 133 and shuts off the communication between the vent valve 131 and the tank 11 when the liquid level rises further than the ROV 133. When the liquid level rises during refueling, the COV 132 is opened even after the ROV 133 is closed and the tank 11 and the vent valve 131 are communicated. However, when the liquid level reaches the COV 132 position due to the fluctuation of the liquid level due to vehicle turning When the vehicle falls, the valve is closed and the fuel oil has a function of preventing the fuel oil from entering the breather pipe 13 through the vent valve 131.
[0032]
Reference numeral 30 in FIG. 1 denotes an engine electronic control unit (ECU). The ECU 30 includes a microcomputer having a known configuration in which a ROM (read only memory), a RAM (random access memory), a CPU (microprocessor), and an input / output port are connected to each other via a bidirectional bus. In addition to the above basic control, in this embodiment, a failure diagnosis operation of the purge system described later is performed.
[0033]
For the above control, the output port of the ECU 30 is connected to the fuel injection valve 101 of the engine 100 via a drive circuit (not shown), and controls the fuel injection amount from the fuel injection valve. The actuator is connected to an actuator of CCV (CANISTER CLOSEURE VALVE) 17 to control the operation of these valves.
In addition, signals representing the engine speed, the intake air amount, the engine coolant temperature, and the like are input to the input port of the ECU 30 from sensors (not shown), and from a pressure sensor 33 provided in the fuel tank 11. A signal corresponding to the pressure in the upper liquid level space of the fuel tank 11 is input.
[0034]
A canister for adsorbing fuel vapor in the fuel tank is indicated by 10 in FIG. The canister 10 is connected to the fuel liquid level upper space of the fuel tank 11 by a breather pipe 13 and the intake passage 1 by a purge pipe 14 as a purge passage. 1 is a purge control valve 15 arranged at a connection portion between the purge pipe 14 and the intake passage 1. The purge control valve 15 includes an appropriate type of actuator such as a solenoid actuator, and is opened by a signal from the ECU 30 to communicate the canister 10 and the intake passage 1.
[0035]
The canister 10 includes a container that accommodates a fuel vapor adsorbent 50 such as activated carbon therein, and a breather pipe 13, a purge pipe 14, and an air communication pipe 18 are connected to the canister 10.
The other end of the atmosphere communication pipe 18 opens near the fuel filler port of the tank 11, and the air filter 19 and the CCV 17 described above are provided on the atmosphere communication pipe 18. The air filter 19 removes foreign substances in the air flowing into the canister 10 from the atmosphere communication pipe 18 when purging is performed. The CCV 17 includes an appropriate type of actuator such as a solenoid actuator, and blocks communication between the atmosphere communication pipe 18 and the canister 11 in accordance with a control signal from the ECU 30.
[0036]
A purge pump 20 is provided on the purge pipe 14.
The purge pump 20 is a pump of the type in which the suction and discharge directions are reversed depending on the rotation direction, such as a turbine pump (so-called Wesco pump).
[0037]
In the present embodiment, the purge pump 20 is provided with a drive source (not shown) such as an electric motor that can be operated independently of the operation of the engine, and can be operated even after the engine is stopped. Further, the drive source of the purge pump 20 is a reversible type, and the rotation direction of the purge pump 20 is the forward rotation direction (the direction in which gas is sent from the canister 10 side to the purge valve 15 side) and the reverse rotation direction (the purge valve 15 side). To the canister 10 side).
[0038]
Next, the function of the purge pump 20 in the present embodiment will be described.
When the purge gas cannot be supplied to the intake passage 1 such as when the engine is stopped, the purge control valve 10 is closed and the CCV 17 of the canister 10 is held in the open state. In this state, when the internal pressure of the fuel tank 11 rises due to the evaporation of fuel and reaches the valve opening pressure of the vent valve 131, the vent valve 131 is opened. As a result, an air-fuel mixture of fuel vapor and air flows into the canister 10 from the space above the liquid level of the fuel tank 11 via the breather pipe 13, passes through the adsorbent 50 in the canister 10, and is connected to the atmospheric communication pipe from the CCV 17. 18 flows into. Since the fuel vapor in the air-fuel mixture is adsorbed by the adsorbent when passing through the adsorbent 50, only air after the fuel vapor is removed by the adsorbent 50 in the canister 10 is released from the atmosphere communication pipe 18. become. This prevents the fuel vapor from being released into the atmosphere.
[0039]
When the amount of fuel vapor adsorbed on the adsorbent 50 increases, the adsorbent 50 is saturated with the fuel vapor and cannot evaporate any more. Therefore, in this embodiment, the adsorbent 50 is adsorbed by purging during engine operation. The removed fuel vapor is desorbed (purged).
In a normal engine, the canister 10 is purged by opening both the CCV 17 and the purge control valve 15 during operation of the engine 100 and introducing air into the canister 10. That is, in a normal engine, negative pressure is generated on the downstream side of the throttle valve 6 in the intake passage 1 during engine operation. Therefore, when the purge control valve 15 is opened during engine operation, a purge pipe 14 is provided in the canister 10. Thus, the negative pressure of the intake passage 1 acts, and the canister internal pressure becomes lower than the atmospheric pressure.
[0040]
For this reason, when the purge control valve 15 is opened, clean air from which foreign matter has been removed by the filter 19 from the atmospheric communication pipe 18 flows into the canister 10 via the CCV 17. The air separates the fuel vapor adsorbed when passing through the adsorbent 50 in the canister 10 from the adsorbent, and becomes a mixed gas (purge gas) of the fuel vapor and air from the purge pipe 14 through the purge control valve 15. It flows into the engine intake passage 1. Thus, the purge gas is purged from the adsorbent 50 and burned in the engine combustion chamber, and the adsorbent 50 is prevented from being saturated with the fuel vapor.
[0041]
However, in this embodiment, the engine 100 that performs lean air-fuel ratio combustion is used, and a negative pressure is hardly generated in the intake passage during the lean air-fuel ratio combustion operation of the engine 100. Therefore, during the lean air-fuel ratio combustion operation of the engine 100, it becomes difficult to suck the purge gas into the intake passage with the negative pressure of the intake passage. Therefore, in this embodiment, the purge pump 20 is disposed on the purge pipe 14 in order to purge the canister. During the engine operation, the purge pump 20 is driven in the forward rotation direction, sucks and raises the purge gas in the canister, and pumps the purge gas from the purge pipe 14 to the intake passage 1. As a result, air is sucked into the canister 10 from the atmosphere communication pipe 18 through the CCV 17, and the fuel vapor is purged from the adsorbent 50. Accordingly, the canister 10 is normally purged even during the lean combustion operation in which a negative pressure is hardly generated in the intake passage, and the adsorbent 50 is prevented from being saturated with the fuel vapor.
[0042]
As will be described later, instead of providing a purge pump on the purge pipe 14, an air pump is provided in the atmosphere communication pipe 18, the air is pumped into the canister to purge the adsorbent 50, and the purge gas is discharged into the intake passage 1. It is also possible to do so. As described above, the purge system can prevent the fuel vapor generated in the fuel tank 11 from being released to the atmosphere, but the fuel vapor generated in the intake passage, particularly the intake passage after the engine is stopped, is released to the atmosphere. Release cannot be prevented.
[0043]
For example, during engine operation, part of the fuel injected from the fuel injection valve 5 adheres in a liquid state to the intake port wall surface to form a wall-attached fuel. This wall-attached fuel gradually evaporates after the engine is stopped and becomes fuel vapor. Also, when the engine is stopped, a small amount of fuel held in the fuel injection valve may leak from the fuel injection valve to the intake port, so-called oil-tight leakage of the fuel injection valve may occur. The spilled fuel evaporates and becomes fuel vapor while the engine is stopped, like the wall-attached fuel. For this reason, after the engine is stopped, the fuel vapor generated at the intake port fills the intake passage 1.
When the fuel vapor is filled in the intake passage 1 while the engine is stopped, the fuel paper flows from the intake passage 1 through the filter element of the air cleaner 3 to the atmosphere, which may cause air pollution.
[0044]
In each embodiment described below, the above-described purge pump 20 is used to prevent the fuel vapor from being released to the atmosphere from the intake passage 1 after the engine is stopped.
Hereinafter, an embodiment of a vapor discharge prevention operation after the engine stop using the purge pump 20 in the canister purge system of FIG. 1 (hereinafter simply referred to as “vapor discharge prevention operation”) will be described.
[0045]
(1) First embodiment
First, the most basic embodiment of the vapor discharge preventing operation of the present invention will be described.
In the present embodiment, the purge pump 20 is operated in the reverse direction for a predetermined time after the engine is stopped. Further, while the purge pump 20 is operated in reverse, the purge control valve 15 is maintained in a fully opened state, and after a predetermined time has elapsed, the purge pump 20 is stopped and the purge control valve 15 is fully closed. The CCV 17 is kept fully open after the engine is stopped. As a result, the purge pump 20 sucks the gas (mixture of fuel vapor and air) in the intake passage 1 through the purge pipe 14 and pumps it to the canister 10 through the purge pipe 14.
[0046]
The fuel vapor in the gas sent to the canister 10 is adsorbed by the adsorbent 50, and only the air not containing the fuel vapor is released to the atmosphere through the CCV 17 and the atmosphere communication pipe 18. That is, the fuel vapor generated in the intake passage 1 is sent to the canister 10 by the purge pump 20 and is adsorbed by the adsorbent 50. After the engine 100 is stopped, the fuel vapor is released from the intake passage 1 to the atmosphere. Is prevented.
It should be noted that the time for reverse operation of the purge pump 20 after the engine is stopped is set in advance to a certain time sufficient to suck the entire amount of fuel vapor generated in the intake passage 1.
[0047]
FIG. 2 is a flowchart for specifically explaining the vapor discharge preventing operation of the present embodiment. This operation is performed as a routine executed by the ECU 30 at regular intervals.
In the operation of FIG. 2, it is first determined in step 201 whether or not the engine is currently stopped. If the engine is not stopped, that is, if the engine is currently operating, the routine proceeds to step 203 where normal control of the purge pump (forward operation) is performed, and normal purge of the canister is performed. In step 205, the value of the time counter CT is reset to zero.
[0048]
If the engine is currently stopped at step 201, the routine proceeds to step 207, where the value of the counter CT is incremented by one. Since the counter CT is always reset to zero in step 205 during operation of the engine, the value of CT increased in step 207 corresponds to the elapsed time from when the engine was stopped.
In step 209, it is determined whether or not the value of the increased counter CT has reached a predetermined constant value A, that is, whether or not a predetermined time corresponding to the counter value A has elapsed since the engine was stopped. . In step 211, the purge pump 211 is operated in the reverse direction until the predetermined time elapses after the engine is stopped, and the purge control valve 15 is kept fully open.
[0049]
Thus, the fuel vapor generated in the intake passage 1 after the engine is stopped is sent to the canister 10 by the purge pump 20 and is adsorbed by the adsorbent 50. On the other hand, when the elapsed time from the engine stop reaches the predetermined time in step 209, next step 213 is executed, the operation of the purge pump 20 is stopped and the purge control valve 15 is closed.
The counter value A in step 209 is set to a value corresponding to the time required for all the fuel in the intake passage 1 to become vapor after the engine stops and be sent from the intake passage to the canister 10 by the purge pump 20. Since this value varies depending on the type of the intake passage 1 and the engine, it is preferable to set in detail by experiments using an actual engine and the intake passage.
[0050]
(2) Second embodiment
Next, a second embodiment of the vapor discharge preventing operation of the present invention will be described.
In the present embodiment, as in the first embodiment, the purge pump is operated in the reverse direction for a certain period of time after the engine is stopped, and the fuel vapor in the intake passage is adsorbed to the canister. However, in this embodiment, the engine coolant temperature is a predetermined value T. ₀ In the case of the following, the operation of the purge pump is not started, and the cooling water temperature is the predetermined value T during the purge pump operation. ₀ In the following cases, the operation of the purge pump is stopped, which is different from the first embodiment.
[0051]
When the engine temperature decreases, the fuel remaining in the intake passage hardly evaporates and the fuel vapor concentration in the intake passage decreases. In this state, even if the purge pump is operated, the fuel vapor in the intake passage cannot be sucked efficiently, and not only the driving energy of the purge pump is wasted, but also the fuel vapor adsorbed on the canister 10 is consumed. May be purged by the air in the intake passage sent from the purge pump 20 and discharged from the atmosphere communication pipe 18. Further, in this state, if left unattended, the fuel vapor concentration in the intake passage is low, and no fuel vapor is released from the intake passage to the atmosphere.
[0052]
Therefore, in the present embodiment, the coolant temperature THW is detected as a parameter representing the engine temperature, and the THW is determined to be a predetermined temperature T ₀ In the following cases, wasteful power consumption is prevented by stopping the purge pump.
[0053]
FIG. 3 is a flowchart specifically showing the vapor discharge operation of the present embodiment. This operation is performed as a routine executed by the ECU 30 at regular intervals.
The operation of FIG. 3 is different from the operation of FIG. 2 only in that steps 307 and 309 are added. That is, in this embodiment, the engine coolant temperature THW is read in step 307, and THW is set to a predetermined value T in step 309. ₀ (T ₀ Is a temperature that is low enough to prevent vapor from the fuel in the intake passage from leaking to the outside due to a drop in the fuel vapor pressure, for example, the cooling water temperature is set to about 10 ° C. In step 317, the operation of the purge pump 20 is stopped and the purge control valve 15 is fully closed. And the coolant temperature THW is T ₀ Only when it is higher, the operation from step 311 is performed, and the purge pump 20 is operated until a predetermined time elapses. The operations in steps 301 to 305 and steps 311 to 317 in FIG. 3 are the same as those in steps 201 to 205 and steps 207 to 213 in FIG.
In the present embodiment, consumption of the driving energy of the purge pump can be reduced without causing fuel vapor discharge from the intake passage by the above operation.
[0054]
(3) Third embodiment
Next, a third embodiment of the vapor discharge preventing operation of the present invention will be described.
In the first embodiment described above, the operation of the purge pump is started simultaneously with the engine stop, and the purge pump is always operated for a certain time. However, in reality, the amount of fuel vapor generated in the intake passage is affected by the engine temperature, particularly when the engine is stopped.
[0055]
For example, when the engine temperature is high when the engine is stopped, the fuel remaining in the intake port suddenly evaporates after the engine is stopped, so that a large amount of fuel vapor is generated in a short time. Further, since the purge pipe 14 is connected to the intake passage 1 at a position relatively away from the intake port, the fuel vapor generated at the intake port reaches the connection portion of the purge pipe 14 for a certain time after the engine stops. However, the time to reach the fuel vapor becomes shorter as the amount of fuel vapor generated increases. Further, since the amount of fuel vapor generated (generation speed) increases as the temperature of the engine increases, the fuel remaining in the intake port is completely vaporized in a short time.
[0056]
On the other hand, when the engine temperature is low when the engine is stopped, the fuel injection amount is warmed up before the stop, and the amount of fuel adhering to the wall surface of the intake port is higher than when the temperature is high. Further, since the engine is at a low temperature, the fuel vaporization rate is slower than that at the high temperature, and it takes a long time for the entire amount to vaporize. Further, the fuel vapor generated at the intake port reaches the intake passage connection portion of the purge pipe 14 as compared with the high temperature.
[0057]
Therefore, in this embodiment, the operation of the purge pump is not started immediately after the engine is stopped, and the operation of the purge pump is started after a certain delay time B has elapsed from the stop of the engine. This delay time corresponds to the time until the fuel vapor generated at the intake port reaches the connection portion of the purge pipe 14 and the fuel vapor is actually sucked into the purge pump 20. Therefore, the higher the engine temperature (cooling water temperature) when the engine is stopped, the shorter the engine temperature is set.
Further, the higher the engine temperature when the engine is stopped, the shorter the time for vaporization of the entire amount of fuel. Therefore, the operation duration time of the purge pump 20 is set shorter as the engine temperature (cooling water temperature) when the engine is stopped is higher.
[0058]
Thereby, in this embodiment, it becomes possible to operate the purge pump 20 at the timing and time when it is truly required, and it is possible to prevent wasteful consumption of the drive energy of the purge pump. Yes.
[0059]
FIG. 4 is a flowchart for specifically explaining the vapor discharge preventing operation of the present embodiment. This operation is performed as a routine executed by the ECU at regular intervals.
In the operation of FIG. 4, first, at step 401, the engine coolant temperature THW is read. In step 403, it is determined whether or not the engine is currently stopped. If the engine is in operation, the process proceeds to step 405, and the coolant temperature THW read in step 401 is changed to THW. ₀ Remember as. Then, in step 407, normal purge pump control is performed, and in step 407, the time counter CT is reset in the same manner as in the operations of FIGS. In step 405, the latest coolant temperature is always THW only when the engine is in operation. ₀ Will be stored as THW after the engine is stopped ₀ The value of represents the coolant temperature when the engine is stopped.
[0060]
If the engine is stopped in step 403, the current cooling water temperature read in step 401 in step 411 (not the cooling water temperature when the engine is stopped) is a predetermined value T. ₀ (T ₀ ≒ 10 ℃) ₀ If it is below, the routine proceeds to step 421, where the operation of the purge pump 20 is stopped and the purge control valve 15 is fully closed. That is, also in this embodiment, as in the second embodiment, the purge pump 20 is not operated when the engine temperature after the engine is stopped is low.
[0061]
In step 413, THW> T ₀ In step 413, the operation start timing and stop timing of the pump 20 are the cooling water temperature THW when the engine is stopped stored in step 405. ₀ To be determined.
The start and stop timings of the purge pump 20 are set as the value of the counter CT as in the above-described embodiments. FIG. 5 shows the coolant temperature THW when the engine is stopped. ₀ FIG. 6 is a diagram showing a relationship between a purge pump 20 operation start counter value B and an operation stop counter value C.
[0062]
As shown in FIG. 5, the counter values B and C (where B <C) are both the coolant temperature THW when the engine is stopped. ₀ The higher the value, the smaller the value, but the difference between C and B is also THW ₀ The higher the value, the smaller. That is, as the cooling water temperature when the engine is stopped is higher, the time B until the operation of the purge pump 20 is started after the engine is stopped becomes shorter, and the operation time (C−B) of the purge pump 20 is also shorter. Since it becomes shorter, it becomes possible to operate the purge pump 20 for a truly necessary period.
[0063]
After the counter values B and C are determined as described above, in step 415, the value of the counter CT is increased by 1. Also in the present embodiment, the CT value represents the elapsed time from the engine stop as in the above-described embodiments.
In steps 417 to 423, the purge pump 20 is operated and the purge control valve 15 is kept open only when the value of the counter CT is B <CT ≦ C. When CT <B and CT> C, the purge pump 20 is stopped and the purge control valve 15 is closed. As a result, the purge pump 20 starts operation when the time corresponding to the counter value B has elapsed after the engine has stopped, and stops when the time corresponding to the counter value B has elapsed. Only the purge pump 20 is operated.
[0064]
(4) Fourth embodiment
Next, a fourth embodiment of the present invention will be described.
In each of the above-described embodiments, the purge pump is operated only once when the engine is stopped, and the fuel vapor is recovered from the intake passage to the canister. However, except for the case where the engine temperature is high when the engine is stopped and the entire amount of fuel remaining in the intake port is recovered as vapor, fuel that has not evaporated even after the purge pump is stopped remains in the intake port. As described above, this residual fuel is not released into the atmosphere as fuel vapor unless the engine temperature becomes high.
[0065]
However, when the engine temperature rises due to the temperature change after the engine stops or the influence of direct sunlight, the fuel remaining in the intake port may evaporate and the fuel vapor may be released to the atmosphere.
In this embodiment, even when the purge pump is operated immediately after the engine is stopped and the fuel vapor is collected into the canister, the engine temperature becomes higher than the temperature at the time of the stop while the engine is stopped. As the temperature rises, the purge pump is operated again to collect the fuel vapor in the canister. This prevents the fuel vapor from being released from the intake passage to the atmosphere even when the engine temperature rises after the engine is stopped.
[0066]
6 and 7 are flowcharts specifically explaining the vapor discharge preventing operation of the present embodiment. This operation is executed by the ECU 30 at regular intervals.
Steps 601 to 625 in FIG. 6 show the operation of the purge pump 20 immediately after the engine is stopped. The operation in FIG. 6 is substantially the same as the operation in FIG. 4 except that the operation of the flag XS in steps 609, 613, and 625 is added.
[0067]
That is, also in this embodiment, the coolant temperature when the engine is stopped is set to THW. ₀ (Step 605) and this THW ₀ Based on the above, the operation start timing B and the operation stop timing C of the purge pump 20 are determined based on the relationship of FIG. 5 (step 615). When the value of the counter CT reaches B after the engine is stopped, the operation of the purge pump 20 (and the opening of the purge control valve 15) is started (steps 627 and 629), and when the value reaches C, the operation of the purge pump 20 is stopped. (Steps 619 and 621). Further, the coolant temperature THW is a predetermined value T ₀ The point that the operation of the purge pump 20 is not performed in the following cases (steps 611 and 621) is the same as the operation of FIG.
[0068]
However, the operation of FIG. 6 is different in that the value of the flag XS is determined in step 613 and if XS = 1, the process proceeds to step 631 in FIG. 7 without executing step 617 and the subsequent steps. The flag XS is a flag indicating whether or not the first purge pump 20 operation immediately after the engine stop has been completed, and is always set to 0 together with the value of the counter CT during the engine operation (steps 610 and 609). It is set to 1 in step 625 when the immediately following purge pump operation is completed. At this time, the value of the counter CT is also reset to zero (step 623).
[0069]
That is, in the present embodiment, when the operation of the first purge pump 20 immediately after the engine stop is completed, the process proceeds to step 631 in FIG. 7 without executing steps 613 to 625 from the next time.
In step 631 in FIG. 7, the current coolant temperature THW read in step 601 is the coolant temperature THW when the engine is stopped. ₀ Then, it is determined whether or not the value is higher than a predetermined value E. If not higher than E, the process proceeds to step 643 to reset the value of the counter CT and the current operation is finished.
[0070]
On the other hand, in step 631, THW ≧ THW ₀ If it is + E, the value of the counter CT is increased in steps 633 to 637 (step 633), and the purge pump 20 is operated and the purge control valve 15 is opened until the CT value reaches the predetermined value D. (Steps 635 and 637). When D is reached, the purge pump is stopped and the purge control valve is closed (steps 635 and 639). When the counter value reaches D and the purge pump is stopped, the THW stored as the coolant temperature at the time of engine stop in step 641. ₀ Is increased by the predetermined value E.
That is, in this embodiment, the purge pump is operated immediately after the engine is stopped, and then the purge pump is operated again when the engine temperature (cooling water temperature) rises to a predetermined value. The temperature at which the operation of the purge pump is started is set higher by a predetermined value E than the temperature at which the purge pump was operated last time. Thus, the temperature at which the operation of the purge pump is started while the engine is stopped is gradually increased for the following reason.
[0071]
That is, when the operation of the purge pump is performed and completed immediately after the engine is stopped, the coolant temperature (THW at the time of engine stop) out of the fuel remaining in the engine intake port ₀ ), All components that become fuel vapor are vaporized and collected in the canister in the form of vapor. For this reason, the engine temperature once decreased after the engine stopped is again THW. ₀ Even if the temperature rises, the remaining fuel evaporates very little, and even if the purge pump is operated, the fuel vapor cannot be recovered in the canister. However, the engine temperature is THW ₀ If higher, the temperature THW ₀ Then, the remaining fuel that has not been vaporized is further vaporized, so that the fuel vapor is filled in the intake passage. Therefore, in the present embodiment, the second purge pump operation is performed when the coolant temperature THW is the temperature THW when the engine is stopped. ₀ This is performed when the value rises by a predetermined value E.
[0072]
When the second purge pump operation is completed, the coolant temperature THW of the fuel remaining in the intake port ₀ All components that vaporize at a temperature below + E are vaporized and all are recovered by the canister by the previous purge pump operation. ₀ Even when + E is reached, fuel evaporation hardly occurs.
Therefore, the temperature at which the third purge pump operation is started is set higher by E than the previous (second) start temperature.
[0073]
Thus, by setting the temperature at which the purge pump operation is started while the engine is stopped to be higher than the previous start temperature by E, the purge pump is actually operated even when there is no fuel vapor in the intake passage. Therefore, it is possible to prevent wasteful consumption of the driving energy of the purge pump and to prevent the canister from being purged by the operation of the purge pump and releasing the fuel vapor from the atmosphere communication pipe. .
[0074]
(5) Other embodiments
Next, modified examples of the first to fourth embodiments will be described.
In the third and fourth embodiments (FIGS. 4 to 7), during the purge pump operation immediately after the engine stops, the pump operation time (time corresponding to CB) depends on the coolant temperature when the engine stops. This time corresponds to a time sufficient to collect the entire amount of fuel vapor generated in the intake passage in the canister. However, when the entire amount of fuel vapor is recovered, the flow rate of the pump can be changed according to the amount of vapor instead of changing the operation time of the pump according to the amount of vapor.
[0075]
For example, in step 413 in FIG. 4 and step 615 in FIG. 6, the number of revolutions of the pump is made constant, and the operation time of the pump is made longer as the coolant temperature when the engine is stopped is higher. However, in reality, the higher the coolant temperature when the engine is stopped, the more rapidly fuel vapor is generated after the engine is stopped, and the fuel vapor recovery from the intake passage to the canister is completed in a short time. In this case, if the operation of the purge pump is continued for a long time after the fuel vapor recovery is completed, air is supplied from the purge pump to the canister, the fuel vapor adsorbed on the canister is purged, and the air communication pipe 18 from the CCV 17 is purged. There is a risk of being released to the atmosphere through. Therefore, for example, the capacity of the purge pump is controlled according to the generation of fuel vapor, and the capacity of the purge pump is increased when the amount of generated fuel vapor is large (that is, when high concentration fuel vapor exists in the intake passage). In addition, the operation time of the pump may be made shorter than in the case of FIGS. As a result, high concentration fuel vapor can be collected in a short time, and thereafter air can be prevented from being sent to the canister, and the fuel vapor can be completely prevented from being released into the atmosphere from the canister.
[0076]
The capacity of the purge pump can be adjusted, for example, by changing the voltage applied to the drive motor. In this case, the capacity of the pump can be increased by increasing the pump speed by increasing the voltage as the coolant temperature when the engine is stopped.
Further, for example, in the case of performing the purge pump operation for the second and subsequent times after the engine is stopped in FIG. ₀ The higher the + E), the higher the rotational speed of the pump. Alternatively, the operation time D (step 635) may be set shorter. Furthermore, instead of changing the pump speed when changing the flow rate of the purge pump, it is also possible to change the pump flow rate by changing the opening of the purge control valve 15.
[0077]
In the second to fourth embodiments, the case where the purge pump 20 is disposed between the purge control valve 15 and the canister 10 as shown in FIG. 1 has been described as an example. The arrangement is not limited to that of FIG.
[0078]
For example, FIG. 8 shows a configuration in which the purge pump 20 and the shutoff valve 20a are arranged in parallel with the CCV 17 in the atmospheric port of the canister 10. In the arrangement of FIG. 8, when sufficient negative pressure is generated in the intake passage 1 during engine operation, the purge pump 20 is stopped, the shutoff valve 20a is closed, and the CCV 17 is opened. As a result, air is introduced from the CCV 17 into the canister, and after the adsorbent 50 has been purged, it flows into the intake passage.
[0079]
On the other hand, when sufficient negative pressure is not generated in the intake passage during engine operation, the CCV 17 is closed, the shutoff valve 20a is opened together with the purge control valve 15, and the purge pump 20 is operated in the forward rotation direction. . As a result, air is pumped into the canister 10 by the purge pump 20, and the adsorbent 50 is purged.
On the other hand, when the engine is stopped, the CCV 17 is closed, the purge control valve 15 and the shut-off valve 20a are opened, and the purge pump 20a is operated in the reverse direction so that fuel is supplied from the intake passage 1 to the canister 10 via the purge pipe 14. Vapor can be recovered. Also in this case, the vapor discharge preventing operation of each of the above embodiments can be executed as it is.
[0080]
FIG. 9 shows an arrangement in the case where a purge pump dedicated to vapor discharge prevention operation is provided. As shown in FIG. 9, in this embodiment, the purge pump 20 is arranged on a branch passage 14 a that branches from the purge pipe 14 and communicates with the canister 10 (or the fuel tank 11). A shutoff valve 14b is disposed between the junction of the branch passage 14a and the junction.
In the present embodiment, the shutoff valve 14b is always opened during engine operation, and the purge pump 20 is not operated. That is, the canister is purged only by the negative pressure in the intake pipe during engine operation.
[0081]
When performing the vapor discharge prevention operation when the engine is stopped, the purge control valve 15 is opened, and the purge pump 20 is operated with the shut-off valve 14b closed. In this embodiment, the purge pump 20 operates only in one direction, that is, in a direction in which fuel vapor is sucked from the intake passage 1 through the purge pipe 14 and the branch passage 14a and is discharged to the canister 10 (or the fuel tank 11). The operation in the reverse direction is not performed. As a result, the fuel vapor in the intake passage can be collected in the canister or the fuel tank.
[0082]
(6) Purge system abnormality detection operation
Next, a purge system abnormality detection operation using the purge pump 20 will be described. In the present embodiment, the purge system is sealed in a state where a differential pressure is generated between the purge system internal pressure and the surrounding atmosphere by operating the purge pump 20 in the reverse direction after a predetermined time has elapsed after the engine is stopped. The presence or absence of leakage is determined based on the subsequent change in the purge system internal pressure.
[0083]
For example, as illustrated in FIG. 1, a configuration in which the purge pump 20 is disposed on the purge pipe 14 between the canister 10 and the intake passage 1 will be described as an example. The CCV 17 of the canister 10 is closed and purge control is performed after the engine is stopped. When the purge pump 20 is operated in the reverse direction with the valve 15 opened, fuel vapor or air is pumped from the intake passage 1 to the canister 10 by the purge pump 20. However, since the CCV 17 of the canister 10 is closed, the air flowing into the canister 10 is not released to the outside. Therefore, when the purge pump 20 is operated, the canister 10, the vapor passage 13, and the vapor passage are connected to the canister 10. The purge system composed of the fuel tank 11 and the like is pressurized.
[0084]
When the purge system internal pressure becomes a predetermined positive pressure, the purge control valve 15 is closed and when the pump 20 is stopped, the purge system is sealed in a pressurized state. In this state, if there is no leak in the purge system, the purge system internal pressure does not change. However, if there is a leak in the purge system, the gas in the purge system leaks to the outside through the leak, so the pressure in the purge system decreases. In addition, the rate of pressure decrease increases with the size of the leak.
[0085]
Therefore, the presence or absence of leakage in the purge system can be determined by measuring the pressure change (pressure drop rate) in a state where the purge system is pressurized and sealed.
However, in actuality, in a state where the purge system is sealed, if the temperature of the fuel in the fuel tank 11 is high, the fuel evaporates and the pressure in the tank rises. For this reason, if the amount of fuel evaporation is large, even if there is a leak, the pressure increase due to the fuel evaporation and the pressure drop due to the leakage may cancel each other out and the pressure drop may be reduced.
[0086]
Therefore, in this embodiment, even when the pressure drop in the purge system is small in a pressurized and sealed state, it is not immediately determined normal, and next, the amount of fuel vapor generated in the tank is measured.
The amount of fuel vapor generated is measured by sealing the purge system with the internal pressure lowered to near atmospheric pressure and measuring the change (increase rate) in the internal pressure. If the pressure inside the system is maintained at atmospheric pressure, the pressure difference between the outside and the purge system will be small, so even if there is a leaking part such as a hole in the purge system, intrusion of air from outside or leakage of gas from inside Does not occur. For this reason, the system pressure change when the purge system is sealed at atmospheric pressure is only due to the evaporation of fuel in the fuel tank, and the pressure change (rise) speed increases as the fuel vapor generation amount increases.
[0087]
In the present embodiment, when the internal pressure reduction rate measured by pressurizing and sealing the purge system is greater than a predetermined value, it is immediately determined that the purge system has leaked and more holes have occurred. However, if the internal pressure decrease rate under pressure sealing is smaller than the predetermined value, it is not immediately determined normal, and then the purge system is sealed at atmospheric pressure and the pressure change (rise) rate is measured. Determine the amount of fuel vapor generation. When the pressure increase rate is large (the amount of fuel vapor generated is large), there is a possibility that the internal pressure decrease rate is reduced due to the influence of the fuel vapor even though there are actually abnormalities such as leakage and holes. Therefore, when the measured pressure increase rate is large (the amount of fuel vapor generated is large), the normal determination is not performed and the determination is suspended.
[0088]
On the other hand, when the internal pressure rise rate of the purge system is small under the atmospheric pressure seal (the amount of fuel vapor generated is small), the internal pressure drop rate is small under the pressure seal, but there is actually no leakage or abnormality such as a hole. It can be judged that it was because of. Therefore, in this case, it is determined that the purge system is normal.
[0089]
10 and 11 are flowcharts for explaining the details of the purge system abnormality diagnosis operation. This operation is performed as a routine executed by the ECU 30 at regular intervals.
When the operation starts in FIG. 10, it is determined in step 1001 whether or not an abnormality diagnosis execution condition is currently satisfied.
[0090]
Here, the abnormality diagnosis execution condition determined in step 1001 is that (a) the engine is stopped, (b) a predetermined time has passed after the engine is stopped, and (c) the engine coolant temperature is It is that it is below a predetermined value, and (d) that an abnormality detection operation is not performed after the engine is stopped.
The condition (a) in step 1001 is that the purge pump 20 is operated in the opposite direction to the normal purge operation in this abnormality diagnosis operation, and the air in the intake passage is sent to the purge system. This is because if the negative pressure is generated in the intake passage, it may be difficult to pressurize the purge system.
[0091]
Further, the above conditions (b) and (c) are for performing an abnormality diagnosis in a state where a sufficient time has elapsed after the engine is stopped and the fuel temperature in the fuel tank has dropped to near the outside air temperature. As described above, when the fuel temperature in the fuel tank is high, the amount of fuel evaporation increases, and even if there is actually a leak in the purge system and there are no abnormalities such as holes, the determination is suspended and the normal determination May not be possible. On the other hand, since the high-temperature return fuel from the fuel injection valve flows into the fuel tank during engine operation, the temperature in the fuel tank is relatively high immediately after the engine is stopped, and the amount of fuel vapor generated is also large. However, when a sufficient time has elapsed after the engine is stopped and the coolant temperature is low, the fuel temperature in the fuel tank is also sufficiently low, so the amount of fuel vapor generated is small. For this reason, it is possible to increase the chances of normal determination by performing the abnormality diagnosis operation in a state where the conditions (b) and (c) are satisfied.
[0092]
Furthermore, the condition (d) is a condition for preventing wasteful consumption of the driving energy of the purge pump by executing the abnormality diagnosis operation many times.
If any one or more of the above conditions is not satisfied, the operation is immediately terminated and no abnormality diagnosis operation is performed. That is, only when all the conditions in step 1001 are satisfied, the abnormality diagnosis operation in step 1003 and subsequent steps is executed.
[0093]
In step 1003, it is first determined whether or not the detection of the pressure drop rate (ΔPL) of the purge system under pressure and sealing has been completed. As described above, the ΔPL measurement result leaks into the purge system and is used to determine whether there is an abnormality such as a hole.
If the measurement of ΔPL is not completed in step 1003, ΔPL is measured in steps 1005 to 1017 with the purge system pressurized and sealed.
[0094]
That is, in step 1005, the CCV 17 of the canister 10 is closed, and in steps 1007 to 1011, the pressure PT in the fuel tank 11 detected by the pressure sensor 33 is a predetermined positive pressure P. ₀ (For example, P ₀ The purge pump 20 is operated in the reverse direction with the purge control valve 15 opened (step 1009) until it reaches ≈20 mmHg (step 1007) (step 1011). As a result, the air in the intake passage 1 is sent to the canister 10 by the purge pump 20, and the purge system such as the canister 10, the vapor passage 13, and the fuel tank 11 is pressurized.
[0095]
The internal pressure PT of the fuel tank 11 becomes P by the reverse operation of the purge pump 20. ₀ Is reached, steps 1013 and 1015 are executed after step 1007, the purge control valve 15 is closed, and the operation of the purge pump 20 is stopped. Thereby, the purge system is sealed in a pressurized state.
In step 1017, the purge system internal pressure decrease width ΔPL (pressure decrease rate) within a predetermined time (for example, about 5 seconds) is measured from the change in the fuel tank internal pressure detected by the pressure sensor 33.
[0096]
If the measurement of ΔPL is completed in step 1017, or if the measurement of ΔPL has already been completed by the previous operation execution in step 1003, then in step 1019, the pressure decrease rate ΔPL is set to the predetermined value ΔPL. ₀ (For example, ΔPL ₀ Is a value of about several mmHg / 5 seconds) or more.
In step 1019, the pressure drop rate ΔPL is set to ΔPL ≧ ΔPL ₀ In this case, the internal pressure drop of the purge system under pressure and hermetic pressure is large, and even if the amount of fuel vapor generated in the fuel tank 11 is large, there is a leakage exceeding that. Accordingly, in this case, the process proceeds to step 1021, where it is immediately determined that an abnormality such as a leak has occurred in the purge system and a hole or the like has occurred (abnormality determination). In step 1023, the CCV 17 of the canister 10 is opened and the operation is performed. finish. Thereby, the purge system internal pressure returns to atmospheric pressure.
[0097]
On the other hand, in step 1019, ΔPL <ΔPL ₀ In this case, it seems that there is no abnormality such as leakage or hole since the rate of pressure reduction in the purge system is small under pressure and sealing. However, in this case, the actual fuel vapor generation amount is large and the pressure rises, so that there is a possibility that ΔPL is apparently small even though leakage, holes, and other abnormalities occur.
Therefore, in the present embodiment, ΔPL <ΔPL in step 1019. ₀ If NO, the normality determination is not performed immediately, and the process proceeds to step 1025 in FIG. 11 in order to measure the current fuel vapor generation amount ΔPV.
[0098]
That is, in this case, it is determined in step 1025 in FIG. 11 whether or not the measurement of the vapor generation amount ΔPV has already been completed by the previous time. If not, the purge system internal pressure PT is determined in steps 1027 to 1031. Predetermined value PT ₁ Until the following (step 1031), the CCV 17 of the canister 10 is opened (step 1027), and PT ≦ PT ₁ The CCV 17 is closed when PT ₁ Is a pressure slightly higher than atmospheric pressure. As a result, the internal pressure of the purge system that has been sealed under pressure is reduced, and the purge system has a predetermined pressure PT. ₁ It is sealed (atmospheric pressure sealed) in the following state.
[0099]
Step 1033 is a measurement operation of the fuel vapor generation amount ΔPV. In the present embodiment, the pressure increase range ΔPV in the system within a certain time (for example, about 15 seconds) in a state where the purge system is sealed under atmospheric pressure is detected by the pressure sensor 33, and this value is used as the fuel vapor generation amount. To do.
When the measurement of the fuel vapor generation amount ΔPV is completed as described above, or when the measurement of ΔPV has already been completed in the previous operation in step 1025, step 1035 is executed next. The fuel vapor generation amount ΔPV is executed. Is the predetermined value ΔPV ₀ It is determined whether or not it is larger. ΔPV ₀ Is set to a value of about several mmHg / 15 seconds, for example.
[0100]
In step 1035, ΔPV ≦ ΔPV ₀ If this is the case, that is, if the current amount of fuel vapor generation is small, it can be considered that the value of ΔPL measured in step 1017 was actually small because there was no leakage or hole. Therefore, in this case, the process proceeds to step 1037, and it is determined that there is no abnormality such as leakage into the purge system and holes (normal determination). In step 1035, ΔPV> ΔPV ₀ In such a case, the value of ΔPL measured in step 1017 is small because the amount of fuel vapor generated is large, and there is a possibility that an abnormality such as leakage to the purge system or a hole actually occurs. Therefore, in this case, the process proceeds to Step 1039, where neither normal determination nor abnormal determination is performed, and the determination is suspended.
[0101]
Even if the normal determination is made in Step 1037 and the determination is suspended in Step 1039, Step 1023 in FIG. 10 is executed next, the CCV 17 of the canister 10 is opened, and the abnormality diagnosis operation ends.
As described above, in this embodiment, the differential pressure is generated between the purge system internal pressure and the atmospheric pressure by operating the purge pump in the opposite direction to that during normal purge after the engine is stopped. For this reason, a flow from the intake passage toward the canister is always generated contrary to the normal purge. In the configuration of FIG. 1, the purge system abnormality diagnosis can be performed by operating the purge pump in the forward rotation direction to lower the purge system internal pressure and sealing it under a negative pressure. In this case, however, the canister As a result, the fuel vapor purged by the canister flows into the intake passage of the stopped engine.
[0102]
On the other hand, when the purge pump is operated in the reverse direction to generate a differential pressure between the purge system internal pressure and the atmospheric pressure as in the present embodiment, fuel vapor may flow from the canister into the intake passage. There is no. Therefore, according to the present embodiment, it is possible to prevent the fuel vapor from being released from the intake passage into the atmosphere at the time of abnormality diagnosis.
Further, in this embodiment, since the abnormality diagnosis of the purge system is performed after the fuel temperature in the fuel tank is sufficiently lowered after the engine is stopped, the influence of the fuel vapor generation amount on the abnormality diagnosis is reduced, and the accurate Abnormal diagnosis is possible.
[0103]
In the present embodiment, the configuration in FIG. 2 has been described as an example. For example, in the canister purge system in which the purge pump 20 is disposed on the atmosphere port side of the canister 10 as shown in FIG. As in the case of the configuration of FIG. 1, it is possible to perform an accurate abnormality diagnosis while preventing the fuel vapor from flowing into the intake passage by operating in the reverse direction.
[0104]
In this case, since the purge system internal pressure becomes negative by operating the purge pump 20 in the reverse direction, the operation of step 1017 in FIG. 10 measures the pressure increase rate ΔPL in a state where the purge system is sealed with negative pressure. . In this case, in step 1019 of FIG. 10, ΔPL ≦ ΔPL ₀ It is determined whether or not ΔPL ≦ ΔPL ₀ In this case, only the difference between FIG. 10 and FIG. 11 is that the normal determination is made immediately at step 1021 and the abnormality determination is made at step 1037 in FIG. 11 instead of the normal determination.
[0105]
【The invention's effect】
According to the invention described in each claim, there is a common effect that fuel vapor can be reliably prevented from being released into the atmosphere from the intake passage not only during engine operation but also after the engine is stopped. Also, Claim 8 In addition to the above-mentioned common effect, this invention also has an effect of reliably preventing fuel vapor from being released from the intake passage to the atmosphere when performing an abnormality diagnosis of the purge system after the engine is stopped.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a schematic configuration of an embodiment when the present invention is applied to a canister purge system for an internal combustion engine for an automobile.
FIG. 2 is a flowchart for explaining a first embodiment of a vapor discharge preventing operation.
FIG. 3 is a flowchart illustrating a second embodiment of a vapor discharge preventing operation.
FIG. 4 is a flowchart illustrating a third embodiment of a vapor discharge preventing operation.
FIG. 5 is a diagram illustrating setting of a pump operation time in the operation of FIG.
FIG. 6 is a part of a flowchart for explaining a fourth embodiment of a vapor discharge preventing operation;
FIG. 7 is a part of a flowchart for explaining a fourth embodiment of the vapor discharge preventing operation;
FIG. 8 is a view showing an arrangement example of a purge pump different from FIG.
9 is a view showing an example of arrangement of a purge pump different from those in FIGS. 1 and 8. FIG.
FIG. 10 is a part of a flowchart for explaining an abnormality diagnosis operation of the purge system.
FIG. 11 is a part of a flowchart for explaining an abnormality diagnosis operation of the purge system.
[Explanation of symbols]
1 ... Intake passage
10 ... Canister
11 ... Fuel tank
12 ... Vapor piping
14 ... Purge piping
15 ... Purge control valve
17 ... CCV
30 ... Electronic control unit (ECU)
33 ... Fuel tank pressure sensor

Claims (8)

A canister that adsorbs evaporated fuel in a fuel tank of an internal combustion engine, a vapor passage that connects a fuel liquid level upper space in the fuel tank to the canister, a purge passage that connects the canister and an engine intake passage, An atmospheric port that communicates the canister and the atmosphere, a purge pump that supplies the gas in the intake passage to the canister via the purge passage, operable independently of the operation of the engine, and after the engine stops, Purge pump control means for operating the purge pump and supplying fuel vapor that stays in the engine intake passage into the canister ,
The purge pump is a pump that can be operated in reverse, and the purge pump control means operates the purge pump in the normal rotation direction during the engine operation so that the fuel vapor in the canister passes through the purge passage through the engine intake passage. A canister purge system for operating the purge pump in the reverse direction when supplying fuel vapor that stays in the engine intake passage after stopping the engine into the canister . The canister purge system according to claim 1, wherein the purge pump is disposed on the purge passage. The canister purge system of claim 1, wherein the purge pump is connected to an atmospheric port of the canister. 2. The canister purge system according to claim 1, wherein the purge pump control unit stops the operation of the purge pump when the engine temperature after engine stop is equal to or lower than a predetermined temperature. The purge pump control means stops the operation of the purge pump after continuing the operation in the reverse direction of the purge pump after stopping the engine for a predetermined time, and sets the predetermined operating time shorter as the engine temperature after the engine stops is higher. The canister purge system according to any one of claims 1 to 3. The purge pump control means starts operation of the purge pump after a predetermined delay time has elapsed after the engine is stopped, and sets the predetermined delay time based on the engine temperature when the engine is stopped. The canister purge system according to claim 1. 7. The purge pump control unit according to claim 1, further comprising: operating the purge pump according to an increase in the engine temperature when the engine temperature has increased since the engine stopped after the engine stopped. 8. Canister purge system. Further, after the engine is stopped, the purge pump control means performs the reverse operation of the purge pump, and the internal pressure of the purge system including the purge passage, the canister, and the fuel tank is adjusted to a value that causes a predetermined pressure difference from the atmosphere. 2. The canister purge system according to claim 1, further comprising an abnormality diagnosis device that seals the purge system and determines whether the purge system leaks based on a change in the purge system internal pressure after the sealing.

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