Title: System and method for vaporized fuel processing
Abstract: An atmosphere-vented valve (a pressure relief section) is opened in a predetermined amount so as to reduce an inside pressure of a canister to a predetermined negative pressure (S14) while preventing an inside pressure in a fuel tank from becoming an excessively negative pressure by closing a charge passageway opening and closing valve (S18), and purging is controlled while the canister inside pressure is being reduced, whereby from a similar principle to that of vacuum distillation, the release of vaporized fuel from an absorbent is promoted so as not only to increase the purge efficiency but also to prevent the application of an unnecessary stress to the fuel tank.
Patent Number: 6,990,963 Issued on 01/31/2006 to Hara, et al.
| Inventors:
|
Hara; Takeshi (Saitama, JP);
Kitamoto; Masakazu (Saitama, JP);
Mihara; Hiroaki (Saitama, JP);
Yoshiki; Koichi (Saitama, JP);
Kubo; Satoru (Saitama, JP)
|
| Assignee:
|
Honda Motor Co., Ltd. (Tokyo, JP)
|
| Appl. No.:
|
892114 |
| Filed:
|
July 16, 2004 |
Foreign Application Priority Data
| Jul 18, 2003[JP] | P.2003-276492 |
| Current U.S. Class: |
123/520; 123/198.D |
| Current Intern'l Class: |
F02M 37/04 (20060101) |
| Field of Search: |
123/516,518,519,520,198.D
|
References Cited [Referenced By]
U.S. Patent Documents
| 5497754 | Mar., 1996 | Ito.
| |
| 6089080 | Jul., 2000 | Takaku et al.
| |
| 6405718 | Jun., 2002 | Yoshioka et al.
| |
| 6431156 | Aug., 2002 | Murakami et al.
| |
| 6814063 | Nov., 2004 | Kawano et al.
| |
| 6874484 | Apr., 2005 | Benjey.
| |
| Foreign Patent Documents |
| 09-151812 | Jun., 1997 | JP.
| |
Primary Examiner: Moulis; Thomas
Attorney, Agent or Firm: Arent Fox, PLLC.
Claims
What is claimed is:
1. A vaporized fuel processing system comprising:
a canister for storing an adsorbent;
a charge passageway which establishes a communication between a fuel tank and
the canister so as to charge vaporized fuel from the fuel tank into the canister
so that the vaporized fuel so charged is adsorbed onto the adsorbent in the canister;
a purge passageway which establishes a communication between the canister and
an induction system of an internal combustion engine so that the vaporized fuel
released from the adsorbent is purged into the induction system;
an atmospheric passageway which establishes a communication between the canister
and the atmosphere;
a purge control valve interposed along the length of the purge passageway for
opening and closing the purge passageway;
a charge passageway opening and closing valve interposed along the length of
the charge passageway for opening and closing the charge passageway;
a pressure relief section interposed along the length of the atmospheric passageway; and
a purge control section for controlling the opening of the purge control valve
so as to control the purging, wherein
the purge control section activates the pressure relief section so as to reduce
an inside pressure of the canister to a first predetermined negative pressure while
preventing an inside pressure of the fuel tank from becoming an excessively negative
pressure by closing the charge passageway opening and closing valve, whereby the
purging is controlled while the inside pressure of the canister is being relieved.
2. The vaporized fuel processing system as set forth in claim 1, further comprising:
a tank inside pressure detecting section for detecting the inside pressure of
the fuel tank, wherein
when the inside pressure of the fuel tank so detected is higher than a predetermined
pressure, the purge control section stops the operation of the pressure relief
section and opens the charge passageway opening and closing valve.
3. The vaporized fuel processing system as set forth in claim 1, further comprising:
a canister inside pressure detecting section for detecting the inside pressure
of the canister, wherein
when the inside pressure of the canister so detected is lower than the predetermined
negative pressure, the purge control section stops the operation of the pressure
relief section and opens the charge passageway opening and closing valve.
4. The vaporized fuel processing system as set forth in claim 1, further comprising:
a canister inside pressure detecting section for detecting the inside pressure
of the canister, wherein
the purge control section opens the charge passageway opening and closing valve
after the inside pressure of the canister has increased to a second predetermined
negative pressure when purge control is shifted from the purge control that is
implemented by relieving the inside pressure of the canister to a normal purge
control that is implemented by stopping the operation of the pressure relief section.
5. The vaporized fuel processing system as set forth in claim 1, wherein
the charge passageway opening and closing valve operates only between the fully
closed position and the fully opened position.
6. The vaporized fuel processing system as set forth in claim 1, wherein
the charge passageway opening and closing valve is capable to be set at any opening
between the fully closed position and the fully opened position.
7. A vaporized fuel processing method comprising the steps of:
storing an adsorbent in a canister;
communicating between a fuel tank and the canister by a charge passageway;
charging vaporized fuel from the fuel tank into the canister;
adsorbing the vaporized fuel so charged onto the adsorbent in the canister;
communicating between the canister and an induction system of an internal combustion
engine by a purge passageway;
purging the vaporized fuel released from the adsorbent into the induction system;
communicating between the canister and the atmosphere by an atmospheric passageway;
opening and closing the purge passageway by a purge control valve interposed
along the length of the purge passageway;
opening and closing the charge passageway by a charge passageway opening and
closing valve interposed along the length of the charge passageway;
interposing a pressure relief section along the length of the atmospheric passageway;
controlling the opening of the purge control valve so as to control the purging
by a purge control section;
activating the pressure relief section by the purge control section; and
reducing an inside pressure of the canister to a first predetermined negative
pressure while preventing an inside pressure of the fuel tank from becoming an
excessively negative pressure by closing the charge passageway opening and closing
valve, whereby the purging is controlled while the inside pressure of the canister
is being relieved.
8. The vaporized fuel processing method as set forth in claim 7, further comprising
the steps of:
detecting the inside pressure of the fuel tank by a tank inside pressure detecting
section, and
when the inside pressure of the fuel tank so detected is higher than a predetermined
pressure, stopping the operation of the pressure relief section and opening the
charge passageway opening and closing valve by the purge control section.
9. The vaporized fuel processing method as set forth in claim 7, further comprising
the steps of:
detecting the inside pressure of the canister by a canister inside pressure detecting
section, and
when the inside pressure of the canister so detected is lower than the predetermined
negative pressure, stopping the operation of the pressure relief section and opening
the charge passageway opening and closing valve by the purge control section.
10. The vaporized fuel processing method as set forth in claim 7, further comprising
the steps of:
detecting the inside pressure of the canister by a canister inside pressure detecting
section, and
opening the charge passageway opening and closing valve by the purge control
section after the inside pressure of the canister has increased to a second predetermined
negative pressure, when purge control is shifted from the purge control that is
implemented by relieving the inside pressure of the canister to a normal purge
control that is implemented by stopping the operation of the pressure relief section.
11. The vaporized fuel processing method as set forth in claim 7, further comprising
a step of:
operating only between the fully closed position and the fully opened position
by the charge passageway opening and closing valve.
12. The vaporized fuel processing method as set forth in claim 7, further comprising
a step of:
setting at any opening between the fully closed position and the fully opened
position by the charge passageway opening and closing valve.
13. A medium for recording a program for performing a vaporized fuel processing
comprising the steps of:
storing an adsorbent in a canister;
communicating between a fuel tank and the canister by a charge passageway;
charging vaporized fuel from the fuel tank into the canister;
adsorbing the vaporized fuel so charged onto the adsorbent in the canister;
communicating between the canister and an induction system of an internal combustion
engine by a purge passageway;
purging the vaporized fuel released from the adsorbent into the induction system;
communicating between the canister and the atmosphere by an atmospheric passageway;
opening and closing the purge passageway by a purge control valve interposed
along the length of the purge passageway;
opening and closing the charge passageway by a charge passageway opening and
closing valve interposed along the length of the charge passageway;
interposing a pressure relief section along the length of the atmospheric passageway;
controlling the opening of the purge control valve so as to control the purging
by a purge control section;
activating the pressure relief section by the purge control section; and
reducing an inside pressure of the canister to a first predetermined negative
pressure while preventing an inside pressure of the fuel tank from becoming an
excessively negative pressure by closing the charge passageway opening and closing
valve, whereby the purging is controlled while the inside pressure of the canister
is being relieved.
14. The medium for recording a program for performing the vaporized fuel processing
as set forth in claim 13, further comprising the steps of:
detecting the inside pressure of the fuel tank by a tank inside pressure detecting
section, and
when the inside pressure of the fuel tank so detected is higher than a predetermined
pressure, stopping the operation of the pressure relief section and opening the
charge passageway opening and closing valve by the purge control section.
15. The medium for recording a program for performing the vaporized fuel processing
as set forth in claim 13, further comprising the steps of:
detecting the inside pressure of the canister by a canister inside pressure detecting
section, and
when the inside pressure of the canister so detected is lower than the predetermined
negative pressure, stopping the operation of the pressure relief section and opening
the charge passageway opening and closing valve by the purge control section.
16. The medium for recording a program for performing the vaporized fuel processing
as set forth in claim 13, further comprising the steps of:
detecting the inside pressure of the canister by a canister inside pressure detecting
section, and
opening the charge passageway opening and closing valve by the purge control
section after the inside pressure of the canister has increased to a second predetermined
negative pressure, when purge control is shifted from the purge control that is
implemented by relieving the inside pressure of the canister to a normal purge
control that is implemented by stopping the operation of the pressure relief section.
17. The medium for recording a program as set forth in claim 13, further comprising
a step of:
operating only between the fully closed position and the fully opened position
by the charge passageway opening and closing valve.
18. The medium for recording a program as set forth in claim 13, further comprising
a step of:
setting at any opening between the fully closed position and the fully opened
position by the charge passageway opening and closing valve.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a system and a method for vaporized fuel processing
as well as a medium recording a program for performing the method.
A vaporized fuel processing system is well known in which vaporized fuel from
a
fuel tank is charged into a canister for adsorption by causing the fuel tank to
communicate with the canister, and vaporized fuel released from the canister is
purged into an induction system of an internal combustion engine in a predetermined
operating condition, and a technique described in a patent literature No. 1 can
be raised as an example of the vaporized fuel processing system.
[Patent Literature No. 1] JP-A-9-151812
In the technique described in the patent literature No. 1, a vacuum or negative
pressure is introduced into a vaporized fuel processing system including a canister
by opening a purge control valve, as well as an atmosphere-vented (open to the
atmosphere) valve, and an accumulated value for each pressure change when the negative
pressure so introduced is maintained is calculated, whereby whether or not an abnormality
such as leakage of vaporized fuel is occurring in the vaporized fuel processing
system is checked based on the accumulated values so calculated. Note that while
the technique described in the patent literature No. 1 discloses the construction
for relieving the pressure in the canister, the pressure relief is carried out
in order to check on the leakage of vaporized fuel only and there is disclosed
no attempt to increase the purge efficiency.
Incidentally, in recent years, as emission control regulations are
strengthened, while the purge flow rate of vaporized fuel needs to be increased
as high as possible, since driving conditions for purging are limited, there exists
a limitation on the increase in purge flow rate. Consequently, it is desired to
increase the purge efficiency by increasing the purge density.
SUMMARY OF THE INVENTION
Consequently, an object of the invention is to provide a vaporized
fuel processing system which can solve the problem so as to increase the purge
efficiency by increasing the purge density.
With a view to attaining the object, according to a first aspect of the invention,
there is provided a vaporized fuel processing system including a canister for storing
an adsorbent, a charge passageway which establishes a communication between a fuel
tank and the canister so as to charge vaporized fuel from the fuel tank into the
canister so that the vaporized fuel so charged is adsorbed onto the adsorbent in
the canister, a purge passageway which establishes a communication between the
canister and an induction system of an internal combustion engine so that the vaporized
fuel released from the adsorbent is purged into the induction system, an atmospheric
passageway which establishes a communication between the canister and the atmosphere,
a purge control valve interposed along the length of the purge passageway for opening
and closing the purge passageway, a charge passageway opening and closing valve
interposed along the length of the charge passageway for opening and closing the
charge passageway, a pressure relief section interposed along the length of the
atmospheric passageway, and a purge control section for controlling the opening
of the purge control valve so as to control the purging, wherein the purge control
section activates the pressure relief section so as to reduce the inside pressure
of the canister to a first predetermined negative pressure while preventing the
inside pressure of the fuel tank from becoming an excessively negative pressure
by closing the charge passageway opening and closing valve, whereby the purging
is controlled while the inside pressure of the canister is being relieved.
Further, there is provided a vaporized fuel processing method including
the steps of storing an adsorbent in a canister, communicating between a fuel tank
and the canister by a charge passageway, charging vaporized fuel from the fuel
tank into the canister, adsorbing the vaporized fuel so charged onto the adsorbent
in the canister, communicating between the canister and an induction system of
an internal combustion engine by a purge passageway, purging the vaporized fuel
released from the adsorbent into the induction system, communicating between the
canister and the atmosphere by an atmospheric passageway, opening and closing the
purge passageway by a purge control valve interposed along the length of the purge
passageway, opening and closing the charge passageway by a charge passageway opening
and closing valve interposed along the length of the charge passageway, interposing
a pressure relief section along the length of the atmospheric passageway, controlling
the opening of the purge control valve so as to control the purging by a purge
control section, activating the pressure relief section by the purge control section,
and reducing an inside pressure of the canister to a first predetermined negative
pressure while preventing an inside pressure of the fuel tank from becoming an
excessively negative pressure by closing the charge passageway opening and closing
valve, whereby the purging is controlled while the inside pressure of the canister
is being relieved.
Still further, there is provided a medium for recording a program for performing
the vaporized fuel processing as set forth in the first aspect.
According to a second aspect of the invention, there is provided a vaporized
fuel processing system as set forth in the first aspect of the invention, further
including a tank inside pressure detecting section for detecting the inside pressure
of the fuel tank, wherein when the inside pressure of the fuel tank so detected
is higher than a predetermined pressure, the purge control section stops the operation
of the pressure relief section and opens the charge passageway opening and closing valve.
Further, there is provided the vaporized fuel processing method as set forth
in the first aspect, further including steps of: detecting the inside pressure
of a fuel tank by a tank inside pressure detecting section, and when the inside
pressure of the fuel tank so detected is higher than a predetermined pressure,
stopping the operation of the pressure relief section and opening the charge passageway
opening and closing valve by the purge control section.
Still further, there is provided a medium for recording a program for performing
the vaporized fuel processing as set forth in the second aspect.
According to a third aspect of the invention, there is provided a vaporized
fuel processing system as set forth in the first aspect of the invention, further
including a canister inside pressure detecting section for detecting the inside
pressure of the canister, wherein when the inside pressure of the canister so detected
is lower than the predetermined negative pressure, the purge control section stops
the operation of the pressure relief section and opens the charge passageway opening
and closing valve.
Further, there is provided the vaporized fuel processing method as set forth
in the first aspect, further including the steps of, detecting the inside pressure
of a canister by a canister inside pressure detecting section, and when the inside
pressure of the canister so detected is lower than the predetermined negative pressure,
stopping the operation of the pressure relief section and opening the charge passageway
opening and closing valve by the purge control section.
Still further, there is provided a medium for recording a program for performing
the vaporized fuel processing as set forth in the third aspect.
According to a fourth aspect of the invention, there is provided a vaporized
fuel processing system as set forth in the first aspect of the invention, further
including a canister inside pressure detecting section for detecting the inside
pressure of the canister, wherein the purge control section opens the charge passageway
opening and closing valve after the inside pressure of the canister has increased
to a second predetermined negative pressure when purge control is shifted from
the purge control that is implemented by relieving the inside pressure of the canister
to a normal purge control that is implemented by stopping the operation of the
pressure relief section.
Further, there is provided the vaporized fuel processing method as set forth
in the first aspect, further including the steps of detecting the inside pressure
of a canister by a canister inside pressure detecting section, and opening the
charge passageway opening and closing valve by the purge control section after
the inside pressure of the canister has increased to a second predetermined negative
pressure, when purge control is shifted from the purge control that is implemented
by relieving the inside pressure of the canister to a normal purge control that
is implemented by stopping the operation of the pressure relief section.
Still further, there is provided a medium for recording a program for performing
the vaporized fuel processing as set forth in the forth aspect.
According to a fifth aspect of the invention, there is provided the vaporized
fuel processing system as set forth in the first aspect, wherein the charge passageway
opening and closing valve operates only between the fully closed position and the
fully opened position.
Further, there is provided the vaporized fuel processing method as set forth
in the first aspect, further including a step of, operating only between the fully
closed position and the fully opened position by the charge passageway opening
and closing valve.
Still further, there is provided a medium for recording a program for performing
the vaporized fuel processing as set forth in the fifth aspect.
According to a sixth aspect of the invention, there is provided the vaporized
fuel processing system as set forth in the first aspect, wherein the charge passageway
opening and closing valve is capable to be set at any opening between the fully
closed position and the fully opened position.
Further, there is provided the vaporized fuel processing method as set forth
in the first aspect, further including a step of, setting at any opening between
the fully closed position and the fully opened position by the charge passageway
opening and closing valve.
Still further, there is provided a medium for recording a program for performing
the vaporized fuel processing as set forth in the sixth aspect.
According to the first aspect of the invention, since the pressure relief
section is activated to reduce the inside pressure of the canister to the first
predetermined negative pressure while preventing the inside pressure in the fuel
tank from becoming an excessively negative pressure by closing the charge passageway
opening and closing valve, where by purging is controlled in that state, the release
of vaporized fuel from the adsorbent is promoted so as to increase the purge density
from a similar principle to vacuum distillation by relieving the pressure in the
canister, thereby making it possible to increase the purge efficiency. In other
words, the same quantity of vaporized fuel can be purged into the induction system
of the internal combustion engine with a smaller purge flow rate. In addition,
since the aforesaid vacuum purge control is carried out while preventing the inside
pressure in the fuel tank from becoming an excessively negative pressure by closing
the charge passageway opening and closing valve, there occurs no case where an
unnecessary stress is given to the fuel tank, this obviating the necessity of providing
reinforcement to the fuel tank.
According to the second aspect of the invention, when the inside pressure
detected is lower than the predetermined pressure, the operation of the pressure
relief section is stopped, and the charge passageway opening and closing valve
is opened. Therefore, even in case the amount of vaporized fuel is drastically
increased and the inside pressure in the fuel tank is increased to a positive pressure
side while the vacuum purge control is being implemented, the pressure can be relieved
to the canister side by opening the charge passageway opening valve, whereby no
unnecessary stress is given to the fuel tank.
According to the third aspect of the invention, when the detected inside
pressure in the canister is lower than the predetermined negative pressure, the
operation of the pressure relief section is stopped, and the charge passageway
opening and closing valve is opened. Therefore, there is no risk that the inside
pressure in the canister becomes an excessively negative pressure, and consequently,
since there is no risk that an unnecessary stress is given to the canister, the
necessity is obviated of providing reinforcement to the canister.
According to the fourth aspect of the invention, when purging control is
shifted from the vacuum purge control that is implemented by relieving the inside
pressure in the canister to the normal purge control, the charge passageway opening
and closing valve is opened after the inside pressure in the canister is increased
to the second predetermined negative pressure. Therefore, there is no risk that
the negative pressure generated in the canister due to the vacuum purge control
acts on the fuel tank, whereby the inside pressure in the fuel tank becomes an
excessively negative pressure. Consequently, there is no risk that an unnecessary
stress is given to the fuel tank.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram showing the whole of a vaporized fuel processing
system according to a first embodiment of the invention.
FIG. 2 is a flowchart illustrating the operation of the vaporized fuel processing
system shown in FIG. 1.
FIG. 3 is an experimental result showing the purge efficiency of butane with
respect to accumulated flow rates, which explains a vacuum purge control process
in the operation shown in FIG. 2.
FIG. 4 is a similar graph to one shown in FIG. 3 showing the characteristics
of saturated vapor pressure of butane with respect to temperatures, which explains
a vacuum purge control process in the operation shown in FIG. 2.
FIG. 5 is a flowchart similar to one shown in FIG. 2 which illustrates the operation
of a vaporized fuel processing system according to a second embodiment of the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, a best mode for carrying out a vaporized fuel processing
system according to the invention will be described by reference to the accompanying drawings.
[First Embodiment]
FIG. 1 is a schematic diagram illustrating the whole of a vaporized fuel processing
system according to a first embodiment of the invention.
In FIG. 1, reference numeral
10 denotes a canister. The canister
10
is produced from a resin material or of a metallic material and stores therein
an absorbent
10a constituted by charcoal in the form of pellet. Reference
numeral
12 denotes a fuel tank, and gasoline fuel
14 is stored in
the fuel tank
12. The fuel tank
12 is also produced from a resin
material or of a metallic material and is made airtight and liquid-tight. An opening
formed in a distal end of a filler neck
12a of the fuel tank
12
is closed with a filler cap
12b.
A communication is established between the canister
10 and a space
12c
above the level of fuel in the fuel tank
12 via a charge passageway
16. Gasoline fuel vaporized (fuel vapor)
14 within the fuel tank
12 passes through the charge passageway
16 to flow (be charged) into
the canister
10. Vaporized fuel that has flowed into the canister
10,
in particular, hydrocarbon components (HC) thereof are adsorbed onto the adsorbent
10a stored in the interior of the canister
10.
Reference numeral
20 denotes an internal combustion engine (hereinafter,
referred to as the "engine"). The engine
20 is a four-cycle, four-cylinder
engine, in which air taken into from an air cleaner (not shown) flows through an
induction pipe
22, passes through an induction manifold
26 with the
flow rate thereof being controlled by a throttle valve
24 and reaches an
induction port of each cylinder. Gasoline fuel
14 stored in the fuel tank
12 is supplied to an injector
30 via a fuel supply pipe (not shown)
and is injected by the injector
30 so as to be mixed with air that has flowed
thereinto to thereby form air-fuel mixture. The air-fuel mixture so formed flows
into a combustion chamber
34 of each cylinder (only one of the combustion
chambers is shown) when an inlet valve
32 is opened.
Air-fuel mixture that has flowed into the combustion chamber
34 is
then ignited to be burned by a spark plug
36 to thereby drive a piston
40.
When an exhaust valve
42 is opened, gas generated due to combustion flows
through an exhaust manifold
44 and is then discharged to the atmosphere
(the outside of the engine) through an exhaust pipe
46.
The canister
10 is caused to communicate with an induction system of the
engine
20 or, to be more specific, with a position downstream of the throttle
valve
24 via a purge passageway
50. In addition, the canister
10
is caused to communicate with the atmosphere via an atmospheric passageway
52.
A purge control valve
50a is interposed along the length of the purge
passageway
50. The purge control valve
50a is made up of an
electromagnetic solenoid valve and opens and closes the purge passageway
50
with an opening in accordance with the amount of energy applied to a solenoid of
the valve. When the purge passageway
50 is opened, vaporized fuel adsorbed
onto the adsorbent
10a is released therefrom and is then purged into
the induction system of the engine
20 with a flow rate according to the
opening of the purge passageway
50.
In addition, a charge passageway opening and closing valve
16a is
interposed along the length of the charge passageway
16. The charge passageway
opening and closing valve
16a operates only at two positions; a fully
closed position and a fully opened position, and fully opens or closes the charge
passageway
16. In addition, an atmosphere-vented (open to the atmosphere)
valve
52a is interposed along the length of the atmospheric passageway
52 as the pressure relief section. The atmosphere-vented vale
52a
is made up of an electromagnetic solenoid valve and opens and closes the atmospheric
passageway
52 with an opening in accordance with the amount of energy applied
to a solenoid thereof.
When the atmosphere-vented valve
52a is driven to the fully opened
position, the canister
10 is made to be open to the atmosphere, and the
inside pressure of the canister
10 becomes the atmospheric pressure. On
the other hand, as the atmosphere-vented valve
52a is driven from
the fully opened position toward a closing direction to gradually reduce the opening
of the atmospheric passageway
52, the inside pressure of the canister
10
becomes a negative pressure. Consequently, the atmosphere-vented valve
52a
functions as a pressure relief section. In addition, when the charge passageway
opening and closing valve
16a is driven to a fully closed position,
in case the inside pressure of the canister
10 is made to be a negative
pressure, since the negative pressure is prevented from being introduced into the
space
12c above the level of fuel in the fuel tank
12, the
atmosphere-vented valve
52a also functions as a means for preventing
the generation of an excessively negative pressure in the tank.
A pressure sensor (a tank inside pressure detecting section)
54 is disposed
in the fuel tank
12 for outputting a signal in accordance with the inside
pressure of the fuel tank
12 or the pressure in the space
12c
above the fuel level. In addition, a similar type of pressure sensor (a canister
inside pressure detecting section)
56 is disposed in the canister
10
for outputting a signal in accordance with the inside pressure of the canister
10 or the pressure in the interior of the canister in which the adsorbent
10a is disposed.
In addition, a crank angle sensor
60 is provided in the vicinity of a
crankshaft
or camshaft (both are not shown) of the engine
20 for outputting a cylinder
identifying signal, a TDC signal for each cylinder and a signal representing a
crank angle resulting from the details of those signals. A absolute pressure sensor
62 is disposed in the induction pipe
22 at a position downstream
of the position where the throttle valve
24 is disposed for outputting a
signal in accordance with an air induction pipe inside pressure PBA (representing
an engine load). Note that, while omitting a drawing, a coolant temperature sensor
is disposed in the vicinity of a coolant passageway (not shown) for outputting
a signal in accordance with the engine coolant temperature, and an air-fuel ratio
sensor is disposed in the exhaust pipe
46 for outputting a signal in accordance
with the oxygen density in exhaust emissions.
Outputs from the group of sensors are sent to an ECU (electronic control
unit)
64. The ECU
64 is constituted by a microprocessor made up of
a CPU, a ROM and a RAM, and outputs from the sensors are adjusted with respect
to waveforms or converted into digital values via an A/D converter circuit (not
shown) and are then stored in the RAM. An output from the crank angle sensor
60
is counted by a counter (not shown) so as to detect the engine rotational speed NE.
FIG. 2 is a flowchart showing the operation of the vaporized fuel processing
system shown in FIG. 1.
Note that the program shown illustrates the operation of the ECU
64 and
is activated every time a predetermined period of time elapses or at a time intervals
of, for example, 10 msec. To be more specific, the program is activated every 10
msec when the engine
20 is in an operating condition which allows for a
canister purging (a vaporized fuel processing) in which vaporized fuel released
from the adsorbent
10a in the canister
10 is purged into the
induction system of the engine
20. The operating conditions which allows
for the canister purging are such as a condition in which an air-fuel ratio feedback
control is implemented with the engine being in a steady-state driving condition.
In the ECU
64, the CPU functions as a purge control section, identifies
an operating condition which allows for a canister purging based on the detected
engine rotational speed NE, air induction pipe inside pressure PAB and coolant
temperature, as well as parameters indicating other operating conditions, not shown,
of the engine, and executes the program.
To describe the operation according to the flowchart, in S
10, whether
or
not the inside pressure of the fuel tank
12 is equal to or lower than a
predetermined pressure A (for example, +50 mm Hg) is determined. If positive in
S
10, proceed to S
12 and whether or not the inside pressure of the
canister
10 is equal to or higher than a predetermined negative pressure
B (for example,-300 mm Hg) is determined. Note that in the flowchart in FIG. 2
(and a flowchart in FIG. 5 which will be described later on), pressures are not
absolute pressures but gauge pressures in which the atmospheric pressure (760 mm
Hg) is made to be zero. Consequently, in S
12, it is determined whether the
canister inside pressure is at -300 mm Hg, a negative pressure which is smaller
than -300 mm Hg or a positive pressure which is larger than -300 mm Hg.
If positive in S
12, proceed to S
14, and the atmosphere-vented valve
53a is opened only through a predetermined opening (namely, the pressure
relief section is activated). To be specific, the atmosphere-vented valve
52a
is driven from the fully closed position through the predetermined opening
toward the opening direction. To be more specific, the atmosphere-vented vale
52a
continues to be opened until an opening is reached which allows the inside
pressure in the canister
10 to become a negative pressure in the order of
-200 mm Hg.
Next, proceed to S
16, and execute a vacuum purge control (which will
be described later on), thereafter proceeding to S
18, where the charge passageway
opening and closing valve
16 is closed. In the above description, the vacuum
purge control means an operation in which the atmosphere-vented valve
52a
is opened by a predetermined amount so as to reduce the inside pressure in
the canister
10 to a predetermined negative pressure (a first predetermined
negative pressure) while preventing the inside pressure in the fuel tank
12
from becoming an excessively negative pressure by closing the charge passageway
opening and closing valve
16, and the purging is controlled or the purge
control valve
52a is opened through a certain opening (that is calculated
from an estimated value of charge amount (adsorption amount)) so as to purge vaporized
fuel that is released from the absorbent
10a into the induction system
of the engine
20 while the canister inside pressure is being reduced. Note
that since the gist of the patent application does not reside in the purge control
itself, the detailed description thereof will be omitted.
Here, the vacuum purge control will be described. As is described before, in
recent years, as the regulations on emissions are strengthened, while the purge
flow rate of vaporized fuel needs to be increased as high as possible, since the
driving conditions where purging is allowed are limited as is described above,
there exists a limitation on the increase in purge flow rate, and hence, it is
desired to increase the purge efficiency by increasing the purge density, for example.
As a result of accumulation of knowledge and judgement based thereon, the inventors
eventually found that the release of butane (saturated aliphatic hydrocarbon) which
is a main component of gasoline fuel from the absorbent
10a is promoted
when the inside pressure of the canister
10 is relieved or reduced. FIG.
3 shows experimental data showing purge efficiency relative to purge flow rate,
and as is seen from the data, the purge flow rate could be reduced by 20% to obtain
the same purge efficiency by reducing the canister inside pressure to -200 mm Hg
when the atmospheric temperature is 45° C., and the purge density could be
increased to such an extent equal to the reduction.
The reason for an increase in purge efficiency by reference to FIG. 4, which
is a graph showing the characteristics of saturated vapor pressure relative to
the temperature of normal butane. As shown in the graph, the saturated vapor pressure
of normal butane at 0° C. is substantially equal to the atmospheric pressure.
There may occur a case where the temperature of the absorbent
10a in
the canister goes down to or below the ice point, and in such a condition, the
saturated vapor temperature is on a negative pressure side, where by butane is
difficult to be vaporized (released). Consequently, as in the case with vacuum
distillation, there is generated an environment easing the release of butane by
reducing the canister inside pressure, and hence it is considered that the release
of butane is promoted.
To return to the description of the flowchart in FIG. 2, if negative in S
10
or S
12, proceed to S
20, where the atmosphere-vented valve
52a
is opened fully (driven to the fully opened position) (namely, the operation
of the pressure relief section is stopped). Next, proceed to S
22 to execute
a normal purge control in which the canister inside pressure is not reduced, and
proceed to S
24 to judge whether or not the canister inside pressure is equal
to or higher than a second predetermined negative pressure C. If negative, proceed
to S
18, whereas if positive, proceed to S
26 to fully open the charge
passageway opening and closing valve
16a (or to drive the valve to
the fully opened position).
To describe the above process, when the tank inside pressure is equal to or lower
than the predetermined pressure A (for example, +50 mm Hg) and the canister inside
pressure is the predetermined negative pressure B (for example,-300 mm Hg), the
canister inside pressure is reduced to -200 mm Hg (S
14), and a vacuum purge
control is executed (S
18), whereby the purge efficiency can be increased
from the aforementioned reason. In addition, when the inside pressure in the canister
10a is negative, in case the charge passageway
16 is opened,
since the negative pressure is introduced into the fuel tank
12 to give
an unnecessary stress to the tank
12, the charge passageway opening and
closing valve
16a is closed (S
18) so as to prevent the application
of the negative pressure to the fuel tank
12.
On the other hand, when the tank inside pressure is determined not to be equal
to or lower than the predetermined pressure A, it is anticipated that there is
occurring a situation where the vaporization of gasoline fuel is enhanced drastically,
and this situation also gives an unnecessary stress to the fuel tank
12.
In addition, when the canister inside pressure is determined not to be equal to
or higher than the predetermined negative pressure B, the canister inside pressure
is at, for example,-400 mm Hg, and this situation also gives an unnecessary stress
to the canister
10. Consequently, in these cases, the atmosphere-vented
valve
52a is fully opened (S
20), or the charge passageway
opening and closing valve
16a is fully opened (S
26), so that
the application of an unnecessary stress to the fuel tank
12 or the canister
10 is prevented. In addition, the purge control utilized is the normal purge
control in which the canister inside pressure is not relieved.
Note that, as this occurs, whether or not the canister inside pressure is equal
to or higher than the second predetermined negative pressure C (for example,-50
mm Hg) is determined, and if positive, the charge passageway opening and closing
valve
16a is fully opened (S
26). This step is also taken to
prevent an unnecessary application of the negative pressure inside the canister
to the fuel tank
12.
As is described heretofore, according to the embodiment, since the atmosphere-vented
valve
52a is opened in the predetermined amount so as to reduce the
inside pressure in the canister
10 to the first predetermined negative pressure
and purging is controlled in that condition, the release of vaporized fuel from
the absorbent
10a is promoted so as to increase the purge density,
thereby making it possible to increase the purge efficiency. In other words, an
equal amount of vaporized fuel can be purged into the induction system of the engine
20 at a smaller flow rate.
In addition, since the aforesaid vacuum purge control is implemented while preventing
the inside pressure in the fuel tank
12 from becoming an excessively negative
pressure by closing the charge passageway opening and closing valve
16a,
there is no risk of imparting an unnecessary stress to the fuel tank
12.
Consequently, the necessity is obviated of reinforcing the fuel tank
12.
Furthermore, since the atmosphere-vented valve
52a and the charge
passageway opening and closing valve
16a are opened when the detected
inside pressure in the fuel tank
12 is higher than the predetermined pressure,
even in case the inside pressure in the fuel tank
12 is increased to a positive
pressure side due to a drastic increase in the amount of vaporized fuel when the
vacuum purge control is being implemented, the pressure so increased can be relieved
to the canister side by opening the charge passageway opening and closing valve,
whereby there is no risk that an unnecessary stress is given to the fuel tank
12.
Furthermore, since, when the detected inside pressure in the canister
10 is lower than the predetermined negative pressure, the atmosphere-vented
valve
52a is opened and the charge passageway opening and closing
vale
16a is opened as well, the inside pressure in the canister
10
becomes an excessively negative pressure, and thus, since no unnecessary stress
is applied to the canister
10, no reinforcement is required therefor. In
addition, since, when the purge control is shifted from the vacuum purge control
to the normal purge control, the charge passageway opening and closing valve
16a
is opened after the canister inside pressure has increased to the second predetermined
negative pressure, there is caused no risk that the canister negative pressure
generated by the vacuum purge control is applied to the fuel tank
12 to
make the inside pressure in the fuel tank
12 become an excessively negative
pressure, whereby there is caused no risk that an unnecessary stress is imparted
to the fuel tank
12.
[Second Embodiment]
FIG. 5 is a flowchart, identical to the flowchart shown in FIG. 2, which illustrates
the operation of a vaporized fuel processing system according to a second embodiment
of the invention.
To describe the operation while focusing on a difference from the first embodiment,
after executing similar processes to those in the first embodiment from S
100
to S
102, proceed to S
104, where whether or not the canister inside
pressure exceeds a target value (for example,-200 mm Hg). Then, if positive, since
this means that vacuum is insufficient, proceed to S
106 to reduce the opening
of the atmosphere-vented valve
52a by ΔG, in other words, the
valve is driven in a valve closing direction to such an extent that the valve opening
is reduced by ΔG. On the other hand, if negative in S
104, proceed
to S
108 to drive the atmosphere-vented valve
52a in a valve
opening direction to such an extent that the valve opening G is increased by ΔG.
Note that processes from S
110 to S
122 are similar to those in the
first embodiment.
Since the second embodiment is constructed as is described above, similar advantages
to those described in the first embodiment are provided except that the canister
inside pressure is feedback controlled to the target value (target negative pressure).
[Third Embodiment]
Next, a vaporized fuel processing system according to a third embodiment of
the invention will be described.
To describe the system while focusing on a difference from the previous embodiments,
in a third embodiment, as shown by phantom lines in FIG. 1, a pressure relief pump
70 as a pressure relief section is connected to the atmospheric passageway
52 at a position upstream of the atmosphere-vented valve
52a (closer
to the canister
10).
In the operation of the system according to the third embodiment, in a process
in S
14 or S
104, with the atmosphere-vented valve
52a being
held at the fully closed position, the pressure relief pump
70 is activated
so that the inside pressure in the canister
10 becomes a negative pressure
in the order of -200 mm Hg.
With the system according to the third embodiment, by the addition of the pressure
relief pump
70, while the configuration is made slightly complicated, a
desired vacuum condition can be produced even when the induction negative pressure
of the engine
20 is weak. Note that the atmosphere-vented valve
52a
may be removed so that only the pressure relief pump
70 is left for
use. The remaining construction and advantages remain the same as those described
in the previous embodiments.
Thus, as is described heretofore, according to the first to third embodiments
of the invention, there is provided the vaporized fuel processing system including
the canister
10 for storing the adsorbent
10a, the charge
passageway
16 which establishes a communication between the fuel tank
12
and the canister
10 so as to charge vaporized fuel (gasoline fuel
14)
from the fuel tank into the canister
10 so that the vaporized fuel so charged
is adsorbed onto the adsorbent in the canister, the purge passageway
50
which establishes a communication between the canister and an induction system
(the induction pipe
22) of the internal combustion engine (the engine)
20
so that the vaporized fuel released from the adsorbent is purged into the induction
system, the atmospheric passageway
52 which establishes a communication
between the canister and the atmosphere, the purge control valve
50a
interposed along the length of the purge passageway for opening and closing
the purge passageway, the charge passageway opening and closing valve
16a
interposed along the length of the charge passageway for opening and closing
the charge passageway, the pressure relief section (the atmosphere-vented valve
52a, the pressure relief pump
70) interposed along the length
of the atmospheric passageway, and the purge control section for controlling the
opening of the purge control valve so as to control the purging, wherein the purge
control section (the ECU
64, S
10 to S
26, S
100 to S
122)
activates the pressure relief section so as to reduce the inside pressure of the
canister to the first predetermined negative pressure (S
14, S
104
to S
108) while preventing the inside pressure of the fuel tank from becoming
an excessively negative pressure by closing the charge passageway opening and closing
valve (S
18, S
112), whereby the purging is controlled (S
16,
S
110) while the inside pressure of the canister is being relieved.
In addition, there is provided the vaporized fuel processing system which further
includes the tank inside pressure detecting section (the pressure sensor
54)
for detecting the inside pressure of the fuel tank, wherein when the inside pressure
of the fuel tank so detected is higher than the predetermined pressure (S
10,
S
100), the purge control section stops the operation of the pressure relief
section (S
20, S
114) and opens the charge passageway opening and closing
valve (S
26, S
122).
Furthermore, there is provided the vaporized fuel processing system
which further includes the canister inside pressure detecting section (the pressure
sensor
56) for detecting the inside pressure of the canister, wherein when
the inside pressure of the canister so detected is lower than the predetermined
negative pressure (S
22, S
116), the purge control section stops the
operation of the pressure relief section and opens the charge passageway opening
and closing valve (S
26, S
122).
Moreover, there is provided the vaporized fuel processing system which
further includes the canister inside pressure detecting section (the pressure sensor
56) for detecting the inside pressure of the canister, wherein the purge
control section opens the charge passageway opening and closing valve (S
26,
S
122) after the inside pressure of the canister has increased to the second
predetermined negative pressure (S
24, S
120) when purge control is
shifted from the purge control that is implemented by relieving the inside pressure
of the canister to the normal purge control that is implemented by stopping the
operation of the pressure relief section (S
22, S
116).
Note that, in the respective embodiments that are described heretofore, while
the charge passageway opening and closing valve is described as operating only
between the fully closed position and the fully opened position, it may be made
to be a valve which can be set at any opening therebetween.
*
