Technical Field
[0001] The present invention relates to a fuel supply device for an internal combustion
engine that is mounted on a vehicle and the like.
Background Art
[0002] In some cases where fuel for an automotive engine and the like (specifically, for
a diesel engine) is used under a low-temperature environment, a paraffinic component
crystallizes and grows up, which results in deposition of wax.
[0003] In a fuel supply system such as the automotive engine, a fuel filter is generally
disposed upstream of a fuel pump so as to prevent the fuel pump from being contaminated
with foreign substance. When the wax deposits upstream of the fuel filter, it is trapped
by a filter element in the fuel filter. For this reason, at an initial stage of starting
of the engine under the low-temperature environment, the filter element may be clogged
in a short time due to the wax. In this case, the amount of fuel supplied to an injector
becomes insufficient, which results in reduction of an engine output.
[0004] Patent Document 1 discloses a configuration to eliminate clogging of a filter element
caused by deposition of wax. Specifically, in a fuel supply device including a fuel
filter upstream of a fuel pump, surplus fuel from a common rail and leaked fuel from
an injector and from the fuel pump are mixed with fuel from a fuel tank so that the
mixed fuel passes through the fuel filter. That is, the fuel is heated by the surplus
fuel and the leaked fuel each having a relatively high temperature, which melts the
wax and eliminates the clogging of the filter element.
Prior Art Document
Patent Document
Summary of Invention
Problem to Be Solved by Invention
[0007] It is conceivable to dispose two fuel filters upstream of the fuel pump in consideration
of use of low-quality fuel that contains not a few foreign substances.
[0008] In this case, the fuel passes through the filter elements of the respective fuel
filters by a negative suction pressure of the fuel pump. Like this, when using the
negative suction pressure of the fuel pump, it is difficult to sufficiently obtain
a pressure to make the fuel pass through the filter elements (i.e., since fuel suction
by the fuel pump makes the fuel pass through the filter elements, the pressure to
pass the fuel is likely to be insufficient). As a result, even when the amount of
foreign substances trapped by the filter elements is relatively small, the amount
of fuel that passes through the filter elements may decreases. Therefore, even when
each amount of foreign substances trapped by the corresponding filter element of each
of the fuel filters is relatively small, it is necessary to replace each filter element.
That is, the greater number of the fuel filters are used, the more replacement parts
are required.
[0009] Furthermore, in a state in which the wax deposits in the fuel under the low-temperature
environment, all filter elements of the fuel filters may be clogged.
[0010] The present invention was made in consideration of the above circumstances, an object
of which is to provide a fuel supply device for an internal combustion engine, which
includes a plurality of fuel filters and is capable of reducing the number of replacement
parts and suppressing clogging of filter elements caused by deposition of wax.
Means for Solving Problem
[0011] The invention is defined by appended claim 1. Further embodiments are defined in
the appended dependent claims.
[0012] In order to resolve the above problems, the present invention is predicated on a
fuel supply device for an internal combustion engine, which includes: a fuel supply
path configured to supply fuel in a fuel tank to a fuel injection valve using a fuel
pump. In the fuel supply device for an internal combustion engine, the fuel supply
path includes: a first fuel filter that is disposed upstream of the fuel pump and
that has a first filter element; and a second fuel filter that is disposed downstream
of the fuel pump and that has a second filter element. Furthermore, a fuel return
path is disposed so that fuel discharged from the fuel pump is returned, via the second
fuel filter, to an upstream side of the first filter element in the first fuel filter.
[0013] With the above constituent features, when the fuel passes through the second filter
element of the second fuel filter, the fuel is caused to pass through the second filter
element by a discharge pressure of the fuel pump. Thus, in the case using the discharge
pressure of the fuel pump, it is possible to sufficiently increase the pressure to
cause the fuel to pass through the filter element (second filter element) (i.e., since
the fuel pump pushes the fuel into the second filter element so that the fuel passes
through the second filter element, the pressure to cause the fuel to pass through
can be sufficiently increased, compared with the case in which the fuel pump sucks
the fuel to cause it to pass through). For this reason, even when the amount of foreign
substances trapped by the second filter element is relatively large, the fuel can
pass through the second filter element. As a result, it is not necessary to replace
the second filter element. Thus, the number of replacement parts can be reduced while
a plurality of fuel filters is provided (i.e., the number of the replacement parts
can be reduced compared with the case in which all of the filter elements of the fuel
filters are needed to be replaced).
[0014] Also, the temperature of the fuel that reaches the second fuel filter is relatively
high because it is pressured by the fuel pump. Then, the fuel is returned to the upstream
side of the first filter element inside the first fuel filter via the fuel return
path. Thus, the temperature on the upstream side of the first filter element can be
increased. Accordingly, even when the first filter element is clogged by wax, it is
possible to quickly melt the wax to eliminate the clogging. Also, when the first filter
element is not clogged by the wax, it is possible to prevent the wax deposition, thereby
preventing the clogging of the first filter element due to the wax.
[0015] According to the invention: the second filter element is housed in a filter casing
of the second fuel filter; the filter casing includes an air vent valve having a suction
port and a discharge port each opened toward a corresponding side of the filter casing;
and a fuel return pipe forming the fuel return path is connected to the discharge
port of the air vent valve.
[0016] With the above configuration, part of the fuel in the filter casing of the second
fuel filter can be discharged from the air vent valve to the fuel return pipe. Thus,
the air vent valve, which is provided to discharge air from the second fuel filter,
can be used also as a fuel outlet port through which the fuel is returned to the first
fuel filter. As a result, it is not necessary to provide, in the second fuel filter,
a fuel outlet port dedicated to returning the fuel to the first fuel filter. Thus,
the configuration of the second fuel filter can be simplified.
[0017] Also, it is preferable that the first fuel filter includes: a returned fuel heater
configured to mix fuel introduced from the fuel tank with fuel introduced via the
fuel return path so that the mixed fuel flows into the first filter element; and a
thermostat valve configured to switch between an open state and a closed state according
to whether a temperature of the fuel introduced via the fuel return path is not more
than a predetermined temperature or is more than the predetermined temperature. Preferably,
the thermostat valve is connected to: a fuel path that is further connected to the
returned fuel heater; and a fuel path that is further connected to the fuel tank.
Also preferably, when the temperature of the fuel introduced via the fuel return path
is not more than the predetermined temperature, the fuel introduced via the fuel return
path flows into the returned fuel heater via the thermostat valve, and when the temperature
of the fuel introduced via the fuel return path is more than the predetermined temperature,
the fuel introduced via the fuel return path flows, via the thermostat valve, into
the fuel tank bypassing the returned fuel heater.
[0018] With the above configuration, when the temperature of the fuel introduced to the
first fuel filter via the fuel return path is more than the predetermined temperature,
the thermostat valve operates so that the fuel is returned to the fuel tank bypassing
the returned fuel heater. That is, the fuel introduced via the fuel return path is
returned to the fuel tank without passing through the first filter element, which
prevents the temperature of the fuel passing through the first filter element from
excessively increasing. Thus, degradation of the first filter element can be prevented
and performance of the first fuel filter can be maintained.
[0019] Also, it is preferable that the second fuel filter is integrally attached to a body
of the internal combustion engine.
[0020] With the above configuration, the heat of the body of the internal combustion engine
(heat generated in the combustion stroke in the cylinders) can be easily transmitted
to the second fuel filter. Thus, the heat of the body of the internal combustion engine
can also increase the temperature of the fuel that is returned to the upstream side
of the first filter element via the fuel return path. In the result, it is possible
to reliably eliminate and prevent the clogging of the first filter element (clogging
due to the wax).
Advantageous Effects of Invention
[0021] In the present invention, the fuel filters are disposed respectively upstream and
downstream of the fuel pump so that the fuel is returned from the downstream second
fuel filter to the upstream side of the first filter element inside the upstream first
fuel filter. For this reason, even when the amount of foreign substances trapped by
the second fuel filter is relatively large, the fuel can pass through the second fuel
filter. As a result, it is not necessary to replace the filter element of the second
fuel filter, which results in reduction of the number of replacement parts. Also,
the fuel returned to the first fuel filter can increase the temperature on the upstream
side of the first filter element. Therefore, it is possible to eliminate and prevent
the clogging of the first filter element due to the wax.
Brief Description of Drawings
[0022]
[FIG. 1] FIG. 1 is a schematic configuration diagram showing a fuel supply device
for a diesel engine according to an embodiment.
[FIG. 2] FIG. 2 is a perspective view showing an engine body by virtual lines to explain
a position where a second fuel filter is disposed.
[FIG. 3] FIG. 3 is a diagram corresponding to FIG. 1 to show a flow of fuel in a state
in which a temperature of the fuel that is returned to a first fuel filter is not
more than a predetermined temperature.
[FIG. 4] FIG. 4 is a diagram corresponding to FIG. 1 to show the flow of the fuel
in a state in which the temperature of the fuel that is returned to the first fuel
filter is more than the predetermined temperature.
Description of Embodiments
[0023] Hereinafter, description will be given on an embodiment of the present invention
with reference to the drawings. In this embodiment, the present invention is applied
to a fuel supply device for a four-cylinder diesel engine that is mounted on a vehicle.
(Overall Configuration of Fuel Supply Device)
[0024] FIG. 1 is a schematic configuration diagram showing a fuel supply device 1 for a
diesel engine according to this embodiment. As shown in FIG. 1, the fuel supply device
1 includes: a fuel tank 2; a first fuel filter 3; a feed pump (fuel pump in the present
invention) 4; a second fuel filter 5; a high-pressure fuel pump 6; a common rail 7;
and injectors (fuel injection valves) 8.
[0025] The fuel tank 2 is connected to the first fuel filter 3 via a first fuel pipe 101.
At the upstream end of the first fuel pipe 101, a strainer 101a is disposed. The first
fuel filter 3 is connected to the feed pump 4 via a second fuel pipe 102. The feed
pump 4 is connected to the second fuel filter 5 via a third fuel pipe 103. The second
fuel filter 5 is connected to the high-pressure fuel pump 6 via a fourth fuel pipe
104. The high-pressure fuel pump 6 is connected to the common rail 7 via a fifth fuel
pipe 105. The common rail 7 is connected to each injector 8 corresponding to each
of four cylinders by respective sixth fuel pipes 106.
[0026] The components 2 to 8 are thus connected via the first to sixth fuel pipes 101 to
106. Thus, a fuel supply path 100 is configured to supply fuel in the fuel tank 2
to the injectors 8.
Fuel (diesel fuel) is stored in the fuel tank 2.
[0027] In a filter casing 31 of the first fuel filter 3, a filter element (first filter
element) 32 is housed. The first fuel filter 3 traps, using the filter element 32,
foreign substances contained in the fuel that is sucked from the fuel tank 2 by an
operation of the feed pump 4, and thus purifies the fuel. The specific configuration
of the first fuel filter 3 will be described later.
[0028] The feed pump 4 is constituted by a trochoid pump, a vane pump or the like. The feed
pump 4 is operated by a rotational force of a crankshaft (not shown) of the engine,
which is transmitted via a chain and the like. The feed pump 4 has a discharge pressure,
for example, of about 400 kPa. However, the discharge pressure is not limited thereto.
[0029] As is the case of the first fuel filter 3, in a filter casing 51 of the second fuel
filter 5, a filter element (second filter element) 52 is housed. The second fuel filter
5 traps, using the filter element 52, foreign substances contained in the fuel that
is discharged from the feed pump 4, and thus purifies the fuel. The specific configuration
of the second fuel filter 5 will also be described later.
[0030] The high-pressure fuel pump 6 is constituted by a plunger pump in which reciprocal
motion of a plunger 62 inside a cylinder 61 makes the volume of a pressurizing chamber
63 variable so as to increase the pressure of the fuel. That is, the rotational force
of the crankshaft (not shown) of the engine is transmitted to a camshaft 64 via the
chain and the like, thus the camshaft 64 is rotated so as to reciprocally move the
plunger 62 inside the cylinder 61, thereby increasing the pressure of the fuel. When
the pressure of the fuel exceeds a predetermined value, a check valve 65 is opened
so as to discharge the fuel into the fifth fuel pipe 105. The amount of the fuel to
be discharged is adjustable by opening/closing operations of an electromagnetic spill
valve 66. Since opening/closing control of the electromagnetic spill valve 66 is well
known, the description thereon is omitted here. Note that the high-pressure fuel pump
6 is not limited to the plunger pump. Various kinds of pumps may be applied.
[0031] The common rail 7 accumulates high-pressure fuel supplied from the high-pressure
fuel pump 6. A relief valve 71 is attached to the common rail 7. The relief valve
71 is opened to decrease a rail pressure when the rail pressure increases and reaches
not less than a predetermined pressure.
[0032] Each of the injectors 8 is provided relative to a corresponding cylinder of the engine.
The injectors 8 operate, responding to instructions from an engine ECU (electronic
control unit, not shown), to inject the fuel into the respective cylinders.
[0033] The high-pressure fuel pump 6, the relief valve 71 of the common rail 7 and the injectors
8 are connected to a fuel return pipe 107. One end of the fuel return pipe 107 is
connected to the first fuel filter 3. The other end of the fuel return pipe 107 is
branched so as to be connected respectively, as above described, to the high-pressure
fuel pump 6, the relief valve 71 of the common rail 7 and the injectors 8. Thus, the
fuel return pipe 107 returns the following, to the first fuel filter 3: fuel that
leaks from a gap between the cylinder 61 and the plunger 62 of the high-pressure fuel
pump 6; surplus fuel in the common rail 7 (i.e., fuel discharged by opening of the
relief valve 71); and leaked fuel from the injectors 8. The flow of the fuel returned
to the first fuel filter 3 will be described later.
(First Fuel Filter)
[0034] Here, the first fuel filter 3 is described. As described above, the first fuel filter
3 is disposed upstream of the feed pump 4 on the fuel supply path 100, and has a configuration
in which the filter element 32 is housed in the filter casing 31.
[0035] The filter casing 31 is a case having a substantially rectangular parallelepiped
shape. The first fuel pipe 101 is connected to an upper portion of one side surface
31a (right side surface in FIG. 1) of the filter casing 31. Also, the second fuel
pipe 102 is connected to an upper portion of another side surface (front side surface
in FIG. 1, not shown) of the filter casing 31.
[0036] The filter element 32 is housed in the filter casing 31, in a portion lower than
the respective positions at which the filter casing 31 is connected to the first fuel
pipe 101 and the second fuel pipe 102. The filter element 32 has a substantially cylindrical
shape and has a fuel introduction path 32a vertically penetrating the central portion
thereof. The fuel flowed from the first fuel pipe 101 to the filter casing 31 flows
down into the fuel introduction path 32a (more specifically, passes through a returned
fuel heater 34 described later and flows down into the fuel introduction path 32a),
and after that, the fuel passes through the filter element 32 from the bottom to the
top. During passing through the filter element 32, foreign substances contained in
the fuel are trapped by the filter element 32.
[0037] A fuel flow-in chamber 32b is formed on the top of the filter element 32. The second
fuel pipe 102 is connected to the fuel flow-in chamber 32b. Thus, the fuel passed
through the filter element 32 flows into the second fuel pipe 102 via the fuel flow-in
chamber 32b, and further flows into the feed pump 4.
[0038] Also, in an upper space of the filter casing 31 of the first fuel filter 3 (i.e.,
the space above the fuel flow-in chamber 32b), a thermostat valve 33 and the returned
fuel heater 34 (shown in the virtual line in FIG. 1) are disposed.
[0039] The fuel return pipe 107 penetrates a top surface 31b of the filter casing 31 and
is inserted into the filter casing 31, thus connected to the thermostat valve 33.
The thermostat valve 33 is configured so that a valving element (valve) is opened/closed
by thermowax as a driving source, the thermowax expanding/contracting according to
the temperature of the fuel that flows from the fuel return pipe 107. The thermostat
valve 33 is connected to: a first pipe 33a that is further connected to the returned
fuel heater 34; and a second pipe 33b that is further connected to the fuel tank 2.
The upstream end of the second pipe 33b penetrates a side surface 31c (left side surface
in FIG. 1) of the filter casing 31 of the first fuel filter 3 so as to be connected
to the thermostat valve 33, and the downstream end of the second pipe 33b is positioned
inside the fuel tank 2. The first pipe 33a constitutes "a fuel path via which the
thermostat valve is connected to the returned fuel heater" in the present invention.
Also, the second pipe 33b constitutes "a fuel path via which the thermostat valve
is connected to the fuel tank" in the present invention.
[0040] When the temperature of the fuel that flows from the fuel return pipe 107 into the
first fuel filter 3 (fuel that flows into the thermostat valve 33) is not more than
a predetermined temperature and accordingly the valving element of the thermostat
valve 33 cuts off the communication of the fuel return pipe 107 with the second pipe
33b due to contraction of the thermowax, the thermostat valve 33 allows the communication
of the fuel return pipe 107 with the first pipe 33a. That is, the fuel from the fuel
return pipe 107 is allowed to flow into the returned fuel heater 34.
[0041] On the other hand, when the temperature of the fuel that flows from the fuel return
pipe 107 into the first fuel filter 3 is more than the predetermined temperature and
accordingly the valving element of the thermostat valve 33 allows the communication
of the fuel return pipe 107 with the second pipe 33b due to expansion of the thermowax,
the thermostat valve 33 cuts off the communication of the fuel return pipe 107 with
the first pipe 33a and allows the communication of the fuel return pipe 107 with the
second pipe 33b. That is, the fuel from the fuel return pipe 107 is allowed to bypass
the returned fuel heater 34 so as to flow into the fuel tank 2.
[0042] The above-mentioned predetermined temperature is set to lower than a temperature
that causes degradation of the filter element 32 (the lower limit temperature causing
the degradation of the filter element 32) by a predetermined temperature. That is,
if there is a possibility that the temperature of the fuel flowing from the fuel return
pipe 107 into the first fuel filter 3 reaches the temperature that causes degradation
of the filter element 32, the valving element of the thermostat valve 33 allows the
communication of the fuel return pipe 107 with the second pipe 33b, while cutting
off the communication of the fuel return pipe 107 with the first pipe 33a, so that
the fuel flowed from the fuel return pipe 107 bypasses the returned fuel heater 34
and flows into the fuel tank 2, without flowing into the filter element 32.
[0043] The returned fuel heater 34 is configured to mix the fuel that is returned from the
fuel return pipe 107 to the first fuel filter 3 (fuel that is introduced via the thermostat
valve 33) with the fuel that is introduced from the first fuel pipe 101 (fuel that
is introduced from the fuel tank 2 via the first fuel pipe 101). That is, in the state
in which the valving element of the thermostat valve 33 is closed (i.e., the state
in which the fuel return pipe 107 communicates with the first pipe 33a), the returned
fuel heater 34 mixes the fuel that is introduced from the fuel tank 2 via the first
fuel pipe 101 and that has a relatively low temperature with the fuel that is returned
from the fuel return pipe 107 and that has a relatively high temperature. Thus, the
temperature of the fuel that flows into the filter element 32 is raised (specifically,
it is raised higher than the temperature of the fuel in the fuel tank 2).
[0044] The returned fuel heater 34 may also be configured as a case to mix the fuel that
is introduced from the fuel return pipe 107 into the first fuel filter 3 with the
fuel that is introduced from the first fuel pipe 101 into the first fuel filter 3,
or may simply be configured as a space that an open end of the first pipe 33a and
an open end of the first fuel pipe 101 face.
(Second Fuel Filter)
[0045] Here, the second fuel filter 5 is described. As described above, the second fuel
filter 5 is disposed downstream of the feed pump 4, and has a configuration in which
the filter element 52 is housed in the filter casing 51.
[0046] The filter casing 51 is a case having a substantially rectangular parallelepiped
shape. The third fuel pipe 103 is connected to one side surface 51a (left side surface
in FIG. 1) of the filter casing 51. Also, the fourth fuel pipe 104 is connected to
the other side surface 51b (right side surface in FIG. 1) of the filter casing 51.
With such a configuration, the fuel that flows from the third fuel pipe 103 into the
filter casing 51 passes through the filter element 52. During passing through the
filter element 52, foreign substances contained in the fuel are trapped by the filter
element 52. Thus, the fuel passed through the filter element 52 flows into the high-pressure
fuel pump 6 via the fourth fuel pipe 104.
[0047] When the fuel passes through the filter element 52 of the second fuel filter 5, the
fuel is caused to pass through the filter element 52 by the discharge pressure of
the feed pump 4. Thus, in the case using the discharge pressure of the feed pump 4,
it is possible to sufficiently increase the pressure to cause the fuel to pass through
the filter element 52 (i.e., since the feed pump 4 pushes the fuel into the filter
element 52 so that the fuel passes through the filter element 52, the pressure to
cause the fuel to pass through can be sufficiently increased, compared with the case
in which the feed pump 4 sucks the fuel to cause it to pass through). For this reason,
even when the amount of foreign substances trapped by the filter element 52 is relatively
large, the fuel can pass through the filter element 52. As a result, it is not necessary
to replace the filter element 52.
[0048] An air vent valve 53 is disposed in the filter casing 51 of the second fuel filter
5. The air vent valve 53 is to discharge the air in the filter casing 51 of the second
fuel filter 5. In the filter casing 51, the air vent valve 53 is disposed in the vicinity
of the one side surface 51a (side surface to which the third fuel pipe 103 is connected),
i.e., disposed upstream of the filter element 52 in the fuel flow direction.
[0049] One of the characteristics of this embodiment is that a suction port 53a of the air
vent valve 53 is opened toward the center in the filter casing 51 (as shown in FIG.
1, the air vent valve 53 is disposed leftward in the filter casing 51, accordingly,
the suction port 53a is opened toward the right side in the Figure), while a discharge
port 53b is opened toward the side (left side in the Figure) of the filter casing
51. Therefore, the suction port 53a of the air vent valve 53 faces the fuel in the
filter casing 51, unless a large volume of air exists in the filter casing 51 of the
second fuel filter 5. The discharge port 53b of the air vent valve 53 is connected
to a fuel return pipe 108 (fuel return pipe that forms part of a fuel return path
in the present invention). The fuel return pipe 108 is constituted by a pipe that
penetrates the side surface 51a (left side surface in FIG. 1) of the filter casing
51 of the second fuel filter 5 and is connected to the discharge port 53b of the air
vent valve 53. The fuel return pipe 108 is connected to the fuel return pipe 107.
That is, the fuel return pipe 108 connects the discharge port 53b of the air vent
valve 53 and the fuel return pipe 107.
[0050] A check valve is housed in the air vent valve 53, which is opened according to the
increase of the pressure inside the filter casing 51. Therefore, when the pressure
inside the filter casing 51 reaches a predetermined pressure, the check valve is opened
so as to discharge the air in the filter casing 51, if exists, to the fuel return
pipe 108. As described above, the suction port 53a of the air vent valve 53 is opened
toward the center in the filter casing 51, while the discharge port 53b is opened
toward the side of the filter casing 51. Thus, when the check valve is opened, part
of the fuel in the filter casing 51 is also discharged from the air vent valve 53
to the fuel return pipe 108. As described above, the fuel return pipe 108 is connected
to the fuel return pipe 107. Thus, the fuel discharged from the air vent valve 53
to the fuel return pipe 108 joins the fuel that flows in the fuel return pipe 107
so as to flow into the first fuel filter 3 (more specifically, into the thermostat
valve 33 disposed in the filter casing 31).
[0051] In this way, part of the fuel in the filter casing 51 of the second fuel filter 5
flows into the filter casing 31 of the first fuel filter 3. Thus, the fuel return
pipe 108 and part of the fuel return pipe 107 (corresponding to the part from the
connecting position of the fuel return pipe 108 to the filter casing 31 of the first
fuel filter 3) constitute the fuel return path (fuel return path to return the fuel,
which is discharged from the fuel pump, to the upstream side of the first filter element
of the first fuel filter via the second fuel filter) in the present invention.
[0052] A differential pressure to open the check valve of the air vent valve 53 (differential
pressure between the suction port 53a side and the discharge port 53b side) is set
equal to or slightly lower than a differential pressure caused by an operation of
the feed pump 4, i.e., the differential pressure between the inside of the filter
casing 51 and the inside of the third fuel pipe 103. Thus, when the fuel is discharged
from the feed pump 4 according to its operation, the check valve is continuously opened
and the fuel is continuously discharged from the air vent valve 53 to the fuel return
pipe 108. That is, the fuel is continuously discharged from the second fuel filter
5 to the fuel return pipe 108, which joins the fuel that flows in the fuel return
pipe 107 (i.e., the above-described leaked fuel and surplus fuel) so as to flow into
the first fuel filter 3. In the case where the leaked fuel and the surplus fuel are
not generated, only the fuel discharged from the air vent valve 53 flows into the
first fuel filter 3 via the fuel return pipe 108 and the fuel return pipe 107. In
this embodiment, the position where the air vent valve 53 is disposed, and the respective
inner diameters and the like of the suction port 53a, the discharge port 53b and the
fuel return pipe 108 are set based on experiments and the like, so that the amount
of fuel that is discharged from the second fuel filter 5 to the fuel return pipe 108
is set at approximately 5 % of the amount of fuel that flows from the third fuel pipe
103 into the second fuel filter 5. However, the value is not limited thereto, it may
be set appropriately.
[0053] As shown in FIG. 2 (perspective view showing an engine body E by virtual lines to
explain the position where the second fuel filter 5 is disposed), the second fuel
filter 5 is integrally attached to the engine body E. Specifically, the second fuel
filter 5 is secured to a cylinder block CB by bolts so that a side surface (back surface
in FIG. 2) of the second fuel filter 5 makes contact with a side surface of the cylinder
block CB. Thus, the heat of the engine body E (heat generated in the combustion stroke
in the cylinders) is easily transmitted to the second fuel filter 5.
(Fuel Supply Operation)
[0054] Here, description is given on an operation for supplying the fuel of the fuel supply
device 1 configured as described above. The following two states are separately described:
the state in which the temperature of the fuel that flows from the fuel return pipe
107 into the first fuel filter 3 is not more than the predetermined temperature; and
the state in which the above temperature is more than the predetermined temperature.
Examples of the states in which the temperature of the fuel is not more than the predetermined
temperature include an initial stage of cold starting of the engine. Examples of the
states in which the temperature of the fuel is more than the predetermined temperature
include completion of warming-up operation of the engine.
-State in Which Temperature of Fuel Is Not More Than Predetermined Temperature-
[0055] FIG. 3 is a diagram corresponding to FIG. 1 to show a flow of the fuel in the state
in which the temperature of the fuel that flows into the first fuel filter 3 is not
more than the predetermined temperature. Solid line arrows in the Figure indicate
the flow of the fuel supplied to the injectors 8. Broken line arrows in the Figure
indicate the flow of the fuel that flows into the first fuel filter 3 via the fuel
return pipe 107 and the fuel return pipe 108.
[0056] When the temperature of the fuel that flows from the fuel return pipe 107 into the
first fuel filter 3 is not more than the predetermined temperature, the valving element
is closed due to contraction of the thermowax of the thermostat valve 33. In this
state, the thermostat valve 33 allows the communication of the fuel return pipe 107
with the first pipe 33a. That is, the fuel from the fuel return pipe 107 is allowed
to flow into the returned fuel heater 34.
[0057] In the fuel return pipe 107, the following flows: the fuel that leaks from the gap
between the cylinder 61 and the plunger 62 of the high-pressure fuel pump 6 (i.e.,
leaked fuel); the surplus fuel inside the common rail 7 (i.e., fuel discharged by
opening of the relief valve 71); and the leaked fuel from the injectors 8. Also, in
this embodiment, the fuel discharged from the air vent valve 53 of the second fuel
filter 5 flows into the fuel return pipe 107 via the fuel return pipe 108. Thus, the
fuel discharged from the air vent valve 53 is returned, together with the leaked fuel
and the surplus fuel, to the first fuel filter 3 via the fuel return pipe 107. In
the result, a large amount of fuel having a relatively high temperature is reliably
returned to the first fuel filter 3.
[0058] As described above, the thermostat valve 33 allows the communication of the fuel
return pipe 107 with the first pipe 33a. Thus, the returned fuel heater 34 mixes the
fuel that is returned from the fuel return pipe 107 to the first fuel filter 3 with
the fuel that is introduced from the first fuel pipe 101 (fuel that is introduced
from the fuel tank 2 via the first fuel pipe 101). Accordingly, the fuel having a
relatively high temperature flows into the filter element 32.
[0059] Under the low-temperature environment, a paraffinic component in the fuel crystallizes
and grows up to result in deposition of wax, which may cause the clogging of the filter
element 32. In this embodiment, the fuel having a relatively high temperature flows
into the upstream side of the filter element 32 of the first fuel filter 3, and furthermore
a relatively large amount of fuel is returned to the first fuel filter 3 via the fuel
return pipe 107. Accordingly, the temperature on the upstream side of the filter element
32 can be increased. Thus, even when the filter element 32 is clogged by the wax,
it is possible to melt quickly the wax to eliminate the clogging of the filter element
32. For example, when the wax deposits in the fuel under the outside air temperature
of -15°C, the fuel discharged from the feed pump 4 has the temperature of 10°C (for
this reason, the fuel flowing in the fuel return pipe 108 also has the temperature
of approximately 10°C), and the leaked fuel and the like from the high-pressure fuel
pump 6 have the temperature of 15°C. Thus, these fuels each having a relatively high
temperature (i.e., temperature higher than, for example, -10°C at which the wax deposits)
increase the temperature on the upstream side of the filter element 32. Therefore,
even when the filter element 32 is clogged by the wax, it is possible to melt the
wax to eliminate the clogging. Also, when the filter element 32 is not clogged by
the wax, it is possible to prevent the wax deposition, thereby preventing the clogging
of the filter element 32 due to the wax.
-State in Which Temperature of Fuel Is More Than Predetermined Temperature-
[0060] FIG. 4 is a diagram corresponding to FIG. 1 to show the flow of the fuel in a state
in which the temperature of the fuel that flows into the first fuel filter 3 is more
than the predetermined temperature. Solid line arrows in the Figure indicate the flow
of the fuel supplied to the injectors 8. Broken line arrows in the Figure indicate
the flow of the fuel that flows into the first fuel filter 3 via the fuel return pipe
107 and the fuel return pipe 108, and that is returned to the fuel tank 2.
[0061] When the temperature of the fuel that flows from the fuel return pipe 107 into the
first fuel filter 3 is more than the predetermined temperature, the valving element
is opened due to expansion of the thermowax of the thermostat valve 33. In this state,
the thermostat valve 33 allows the communication of the fuel return pipe 107 with
the second pipe 33b. That is, the fuel from the fuel return pipe 107 is allowed to
bypass the returned fuel heater 34 so as to flow into the fuel tank 2.
[0062] In this case, the fuel flows into the first fuel filter 3 via the fuel return pipe
107 and the fuel return pipe 108 similarly to the case as described above, i.e., the
case in which the temperature of the fuel is not more than the predetermined temperature.
However, since the thermostat valve 33 allows the communication of the fuel return
pipe 107 with the second pipe 33b while cutting off the communication of the fuel
return pipe 107 with the first pipe 33a, the total amount of the fuel flowed into
the thermostat valve 33 is returned to the fuel tank 2 via the second pipe 33b.
[0063] As a result, only the fuel sucked from the fuel tank 2 passes through the filter
element 32 of the first fuel filter 3. That is, the fuel that is returned from the
fuel return pipe 107 and that has a relatively high temperature does not pass through
directly the filter element 32 without going through the fuel tank 2, which prevents
the temperature of the fuel passing through the filter element 32 from excessively
increasing. Thus, degradation of the filter element 32 can be prevented and performance
of the first fuel filter 3 can be maintained.
[0064] As described above, in this embodiment, when the fuel passes through the filter element
52 of the second fuel filter 5, the fuel is caused to pass through the filter element
52 by the discharge pressure of the feed pump 4. Thus, in the case using the discharge
pressure of the feed pump 4, it is possible to sufficiently increase the pressure
to cause the fuel to pass through the filter element 52 (i.e., since the feed pump
4 pushes the fuel into the filter element 52 so that the fuel passes through the filter
element 52, the pressure to cause the fuel to pass through can be sufficiently increased).
For this reason, even when the amount of foreign substances trapped by the filter
element 52 is relatively large, the fuel can pass through the filter element 52. As
a result, it is not necessary to replace the filter element 52. Thus, the number of
replacement parts can be reduced while two fuel filters 3 and 5 are provided (i.e.,
the number of the replacement parts can be reduced compared with the case in which
all of the filter elements are needed to be replaced). Note that the filter element
32 of the first fuel filter 3 is a part that is needed to be replaced.
[0065] Also, in this embodiment, the temperature of the fuel that reaches the second fuel
filter 5 is relatively high because it is pressured by the feed pump 4. As described
above, the second fuel filter 5 is integrally attached to the engine body E. Thus,
the heat of the engine body E (heat generated in the combustion stroke in the cylinders)
is transmitted to the second fuel filter 5, which also makes the temperature of the
fuel in the second fuel filter 5 relatively high. Then, the fuel is returned to the
upstream side of the filter element 32 inside the first fuel filter 3 via the fuel
return pipe 108 and the fuel return pipe 107. Such returned fuel increases, along
with the leaked fuel and the surplus fuel, the temperature on the upstream side of
the filter element 32. Therefore, even when the filter element 32 is clogged by the
wax, it is possible to quickly melt the wax to eliminate the clogging. Also, when
the filter element 32 is not clogged by the wax, it is possible to prevent the wax
deposition, thereby preventing the clogging of the filter element 32 due to the wax.
[0066] Furthermore, in this embodiment, the air vent valve 53, which is provided to discharge
the air from the second fuel filter 5, is used also as a fuel outlet port through
which the fuel is returned to the first fuel filter 3. As a result, it is not necessary
to provide, in the second fuel filter 5, a fuel outlet port dedicated to returning
the fuel to the first fuel filter 3. Thus, the configuration of the second fuel filter
5 can be simplified.
-Other Embodiments-
[0067] In the embodiment as described above, the fuel discharged from the second fuel filter
5 to the fuel return pipe 108 is mixed with the fuel that flows in the fuel return
pipe 107 so that the mixed fuel flows into the first fuel filter 3. However, the present
invention is not limited thereto. The fuel discharged from the second fuel filter
5 to the fuel return pipe 108 can flow into the first fuel filter 3 without being
mixed with the other fuel.
[0068] Also in the embodiment as described above, the fuel supply path 100 includes only
two fuel filters, i.e., the first fuel filter 3 and the second fuel filter 5. However,
the fuel supply path 100 may include, in addition to the above two fuel filters, another
fuel filter. In this case, when a fuel filter is disposed upstream of the feed pump
4, a filter element of such a fuel filter is a part that is needed to be replaced.
On the other hand, when a fuel filter is disposed downstream of the feed pump 4, a
filter element of such a fuel filter is a part that is not needed to be replaced,
as mentioned above.
[0069] Also in the embodiment as describe above, the description was given on the case in
which the present invention is applied to a fuel supply device for a four-cylinder
diesel engine that is mounted on a vehicle. However, the present invention is not
limited thereto. It may be applied to a fuel supply device for a diesel engine that
is mounted on something other than the vehicle. Also, the present invention may be
applied to an engine having less than four cylinders or an engine having more than
four cylinders.
Industrial Applicability
[0070] The present invention may be applied to a fuel supply device for a diesel engine
that is mounted on a vehicle.
Reference Signs List
[0071]
- 1
- Fuel supply device
- 2
- Fuel tank
- 3
- First fuel filter
- 32
- First filter element
- 33
- Thermostat valve
- 33a
- First pipe
- 33b
- Second pipe
- 34
- Returned fuel heater
- 4
- Feed pump (fuel pump)
- 5
- Second fuel filter
- 51
- Filter casing
- 52
- Second filter element
- 53
- Air vent valve
- 53a
- Suction port
- 53b
- Discharge port
- 8
- Injector (fuel injection valve)
- 100
- Fuel supply path
- 107
- Fuel return pipe (fuel return path)
- 108
- Fuel return pipe (fuel return path)
- E
- Engine body (internal combustion engine body)