JP2002327658A - Fuel device of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel device for internal combustion engine to well serve for the case in which different sorts of fuels stored in a plurality of fuel tanks are used in changing-over, capable of suppressing a return of the surplus fuel in the engine to a wrong tank. SOLUTION: As the fuel of internal combustion engine 1, LPG stored in an LPG tank 9 and gasoline stored in a gasoline tank 10 are used in changing- over. The surplus fuel not supplied to the engine 1 is sent out to a pump side return passage 14 from a high pressure fuel pump 12. The pump side return passage 14, an LPG return passage 16 leading to the LPG tank 9, and a gasoline return passage 17 leading to the gasoline tank 10 are connected with a tank selector valve 15. In accordance with the fuel which the engine 1 uses, the tank selector valve 15 is driven under control so that the surplus fuel (LPG or gasoline) is returned to the proper tank.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel system for an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Unexamined Patent Application Publication No.
As in the fuel device for an internal combustion engine described in Japanese Patent Publication No. 49,
2. Description of the Related Art There is known a fuel in which a fuel used in an internal combustion engine is switched between a plurality of kinds of fuels such as gasoline and LPG (liquefied petroleum gas). In such a fuel device, for example, gasoline fuel tanks and LPG fuel tanks are provided as fuel tanks, and either gasoline or LPG supplied from these tanks is used as fuel for the internal combustion engine.

By the way, the surplus fuel supplied from the fuel tank to the internal combustion engine is usually returned to the fuel tank through a return passage. Even in an internal combustion engine that uses a plurality of types of fuel by switching, as described in Japanese Patent Application Laid-Open No. H10-504364, each fuel tank is used to return excess fuel to the fuel tank. It is conceivable to provide a return passage every time.

[0004]

However, in the above-mentioned publication, return passages are individually provided for each fuel tank, and these return passages are simply connected to one fuel rail into which surplus fuel is fed. . Therefore, for example, when one of gasoline and LPG is used as fuel, a surplus of the fuel may be returned to an inappropriate fuel tank. That is, when gasoline is used, surplus gasoline is returned to the LPG fuel tank,
During use, excess LPG is returned to the gasoline fuel tank.

If the surplus fuel is not returned to the appropriate fuel tank, LPG is mixed when gasoline is supplied as fuel to the internal combustion engine, or LPG is supplied to the internal combustion engine.
When supplying G as fuel, gasoline will be mixed. In this case, since the fuel supplied to the internal combustion engine is mixed with fuel having a property different from that of the original fuel, even if an attempt is made to control the operation of the internal combustion engine by adjusting the fuel injection amount, for example, the operation control cannot be performed properly. There is a risk.

[0006] The present invention has been made in view of such circumstances, and an object of the present invention is to provide an internal combustion engine in which a plurality of types of fuel stored in different fuel tanks are switched and used. It is an object of the present invention to provide a fuel device for an internal combustion engine that can prevent excess fuel in the engine from being returned to an inappropriate fuel tank.

[0007]

The means for achieving the above object and the effects thereof will be described below. In order to achieve the above object, according to the first aspect of the present invention, a plurality of fuel tanks for storing different fuels are provided, and any one of the plurality of types of fuel stored in the fuel tanks is switched as fuel for the internal combustion engine. And a return passage provided for each of the fuel tanks for returning an excess amount of fuel supplied to the internal combustion engine to the fuel tank. Switching means for switching a return passage actually used to return surplus fuel to the fuel tank in accordance with fuel used in the internal combustion engine is provided.

According to the above configuration, the return passage actually used can be switched according to the fuel used in the internal combustion engine so that the excess fuel is returned to the appropriate fuel tank. It is possible to suppress the surplus fuel from being returned to the inappropriate fuel tank.

According to a second aspect of the present invention, in the first aspect of the present invention, the switching means is configured to return the surplus fuel to a fuel tank serving as a fuel supply source used in the internal combustion engine. The return passage is switched.

According to the above configuration, the surplus fuel is returned to the fuel tank which is a supply source of the fuel, so that the surplus fuel is returned to the improper fuel tank and a plurality of types of fuel are returned in the fuel tank. Can be prevented from being mixed.

According to the third aspect of the present invention, the first or second aspect is provided.
In the described invention, the switching means switches the return passage in conjunction with switching of fuel used in the internal combustion engine.

According to the above configuration, when the fuel used in the internal combustion engine is switched, the return passage is switched in conjunction therewith, so that excess fuel is returned to the inappropriate fuel tank. Can be suppressed.

According to a fourth aspect of the present invention, in the third aspect of the present invention, the switching means is included when a plurality of types of fuel are included in the surplus fuel in the process of switching the fuel used in the internal combustion engine. The return passage is switched so that the surplus fuel is returned to the fuel tank, which is the supply source of the type of fuel whose amount is the largest.

In the process of switching the fuel used by the internal combustion engine, the fuel is supplied to the internal combustion engine in a state where a plurality of types of fuels are mixed, and the surplus fuel contains a plurality of types of fuels. Become. According to the above configuration, even in such a state, it is possible to minimize mixing of a plurality of types of fuel in the fuel tank.

According to a fifth aspect of the present invention, in the third aspect of the present invention, after the fuel used in the internal combustion engine is switched, the fuel before the switching is a fuel source after the switching. The return passage is switched so as not to be returned to a certain fuel tank.

According to the above configuration, when the fuel used in the internal combustion engine is switched, the fuel before the switching is returned to the fuel tank that is the supply source of the fuel after the switching, and a plurality of fuels are returned in the fuel tank. It is possible to prevent mixing of seed fuels.

According to the invention of claim 6, in claim 4 or 5,
In the invention described above, the switching means determines a ratio of a plurality of types of fuel contained in the surplus fuel based on an elapsed time since a fuel used in the internal combustion engine is switched, and based on the determination result. The return passage is switched.

After the switching of the fuel used in the internal combustion engine is performed, the ratio of the plurality of types of fuel contained in the surplus fuel changes according to the elapsed time after the switching. According to the above configuration, the ratio of the plurality of types of fuel included in the surplus fuel is determined based on the elapsed time, and the return path is switched based on the determination result. The return passage can be accurately switched according to the proportion of the kind of fuel. For example, when the elapsed time exceeds the time required for one of the plurality of fuels included in the surplus fuel to become larger than the other fuel, if the return passage is switched, the surplus fuel is obtained. Can be accurately returned to the fuel tank, which is the supply source of the type of fuel contained therein in the largest amount. Further, when the elapsed time exceeds the time required for the surplus fuel to become a single type of fuel, by switching the return passage, the fuel tank which is the fuel supply source after the fuel switching is performed. It is possible to accurately prevent the fuel before the fuel switching from being returned.

According to the invention of claim 7, in claim 4 or 5,
In the invention described, the switching means determines a ratio of a plurality of types of fuel contained in the surplus fuel based on at least one of a temperature and a pressure in the surplus fuel,
The switching of the return fuel is performed based on the determination result.

After the switching of the fuel used in the internal combustion engine is performed, if the ratio of the plurality of types of fuel contained in the surplus fuel changes, the temperature and pressure of the surplus fuel change accordingly. It changes. According to the above configuration, the ratio of the plurality of types of fuel contained in the surplus fuel is determined based on at least one of the temperature and the pressure, and the return path is switched based on the determination result. The return passage can be accurately switched in accordance with the ratio of a plurality of types of fuel contained in the fuel. For example, when the temperature or the pressure becomes a value at which one of the plurality of fuels contained in the surplus fuel becomes larger than the other fuel, if the return passage is switched, the surplus fuel is removed therefrom. The fuel can be accurately returned to the fuel tank, which is the supply source of the type of fuel containing the largest amount of fuel. If the return passage is switched when the temperature or pressure reaches a value in which the surplus fuel becomes a single type of fuel, the fuel tank as the fuel supply source after the fuel switching is switched to the fuel tank before the fuel switching. The fuel can be properly prevented from being returned.

According to an eighth aspect of the present invention, in the first aspect of the present invention, the internal combustion engine is used by switching between a high boiling point fuel and a low boiling point fuel. According to the above configuration, the excess fuel is returned to the inappropriate fuel tank, so that mixing of the high-boiling fuel and the low-boiling fuel in the fuel tank can be suppressed.

According to a ninth aspect of the present invention, in the invention of the eighth aspect, a high-boiling-point fuel contained in the surplus fuel is connected to a return passage different from a return passage provided for each fuel tank. A fuel separation device that separates the low-boiling-point fuel from the fuel and returns the separated fuel to the corresponding fuel tank, wherein the switching unit is configured to switch the excess fuel at least in a process of switching fuel used in the internal combustion engine. The return path is switched so that the another return path is used as a return path for returning the fuel to the fuel tank.

According to the above configuration, even when the surplus fuel includes both the high-boiling fuel and the low-boiling fuel in the fuel switching process, the surplus fuel is separated into the high-boiling fuel and the low-boiling fuel. Then, the fuel is returned to an appropriate fuel tank, so that mixing of the high-boiling fuel and the low-boiling fuel in the fuel tank can be suppressed.

According to a tenth aspect of the present invention, in the ninth aspect of the present invention, the fuel separation device adjusts the temperature of the surplus fuel to convert the low-boiling fuel into a gas and convert the high-boiling fuel into a liquid. By separating the surplus fuel into a gas and a liquid, returning the separated gas to a fuel tank for a low-boiling fuel, and returning the separated liquid to a fuel tank for a high-boiling fuel. did.

According to the above arrangement, the temperature of the surplus fuel is adjusted to convert the low-boiling fuel into a gas and the high-boiling fuel into a liquid, so that the surplus fuel can be accurately converted to a low-boiling fuel. The fuel is separated into the boiling fuel and the separated fuel can be returned to an appropriate fuel tank.

According to the eleventh aspect of the present invention, there is provided an internal combustion engine having a plurality of fuel tanks for storing different fuels, and using any one of a plurality of types of fuel stored in the fuel tanks as fuel for an internal combustion engine. In a fuel device of an engine, a fuel separation device in which a surplus of fuel supplied to an internal combustion engine is introduced, the surplus fuel is separated for each type, and the separated fuel is returned to a corresponding fuel tank. Equipped.

According to the above configuration, when a plurality of types of fuel are included in the surplus fuel, the fuels are returned to the corresponding fuel tanks in a state of being separated for each type. It is possible to surely suppress the mixing of seed fuels.

According to a twelfth aspect of the present invention, in the invention of the eleventh aspect, the internal combustion engine switches between a low-boiling fuel and a high-boiling fuel and uses the fuel. The excess fuel is separated into a gas and a liquid by adjusting the temperature of the fuel for the low-boiling fuel into a gas and the high-boiling fuel into a liquid, and the separated gas is used for the low-boiling fuel. Return to the fuel tank,
The separated liquid is returned to the fuel tank for the high boiling point fuel.

According to the above configuration, the temperature of the surplus fuel is adjusted to convert the low-boiling fuel into a gas and the high-boiling fuel into a liquid, so that the surplus fuel can be accurately converted to a low-boiling fuel. The fuel is separated into the boiling fuel and the separated fuel can be returned to an appropriate fuel tank.

[0030]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment Hereinafter, a first embodiment in which the present invention is applied to an automobile engine using gasoline and LPG (liquefied petroleum gas) as fuels by switching will be described with reference to FIGS. This will be described with reference to FIG.

In the engine 1 shown in FIG. 1, fuel is directly injected from an injector 4 into a combustion chamber 3 into which air is sucked through an intake passage 2, and fuel is supplied from an auxiliary injector 5 into the intake passage 2. Is injected and supplied. The engine 1 is driven by burning a mixture of air and fuel in the combustion chamber 3, and the mixture after combustion is discharged from the combustion chamber 3 to the exhaust passage 6 as exhaust gas. When the engine 1 is driven, the intake camshaft 7 and the exhaust camshaft 8 rotate accordingly.

One of the LPG stored in the LPG tank 9 and the gasoline stored in the gasoline tank 10 is supplied to the injector 4 and the auxiliary injector 5.

That is, the LPG tank 9 and the gasoline tank 10 include a supply fuel switching valve 11 for switching fuel supplied to the injector 4 and an exhaust camshaft 8.
Is connected to the injector 4 via a high-pressure fuel pump 12 driven based on the rotation of. Further, the LPG tank 9 and the gasoline tank 10 are connected to the auxiliary injector 5
Fuel switching valve 1 for switching fuel supplied to fuel supply
3, it is also connected to the auxiliary injector 5.

The fuel delivered from the LPG tank 9 and the gasoline tank 10 is supplied to the injector 4 after being pressurized by the high-pressure fuel pump 12 and also supplied to the auxiliary injector 5. From these injectors 4 and auxiliary injectors 5, the engine 1
Either gasoline or LPG is injected as fuel.

Of the fuel pressurized by the high-pressure fuel pump 12, surplus fuel not supplied to the injector 4 is sent out to the pump-side return passage 14.
The pump-side return passage 14 is connected to a tank switching valve 15 that switches the fuel tank in which the excess fuel is returned to one of the LPG tank 9 and the gasoline tank 10. Further, an LPG return passage 16 connected to the LPG tank 9 and a gasoline return passage 17 connected to the gasoline tank 10 are connected to the tank switching valve 15.

A supply fuel switching valve 11, which switches fuel supplied to the injector 4 and the auxiliary injector 5,
13 and a tank switching valve 15 for switching a fuel tank for returning surplus fuel not used by the engine 1 are controlled by an electronic control unit 18 mounted on the vehicle. Also, the electronic control unit 18 receives detection signals from a temperature sensor 19 for detecting the temperature of the surplus fuel flowing through the pump-side return passage 14 and a pressure sensor 20 for detecting the pressure of the fuel.

The electronic control unit 18 controls the switching of the supplied fuel switching valves 11 and 13 in accordance with, for example, the operating state of the engine 1 and converts the fuel supplied to the injector 4 and the auxiliary injector 5 to either gasoline or LPG. Switch.
In this way, either gasoline or LPG is used as the fuel used in the engine 1.

When LPG is used as fuel for the engine 1, the supply fuel switching valve 11 is switched so that the LPG tank 9 and the high-pressure fuel pump 12 communicate with each other, and the gasoline tank 10 and the high-pressure fuel pump 12 are shut off. .
Further, the supply fuel switching valve 13 is switched so that the LPG tank 9 and the auxiliary injector 5 communicate with each other, and the gasoline tank 10 and the auxiliary injector 5 are shut off.
As a result, the fuel injected from the injector 4 and the auxiliary injector 5 becomes LPG, and the high-pressure fuel pump 12
The surplus fuel delivered from the pump to the pump-side return passage 14 also becomes LPG.

When gasoline is used as fuel for the engine 1, the gasoline tank 10 and the high-pressure fuel pump 1
2 and the LPG tank 9 and the high-pressure fuel pump 1
The supply fuel switching valve 11 is switched so as to shut off the fuel cell 2. Further, the gasoline tank 10 and the auxiliary injector 5
And the LPG tank 9 and the auxiliary injector 5
The supply fuel switching valve 13 is switched so as to be shut off. As a result, the fuel injected from the injector 4 and the auxiliary injector 5 becomes gasoline, and the surplus fuel sent from the high-pressure fuel pump 12 to the pump-side return passage 14 also becomes gasoline.

When either LPG or gasoline is used as fuel in the engine 1, excess fuel is supplied to the LPG.
If the fuel is not returned to the appropriate one of the tank 9 and the gasoline tank 10, two types of fuel, LPG and gasoline, are mixed in the fuel tank. Therefore, in the present embodiment, by switching the tank switching valve 15 through the electronic control unit 18, the return passage for returning the surplus fuel to the fuel tank is changed to the LPG return passage 16 according to the fuel used in the engine 1. And the gasoline return passage 17.

That is, when LPG is used as fuel for the engine 1, the pump-side return passage 14 and the LPG
The tank switching valve 1 is connected so that the tank 9 is in communication with the pump-side return passage 14 and the gasoline tank 10 is shut off.
5 is performed. In this state, as a return passage for returning excess fuel to the fuel tank,
The LPG return passage 16 will be used. As a result, the LP as a fuel tank for returning excess fuel
G tank 9 is selected, and LPG which is the surplus fuel is selected.
Is returned to the LPG tank 9 appropriately.

When gasoline is used as fuel for the engine 1, the pump-side return passage 14 communicates with the gasoline tank 10, and the pump-side return passage 14
And the LPG tank 9 is shut off so that the tank switching valve 1
5 is performed. In this state, as a return passage for returning excess fuel to the fuel tank,
The gasoline return passage 17 will be used. As a result, the gasoline tank 10 is selected as a fuel tank for returning the surplus fuel, and the surplus fuel gasoline is appropriately returned to the gasoline tank 10.

Next, a procedure for switching the return passage at the time of switching the fuel of the engine 1 will be described with reference to a flowchart of FIG. 2 showing a return passage switching routine.
This return passage switching routine is periodically executed by the electronic control unit 18 by, for example, a time interruption at predetermined time intervals.

As a process of the return passage switching routine,
First, it is determined whether or not a switching flag F for determining whether or not fuel switching has been performed is "0 (no fuel switching)" (S101). Here, if the determination is negative and the switching flag F is “1 (fuel is switched)”, the processing of the subsequent steps S102 to S104 is skipped, and the process proceeds to step S105.

On the other hand, if an affirmative determination is made in step S101, it is determined whether or not the fuel used in the engine 1 has been switched (S102). If the affirmative determination has been made, the switching flag F is set to "1". (With fuel switching) "(S103). The fuel used in the engine 1 does not switch immediately based on the switching of the supply fuel switching valves 11 and 13 but gradually switches after the switching of the valves 11 and 13 is performed.

That is, for a while from the start of switching, LPG
The fuel mixed with the fuel and gasoline is supplied to the injector 4 and the auxiliary injector 5, and the ratio of the fuel after switching in the mixed fuel gradually increases with time. Then, when all the fuel supplied to the injectors 4 and the auxiliary injectors 5 becomes the switched fuel, the switching of the fuel used in the engine 1 is completed. When the fuel supplied to the injectors 4 and the auxiliary injectors 5 are in a mixed state as described above, the surplus fuel sent from the high-pressure fuel pump 12 to the pump-side return passage 14 is also in a mixed state. .

When the fuel used in the engine 1 is switched, the value of the counter C is reset to "0" in the process of step S104. The value of the counter C is increased by "1" with time in the subsequent process of step S105, and thus increases in accordance with the elapsed time after the fuel is switched. Here, FIG. 3 shows how the ratio between the fuel before switching and the fuel after switching included in the surplus fuel changes as the value of the counter C increases.

As can be seen from the figure, as the value of the counter C (elapsed time from the start of fuel switching) increases,
Fuel before switching included in surplus fuel gradually decreases,
The fuel after switching included in the surplus fuel gradually increases. When the value of the counter C becomes larger than the predetermined value a, the fuel after switching included in the surplus fuel becomes larger than the fuel before switching. Further, when the value of the counter C exceeds the predetermined value a and reaches the predetermined value b, all the surplus fuel becomes the switched fuel (single fuel).

Accordingly, the amount of fuel before and after the fuel switching included in the surplus fuel, that is, the ratio of the fuel before the fuel switching and the fuel after the fuel switching, is determined by the elapsed time from the start of the fuel switching. The determination can be based on time. Utilizing this, the process of step S106 in the return passage switching routine (FIG. 2) is executed.

In step S106, it is determined whether or not the value of the counter C is greater than the predetermined value a, that is, the elapsed time from the start of fuel switching is determined by the amount of fuel after switching included in surplus fuel before switching. It is determined whether or not a time that is larger than the amount of fuel has been exceeded. If the determination is affirmative, the return path for returning the surplus fuel to the fuel tank is switched to the return path corresponding to the switched fuel by switching the tank switching valve 15 (S107).

That is, when the fuel of the engine 1 is switched from LPG to gasoline, the tank switching valve 15 is switched so that the return passage for returning the surplus fuel to the fuel tank becomes the gasoline return passage 17. Will be
When the fuel of the engine 1 is switched from gasoline to LPG, the switching of the tank switching valve 15 is performed so that the return passage for returning the surplus fuel to the fuel tank becomes the LPG return passage 16.

After the switching of the return passage is performed, the switching flag F is set to "0 (no fuel switching)" (S108). According to the embodiment described in detail above,
The following effects can be obtained.

(1) Based on the switching of the tank switching valve 15, the excess fuel is returned to the fuel tank so that the excess fuel is returned to the fuel tank serving as the fuel supply source used in the engine 1. LP as return path for
Either the G return passage 16 or the gasoline return passage 17 is selectively used. Therefore, the surplus fuel is returned to the inappropriate fuel tank, and the LPG is stored in the fuel tank.
It is possible to suppress mixing of two types of fuels, namely, fuel and gasoline.

(2) When the fuel used in the engine 1 is switched, the return passage for returning the surplus fuel to the fuel tank is switched to the one corresponding to the used fuel after the switching. . Therefore, it is possible to suppress the surplus fuel from being returned to the inappropriate fuel tank when the used fuel is switched.

(3) The switching of the return passage accompanying the switching of the used fuel is performed when the amount of fuel after fuel switching included in the surplus fuel becomes larger than the amount of fuel before fuel switching. Will be For this reason, in the process of switching the used fuel, the surplus fuel is returned to the fuel tank, which is the supply source of the type of fuel containing the largest amount of the surplus fuel, whereby the LPG and the LPG are stored in the fuel tank. Mixing of two types of fuel with gasoline can be minimized.

(4) It is determined whether or not the amount of fuel after the fuel switching included in the surplus fuel is greater than the amount of fuel before the fuel switching, by determining whether the elapsed time after the start of the fuel switching is equal to the surplus fuel. The determination is made based on whether or not a time period (corresponding to a predetermined value a) in which the amount of fuel after switching is greater than the included fuel before switching. Then, since the return path is switched based on the determination result, it is necessary to accurately return the surplus fuel to the fuel tank that is the supply source of the type of fuel containing the largest amount of surplus fuel. Can be.

In the first embodiment, the return passage is switched when the amount of fuel after the fuel switching included in the surplus fuel becomes larger than the amount of fuel before the fuel switching.
Alternatively, the return passage may be switched when all of the surplus fuel becomes fuel after the fuel switching.

In this case, when the value of the counter C reaches the predetermined value b, that is, the elapsed time after the start of the fuel switching is the time during which all the fuel contained in the surplus fuel becomes the switched fuel (corresponding to the predetermined value b). ), The return path is switched. With this configuration, it is possible to appropriately prevent the fuel before switching from being returned to the fuel tank that is the supply source of the fuel after switching.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIGS. In this embodiment,
Instead of determining the ratio of the two types of fuel, LPG and gasoline, included in the surplus fuel based on the elapsed time from the start of the fuel switch as in the first embodiment, the surplus fuel after the start of the fuel switch is used. Based on the temperature and the pressure, the ratio of the above two types of fuel contained in the surplus fuel is determined.

FIG. 4 is a flowchart showing a return passage switching routine according to this embodiment. In this return passage switching routine, steps S104 to S1 in the return passage switching routine (FIG. 2) of the first embodiment are performed.
Only the processing corresponding to 06 (S204 to S206) is the first
This is different from the embodiment.

As a process of the return passage switching routine shown in FIG. 4, when the fuel used in the engine 1 is switched, the switching flag F is set to "1 (fuel switching is performed)" (S201). To S203).

For a while after the start of the fuel switching, the surplus fuel contains two types of fuel, LPG and gasoline. LPG contained in surplus fuel
The ratio between gas and gasoline can be determined based on the temperature and pressure of the surplus fuel. This is because under the condition that the temperature of the surplus fuel is constant, there is a tendency that the pressure of the surplus fuel increases as the ratio of LPG increases and as the temperature of the surplus fuel increases.

Here, the change in the temperature and the pressure of the surplus fuel after the start of the fuel switching is performed with respect to the L included in the surplus fuel.
Figure 5 shows how the ratio between PG and gasoline changes
And FIG.

FIG. 5 shows that when the fuel of the engine 1 is switched from gasoline to LPG, the LPG and gasoline contained in the fuel are changed according to the change in the pressure of the surplus fuel under the condition that the temperature of the fuel is constant. Shows how the ratio changes.

As can be seen from the figure, under the above conditions, when the pressure of the surplus fuel is the predetermined value c, the surplus fuel is all the fuel (gasoline) before switching. When the pressure of the surplus fuel becomes higher than a predetermined value d which is larger than the predetermined value c, the amount of the switched fuel (LPG) included in the surplus fuel becomes larger than the amount of the fuel (gasoline) before the switching. . Further, when the pressure of the surplus fuel reaches a predetermined value e which is larger than the predetermined value d, all the surplus fuel becomes the switched fuel (LPG).

FIG. 6 shows that the fuel of the engine 1 is LPG.
Shows how the ratio between LPG and gasoline contained in the fuel changes according to changes in the pressure of the fuel under the condition that the temperature of the surplus fuel is constant when the fuel is switched from gasoline to gasoline It is.

As can be seen from the figure, under the above conditions, when the pressure of the surplus fuel is the predetermined value e, all the surplus fuel is the fuel before switching (LPG). When the pressure of the surplus fuel drops below a predetermined value c smaller than the predetermined value e, the amount of fuel (gasoline) after switching included in the surplus fuel becomes larger than the amount of fuel (LPG) before switching. . Further, when the pressure of the surplus fuel reaches a predetermined value c smaller than the predetermined value d, all the surplus fuel becomes the switched fuel (gasoline).

A predetermined value c representing the pressure of the surplus fuel when all the fuel is gasoline, and a predetermined value d representing the pressure of the same fuel when the amount of LPG contained in the surplus fuel is equal to the amount of gasoline , And the predetermined value e representing the pressure of the surplus fuel when all the fuel is LPG are shown in FIGS.
As shown in (c), the variable value increases as the temperature of the surplus fuel increases. Thus, the predetermined values c, d, e
Changes because the pressure (vapor pressure) of LPG contained in the surplus fuel increases as the temperature of the surplus fuel increases.

From the above, the amount of fuel before the fuel switching and the amount of fuel after the fuel switching included in the surplus fuel, that is, the ratio of the fuel before the fuel switching and the fuel after the fuel switching, is as follows.
Obviously, it can be determined from the temperature and pressure of the surplus fuel. By utilizing this fact, steps S204 to S204 in the return passage switching routine (FIG. 4) are performed.
The process of S206 is performed.

In step S204, it is determined whether switching of fuel is switching from gasoline to LPG. Here, if the determination is affirmative, it is determined whether or not the pressure of the surplus fuel obtained from the detection signal of the pressure sensor 20 is greater than the predetermined value d, that is, the pressure of the surplus fuel after the switching included in the fuel. It is determined whether the fuel (LPG) has increased beyond a value that is greater than the fuel (gasoline) before switching (S205). This predetermined value d corresponds to the temperature sensor 19
Is made variable based on the temperature of the surplus fuel obtained from the detection signal.

When an affirmative determination is made in step S205, the return path for returning the surplus fuel to the fuel tank by switching the tank switching valve 15 is changed to the return path corresponding to the switched fuel (LPG) (in this case, the return path). LPG
The mode is switched to the return path 16) (S207).
Thereafter, the switching flag F is set to "0 (no fuel switching)" (S208).

On the other hand, if a negative determination is made in step S204, and it is determined that the fuel switching is a switching from LPG to gasoline, the process proceeds to step S206.
Here, it is determined whether or not the pressure of the surplus fuel is smaller than the predetermined value d, that is, the pressure of the surplus fuel is such that the fuel (gasoline) after switching included in the fuel is lower than the fuel (LPG) before switching. It is determined whether the value has become lower than the increased value.

When an affirmative determination is made in step S206, the processing in steps S207 and S208 is sequentially performed. In the process of step S207 in this case, by switching the tank switching valve 15, the return passage for returning the surplus fuel to the fuel tank is switched to the return passage (gasoline return passage 17) corresponding to the switched fuel (gasoline). Can be

In this embodiment described in detail above, the following effects can be obtained in addition to the effects (1) to (3) described in the first embodiment. (4) Switching of the return passage accompanying switching of the fuel used in the engine 1 is performed when the amount of fuel included in the surplus fuel after the fuel switching is larger than the amount of fuel before the fuel switching. Then, it is determined whether the amount of fuel after fuel switching included in the surplus fuel has become larger than the amount of fuel before fuel switching, and the pressure of the surplus fuel is determined with respect to the fuel before switching included in the surplus fuel. This is performed based on whether or not the pressure after the switching exceeds the pressure (corresponding to the predetermined value d) at which the amount of fuel increases.
Since the return path is switched based on the determination result, it is possible to accurately return the surplus fuel to the fuel tank, which is the supply source of the type of fuel containing the largest amount of surplus fuel. it can.

In the second embodiment, the return passage is switched when the amount of fuel after the fuel switching included in the surplus fuel is larger than the amount of fuel before the fuel switching.
Alternatively, the return passage may be switched when all of the surplus fuel becomes fuel after the fuel switching.

In this case, when switching from gasoline to LPG, when the pressure of the surplus fuel reaches the predetermined value e, that is, when the pressure of the surplus fuel becomes equal to the fuel (LPG ), The return path is switched. Also, when switching from LPG to gasoline,
When the pressure of the surplus fuel reaches the predetermined value c, that is, when the pressure of the surplus fuel reaches a pressure at which all of the fuel contained in the surplus fuel becomes the post-switching fuel (gasoline), the switching of the return passage is performed. Will be performed. With this configuration, it is possible to appropriately prevent the fuel before switching from being returned to the fuel tank that is the supply source of the fuel after switching.

Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIGS. In the present embodiment, in the process of switching the fuel used in the engine, when the surplus fuel contains two types of LPG and gasoline,
The surplus fuel is separated into LPG and gasoline by a fuel separation device, and the separated fuel is returned to an appropriate fuel tank, so that mixing of LPG and gasoline in the fuel tank is reliably suppressed. .

As shown in FIG. 8, the high-pressure fuel pump 1
Pump-side return passage 1 through which excess fuel is sent out from 2
4 is connected to a tank switching valve 21 for switching the destination of the surplus fuel among the LPG tank 9, the gasoline tank 10, and the fuel separator 22. The tank switching valve 21 is connected to an LPG return passage 16 and a gasoline return passage 17, as well as a separation return passage 23 connected to a fuel separation device 22. And the tank switching valve 21 by the electronic control unit 18
, The pump-side return passage 14 communicates with the separation return passage 23 and the LPG return passage 1
6 and the gasoline return passage 17, the surplus fuel is introduced into the fuel separation device 22.

The fuel separation device 22 has a heater 24 for heating the introduced surplus fuel. The heater 24 heats the surplus fuel to, for example, a temperature slightly higher than the temperature of the LPG in the LPG tank 9. ing.
Heating the surplus fuel in this way is performed by keeping the gasoline in a liquid state while keeping the gasoline at a lower boiling point than LPG.
Is heated and vaporized to separate surplus fuel into gasoline and LPG.

Of the LPG and gasoline separated by the fuel separator 22, LPG is returned to the LPG tank 9 through the LPG separation passage 25, and gasoline is returned to the gasoline tank 10 through the gasoline separation passage 26. In the middle of the LPG separation passage 25, the LPG cutoff valve 2 is provided.
The gasoline separation passage 26 is provided with a gasoline shut-off valve 28. These shutoff valves 27, 28
Is controlled by the electronic control unit 18 to return LPG from the fuel separation device 22 to the LPG tank 9 and return gasoline from the fuel separation device 22 to the gasoline tank in appropriate situations. The valve is opened.

Next, the procedure of switching the return passage for returning the surplus fuel to the fuel tank will be described with reference to the flowchart of FIG. 9 showing the return passage switching routine of the present embodiment.

In this return passage switching routine, the return passage switching routine of the second embodiment (FIG. 4)
Only the processes (S304 to S307) corresponding to Steps S204 to S208 in are different from those of the second embodiment.

As the process of the return passage switching routine shown in FIG. 9, first, when the fuel used in the engine 1 is switched, the switching flag F is set to "1 (fuel is switched)" (S301). To S303). And
When the switching flag F is “1”, the surplus fuel is LP
It is determined whether or not the state is a mixed state of G and gasoline (S304). Such a determination can be made based on the elapsed time from the start of the fuel switching and the temperature and pressure of the surplus fuel.

If an affirmative determination is made in step S304, the return path for returning the surplus fuel to the fuel tank side is switched to the separation return path 23 by switching the tank switching valve 21. In this state, surplus fuel is introduced into the fuel separator 22, where it is separated into LPG and gasoline. LPG after separation is L
The gasoline returned to the PG tank 9 and separated is returned to the gasoline tank 10.

On the other hand, if a negative determination is made in step S304 and it is determined that all of the surplus fuel has become the fuel after switching (single fuel), the surplus fuel is stored in the fuel tank by switching the tank switching valve 21. The return turn passage for returning is switched to a return passage corresponding to the fuel after the switch (S306). After that, the switching flag F becomes “0”.
(No fuel switching) "(S307).

According to the present embodiment described in detail above, the following effects can be obtained in addition to the effects (1) and (2) described in the first embodiment. (5) When the surplus fuel contains two kinds of fuels, LPG and gasoline, the surplus fuel is converted into L
Since the separated fuel is separated into PG and gasoline, and the separated fuel is returned to an appropriate fuel tank, mixing of LPG and gasoline in the fuel tank can be reliably suppressed.

The above embodiments can be modified as follows, for example. In the above embodiments, LPG and gasoline are exemplified as fuels used in the engine. However, LNG (liquefied natural gas) may be used instead of LPG, or light oil may be used instead of gasoline. .

In the second embodiment, the amounts of LPG and gasoline contained in the surplus fuel are determined based on both the temperature and the pressure of the surplus fuel. However, this determination is made based on either the temperature or the pressure of the surplus fuel. It may be performed based on. in this case,
The above-mentioned predetermined values c, d, and e are variable values that increase as the temperature of the surplus fuel increases, or variable values that increase as the pressure of the surplus fuel increases.

In the third embodiment, the surplus fuel may be always introduced into the fuel separation device 22 irrespective of whether the fuel used in the engine 1 is switched or not. In this case, by omitting the LPG return passage 16 and the gasoline return passage 17, the passage structure for flowing excess fuel can be simplified.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the overall structure of an engine fuel system to which a fuel device according to a first embodiment is applied.

FIG. 2 is a flowchart showing a procedure for switching a return passage according to the first embodiment;

FIG. 3 is an explanatory diagram for explaining a relationship between a value of a counter C and a ratio between fuel before switching and fuel after switching included in the surplus fuel.

FIG. 4 is a flowchart showing a procedure for switching a return passage according to the second embodiment;

FIG. 5 is an explanatory diagram for explaining how the ratio between LPG and gasoline contained in the surplus fuel changes with respect to changes in the temperature and pressure of the surplus fuel after the start of fuel switching.

FIG. 6 is an explanatory diagram for explaining how the ratio between LPG and gasoline contained in the surplus fuel changes with respect to changes in the temperature and pressure of the surplus fuel after the start of fuel switching.

FIG. 7 shows predetermined values c, d, and e with respect to a temperature change of surplus fuel.
The graph which shows the transition tendency of.

FIG. 8 is a schematic diagram showing the overall structure of an engine fuel system to which the fuel device according to the third embodiment is applied.

FIG. 9 is a flowchart showing a procedure for switching a return passage according to the third embodiment;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Engine, 9 ... LPG tank, 10 ... Gasoline tank, 11 ... Supply fuel switching valve, 12 ... High pressure fuel pump, 1
3 ... supply fuel switching valve, 14 ... pump side return passage, 1
5 tank switching valve, 16 LPG return passage, 17 ...
Gasoline return passage, 18 electronic control unit, 19 temperature sensor, 20 pressure sensor, 21 tank switching valve, 2
2 ... fuel separation device, 23 ... separation return passage, 24 ...
Heater, 25: LPG separation passage, 26: Gasoline separation passage, 27: LPG shutoff valve, 28: Gasoline shutoff valve.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F02M 21/02 F02M 21/02 R 301 301A F term (Reference) 3G084 AA05 BA11 FA14 3G092 AA06 AA08 AB02 AB07 AB12 DF09 EA11 HB03Z HB04Z

Claims (12)

[Claims] 1. A fuel system for an internal combustion engine, comprising: a plurality of fuel tanks for storing different fuels, wherein one of a plurality of types of fuel stored in the fuel tanks is switched and used as fuel for the internal combustion engine. A return passage provided for each fuel tank and returning a surplus of fuel supplied to the internal combustion engine to the fuel tank; and, in each of the return passages, the surplus fuel to the fuel tank. Switching means for switching a return passage actually used to return according to the fuel used in the internal combustion engine. 2. The return passage according to claim 1, wherein the switching means switches the return passage so that the surplus fuel is returned to a fuel tank serving as a fuel supply source used in the internal combustion engine. Fuel device for internal combustion engine. 3. A fuel system for an internal combustion engine according to claim 1, wherein said switching means switches said return passage in conjunction with switching of fuel used in the internal combustion engine. 4. The switching means, when a plurality of types of fuel are included in the surplus fuel in the process of switching the fuel used in the internal combustion engine, is a fuel supply source of the type of fuel most contained. To return the excess fuel to the tank,
4. The fuel device for an internal combustion engine according to claim 3, wherein the return passage is switched. 5. The switching means switches the return passage after the fuel used in the internal combustion engine is switched so that the fuel before the switching is not returned to the fuel tank which is the supply source of the fuel after the switching. The fuel device for an internal combustion engine according to claim 3, wherein the fuel device is used. 6. The switching means determines a ratio of a plurality of types of fuel contained in the surplus fuel based on an elapsed time since switching of fuel used in the internal combustion engine, and based on the determination result. 6. The fuel device for an internal combustion engine according to claim 4, wherein the return passage is switched. 7. The switching means determines a ratio of a plurality of types of fuel contained in the surplus fuel based on at least one of a temperature and a pressure in the surplus fuel, and determines the return based on a result of the determination. 6. The fuel device for an internal combustion engine according to claim 4, wherein the fuel is switched. 8. A fuel system for an internal combustion engine according to claim 1, wherein said internal combustion engine is used by switching between a high boiling point fuel and a low boiling point fuel. 9. The fuel system for an internal combustion engine according to claim 8, wherein a high-boiling fuel and a low-boiling fuel contained in the surplus fuel are connected to a return passage different from a return passage provided for each fuel tank. A fuel separation device that separates the fuel from the fuel and returns the separated fuel to the corresponding fuel tank, wherein the switching unit is configured to switch the surplus fuel at least in a process of switching fuel used in the internal combustion engine. A fuel supply device for an internal combustion engine, wherein the return passage is switched so that the another return passage is used as a return passage for returning the fuel to the fuel tank. 10. The fuel separation device separates the surplus fuel into a gas and a liquid by adjusting the temperature of the surplus fuel to convert the low-boiling fuel into a gas and converting the high-boiling fuel into a liquid. 10. The fuel device for an internal combustion engine according to claim 9, wherein the separated gas is returned to a fuel tank for a low-boiling fuel, and the separated liquid is returned to a fuel tank for a high-boiling fuel. 11. A fuel system for an internal combustion engine, comprising: a plurality of fuel tanks for storing different fuels, wherein one of a plurality of types of fuel stored in the fuel tanks is switched and used as fuel for the internal combustion engine. A surplus fuel supplied to the internal combustion engine is introduced, the surplus fuel is separated for each type, and the separated fuel is returned to the corresponding fuel tank. Fuel device for internal combustion engine. 12. The internal combustion engine uses a low-boiling fuel and a high-boiling fuel by switching, and the fuel separation device adjusts the temperature of the surplus fuel to convert the low-boiling fuel into a gas. The excess fuel is separated into a gas and a liquid by converting the high-boiling fuel into a liquid, and the separated gas is returned to the fuel tank for the low-boiling fuel. The fuel device for an internal combustion engine according to claim 11, wherein the fuel is returned to a fuel tank for fuel.