JP2003227416A - Liquefied gas fuel feeding system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a leakage of a fuel from respective injection holes by maintaining the injection holes of respective fuel injector to an approximately atmospheric pressure at the time of stopping of an engine in the engine using a liquefied gas fuel. <P>SOLUTION: A high pressure route closing valve 11 is provided on a high pressure fuel feeding passage S at an upstream side of a common rail 4 and a return route switch valve 12 and a pressure adjuster 7 are provided on a fuel return route at a downstream side of the common rail 4 to constitute a separation part K between both valves 11, 12. A first by-path route R1 connected to the fuel return route R through the pressure adjuster 7 is provided on the return route switch valve 12. A second by-path route R2 is provided between the separation part K and the fuel return route R and a by-path route closing valve 13 and a compressor 10 are provided thereon. A gas/liquid sensor 21 and a pressure sensor 22 are provided at the separation park K. The respective valves or the like are controlled at the time of stopping of the engine, and a pressure in the separation part K is reduced. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquefied gas fuel supply system using liquefied gas as fuel, and more particularly to a system for preventing leakage of liquefied gas fuel into an engine cylinder while the engine is stopped.

[0002]

2. Description of the Related Art When liquefied gas fuel is injected into an engine cylinder and burned, it is necessary to pressurize the liquefied gas and supply it in a liquid state to an injection system, especially in a high compression engine such as a diesel engine. When used, it is necessary to pressurize the liquefied gas at an extremely high pressure and supply it to the fuel injection system.

Among various liquefied gases, dimethyl ether (hereinafter referred to as DME), which has a high cetane number, generates little PM and NOx, and produces very little soot, is used as a low-pollution fuel instead of diesel oil. Although it has been studied, the viscosity is much lower than that of light oil, so the high fuel residual pressure in the fuel pipe when the engine is stopped causes the injector injection hole even if the injector has a metal seal solenoid valve. There is a problem in that DME gradually leaks and stays in the engine cylinder, causing abnormal combustion when the engine is started.

In order to solve this problem, various proposals have been made in the past, but a typical example is German Patent No. 1961434A1.

In the above publication, high-pressure liquid DME remaining in the high-pressure fuel supply system including a common rail for supplying high-pressure fuel to the injector while the engine is stopped, and the fuel return system for returning excess fuel to the injector to the fuel tank.
By controlling the opening and closing of a plurality of valve devices and collecting them in a low-pressure collection container (also called a purge tank) to maintain the injector injection hole at atmospheric pressure and prevent leakage of DME from the injection hole. It is a thing.

[0006]

However, the purge tank disclosed in the above publication has a high-pressure liquid residue D.
Since ME is inevitably large in capacity to be collected and stored in a low-pressure gas state, for example, it becomes a large tank of 180 liters, so that it is particularly difficult to mount it on a vehicle and the cost of the apparatus also increases. Therefore, there was a problem in practical application.

The present invention has been made in view of the above problems, and prevents liquefied gas fuel with low viscosity such as DME from leaking from the injection hole of the fuel injector into the engine cylinder while the engine is stopped. At the same time, it is an object of the present invention to provide a liquefied gas fuel supply system which has no problem in mountability on a vehicle and is low in device cost.

[0008]

The present invention uses the following technical means in order to solve the above-mentioned problems.

According to a first aspect of the present invention, a fuel tank for storing liquefied gas supplies a fuel to a fuel injector to an engine through a high pressure pump to adjust the fuel pressure to a predetermined fuel injection pressure. In a liquefied gas fuel supply system for returning fuel to the fuel tank via a fuel injector, a high-pressure passage that is provided in a high-pressure fuel supply passage connected from the high-pressure pump to the fuel injector and opens and closes the high-pressure fuel supply passage A first return valve provided on a fuel return path for returning fuel to a fuel tank via the on-off valve and the pressure regulator, and opening and closing the fuel return path and bypassing the pressure regulator and connected to the fuel return path. A return path switching valve for switching to a bypass path of the fuel cell, and a branch from an isolation portion defined by the high-pressure path opening / closing valve and the return path switching valve, A second bypass path connected to the path, provided in the bypass passage of the second, and the bypass passage on-off valve for opening and closing the bypass path of the second, the second
A compressor that is provided in a bypass path for sucking and compressing the gas in the isolated portion and returning it to the fuel tank; a gas-liquid sensor that is provided in the isolated portion and detects the gas ratio of the isolated portion; A pressure sensor that is provided to detect the pressure in the isolated portion, and when the engine is stopped, opens and closes the high-pressure passage opening / closing valve, the return passage switching valve, and the bypass passage opening / closing valve based on the detection values of the gas-liquid sensor and the pressure sensor. Control means for performing switching and operating the compressor to recover the fuel remaining in the isolated portion into the fuel tank.

According to the above invention, the isolation portion defined by the high-pressure passage opening / closing valve and the return passage switching valve communicates with the injection hole of the fuel injector, and the both valves make the above-mentioned configuration possible. The volume is set to be significantly smaller than that of the fuel tank.

Here, when the engine is stopped, the gas ratio and pressure of the isolated portion are detected, and the high pressure passage opening / closing valve, the return passage switching valve, the bypass passage opening / closing valve and the compressor are controlled based on the detected values. Therefore, as will be described later, the high-pressure liquid fuel remaining in the isolated portion is directly collected in the fuel tank, and the residual fuel in the isolated portion becomes a gas state, and then the pressure in the isolated portion decreases to substantially atmospheric pressure. Since the air is sucked by the compressor and decompressed, no fuel leaks from the injection hole of the fuel injector communicating with the isolated portion into the engine cylinder when the engine is stopped.

A second invention according to claim 2 is the first invention according to claim 1, wherein when the engine is stopped,
The high-pressure path opening / closing valve and the bypass path opening / closing valve are closed, the return path switching valve is switched to the first bypass path, and the return path switching valve is closed when the detection value of the gas / liquid sensor becomes equal to or more than a set value. The bypass passage opening / closing valve is opened and the compressor is operated, and when the detection value of the pressure sensor is equal to or less than a set value, the bypass passage opening / closing valve is closed to stop the operation of the compressor. To do.

According to the above invention, when the engine is stopped, the high pressure passage opening / closing valve and the bypass passage opening / closing valve are closed, and the return passage switching valve is switched to the first bypass passage. The high-pressure liquid fuel portion communicating with the hole is partitioned to form the isolation portion, and the high-pressure liquid fuel remaining in the isolation portion is directly returned to the fuel tank via the first bypass path.

Here, since the high pressure liquid fuel remaining in the isolation portion has a small volume in the isolation portion, it rapidly changes to a relatively low pressure gaseous fuel and is balanced by the vapor pressure determined by the temperature of the isolation portion. When the gas ratio of the isolated part detected by the gas-liquid sensor becomes equal to or higher than the set value, the return path switching valve closes, the bypass path open / close valve opens, and the compressor operates. So-called degassing is performed, which is suction-compressed and returns to the fuel tank via the second bypass path, and the isolated portion having a small volume is rapidly depressurized.

When the pressure in the isolated portion detected by the pressure sensor reaches a set value (for example, atmospheric pressure), the bypass passage opening / closing valve is closed and the operation of the compressor is stopped, so that the fuel injector communicating with the isolated portion is closed. The injection holes are also at atmospheric pressure where fuel does not leak.

According to a third aspect of the present invention, the fuel is supplied from a fuel tank for storing liquefied gas to a fuel injector to the engine through a high-pressure pump to adjust the pressure to a predetermined fuel injection pressure. In a liquefied gas fuel supply system for returning fuel to the fuel tank via a fuel injector, a high-pressure passage that is provided in a high-pressure fuel supply passage connected from the high-pressure pump to the fuel injector and opens and closes the high-pressure fuel supply passage An opening / closing valve, a return path opening / closing valve that is provided in a fuel return path for returning fuel to the fuel tank through the pressure regulator, and opens / closes the fuel return path, the high-pressure path opening / closing valve, and the return path opening / closing valve. A second bypass path that branches from the isolated portion and is connected to the fuel return path, and that is provided in the second bypass path and that opens the second bypass path. A third bypass path switching valve for switching to the bypass path connected to the bypass to the fuel return path the pressure regulator as well as, the second
A compressor that is provided in a bypass path for sucking and compressing the gas in the isolated portion and returning it to the fuel tank; a gas-liquid sensor that is provided in the isolated portion and detects the gas ratio of the isolated portion; A pressure sensor that is provided to detect the pressure in the isolated portion, and when the engine is stopped, opens and closes the high-pressure path opening / closing valve, the return path opening / closing valve, and the bypass path switching valve based on the detection values of the gas-liquid sensor and the pressure sensor. Control means for performing switching and operating the compressor to recover the fuel remaining in the isolated portion into the fuel tank.

According to the above invention, different points from the invention according to claim 1 are that a return path switching valve is used instead of the return path switching valve according to claim 1, and that a bypass path opening / closing is used. This is a point that a bypass path switching valve is used instead of the valve, and accordingly, the valve that partitions the isolated portion is different from the valve that switches to the third bypass path corresponding to the first bypass path. Therefore, the function and effect described in the above-mentioned invention of claim 1 can be obtained.

According to a fourth aspect of the present invention, in the third aspect of the present invention, when the engine is stopped, the high pressure passage opening / closing valve and the return passage opening / closing valve are closed and the bypass passage is formed. When the switching valve is switched to the third bypass path, and the detection value of the gas-liquid sensor becomes equal to or more than a set value, the bypass path switching valve is switched to the second bypass path and the compressor is operated to operate the pressure sensor. When the detected value of is less than or equal to the set value, the bypass path switching valve is closed to control the operation of the compressor.

According to the above invention, the on-off valve and the switching valve which are controlled with respect to the invention according to claim 2 are different, but when the engine is stopped, the high pressure liquid fuel remaining in the isolated portion is changed to the third one. By directly returning to the fuel tank via the bypass path of the above, the isolated portion is made into low-pressure gaseous fuel, and then the gaseous fuel of the isolated portion is sucked by the compressor through the second bypass path and returned to the fuel tank. The action of reducing the pressure of the isolated portion to the atmospheric pressure is the same as that of the invention described in claim 2.

A fifth invention according to claim 5 is the first invention.
In the invention according to any one of 4 to 4, a temperature sensor is used in place of the gas-liquid sensor, the gas ratio of the isolated portion is calculated based on each detection value of the temperature sensor and the pressure sensor, It is characterized in that it substitutes the function of a gas-liquid sensor.

According to the above invention, by using the temperature sensor in place of the gas-liquid sensor, the temperature of the isolated portion and the pressure of the isolated portion detected by the pressure sensor are used to obtain D
Since the gas ratio of the isolated portion is obtained from the vapor pressure diagram of ME (see FIG. 9), the function of the gas-liquid sensor is substituted.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a system configuration diagram showing a first embodiment of the present invention. In the figure, 1 is a fuel tank for storing liquefied gas, for example, a DME having a vapor pressure of about 0.5 MPa at 20.degree. It is stored. In this fuel tank 1, D
A feed pump 2 is arranged to increase the pressure of ME to a predetermined pressure (for example, about 3 MPa) and feed the pressure.
The DEM that has been pressure-fed from the
A high pressure pump 3 for increasing the pressure to a high pressure of up to 35 MPa), and a high pressure DM pumped from the high pressure pump 3
An injector 5 having a solenoid valve (not shown) for injecting high-pressure DME is provided in each cylinder (not shown) of the engine 6 through a common rail 4 for accumulating E.

A high-pressure fuel supply passage S connecting the high-pressure pump 3 and the common rail 4 is provided with a high-pressure passage opening / closing valve 11 which is an electromagnetic two-way valve for opening / closing the passage S. Further, a fuel return path R communicating from the common rail 4 to the fuel tank 1 via a pressure regulator 7 is provided, and a high-pressure surplus DME from the common rail 4 is supplied to the fuel regulator 1 at a predetermined fuel injection pressure ( For example, 25 MPa to 35
After adjusting the pressure to (MPa), the fuel is returned to the fuel tank 1 through the fuel return path R through the cooler 8 including a heat exchanger and the check valve 9.

The cooler 8 is used for cooling the DME returning to the fuel tank 1 as much as possible and returning it to the fuel tank 1, and the check valve 9 has an excessive pressure in the fuel tank 1. In the case of, the DME is prevented from flowing back into the fuel return route R.

Here, in the fuel return path portion connecting the common rail 4 and the pressure regulator 7, the fuel return path portion is opened and closed, and the pressure regulator 7 is bypassed and connected to the fuel return path R. Bypass route R1
A return path switching valve 12 including an electromagnetic three-way valve that can be switched to is provided. Further, a second bypass route R branched from the common rail 4 and bypassing the pressure regulator 7 and connected to the fuel return route R
2 is provided, and the second bypass route R2 is provided with a bypass route opening / closing valve 13 and a compressor 10 which are electromagnetic two-way valves that open and close the route R2.

In the high-pressure fuel passage portion including the common rail 4 and the injector 5, an isolation portion K defined by closing the high-pressure passage opening / closing valve 11 and the return passage switching valve 12 is formed. The injection holes (not shown) of the injector 5 communicate with each other. The volume of the isolated portion K is such that the residual DME can be quickly removed when the engine is stopped.
For recovery, the positions of the valves 11 and 12 are set so that the volume is much smaller than that of the fuel tank 1.

Further, in the common rail 4, a gas-liquid sensor 21 for detecting the gas ratio and a pressure sensor 22 for detecting the pressure are provided by the impedance between the electrodes, for example.

The above-mentioned feed pump 2, high-pressure pump 3,
The electromagnetic valve of each injector 5, the compressor 10, the high-pressure path opening / closing valve 11, the return path switching valve 12, the bypass path opening / closing valve 13, the gas-liquid sensor 21, the pressure sensor 22 and the like are electronic control devices (hereinafter referred to as ECUs). ) 30, the operation of the feed pump 2, the high-pressure pump 3, the compressor 10, and the injectors 5 based on the operating start and stop operation of the engine and the detection values of the gas-liquid sensor 21 and the pressure sensor 22. Solenoid valve, high-pressure path open / close valve 1
1, return path switching valve 12, bypass path opening / closing valve 13
The open / close switching of is controlled by the ECU 30.

Next, FIG. 2 is a system configuration diagram showing a second embodiment of the present invention, in which the same reference numerals as those in the first embodiment of FIG. 1 indicate the same or equivalent parts.

As shown in FIG. 2, the difference from the above-described first embodiment in structure is that the return path switching valve 12 is replaced by a return path opening / closing valve 14 composed of an electromagnetic two-way valve. And the bypass path opening / closing valve 13 described above.
Instead of this, a bypass path switching valve 15 composed of an electromagnetic three-way valve is used.

Accordingly, the isolated portion K is partitioned by the return passage opening / closing valve 14 instead of the return passage switching valve 12 and the first bypass passage R is provided.
In place of 1, the third bypass path R3 that connects the bypass path switching valve 15 and the fuel return path R is provided, and the switching that bypasses the pressure regulating valve 7 is replaced by the return path switching valve 12 and the first bypass path R1. The third embodiment is different from the first embodiment shown in FIG. 1 in that it is switched by the bypass path switching valve 15 and the third bypass path R3.

Next, the operation of the first embodiment of the present embodiment will be described.

First, at the time of engine startup and operation, in FIG. 1, the ECU 30 operates the feed pump 2 and the high-pressure pump 3, and at the same time, the solenoid valve of each injector 5, the high-pressure path opening / closing valve 11, and the return path switching valve 12 are operated. Is opened, and the bypass passage opening / closing valve 13 is closed. Therefore, the DME in the fuel tank 1 flows into the common rail 4 through the high-pressure fuel supply path S to accumulate pressure, and is high-pressure injected into the cylinders (not shown) of the engine 6 from the injection holes of the injectors 5 to generate high pressure. Will start. Excess fuel of DME injected into each cylinder is pressure-regulated by the pressure regulator 7, then passes through the cooler 8 and the check valve 9 via the fuel return route R, and returns to the fuel tank 1. Engine start and operation The well-known fuel circulation of time is performed.

Here, when the engine is stopped, FIG.
And the fuel flow path diagram of FIG. 4 and the control flowchart of FIG. 7.

First, when the engine is stopped, as shown in FIG. 7, an engine switch (not shown) is turned off (step 101), and this OFF signal is input to the ECU 30. As a result, as well known, the operation of the feed pump 2 and the high pressure pump 3 is stopped, and the solenoid valve of each injector 5 is closed. In addition to this, in the present invention, the high pressure passage opening / closing valve 11 is closed and the bypass passage opening / closing valve 13 is closed. Is continuously closed (step 102), and the return path switching valve 12 is switched to the first bypass path R1 side (step 103).

In this case, as shown by the arrow in FIG. 3, the high-pressure liquid DME remaining in the isolation portion K including the common rail 4 and each injector 5 communicates with the return path switching valve 12 and the first bypass path R1. Through the cooler 8 and the check valve 9 to directly return to the inside of the fuel tank 1.

Since the isolated portion K has a small volume,
The high-pressure liquid DME rapidly changes to a relatively low-pressure gaseous DME and balances with the vapor pressure determined by the temperature of the isolation portion K. In FIG. 7, the isolation portion directly detected by the gas-liquid sensor 21. When the gas ratio of K becomes equal to or more than the set value (for example, gas ratio of 90% or more) (step 104),
The return path switching valve 12 is closed (step 105),
The bypass passage opening / closing valve 13 is opened (step 106), and the compressor 10 is operated (step 107). In addition,
When the detected value of the gas-liquid sensor 21 is less than or equal to the set value in step 104, the process returns to step 102 and the above flow is repeated.

By the operation of the compressor 10, the gaseous DME remaining in the isolated portion K (for example, as shown in FIG. 9, DME has a vapor pressure of about 2.2 MPa at 80 ° C.) is shown in the figure. As indicated by the arrow 4, the compressor 10 is sucked from the isolated portion K via the second bypass route R2, passes through the cooler 8 and the check valve 9, and passes through the fuel tank 1
The flow returns to.

Here, by the operation of the compressor 10,
The pressure in the isolated portion K is rapidly reduced, but as shown in FIG. 7, when the pressure in the isolated portion K detected by the pressure sensor 22 becomes equal to or lower than a set value (for example, pressure 0.12 MPa or less) (step 108). ), The bypass passage opening / closing valve 13 is closed (step 109), and the operation of the compressor 10 is stopped (step 110). When the detected value of the pressure sensor 22 is equal to or larger than the set value in step 108, the process returns to step 105 and the above flow is repeated. As a result, the pressure of the isolated portion K communicating with the injection hole of each injector 5 becomes close to the atmospheric pressure, so that DM is injected from the injection hole into the engine cylinder.
E will not leak.

Next, the operation of the second embodiment of the present embodiment will be described.

First, since the fuel circulation is the same as in the case of the first embodiment at the time of starting and operating the engine, the description thereof will be omitted.

The time when the engine is stopped will be described based on the fuel flow path diagrams of FIGS. 5 and 6 and the control flowchart of FIG. 8 while omitting the same portions as those in the first embodiment.

First, when the engine 6 is stopped, as shown in FIG. 8, the engine switch is turned off (step 20).
Due to 1), the high pressure passage opening / closing valve 11 and the return passage opening / closing valve 14 are closed (step 202), and the bypass passage switching valve 1
5 is switched to the third bypass route R3 side (step 203).

In this case, as shown by the arrow in FIG. 5, the high-pressure liquid DME remaining in the isolated portion K passes through the bypass path switching valve 15 and the third bypass path R3 and the cooler 8 and the check valve. The flow passes through 9 and returns directly to the fuel tank 1.

Next, as shown in FIG. 8, the gas-liquid sensor 2
When the gas ratio of the isolated portion K detected by 1 becomes equal to or more than a set value (for example, gas ratio of 90% or more) (step 20
4), the bypass path switching valve 15 is the second bypass path R
Switch to 2 side (step 205), compressor 1
0 is activated (step 206).

In this case, the gaseous DME remaining in the isolated portion K is sucked by the compressor 10 via the second bypass route R2 as shown by the arrow in FIG.
Then, the flow returns to the inside of the fuel tank 1 through the check valve 9.
Then, as shown in FIG. 8, the pressure of the isolated portion K detected by the pressure sensor 22 is equal to or lower than a set value (for example, pressure 0.
12 MPa or less) (step 207), the bypass path switching valve 15 is closed (step 208) and the operation of the compressor 10 is stopped (step 209). Therefore, as in the case of the first embodiment, the injection holes of each injector 5 are injected. No longer leaks DME into each cylinder of the engine.

Next, in the present embodiment, a method of directly detecting the gas ratio of the isolated portion K with the gas-liquid sensor 21 was used.
By using a temperature sensor instead of the gas-liquid sensor 21, the temperature of the isolated portion K detected by the temperature sensor and the pressure of the isolated portion K detected by the pressure sensor 22 are used to detect the DME shown in FIG. It is possible to indirectly determine the gas ratio of the isolated portion K from the vapor pressure diagram.

Furthermore, if the time required for switching from the first bypass route R1 or R3 side to the second bypass route R2 side is previously obtained by an experiment, this time can be controlled by a timer. The gas-liquid sensor 21 is eliminated because it is the same as indirectly detecting and controlling the gas ratio of the isolated portion K.

Next, in the present embodiment, the case of application to the common rail type fuel injection device has been described, but the present invention can also be applied to a conventional jerk type fuel injection device.

Although DME was taken as the liquefied gas fuel, the same effect as that of the present embodiment can be obtained with liquefied gas having a low viscosity such as DME. Further, although the electromagnetic three-way valve is used as the switching valve for the fuel return path and the bypass path, the same function can be obtained by using two ordinary two-way electromagnetic valves.

[0052]

Since the present invention is constructed as described above, it has the following effects.

(1) Since the injection holes of each fuel injector communicating with the isolated portion are maintained at substantially atmospheric pressure when the engine is stopped, the fuel injected from each injection hole into each cylinder of the engine is maintained. Is eliminated, which prevents the occurrence of abnormal combustion at engine start.

(2) Since a large purge tank for collecting the high-pressure liquid fuel is not required, there is no problem in mountability on the vehicle, and the system is composed of a relatively simple structure and simple control. , The equipment cost of the system is reduced.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing a first embodiment of the present invention.

FIG. 2 is a system configuration diagram showing a second embodiment of the present invention.

FIG. 3 is a path diagram showing a fuel flow when the engine is stopped in the first embodiment.

FIG. 4 is a route diagram showing a fuel flow after the engine is stopped in the first embodiment.

FIG. 5 is a route diagram showing a fuel flow when the engine is stopped in the second embodiment.

FIG. 6 is a route diagram showing a fuel flow after the engine is stopped in the second embodiment.

FIG. 7 is a control flowchart when the engine is stopped in the first embodiment.

FIG. 8 is a control flowchart when the engine is stopped in the second embodiment.

FIG. 9 is a vapor pressure diagram of DME (dimethyl ether).

[Explanation of symbols]

1 fuel tank 2 feed pump 3 high pressure pump 4 common rail 5 Fuel injector (injector) 6 engine 7 Pressure regulator 8 cooler 9 Check valve 10 compressor 11 High pressure path open / close valve 12 Return path switching valve 13 Bypass path open / close valve 14 Return path open / close valve 15 Bypass path switching valve 21 Gas-liquid sensor 22 Pressure sensor 30 electronic control unit (ECU) S High pressure fuel supply route R fuel return route R1 First bypass path R2 Second bypass route R3 Third bypass route

Claims (5)

[Claims] Claim: What is claimed is: 1. A fuel tank for storing liquefied gas supplies fuel to a fuel injector to an engine via a high-pressure pump, and supplies fuel to the fuel tank via a pressure regulator that regulates a predetermined fuel injection pressure. In the liquefied gas fuel supply system for returning, a high pressure passage opening / closing valve which is provided in a high pressure fuel supply passage connected from the high pressure pump to the fuel injector and opens and closes the high pressure fuel supply passage, and the pressure regulator are provided. A return path switching valve that is provided in a fuel return path for returning fuel to a fuel tank, opens and closes the fuel return path, and bypasses the pressure regulator to switch to a first bypass path connected to the fuel return path. A second bypass branching from an isolation portion defined by the high-pressure passage opening / closing valve and the return passage switching valve and connected to the fuel return passage. A bypass path, a bypass path opening / closing valve provided in the second bypass path and opening / closing the second bypass path, and a bypass path provided in the second bypass path for sucking and compressing the gas in the isolated portion A compressor for returning to a fuel tank, a gas-liquid sensor provided in the isolated portion for detecting a gas ratio of the isolated portion, a pressure sensor provided in the isolated portion for detecting the pressure of the isolated portion, and when the engine is stopped. Is for switching the high-pressure path opening / closing valve, the return path switching valve and the bypass path opening / closing valve based on the detection values of the gas-liquid sensor and the pressure sensor,
A liquefied gas fuel supply system comprising: a control unit that operates the compressor to recover the fuel remaining in the isolated portion into the fuel tank. 2. When the engine is stopped, the high pressure passage opening / closing valve and the bypass passage opening / closing valve are closed, the return passage switching valve is switched to the first bypass passage, and the detection value of the gas / liquid sensor is equal to or higher than a set value. Then, the return path switching valve is closed to open the bypass path opening / closing valve and the compressor is operated, and when the detection value of the pressure sensor is equal to or less than a set value, the bypass path opening / closing valve is closed to operate the compressor. The liquefied gas fuel supply system according to claim 1, wherein the liquefied gas fuel supply system is controlled to stop. 3. Fuel is supplied from a fuel tank for storing liquefied gas to a fuel injector to an engine via a high-pressure pump, and the fuel is supplied to the fuel tank via a pressure regulator for adjusting a fuel injection pressure to a predetermined value. In the liquefied gas fuel supply system for returning, a high pressure passage opening / closing valve which is provided in a high pressure fuel supply passage connected from the high pressure pump to the fuel injector and opens and closes the high pressure fuel supply passage, and the pressure regulator are provided. A return path opening / closing valve for opening and closing the fuel return path, which is provided in a fuel return path for returning fuel to a fuel tank, and is branched from an isolated portion defined by the high pressure path opening / closing valve and the return path opening / closing valve, A second bypass path connected to the fuel return path; and a second bypass path provided in the second bypass path for opening and closing the second bypass path and adjusting the pressure. And a bypass path switching valve that switches to a third bypass path that is connected to the fuel return path, and that is provided in the second bypass path and sucks and compresses the gas in the isolated portion to return it to the fuel tank. A compressor, a gas-liquid sensor provided in the isolated portion to detect the gas ratio of the isolated portion, a pressure sensor provided in the isolated portion to detect the pressure of the isolated portion, and the gas sensor when the engine is stopped. Based on the detection values of the liquid sensor and the pressure sensor, the high pressure path opening / closing valve, the return path opening / closing valve, and the bypass path switching valve are opened / closed, and
A liquefied gas fuel supply system comprising: a control unit that operates the compressor to recover the fuel remaining in the isolated portion into the fuel tank. 4. When the engine is stopped, the high pressure passage opening / closing valve and the return passage opening / closing valve are closed, the bypass passage switching valve is switched to the third bypass passage, and the detected value of the gas-liquid sensor becomes equal to or higher than a set value. Then, the bypass path switching valve is switched to the second bypass path and the compressor is operated, and when the detection value of the pressure sensor becomes equal to or less than a set value, the bypass path switching valve is closed and the operation of the compressor is stopped. The liquefied gas fuel supply system according to claim 3, wherein the liquefied gas fuel supply system is controlled to 5. A temperature sensor is used instead of the gas-liquid sensor, the gas ratio of the isolated portion is calculated based on the detection values of the temperature sensor and the pressure sensor, and the function of the gas-liquid sensor is substituted. The liquefied gas fuel supply system according to any one of claims 1 to 4, characterized in that.