JP2008045463A - Fuel injection device for supercritical fuel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel injection device for a vehicle, which keeps supercritical fuel in a fuel tank under a liquid form with keeping cost low. <P>SOLUTION: The fuel tank 7 is comprised of a main tank 21 of large capacity and a heat insulating structure sub tank 2 of small capacity, and an electric heater 26 heating fuel in the sub tank 22 is provided. DME in the fuel tank 7 is heated by the electric heater 26 and pressure in the fuel tank 7 rises due to evaporation of fuel. Concretely, pressure in the main tank 21 is controlled to keep fuel in a fuel suction side of a high pressure pump 6 under a liquid form. Pressure in the fuel tank 7 is raised, and DME in the fuel tank 7 is liquefied by the light weight low cost electric heater 26 instead of high cost compressor and nitrogen bomb which are used in former technology, and cost of the fuel injection device is reduced. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel injection device for a vehicle using a supercritical fuel (low critical fuel) that does not liquefy at normal temperature and pressure.

(Prior art 1)
As an example of supercritical fuel, a vehicle fuel injection device using DME (dimethyl ether) is known (for example, Patent Document 1).
An example of a fuel injection device using DME will be described with reference to FIG.
DME is refined using natural gas, coal, biomass and the like as raw materials. This DME has a relatively low vapor pressure. For this reason, it is stored in the fuel tank J1 in a state of being pressurized and liquefied around 10 atm.

The DME stored in the fuel tank J1 is supplied to the injector J5 at a high pressure via the high pressure feed pump J2, the high pressure pump J3, and the common rail J4, and is injected from the injector J5 into the engine cylinder. The required injection pressure of the injector J5 is high, and the leaked fuel led from the injector J5 to the return pipe J6 has a high temperature. For this reason, the leak fuel led to the return pipe J6 is easily vaporized in the return pipe J6.
In order to liquefy the vaporized leaked fuel and return it to the fuel tank J1, a dedicated compressor J7 has been conventionally mounted.
However, by installing an expensive compressor J7 only for liquefying leaked fuel and returning it to the fuel tank J1, the cost of the fuel injection device using DME has been increased.

(Prior art 2)
As another fuel injection device using DME, a method of liquefying DME by supplying nitrogen gas to the fuel tank and setting the pressure inside the fuel tank to exceed the saturated vapor pressure has been proposed (not shown: For example, Patent Document 2).
The fuel injection device that boosts the pressure by supplying nitrogen gas to the fuel tank is less problematic as long as it is stationary.
However, if this technology is applied to a vehicle, it is necessary to mount a nitrogen cylinder on the vehicle, which is expensive and heavy. In addition to DME, it is necessary to replenish nitrogen gas, so that it is difficult to apply to a vehicle.
JP 2003-3925 A JP-A-10-306760

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a fuel injection device for a vehicle that can maintain supercritical fuel in a fuel tank in a liquid state at a reduced cost.

[Means of claim 1]
The fuel injection device for a supercritical fuel employing the means of claim 1 raises the internal pressure of the fuel tank by heating the supercritical fuel in the fuel tank by the heating means. Thereby, the pressure in the fuel tank can be made to exceed the saturated vapor pressure, and the supercritical fuel in the fuel tank can be liquefied. That is, the supercritical fuel can be liquefied by increasing the pressure in the fuel tank by a heating means instead of the expensive compressor or nitrogen cylinder used in the prior art.
When using compressors and nitrogen cylinders that have been used in the prior art, you can use inexpensive, lightweight and compact electric heaters and vehicle exhaust heat (engine exhaust heat, cooling water heat, intercooler exhaust heat, etc.) as heating means. In comparison, the cost of the fuel injection device for supercritical fuel can be reduced.

[Means of claim 2]
The fuel tank of the fuel injection apparatus for supercritical fuel adopting the means of claim 2 is composed of a main tank and a sub tank, and heating means is provided in the sub tank. Thereby, the temperature of the supercritical fuel can be easily raised by the heating means, and the pressure in the fuel tank can be easily increased.
The main tank and the sub tank communicate with each other through a gas communication portion having a small passage resistance in the upper portion and communicate with each other through a liquid communication portion having a large passage resistance in the lower portion. Thereby, the high pressure generated in the sub tank is applied to the main tank through the gas communication portion having a small passage resistance. On the other hand, since the high-temperature liquid fuel heated in the sub-tank and the liquid fuel in the main tank communicate with each other via a liquid communication portion having a large passage resistance, an increase in the temperature of the liquid fuel in the main tank can be suppressed. The heat of the liquid fuel in the sub tank can be prevented from leaking outside.

[Means of claim 3]
The sub-tank of the fuel injection device for supercritical fuel adopting the means of claim 3 is provided outside the main tank.
Thus, by separating the sub tank from the main tank, it becomes easy to mount a heating means or the like and adopt a heat insulating structure.

[Means of claim 4]
The sub tank of the fuel injection device for supercritical fuel adopting the means of claim 4 is provided inside the main tank.
Thereby, the mounting space of the fuel tank can be reduced.

[Means of claim 5]
A fuel injection device for a supercritical fuel employing the means of claim 5 includes a cooling means for cooling the fuel in the fuel tank.
Thereby, it is possible to prevent the temperature in the fuel tank (the temperature in the sub-tank in claims 2 to 4) from becoming abnormally high due to the operation of the heating means, or to prevent the fuel tank from becoming abnormally high in pressure.

[Means of claim 6]
In the fuel injection device for supercritical fuel adopting the means of claim 6, pressurized air is supplied into the fuel tank by the air supply means to increase the internal pressure of the fuel tank. Thereby, the pressure in the fuel tank can be made to exceed the saturated vapor pressure, and the supercritical fuel in the fuel tank can be liquefied. In other words, the supercritical fuel can be liquefied by increasing the pressure in the fuel tank by the air supply means instead of the expensive compressor or nitrogen cylinder used in the prior art.
As an air supply means, a versatile and inexpensive air compressor or an existing air pump (air brake pump, etc.) mounted on a vehicle can be used. Therefore, when using a compressor or nitrogen cylinder used in the prior art In comparison, the cost of the fuel injection device for supercritical fuel can be reduced.

[Means of Claim 7]
In the fuel injection device for supercritical fuel employing the means of claim 7, the pressure in the fuel tank or the fuel pressure on the fuel suction side of the high pressure pump that compresses and discharges the fuel to a high pressure is equal to or higher than the saturated vapor pressure. A control device for controlling the heating means or the air supply means.
In this way, the control device controls the heating means or the air supply means, so that the supercritical fuel in the fuel tank can be maintained in a liquefied state, or the fuel in the fuel tank can be liquefied and the high pressure pump can be maintained. The fuel on the fuel suction side can be maintained in a liquefied state.

  The fuel injection device for supercritical fuel according to the best mode 1 is a heating means (for example, an electric heater, engine exhaust heat, cooling water) that heats fuel in a fuel tank that stores supercritical fuel to increase the internal pressure of the fuel tank. Heat, intercooler exhaust heat, etc.). The heating means heats the supercritical fuel in the fuel tank to increase the internal pressure of the fuel tank, whereby the supercritical fuel in the fuel tank can be liquefied.

  The fuel injection device for supercritical fuel according to the best mode 2 is an air supply means (for example, an air brake pump) that supplies pressurized air into a fuel tank that stores supercritical fuel to increase the internal pressure of the fuel tank. Is provided.

A fuel injection device using DME as an example of supercritical fuel will be described with reference to FIGS.
The fuel injection device is a system that injects fuel into each cylinder of an engine (not shown), and includes a supply pump 1, a common rail 2, an injector 3, and a control device 4 as shown in FIG.
The control device 4 is composed of an ECU (engine control unit) 4a and an EDU (drive unit) 4b. The ECU 4a and the EDU 4b may be provided separately or in one case. It may be a built-in device.

(Description of supply pump 1)
The supply pump 1 is an integrated fuel pump that drives the feed pump 5 and the high-pressure pump 6 by a common camshaft (a drive shaft that is rotationally driven by the engine). The supply pump 1 is obtained by adding an improvement for DME to a type mounted on a commonly used common rail fuel injection device (fuel injection device for a diesel engine).

The feed pump 5 is connected to the fuel tank 7 via a fuel pipe 8, and the fuel pump 7 is disposed in the fuel tank 7 through a shutoff valve 9 and a fuel filter 10 provided in the middle of the fuel pipe 8. This is a fuel suction pump that sucks the fuel in the tank 21 and sends it to the high-pressure pump 6.
The shut-off valve 9 is, for example, a normally closed solenoid valve, and is energized from the ECU 4a to open the fuel pipe 8 while the engine is operating (when the ignition switch is ON), and is de-energized when the engine is stopped (when the ignition switch is OFF). The fuel pipe 8 is closed.
The fuel filter 10 has a pulsation (caused by the operation of the feed pump 5 and the high-pressure pump 6) generated in the fuel pipe 8 due to its internal volume and the cross-sectional area of the connection passage of the fuel pipe 8 in addition to the original role of filtering the fuel. It plays a role in absorbing pulsation and the like.
Needless to say, the shutoff valve 9 and the fuel filter 10 have a structure that can cope with a high feed pressure.

The supply pump 1 is equipped with a pressure regulating valve 11 that adjusts the gallery pressure on the fuel suction side of the high-pressure pump 6 to a predetermined feed gallery pressure.
The fuel vapor pressure in the fuel tank 7 is added behind the pressure regulating valve 11, and the valve opening pressure is automatically adjusted in accordance with the fuel vapor pressure, that is, the fuel temperature, and the inside of the gallery on the fuel suction side of the high-pressure pump 6. The DME is provided so as not to vaporize. The DME that has passed through the pressure regulating valve 11 is guided to the return pipe 12 and returned to the fuel tank 7 (specifically, a main tank 21 described later) via the check valve 13.

The high pressure pump 6 is a fuel compression pump that compresses the fuel regulated by the pressure regulating valve 11 to a high pressure and pumps the fuel to the common rail 2 via a discharge valve (check valve) 14.
An SCV (suction metering valve) for adjusting the degree of opening of the fuel flow path is provided in a fuel flow path for sending fuel from the feed pump 5 to the high pressure pump 6 (specifically, a fuel pressurizing chamber in the high pressure pump 6). ) 15 is mounted. The SCV 15 is a metering valve that adjusts the amount of fuel sucked into the high-pressure pump 6 by being controlled by a pump drive signal from the control device 4 and changes the amount of fuel discharged to the common rail 2. The common rail pressure is adjusted by adjusting the discharge amount of fuel pumped to the common rail 2. That is, the control device 4 controls the SCV 15 to control the common rail pressure to a pressure corresponding to the vehicle running state.

(Description of common rail 2)
The common rail 2 is a pressure accumulating container for accumulating high-pressure fuel supplied to the injector 3, and is connected to the discharge valve 14 of the high-pressure pump 6 via the high-pressure pump pipe 16 so that the common rail pressure corresponding to the fuel injection pressure is accumulated. In addition, a plurality of injector pipes 17 for supplying high pressure fuel to each injector 3 are connected.

  A pressure reducing valve 18 that also serves as a pressure limiter is attached to one end of the common rail 2. The pressure reducing valve 18 is opened by a valve opening instruction signal given from the control device 4 and rapidly reduces the common rail pressure via the return pipe 12. Thus, by mounting the pressure reducing valve 18 on the common rail 2, the control device 4 can quickly control the common rail pressure to be reduced to a pressure corresponding to the vehicle running state.

(Description of injector 3)
The injector 3 is mounted in each cylinder of the engine and supplies fuel into each cylinder, and is connected to the downstream ends of a plurality of injector pipes 17 branched from the common rail 2.
The injector 3 is equipped with an electric actuator such as a solenoid or a piezo actuator. The electric actuator is controlled by an injection signal from the control device 4 to inject high-pressure fuel accumulated in the common rail 2 from the nozzle 3a at the tip.

Low-pressure leaked fuel leaking from the injector 3 is guided to the return pipe 12 and returned to the fuel tank 7 via the check valve 13.
Here, a fuel switching valve 19 is provided in the return pipe 12 upstream of the check valve 13. The fuel switching valve 19 is, for example, an electromagnetic three-way valve, which normally returns leaked fuel to the fuel tank 7 and purges the return pipe 12 when a purge signal (for example, energization stop due to engine stop) is given from the control device 4. It connects to the passage. The purge passage is connected to an intake pipe of the engine, a purge tank or the like.

(Description of fuel tank 7)
The fuel tank 7 is a container having excellent pressure resistance, corrosion resistance, flammability, and the like that is safe and can be replenished with DME that has been pressurized to about 10 atm from the outside, and has a large volume. It consists of a main tank 21 and a sub tank 22 having a small volume.
The sub tank 22 of this embodiment is provided independently of the main tank 21 and is mounted on the vehicle at substantially the same height as the main tank 21.
The main tank 21 and the sub tank 22 communicate with each other via a gas communication portion 23 having a small passage resistance in the upper portion and communicate with each other via a liquid communication portion 24 having a large passage resistance in the lower portion.

Specifically, the upper part of the main tank 21 and the sub tank 22 is connected by an upper pipe (an example of the gas communication part 23) having a large channel cross section, and the pressure generated in the sub tank 22 (operation of an electric heater 26 described later) The rising pressure in the sub tank 22 generated by the above is easily applied to the main tank 21.
The lower part of the main tank 21 and the sub tank 22 is connected by a lower pipe (an example of the liquid communication part 24) having a small channel cross section, and the liquid fuel whose temperature has risen in the sub tank 22 (operation of an electric heater 26 described later) The fuel in the sub-tank 22 heated by the gas does not easily flow into the main tank 21.

The sub tank 22 is provided in a heat insulating structure or a simple heat insulating structure, and has a structure in which the fuel temperature in the sub tank 22 heated by the operation of an electric heater 26 described later does not easily cool.
In addition, a safety valve 25 that opens when the internal pressure of the fuel tank 7 reaches a predetermined upper limit pressure and releases the pressure in the fuel tank 7 to the outside is provided at one upper portion of the main tank 21 or the sub tank 22. Yes.

Inside the sub tank 22, heating means for heating the DME in the sub tank 22 and increasing the internal pressure of the sub tank 22 is provided. The heating means of this embodiment is an electric heater 26 that is installed, for example, in the lower part of the sub tank 22 and generates heat when energized to heat the liquid fuel in the sub tank 22.
The electric heater 26 is energized by the control device 4 to adjust the temperature of the liquid fuel in the sub tank 22 and control the pressure in the main tank 21 and the sub tank 22. The energization control of the electric heater 26 will be described later.

  A fuel cooler 27 (cooling means) that cools the DME in the sub tank 22 is provided inside the sub tank 22. The fuel cooler 27 is a means for cooling the DME of the sub-tank 22 by the cooling fluid such as the cooling water on the low temperature side of the engine, the cooling / cooling refrigerant for cooling, the vehicle running wind, and the like. Supply and stop of the fluid (opening and closing of a valve provided in a pipe for guiding the cooling fluid to the fuel cooler 27) is controlled by the control device 4. The control of the fuel cooler 27 will be described later.

(Description of the control device 4)
The control device 4 controls energization of each electrical functional component described above, and is configured by an ECU 4a and an EDU 4b.
The ECU 4a is a well-known structure including a CPU that performs control processing and arithmetic processing, a storage device (memory such as ROM, RAM, SRAM, and EEPROM) that stores various programs and data, an input circuit, an output circuit, and a power supply circuit. Of computers.
The ECU 4a performs various arithmetic processes based on the read sensor signals (engine parameters: signals corresponding to the operating state of the occupant and the operating state of the engine).

  The ECU 4a includes, as sensors for detecting engine parameters, an accelerator sensor for detecting an accelerator opening, a rotational speed sensor for detecting engine speed and crank angle, a water temperature sensor for detecting engine cooling water temperature, a common rail pressure, and the like. In addition to the sensors of a common rail fuel injection device for a normal diesel engine, such as a common rail pressure sensor 31 for detecting the fuel pressure, a common rail temperature sensor 32 for detecting the fuel temperature accumulated in the common rail 2 and a fuel suction side of the high pressure pump 6 A gallery temperature sensor 33 for detecting the fuel temperature, a sub tank temperature sensor 34 for detecting the fuel temperature in the sub tank 22, and a main tank pressure sensor 35 for detecting the pressure in the main tank 21 are connected.

(Explanation of pressure control function)
In addition to the normal injection control function for controlling the injector 3 and the SCV 15 according to the driving state of the vehicle, the control device 4 has a fuel pressure (feed gallery pressure) on the fuel suction side of the high-pressure pump 6 as the saturated vapor pressure of DME. As described above, that is, a pressure control function for controlling the energization state of the electric heater 26 is mounted so that the DME on the fuel suction side of the high-pressure pump 6 is in a liquid state.
This pressure control function is a control program stored in the memory of the ECU 4a and executed by the ECU 4a. A specific example of the energization control of the electric heater 26 by the pressure control function is shown in the flowchart of FIG. 2 and the saturated steam of FIG. This will be described with reference to the pressure curve.

When entering the control routine for the pressure control function (start), the ECU 4a executes the following control.
Step S1: The fuel temperature (gallery temperature Tgr) on the fuel suction side of the high-pressure pump 6 detected by the gallery temperature sensor 33 is read.
Step S2: The tank target pressure Ptt (= gallery target pressure Pft) is calculated from the gallery temperature Tgr read in step S1.

A specific example of step S2 will be described. The ECU 4a stores a map of the saturated vapor pressure curve shown in FIG. Then, the tank target pressure Ptt (= gallery target pressure Pft) at which the feed gallery pressure becomes equal to or higher than the saturated vapor pressure of DME is calculated from the read saturation pressure of the gallery temperature Tgr.
Furthermore, the calculation flow of the tank target pressure Ptt (= gallery target pressure Pft) will be described based on a specific example.

First, when the read gallery temperature Tgr is (1) in FIG. 3, the basic gallery pressure Pg corresponding to the gallery temperature Tgr is (2) in FIG.
Since the feed pump 5 has the DME pressure Pfp indicated by (3) in FIG. 3, the pressure in the fuel tank 7 may be (2)-(3). However, in actuality, there is a pressure drop in fuel intake in the high-pressure pump 6. Therefore, the margin control width Pgm shown by (4) in FIG. 3 is given as the margin pressure equal to or higher than the saturated vapor pressure of DME.
In this way, the tank target pressure Ptt for bringing the DME on the fuel suction side of the high-pressure pump 6 into a liquid state is calculated by (5) = (2) − (3) + (4).
That is, it is calculated by Ptt = Pg−Pfp + Pgm.

Step S3: The fuel temperature (tank temperature Ttr) in the sub tank 22 detected by the sub tank temperature sensor 34 is read.
Step S4: Based on the tank target pressure Ptt (= gallery target pressure Pft) calculated in Step S2, the target temperature Ttt in the sub tank 22 is calculated. Specifically, the tank target temperature Ttt is calculated from the tank target pressure Ptt (= gallery target pressure Pft) based on the map of the saturated vapor pressure curve shown in FIG. That is, if the tank target pressure Ptt (= gallery target pressure Pft) is (5) in FIG. 3, (6) in FIG. 3 is obtained as the tank target temperature Ttt corresponding to (5).

Step S5: The electric heater 26 or the fuel cooler 27 is controlled so as to be the tank target temperature Ttt obtained in step S4.
Specifically, the tank internal temperature Ttt obtained in step S4 is subtracted from the tank internal temperature Ttr read in step S3 (Ttr−Ttt). If Ttr <Ttt, the electric heater 26 is energized to turn on the tank internal temperature. When Ttr is raised to the in-tank target temperature Ttt, conversely, when Ttr> Ttt, the fuel cooler 27 is operated to lower the in-tank temperature Ttr to the in-tank target temperature Ttt.

Step S6: The pressure in the main tank 21 (tank pressure Ptr) detected by the main tank pressure sensor 35 is read.
Step S7: When the tank internal temperature Ttr and the tank internal target temperature Ttt are substantially equal (Ttr≈Ttt) and the tank internal pressure Ptr and the tank internal target pressure Ptt are different (Ptr ≠ Ptt) in step S5 Correction control is performed based on a difference (Ptr−Ptt) between the pressure Ptr and the tank target pressure Ptt.
In the correction control, a correction value is obtained and the tank internal pressure Ptr and the tank target pressure Ptt are made to coincide with each other based on the correction value. The operation output of the cooler 27 may be corrected and controlled.

(Modification of control)
In this embodiment, in the case where Ttr> Ttt in step S5, the fuel cooler 27 is operated to lower the tank temperature Ttr to the tank target temperature Ttt. However, the tank temperature Ttr is set to the upper limit set in advance. The fuel cooler 27 may be operated so as not to reach the temperature, or the fuel cooler 27 may be operated so that the tank internal pressure Ptr does not reach a preset upper limit pressure.
Further, the correction control in steps S6 and S7 may be abolished, and the tank target pressure Ptt or the tank target temperature Ttt may be calculated in consideration of the error.

(Operation of Example 1)
When the electric heater 26 is energized by the operation of the control device 4 and the inside of the sub tank 22 is heated, a part of the liquid fuel in the sub tank 22 is vaporized and the internal pressure rises. The pressure increased in the sub tank 22 is guided into the main tank 21 via the upper pipe having a large flow path cross section, and the pressure in the main tank 21 is increased. The pressure in the main tank 21 is controlled to the tank target pressure Ptt by the pressure control function described above. That is, the pressure in the main tank 21 is controlled so that the fuel on the fuel suction side of the high-pressure pump 6 is in a liquid state.

(Effect of Example 1)
As described above, the fuel injection device according to the first embodiment increases the internal pressure of the fuel tank 7 by heating the DME in the fuel tank 7 with the electric heater 26. Thereby, the inside of the fuel tank 7 can be set to a pressure exceeding the saturated vapor pressure, and the DME in the fuel tank 7 can be liquefied. In other words, the DME in the fuel tank 7 can be liquefied by increasing the pressure in the fuel tank 7 with a light and inexpensive electric heater 26 instead of the expensive compressor or nitrogen cylinder used in the prior art.
Thereby, the cost of the fuel injection device using DME can be reduced as compared with the conventional technique (when a compressor or a nitrogen cylinder is used). Specifically, the high pressure feed pump J2, the compressor J7, the purge tank J8, etc. can be eliminated from the prior art (Patent Document 1) shown in FIG.

  The fuel injection device according to the first embodiment controls the pressure in the main tank 21 so that the fuel on the fuel suction side of the high-pressure pump 6 is in a liquid state. For this reason, the fuel supply cooler 51 (symbol, see FIG. 8 of Embodiment 6) for cooling DME guided from the fuel tank 7 to the feed pump 5 can be eliminated, and the cost of the fuel injection device using DME can be reduced. .

In the fuel injection device of Example 1, the fuel tank 7 is divided into a main tank 21 and a sub tank 22, and an electric heater 26 is mounted in the sub tank 22 having a small volume. Thereby, since the fuel temperature easily rises by the electric heater 26, the capacity of the electric heater 26 can be reduced, and the power consumption of the electric heater 26 can be suppressed.
Further, the upper part of the main tank 21 and the sub tank 22 is communicated with a gas communication part 23 having a small passage resistance, and the lower part of the main tank 21 and the sub tank 22 is communicated with a liquid communication part 24 having a large passage resistance. As a result, the high pressure generated in the sub tank 22 is applied to the main tank 21 via the gas communication portion 23 having a small passage resistance, but the high-temperature liquid fuel heated in the sub tank 22 is connected to the liquid communication having a large passage resistance. Since the portion 24 hardly flows into the main tank 21, an increase in the temperature of the fuel in the main tank 21 can be suppressed, and the heat of the fuel in the sub tank 22 can be prevented from leaking to the outside.
Further, in this embodiment, the sub tank 22 is provided outside the main tank 21. Thereby, the mounting property of the electric heater 26 and the fuel cooler 27 can be improved, and the heat insulating structure of the sub tank 22 can be easily adopted.

  Further, the fuel injection device of the first embodiment is provided with a fuel cooler 27 that cools the DME in the sub tank 22. As a result, it is possible to prevent the fuel temperature in the sub tank 22 from becoming abnormally high due to the operation of the electric heater 26, and to avoid the fuel tank 7 from becoming abnormally high in pressure.

A second embodiment will be described with reference to FIG. In the following examples, the same reference numerals as those in Example 1 denote the same functional objects.
In this second embodiment, in place of the electric heater 26 (reference numeral, see FIG. 1) shown in the first embodiment, exhaust heat (engine exhaust heat, cooling water heat, intercooler exhaust heat, etc.) in the vehicle is used. The DME in the 22 is heated.

Specifically, in this embodiment, a heat exchanger 41 into which a high-temperature fluid by exhaust heat is introduced is provided in the sub tank 22 as a heating means. This heat exchanger 41 exchanges heat between the high-temperature fluid flowing inside and the DME in the sub tank 22 to heat the DME in the sub tank 22, thereby increasing the internal pressure of the fuel tank 7 and liquefying the DME. It is intended.
As an example of the high-temperature fluid led to the heat exchanger 41, there are cooling water on the high temperature side of the engine, supercharged air pressurized by the supercharger, EGR gas returned from the exhaust pipe to the intake pipe, and the like. That is, when the cooling water is guided to the heat exchanger 41, the heat exchanger 41 serves as a part of the radiator, and when the supercharged air is guided to the heat exchanger 41, the heat exchanger 41 serves as the intercooler. And the EGR gas is guided to the heat exchanger 41 so that the heat exchanger 41 serves as an EGR cooler.

  When the high-temperature fluid guided to the heat exchanger 41 heats the liquid fuel in the sub tank 22, the DME in the sub tank 22 is vaporized by receiving the heat. When this DME vaporizes, the heat of vaporization efficiently cools the high-temperature fluid flowing in the heat exchanger 41. In other words, even if the heat exchanger 41 mounted in the sub tank 22 is small, the fuel in the sub tank 22 can be efficiently heated. In addition, since engine cooling water, supercharger, and EGR gas, which are high-temperature fluids, are efficiently cooled, engine output can be improved and exhaust gas can be reduced.

  In the first embodiment, energization of the electric heater 26 is controlled as a means for controlling the heating amount of the fuel in the sub-tank 22, but in this embodiment, the pipe 42 that guides the high-temperature fluid to the heat exchanger 41 is used. The heating amount of the fuel in the sub tank 22 is controlled by controlling the opening of the metering valve 43 provided by the control device 4.

  Further, in the second embodiment, the fuel switching valve 19 (symbol, see FIG. 1) shown in the first embodiment is abolished, and the internal pressure of the return pipe 12 is adjusted by the opening pressure of the check valve 13 and the safety valve 25. ing. That is, the internal pressure of the return pipe 12 is determined by the set pressure of the check valve 13 and the pressure in the fuel tank 7. For this reason, the safety valve 25 becomes the final pressure setting means. When the pressure in the fuel tank 7 rises to the opening pressure of the safety valve 25, or when the internal pressure of the return pipe 12 rises and the check valve 13 opens, the pressure in the fuel tank 7 opens the safety valve 25. When the valve pressure rises, the safety valve 25 is opened to prevent abnormal high pressure.

A third embodiment will be described with reference to FIG.
In the first embodiment, an example in which the sub tank 22 is provided separately from the main tank 21 has been described.
On the other hand, in the third embodiment, the sub tank 22 is provided inside the main tank 21. Specifically, a partition wall 44 that partitions the inside of the main tank 21 is provided inside the main tank 21, and a small-capacity sub-tank 22 is provided inside the main tank 21.

The partition wall 44 has a heat insulating structure and is provided so as to suppress the heat of the fuel in the sub tank 22 from being transmitted to the fuel in the main tank 21.
The partition wall 44 has a large opening in the upper part to communicate the inside of the main tank 21 and the sub tank 22, and the opening in the upper part of the partition wall 44 corresponds to the gas communication part 23. Further, the partition wall 44 is provided with a small through hole in the lower part, and this through hole corresponds to the liquid communication part 24.
As shown in the third embodiment, since the sub tank 22 is configured by providing the partition wall 44 inside the main tank 21, the fuel tank 7 can be made compact and the mounting property to the vehicle can be improved. It is to be noted that the fuel switching valve 19 (reference numeral, see FIG. 1) is omitted as in the second embodiment.

A fourth embodiment will be described with reference to FIG.
In the said Example 1, the example using the supply pump 1 which integrated the feed pump 5 and the high pressure pump 6 was shown.
On the other hand, in the fourth embodiment, the feed pump 5 is eliminated, and an electric fuel pump 45 is mounted in the fuel tank 7 instead.

The electric fuel pump 45 can be a small pump used in a gasoline engine, and further pressurizes the liquefied DME by the pressure of the fuel vapor in the fuel tank 7 to about 300 kPa to increase the pressure of the high pressure pump 6. Therefore, the fuel pressure in the fuel pipe 8 can always be higher than the pressure in the fuel tank 7.
By adopting this electric fuel pump 45, the fuel pressure in the fuel pipe 8 can always be higher than the pressure in the fuel tank 7, so that the fuel on the fuel suction side of the high-pressure pump 6 can be kept in a liquefied state.

In the first embodiment, in order to keep the fuel on the fuel suction side of the high-pressure pump 6 in a liquefied state, the pressure on the fuel suction side of the high-pressure pump 6 needs to be kept equal to or higher than the saturated vapor pressure of DME. However, in this embodiment, the fuel on the fuel suction side of the high-pressure pump 6 can be kept in a liquefied state simply by keeping the fuel tank 7 at or above the saturated vapor pressure, so that the pressure in the fuel tank 7 can be reduced. And power consumption of the electric heater 26 can be suppressed.
Further, by using the electric fuel pump 45, DME can be sent to the high-pressure pump 6 in accordance with the load state of the engine, and an improvement effect of fuel consumption can be expected.

A fifth embodiment will be described with reference to FIG.
In the first to fourth embodiments, the DME in the fuel tank 7 is heated to increase the pressure in the fuel tank 7.
On the other hand, in the fifth embodiment, the heating means is abolished, air supply means is used instead, and pressurized air is supplied into the fuel tank 7 storing DME by the air supply means. The internal pressure is increased.
Specifically, in this embodiment, an air pump 46 for air brake is used as an example of the air supply means.

In the first to fourth embodiments, the heating amount of the DME in the fuel tank 7 (specifically, the sub tank 22) is controlled to control the pressure in the fuel tank 7, but in this embodiment, the air pump 46 (specifically, The pressure in the fuel tank 7 is controlled by controlling the opening degree of the air pressure regulating valve 48 provided in the pipe 47 for guiding the high-pressure air from the inside of the air tank into the fuel tank 7 by the control device 4. . A check valve 49 provided on the fuel tank 7 side of the pipe 47 prevents the pressure in the fuel tank 7 from leaking outside through the pipe 47.
In this embodiment, the fuel return cooler 50 is provided on the fuel tank 7 side of the return pipe 12 so as to lower the temperature of the fuel returned into the fuel tank 7. As with the fuel cooler 27 described above, the fuel return cooler 50 is a means for cooling the DME through the introduction of cooling fluid such as cooling water on the low temperature side of the engine, cooling / cooling refrigerant for cooling, and vehicle running wind.

By adopting the fifth embodiment, the sub-tank 22 disclosed in the first to fourth embodiments is not necessary, and the cost can be suppressed.
Further, the high pressure given from the air pump 46 allows the pressure in the fuel tank 7 to be higher than those in the first to fourth embodiments, and the high pressure given in the fuel tank 7 causes the fuel in the fuel tank 7 to be transferred to the high-pressure pump 6. Can supply. Thereby, the feed pump 5 or the electric fuel pump 45 disclosed in the first to fourth embodiments can be eliminated, and the cost can be suppressed by this.
Furthermore, since DME can be sent to the high pressure pump 6 at the time of start-up by the high-pressure air accumulated in the air tank, startability can be improved.

A sixth embodiment will be described with reference to FIG.
In the first to fifth embodiments, the example in which the pressure in the fuel tank 7 is controlled so that the fuel on the fuel suction side of the high-pressure pump 6 is in a liquid state.
On the other hand, in the sixth embodiment, the pressure in the fuel tank 7 is controlled to be equal to or higher than the saturated vapor pressure of DME so that the DME in the fuel tank 7 is in a liquid state. Specifically, in the sixth embodiment, the pressure in the fuel tank 7 is controlled to be equal to or higher than the saturated vapor pressure of DME so that the DME in the fuel tank 7 is in a liquid state in the first embodiment. Of course, you may combine with another Example.

When such control is performed, there is a problem that the DME receives heat from the surroundings and vaporizes in the fuel pipe 8 that sends DME from the fuel tank 7 to the high-pressure pump 6. Therefore, in this embodiment, the fuel supply cooler 51 for preventing vaporization is provided in the fuel pipe 8 to avoid the problem that DME vaporizes in the fuel pipe 8.
The fuel supply cooler 51 is a means for cooling the DME by introducing cooling fluid such as cooling water on the low temperature side of the engine, cooling / cooling refrigerant for cooling, vehicle traveling wind, and the like, similar to the fuel cooler 27 described above.
In the sixth embodiment, since it is only necessary to keep the fuel tank 7 at the saturated vapor pressure or higher, the pressure in the fuel tank 7 can be reduced, and the power consumption of the electric heater 26 can be suppressed.

[Modification]
In the above embodiment, DME is shown as an example of a supercritical fuel. However, the present invention is applied to a fuel injection device using other DME, such as propane and butane, which is easily vaporized at a low temperature and has a high pressure vapor pressure. May be applied.

It is the schematic of a fuel-injection apparatus (Example 1). It is a flowchart which shows the example of control of a pressure control function. It is a graph which shows the relationship between the temperature and saturated vapor pressure in DME. (Example 2) which is the schematic of a fuel-injection apparatus. (Example 3) which is the schematic of a fuel-injection apparatus. (Example 4) which is the schematic of a fuel-injection apparatus. (Example 5) which is the schematic of a fuel-injection apparatus. (Example 6) which is the schematic of a fuel-injection apparatus. It is the schematic of a fuel-injection apparatus (conventional example).

Explanation of symbols

4 Control device 6 High pressure pump 7 Fuel tank 21 Main tank 22 Sub tank 23 Gas communication part 24 Liquid communication part 26 Electric heater (heating means)
27 Fuel cooler (cooling means)
41 Heat exchanger (heating means)
46 Air pump (air supply means)

Claims (7)

A fuel injection device for vehicles using supercritical fuel,
The fuel injection device includes a heating unit that heats fuel in a fuel tank that stores supercritical fuel to increase the internal pressure of the fuel tank. The fuel injection device for a supercritical fuel according to claim 1,
The fuel tank comprises a main tank and a sub tank,
The main tank and the sub tank communicate with each other through a gas communication portion having a small passage resistance in the upper portion and communicate with each other through a liquid communication portion having a large passage resistance in the lower portion,
The fuel injection device for supercritical fuel, wherein the heating means heats the liquid fuel in the sub tank. The fuel injection device for a supercritical fuel according to claim 2,
The fuel injection device for a supercritical fuel, wherein the sub tank is provided outside the main tank. The fuel injection device for a supercritical fuel according to claim 2,
The fuel injection device for a supercritical fuel, wherein the sub tank is provided in the main tank. The fuel injection device for a supercritical fuel according to any one of claims 1 to 4,
The fuel injection device for a supercritical fuel is provided with a cooling means for cooling the fuel in the fuel tank. A fuel injection device for vehicles using supercritical fuel,
The fuel injection device comprises a fuel supply device for supercritical fuel, comprising air supply means for supplying pressurized air into a fuel tank for storing supercritical fuel to increase the internal pressure of the fuel tank. The fuel injection device for a supercritical fuel according to any one of claims 1 to 6,
The fuel injection device for supercritical fuel is configured so that the pressure in the fuel tank or the fuel pressure on the fuel suction side of the high-pressure pump that compresses and discharges the fuel to a high pressure is equal to or higher than the saturated vapor pressure. A fuel injection device for a supercritical fuel, comprising a control device for controlling the air supply means.

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