JP2003056410A - Fuel supply device for dme engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the leakage of a fuel vaporized gas from a high pressure pump and the seizure of such high pressure pump in stopping an engine, and to realize quick restarting of a DME engine. SOLUTION: A fuel supply device for the DME engine is provided with a bypass line 21 for taking out properly a fuel from the more downstream side than a fuel cooler 17 on a fuel return line 16 to send it back to a fuel tank 1; a flow passage switching valve 22 for selectively delivering the fuel from the cooler 17 to the line 21 side only when a switching command 22a is inputted to a connecting part with the line 16 on the line 21; and a control device 24 for outputting the switching command 22a to the switching valve 22 in stopping the engine, and for outputting properly start commands 2a and 19a to a feed pump 2 and an electric fan 19 of the fuel cooler 17, respectively, only under the condition where fuel temperature in a fuel gallery 12 is over a predetermined specified temperature T1 .

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel supply device for a DME engine that uses dimethyl ether as a fuel.

[0002]

2. Description of the Related Art In recent years, smoke-free dimethyl ether with a high cetane number (55 or more) (hereinafter abbreviated as DME)
Is attracting attention as an alternative fuel for petroleum and light oil, especially E
From the viewpoint that low NOx can be realized by GR (exhaust gas recirculation) and a catalyst, and strict exhaust emission regulations in the future can be satisfied, studies are underway as alternative fuels for diesel engines.

However, since the boiling point of DME is as low as -25 ° C. and it is easy to evaporate, DME is used.
It is considered that a fuel supply device that fully considers such characteristics of the DME is necessary for the practical application of the DME engine that uses as a fuel. For example, the fuel supply of the DME engine as shown in FIG. The device has already been proposed.

In the example shown here, the fuel tank 1
The fuel (DME) stored at a pressure of about 0.4 to 1 MPa inside is sent out to the high pressure pump 4 via the fuel supply line 3 by the feed pump 2 installed in the fuel tank 1, and the high pressure About 20 to 70 depending on pump 4
The pressure is increased to MPa and the pressure is accumulated in the common rail 6 via the pressure feed line 5, and the fuel is guided from the common rail 6 to the injector 8 of each cylinder via the injection line 7 and injected into the combustion chamber 9 by the valve opening control. Like the engine, it is burned by compression ignition.

Here, the high pressure pump 4 employs a piston type pressure feed system similar to the conventional row type pump in which the plunger 10 is moved up and down by the engine drive via a cam or tappet (not shown) to compress the fuel. A solenoid valve 11 for controlling the discharge amount is provided for each pump cylinder.

The solenoid valve 11 is opened and fuel is introduced into the pump chamber 13 in the descending stroke of the plunger 10, but the solenoid valve 11 is energized in the next ascending stroke of the plunger 10. When the valve is opened without being opened, the fuel taken from the fuel gallery 12 into the pump chamber 13 is discharged to the fuel gallery 12 again without being boosted through the solenoid valve 11, and on the other hand, the required discharge amount is not reached. In the state where the solenoid valve 11 is energized and closed at a suitable timing, the fuel that has been cut off from the retreat path is compressed by the plunger 10 in the pump chamber 13 and delivered to the delivery valve 14.
The pressure is fed to the common rail 6 via the (check valve).

That is, the lift amount of the plunger 10 after the solenoid valve 11 is closed becomes the discharge amount, and the discharge amount changes at the closing timing of the solenoid valve 11, and the pressure of the common rail 6 is generated and controlled. It is supposed to be.

Further, the fuel gallery 12 in the high-pressure pump 4
Overflow valve 15 when the pressure exceeds a specified value at
(Relief valve) causes excess fuel to return to fuel line 1
However, since the temperature of the fuel released to the fuel return line 16 rises due to the heat received from the engine and bubbles are easily generated, the fuel installed in the middle of the fuel is returned to the fuel return line 16. After being sufficiently cooled through the cooler 17, it is recirculated in the middle of the fuel supply line 3 through the check valve 18. The fuel cooler 17 in the drawing is of an air cooling type by an electric fan 19 driven by a battery.

[0009]

However, in such a fuel supply device, when the high-pressure pump 4 is stopped and the flow of fuel is stagnated when the engine is stopped, heat is transferred from the engine or the exhaust system to the inside of the flow path. Fuel temperature rises and DME
When the temperature exceeds 127 ° C., which is the critical temperature, the combustion is vaporized regardless of the pressure. Therefore, the vaporized gas accumulates in the fuel gallery 12 in the high pressure pump 4 and becomes high in pressure, and a sealing means such as an O-ring or an oil seal. The vaporized gas of the fuel leaks to the outside from 20 (it is difficult to seal the leak of the gas even if it has liquid tightness), or the inside of the high-pressure pump 4 is in the liquid phase state when the engine is started next time. There is a risk that seizure may be caused due to not being filled with the above fuel.

At present, a method of extracting fuel from the fuel supply line 3 and the fuel return line 16 and the high-pressure pump 4 when the engine is stopped is being studied as a countermeasure, but such a method is adopted. When it is attempted to restart after the engine is stopped, it takes time until the fuel is filled in the fuel supply line 3 and the fuel return line 16 and the high pressure pump 4, so that the engine can be restarted quickly. There was a problem that I could not do it.

The present invention has been made in view of the above situation, and prevents leakage of fuel vaporized gas from the inside of the high-pressure pump and seizure of the high-pressure pump when the engine is stopped, and promptly restarts the DME engine. The purpose is to achieve starting.

[0012]

SUMMARY OF THE INVENTION The present invention is a fuel for a DME engine in which fuel in a fuel tank is boosted by a high-pressure pump to accumulate pressure in a common rail, and fuel is introduced from the common rail to an injector for injection into a combustion chamber. In the supply device, a fuel supply line that guides the fuel sent from the fuel tank by the feed pump to the high-pressure pump, and a surplus fuel released when the pressure exceeds a predetermined value in the fuel gallery inside the high-pressure pump. A fuel return line that is cooled through the fuel supply line and is recirculated in the middle of the fuel supply line; a bypass line that appropriately withdraws fuel from the downstream side of the fuel cooler of the fuel return line and returns it to the fuel tank; Fuel that has been installed at the connection point for the fuel return line and has passed through the fuel cooler. A flow path switching valve that selectively distributes to the bypass line side only when a switching command is input, and a switching command is output to the flow path switching valve when the engine is stopped, and an appropriate start command is also issued to the feed pump and the fuel cooler. And a control device for outputting.

Thus, in this way, when the engine is stopped, a switching command is output from the control device to the flow path switching valve, the flow path switching valve is switched, and the fuel passing through the fuel cooler is selected to the bypass line side. On the other hand, at the same time, a start command is appropriately output to the feed pump and the fuel cooler, and these feed pump and the fuel cooler are started, so even when the engine is stopped,
Fuel is pumped up from the fuel tank by the feed pump and sent out to the fuel supply line, and a fuel flow that flows into the fuel return line via the fuel gallery in the high pressure pump is formed, and flows into the fuel return line. After being cooled by the fuel cooler, the fuel is returned to the fuel tank through the flow path switching valve.

Further, in the present invention, a temperature sensor for detecting the fuel temperature of the fuel gallery in the high pressure pump is provided,
The control device is configured to input the detection signal of the temperature sensor and output the start command to the feed pump and the fuel cooler only under the condition that the detected temperature exceeds a predetermined set temperature when the engine is stopped. good.

With this configuration, the control device controls the feed pump and the fuel cooler to start when the fuel temperature of the fuel gallery in the high pressure pump rises to a critical temperature range close to the critical temperature. It is possible to significantly reduce power consumption by limiting the drive time of the feed pump and the fuel cooler to the necessary minimum.

Further, every time the feed pump and the fuel cooler started when the engine is stopped are stopped due to the temperature detected by the temperature sensor falling below the set temperature, the set temperature for outputting the next start command is set at the immediately preceding start. The control device may be configured to change to a higher set temperature.

That is, after the engine is stopped, until the engine and the exhaust system cool down and become stable in temperature, even if the temperature detected by the temperature sensor falls below the set temperature and the feed pump and the fuel cooler stop, the high pressure pump The fuel temperature in the fuel gallery will rise again, but if the set temperature for outputting the next startup command is changed to a higher set temperature than the previous startup, the feed pump and fuel A situation in which the cooler frequently starts and stops will be avoided.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 and FIG. 2 show an example of an embodiment for carrying out the present invention, and the parts denoted by the same reference numerals as those in FIG. 3 represent the same things.

With respect to the fuel supply device for the DME engine having a structure substantially similar to that of FIG. 3 described above, in this embodiment, as shown in FIG. 1, the fuel cooler 1 of the fuel return line 16 is provided.
Fuel tank 1 by appropriately extracting fuel from the downstream side of 7
A bypass line 21 for returning the fuel to the fuel return line 16 is provided at the connection point of the bypass line 21 to the bypass line 21 side only when the switching command 22a is input. A flow path switching valve 22 that selectively distributes is provided.

Further, a fuel gallery 1 is provided for the high pressure pump 4.
A temperature sensor 23 for detecting the fuel temperature inside the fuel cell 2 is newly provided, and a detection signal 23a of the temperature sensor 23 is input to a control device 24 provided at a predetermined location.

In the control device 24, the switching command 22 is directed to the flow path switching valve 22 when the engine is stopped.
In addition to outputting a, the feed pump 2 and the fuel cooler 1 only under the condition that the detected temperature exceeds a predetermined set temperature T ₁ based on the detection signal 23a from the temperature sensor 23.
7. The start commands 2a and 19a are appropriately directed to the electric fan 19 of FIG.
Is output.

FIG. 2 shows a specific control procedure in the control device 24. When the engine stop is confirmed in step S1, the flow path switching valve 22 is switched by the switching command 22a in step S2. , Then step S
At 3 it is determined whether the fuel temperature in the fuel gallery 12 exceeds the set temperature T ₁ based on the detection signal 23a from the temperature sensor 23. If it exceeds the set temperature T ₁ , the process proceeds to step S4. electric fan 19 start command 2a of in feed pump 2 and the fuel cooler 17 is activated by 19a, which thereafter feed pump 2 and the fuel to decrease in the detected temperature is set temperatures T ₁ under repeated determination of the step S3 The electric fan 19 of the cooler 17 continues to be activated, while the fuel temperature in the fuel gallery 12 is determined to be the set temperature T _{1 as} determined in step S3.
If it does not exceed, the process proceeds to step S5, and the feed pump 2 and the electric fan 19 of the fuel cooler 17 are stopped.

Here, the set temperature T ₁ used for the determination in step S3 is set _every time the feed pump 2 and the fuel cooler 17 started when the engine is stopped, are stopped by the temperature detected by the temperature sensor 23 being lowered to the set temperature. The set temperature is set to be higher than the set temperature used at the last startup.

When the fuel supply device is constructed as described above, the switching command 22a is output from the control device 24 to the flow passage switching valve 22 when the engine is stopped, and the flow passage switching valve 2 is output.
2 is switched, and the fuel that has passed through the fuel cooler 17 is selectively distributed to the bypass line 21 side.

When the engine is stopped, the temperature sensor 23
When the detection signal exceeds the predetermined set temperature T ₁ , the controller 24 outputs the start-up commands 2a and 19a to the feed pump 2 and the fuel cooler 17, and the feed pump 2 and the fuel cooler 17 are started. Even when the engine is stopped, the fuel tank 1 is fed by the feed pump 2
Fuel is pumped from the fuel supply line 3 to the fuel supply line 3, and flows into the fuel return line 16 via the fuel gallery 12 in the high-pressure pump 4 to form a fuel flow, which flows into the fuel return line 16. After the fuel is cooled through the fuel cooler 17, the flow path switching valve 2
It will be returned to the fuel tank 1 via 2.

It should be noted that until the engine or the exhaust system cools and the temperature becomes stable after the engine is stopped, the temperature sensor 2
Even if the temperature detected by _No. 3 temporarily drops below the set temperature T ₁ and the feed pump 2 and the fuel cooler 17 stop, the fuel temperature in the fuel gallery 12 of the high-pressure pump 4 again rises. However, since the set temperature T ₁ for outputting the next start command 2a, 19a is changed to a set temperature higher than that at the time of the immediately preceding start, the feed pump 2 and the fuel cooler 17 are frequently started and stopped. The situation of repeating is avoided.

Therefore, according to the above-mentioned embodiment, even if the high-pressure pump 4 is stopped when the engine is stopped, it is possible to prevent the fuel flow from being circulated between the fuel tank 1 and the high-pressure pump 4 and stagnation of the combustion flow. Therefore, the vaporization of the fuel in the fuel gallery 12 in the high-pressure pump 4 can be significantly suppressed, and the leakage of the fuel vaporized gas from the high-pressure pump 4 and the seizure of the high-pressure pump 4 can be prevented when the engine is stopped. This can be avoided, and since the fuel supply line 3 and the fuel return line 16 and the high pressure pump 4 can be kept filled with fuel even after the engine is stopped, the DME engine can be quickly operated after the engine is stopped. Can be restarted.

Further, particularly in this embodiment, control is performed so that the feed pump 2 and the fuel cooler 17 are activated when the fuel temperature of the fuel gallery 12 in the high-pressure pump 4 has risen to a critical temperature range close to the critical temperature. The feed pump 2 and the fuel cooler 1 are controlled by the device 24.
Since the driving time of 7 can be limited to the necessary minimum, the power consumption required for the feed pump 2 and the fuel cooler 17 can be significantly suppressed.

Further, the feed pump 2 and the fuel cooler 1
7, the set temperature T ₁ for outputting the start commands 2a and 19a is supplied to the feed pump 2 and the fuel cooler 17
Therefore, it is possible to avoid a situation in which the feed pump 2 and the fuel cooler 17 are repeatedly started and stopped, because the feed pump 2 and the fuel cooler 17 are gradually increased each time.

The fuel supply device for the DME engine of the present invention is not limited to the above-mentioned embodiment, and the fuel cooler is not limited to the air cooling type, and within the scope not departing from the gist of the present invention. It goes without saying that various changes can be made in.

[0032]

According to the fuel supply device for a DME engine of the present invention described above, various excellent effects as described below can be obtained.

(I) According to the first aspect of the present invention, even if the high-pressure pump is stopped when the engine is stopped, the fuel is circulated between the fuel tank and the high-pressure pump, and the combustion flow is stagnated. Since it can be avoided that the fuel vaporization in the fuel gallery inside the high-pressure pump can be significantly suppressed, the leakage of fuel vaporized gas from the high-pressure pump and the seizure of the high-pressure pump can be prevented when the engine is stopped. It is possible to avoid, and since it is possible to keep the fuel supply line and the fuel return line and the high pressure pump filled with fuel even after the engine is stopped,
It is possible to realize quick restart of the DME engine after the engine is stopped.

(II) According to the second aspect of the present invention, the feed pump and the fuel cooler are started when the fuel temperature of the fuel gallery in the high pressure pump rises to a critical temperature range close to the critical temperature. By controlling the control device so that the driving time of the feed pump and the fuel cooler can be limited to the necessary minimum, the power consumption required for the feed pump and the fuel cooler can be significantly suppressed. it can.

(III) According to the third aspect of the present invention, the set temperature for outputting the start command to the feed pump and the fuel cooler is gradually set every time the feed pump and the fuel cooler are stopped. Since it can be changed to a higher value, it is possible to avoid a situation where the feed pump and the fuel cooler frequently start and stop repeatedly.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment for carrying out the present invention.

FIG. 2 is a flowchart showing a control procedure of the control device of FIG.

FIG. 3 is a schematic view showing a conventional example.

[Explanation of symbols]

1 fuel tank 2 feed pump 2a Start command 3 Fuel supply line 4 high pressure pump 6 common rail 8 injectors 9 Combustion chamber 12 Fuel gallery 16 Fuel return line 17 Fuel cooler 19 electric fan 19a Start command 21 Bypass line 22 Flow path switching valve 22a switching command 23 Temperature sensor 23a detection signal 24 Control device

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02M 37/00 341 F02M 37/00 341C 53/00 53/00 CN 55/00 55/00 B D F Term (reference) 3G066 AA07 AB04 AC01 AC09 AD12 BA00 BA29 BA35 CA04U CA05T CA09 CB01 CB12 CB15 CB16 CC01 CD01 CD02 CD23 CD25 CD26 CE13 CE22 DB02 DB19 DC15

Claims (3)

[Claims] 1. A fuel supply device for a DME engine, wherein the fuel in a fuel tank is pressurized by a high-pressure pump to be accumulated in a common rail, and the fuel is guided from the common rail to an injector for injection into a combustion chamber. A fuel supply line that guides the fuel delivered by the feed pump to the high-pressure pump, and the excess fuel released when the pressure exceeds a predetermined value in the fuel gallery inside the high-pressure pump is cooled by a fuel cooler to supply the fuel. A fuel return line that recirculates in the middle of the line, a bypass line that appropriately withdraws fuel from the downstream side of the fuel cooler of the fuel return line and returns it to the fuel tank, and a connection point of the bypass line to the fuel return line. Equipped with the fuel that has passed through the fuel cooler Only when inputting a switching command A flow path switching valve that selectively distributes to the bypass line side, and a control device that outputs a switching command to the flow path switching valve when the engine is stopped and that also appropriately outputs a start command to the feed pump and the fuel cooler. A fuel supply device for a DME engine, which is characterized by being provided. 2. A temperature sensor for detecting a fuel temperature of a fuel gallery in a high pressure pump, and only under a condition that a detection signal of the temperature sensor is input and the detected temperature exceeds a predetermined set temperature when the engine is stopped. The fuel supply device for a DME engine according to claim 1, wherein the control device is configured to output a start command to the feed pump and the fuel cooler. 3. A feed pump and a fuel cooler which are started when the engine is stopped are stopped each time the temperature detected by the temperature sensor is stopped due to a decrease in the set temperature. The fuel supply device for a DME engine according to claim 2, wherein the control device is configured to change to a higher set temperature.