JP2003113741A - High pressure fuel supplying device for liquefied gas fuel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high pressure fuel supplying device for liquefied gas fuel capable of improving the controllability for the fuel amount forcibly fed by a high pressure pump. SOLUTION: A low pressure pump 11 pressurizes the liquefied gas fuel in a fuel tank 10 and discharges, while the high pressure pump 13 sucks in a low pressure fuel from the low pressure pump 11 and discharges it upon compressing to a high pressure. A flow regulating valve 14 to regulate the fuel amount to a fuel force feed part 16 of the high pressure pump 13 is installed to a fuel passage 15 leading from the low pressure pump 11 to the fuel force feed part 16, and a throttle 18 is installed in a branch passage 17 branching from the fuel passage 15 in its part downstream of the flow regulating valve 14. The branch passage 17 is furnished with a constant pressure valve 19 on the side nearer the tank 10 than the throttle 18, and this valve 19 opens at a specified pressure higher than the saturated vapor pressure of the liquefied gas fuel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high pressure fuel supply system for liquefied gas fuel.

[0002]

2. Description of the Related Art In recent years, a common rail type fuel injection device has been proposed and realized as a fuel injection device for a diesel engine, and a fuel pump unit used for the common rail type fuel injection device is disclosed in, for example, Japanese Patent Laid-Open No. 11-315767. There is. This fuel pump unit supplies high-pressure fuel to a common rail (accumulation pipe), and its configuration is shown in FIG.

In FIG. 3, the fuel in the fuel tank 61 is discharged at a low pressure by the low pressure pump 62. Low pressure pump 6
An overflow pipe 63 is provided between the outlet and the inlet of the second pipe 2, and an overflow valve 64 that opens at a predetermined pressure is provided in the middle of the overflow pipe 63. A metering valve 66 is provided in a fuel passage 65 extending from the low pressure pump 62 to the high pressure pump 67. The metering valve 66 is a flow rate control valve that moves the valve body by driving an electromagnetic solenoid or the like to adjust the flow passage area, and is closed when the fuel discharge amount by the high pressure pump 67 is zero. However, even though the metering valve 66 is closed, a small amount of fuel flows into the downstream side of the metering valve 66 due to leakage from the clearance of each part of the metering valve 66. In order to prevent this fuel from flowing into the high-pressure pump 67, a branch passage 68 that branches downstream of the metering valve 66 and communicates with the fuel tank 61 is provided.
A diaphragm 69 is provided in the middle of 8.

By providing the throttle 69 in the branch passage 68, the high-pressure fuel flowing back from the high-pressure pump 67 can be released when the high-pressure pump 67 starts to pump the fuel, thus protecting the metering valve 66. Can be planned. The details are also disclosed in Japanese Patent Application Laid-Open No. 11-93796 filed by the applicant of the present application in the past.

[0005]

By the way, diesel oil generally uses diesel fuel as a fuel, but DME (dimethyl ether) and cetane number are taken into consideration in consideration of fuel vaporization property, ignition and combustion property, emission and the like. It has been proposed to use a liquefied gas such as LPG (liquefied petroleum gas) with an additive for improvement as a fuel. In this case, as the fuel injection device for liquefied gas fuel, a common rail fuel injection device for diesel engines can be applied. However, if the device of FIG. 3 is applied to a fuel supply device for liquefied gas fuel, the following problems occur.

That is, the liquefied gas fuel in the fuel passage 65 on the downstream side of the metering valve 66 may be gas or liquid depending on temperature and pressure. For example, when DME is used as the liquefied gas fuel, at room temperature (25 ° C),
It becomes a gas at a pressure of about 0.6 MPa or less, and becomes a liquid at a pressure of about 0.6 MPa or more. When the gas-liquid state of the fuel changes in this way,
The amount of fuel passing through the diaphragm 69 changes greatly. As a result, the amount of fuel flowing from the low-pressure pump 62 to the high-pressure pump 67 changes significantly depending on the temperature and pressure, and the high-pressure pump 67
Therefore, there is a problem in that the controllability of the fuel pumping amount is deteriorated.

The present invention has been made in view of the above problems, and an object thereof is to supply a high pressure fuel for a liquefied gas fuel which can improve the controllability of the fuel pressure feed amount by a high pressure pump. It is to provide a device.

[0008]

According to the first aspect of the invention, the liquefied gas fuel in the fuel tank is discharged by the low pressure pump and fed to the high pressure pump. The high-pressure pump compresses the liquefied gas fuel to a high pressure and discharges it. A metering valve is provided in the fuel passage between the low pressure pump and the high pressure pump,
The amount of fuel to the fuel pumping section is adjusted by this metering valve.
In addition, a throttle member is provided in a branch passage that branches from the fuel passage downstream of the metering valve, and a predetermined valve opening higher than the saturated vapor pressure of the liquefied gas fuel is provided on the fuel tank side of the throttle member. A constant pressure valve that opens with pressure is provided.

In short, the fuel flowing from the fuel passage into the branch passage is decompressed by the throttle member, and the pressure is maintained at the valve opening pressure of the constant pressure valve. In this case, the valve opening pressure of the constant pressure valve is higher than the saturated vapor pressure of the liquefied gas fuel, and the liquefied gas fuel flowing through the throttle member is always liquid. Therefore, the flow rate of the liquefied gas fuel becomes substantially constant depending on the pressure, and the fluctuation of the fuel pressure feed amount by the fuel pressure feed unit is suppressed. As a result, as the high pressure fuel supply device for liquefied gas fuel, it is possible to improve the controllability of the fuel pressure feed amount by the high pressure pump.

According to the second aspect of the invention, the inlet of the pump chamber for pumping the fuel by the reciprocating movement of the plunger in the fuel pumping unit of the high pressure pump opens when the pressure of the sucked fuel is equal to or higher than a predetermined pressure. The check valve is provided, and the valve opening pressure of the check valve is set slightly higher than the valve opening pressure of the constant pressure valve. In this case, even if the metering valve is closed, it is considered that fuel will flow into the fuel passage due to leakage at the metering valve.
Since the check valve at the inlet of the pump chamber has a higher valve opening pressure than the constant pressure valve, the fuel does not flow into the pump chamber and is returned to the fuel tank through the throttle member and the constant pressure valve. Therefore, it is possible to prevent erroneous discharge of the high-pressure pump due to leaked fuel from the metering valve.

According to the third aspect of the invention, the high pressure pump is provided with the metering valve at the fuel suction portion thereof and the throttle member and the constant pressure valve downstream of the metering valve. In this case, a structure in which a metering valve, a throttle member and a constant pressure valve are integrally provided as a high pressure pump can be realized.

According to a fourth aspect of the invention, means for cooling the throttle member and the constant pressure valve is provided. When the temperature of the liquefied gas fuel rises, its saturated vapor pressure becomes high and bubbles (vapor) are easily generated, which can be prevented.

According to the fifth aspect of the invention, the pressure in the fuel tank is made substantially equal to the saturated vapor pressure of the liquefied gas fuel, and the low pressure pump is arranged in the fuel tank. That is, when the pressure in the fuel tank is substantially equal to the saturated vapor pressure of the liquefied gas fuel, the temperature of the liquefied gas fuel locally rises slightly or the pressure in the fuel tank slightly drops, and bubbles (vapor) are generated. Occur. In this case, by incorporating the low-pressure pump in the fuel tank, it is possible to prevent bubbles from being generated due to a pressure drop in the path from the fuel tank to the low-pressure pump, and to prevent suction failure of the low-pressure pump. At the same time, the temperature difference between the fuel tank and the low-pressure pump decreases,
It is possible to prevent bubbles from being generated due to a temperature difference and a suction failure of the low-pressure pump due to the bubbles.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIG. In the present embodiment, D
In a vehicle diesel engine that uses liquefied gas such as ME or LPG as fuel, the present invention is embodied in a common rail fuel injection device for injecting fuel into the engine.

FIG. 1 is a configuration diagram showing a main part of a fuel injection device according to the present embodiment. In FIG. 1, a fuel tank 10 is a closed tank, and liquefied gas fuel (DME or LPG) is stored therein at a saturated vapor pressure. A low-pressure pump 11 is arranged in the fuel tank 10, and the liquefied gas fuel pressurized to a predetermined feed pressure (about 3 MPa) by the low-pressure pump 11 is supplied to the pipe 12
Is discharged to the high-pressure pump 13 via.

Here, the pressure in the fuel tank 10 is equal to the saturated vapor pressure of the liquefied gas fuel.
In 0, bubbles (vapor) are generated only when the temperature of the liquefied gas fuel is slightly increased or the pressure is slightly decreased. In such a case, the low pressure pump 11 is added to the fuel tank 10.
By incorporating a low pressure pump 11 from the fuel tank 10
It is possible to prevent bubbles from being generated due to the pressure drop in the path leading to and the suction failure of the low pressure pump 11 due to the bubbles. At the same time, the temperature difference between the fuel tank 10 and the low-pressure pump 11 is reduced, and the generation of bubbles due to the temperature difference and the suction failure of the low-pressure pump 11 due to this are prevented.

An electromagnetically driven and normally closed metering valve 14 is provided at the fuel suction portion of the high-pressure pump 13. When the metering valve 14 is opened, the liquefied gas fuel is supplied to the fuel passage 1.
The fuel is fed to the fuel pressure feeding unit 16 on the downstream side of the pump via the No. 5. The metering valve 14 is configured as a linear solenoid valve (flow rate control valve) capable of adjusting the flow rate of the liquefied gas fuel, and the opening of the metering valve 14 is controlled by an electronic control unit (ECU) not shown, The amount of fuel supplied to the pumping unit 16 is adjusted.

More specifically, as shown in FIG. 2, a valve body 32 is slidably accommodated in a valve case 31 as the structure of the metering valve 14. Flow paths 33 are formed in a plurality of locations in the valve case 31. Further, the valve body 32 is formed with a communication passage 34 extending in the axial direction and penetrating the inside thereof, and a passage 35 is formed at a position corresponding to the passage 33 of the valve case 31. The valve body 32 is a spring 36.
Therefore, the valve closing position of the valve element 32 is regulated by a ring-shaped stopper 37 press-fitted and fixed to the valve case 31.

The valve case 31 has not only a cylinder function for slidably accommodating the valve element 32 but also a stator function for forming a magnetic path, and the accommodating portion 31a for accommodating the valve element 32 has an accommodating portion 31a. The stator portion 31c is provided so as to be connected via the thin portion 31b. In addition, the valve body 32
Has a function of the armature for forming a magnetic path in addition to the original function of the valve body such as sliding the inside of the valve case 31 to change the flow passage area.
The armature part 32a is integrally provided so as to face the stator part 31c. Incidentally, the valve case 31 and the valve body 32 are provided with thin hardened layers on their sliding surfaces by surface treatment (NiP plating, DLC, etc.) and heat treatment (soft nitriding, etc.).

The valve case 31 (mainly the stator portion 31
A coil 38 is wound around c), and a housing 39 made of a magnetic material is attached around the coil 38.

In the metering valve 14 having the above structure, when the coil 38 is energized, the magnetic flux flowing through the valve case 31 is throttled by the thin portion 31b and flows through the armature portion 32a of the valve body 32. As a result, a suction force is generated with respect to the valve body 32 (armature portion 32a), and the valve body 32 moves to a desired position against the biasing force of the spring 36. At this time, when the flow passage 33 of the valve case 31 and the flow passage 35 of the valve body 32 are communicated with each other, fuel flows according to the area of the communicated flow passages. The displacement position of the valve element 32 is determined by the amount of electricity supplied to the coil 38. When the amount of electricity supplied is increased, the opening area of the communicating portion, that is, the flow passage area is increased.

However, the structure of the metering valve 14 shown in FIG. 2 is merely an example, and it can be arbitrarily changed as long as the amount of fuel supplied to the fuel pumping section 16 can be adjusted. For example, a configuration in which the valve member and the armature member are provided separately,
For example, the valve case member and the stator member may be separately provided.

Returning to the explanation of FIG. 1, in the fuel pumping section 16 of the high-pressure pump 13, a plunger 42 is reciprocally housed in the pump body 41. A pump chamber 43 is provided above the plunger 42, and the pump chamber 43
Check valves 44 and 45 are provided on the upstream side (inlet side) and the downstream side (outlet side), respectively. The plunger 42 is pressed against the upper surface of the tappet 48 by a spring receiver 46 and a spring 47, and the plunger 42 reciprocates up and down as the tappet 48 moves up and down. Incidentally, reference numeral 49
Is a cam shaft that rotates in synchronization with the rotation of the engine, reference numeral 5
Reference numeral 0 is a roller for transmitting the rotation of the cam shaft 49 to the tappet 48.

In the fuel pumping section 16 having the above structure, when the plunger 42 is at the bottom dead center, the liquefied gas fuel is pumped into the pump chamber 43.
Inhaled into. Here, the discharge pressure of the low-pressure pump 11 is 3M.
Pa, the valve opening pressure of the check valve 44 is 1.05 MPa, and if the metering valve 14 is open (ON), the check valve 44 opens and the liquefied gas fuel is sucked into the pump chamber 43. To be done. The reason why the valve opening pressure of the check valve 44 is set to 1.05 MPa will be described later.

Thereafter, as the cam shaft 49 rotates, the plunger 42 moves together with the tappet 48 in the upward direction of the drawing.
The fuel in the pump chamber 43 starts to be pressurized. Then, when the fuel pressure in the pump chamber 43 becomes higher than the valve opening pressure of the check valve 45, the high pressure fuel is pumped to the common rail via the check valve 45. As a result, about 30MPa is applied to the common rail.
A high-pressure fuel of a certain degree is stored and appropriately injected and supplied to each cylinder of the engine from a fuel injection valve (not shown).

A branch passage 17 is provided in the fuel passage 15 connecting the metering valve 14 and the fuel pumping portion 16, and the tip of the branch passage 17 communicates with the fuel tank 10. A throttle (throttle member) 18 is provided in the branch passage 17, and a constant pressure valve 19 for opening at a predetermined valve opening pressure higher than the saturated vapor pressure of the liquefied gas fuel is provided on the fuel tank 10 side of the throttle 18. It is provided.

Here, the valve opening pressure of the constant pressure valve 19 is 1 MPa, and comparing the valve opening pressure of the constant pressure valve 19 with the valve opening pressure of the check valve 44 described above, the latter value is slightly higher. Is set to. In this case, even if the metering valve 14 is closed, it is considered that the fuel flows into the fuel passage 15 due to leakage at the metering valve 14, but the check valve 44 at the inlet of the pump chamber is better than the constant pressure valve 19. Since the valve opening pressure is high, the fuel does not flow into the pump chamber 43, and the fuel is returned to the fuel tank 10 through the throttle 18 and the constant pressure valve 19.

A cooling fan 20 is provided near the throttle 18 and the constant pressure valve 19. The cooling fan 20 may be engine-driven or motor-driven, and is turned on when the high-pressure pump 13 is driven. in this case,
As the temperature rises, the saturated vapor pressure of liquefied gas fuel increases,
Along with that, the inconvenience that bubbles are generated is prevented.

During operation of the diesel engine, the fuel pressurized to about 3 MPa by the low-pressure pump 11 flows into the fuel passage 15 with its flow rate controlled by the metering valve 14, and most of it is in the pump chamber of the fuel pumping unit 16. Flows into 43. However, a part of the liquefied gas fuel does not flow into the pump chamber 43,
It is returned to the fuel tank 10 through the throttle 18. At this time, the fuel flowing from the fuel passage 15 into the branch passage 17 is decompressed by the throttle 18, and the pressure is maintained by the valve opening pressure of the constant pressure valve 19. In this case, the opening pressure of the constant pressure valve 19 is higher than the saturated vapor pressure of the liquefied gas fuel, and the liquefied gas fuel flowing through the throttle 18 is always liquid. Therefore, the flow rate of the liquefied gas fuel becomes substantially constant depending on the pressure, and the fluctuation of the fuel pressure feeding amount by the fuel pressure feeding unit 16 is suppressed.

According to this embodiment described in detail above, the following effects can be obtained. As described above, since the fluctuation of the fuel pressure feed amount by the fuel pressure feed unit 16 is suppressed, it is possible to improve the controllability of the fuel pressure feed amount by the high pressure pump 13 as the high pressure fuel supply device for the liquefied gas fuel. In this case, it becomes possible to satisfactorily control the amount of fuel pumped from the fuel pumping unit 16 to the common rail.

Check valve 44 disposed at the inlet of pump chamber 43
Since the valve opening pressure of is set to be slightly higher than the valve opening pressure of the constant pressure valve 19, it is possible to prevent erroneous discharge of the high pressure pump 13 due to the leaked fuel of the metering valve 14.

The high-pressure pump 13 is provided with a metering valve 14 at its fuel suction portion, and the throttle 1 is provided downstream of the metering valve 14.
8 and a constant pressure valve 19 are provided. In this case, the high pressure pump 13
As a result, a configuration in which the metering valve 14, the throttle 18, and the constant pressure valve 19 are integrally provided can be realized.

Since the cooling fan 20 for cooling the throttle 18 and the constant pressure valve 19 is provided, it is possible to prevent the generation of bubbles (vapor) due to the temperature rise of the liquefied gas fuel. Therefore, the liquefied gas fuel passing through the throttle 18 and the constant pressure valve 19 can be more reliably held in the liquid state.

Further, since the low pressure pump 11 is built in the fuel tank 10, the pressure drop in the path from the fuel tank 10 to the low pressure pump 11 and the fuel tank 10 and the low pressure pump 1
It is possible to prevent bubbles from being generated due to a temperature difference from the temperature difference between the low pressure pump 1 and the low pressure pump 11.

Although the present invention has been embodied as a common rail type fuel injection device in the above-described embodiment, it can be embodied in other configurations. For example, instead of using a common rail, a distribution type fuel injection pump may be used to increase the pressure of the liquefied gas fuel and supply it to the fuel injection valve.

Further, the configuration in which the cooling fan 20 is provided near the throttle 18 and the constant pressure valve 19 and the configuration in which the low-pressure pump 11 is built in the fuel tank 10 are not essential requirements for the present invention, and these configurations are excluded. It is also possible to embody the present invention. Even in such a case, there is no doubt that the desired effect described above can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an outline of a high-pressure fuel supply device according to an embodiment of the invention.

FIG. 2 is a sectional view showing the structure of a metering valve.

FIG. 3 is a diagram showing a high-pressure fuel supply device according to a conventional technique.

[Explanation of symbols]

10 ... Fuel tank, 11 ... Low pressure pump, 13 ... High pressure pump, 14 ... Metering valve, 15 ... Fuel passage, 16 ... Fuel pumping section, 17 ... Branch passage, 18 ... Throttle, 19 ... Constant pressure valve, 20
… Cooling fan, 42… Plunger, 43… Pump room, 4
4 ... Check valve.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02M 59/36 F02M 59/36 59/46 59/46 Y (72) Inventor Moriyasu Goto Shimohazumi, Nishio City, Aichi Prefecture Machi Iwatani 14 Japan Automotive Parts Research Institute, Inc. (72) Inventor Tetsuo Morita 14 Iwatani Shimohakakucho, Nishio City, Aichi Prefecture Japan Auto Parts Research Institute (72) Inventor Masaaki Kato Showa Kariya, Aichi Prefecture Showa Town 1-chome DENSO Co., Ltd. (72) Inventor Hisaharu Takeuchi 1-chome Showa-cho Kariya, Aichi Prefecture DENSO F-term (reference) 3G066 AA07 AB05 AC09 AD02 BA00 BA37 CA01S CA04S CA04U CA08 CA09 CA20S CA34 CA36 CB09 CB11 CB16 CD02

Claims (5)

[Claims] 1. A low-pressure pump that pressurizes and discharges liquefied gas fuel in a fuel tank, a high-pressure pump that sucks low-pressure fuel from the low-pressure pump, compresses it to high pressure, and discharges it, and fuel for the low-pressure pump and high-pressure pump. A metering valve that is provided in the fuel passage between the pressure feeding portion and adjusts the amount of fuel to the fuel pressure feeding portion, and a branch passage that branches in the fuel passage downstream of the fuel feeding valve and communicates with the fuel tank. A high-pressure fuel supply device including a throttle member, which is opened in the branch passage on the fuel tank side of the throttle member at a predetermined valve opening pressure higher than a saturated vapor pressure of the liquefied gas fuel. A high-pressure fuel supply device for liquefied gas fuel, which is provided with a constant pressure valve for valve operation. 2. A check valve, which opens when the pressure of intake fuel is equal to or higher than a predetermined pressure, is provided at an inlet of a pump chamber for pressure-feeding fuel by reciprocating movement of a plunger in a fuel pumping portion of a high-pressure pump. The high-pressure fuel supply device for liquefied gas fuel according to claim 1, wherein the valve opening pressure of the check valve is slightly higher than the valve opening pressure of the constant pressure valve. 3. The liquefied gas fuel according to claim 1, wherein the high-pressure pump is provided with the metering valve at its fuel suction portion, and is provided with the throttle member and the constant pressure valve on the downstream side of the metering valve. High pressure fuel supply system. 4. A high-pressure fuel supply apparatus for liquefied gas fuel according to claim 1, further comprising means for cooling the throttle member and the constant pressure valve. 5. The high pressure for liquefied gas fuel according to claim 1, wherein the pressure in the fuel tank is made substantially equal to the saturated vapor pressure of the liquefied gas fuel, and a low pressure pump is arranged in the fuel tank. Fuel supply device.