JP4302908B2 - Fuel injector for liquefied gas fuel - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel injection device for liquefied gas fuel applied to an engine using liquefied gas as fuel.
[0002]
[Prior art]
Diesel engines generally use light oil as fuel, but LPG (dimethyl ether) and LPG with additives for improving cetane number are added in consideration of fuel vaporization, ignition and combustion, and emissions. The use of liquefied gas fuel (liquefied petroleum gas) has been proposed. In the following description, what is referred to as LPG refers to a material added with a cetane number improver unless otherwise specified.
[0003]
As a fuel injection device for liquefied gas fuel, a common rail fuel injection device for diesel engines is generally applicable. That is, a high-pressure pump is connected to a fuel tank that stores liquefied gas fuel through a fuel supply pipe, and high-pressure fuel is discharged from the high-pressure pump to the common rail as the high-pressure pump is driven. The high-pressure fuel is accumulated at the common rail at a pressure corresponding to a predetermined injection pressure, and then injected from the injector.
[0004]
In addition, as a light oil injector, an injector using a hydraulic servo mechanism is used. In this injector, it is necessary to leak fuel for hydraulic control. An injector using a hydraulic servo mechanism is well known as an injector using a two-way valve or a three-way valve. A high-pressure fuel is introduced into a pressure control chamber provided at the back of the valve body, and the high-pressure fuel in the pressure control chamber is The valve opening operation of the valve body is realized by leaking fuel (hydraulic pressure) to the low pressure side for each injection. In this case, the liquefied gas fuel such as DME and LPG is a gas at normal temperature and normal pressure, and the fuel leaked from the injector is vaporized, so that a processing device for collecting and liquefying is required. Therefore, there is a problem that the configuration of the fuel injection device becomes complicated. For example, in the apparatus disclosed in Japanese Patent Laid-Open No. 11-22590, a purge tank (pressure release storage tank) and a fuel low pressure pump are provided as apparatuses for collecting leaked fuel.
[0005]
Furthermore, the amount of heat generated per unit volume of DME is smaller than that of light oil, and in order to obtain an output equivalent to that of an engine using light oil as fuel, it is necessary to inject twice as much fuel. Further, in the case of LPG, since the calorific value per unit volume is larger than that of light oil, the density is small, so that an injection amount of about 1.5 times is required to obtain an equivalent output. Therefore, in order to divert the injector and the high pressure pump of the light oil fuel injection device to the fuel injection device for the liquefied gas fuel, the discharge amount of the high pressure pump must be increased, resulting in an increase in the size of the high pressure pump. Therefore, an improved technique for suppressing an increase in size of the high-pressure pump is desired.
[0006]
[Problems to be solved by the invention]
The present invention has been made paying attention to the above problems, and an object of the present invention is to provide a fuel injection device for liquefied gas fuel having a simple configuration and high reliability.
[0007]
[Means for Solving the Problems]
In the fuel injection device according to the first aspect, the liquefied gas fuel is stored in the fuel tank, and the liquefied gas fuel is increased in pressure by the high pressure pump. Then, the high-pressure fuel discharged from the high-pressure pump is accumulated at a pressure corresponding to a predetermined injection pressure on the common rail, and then injected from the injector. In particular, an injector having a leakless structure in which the high pressure fuel supplied from the common rail is not leaked to the low pressure side (leak) is used. In this case, unlike the conventional injector that leaks the high-pressure fuel in the pressure control chamber to the low-pressure side every time it is injected, a processing device for collecting the leaked fuel becomes unnecessary. In addition, since the leakage of the high-pressure fuel is eliminated, the extra load on the high-pressure pump is reduced, and the enlargement of the pump can be suppressed. In addition, there is no inconvenience such as fuel leakage to the atmosphere. As a result, according to the present invention, a highly reliable fuel injection device for liquefied gas fuel can be provided with a simple configuration.
In addition, in the fuel injection device according to the first aspect, the first on-off valve is provided in the middle of the fuel discharge passage leading from the common rail to the fuel tank. The first on-off valve is closed during engine operation, and the first on-off valve is opened when the engine is stopped. In this case, the first on-off valve is opened when the engine is stopped, so that the high-pressure fuel in the common rail is discharged to the fuel tank through the fuel discharge passage. Thereby, the high-pressure fuel in the common rail can be collected in the fuel tank when the engine is stopped. In this case, the residual fuel in the injector is also collected in the fuel tank through the common rail and the fuel discharge passage. Therefore, it is not sealed in the liquid state, and inconveniences such as breakage can be avoided even if the temperature rises after the engine is stopped.
In the first aspect of the present invention, as described in the second aspect, the fuel discharge passage and the high pressure pump are connected by the fuel passage, and when the engine is stopped, the high pressure pump and the fuel are opened along with the opening of the first on-off valve. It is good to communicate with the tank. Thereby, the high-pressure fuel in the high-pressure pump can be collected in the fuel tank when the engine is stopped.
[0008]
Further, it is preferable to configure the injector as claimed in claim 3. That is, in the invention described in claim 3 , the injector is configured such that the valve body is directly driven by the actuator, and the portions sandwiching the sliding portion of the valve body are under high pressure. In this case, fuel leakage such as fuel leaking from the high pressure portion to the low pressure portion is eliminated in the sliding portion of the valve body.
[0011]
On the other hand, in the invention described in claim 4 , the high-pressure pump is driven in synchronization with the operation of the engine, whereas the feed pump is driven by an electric motor or the like. Further, a bypass passage is provided between the feed pump and the common rail so as to bypass the high-pressure pump, and a second on-off valve is provided in the middle of the bypass passage. When the engine is started, the second on-off valve is opened for a predetermined period from the start of the start (startup control means). At this time, the feed pump is communicated with the common rail through the bypass passage by opening the second on-off valve, and pressurized fuel at a feed pressure (for example, about 2.5 to 3 MPa) by the feed pump is supplied to the common rail. At the beginning of the engine start, there is no fuel in the common rail, and there is a mixture of liquid fuel and gaseous fuel inside, but the fuel is supplied to the common rail by the feed pump, and that fuel is injected from the injector into the engine. Supplied. In this case, since the feed pump is an electric type, fuel can be supplied with a predetermined feed pressure from the beginning of the start regardless of the operation of the engine.
[0012]
At this time, fuel is also supplied to the fuel supply passage extending from the feed pump and the high pressure pump by the feed pump. When the second on-off valve is closed after a predetermined period from the start of the start, the fuel from the high pressure pump is used. Pressurization can be performed properly. Thereafter, the high-pressure fuel discharged from the high-pressure pump is accumulated in the common rail, and the injector is injected at a normal injection pressure. As described above, the startability of the engine can be improved by supplying the fuel from the feed pump to the common rail immediately after the engine is started.
[0013]
In particular, as described in claims 1 and 2 , when the fuel in the common rail or the high-pressure pump is recovered to the fuel tank when the engine is stopped, the inside of the common rail or the high-pressure pump is in a liquid state and gas. In this case, a good engine start can be realized.
[0014]
In the invention of claim 4 , as described in claim 5 , the second on-off valve may be opened at the beginning of engine startup until the engine speed reaches a predetermined value.
[0015]
In a sixth aspect of the invention, a third on-off valve is provided immediately after the feed pump in the fuel supply passage. The third on-off valve is opened during engine operation, and the third on-off valve is closed when the engine is stopped. In this case, fuel supply from the fuel tank can be appropriately performed according to the engine operating state.
[0016]
In the invention according to claim 7 , the feed pump pressurizes the fuel at a pressure higher than the saturated vapor pressure of the liquefied gas fuel at a temperature in a normal operation state of the engine. In this case, the liquefied gas fuel is prevented from being vaporized in the fuel supply passage and the high-pressure pump downstream from the feed pump, and problems due to the generation of bubbles can be prevented.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In the present embodiment, the present invention is embodied in a fuel injection device for injecting fuel into a vehicle diesel engine using liquefied gas such as DME or LPG as fuel.
[0018]
FIG. 1 is a schematic configuration diagram showing a fuel injection device in the present embodiment. In FIG. 1, liquefied gas fuel (DME or LPG) is stored in a fuel tank 1 at a saturated vapor pressure, and a feed pump 2 is attached to the outlet of the fuel tank 1. The feed pump 2 is an electric type driven by a motor or the like, and fuel of a predetermined feed pressure (about 2.5 to 3 MPa) is discharged by the feed pump 2. However, the attachment position of the feed pump 2 may be in the fuel tank 1.
[0019]
An electromagnetically driven fuel supply valve 5 is provided in the middle of the fuel supply pipe 3 from the feed pump 2 to the high pressure pump 4. When the fuel supply valve 5 is opened, the feed pump 2 is connected to the high pressure pump 4. When the fuel supply is allowed and the fuel supply valve 5 is closed, the fuel supply from the feed pump 2 to the high-pressure pump 4 is shut off. A common rail 6 is connected to the downstream side of the high-pressure pump 4, and injectors 7 are connected to the common rail 6 by the number of engine cylinders. The high-pressure pump 4 is drivingly connected to the output shaft of the engine by a belt, a chain or a gear, and is driven in synchronization with the rotation of the engine. The fuel in the fuel tank 1 is pressurized to 2.5 to 3 MPa by the feed pump 2 and then supplied to the high-pressure pump 4, and the high-pressure pump 4 applies a high-pressure state equivalent to the injection pressure (up to about 50 MPa). Pressed. This high-pressure fuel is pumped to the common rail 6 and once accumulated, then injected and supplied from the injector 7 to each cylinder of the engine.
[0020]
The common rail 6 and the fuel tank 1 are connected by a return pipe 8, and an electromagnetically driven pressure reducing valve 9 is provided in the middle of the return pipe 8. In this case, when the pressure reducing valve 9 is opened, the fuel in the common rail 6 is returned to the fuel tank 1 via the return pipe 8 so that the common rail pressure is reduced.
[0021]
Further, the fuel supply pipe 3 and the return pipe 8 are communicated by a branch pipe 10 between the downstream side of the fuel supply valve 5 (high pressure pump side) and the upstream side of the pressure reducing valve 9 (common rail side). An electromagnetically driven bypass valve 11 is provided in the middle of the branch pipe 10.
[0022]
In the present embodiment, the fuel supply pipe 3 is the “fuel supply passage”, the return pipe 8 is the “fuel discharge passage”, the branch pipe 10 from the downstream side of the fuel supply valve 5 to the common rail 6, the return pipe 8, Respectively correspond to “bypass passages”. The fuel supply valve 5 corresponds to a “third on-off valve”, the pressure reducing valve 9 corresponds to a “first on-off valve”, and the bypass valve 11 corresponds to a “second on-off valve”.
[0023]
The ECU 20 is mainly composed of a well-known microcomputer, and inputs detection signals such as the accelerator opening degree and the engine speed from various sensors (not shown), and a common rail pressure (injection pressure) from a pressure sensor 12 provided on the common rail 6. input. The ECU 20 controls the fuel discharge amount of the high-pressure pump 4 based on various input information so that the common rail pressure (injection pressure) becomes an optimum value. Further, the ECU 20 calculates the fuel injection amount and the fuel injection timing based on various input information, and controls the drive of the injector 7 accordingly. Further, the ECU 20 controls the opening / closing operations of the fuel supply valve 5, the pressure reducing valve 9, and the bypass valve 11 described above. In the present embodiment, the ECU 20 constitutes “starting time control means”.
[0024]
By the way, since liquefied gas fuel (DME and LPG) has a high saturated vapor pressure and low viscosity, for example, unlike a fuel injection device using light oil as a fuel, fuel leaks at the sliding portion of the high-pressure pump 4 or the injector 7. Is likely to occur. Further, when the amount of fuel leakage increases, the size of the high-pressure pump 4 will be increased accordingly. Therefore, measures against fuel leakage must be taken.
[0025]
Specifically, in the high pressure pump 4, as an example, a piston is accommodated in a cylinder, and fuel is pressurized by the reciprocation of the piston. In this case, it is considered that fuel leaks from the sliding portion of the piston. Therefore, for example, a communication passage (not shown) that connects the high-pressure pump 4 and the fuel tank 1 is provided, and the fuel (DME) leaked from the piston sliding portion is returned to the fuel tank 1 through the communication passage. It is desirable to do. Incidentally, it is also possible to use a diaphragm drive pump as the high pressure pump 4, and the problem of fuel leakage does not occur when using the diaphragm drive pump.
[0026]
On the other hand, in an existing common rail fuel injection device using light oil as a fuel, a two-way solenoid valve (or a three-way solenoid valve) is generally used as an injector. In this case, the high pressure fuel is introduced into the pressure control chamber provided on the back of the valve body, and the high pressure fuel (hydraulic pressure) in the pressure control chamber is leaked to the low pressure side for each injection, thereby opening the valve body. It is realized. Therefore, a high-pressure fuel leak occurs at every injection. Further, high-pressure fuel leaks also in the valve body sliding portion. Therefore, in the present embodiment, a so-called direct-acting injector that directly moves the valve element by an electromagnetic solenoid (actuator) is employed as the injector 7 so that fuel leakage is prevented. The configuration is shown in FIG.
[0027]
In FIG. 2, the casing 31 and the valve body 32 are provided coaxially, and are integrated by tightening a retaining nut 33. The casing 31 and the valve body 32 are provided with through holes 31a and 32a, and needles 34 as valve bodies are accommodated in the through holes 31a and 32a. The needle 34 has sliding portions 34a and 34b at two locations in the upper and lower directions in the figure. The tip of the valve body 32 is provided with a plurality of injection holes 32b. When the tip of the needle 34 abuts the valve body 32, the injection hole 32b is closed, and the tip of the needle 34 is separated from the valve body 32. Thus, the injection hole 32b is opened. A suction port 35 is assembled to the casing 31.
[0028]
Further, as a configuration of the actuator, an armature 36 is fixed to an upper end of the needle 34 in the figure, and a stator 37 is provided so as to face the armature 36. The needle 34 is biased to the valve closing side (the lower side in the figure) by a spring 38. Further, a coil 39 is disposed on the outer periphery of the stator 37. When the coil 39 is energized, the armature 36 is attracted by the stator 37, and the needle 34 moves to the valve opening side (upper side in the figure) against the urging force of the spring 38. Thereby, the injection hole 32b is opened and fuel injection is performed. That is, the injector 7 realizes the valve opening operation of the needle 34 without leaking high-pressure fuel.
[0029]
Further, the through hole 31 a into which high-pressure fuel is introduced from the suction port 35 is communicated with the armature chamber 42 via the communication path 41. Therefore, high pressure fuel acts on the needle 34 at any part, and fuel leakage such as fuel leakage from the high pressure part to the low pressure part is eliminated in the sliding portions 34a and 34b.
[0030]
In the fuel injection device of the present embodiment, as described above, measures are taken in the high pressure pump 4 and the injector 7 to prevent leakage fuel from leaking to the outside or to reduce the leakage fuel itself. By reducing the amount of fuel leak, the amount of high-temperature fuel returned to the fuel tank 1 is also reduced, and the temperature rise of the fuel tank 1 is suppressed.
[0031]
Next, the operation of the fuel injection device having the above configuration will be described. FIG. 3 is a time chart showing the operation of each solenoid valve from the start to the stop of the engine, and the transition of the injection pressure and the engine speed.
[0032]
In FIG. 3, at the timing t <b> 1 when the engine start is started, the ECU 20 opens the fuel supply valve 5 from the previous closed state and closes the pressure reducing valve 9 from the previous open state. However, the bypass valve 11 is maintained in the open state until then. At this time, power is supplied to the feed pump 2 as the engine is started, and driving thereof is started.
[0033]
Therefore, after t1, the fuel in the fuel tank 1 is discharged downstream by the feed pump 2 at a predetermined feed pressure (about 2.5 to 3 MPa). In this case, the fuel discharged from the feed pump 2 is fed to the high pressure pump 4 through the fuel supply pipe 3 and the bypass valve 11 is opened, so that the fuel is supplied to the common rail 6 via the branch pipe 10 and the return pipe 8. Be fed. At the beginning of the engine start, there is no fuel in the fuel supply pipe 3, the high-pressure pump 4, the common rail 6 and the like, and the inside remains space. Therefore, immediately after starting, the high-pressure pump 4 cannot normally pump fuel, and the common rail 6 is supplied with fuel from the feed pump 2 so that the discharge pressure of the pump 2 (about 2.5 to 3 MPa). A considerable amount of fuel will be stored. In this case, since the feed pump 2 is an electric type, fuel can be supplied with a predetermined feed pressure from the start of the operation regardless of the operation of the engine.
[0034]
That is, during the period from t1 to t2, fuel injection by the injector 7 is performed at an injection pressure of about 2.5 to 3 MPa. In this case, although the injection pressure is low, the injection period is long because of the low rotation immediately after the engine is started, and there is no problem in the operation of the engine. Actually, fuel injection is performed at an injection pressure of about 2.5 to 3 MPa during the cranking period by the starter.
[0035]
At the timing t2, the engine speed increases to a predetermined speed (for example, about 300 rpm), and the ECU 20 closes the bypass valve 11. Thereby, the communication from the feed pump 2 through the branch pipe 10 to the common rail 6 is blocked. At this time, the fuel supply pipe 3 and the high-pressure pump 4 are filled with the liquefied fuel by the fuel supply from the feed pump 2, and the fuel is normally pressurized by the high-pressure pump 4. 6 is pumped. That is, after t2, fuel injection by the injector 7 is performed at a normal injection pressure (for example, 50 MPa).
[0036]
Incidentally, since the fuel in the fuel tank 1 is pressurized to about 2.5 to 3 MPa by the feed pump 2, the fuel supplied to the fuel supply pipe 3 and the high-pressure pump 4 is higher than the saturated vapor pressure of the fuel in the normal operation state. Is also held at high pressure. For example, if the fuel temperature in the normal operation state is 80 ° C., the saturated vapor pressure of the fuel (DME) is about 2.2 MPa. Therefore, vaporization of the liquefied gas fuel is prevented in the fuel supply pipe 3 and the high-pressure pump 4, and problems due to the generation of bubbles can be prevented.
[0037]
On the other hand, at the timing t3 when the operation of the engine is stopped, the ECU 20 closes the fuel supply valve 5 and opens both the pressure reducing valve 9 and the bypass valve 11. As a result, the fuel in the common rail 6 is recovered in the fuel tank 1 via the return pipe 8, and the fuel in the high-pressure pump 4 is recovered in the fuel tank 1 via the branch pipe 10 and the return pipe 8. As a result, the pressure in the common rail 6 becomes equal to the pressure in the fuel tank 1.
[0038]
According to the embodiment described in detail above, the following effects can be obtained.
The injector 7 employs a leakless structure in which the high pressure fuel supplied from the common rail 6 does not leak to the low pressure side. Therefore, a processing device for collecting leaked fuel becomes unnecessary. Further, since the leakage of the high-pressure fuel is eliminated, an extra load on the high-pressure pump 4 is reduced, and an increase in size of the pump 4 can be suppressed. In addition, there is no inconvenience such as fuel leakage to the atmosphere. As a result, according to the present embodiment, a highly reliable fuel injection device for liquefied gas fuel can be provided with a simple configuration.
[0039]
Further, since both the pressure reducing valve 9 and the bypass valve 11 are opened when the engine is stopped, the high pressure fuel (the high pressure fuel in the common rail 6 and the high pressure pump 4) can be recovered through the return pipe 8 and the branch pipe 10. .
[0040]
Since the fuel is supplied to the common rail 6 by the electric feed pump 2 only for a predetermined period immediately after the engine is started, the fuel can be reliably injected at the time of starting the engine and the startability of the engine can be improved. It becomes like this. In particular, when the fuel in the common rail 6 or the high-pressure pump 4 is recovered in the fuel tank 1 when the engine is stopped, the liquid fuel and the gas fuel are mixed in the common rail 6 or the high-pressure pump 4. In this case, a good engine start can be realized.
[0041]
In addition to the above, the present invention can be embodied in the following forms.
In the above embodiment, the bypass valve 11 is opened for a predetermined period after the engine starts until the engine speed reaches a predetermined value. Instead, the bypass valve 11 is bypassed until a certain time has elapsed after the engine starts. The valve 11 may be opened.
[0042]
In the above embodiment, as shown in the time chart of FIG. 3, the pressure reducing valve 9 is opened when the engine is stopped and is kept open until the next engine start. The valve 9 may be closed and the fuel tank 1 may be sealed while the engine is stopped.
[0043]
In the above embodiment, the solenoid coil drive type structure of FIG. 2 is used as the injector 7, but other structures such as a piezo drive type may be used instead. In any case, a direct acting structure using an actuator may be used.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an outline of a fuel injection device according to an embodiment of the invention.
FIG. 2 is a cross-sectional view showing a configuration of an injector.
FIG. 3 is a time chart for explaining the operation of the fuel injection device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Fuel tank, 2 ... Feed pump, 3 ... Fuel supply piping, 4 ... High pressure pump, 5 ... Fuel supply valve (3rd on-off valve), 6 ... Common rail, 7 ... Injector, 8 ... Return piping, 9 ... Pressure reduction Valve (first on-off valve), 10 ... branch piping, 11 ... bypass valve (second on-off valve), 20 ... ECU, 34 ... needle.

Claims (7)

A high-pressure pump is connected to the fuel tank that stores the liquefied gas fuel through a fuel supply passage. The high-pressure fuel discharged from the high-pressure pump is stored in the common rail at a pressure corresponding to a predetermined injection pressure, and then injected from the injector. In a fuel injection device for liquefied gas fuel,
As the injector, with using those Rikuresu structure without leakage to the low pressure side of the high pressure fuel supplied from the common rail, and the fuel discharge passage leading to the fuel tank from the common rail, in the middle of the fuel discharge passage A fuel injection for liquefied gas fuel, wherein the first on-off valve is closed during engine operation, and the first on-off valve is opened when the engine is stopped. apparatus. 2. The fuel injection device for liquefied gas fuel according to claim 1, wherein the fuel discharge passage and the high pressure pump are connected by a fuel passage, and when the engine is stopped, the high pressure pump and the fuel are opened when the first on-off valve is opened. A fuel injection device for liquefied gas fuel that communicates with a tank . The injector is driven directly at the valve body actuator and the valve body fuel for liquefied gas fuel according to claim 1 or 2 sites flanking the sliding portion are both also being configured to be under high pressure Injection device. The high-pressure pump is a fuel injection device driven in synchronism with the operation of the engine,
An electric feed pump that is disposed closer to the fuel tank than the high-pressure pump and discharges fuel at a predetermined feed pressure;
A bypass passage provided between the feed pump and the common rail so as to bypass the high-pressure pump;
A second on-off valve provided in the middle of the bypass passage for opening and closing the bypass passage;
The fuel injection device for liquefied gas fuel according to any one of claims 1 to 3, further comprising a start-time control means that opens the second on-off valve for a predetermined period from the start of the engine when the engine is started . Te fuel injector smell for liquefied gas fuel according to claim 4, wherein the start control means, the liquefied gas fuel engine speed to open the second on-off valve at the beginning the engine starting to reach a predetermined value Fuel injection device. The third on-off valve is provided immediately after the feed pump in the fuel supply passage, during engine operation opening the third on-off valve, according to claim 1 when the engine is stopped you close said third opening and closing valve The fuel injection device for liquefied gas fuel according to any one of 5 . The feed pump, fuel for liquefied gas fuel according to any one of claims 1 to 6, pressurized fuel at a pressure higher than the saturated vapor pressure of the liquefied gas fuel at a temperature in the normal operation state of the engine Injection device.

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