JPH0430376Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a unit injector mainly used in diesel engines.

[Conventional technology]

A unit injector is a well-known fuel injection device in which a fuel pumping section and a fuel injection nozzle, which serve as a conventional fuel injection pump, are integrally constructed. Conventional unit injectors are mechanical metering systems that include complex link mechanisms, which pose problems in that they are difficult to adjust and assemble, and are difficult to precisely control. Further, examples of unit injectors incorporating electrical or electronic control means are disclosed in Utility Model Application Publication No. 56-31655 and Japanese Patent Application Publication No. 1983-1999.
Publication No. 103960 is known.

[Problem that the invention attempts to solve]

Unit injectors have superior injection characteristics compared to conventional injection devices that have separate fuel injection pumps and fuel injection nozzles, and are therefore advantageous in improving engine output and fuel efficiency. Therefore, once a failure occurs, the disassembly and assembly work for repair is complicated and requires a large amount of time, which is why it has not been widely used. Most of the causes of this failure are that foreign matter such as iron powder mixed into the fuel supply system during assembly or operation of the unit injector enters the unit injector and gets caught mainly in the nozzle part, which causes the needle valve to This can lead to burn-in and sheet defects. If a failure occurs in the nozzle that injects fuel, it will lead to deterioration in engine performance and exhaust gas.

The generation of foreign matter is not limited to those that enter the fuel from the outside, but also occurs inside the unit injector due to burrs on the component parts of the unit injector. In particular, if the deburring during machining of parts that come in contact with high fuel pressure is insufficient, the burrs may be ripped off by the hydraulic pressure generated by the impact, or fine particles may be generated on the sliding part of the plunger that reciprocates at high speed. occurs, and this causes failure in the nozzle part, which is machined with high precision.

[Means for solving problems]

In order to solve the above-mentioned problems, the unit injector according to the present invention is provided with a fuel pumping section in which a plunger is disposed in a part of the main body and a pressure chamber is formed on the tip side thereof, and a nozzle is provided at the tip of the main body. In the fuel injection nozzle, an overflow passage is provided for overflowing the fuel supplied from the pressure chamber to the fuel injection nozzle, an overflow valve is disposed in the overflow passage, and a fuel injection nozzle is provided in the fuel passage. A filter is disposed in a portion between the pressure chamber and the overflow valve, and in a portion between the overflow valve and the fuel supply port in the fuel return passage.

〔Example〕

In FIGS. 1 and 2, 10 is a pumping section main body, and a fuel injection nozzle main body 14 having a nozzle 12 is fixed to the lower part thereof. These bodies 10, 14 form a unit injector body. 15 is a needle valve, which cooperates with a valve seat formed around the nozzle 12. Pressure feeding unit main body 10
A plunger barrel 16 is fixedly inserted therein. An annular fuel passage 18 is formed between the pumping section main body 10 and the plunger barrel 16, and fuel is supplied to the annular fuel passage 18 from a fuel supply port 20 attached to the pumping section main body 10. A radial through hole 22 is formed in the plunger barrel 16 and fuel is supplied from the annular fuel passage 18 through the through hole 22 into the interior of the plunger barrel 16 .

A plunger 24 is slidably inserted into the plunger barrel 16, and a pressure chamber 26 is formed at the tip side of the plunger 24. The upper end of the plunger 24 is connected to a tappet 30 supported by a tappet body 28 formed separately from the pressure feeding section body 10, and the tappet 30 is biased by a spring 32 and driven by a cam (not shown). ,
The plunger 24 is driven in the vertical direction in FIG.

In order to communicate the pressure chamber 26 and the injection port 12, fuel supply passages 34 and 36 are provided in the pressure feeding section main body 10 and the fuel injection nozzle main body 14, respectively. Furthermore, an annular fuel passage 18 and a fuel injection nozzle body 14
A fuel return passage 38 connecting the spring chamber 40 of
is formed parallel to the fuel supply passage 34, and a fuel overflow passage 42 is provided by connecting the fuel supply passage 34 and the fuel return passage 38. Fuel overflow passage 4
A needle-shaped overflow valve 44 is arranged at 2. That is, the tip of the overflow valve 44 engages with a valve seat 46 provided in the fuel overflow passage 42 . The fuel overflow passage 42 has a substantially constant diameter and further extends perpendicular to the fuel supply passage 34 and opposite the fuel return passage 38 . The overflow valve 44 is formed in a stepped manner and has a small diameter portion at the front and a large diameter portion at the rear. The rear large diameter portion is fitted into the extended portion of the fuel overflow passage 42 in a piston-cylinder relationship.

A bore 48 having a larger diameter than the rear large diameter portion of the overflow valve 44 is formed behind the overflow valve 44, and an actuator piston 50 is slidably inserted into the bore 48. Actuator piston 50
comes into contact with a holder 54 that deformably houses the piezoelectric element 52. The piezoelectric element 52 is mounted by screwing a nut 56 onto the main body 10 of the pumping section so that displacement to the right in FIG. 1 is restricted. Then,
The piezoelectric element 52 can only be displaced to the left in FIG. 1, and is constantly urged to the right together with the actuator piston 50 by a disc spring 58 attached to the actuator piston 50. The piezoelectric element 52 is connected to a controller 59 depending on the operating state of the engine.
energization is controlled by

As is clear from FIG. 2, the overflow valve 44 and the actuator piston 50 do not directly abut, but a valve actuation pressure chamber 60 is formed between them. Further, the actuator piston 50 includes an adjustment pin 62 that protrudes into the valve actuation pressure chamber 60.
is installed. The diameter of adjustment pin 62 is significantly smaller than the diameter of overflow valve 44. Note that fuel oil can enter the valve operating pressure chamber 60 through a minute clearance between the overflow valve 44 and the cylinder wall surrounding it.

In the present invention, a filter 70 is disposed in the fuel supply passage 34 provided in the main body 10 of the pumping section. The filters 70 are disposed in a portion of the fuel supply passage 34 between the pressure chamber 26 and the overflow valve 44 and in a portion of the fuel return passage 38 between the overflow valve 44 and the fuel supply port 20. be done. This filter 70 is a bar edge type filter having a plurality of elongated passage holes. A bar edge type filter (or bar filter) can remove foreign matter without reducing the pressure of flowing fuel, and is resistant to clogging even after long-term use. Bar edge type filters are much smaller and more durable than other types of filters such as mesh filters. For example, mesh type filters are damaged by pressure waves and are too bulky, making them difficult to wear. This filter 70 separates and removes foreign matter mixed into the fuel, foreign matter generated at the sliding part between the plunger barrel 16 and the plunger 24, or burrs on parts that come into contact with high fuel pressure, and removes foreign matter from the fuel. Clean fuel can be sent to the valve seat of the valve. Thereby, the needle valve 1
5 and its valve seat due to foreign matter getting caught, and failure of the unit injector can be prevented.

Next, the effect will be explained.

FIG. 1 shows a state in which the plunger 24 is in the raised position, and at this time, fuel flows into the radial through hole 24.
The air is sucked into the pressure chamber 26 from above. Eventually, the plunger 24 begins to descend, and the plunger 24 enters the through hole 22.
The fuel in the pressure chamber 26 is pressurized by closing the pressure chamber 26. At this time, the piezoelectric element 52 is not energized, and the actuator piston 50 is in the retracted position on the right side in FIG. 1 together with the retracted piezoelectric element 52. Therefore, as soon as pressurization of the pressure chamber 26 begins, the pressure of the fuel acts on the tapered portion and tip of the overflow valve 44, causing the overflow valve 44 to retreat, thereby opening the fuel overflow passage 42. Therefore, the pressure chamber 26
Since the fuel overflows from the overflow passage 42 to the return passage 38, the pressure does not increase significantly and the needle valve 1
5 does not open.

At this time, the rear end surface of the overflow valve 44 hits the tip of the adjustment pin 62 supported by the actuator piston 50 in the retracted position, and the overflow valve 44 cannot be retracted any further. That is, the overflow valve 44 is opened while waiting at a certain position in preparation for the upcoming valve closing. If the adjustment pin 62 were not present, the stop position of the overflow valve 44 would not be determined.

Eventually, when the needle valve 15 should be opened depending on the operating state, the piezoelectric element 5 is activated by the controller 59.
2 is energized. The piezoelectric element 52 immediately expands when energized, and since the right end position is restricted, it is displaced to the left end, and the actuator piston 50
Push to the left. This movement of actuator piston 50 reduces the volume of valve actuation pressure chamber 60 and the resulting hydraulic pressure forces overflow valve 44 to close fuel overflow passage 42 . During this time, the plunger 24 continues to descend, and by closing the overflow passage 42, the pressure of the fuel in the pressure chamber 26 increases, and the needle valve 15 opens to inject fuel. Next, the injection is completed by stopping the current supply to the piezoelectric element 52. That is, the spring force of the disc spring 58 causes the actuator piston 50 and the piezoelectric element 52 to return to the original retracted position, and the pressure acting on the tapered portion of the overflow valve 44 opens the overflow valve 44, so that the plunger 24 Even when the pressure chamber 2 is descending,
The pressure of 6 fades.

In the present invention, a piezoelectric element actuator is used to operate the overflow valve 44, and the plunger 24 only mechanically continues its downward movement for a relatively long period of time to actually open and close the fuel injection nozzle. is not relevant. It is the piezoelectric element 52 that actually opens and closes the fuel injection nozzle. Piezoelectric element 52
has excellent responsiveness in an extremely short period of time, and therefore, by electrically controlling the piezoelectric element, it is possible to perform precise control of fuel injection timing and injection amount with excellent responsiveness. By using the piezoelectric element 52, pilot injection, which is difficult to perform with a mechanical unit injector, can also be performed.
Furthermore, since the hydraulic pressure in the valve operating pressure chamber 60 is used to drive the overflow valve 44, there is no need to accurately connect the actuator piston 50 and the overflow valve 44, and the opposing surfaces of these parts do not need to be connected accurately. It is not necessary to perform the finishing process precisely. Since the diameter of the actuator piston 50 for generating pressure is large and the diameter of the overflow valve 44 receiving the pressure is small, the driving force of the actuator piston 50 may be relatively small. This means that the amount of power required for the piezoelectric element 52 may also be relatively small.

When the plunger 24 then begins to rise, fuel can be drawn back into the pressure chamber 26 from the open fuel overflow passage 42, thereby preventing the injection system from being under negative pressure as the plunger 24 rises. , the generation of bubbles is prevented and the residual pressure is stabilized.

Even if foreign matter such as iron powder is mixed into the pressure chamber 26 during the pressure feeding of fuel by lowering the plunger 24, this foreign matter is prevented from reaching the overflow valve 44 by the filter 70, and the plunger 24 is prevented from reaching the overflow valve 44. Even when fuel is supplied to the pressure chamber 26 during the upward stroke, there is a passage (fuel return passage 38) that supplies fuel from the fuel supply port 20 to the pressure chamber 26 via the overflow valve 44 on the upstream side of the overflow valve 44. The presence of the filter 70 prevents foreign matter from entering the overflow valve 44 from the outside. Therefore, the overflow valve 44 is prevented from getting caught in foreign matter, and failure of the overflow valve itself can be prevented.

[Effect of idea]

As explained above, according to the present invention, in a unit injector in which an overflow passage and an overflow valve are provided in the high-pressure fuel passage, the fuel passage on the upstream side of the overflow valve is always provided both during fuel supply and during fuel pressure injection. The presence of the filter prevents foreign matter from entering the overflow valve from the outside or from the pressure chamber, thereby preventing the failure of the overflow valve itself, and thereby preventing the main cause of failure of the unit injector. It is possible to prevent seizure of the nozzle seat section due to foreign matter entering a certain nozzle section.

[Brief explanation of drawings]

Fig. 1 is a sectional view of the unit injector according to the present invention, Fig. 2 is an enlarged view of the unit injector shown in Fig. 1 near the overflow valve, 10... main body of the pumping section, 12... nozzle, 14...
Injection nozzle body, 15... Needle valve, 24...
Plunger, 26...pressure chamber, 34, 36...fuel supply passage, 44...overflow valve, 52...piezoelectric element, 70...filter.

Claims (1)

[Scope of utility model registration request] In a unit injector, a fuel pumping section is provided in which a plunger is disposed in a part of the main body and a pressure chamber is formed at the tip side thereof, and a fuel injection nozzle having a nozzle is provided at the tip of the main body. An overflow passage is provided for overflowing the fuel supplied from the fuel injection nozzle to the fuel injection nozzle, an overflow valve is disposed in the overflow passage, and a portion between the pressure chamber and the overflow valve in the fuel passage and the fuel A unit injector characterized in that a filter is disposed in each portion of the return passage between the overflow valve and the fuel supply port.