JPH0429082Y2 - - 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. As a means to solve this problem, unit injectors incorporating electrical or electronic control means have been proposed in Japanese Utility Model Application Publication No. 56-31655 and Japanese Patent Application Publication No. 59-103960.

[Problem that the invention attempts to solve]

In the unit injector shown in Japanese Utility Model Application Publication No. 56-31655, a solenoid valve is placed in the fuel discharge passage leading to the pressure chamber, and the timing and amount of fuel injection can be controlled by controlling this solenoid valve. .
However, since high hydraulic pressure is generated in the pressure chamber of the unit injector, it is necessary to operate the solenoid valve against this pressure, and a very large amount of driving power is required. Furthermore, currently available solenoid valves have a minimum response time limit, which makes it impossible to precisely control pilot injections and the like.

In the unit injector shown in Japanese Patent Application Laid-open No. 59-103960, the force applied to the solenoid valve is reduced and the amount of electric power can be reduced, but the problem with response is similar to that mentioned above. Furthermore, since there are many fuel passages and the back of the metering valve is communicated with the pressure chamber of the unit injector, the compressed volume of the unit injector's pressure chamber becomes large. The characteristic of the unit injector, which is that the high-pressure space leading to the fuel injection nozzle can be reduced by more than half, is halved.

If a valve device using a piezoelectric element actuator is used instead of these electromagnetic valves, responsiveness can be improved. However, a mechanical coupling means is required to couple the piezoelectric element and the valve body, and it may be difficult to adjust the minute positional relationship between them due to variations in the characteristics of the piezoelectric elements or individual variations. many. The object of the present invention is to provide a unit injector that can optimally utilize piezoelectric elements.

[Means for solving problems]

The unit injector according to the present invention has a plunger disposed in a part of the main body, and a fuel pumping section with a pressure chamber formed at the tip thereof, and a fuel injection nozzle communicating with the pressure chamber at the tip of the main body. In the unit injector provided,
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 the overflow valve receives the pressure of the pressure chamber from the front side thereof. A control valve having a pressure receiving part and a valve operating pressure chamber formed behind the pressure receiving part to receive the pressure of the pressure chamber, further connecting a relief passage to the valve operating pressure chamber, and connected to the relief passage driven by a piezoelectric element. and the control valve is arranged such that:
The valve is composed of a ball control valve that opens and closes the relief passage, a control rod that drives the ball control valve, and an actuator piston that is driven by a piezoelectric element that drives the control rod via an intermediate pressure chamber. It is characterized in that the end area of the actuator piston facing the pressure chamber is larger than the end area of the control rod facing the intermediate pressure chamber.

〔Example〕

1 and 2, reference numeral 10 indicates a pressure feeding section main body, and a fuel injection nozzle main body 14 having a nozzle 12 is fixed below it. These bodies 1
0 and 14 form the body of the unit injector. It is a 16 needle valve and engages a valve seat around the spout 12. A spring 18 biases the needle valve 16 in the closing direction. Pressure feeding unit body 1
0, a plunger barrel 20 is fixed, and a plunger 22 is inserted into the plunger barrel 20. In this way, a pressure chamber 24 is formed within the plunger barrel 20 on the distal end side of the plunger 22. Fuel is supplied from the inlet section 26 and the annular passage 2 between the pump body 10 and the plunger barrel 20.
8 and enters the pressure chamber 24 through a feed hole 30 passing through the plunger barrel.

In order to communicate the pressure chamber 24 and the injection port 12, fuel supply passages 32 and 34 are provided in the pressure feeding section main body 10 and the fuel injection nozzle main body 14, respectively. A fuel return passage 36 is formed parallel to the fuel supply passage 32 toward the annular fuel passage 28, and a fuel overflow passage 38 is provided by connecting the fuel supply passage 32 and the fuel return passage 36. 37 is a bar filter. A needle-shaped overflow valve 40 is arranged in the fuel overflow passage 38 . The overflow valve 40 is an inward-opening valve, and the tip of the overflow valve 40 engages with a valve seat 42 provided in the fuel overflow passage 38. The fuel overflow passage 38 has a substantially constant diameter and further extends perpendicular to the fuel supply passage 32 and opposite the fuel return passage 36 . The overflow valve 40 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 38 in a piston-cylinder relationship. A tapered portion 44 between the small diameter portion and the large diameter portion of the overflow valve 40 serves as a pressure receiving portion on the front side.

On the rear side of the overflow valve 40, a plug 46 is fitted into the pressure feeding section main body 10, and a back pressure chamber 48 is formed between the front end surface of the plug 46 and the rear end surface of the overflow valve 40. The overflow valve 40 is formed with a through hole 50 that communicates the tapered portion 44 with the rear end surface.
4 receives the pressure of the fuel in the pressure chamber 24,
The pressure of the fuel in the pressure chamber 24 introduced into the back pressure chamber 48 through the through hole 50 is received on the rear side. However, the pressure receiving area of the rear end surface is
4, the overflow valve 40 is pushed forward by the spring 101 and closes the overflow passage 38 when both the front and rear are receiving the pressure of the pressure chamber 24. After the overflow valve 40 is seated by the spring 101, a seating force proportional to the generated oil pressure is applied due to the difference in pressure receiving areas before and after the overflow valve 40.

The plug 46 is formed with a hole 52a extending in the axial direction and a hole 52b extending in the semi-hole direction, and the pumping section main body 10 is formed with a hole 52c extending toward the annular fuel passage 28. These holes 52a, 52
b and 52c are continuous to form one relief hole, which relieves the back pressure chamber 48 to the low pressure annular fuel passage 28. Therefore, when the back pressure chamber 48 is in communication with the annular fuel passage 28, the overflow valve 40 receives the pressure of the pressure chamber 24 only on the front side thereof, and is pushed rearward to the overflow passage. Open 38.

A control valve 54 made of a ball is provided to open and close this relief passage. Ball control valve 54
A control rod 56 is provided so as to be able to come into contact with it, and an actuator piston 60 is also provided via an intermediate pressure chamber 58. The area of the end surface of the actuator piston 60 facing the intermediate pressure chamber 58 is larger than the area of the end surface of the control rod 56 facing the intermediate pressure chamber 58. The actuator piston 60 is connected to a piezoelectric element 62 and biased rearward by a spring 64. The piezoelectric element 62 is restricted from being positioned on the right side in FIG. control rod 56
Push the ball control valve 54 through to shut off the relief hole. The energization of the piezoelectric element 62 is controlled by a controller 68 .

Above the main body 10 of the pumping section is a tappet 70 connected to the upper end of the plunger 22, and the tappet 70 comes into contact with a cam (not shown). Therefore, the plunger 22 can move up and down following the movement of the cam. The tappet 70 is slidably supported by a tappet body 72 and is supported by a spring 74.
The cam is biased toward the cam by the cam.

Next, the operation will be described.

FIG. 1 shows a state in which the plunger 22 is in the raised position, and at this time, fuel flows into the feed hole 30.
A pressure chamber is drawn into 24 from the air. Eventually, the plunger 22 begins to descend, and as the plunger 22 closes the feed hole 30, the fuel in the pressure chamber 24 is pressurized. At this time, the piezoelectric element 62 is not energized, and the actuator piston 60
is in the retracted position on the right side with the retracted piezoelectric element 62, and the ball control valve 54 and control rod 56
is pushed by the pressure of the valve actuation pressure chamber 48 to open the relief hole 52a. The overflow valve 40 therefore overcomes the force of the spring 101 due to the differential pressure generated by the throttle passage 50 within the overflow valve and opens the overflow passage 38. Therefore, since the fuel in the pressure chamber 24 overflows from the overflow passage 38 to the return passage 36, the fuel is not pressurized and the needle valve 16 does not open.

Eventually, electricity is supplied from the controller 68 to the piezoelectric element 62 based on the output of a sensor (not shown) that detects the operating state of the engine. The piezoelectric element 62 immediately expands when energized, and since the right end position is restricted, it is displaced to the left end, pushing the actuator piston 60 to the left. Actuator piston 60
This movement reduces the volume of the intermediate pressure chamber 58,
The control rod 56 is controlled by the resulting hydraulic pressure.
and the ball control valve 54 is pushed, and the ball control valve 5
4 blocks the relief passage. Furthermore, the intermediate pressure chamber 5
Since the pressure area of the actuator piston 60 at 8 is larger than the pressure area of the control rod 56, the piezoelectric element 62 can move the control rod 56 with a relatively small force. In addition, the piezoelectric element 62
Since the stroke is amplified and transmitted to the control rod 56 via the intermediate pressure chamber 58, the ball control valve 54 operates reliably even with a small amount of displacement of the piezoelectric element. Furthermore, compared to a configuration in which the piezoelectric element directly moves the overflow valve 40, in the present invention, the piezoelectric element 62 only needs to drive the ball control valve 54 arranged in a relief passage with a small area. This means that the amount of power required by the piezoelectric element 62 may be even smaller. Further, even if the amount of displacement of the piezoelectric element is small, the overflow valve 40 can be displaced by a sufficient amount, so the amount of overflow can be increased and the injection can be cut off easily.

When the ball control valve 54 closes the relief passage,
As mentioned above, since the pressure of the pressure chamber 24 is also applied to the rear end surface of the overflow valve 40, the overflow valve 40 moves to the left by the force of the spring 101, and the overflow passage 3
Close 8. During this time, the plunger 22 continues to descend, and by closing the overflow passage 38, the pressure of the fuel in the pressure chamber 24 increases, and the needle valve 16
Open the valve and inject fuel. Next, the injection is terminated by stopping the energization to the piezoelectric element 62. That is, the actuator piston 60 returns to its original retracted position due to the spring force of the spring 64, and the ball control valve 54 is pushed by the pressure of the valve actuation pressure chamber 48 to open the relief hole, thereby reducing the back pressure. As the pressure in chamber 48 is relieved, overflow valve 40 moves to the right, opening overflow passage 38. As a result, the pressure in the pressure chamber 24 decreases even when the plunger 22 is descending.

In the present invention, a piezoelectric element actuator is used to actuate the overflow valve 40, and the plunger 22 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 62 that actually opens and closes the fuel injection nozzle. Piezoelectric element 62
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 62, pilot injection, which is difficult to perform with a mechanical unit injector, can also be performed.

[Effect of idea]

As explained above, according to the present invention, it is possible to obtain a unit injector with extremely excellent responsiveness due to the structure that allows the characteristics of the piezoelectric element to be fully utilized. Through such control, it is possible to reduce noise by improving injection characteristics and reduce fuel consumption by reducing the minimum injection amount. Furthermore, if the fuel overflow passage is formed so as to run directly into the fuel supply passage, the fuel overflow passage can be extremely short and the dead volume for arranging the overflow valve can be minimized. As a result, the structure of the unit injector becomes compact, and the unit injector features a short high-pressure fuel supply passage. Furthermore, the piezoelectric element only needs to drive a small control valve disposed in a small relief passage instead of directly driving the overflow valve, which means that the piezoelectric element requires less power.

Furthermore, since the stroke of the piezoelectric element is amplified and transmitted to the control rod via the intermediate pressure chamber, the control valve can operate reliably even with a small amount of displacement of the piezoelectric element. Furthermore, compared to the case where the overflow valve is directly driven by a piezoelectric element, even if the displacement amount of the piezoelectric element is small, the overflow valve can be displaced by a sufficient amount, so the overflow amount can be increased, and the fuel injection is improved. Furthermore, since the control valve has a structure in which the control ball valve and the control rod are separated, the machining accuracy of the diameter and position of the relief passage can be reduced, and work efficiency is improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a unit injector according to the present invention, and FIG. 2 is an enlarged view of the unit injector shown in FIG. 1 near the overflow valve. 10... Pressure feeding unit main body, 14... Injection nozzle main body, 22... Plunger, 24... Pressure chamber, 3
2, 34...Fuel passage, 38...Overflow passage, 40
...Overflow valve, 48...Back pressure chamber, 52a, 52b,
52c...Relief hole, 54...Ball control valve,
62...Piezoelectric element.

Claims (1)

[Scope of utility model registration request] In addition to providing a fuel pumping section with a plunger arranged in a part of the main body and a pressure chamber formed on the tip side,
In a unit injector in which a fuel injection nozzle communicating with the pressure chamber is provided at the tip of the main body, an overflow passage is provided for causing fuel supplied from the pressure chamber to the fuel injection nozzle to overflow, and the overflow passage is An overflow valve is disposed in the passage, and the overflow valve has a pressure receiving part that receives the pressure of the pressure chamber from the front side thereof, and a back pressure chamber that receives the pressure of the pressure chamber at the rear side thereof. Further, a relief passage is connected to the back pressure chamber, and a control valve driven by a piezoelectric element is disposed in the relief passage, and the control valve includes a ball control valve for opening and closing the relief passage, and the ball control valve. It consists of a control rod to be driven and an actuator piston driven by a piezoelectric element that drives the control rod through an intermediate pressure chamber, and the end area of the actuator piston facing the intermediate pressure chamber is A unit injector characterized in that the area of the end of the control rod facing the intermediate pressure chamber is larger than that of the control rod.