JP2714841B2 - Variable pressure device for high pressure fuel injector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable pressure device of a high-pressure fuel injection device used for a high-speed diesel engine, for example.

[Conventional technology]

2. Description of the Related Art A high-pressure fuel injection device used in a diesel engine is configured to supply a fuel pressurized to a substantially constant pressure by a fuel injection pump to a fuel injection valve and inject the fuel.

[Problems to be solved by the invention]

By the way, in an engine having a wide operating speed range, the fuel injection time is adjusted according to the engine speed so that the fuel injection crank angle range is constant and the fuel injection amount is constant even if the engine speed changes. It is desirable to change. Therefore, it is conceivable to change the fuel injection pressure by using an electromagnetic valve or the like to release a part of the fuel supplied from the fuel injection pump to the fuel injection valve. However, since the fuel supply pressure is extremely high, there is a problem in the sealing property, and control becomes difficult. In other words, if you use a solenoid valve that matches the fuel supply pressure,
There is a problem that the device becomes large and expensive. The present invention has been made in view of such circumstances, and provides a pressure variable device of a high-pressure fuel injection device that can change the fuel injection pressure while suppressing increase in size and cost.

[Means for solving the problem]

The variable pressure device according to the present invention is configured such that a device main body having a fuel inlet and a fuel outlet slidably holds a piston having a large piston at one end and a small piston at the other end, and a front side and a back side of the piston. Between the piston side and the fuel inlet, and between the piston front side and the fuel inlet through the first valve port facing the small piston, and between the piston back side and the fuel outlet. Through a second valve port that is opened and closed by an electromagnetic valve, and a valve body that opens and closes the first valve port by movement of the piston is provided on the piston side of the first valve port.

[Action]

In the present invention, a part of the fuel in the fuel supply passage is the first fuel.
The pressure is reduced by the valve body that opens and closes the valve port, flows into the front side of the piston, and is guided to the rear side of the large piston through the communication passage, so that the first valve port is controlled by the low pressure of the fuel itself. Then, when the second valve port is opened by the solenoid valve, the fuel on the back side of the large piston flows into the fuel return passage, and a part of the fuel in the fuel supply passage flows into the back side of the large piston. On the other hand, when the second valve port is closed by the solenoid valve, the first valve port is closed by the fuel pressure on the back side of the large piston, and the fuel in the fuel supply passage is prevented from flowing to the back side of the large piston.

〔Example〕

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.
1 is a longitudinal sectional view showing a variable pressure device of a high-pressure fuel injection device according to the present invention, FIG. 2 is a sectional view showing an enlarged valve body,
FIG. 3 is an enlarged sectional view showing a seating portion of the valve body. In FIG. 1, reference numeral 1 denotes a fuel injection valve. A fuel injection port is opened at a front end of the fuel injection valve 1, and a fuel supply passage 2 is connected to a rear end. The fuel supply passage 2 is connected to the discharge side of a fuel injection pump 4 that pressurizes the fuel in the fuel tank 3 to a high pressure. Reference numeral 5 denotes a fuel return passage for returning excess fuel among the fuel discharged from the fuel injection pump 4 to the fuel tank 3.

Reference numeral 6 denotes a pressure variable device, which comprises a device main body 7 formed in a substantially columnar shape as a whole, a pressure sensor 8 attached to the device main body 7, an electromagnetic valve 9, and the like. The apparatus main body 7 includes a cylindrical body 7a and a lid 7b.
A large cylinder 11 is recessed at one end of the body 7a, and a small cylinder 12 is formed inside the large cylinder 11. A low-pressure chamber 13 having a diameter larger than that of the small cylinder 12 is formed below the small cylinder 12, and the low-pressure chamber 13 is opened to the other end of the body 7a by a screw hole. Here, these cylinders and screw holes 14 are arranged coaxially. The lid 7b is attached so as to cover the opening of the large cylinder 11 with bolts or the like screwed to the body 7a.

Reference numeral 15 denotes a piston slidably held in the large cylinder 11 and the small cylinder 12.A large piston 16 is formed at one end of the large cylinder 11 and a small piston 17 is formed at the other end of the small cylinder 12. Have been. On the back side of the large piston 16, a concave portion 16a that forms a space between the large piston 16 and the lid 7b is provided. A communication passage 18 is formed on the axis of the piston 15 so as to penetrate the piston 15 in the axial direction. Through the communication passage 18, the front side and the back side of the piston communicate with each other. The outer surfaces of the large and small pistons 16 and 17 have O-rings 21 and
22 is fitted.

23 is a connection joint member screwed into the screw hole 14. The connection joint member 23 is provided with an inflow passage 24 on an axis, and a fuel inlet 25 is formed at one end of the inflow passage 24,
A first valve port 26 is opened at the other end. The fuel inlet 25 communicates with the fuel supply passage 2. The first valve port 26 is opened facing the front side of the small piston 17, and communicates between the front side of the communication path 18 and the fuel inlet 25.

27 is a fuel return pipe connected to the cover 9a covering the solenoid valve 9.
It is a fuel outlet molded into 28. The fuel outlet 27 communicates with the back side of the large piston 16 in the large cylinder 11 via a second valve port 31 opened and closed by the solenoid valve 9 and also communicates with the fuel return passage 5. That is, reference numeral 32 denotes an electromagnetic valve disposed downstream of the second valve port 31 and moving forward and backward with respect to the second valve port 31. On the other hand, a valve body 33 that opens and closes the first valve port 26 is interposed between the connection joint member 23 and the small piston 17.

The valve body 33 has a spherical seating portion and a flat portion that abuts on the end face of the small piston 17, and the flat portion communicates with the communication passage 18 of the piston 15 and the inside of the cylinder as shown in FIG. A groove 34 is provided. Since the fuel pressure always acts on the seat portion side of the valve body 33, the valve body 33 moves with the movement of the piston 15. A conical seating surface 35 is provided on the periphery of the first valve port 26. Here, the inclination angle of the seat surface 35 is set smaller than the inclination angle of the seat portion of the valve body 33.

The pressure sensor 8 is attached to the lid 7b.
The pressure on the back side of the large piston 15 in the large cylinder 11 is detected from a pressure introduction hole 36 formed in 7b. As the pressure sensor 8, for example, a sensor utilizing a strain gauge made of a silicon wafer can be used.

41 is a control device for controlling the energization of the electromagnetic coil of the electromagnetic valve 9. The control device 41 includes an engine speed detector
The power supply time to the electromagnetic coil per unit time is controlled in accordance with a signal corresponding to the engine rotation speed output from 42 and a signal corresponding to the large piston 16 side pressure output from the pressure sensor 8. The controller 41 receives a signal output from a throttle opening detector (not shown) that detects the throttle opening of the engine instead of the signal output from the engine rotation speed detector 42, or The signal of the detector 42 and the signal of the throttle opening detector may be input in parallel.

In the variable pressure device of the high-pressure fuel injection device configured as described above, since the area difference between the large piston 16 and the small piston 17, the fuel on the rear side of the large piston 16 has a small pressure. Even so, the piston 15 is pressed toward the small piston 17 by the pressure of the fuel itself, and the first valve port 26 can be kept closed. When the second valve port 31 is opened by the solenoid valve 9, fuel on the back side of the large piston 15 flows from the fuel outlet 27 to the fuel return passage 5. For this reason, the piston 15 moves to the large piston 16 side and the first valve port 26 is opened,
Part of the high-pressure fuel in the fuel supply passage 2 from the first valve port 26 is reduced in pressure by the valve body 33 to a low pressure, flows into the front side of the piston 15, and passes through the communication passage 18 to the rear side of the large piston 16 Therefore, the fuel pressure in the fuel supply passage 2 is reduced. As a result, the fuel pressure injected from the fuel injection valve 1 decreases accordingly. On the other hand, when the second valve port 31 is closed by the solenoid valve 9, the first valve port 26 is closed by the fuel pressure on the back side of the large piston 16, and the fuel in the fuel supply passage 2 is
Since the fuel is prevented from flowing to the rear side 16 and the fuel in the fuel supply passage 2 is supplied to the fuel injection valve 1 as it is, the fuel injection pressure increases.

Therefore, the fuel injection pressure can be lowered by increasing the energizing time per unit time of the solenoid valve 9, and the fuel injection pressure can be increased by shortening the energizing time. In addition, since the control can be performed by controlling the low-pressure fuel on the back side of the large piston 16, a low-pressure solenoid valve can be used. Further, since the pressure of the fuel which is going to flow into the cylinder can be reduced by the valve element 33, a large pressure is prevented from acting on the piston 15 and the O-ring 22, and the operation of the piston 15 is facilitated. be able to.

Further, in the embodiment, since the sealing is performed by combining the spherical surface of the valve body 33 and the conical surface of the valve seat 35, at the time of assembly, as shown by the solid line in FIG. Only the inner peripheral edge is brought into line contact with the valve body 33, and when the seat surface 35 is worn, the seat surface 35 and the valve body 33 can be brought into surface contact as indicated by a chain line A. Therefore, the life of the seal structure can be extended. Note that the chain line B in FIG.
This shows a state where the valve port 26 is open. Then, the fuel is supplied to the first valve port 26.
As the seat surface 35 wears out, the length of the contact surface increases in the outer diameter direction as the seat surface 35 wears, so the fuel pressure gradient at the time of sealing decreases as it wears out. You can do so. as a result,
Even if the seat surface 35 is worn, a change in the fuel pressure on the downstream side of the first valve port 26 can be suppressed.

FIG. 5 is an enlarged sectional view showing a valve body of another embodiment. In FIG. 5, the same or equivalent members as those shown in FIG. 2 are denoted by the same reference numerals, and the description thereof will be omitted. In this embodiment, a steel ball is used as a valve body for opening and closing the first valve port 26.
45 are used. At the tip of the small piston 17, an uneven surface 46 for pressing the steel ball 45 is formed.
It is open to the side. In this way, relatively inexpensive steel balls can be used as one component.

〔The invention's effect〕

As described above, according to the present invention, a device body having a fuel inlet and a fuel outlet, slidably holds a piston having a large piston at one end and a small piston at the other end,
The front side and the back side of the piston communicate with each other through a communication passage provided in the piston, and the front side of the piston communicates with the fuel inlet via a first valve port facing the small piston. And the fuel outlet is communicated through a second valve port that is opened and closed by an electromagnetic valve, and a valve body that opens and closes the first valve port by movement of the piston is provided on the piston side of the first valve port. In addition, a part of the fuel in the fuel supply passage is depressurized by the valve body and guided to the rear side of the large piston, and the first valve port can be controlled using the low pressure of the fuel itself.

Therefore, by controlling the low-pressure fuel on the back side of the large piston with the solenoid valve, the amount of fuel returned from the fuel supply passage to the fuel return passage is changed, and the pressure of the fuel supplied to the fuel injection valve, that is, the fuel The injection pressure can be changed. As a result, even if the fuel injection pressure is changed, a low-pressure solenoid valve or the like can be used, so that it is possible to suppress an increase in the size and cost of the device. Moreover, since the fuel is depressurized by the valve body that opens and closes the first valve port, it is possible to prevent a large pressure from acting on the piston, the member that seals between the piston and the cylinder, and to smoothly operate the piston. it can.

[Brief description of the drawings]

1 is a longitudinal sectional view showing a variable pressure device of a high-pressure fuel injection device according to the present invention, FIG. 2 is a sectional view showing an enlarged valve body,
3 is an enlarged sectional view showing a seating portion of the valve body, FIG. 4 is a sectional view taken along line IV-IV of FIG. 2, and FIG. 5 is an enlarged sectional view showing a valve body of another embodiment. It is. 1 ... fuel injection valve, 2 ... fuel supply passage, 5 ... fuel return passage, 7 ... device body, 9 ... solenoid valve, 15 ... piston, 16 ... large piston, 17 ... small piston, 18 communicating passage, 25 fuel inlet, 26 first valve opening, 27 fuel outlet, 31 second valve opening.

Claims (1)

(57) [Claims] An apparatus body having a fuel inlet connected to a fuel supply passage on the fuel injection pump discharge side and a fuel outlet connected to a fuel return passage has a large piston at one end and a small piston at the other end. A piston having a piston slidably held therein and communicating between a front side and a rear side of the piston through a communication passage provided in the piston, and a small piston facing a small piston between the piston front side and the fuel inlet. The first valve port communicates through a second valve port that is opened and closed by an electromagnetic valve, and the piston rear side communicates with the fuel outlet through the second valve port. A variable pressure device for a high-pressure fuel injection device comprising a valve body for opening and closing a first valve port.