JPH0236939Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Technical Field> The present invention relates to an electromagnetic control valve for a unit injector suitable for controlling high-pressure fluid used in, for example, a diesel engine.

<Prior Art> A fuel injection device for a compression ignition internal combustion engine, for example, a diesel engine, usually includes an injection pump that increases the pressure of fuel, a nozzle installed in a combustion chamber, and a fuel pump that pumps the fuel from the injection pump into the nozzle. A fuel injection pipe leading to the fuel injection pipe is provided. A unit injector that integrates these components eliminates the need for a long fuel injection pipe, resulting in a small injection delay, and since the volume to be compressed is reduced by the lack of a fuel injection pipe, a high injection rate can be achieved, resulting in fine particles of fuel. It has advantages such as good fuel efficiency, high injection rate, and little dripping of fuel at the end of injection.

For example, a fuel injection device in which such a unit injector is installed in each cylinder is disclosed in Japanese Patent Application Laid-Open No.
50726 (US Pat. No. 4,129,253).

This is configured as shown in Figure 1,
A plunger 1 that reciprocates in synchronization with engine rotation forces the fuel in a pump chamber 2 into a needle chamber 4 through an injection fuel passage 3, and the fuel pressure in this needle chamber 4 acts on a needle valve 5. Then, by lifting the needle valve 5 against the urging force of the spring 6 acting in the valve closing direction and opening the nozzle 7, fuel is injected and supplied from the nozzle 7 into a combustion chamber (not shown). It's summery.

A fuel supply passage 8 is connected to the pump chamber 2 through which low-pressure fuel is sent from a fuel tank (not shown) by a feed pump.
is opened and closed by a solenoid valve 9. That is, the excitation coil 10 of the solenoid valve 9 is energized and energized according to the engine operating state, and the valve body 11 is seated on the valve seat 13 against the elastic force of the spring 12 acting in the valve opening direction. and close the valve.

Therefore, even if the plunger 1 is in the compression stroke in which it moves downward in FIG. 1, if the solenoid valve 9 is open, the fuel in the pump chamber 2 will be relieved to the low pressure side through the fuel supply passage 8. The fuel pressure in the needle chamber 4 does not rise, and therefore the needle valve 5 does not open, so fuel injection is not performed. On the other hand, when the electromagnetic valve 9 is closed, the fuel pressure in the needle chamber 4 rises and lifts the needle valve 5 against the elastic force of the spring 6, so the nozzle 7 opens and the fuel is injected. Thus, the fuel injection timing can be controlled by opening and closing the electromagnetic valve 9, and by extension, the injection period can be controlled freely and with high precision.

However, in the conventional solenoid control valve of the unit injector described above, the maximum lift amount of the valve body 11 is uniquely determined by the gap amount between the armature 14 and the core 15, and furthermore, the solenoid valve The area of the leak orifice formed by the valve body 11 and the valve seat 13 due to the lift of the valve body 11 of 9 is limited by the maximum lift amount. If it is made smaller, the area of the leak orifice becomes smaller, which slows down the drop in injection pressure at the end of injection, making it difficult to cut the injection.

By the way, in order to increase the area of the leak orifice, the seat diameter of the valve body 11 may be increased or the maximum lift amount of the valve body 11 may be increased. However, when increasing the seat diameter of the valve body 11 as in the former case, it is necessary to increase the electromagnetic force for seating the valve body 11 as the seat diameter increases.For example, the fuel injection pressure must be increased to 1000 In the case of atmospheric pressure, even if the seat diameter is as small as 2 mm, the valve body 1
1 requires a force of at least 30kg to sit.

On the other hand, when increasing the maximum lift amount of the valve body 11 as in the latter case, since the suction force of the armature 14 by the core 15 is inversely proportional to the square of the gap between them, as the maximum lift amount is increased, In either case, it is necessary to increase the size of the electromagnetic valve 9 to increase the electromagnetic attraction force.

Furthermore, in order to incorporate the solenoid valve into a fuel supply amount control mechanism of a small engine, it is necessary to increase the high-speed response of the solenoid valve. Therefore, if an attempt is made to improve the stability, high-speed response, etc. of a solenoid valve in order to satisfy such requirements, there is a problem in that the solenoid valve becomes larger or more expensive.

<Purpose of the invention> The present invention was devised in view of the above-mentioned problems, and it is possible to increase the leak orifice area without increasing the electromagnetic force, and improve the opening stability of the solenoid valve. The aim is to improve.

<Structure of the invention> In order to achieve the above objectives, this invention
A control passage is provided that branches toward the low-pressure side from a fuel passage that communicates the pump chamber of the unit injector body with the nozzle and pumps fuel, and operates the valve body by controlling the energization to the excitation coil. In a unit injector electromagnetic control valve configured to open and close a control passage, a piston that slides on a cylinder formed facing the back of the valve body is formed integrally with the valve body, and the cylinder and the piston are connected to each other. A pressure balance passage is formed inside the valve body to communicate a back pressure chamber formed by the above with the control passage on a higher pressure side than the seat portion of the valve body, and an opening on the seat side of the pressure balance passage is formed in the valve body. By making at least one opening direction of the valve body substantially perpendicular to the direction of fluid flow around the valve body,
The valve body is constructed by statically balancing the opening force due to fluid pressure acting on the valve body from the tip (seat) side via the control passage and the valve closing force due to fluid pressure acting on the valve body from the back side. It is not necessary to strengthen the spring that biases the valve in the valve opening direction, or to increase the electromagnetic force of the electromagnet that biases the valve body to close.
When the valve body is operating in the valve opening direction, the force in the valve opening direction due to fluid pressure acting on the tip of the valve body exceeds the force in the valve closing direction acting on the back of the valve body. This is intended to increase valve stability.

Furthermore, by installing a flow guide that covers the tip of the valve body in which the opening is formed in a non-contact state in the control passage on the high pressure side from the opening, the stagnation of the flow due to the flow guide can be effectively utilized. When the valve body is opened, the entire pressure of the fluid is applied in the valve opening direction, while only the static pressure of the fluid is introduced into the exhaust pressure chamber to further improve the stability of the valve opening.

<Examples> Examples of the present invention will be described below based on the accompanying drawings.

FIG. 2 shows an embodiment of a solenoid control valve for a unit injector to which the present invention is applied.
A support 22 is screwed into the holder 21 of the unit injector main body 20 in an oil-tight manner. A plunger 23 is slidably inserted and held in a cylinder portion formed on this support body 22, and this plunger 23 is held by a spring 24 and a retainer 2.
5 is biased upward in the figure, the plunger 23 is held by the cam 26 that rotates in synchronization with the rotation of the engine, and when the plunger 23 is lowered, the plunger 23 is formed facing the lower end of the plunger 23. The fuel in the pump chamber 27 is compressed.

On the other hand, a plunger 2 is provided at the bottom of the main body 20.
A nozzle 28 is formed for injecting the fuel in the pump chamber 27 compressed by the lowering of the fuel pump 3 into a combustion chamber (not shown). Specifically, the nozzle 28 includes a needle chamber 30 that communicates with the pump chamber 27 via a fuel passage 29, and a needle valve 32 that is slidably fitted and held in a cylinder portion formed in a holder 31.
It consists of a nozzle 33 that opens into the combustion chamber, a spring 34 that biases the needle valve 32 to close, a spring chamber 35, etc., and the spring 34 normally moves the needle valve 32 downward in the figure via a spring guide 36. However, when the fuel in the pump chamber 27 is supplied to the needle chamber 30 through the fuel passage 29 and the pressure in the needle chamber 30 becomes stronger than the valve closing force by the spring 34, The needle valve 32 lifts upward in the figure against the spring 34 to open the injection port 33 and inject the fuel in the needle chamber 30 into the combustion chamber.
37 is a distance piece that regulates the lift amount of the needle valve 32; 38 is a needle valve 32;
The shim 39 is a nozzle nut that tightens and fixes both holders 21, 31 in an oil-tight manner.

Further, a control passage 40 branched from the fuel passage 29 is connected to an electromagnetic control valve 41 to be described later, and an annular groove 42 surrounding the plunger 23 and the spring chamber 35 are connected through a group 43 formed in the holder 21. After communicating with each other, these are collected in a return passage 44.

The electromagnetic control valve 41 is constructed as shown in FIG. 3, and an electromagnet 47 is fixed to the valve holder 45 with a screw 46. In addition, the valve holder 45
is screwed into the holder 21 through a seal ring 48 in an oil-tight manner.

An excitation coil 49 is fixed to the electromagnet 47 described above, and a terminal wire 50 of the excitation coil 49 is drawn out to the outside in an oil-tight manner.

The valve body 51 is slidably inserted and held in a cylinder 52 formed in the valve holder 45, and is fastened to the armature 55 with a screw 54 with a shim 53 for gap adjustment sandwiched therebetween. Further, a stopper 56 is attached to the valve body 51, and a spring 57 is stretched between the stopper 56 and the valve holder 45, so that the valve body 5
1 upward in the figure, the fuel passage 2
A control passage 40 branched from 9 is connected to a feed passage 5.
8 is kept connected.

On the other hand, a piston 59 is integrally formed on the back of the valve body 51 (upper end in the figure), and the piston 59 is slidably fitted into a cylinder 61 that is slidably mounted on the case 60 in the vertical direction. A back pressure chamber 62 is formed at the back of the valve body 51, and a pressure balance passage 6 communicates this back pressure chamber 62 with the control passage 40.
3 is formed vertically inside the valve body 51, so that the pressure in the control passage 40 on the higher pressure side than the valve seat 64 on which the tip of the valve body 51 seats is transferred to the back pressure chamber 6.
I am planning to introduce it in 2. The opening 7 on the valve seat 64 side in this pressure balance passage 63
The opening direction of at least one of the valve body 51
A flow guide 76 is installed in the control passage 40 on the higher pressure side than the valve seat 64 with an opening 75 that is substantially perpendicular to the direction of fluid flow around the valve body 51 and coincides with the axial direction of the valve body 51. Covered in a non-contact manner. The upper end position of the valve body 51 is set by a stopper 65 via a cylinder 61.
This stopper 65 is fixed by a positioning screw 66.

Further, the armature chamber 67 housing the armature 55 and the spring chamber 68 are communicated through a communication passage 69, and these chambers 67, 68 are connected to each other through a communication passage 69.
is communicated with a return passage 72 via a passage 70 and a groove 71, and this return passage 72 and the return passage 44 are merged and both are connected to a fuel tank (not shown). Reference numerals 73 and 74 are passages and grooves for communicating the control passage 40 with the feed passage 58, which is a low pressure side passage.

In the unit injector configured as described above, the voltage applied to the excitation coil 49 is
As shown in Figure A, the plunger 23 is turned on at a certain time point _T1 during the pumping stroke when it moves downward in the figure, and is turned off at a time point _T3 after a predetermined period of time has elapsed. Furthermore, when the plunger 23 moves downward in the figure as the engine operates, the fuel in the pump chamber 27 is compressed and the pressure in the control passage 40 increases.
The biasing action of the spring 57 causes the valve body 51 to close the valve seat 64 with a predetermined response delay until the valve body 51 closes at a predetermined time _T2 as shown in FIG. 4B.
Since the valve maintains the open state floating from the control passage 4
0 is maintained in communication with the feed passage 58. For this reason, the fuel pressure in the pump chamber 27 is adjusted to the low pressure side pressure (2 to 10
kg/cm ² ), and the pressure in the control passage 40 passes through the pressure balance passage 63 to the back pressure chamber 62.
It will also be introduced.

That is, the opening direction of at least one of the openings 75 of the pressure balance passage 63 is made substantially perpendicular to the direction of fluid (fuel) flow around the tip of the valve body 51, and then Opening 7 along
5 is covered by the flow guide 76 in a non-contact state, stagnation occurs at the back (downstream) of the flow guide 76, and the pressure of this stagnation (static pressure of the fluid) is discharged through the pressure balance passage 63. It is introduced into the pressure chamber 62.

Therefore, the fuel pressure in the control passage 40 upstream of the seat section acting on the tip (tip) of the valve body 51 and the fuel pressure in the back pressure chamber 62 at the back of the valve body 51 are statically approximately equal. In addition, since the diameter of the piston 59 provided at the back of the valve body 51 is set so that the pressure receiving area for these fuel pressures is approximately equal at the tip and back of the valve body 51, the diameter of the piston 59 provided at the back of the valve body 51 is The difference between the valve opening force acting on the back of the valve body 51 and the valve closing force acting on the back of the valve body 51 is the difference between the total pressure at the stagnation point of the flow generated by the flow guide 76 at the tip of the valve body 51 and the exhaust pressure chamber 62.
Only the dynamic pressure in the valve opening direction acts on the tip of the valve body 51, which is the difference between the static pressures acting on the valve body 51. Therefore, even if the fuel pressure from the pump chamber 27 becomes high, this fuel pressure does not affect the driving of the valve body 51, and the force driving the valve body 51 in the valve opening direction is generated by the spring 57. Upward (valve opening direction)
and the force due to the dynamic pressure, the valve body 5
1 in the valve closing direction, all that is needed is the weight of the movable parts such as the valve body 51 and the armature 55, and a force that counteracts the viscosity of the fuel. 51 can be reliably driven to open and close.

In the past, when increasing the seat diameter, it was necessary to increase the valve closing electromagnetic force to deal with the influence of fuel pressure, but in the present invention, the influence of fuel pressure is removed as described above, so the seat diameter Even if the electromagnet 47 is increased, the driving electromagnetic force can be reduced, and the seat portion can be made sufficiently large without increasing the size of the electromagnet 47.

Therefore, the excitation coil 49 is energized at a predetermined time T ₁ while the plunger 23 is descending, and at the injection time T ₂ the valve body 51 is lifted as shown in FIG. 64, communication between the control passage 40 and the feed passage 58 is cut off, so the fuel pressure in the pump chamber 27 quickly rises.
Fuel is introduced into the needle chamber 30 via the fuel passage 29. When the pressure in the chamber 30 rises and the force for lifting the needle valve 32 becomes higher than the biasing force of the spring 34, the needle valve 32
is lifted and fuel is injected from the injection port 33.

At time _T3 , which is a predetermined time before the scheduled end of injection, the excitation coil 49 is de-energized. Then, the force by which the core attracts the armature 55 disappears, and at time _T4 , when a predetermined time has elapsed from the shutoff time _T3 , the valve body 51 is lifted from the valve seat 64 by the biasing force of the spring 57, and the control passage 40 is opened again. It communicates with the feed passage 58. At this time, dynamic pressure acts on the tip of the valve body 51 in the valve opening direction, but the back pressure chamber 62 has an opening 75 at the tip of the valve body 51 that prevents the flow of fuel at the tip of the valve body 51. substantially perpendicular to the direction, and
Since the tip of the valve body 51 is covered by the flow guide 76 to generate stagnation, only the static pressure component of the total pressure of the fuel is introduced into the exhaust pressure chamber 62. For this reason, even in the unlikely event that the valve closing force (static pressure) acting on the back of the valve body 51 exceeds the valve opening force (total pressure) acting on the tip of the valve body 51, the valve body 51 is opened smoothly.

Therefore, the fuel in the pump chamber 27 escapes from the control passage 40 to the feed passage 58 via the valve body 51, and the pressure in the needle chamber 30 decreases, causing the needle valve 32 to move downward in the figure and complete fuel injection. However, at this time, as the valve body 51 opens, the fourth
As shown in Figure C, the pressure in the control passage 40 drops rapidly, so the time from the opening of the valve body 51 to the end of the injection liquid is shortened. FIG. 4D is a characteristic diagram of the injection rate.

When the plunger 23 moves upward in the figure to the suction stroke, the fuel in the feed passage 58 flows into the valve body 5.
1', the control passage 40 and the fuel passage 29, and are sucked into the pump chamber 27. Thereafter, similar operations are repeated to perform fuel injection, but the fuel injection timing is controlled by the timing of applying voltage to the excitation coil 49, and the injection end timing is controlled by the timing of cutting off the current to the excitation coil 49. controlled.

<Effects of the invention> As explained above, according to the solenoid control valve of the unit injector according to the invention, only the static pressure of the fluid flowing upstream from the seat portion of the valve body is reduced to the back pressure formed at the back of the valve body. The influence of the pressure introduced into the chamber and acting on the valve body is statically balanced, and the opening end of the pressure balance passage formed in the valve body on the valve body tip side is made substantially perpendicular to the direction of fluid flow. By covering the tip of the valve body in a non-contact manner with a flow guide, the dynamic pressure of the fluid is not introduced into the back pressure chamber, so when the valve body is opened, the pressure in the back pressure chamber is reduced. The valve-closing force will not exceed the valve-opening force. For this reason, there is no need to increase the electromagnetic force (attractive force) of the excitation coil that closes the valve body, and the seat diameter of the valve body can be increased without strengthening the spring that biases the valve body to open. It can be made larger to improve the opening/closing characteristics and high-speed response of the solenoid valve.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a unit injector equipped with a conventional example, FIG. 2 is a sectional view of a unit injector equipped with an embodiment of the present invention, FIG. 3 is a sectional view of the same solenoid valve device, and FIG. The figure is a characteristic diagram of the lift of the valve body, injection pressure, and injection rate with respect to the voltage applied to the excitation coil. 41... Solenoid control valve, 49... Excitation coil,
51... Valve body, 59... Piston, 61... Cylinder, 62... Back pressure chamber, 63... Pressure balance passage, 64... Valve seat, 75... Opening of pressure balance passage, 76... Flow guide.

Claims (1)

[Scope of utility model registration request] Pump chamber 27 of unit injector main body 20
A control passage 40 branches toward the low pressure side from a fuel passage 29 that communicates with the nozzle 28 and pumps fuel.
In the electromagnetic control valve of the unit injector, which is configured to open and close the control passage 40 by operating the valve body 51 by controlling the energization to the excitation coil 49, Piston 5 sliding in cylinder 61 provided in
9 is integrally formed with the valve body 51, and communicates a back pressure chamber 62 formed by the cylinder 61 and the piston 59 with the control passage 40 on the higher pressure side than the seat portion of the valve body 51. 63 is formed inside the valve body 51, and the opening direction of at least one of the openings 75 on the seat side in the pressure balance passage 63 is made substantially perpendicular to the direction of fluid flow around the valve body 51. ,
An electromagnetic control valve of a unit injector, characterized in that a flow guide 76 that covers the tip of the valve body in which the opening 75 is formed in a non-contact manner is attached to the control passage 40 on the high pressure side from the opening. .