JPS61149568A - Fuel injection valve - Google Patents

Abstract

PURPOSE:To allow the electronic control of injection timing and improve responsiveness by providing a piezo-actuator and applying the fuel pressure in a control hydraulic chamber expanded or shrinked by the said actuator to the closing direction of a needle valve. CONSTITUTION:This accumulator nozzle 1 provided on a direct-injection type Diesel engine has a housing constituted with a piezo-holder 20, a distance piece 21, a nozzle holder 22, and a nozzle tip 23, and the said items 20-22 are combined by a large retainer 25. A columnar piezo-actuator 31 laminated with disk-like PZT elements and copper plates in turn, a piston 32, and a dish spring 33 are stored in the bore 30 of the piezo-holder 20. When the piezo-actuator 31 is deenergized and shrink by the fuel pressure in a control hydraulic chamber 34, a needle valve 12 is lifted to open a nozzle hole 13, and on the other hand when the piezo-actuator 31 is energized and extended, the nozzle hole 13 is closed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to fuel injection valves for internal combustion engines, particularly diesel engines, and more particularly to fuel injection valves known as akineumulator nozzles.

Conventional technology Conventionally, in this type of fuel injection valve, the pressure of the fuel supplied from the fuel supply source does not act on the needle valve in the valve closing direction, but only in the valve opening direction, and the elastic force of the spring is used. is configured to work in the valve closing direction.

When the fuel supply is stopped, the needle valve opens and injects fuel from the nozzle, and as a result, the fuel pressure in the pressure accumulation chamber decreases and the needle valve closes, ending the injection.

Problems to be Solved by the Invention According to the conventional fuel injection valve having the above configuration, the valve closing pressure is determined by the elastic force of the spring, so there is a limit to its magnitude. There was a problem in that the needle valve opened, making it impossible to obtain sufficient fuel injection pressure. That is, there are limits to fuel atomization, making it difficult to further improve engine performance.

In addition, conventional fuel injection valves have a configuration in which the needle valve opens when the fuel supply is stopped and closes when the fuel pressure in the pressure accumulation chamber decreases, so the fuel injection time is extremely short (and therefore There was a problem with loud noise.

Means for Solving the Problems In order to solve the above problems, the fuel injection valve according to the present invention is provided with a piezo actuator, and the piezo actuator controls the fuel pressure in the control hydraulic chamber to be adjusted in the needle valve closing direction. It is characterized by being made to act on

Example The present invention will be explained below with reference to illustrated embodiments.

FIG. 1 shows a fuel injection valve or accumulator nozzle 1 according to an embodiment of the present invention. This accumulator nozzle 1 is used to inject fuel into the combustion chamber of a direct injection diesel engine, and one for each cylinder.
They are installed one at a time, for example four in the case of a four-cylinder engine. The fuel is pressure-fed from a known format-type injection pump (not shown).
As will be described later, the water flows into the accumulator nozzle 1 from the inlet boat 11 and is injected from the nozzle 13 by opening and closing the needle valve 12. The oil supply timing by the injection pump is not near the compression top dead center of each cylinder as usual, but ends sufficiently before that point, for example, at a crank angle of 60 degrees before the compression top dead center. As is conventionally known, the amount of oil fed at one time by the injection pump is adjusted by the opening degree of the lever of the injection pump.

The housing of the accumulator nozzle 1 includes a piezo holder 20, a distance piece 21, a nozzle holder 22,
and the nozzle tip 23. The piezo holder 20 has a cylindrical shape with a bottom, and a distance piece 21 is disposed on the opening side of the piezo holder 20.
A nozzle holder 22 is located on the opposite side from the piezo holder 20 of No. 1.
is provided. The nozzle holder 22 has a flange 24 in close contact with the distance piece 21, and the nozzle holder 22, the distance piece 21, and the piezo holder 20 are coupled by a large retainer 25 in close contact with each other. Similarly, a nozzle tip 23 is tightly coupled to the tip of the nozzle holder 22 via a small retainer 26.

A piezo actuator 31 , a piston 32 , and a disc spring 33 are housed in a bore 30 formed inside the piezo holder 20 . The upper end of the piezo actuator 31 is the bore 3
0, and a piston 32 is connected to the lower end of the piezo actuator 31. Although the outer diameter of the piezo actuator 31 is smaller than the inner diameter of the bore 30, the piston 32 has approximately the same diameter as the bore 30 and is slidably supported within the bore 30. The I spring 33 engages with the lower surface of the piston 32 and the upper surface of the distance piece 21, and constantly urges the piston 32 upward to bring it into contact with the piezo actuator 31. Therefore, between the lower surface of the piston 32 and the upper surface of the distance piece 21, there is a control hydraulic chamber 3.
4 is formed.

This control hydraulic chamber 34 contracts when the piezo actuator 31 expands and pushes down the piston 32 against the disk spring 33, and when the piezo actuator 31 contracts, or when the piezo actuator 31 contracts Expands when high pressure fuel is supplied.

The piezo actuator 31 has a diameter of 15 m and a thickness of 0.5 m.
A crane disk-shaped PZT element with a diameter of 15 sn.

Copper plates having a thickness of 0.01 mm are alternately laminated to form a columnar shape, and the lead wires 35 and the copper plates are coupled so that a voltage can be applied in parallel in the thickness direction of each PZT element. The lead wire 35 extends to the outside of the piezo holder 20 via the grommet 36, and forms part of an electric circuit 100, which will be described later. PZT elements are ferroelectric ceramics fired with lead zirconate titanate as the main component.
This is a typical element that has a piezo effect. Its physical properties are
When a voltage of 500V is applied in the thickness direction, the thickness increases by 0.5μm, and conversely, when a voltage of 500V is generated, when this is applied, the thickness decreases by 0.5μmat, and a pressure of 200kg/c+4 is applied in the thickness direction. When applied, a voltage of 200 V is generated in the thickness direction.

In this embodiment, the piezo actuator 31 is P
Since 100 ZT elements are electrically connected in parallel,
Applying a voltage of 500v results in an elongation of 50 μm.

The needle valve 12 is housed in the stepped space formed by the nozzle holder 22 and the nozzle tip 23 so as to be able to rise and fall freely, and a spring 41 and a non-return check are housed in the large diameter bore 40 formed in the nozzle holder 22. A valve 42 is provided. Inside the nozzle holder 22, there is a large diameter bore 4 on the distance piece 21 side.
0, a small diameter bore 43 is bored on the nozzle tip 23 side. The large diameter bore 40 can communicate with the control hydraulic chamber 34 via a communication hole 44 formed in the center of the distance piece 21, and the small diameter bore 43 has the same diameter as the small diameter bore 45 bored in the nozzle tip 23. This bore 45
Connect to. Therefore, the large diameter bore 40 and the small diameter bore 43,
45 forms the stepped space. On the other hand, at the lower end of the small-diameter bore 45 of the nozzle tip 23, a conical seat surface 46 that narrows downward is formed, and one or more nozzle holes 13 are provided below the seat surface 46.

The lower end 50 of the needle valve 12 is formed into a conical shape and can be brought into close contact with the seat surface 46, thereby making it possible to block the nozzle 13 from the small diameter bore 45. is communicated with the small diameter bore 45.

The needle valve 12 extends straight upwards, and its upper end 51 always fits into the communication hole 4.4 of the distance piece 21. A flange-shaped spring seat 52 is formed approximately in the center of the needle valve 12 and near the lower end surface of the large diameter bore 40, and a cylindrical check valve 42 is slidably provided in the upper portion of the needle valve 12. mated. The coiled spring 41 is fitted around the outer periphery of the needle valve 12 , its upper end engages with the lower surface of the check valve 42 , and its lower end engages with the upper surface of the spring seat 52 . Thus, the spring 41 biases the check valve 42 and the spring seat 52 in a direction that separates them from each other. Therefore, when not in operation, the check valve 42 is in close contact with the lower surface of the distance piece 21, and the needle valve 12 is urged downward to seat the lower end 50 on the seat surface 46.

The outer diameter of the check valve 42 is about 0.2 mm smaller in radius than the inner diameter of the large diameter bore 40, and the inner diameter of the check valve 42 is about 2 μm larger in radius than the outer diameter of the needle valve 12. .

As will be described later, the check valve 42 receives the pressure of fuel supplied from the passage 54 formed in the piezo holder 20, compresses the spring 41 and moves downward, guiding high pressure fuel into the large diameter bore 40. This is held until it is injected from the nozzle 13. The large diameter bore 40 thus constitutes a pressure accumulation chamber that holds high pressure fuel.

The communication hole 44 of the distance piece 21 is connected to the needle valve 1.
The radius is approximately 0.5 mm larger than the upper end 51 of the check valve 42, so that the fuel pressure within the control hydraulic chamber 34 always acts on the upper surface of the check valve 42. This communication hole 44 is provided on the outer circumferential side of the communication hole 44.
An annular groove 53 is carved concentrically with. The annular groove 53 is formed on the lower surface of the distance piece 21, and its inner diameter is approximately 1 m larger in radius than the inner diameter of the communication hole 44, and its outer diameter is approximately 1 mm smaller in radius than the outer diameter of the check valve 42.

Therefore, when the check valve 42 comes into close contact with the lower surface of the distance piece 21, the opening side of the annular groove 53 is completely closed by the check valve 42. The annular groove 53 communicates with a passage 55 formed in the radial direction of the distance piece 21 . This passage 55 communicates with a passage 54 formed in the axial direction in the side wall of the piezo holder 20, and therefore the distance piece 21 is positioned with respect to the piezo holder 20 and the nozzle holder 22 by the knock pin 56. . The fuel entering the inlet boat 11 is thus led into the annular groove 53 leaving passages 54 , 55 .

FIG. 2 shows an electrical circuit 100 that controls the voltage applied to piezo actuator 31. FIG.

The basic function of this circuit 100 is the exchange of electric charges between the piezo actuator 31 and the capacitor lO1. , thyristor 104 , coil 10
2 to the piezo actuator 31. After the electric charge of the piezo actuator 31 is transferred to the capacitor 101, when the hydraulic pressure in the control hydraulic chamber 34 decreases, a voltage opposite to the polarization is generated in the piezo actuator 31, which may deteriorate the piezo actuator 31. A diode 105 is provided as a measure to prevent voltage application.

Since this embodiment has the above configuration, the fuel is injected by operating as follows.

When the piston of a cylinder in the engine reaches a position at a crank angle of 90 degrees before compression top dead center, fuel begins to be discharged from the corresponding pump unit of the rectangular injection pump to the accumulator nozzle l attached to that cylinder. . This discharged fuel passes through the injection steel pipe and reaches the inlet port 11 of the accumulator nozzle l, and passes through the passages 54 and 5.
5 to reach the annular groove 53 of the discance piece 21.

The annular groove 53 is connected to the check valve 42 which was previously biased by the spring 41.
However, the pressure-fed fuel pushes it open and flows into the large-diameter bore 40, which is a pressure accumulation chamber, and also flows into the control hydraulic chamber 34 through the communication hole 44.

Here, regarding the fuel pressure acting on the needle valve 12, the pressure receiving area for the pressure acting downward is the needle valve 12.
is equal to the maximum cross-sectional area of the needle valve 12, whereas the pressure-receiving area for upwardly acting pressure is calculated from the maximum cross-sectional area of the needle valve 12.
This is the cross-sectional area obtained by subtracting the portion where the lower end portion 50 of 2 is in close contact with the sheet surface 46. Therefore, the downward component of the force acting on the needle valve 12 is larger, and the needle valve 12 maintains its seated state and closes the nozzle 13. The fuel supplied to the accumulator nozzle 1 flows into the large-diameter bore 40 and the control hydraulic chamber 34 while being compressed, and the pressure is accumulated. When the amount supplied from the pump is small, this pressure is around 500 kg/aJ, but when it is large, it is 1000 kg/c.
Become J place. The oil supply from the pump ends 60" before compression top dead center. At the same time, the check valve 42 rises due to the elastic force of the spring 41, closes the annular groove 53, and closes the large diameter bore 40 and the control hydraulic chamber. 34 is also cut off.The accumulator nozzle 1 maintains this state and waits until injection.

At this time, the piezo actuator 31 is contracted by the fuel pressure in the control hydraulic chamber 34, thereby generating an electric charge and increasing the voltage. The amount of contraction of the piezo actuator 31 at this time is shown at point B in FIG. 3, and the voltage at point B in FIG. 4, respectively. In addition, in both Figures 3 and 4, the horizontal axis represents the control hydraulic chamber 3.
4, and there are two points B in both figures,
The same applies to points C, D, E, and A, which will be described later, where the O mark indicates a large amount of oil delivered from the pump, and the Δ mark indicates a small amount of oil delivered.

At the injection timing, for example, when compression top dead center is reached, thyristor 1
03 is turned on, the electric charge of the piezo actuator 31 is transferred to the capacitor 101, and the voltage of the piezo actuator 31 becomes approximately Ov as shown by the 0 point in FIG. At the same time, the piezo actuator 31 contracts,
The amount of contraction increases from point B to the value shown at point 0, as shown in FIG. Note that even if the potential of the capacitor 101 exceeds the potential of the piezo actuator 31, the charge still moves because of the action of the coil 102.
This is known as the C resonance phenomenon. In this L-C resonance, the electric charge of the capacitor 101 then tries to return to the piezo actuator 31, but using this, the thyristor 1
03 is turned off.

As described above, as the piezo actuator 31 contracts from point B to point 0 in FIG. 3, the volume of the control hydraulic chamber 34 is expanded, and the control hydraulic chamber 34 is
The internal pressure decreases. As a result, an upward force is applied to the needle valve 12, and the needle valve 12 rises to open the injection port 13 and inject the fuel in the large diameter bore 40 into the combustion chamber of the engine. Due to this fuel injection, the fuel pressure inside the large diameter bore 40 decreases, and the needle valve 1 accordingly decreases.
A downward force acts on the needle valve 2, causing the needle valve 12 to descend and finally sit on the seat surface 46, ending the injection.

This lowering of the needle valve 12 lowers the pressure within the control hydraulic chamber 34, and as a result, the piezo actuator 31 expands slightly. Therefore, as shown in FIG. 3, the amount of contraction of the piezo actuator 31 decreases from point 0 to point D. Further, the pressure within the control hydraulic chamber 34 decreases from point 0 toward point D, as shown in FIG. Note that when the amount of contraction of the piezo actuator 31 becomes small and the piezo actuator 31 attempts to return to its original length, the piezo actuator 3
1 requires supply of charge, which is diode 10
5.

Thyristor 104 is turned on at a time when there is no need for fuel injection under any operating conditions, for example at a crank angle of 60 degrees after top dead center of compression. Then, the electric charge in the capacitor 101 moves to the piezo actuator 31 via the coil 102 and causes it to expand. As a result, the control hydraulic chamber 34 contracts, and its fuel pressure becomes high. This state is shown at point E in FIGS. 3 and 4. Furthermore, E
The reason that point and point B do not match is due to loss that occurs during charge movement.

When the pressure in the control hydraulic chamber 34 sufficiently exceeds the pressure in the large-diameter bore 40 due to the expansion of the piezo actuator 31, the check valve 42 descends to conduct the control hydraulic chamber 34 through the annular groove 53, causing an injection (not shown) to occur. Relieve the hydraulic pressure by knocking down the pump. When the pressure in the control hydraulic chamber 34 becomes approximately equal to the pressure in the large diameter bore 40, the check valve 42 closes the annular groove 53 again by the elastic force of the spring 41. This state is shown at point A.

Next, when the piston reaches 90'' before the top dead center of compression, one pressure of fuel is delivered from the injection pump and the state is at point B. Thereafter, repeat B-C-D-E→A.

According to the first embodiment, the following effects (1) to (4) can be obtained.

■ Electronic control of injection timing is possible while using any conventional injection pump.

- Since the piezo actuator 31 is used to open the accumulator nozzle l, the response to opening and closing operations is quick.

(2) Since the piezo actuator 31 is driven using the voltage generated in the actuator itself, no special drive power source is required.

- Since fuel pressure is used for the seating force of the needle valve 12, the valve closing pressure can be increased even if the force of the spring 41 is weak.

(2) As can be seen from FIG. 3, the larger the injection amount, the higher the injection start pressure and injection end pressure, which is desirable in terms of engine performance.

FIG. 5 shows an electric circuit 200 in a second embodiment of the present invention, and the other configuration of this second embodiment is completely the same as that of the first embodiment. In this second embodiment, the accumulator nozzle l performs so-called pilot injection.

That is, a small amount of injection is performed before the main injection to suppress sudden changes in the fuel injection amount and to reduce noise.

In order to perform this viroft injection, the electric circuit 200 of the second embodiment further includes a thyristor 201, a capacitor 202, and a transistor 2 in addition to the electric circuit 100 of the first embodiment.
03 is added. The thyristor 201 functions to discharge a portion of the charge of the piezo actuator 31 to the capacitor 202, and the transistor 203 is located downstream of the thyristor 201 and functions to adjust the terminal voltage of the capacitor 202.

Since this embodiment has the electric circuit 200 described above, it operates as follows.

It is assumed that the accumulator nozzle 1 is supplied with fuel from the injection pump and is maintained in a closed state.

Here, if the crank angle is 10 degrees before compression top dead center,
When the Cyrisk 201 is turned on, a part of the electric charge of the piezo actuator 31 (a voltage drop of several tens of volts at most) is released to the capacitor 202. As a result, a small amount of biloft injection is performed in proportion to the amount of voltage drop. Then, after reaching compression top dead center, thyristor 10
3 is turned ON and main injection is performed. The main injection is the same as in the first embodiment. Thereafter, the transistor 203 discharges the charged capacitor 202 until the next pilot injection. At this time, the transistor 203 discharges the charge of the capacitor 202 so as to obtain a terminal voltage of the capacitor 202 such that the amount of voltage drop of the piezo actuator 31 becomes a set value when the thyristor 201 is turned on.

Effects of the Invention As described above, according to the present invention, the closing pressure of the needle valve can be increased, so the fuel injection pressure can be sufficiently increased, and engine performance can be improved. Further, since pilot injection becomes possible, noise during fuel injection can be reduced.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing the first embodiment of the present invention, Fig. 2 is a circuit diagram showing the electric circuit of the first embodiment, and Fig. 3 is the relationship between the pressure in the control hydraulic chamber and the amount of contraction of the piezo actuator. FIG. 4 is a graph showing the relationship between the pressure in the control hydraulic chamber and the voltage of the piezo actuator, and FIG. 5 is a circuit diagram showing the electric circuit of the second embodiment. ■...Fuel injection valve, 12...Needle valve, 13
... Spout, 31... Piezo actuator, 34... Control hydraulic chamber, 40... Large diameter bore (pressure accumulation chamber) 42... Check valve, 54, 55... Passage, 100, 200 ...Electric circuit (control means).

Claims (1)

[Claims] 1. A control hydraulic chamber and a pressure accumulation chamber for temporarily holding fuel are formed, and a passage is formed for guiding fuel intermittently pumped from a fuel supply source to these control hydraulic pressure chamber and pressure accumulation chamber, and a housing provided with a nozzle for injecting the fuel in the pressure accumulation chamber to the outside; a piezo actuator that expands and contracts the control hydraulic chamber, a needle valve that is provided in the housing so as to be able to reciprocate and receive pressure in the control hydraulic chamber and the pressure accumulator chamber, and communicates or shuts off the pressure accumulator chamber and the nozzle, and the passageway. , a check valve that normally shuts off the control hydraulic chamber, and the pressure accumulation chamber, and opens depending on the pressure in the passage and the control hydraulic chamber, and means for controlling the voltage of the piezo actuator, the fuel being supplied from the fuel supply source. The fuel passes through the passage and is force-fed to the control hydraulic chamber and the pressure accumulation chamber via the check valve, and when the fuel pressure in the control hydraulic chamber is relatively high, the needle valve closes the pressure accumulation chamber and the nozzle. The fuel injection valve is characterized in that when the fuel pressure in the control hydraulic chamber is relatively low, the needle valve communicates the pressure accumulation chamber with the injection port and injects fuel from the injection port.