JPH0454065B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a piezoelectrically actuated fluid control valve whose valve body is opened and closed by a piezoelectric actuator.

[Conventional technology]

An example of a piezoelectrically actuated fluid control valve is a fuel injection valve, and the shorter the time required for opening and closing the fuel injection valve, that is, the better the opening and closing response, the better the control accuracy and the better the engine performance. Solenoids are used as actuators to open and close valves, but the response time is
It takes more than 1msec. On the other hand, piezoelectric actuators are known as actuators with quick response.

A fluid control valve using this piezoelectric actuator is known, for example, as shown in Japanese Patent Publication No. 44-6659. In this valve, when the pump chamber expands, the check valve opens and the poppet valve closes. When the pump chamber is contracted, the check valve closes and the poppet valve opens, and when the pressure in the pump chamber falls below the spring force provided on the poppet valve, the poppet valve closes.

[Problem to be solved by the invention]

However, in this conventional type, after the poppet valve is opened, the pressure of the fluid in the pump chamber gradually decreases, and when the pressure decreases below the spring force provided in the poppet valve, the poppet valve is closed. However, there was a problem in that the closing timing of the poppet valve could not be arbitrarily controlled.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a piezoelectrically actuated fluid control valve that can arbitrarily control the closing timing of the valve body.

[Means to solve the problem]

In order to achieve the above object, the present invention includes: a piezoelectric actuator 2; a fluid is filled inside the piezoelectric actuator 2; the internal volume changes according to the expansion and contraction of the piezoelectric actuator 2; A pump chamber 28 that generates pressure; a valve body 3 that reciprocates in the axial direction due to the application of fluid pressure according to changes in the internal volume of the pump chamber 28; Fluid passages 22, 23, 2 that can be switched between a blocked state and a conductive state
4, 26, the pump chamber 28 and the fluid passages 22, 23,
24, 26, the communication passages 21, 27 are arranged between the fluid passages 21, 27, and are switched between a fluid cutoff state and a conduction state according to the reciprocating movement of the valve body 3, and the fluid passages 22, 23, 24, 26 are In the case of a cutoff state, the communication passages 21 and 27 are brought into a conductive state to bring the pump chamber 28 and the fluid passages 22, 23, 24, and 26 into communication, and the fluid passages 22, 23, 24, and 26 are in a conductive state, the communication passages 21 and 27 are cut off, thereby connecting the pump chamber 28 and the fluid passage 22,
23, 24, and 26 are in a non-communicating state.

[Effect]

In the present invention configured as described above, the internal volume of the pump chamber changes in accordance with the expansion and contraction of the piezoelectric actuator, and fluid pressure is generated in the pump chamber in accordance with the change in internal volume. This fluid pressure acts on the valve body and moves the valve body, thereby closing or communicating the fluid passage.

When the fluid passage is in a blocked state, the valve body brings the pump chamber and the fluid passage into communication by bringing the communication passage arranged between the pump chamber and the fluid passage into a conductive state. is supplied to the pump chamber.

On the other hand, when the fluid passage is in a conductive state, the valve body disconnects the communication passage from the pump chamber and the fluid passage, so that the fluid inside the pump chamber does not flow out into the fluid passage. At this time, the internal volume of the pump chamber does not change, so no hydraulic pressure acts on the valve body. Therefore, the valve body does not move, and the conductive state of the fluid passage is maintained.

〔Example〕

Hereinafter, the present invention will be explained with reference to Examples.

FIG. 1 shows a cross-sectional view along the central axis of a first embodiment of the invention. The fuel injection valve 1 of this embodiment is similar in appearance and components to a fuel injection valve that is a combination of a commercially available diesel engine hole nozzle and its nozzle holder. The functional difference is that the commercially available one is an automatic valve, whereas the fuel injection valve 1 of this embodiment is a control valve driven by a piezoelectric actuator. There is no pressure spring for pressing the nozzle needle 3, which functions as a valve body, against the nozzle body 4 to close the nozzle needle 3, and there is no overflow mechanism. The casing 5 of the fuel injection valve 1 includes a nozzle holder 6 and a retaining nut 7.
The nozzle holder 6 has a cylindrical space 8 formed therein, and a retaining nut 7.
A cylindrical space 9 having an inner diameter larger than the space 8 is formed in the space 8 . The two are connected by a screw 10 of the nozzle holder 6 and a female screw 11 of the retaining nut 7, forming a stepped cylindrical space inside. A piezoelectric actuator 2, a pump piston 12, a disc spring 13, a distance piece 14, and a nozzle body 4 are housed in this space from the top in FIG. The nozzle body 4 has a stepped cylindrical shape, and its thin cylindrical portion 15 is connected to the retaining nut 7.
It protrudes below the bottom edge of. A nozzle needle 3 serving as a valve body is housed in a stepped cylindrical space inside the nozzle body 4. The nozzle needle 3 also has a stepped cylindrical shape, and its small diameter portion 1
6 is housed in the small diameter part 17 of the nozzle body 4, and its large diameter part 18 is housed in the large diameter part 19 of the nozzle body 4, and can slide in the axial direction. The movable range of the nozzle needle 3 is about 50 μm, and the lower end is limited by a valve seat 20 provided on the nozzle body 4, and the upper end is limited by a distance piece 14. The clearance 22 between the small diameter portions 16 and 17 is approximately 1 mm in diameter, and the clearance (communication path) 21 between the large diameter portions 18 and 19 is approximately 20 μm in diameter. The connecting portion between the large diameter portion 19 and the small diameter portion 17 of the nozzle body 4 is an annularly enlarged space, forming a fuel reservoir 23 . The fuel reservoir 23 is the nozzle body 4,
A fuel passage 24 is connected as a part of the first fluid passage that communicates the distance piece 14 and the nozzle holder 6, and the fuel passage 24 functioning as this fluid passage is connected to the inlet port 25 at the upper end of the nozzle holder 6. It's open. The fuel that functions as the fluid in the fuel reservoir 23 passes through the clearance 22 that is a part of the first fluid passage, and is injected into the internal combustion engine from the nozzle 26 that forms the second fluid passage provided at the lower end of the nozzle body 4. However, when the nozzle needle 3 is at the lowest position, the valve seat 20 is closed and no fuel reaches the nozzle 26. The upper end surface of the nozzle needle 3 is polished to have a smooth flat surface, and can be brought into close contact with the lower surface of the distance piece 14, which is also polished and has a smooth flat surface. Due to the close contact between the two, the discharge hole 27 passing through the disc-shaped distance piece 14 in the axial direction is closed. The upper end surface of the distance piece 14 and the lower end surface of the pump piston 12 face each other with a predetermined gap, and a pump chamber 28 is formed by this gap. A discharge hole 27 (communication path) passing through the distance piece 14 communicates with this pump chamber 28 . Also, within the pump chamber 28 is a disc spring 13 that biases the pump piston 12 upward. The pump piston 12 is driven by the expansion and contraction of the piezoelectric actuator 2 above it, and produces a pumping action in the pump chamber 28.
An O-ring 29 is used for sealing. Piezoelectric actuator 2 consists of approximately 50 thin disc-shaped piezoelectric elements.
It is made by laminating layers to form a cylindrical shape. This piezoelectric element is a ceramic called PZT, whose main components are zirconate titanate and lead, and it expands by 1 μm when a voltage of 500 V is applied in the thickness direction. If 50 of these are stacked and a voltage of 500V is applied in the thickness direction of each element, the total thickness will be 50μ.
An elongation of m is obtained. If this voltage is removed or a slight negative voltage is applied, the film will shrink by 50 μm and return to its original length. Application and release of the voltage are performed by an external controller via the lead wire 30. Note that a knock pin 31 is used to secure the fuel passage 24 by regulating the relative positions of the nozzle holder 6, distance piece 14, and nozzle body 4.

Further, an accumulator 32 is used to supply fuel to the fuel injection valve 1. A fuel pressure of 200 atmospheres is stored in the accumulator 32 by a pump and a pressure setting valve (not shown), and this pressure is continuously maintained.

The operation of this embodiment configured as described above will be explained. When a voltage of 500V is applied to the piezoelectric actuator 2 at the time when fuel injection should be stopped, the piezoelectric actuator 2 extends by about 50 μm and lowers the pump piston 12, so the fuel in the pump chamber 28 is compressed and reaches a high pressure. It then acts on the upper end of the nozzle needle 3 through the discharge hole 27 to lower it, presses the lower end of the nozzle needle 3 against the valve seat 20 to close it, and cuts off the fuel supply to the nozzle 26. At this time, clearance 2 as a communication path
1 is a pump chamber 28 and a fuel passage 2 as a fluid passage.
The high-pressure fuel acting on the upper end of the nozzle needle 3 leaks into the fuel reservoir 23 through the clearance 21 serving as a communication path, but naturally the fuel pressure in the fuel reservoir 23, that is, the The fuel pressure does not drop below the fuel pressure in the mullet 32, and a fuel pressure of at least 200 atmospheres continues to act on the entire upper end surface of the nozzle needle 3. Although the fuel pressure of 200 atmospheres in the fuel reservoir 23 acts upward on the area corresponding to the difference in cross-sectional area between the large diameter part 18 and the small diameter part 16 of the nozzle needle 3, the downward force cannot be overcome due to the area ratio. First, the difference in force presses the lower end of the nozzle needle 3 against the valve seat 20 and continues to hold it. That is, the fuel injection valve 1 is maintained in the closed state.

Next, at the timing to start fuel injection, a slight negative voltage is applied to the piezoelectric actuator 2, and the
When the voltage of 500V is released, the piezoelectric actuator 2 contracts by approximately 50μm, and the pump piston 12
is raised by the disc spring 13, and the pump chamber 28 expands to generate negative pressure, reducing the pressure acting on the upper end surface of the nozzle needle 3 through the discharge hole 27. Therefore, the nozzle needle 3 receives the fuel pressure in the fuel reservoir 23.
It is pushed up by 200 atmospheres, and its upper end surface comes into close contact with the lower end surface of the distance piece 14. In this state, clearance 2 as a communication path
1 is a pump chamber 28 and a fuel passage 2 as a fluid passage.
4 is in a non-communicating state, and therefore the internal volume of the pump chamber 28 does not change, so there is no downward force acting on the nozzle needle 3, the nozzle needle 3 remains at the upper end position, and the nozzle 26 is in a state of no communication with the fuel. It is electrically connected to the reservoir 23 to continue fuel injection. That is, the fuel injection valve 1 is kept open.

Thereafter, the operation when stopping fuel injection is as described above, and fuel can be injected at any time and for any period according to the request of the internal combustion engine. Here, the clearance 21 as a communication means
is set to 20 μm, but since this value has an influence on the response time as shown in Figure 2, it needs to be smaller than 40 μm. Also, if it is too small, the fuel in the pump chamber 28 will remain trapped, causing problems such as fuel deterioration and air bubbles.
It is better to keep it warmer than 10μm. in any case,
Compared to general diesel engine injection valves that have pressure springs and overflow mechanisms,
It can be said that the clearance system of the nozzle needle to the nozzle body is relaxed by nearly an order of magnitude. Further, the ratio of the stroke volume of the pump piston 12 to the stroke volume of the nozzle needle large diameter portion 18 has an influence on the response time as shown in FIG. 3. Although it is better to have a larger stroke volume ratio from the viewpoint of responsiveness, it is better to have a stroke volume ratio of 1.5 to 2.5 when downsizing the fuel injector 1.
should be selected. This is because if this value is less than 1, it will not function when the valve is opened.

Note that in this embodiment, the nozzle needle 3
corresponds to the valve body, clearance 22, fuel reservoir 2
3. The fuel passage 24 and the injection hole 26 correspond to a fluid passage, and the clearance 21 and the discharge hole 27 correspond to a communication passage.

〔Effect of the invention〕

As explained above, according to the present invention, when the fluid passage is in a conductive state, the valve body brings the pump chamber and the fluid passage into a non-communicating state by blocking the communicating passage. Internal fluid does not flow into the fluid passage. At this time, the internal volume of the pump chamber does not change, so no hydraulic pressure acts on the valve body. Therefore, the valve body does not move and the conduction state of the fluid passage is maintained, so that when it is desired to close the valve body,
Since the valve is closed when the piezoelectric actuator is driven, there is an excellent effect that the valve closing timing of the valve body can be arbitrarily controlled.

[Brief explanation of the drawing]

FIG. 1 is a sectional view taken along the central axis of the first embodiment of the present invention, and FIGS. 2 and 3 are characteristic diagrams showing the response time to the ratio of clearance (communication means) and stroke volume. 2... Piezoelectric actuator, 3... Nozzle needle (valve body), 21... Clearance (communication path), 27... Discharge hole (communication path), 22... Clearance (fluid path), 23... Fuel reservoir (fluid passage), 24... fuel passage (fluid passage), 26... nozzle hole (fluid passage), 28... pump chamber.

Claims (1)

[Claims] 1. A piezoelectric actuator 2, and a pump whose interior is filled with fluid, whose internal volume changes in response to expansion and contraction of the piezoelectric actuator 2, and which generates fluid pressure in accordance with the change in internal volume. a chamber 28; a valve body 3 that reciprocates in the axial direction under the action of fluid pressure according to changes in the internal volume of the pump chamber 28; and a fluid cutoff state and a conduction state according to the reciprocating movement of the valve body 3. Fluid passages 22, 23, 2 that are switched
4, 26, the pump chamber 28 and the fluid passages 22, 23,
24, 26, the communication passages 21, 27 are arranged between the fluid passages 21, 27, and are switched between a fluid cutoff state and a conduction state according to the reciprocating movement of the valve body 3, and the fluid passages 22, 23, 24, 26 are In the case of a cutoff state, the communication passages 21 and 27 are brought into a conductive state to bring the pump chamber 28 and the fluid passages 22, 23, 24, and 26 into communication, and the fluid passages 22, 23, 24, and 26 are in a conductive state, the communication passages 21 and 27 are cut off, thereby connecting the pump chamber 28 and the fluid passage 22,
A piezoelectrically actuated fluid control valve characterized in that 23, 24, and 26 are in a non-communicating state.