JP3680461B2 - Injection valve - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a valve structure using a piezoelectric element as an actuator, which is applied to a fuel injection valve of an engine.
[0002]
[Prior art]
2. Description of the Related Art Some fuel injection valves and the like provided in automobile engines open a needle (valve element) using a laminated piezoelectric element (piezo element) that expands according to an applied voltage. By driving the needle with a piezoelectric element, the high-speed response of the fuel injection valve is enhanced and the output can be increased. In addition, a small amount of fuel can be stably injected, and fuel consumption can be reduced.
[0003]
Conventionally, there is a fuel injection valve of this type as shown in FIG. (See JP-A-2-112663).
[0004]
This will be described. The needle 52 is slidably mounted on the nozzle body 51. A fuel chamber 53 is defined around the needle 52 in the nozzle body 51. A nozzle hole 51 b opens at the tip of the nozzle body 51, and the nozzle hole 51 b is opened and closed by a needle 52.
[0005]
Fuel pumped from a fuel injection pump (not shown) is introduced into the fuel chamber 53 from the fuel inlet 63 through the fuel passage 62 and is injected from the nozzle 51 b as the needle 52 is lifted.
[0006]
A coiled spring 54 that urges the needle 52 in the valve closing direction is provided.
[0007]
A piezoelectric element 60 that drives the needle 52 in the valve opening direction is provided. The piezoelectric element 60 extends against the spring 54 when a voltage is applied via the lead wire 68, and lifts the needle 62 via the retainer 67.
[0008]
[Problems to be solved by the invention]
However, in such a conventional fuel injection valve, since the piezoelectric element 60 having a different linear expansion coefficient is interposed between the metal needle 52 and the nozzle body 51, the temperature of the fuel injection valve is low. If the change occurs, a difference in thermal expansion occurs between the nozzle body 51 and the piezoelectric element 60. As a result, the lift amount of the needle 52 changes, and the desired fuel injection amount cannot be obtained.
[0009]
The present invention has been made in view of the above-described problems, and an object of the present invention is to suppress variations in the injection amount in an injection valve using a piezoelectric element as an actuator.
[0010]
[Means for Solving the Problems]
The injection valve according to claim 1 is provided with a nozzle for injecting pressurized fluid guided from a fluid passage, a needle that moves in the axial direction to open and close the nozzle, and a needle that biases the needle in the valve opening direction. A biasing means, a piezoelectric element that extends by an applied voltage and presses the needle in a valve closing direction, a piston that is coupled to a proximal end of the piezoelectric element, and a casing that slidably houses the piston. A piston urging means for urging the piston in a direction in which the piezoelectric element is compressed, a damper chamber defined between the piston and the casing, and a communication passage communicating the fluid passage and the damper chamber And a throttle passage that is provided in the communication passage and imparts resistance to the pressurized fluid that enters and exits the damper chamber, and the elastic restoring force of the piston urging means is elastically restored by the needle urging means. Power Ri was assumed to be set large.
[0011]
According to a second aspect of the present invention, there is provided the injection valve according to the first aspect of the present invention, wherein the resistance applied to the fluid entering and exiting the damper chamber by the throttle passage is determined by the damper chamber pressure drop ΔP during the valve opening period of the needle. It was set to be within 10% of the maximum pressure difference in the chamber.
[0012]
Injection valve according to claim 3 is the invention according to claim 1 or 2, and as forming the communicating passage on the casing.
[0013]
According to a fourth aspect of the present invention, in the invention of the third aspect, the injection valve includes a bolt that is screwed into the casing, and forms a throttle passage that connects the damper chamber and the communication passage to the bolt.
[0014]
The injection valve according to a fifth aspect is the invention according to any one of the first to fourth aspects, wherein the injection valve is disposed concentrically with the piston as means for urging the piston in a direction in which the piezoelectric element is compressed. And a means for adjusting the screwing position of the rear end member with respect to the casing.
[0016]
Operation and effect of the invention
In the injection valve according to claim 1, by intermittently applying a voltage applied to the piezoelectric element, the piezoelectric element is expanded and contracted to move the needle in the axial direction, thereby opening and closing the injection hole.
[0017]
The piston tries to change the volume of the damper chamber as the piezoelectric element expands and contracts when the nozzle is opened and closed, but the throttle passage gives resistance to the fluid entering and exiting the damper chamber, so that the displacement of the piston is suppressed and the piezoelectric element is suppressed. The base end of the element is held as a fixed end.
[0018]
On the other hand, the thermal expansion difference generated between the needle and the casing and the piezoelectric element accompanying the change in the ambient temperature of the injection valve is absorbed when the piston coupled to the base end of the piezoelectric element expands and contracts the damper chamber to displace the needle. The desired amount of injection can be obtained by keeping the lift amount constant. When a voltage is applied to the piezoelectric element, the piezoelectric element expands to bring the needle closer to the seating surface and close the nozzle. When the voltage applied to the piezoelectric element is interrupted, the urging means causes the needle to follow the contraction of the piezoelectric element to move the needle away from the seating surface and open the nozzle hole. Since the displacement direction of the piezoelectric element and the displacement direction of the needle coincide with each other, the piezoelectric element and the needle can be arranged in series, and the needle can be brought into contact with the piezoelectric element for driving. As a result, a mechanism for reversing the driving force of the piezoelectric element and transmitting it to the needle becomes unnecessary, and the structure can be simplified.
[0019]
3. The injection valve according to claim 2, wherein the resistance imparted to the fluid entering and exiting the damper chamber by the throttle passage is set so that the pressure drop ΔP of the damper chamber during the valve opening period is within 10% of the maximum pressure difference of the damper chamber. With this setting, the displacement amount of the piston during the valve opening period of the needle is sufficiently reduced, and the base end of the piezoelectric element is held as a fixed end. As a result, a small amount of fuel can be stably injected, and fuel consumption can be reduced.
[0020]
In the injection valve according to claim 3, by forming the communication passage in the casing so as to connect the fluid passage and the throttle passage, the fluid entering and exiting the damper chamber is guided from the fluid passage, and the structure is simplified.
[0021]
In the injection valve according to claim 4, by forming the throttle passage in the bolt screwed into the casing, it becomes possible to change the size of the throttle passage by exchanging the bolt, and the productivity and maintainability can be improved. Improvement is planned.
[0022]
6. The injection valve according to claim 5, wherein as a means for biasing the piston in a direction in which the piezoelectric element is compressed, a flat spring arranged concentrically with the piston gives a force evenly distributed in the circumferential direction to the piston. Therefore, the piston is smoothly moved without urging the piston in the eccentric direction, and stable operability is ensured.
[0023]
By adjusting the screwing position of the rear end member with respect to the casing, the biasing force of the flat spring can be easily adjusted.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is applied to a fuel injection valve provided in a cylinder injection spark ignition engine will be described with reference to the accompanying drawings.
[0028]
As shown in FIGS. 1 and 2, the needle 2 is slidably housed inside the nozzle body 1 and the cylinder 9. A fuel chamber (fluid chamber) 3 is defined around the needle 2 in the nozzle body 1 and the cylinder 9. A nozzle hole 1 b opens at the tip of the nozzle body 1, and the nozzle hole 1 b is opened and closed by a needle 2.
[0029]
Fuel pumped from a fuel injection pump (not shown) is introduced into the fuel chamber 3 from the fuel inlet 13 through the fuel passage (fluid passage) 12 and is injected from the nozzle 1 b as the needle 2 is lifted. The nozzle body 1 faces the combustion chamber from the ceiling wall of the combustion chamber of the engine and jets fuel spray from the nozzle 1b toward the crown of the piston.
[0030]
Inside the nozzle body 1, a seating surface 1a is recessed in a conical shape around the nozzle hole 1b. On the other hand, at the tip of the needle 2, a sheet portion 2a projects in a conical surface shape. When the seat portion 2a is seated on the seating surface 1a, the nozzle hole 1b is closed. When the seat portion 2a is separated from the seating surface 1a, the nozzle hole 1b is opened.
[0031]
The support portion 2b protrudes from the middle of the needle 2 in the outer diameter direction, and the support portion 2b is in sliding contact with the cylindrical inner wall surface of the nozzle body 1, thereby guiding the seat portion 2a coaxially with the seat surface 1a. A passage through which fuel flows is formed between the support portion 2b and the inner wall surface of the nozzle body 1.
[0032]
The needle 2 has a piston portion 2c formed in an annular shape on the base end side. An O-ring 5 is interposed in an annular groove formed on the outer periphery of the piston portion 2c. When the O-ring 5 is in sliding contact with the cylindrical inner wall surface of the cylinder 9, the fuel chamber 3 is sealed. A backup ring 6 is interposed behind the O-ring 5 in the annular groove so that the O-ring 5 does not protrude from the annular groove due to hydraulic pressure.
[0033]
A flat spring 4 is provided to urge the needle 2 in the valve opening direction. The flat spring 4 is interposed between the piston portion 2 c of the needle 2 and the nozzle body 1 in a compressed state, and is disposed concentrically with the needle 2. As a result, the spring spring 4 separates the seat portion 2a of the needle 2 from the seating surface 1a by its elastic restoring force.
[0034]
A piezoelectric element 10 that presses the needle 2 in the valve closing direction is provided in the cylinder 9. When a voltage is applied to the piezoelectric element 10 via the lead wire 23, the piezoelectric element 10 instantaneously extends in the sliding direction of the needle 2, and the seat portion 2a is seated on the seat surface 1a. On the other hand, the piezoelectric element 10 is instantaneously contracted by cutting off the voltage applied to the piezoelectric element 10 and short-circuiting both terminals of the piezoelectric element 10, so that the needle 2 generates the fuel pressure in the fuel chamber 3 and the biasing force of the flat spring 4. The seat portion 2a moves away from the seating surface 1a by moving in the axial direction by the combined force. The force with which the piezoelectric element 10 presses the needle 2 in the valve closing direction is set to be larger than the combined force of the fuel pressure in the fuel chamber 3 and the biasing force of the flat spring 4.
[0035]
In such a piezoelectric element 10, a plurality of disk-shaped piezoelectric single bodies (piezo elements) are stacked with a disk-shaped internal electrode plate interposed therebetween. The thickness of the piezoelectric single body is increased by applying voltage and storing electric charge, and the thickness is reduced by cutting off the voltage and short-circuiting both terminals.
[0036]
An end plate 11, a ball 8, and a shim 7 are interposed between the driving end (tip) of the piezoelectric element 10 and the needle 2.
[0037]
An end plate 11 is coupled to the driving end of the piezoelectric element 10. The ball 8 is interposed between the end plate 11 and the needle 2. A pair of recesses recessed in a spherical shape are formed on the base end surfaces of the end plate 11 and the needle 2, respectively. The ball 8 is sandwiched between the recesses.
[0038]
The shim 7 is formed in a disk shape. The shim 7 is interposed between the proximal end of the needle 2 and the cylinder 9 and restricts the movement of the needle 2 in the axial direction. That is, since the displacement amount of the piezoelectric element 10 is set larger than the full lift amount A of the needle 2, the full lift amount A of the needle 2 is determined by the plate thickness of the shim 7.
[0039]
The lead wire 23 is taken out from the hole 22 of the cylinder 9, and the space between the hole 22 and the lead wire 23 is sealed through a seal 24.
[0040]
The lead wire 23 extends to a drive circuit (not shown). A control unit (not shown) calculates the fuel injection amount according to the intake air amount and the rotational speed of the engine. A pulse signal corresponding to the fuel injection amount calculated by the control unit is generated by the pulse generator, and a voltage corresponding to the pulse signal is applied to the piezoelectric element 10 via the drive circuit.
[0041]
A piston 16 is coupled to the base end of the piezoelectric element 10 and is provided so as to be displaceable with respect to the cylinder 9.
[0042]
A rear end member 20 that is screwed into the opening end of the cylinder 9 is provided. A flat spring 17 is interposed between the front end of the rear end member 20 and the piston 16 in a compressed state. The elastic restoring force of the flat spring 17 is set larger than the elastic restoring force of the flat spring 4, and the driving end of the piezoelectric element 10 is pressed against the base end of the needle 2 via the ball 8 by the elastic restoring force of the flat spring 17 to 2a is pressed against the seating surface 1a.
[0043]
The rear end member 20 is fastened to the cylinder 9 via a nut 21 screwed to the rear end member 20, and the elastic restoring force of each of the flat springs 17 and 4 is adjusted by changing the screwing position with respect to the cylinder 9.
[0044]
A damper chamber 27 is defined between the rear end member 20 and the piston 16. Since the damper chamber 27 communicates with the fuel chamber 3 through the throttle passage 25 as described later, the volume of the damper chamber 27 is kept substantially constant with respect to the instantaneous expansion and contraction of the piezoelectric element 10. For this reason, the base end of the piezoelectric element 10 is held as a fixed end via the piston 16.
[0045]
An O-ring 15 and a backup ring 14 are interposed in an annular groove formed on the outer periphery of the piston 16. An O-ring 18 and a backup ring 19 are interposed in an annular groove formed on the outer periphery of the rear end member 20. The damper chamber 27 is sealed through the O-rings 15 and 18.
[0046]
The damper chamber 27 communicates with the fuel chamber 3 through a communication passage 26 formed in the cylinder 9 and a throttle passage 25.
[0047]
The communication path 26 is defined by two through holes 26a and 26b formed in the cylindrical wall portion of the cylinder 9 by drilling. One end of the through hole 26a communicates with the fuel chamber 3, and a plug body 28 is interposed at the open end of the through hole 26b to close it.
[0048]
Bolts 31 are provided in the cylinder 9 so as to pass through the communication passages 26 and are screwed together.
[0049]
As shown in FIGS. 3 and 4, the bolt 31 has a screw portion 32 that is screwed into the cylinder 9 and a head portion 33 that is joined to the outer wall of the cylinder 9, and a tool that engages with the hexagonal hole 34 of the head portion 33. It is fastened to the screw hole of the cylinder 9 via
[0050]
An annular groove 35 is formed on the outer periphery of the screw portion 32. The throttle passage 25 is defined by a through hole 36 that opens to the annular groove 35 and a through hole 37 that communicates with the through hole 36 and opens at the tip thereof.
[0051]
FIG. 5 is a model diagram of the throttle passage 25. If the diameter of the throttle passage 25 is d, the length is r, the pressure in the damper chamber 27 is P1, and the pressure in the fuel chamber 3 is P2, the flow rate Q of the fuel passing through the throttle passage 25 is calculated by the following equation.
[0052]
Q = C × A × (2 × ΔP / ρ) ^1/2 (1)
However, C: [(Re / 64) / (r / d + 0.495)] ^1/2
A: Cross-sectional area ΔP: Pressure difference (= P1−P2)
ρ: Density Re: Reynolds number (= vd / υ)
FIG. 6 is a characteristic diagram showing the relationship between the elapsed time (injection period) during which the piezoelectric element 10 is contracted and the pressure difference ΔP calculated using the equation (1). When the pressure rises by about 20 kg / m ² due to the displacement of the element 10 and the displacement amount of the piezoelectric element 10 is about 50 μm, the diameter d of the throttle passage 25 is set to 0.5 mm or less, preferably about 0.3 mm. Therefore, the pressure difference ΔP is suppressed to about 2 kg / m ² until the elapsed time reaches 10 ms. Therefore, in the fuel injection valve having a maximum injection period of about 10 ms, the damper chamber during the valve opening period of the needle 2 is set by setting the diameter d of the throttle passage 25 to about 0.5 mm or less and about 0.3 mm. The pressure drop ΔP of 27 is within 10% of the maximum pressure difference of the damper chamber 27, so that the volume of the damper chamber 27 hardly changes and the base end of the piezoelectric element 10 can be held.
[0053]
It is comprised as mentioned above, Next, an effect | action is demonstrated.
[0054]
1 and 2 show the fuel injection valve in a state before the engine is started. The piezoelectric element 10 is extended by applying a voltage, and the seat portion 2a of the needle 2 is seated on the seat surface 1a. . In this state, a fuel injection pump (not shown) is driven by an electric motor, and the pressure in the fuel chamber 3 and the damper chamber 27 is increased to about 5 MPa.
[0055]
Even when the engine is stopped, the driving end of the piezoelectric element 10 is pressed against the base end of the needle 2 via the ball 8 by the elastic restoring force of the flat spring 17, and the seat portion 2a of the needle 2 is seated on the seating surface 1a. To prevent leakage.
[0056]
The opening operation of the fuel injection valve at the time of engine start and after the engine start is instantaneously contracted by blocking the voltage applied in synchronism with the engine rotation of the piezoelectric element 10 and short-circuiting both terminals of the piezoelectric element 10. The needle 2 moves in the axial direction by the combined force of the fuel pressure in the fuel chamber 3 and the biasing force of the flat spring 4, and the seat portion 2a is separated from the seat surface 1a. When the seat portion 2a is separated from the seat surface 1a, the high-pressure fuel in the fuel chamber 3 is injected into the combustion chamber of the engine through the nozzle 1b.
[0057]
The closing operation of the fuel injection valve is extended by applying a voltage to the piezoelectric element 10 in synchronization with the engine rotation, and the needle 2 resists the combined force of the fuel pressure in the fuel chamber 3 and the urging force of the spring spring 4. Then, it moves in the axial direction, and the seat 2a approaches the seat surface 1a and sits down. When the seat portion 2a is seated close to the seating surface 1a, the injection hole 1b is closed and fuel injection is stopped.
[0058]
By the way, the flat spring 17 presses the needle 2 against the seating surface 1 a via the piston 16. For this reason, when the environmental temperature of the fuel injection valve changes, the difference in thermal expansion between the needle 2 and the casing 9 and the piezoelectric element 10 causes the piston 16 coupled to the base end of the piezoelectric element 10 to expand and contract the damper chamber 27. The end plate 11 of the piezoelectric element 10 is held at a position where the nidol 2 closes the nozzle hole 1b.
[0059]
The resistance imparted to the fluid entering and exiting the damper chamber 27 by the throttle passage 25 is set so that the pressure drop ΔP in the damper chamber 27 during the valve opening period of the needle is within 10% of the maximum pressure difference in the damper chamber 27 as described above. By setting as described above, the displacement amount of the piston 16 in the short-circuit valve-opening operation of the needle 2 is sufficiently reduced, and the base end of the piezoelectric element 10 is held. As a result, a small amount of fuel can be stably injected, and fuel consumption can be reduced.
[0060]
On the other hand, by forming the communication passage 26 in the casing 9 that communicates the fuel chamber 3 and the throttle passage 25, the fluid entering and exiting the damper chamber 27 is guided from the fuel passage 13, thereby simplifying the structure.
[0061]
In addition, by forming the throttle passage 25 in the bolt 31 that is screwed into the casing 9, it is possible to change the size of the throttle passage 25 by replacing the bolt 9, thereby improving productivity and maintainability. .
[0062]
As a means for urging the piston 16 in the direction in which the piezoelectric element 10 is compressed, the flat spring 17 disposed concentrically with the piston 16 applies a force uniformly distributed in the circumferential direction to the piston 16. Without urging the shaft in the eccentric direction, the piston 16 can be smoothly moved to ensure stable operability.
[0063]
By adjusting the screwing position of the rear end member 20 with respect to the casing 9, the urging force of the flat spring 17 can be easily adjusted.
[0064]
Further, during the valve opening operation, the displacement amount of the piezoelectric element 10 is set larger than the full lift amount of the needle 2, so that the needle 2 is seated on the shim 7 and moves by a predetermined full lift amount. Therefore, when the needle 2 is fully lifted, a fixed fuel flow path is defined between the seat portion 2a of the needle 2 and the seat surface 1a, and a fuel injection rate determined by the fuel pressure guided to the fuel chamber 3 is obtained.
[0065]
During the valve opening operation, the piezoelectric element 10 contacts the needle 2 via the ball 8, so that the movement of the needle 2 is made smooth without being affected by the dimensional error of the piezoelectric element 10, the inclination of the piezoelectric element 10, etc. Stable operability is ensured. Further, since no bias load is applied to the piezoelectric element 10, the durability of the piezoelectric element 10 can be improved.
[0066]
Since the displacement direction of the piezoelectric element 10 and the displacement direction of the needle 2 coincide with each other, the fuel injection valve can be driven by arranging the piezoelectric element 10 and the needle 2 in series and bringing the needle 2 into contact with the piezoelectric element 10. It becomes possible. As a result, a mechanism for reversing the driving force of the piezoelectric element 10 and transmitting it to the needle 2 becomes unnecessary, and the structure can be simplified.
[0067]
In the present embodiment, the displacement of the piezoelectric element 10 is directly transmitted to the needle 2. However, the displacement of the piezoelectric element 10 may be expanded or contracted and transmitted to the needle 2.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a fuel injection valve showing an embodiment of the present invention.
FIG. 2 is a cross-sectional view of the fuel injection valve.
FIG. 3 is a front view of the bolt.
FIG. 4 is a side view of the bolt.
FIG. 5 is a model view of the throttle passage.
FIG. 6 is a characteristic diagram showing the relationship between the elapsed time for contracting the piezoelectric element and the pressure difference ΔP.
FIG. 7 is a sectional view of a fuel injection valve showing a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Nozzle body 1a Seat surface 1b Injection hole 2 Needle 2a Seat part 3 Fuel chamber 4 Sarah spring 5 O ring 6 Backup ring 7 Shim 8 Ball 9 Cylinder 10 Piezoelectric element 11 End plate 12 Fuel inlet 13 Fuel passage 14 Backup ring 15 O ring 16 Piston 17 Flat spring 18 O-ring 19 Flat spring 20 Rear end member 23 Lead wire 25 Restriction passage 27 Damper chamber 31 Bolt

Claims (5)

A nozzle for injecting pressurized fluid guided from the fluid passage;
A needle that moves in the axial direction to open and close the nozzle,
Needle urging means for urging the needle in the valve opening direction;
A piezoelectric element that extends by an applied voltage and presses the needle in the valve closing direction;
A piston coupled to the proximal end of the piezoelectric element;
A casing for slidably housing the piston;
A piston urging means for urging the piston in a direction in which the piezoelectric element is compressed; a damper chamber defined between the piston and the casing;
A communication passage communicating the fluid passage and the damper chamber;
A throttle passage that is provided in the communication passage and imparts resistance to the pressurized fluid that enters and exits the damper chamber;
An injection valve characterized in that an elastic restoring force of the piston urging means is set larger than an elastic restoring force of the needle urging means .   The resistance imparted to the fluid entering and exiting the damper chamber by the throttle passage is set such that the pressure drop ΔP in the damper chamber during the valve opening period of the needle is within 10% of the maximum pressure difference in the damper chamber. The injection valve according to claim 1.   The injection valve according to claim 1, wherein the communication path is formed in the casing.   The injection valve according to claim 3, further comprising a bolt that is screwed into the casing, and a throttle passage that connects the damper chamber and the communication passage is formed in the bolt.   As means for urging the piston in the direction of compressing the piezoelectric element, a flat spring arranged concentrically with the piston, a rear end member supporting one end of the flat spring, and a screwing position of the rear end member with respect to the casing are adjusted. The injection valve according to any one of claims 1 to 4, further comprising:

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