JP3767082B2 - Fuel injection valve manufacturing apparatus and manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel injection valve manufacturing apparatus and method using a piezo actuator.
[0002]
[Prior art]
High responsiveness and opening / closing accuracy are required for a fuel injection valve applied to a spark ignition internal combustion engine of an in-cylinder fuel injection system. As a fuel injection valve that meets such demands, there is known a fuel injection valve that controls the opening and closing of a needle valve by supplying a signal current to a piezoelectric actuator having a structure in which a large number of piezoelectric elements are stacked to expand and contract ( For example, see Japanese Utility Model Laid-Open No. 5-7957).
[0003]
[Problems to be solved by the invention]
Piezo elements exhibit a specific piezoelectric characteristic by applying a polarization voltage corresponding to the material or the like at the time of manufacture, but this characteristic varies due to changes over time and factors in manufacturing errors. An error in component accuracy or assembly accuracy is added to the variation in the characteristics, and the fuel injection characteristics using the piezoelectric actuator cause individual differences in the fuel injection characteristics.
[0004]
[Means for Solving the Problems]
The invention of claim 1 is a fuel injection valve manufacturing apparatus that converts displacement of a piezo actuator into pressure and opens and closes a needle valve based on the pressure change.
Sealing means for sealing the fuel injection valve in a state where a predetermined pressure is introduced; pressure measuring means for measuring the internal pressure of the sealed fuel injection valve; and polarization voltage applying means for applying a polarization voltage to the piezoelectric actuator; And a control means for controlling the polarization voltage so that the measured internal pressure becomes a predetermined reference value.
[0005]
According to a second aspect of the present invention, the fuel injection valve according to the first aspect is provided with a needle valve that opens and closes a nozzle hole that opens at the tip, and a fuel chamber and a pressure chamber that are connected to the needle valve in the injection valve before and after. A fuel supply port for supplying fuel from an external fuel supply system to the fuel chamber, each of which includes a piston portion and a piezo actuator that is located behind the needle valve and expands and contracts the pressure chamber according to an applied voltage. And an orifice portion that communicates the fuel chamber with the pressure chamber is formed, and the pressure measuring means is configured to measure the pressure of the fuel chamber.
[0006]
According to the invention of claim 3, the control means of the invention of claim 1 or claim 2 is configured such that the polarization voltage exceeds a predetermined allowable value before the measured value of the internal pressure reaches the reference value in the adjustment process of the polarization voltage. It is sometimes assumed that a means for determining that the fuel injection valve is defective is provided.
[0007]
According to a fourth aspect of the present invention, the sealing means of the second aspect includes a plug for closing the nozzle hole of the fuel injection valve from the outside, and a shutoff valve interposed in the middle of the fuel passage connected to the fuel supply port. Shall be.
[0008]
According to a fifth aspect of the present invention, in the first to fourth aspects of the present invention, the internal pressure reference value is set to be at least 2% larger than the operating pressure value of the fuel injection valve.
[0009]
According to a sixth aspect of the present invention, in the first to fourth aspects of the present invention, the internal pressure reference value is set to be 7% or more larger than the operating pressure value of the fuel injection valve.
[0010]
The invention according to claim 7 is a method of manufacturing a fuel injection valve in which the displacement of the piezo actuator is converted into pressure, and the needle valve is opened and closed based on the pressure change, and the fuel injection valve is predetermined in the fuel injection valve. After introducing pressure and sealing, a polarization voltage was applied to the piezo actuator while measuring the internal pressure, and the polarization voltage was adjusted so that the internal pressure reached a predetermined reference value.
[0011]
[Action / Effect]
According to each of the above inventions, the polarization voltage is applied to the piezo actuator based on the pressure generated in the actual usage state inside the fuel injection valve. That is, the characteristics of the actuator are compensated based on the pressure under the use conditions rather than the displacement. For this reason, fuel injection with the desired injection characteristics is possible regardless of variations in individual characteristics of the piezo actuator caused by errors during manufacturing of the elements, changes in the characteristics of the piezoelectric actuator, and error factors caused by parts and assembly accuracy of the fuel injection valve. A valve is obtained.
[0012]
When the piezo actuator is defective or the fuel injection valve is not properly assembled, the internal pressure does not rise sufficiently with respect to the application of the polarization voltage. Therefore, according to the configuration in which the failure determination means is provided in the control means, the failure point in the actuator or the fuel injection valve is determined based on the fact that the polarization voltage exceeds the predetermined allowable value before the measured value of the internal pressure reaches the reference value. Can be determined.
[0013]
The pressure that serves as a reference for determining the polarization voltage is set to a value that is at least 2%, preferably 7% or more larger than the working pressure. As a result, it is possible to effectively compensate for fluctuations in the characteristics of the piezo actuator mainly due to deterioration over time. The working pressure is a pressure value that should be generated inside the injection valve when a piezoelectric actuator that exhibits the desired characteristics is incorporated in the fuel injection valve and a predetermined polarization voltage is applied thereto.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In FIG. 1, 1 is a fuel injection valve, 2 is a control circuit as control means, 3 is a polarization circuit as polarization voltage application means, and 4 is a pressure sensor as pressure measurement means.
[0015]
In the fuel injection valve 1, an actuator 12 is accommodated in a cylindrical main body 11, and a nozzle body 14 in which a needle valve 13 is accommodated is provided at a distal end portion of the main body 11.
[0016]
The actuator 12 is formed in a cylindrical shape by laminating a large number of thin plate-like piezoelectric elements. An end plate 15 provided at an end portion on the back side is positioned through a ball 17 with respect to a cap 16 fitted to the main body 11. A piston 18 is provided on the distal end side, and this piston 18 is fitted in a cylinder portion 19 formed in the main body through a seal ring 20 in an oil-tight and slidable manner.
[0017]
A pressure chamber 21 is defined in front of the piston 18 with the cylinder portion 19, and the piston 18 is urged backward by the tension of the disc spring 22 housed in the pressure chamber 21.
[0018]
The nozzle body 14 is provided with a needle valve 13 for opening and closing a nozzle hole 23 opened at the tip thereof. The needle valve 13 has a piston portion 24 having a large base end, and the piston portion 24 is slidably held along a cylinder portion 25 formed on the inner periphery of the holder. A coil spring 27 is interposed in the pressure chamber 26 defined behind the piston portion 24, and the needle valve 13 is urged in the valve closing direction by the tension of the spring 27.
[0019]
A space in the nozzle body 14 in front of the piston portion 24 is a fuel chamber 28, and fuel adjusted to a predetermined pressure via a fuel passage 31 connected to the fuel supply port 29 is stored in the fuel chamber 28. Supplied. Further, the pressure chamber 26 behind is in communication with the pressure chamber 21 behind it through a passage 30.
[0020]
In this fuel injection valve, a fuel injection control circuit (not shown) determines a fuel injection amount using, for example, the rotational speed of the internal combustion engine and an intake air amount as parameters, and sends an injection signal having a pulse width corresponding to the fuel injection amount to the actuator 12. To inject fuel.
[0021]
Details of the operation of the fuel injection valve 1 when such an injection signal is input are as follows. First, in this fuel injection valve 1, a voltage of about 200 V is applied to the actuator 12 during non-injection. At this time, the actuator 12 extends to keep the volume of the pressure chamber 21 small. Since the pressure of the fuel supplied to the fuel chamber 28 also acts on the pressure chambers 26 and 21 via the sliding gap between the needle valve piston portion 24 and the cylinder portion 25, The pressure is balanced, so the needle valve 13 is held closed by the tension of the spring 27.
[0022]
When the application of voltage is stopped from this state, the actuator 12 and the piston 19 quickly contract to the initial position, so that the pressure chamber 21 expands its volume and decreases the pressure. This pressure drop is immediately transmitted to the pressure chamber 26 behind the needle valve via the passage 30. At this time, the sliding gap 35 between the needle valve piston part 24 and the cylinder part 25 acts as an orifice part. The pressure change in the fuel chamber 28 is delayed with respect to the pressure drop in the chamber 26, and the fuel chamber 28 has a relatively high pressure. Based on the pressure difference between the front and rear of the piston portion 24, the needle valve 13 is lifted backward against the spring 27 to open the injection hole 23 and perform fuel injection.
[0023]
When a drive voltage is applied again after a time determined according to the required fuel injection amount at that time, the actuator 12 expands again to increase the pressure in the pressure chambers 21 and 26, so that the needle valve 13 is closed. The fuel injection is terminated. The closed state of the needle valve 13 at the time of non-injection is maintained by the pressure equilibrium state around the piston 24 as described above.
[0024]
By the way, the actuator 12 using this kind of piezo element has different element displacement even when the same drive voltage is applied due to variations in the element manufacturing stage, and the pressure change amount in the pressure chamber 26 varies, resulting in fuel injection. An error occurs in the quantity. In addition, even when the same element displacement amount, the amount of change in pressure in the pressure chamber 26 varies due to errors due to parts and assembly accuracy of the fuel injection valve 1, actuator 12, end plate 15, cap 16, and piston 18. Will cause an error.
[0025]
Further, the actuator 12 using this type of piezo element, as shown in FIG. 3, decreases in capacitance as the standing time after polarization in the manufacturing stage elapses. It deteriorates in the direction that the amount (stretching amount) decreases. For this reason, in the configuration of the fuel injection valve, the contraction amount of the actuator 12 and the pressure drop amount of the pressure chamber 21 at the start of injection are insufficient, and the fuel injection amount causes an error in the decreasing direction.
[0026]
In the present invention, in order to solve such a problem, the piezoelectric actuator 12 is incorporated into the fuel injection valve 1 and then the actuator 12 is polarized while measuring the internal pressure while the fuel injection valve 1 is sealed at a predetermined pressure. The error is compensated by applying a voltage.
[0027]
As an embodiment for this purpose, in addition to the pressure sensor 4, the polarization circuit 3, and the control circuit 2 described above, as shown in FIG. 1, a plug body 32 that is fitted and fixed to the nozzle body 14 as a sealing means is provided. In the middle of the fuel passage 31, an electromagnetic shut-off valve 33 that opens and closes in response to a signal from the control circuit 2 is interposed.
[0028]
The plug body 32 is oil-tightly fitted to the nozzle body 14 via the seal ring 34, and in this fitted and fixed state, the seal 35 is brought into close contact with the nozzle hole 23 portion of the nozzle body 14 to thereby apply pressure from the nozzle hole 23. Prevent leakage. On the other hand, the shut-off valve 33 is for sealing the fuel supply port 29 side during pressure measurement, and fuel or oil adjusted to an initial setting pressure for measurement by a supply means (not shown) is passed through the fuel supply port 29. After the fuel chamber 28 and the pressure chambers 21 and 26 inside the fuel injection valve 1 are filled, the valve is closed.
[0029]
FIG. 2 is a flow chart showing a manufacturing process of a fuel injection valve that performs calibration using such a sealing means, which will be described below. First, after the assembly of the fuel injection valve 1 is completed by incorporating the actuator 12 into the main body 11, the sealing means described above is connected (steps 201 and 202). That is, the plug body 32 is fitted to the nozzle body 14 and the fuel passage 31 is connected to the fuel supply port 29. After supplying a predetermined pressure into the injection valve, the shutoff valve 33 is closed. Further, the detection part of the pressure sensor 4 is connected to the fuel passage 31 to prepare for pressure measurement.
[0030]
Next, an initial value of the polarization voltage V is set and applied to the actuator 12 (steps 203 and 204). The initial value of the polarization voltage V is set to, for example, about 2 KV, which is slightly lower than the polarization voltage at the time of manufacturing the actuator 12.
[0031]
In a state where the polarization voltage V is applied, the fuel chamber pressure P is measured by a pressure sensor (step 205). Since the actuator 12 extends in response to the application of the polarization voltage, the pressure P of the fuel chamber 28 increases. Therefore, the pressure P is measured and compared with the reference value Po (step 206). The pressure reference value Po is set slightly larger than the operating pressure, that is, the pressure value that should be originally reached when there is no deterioration or error in the actuator 12. This is because, as shown in FIG. 3, since the capacitance indicating the degree of deterioration from the time when the actuator 12 was first polarized is decreased with time, a higher polarization voltage is applied to compensate for this. To do. Specifically, as shown in the figure, the capacitance rapidly decreases to about −2% by the first 10 hours, and then gradually decreases to about −7%. The value Po is at least 2% higher than the operating pressure, and preferably 7% or more, so that the capacitance can be set larger. Therefore, the actual injection amount becomes larger than the required injection amount over time. It is possible to prevent problems that are greatly reduced.
[0032]
In this way, the preset reference value Po and the measured pressure P are compared, and if P ≧ Po, the actuator 12 is in a state where it can exhibit its original performance, and the processing is terminated. On the other hand, if P ≧ Po is not satisfied, a value obtained by adding a predetermined increment ΔV to the polarization voltage V is applied to the actuator 12 as a new polarization voltage V, and the pressure P is measured again (step 207). ~ 204). By repeating such processing until P ≧ Po, it is possible to compensate for manufacturing variations of the actuator 12, errors due to injection valve parts and assembly accuracy, and degradation of the actuator, so that the original performance can be exhibited.
[0033]
However, when the polarization voltage V exceeds the allowable value Vmax as a result of adding the increment ΔV, it is determined that the assembly of the actuator 12 or the fuel injection valve is defective and processing such as replacement is performed (step 209). ). The allowable value Vmax is experimentally determined. As an example, it is assumed that about 10% is added to the initial value. This is because the capacitance indicating the degree of deterioration of the actuator 12 does not normally decrease by more than −10% even after 1000 hours or more have elapsed since the manufacture as shown in FIG. This is because it can be determined that there is some abnormality rather than simple deterioration if the reference pressure Po is not reached even if the pressure increases by 10%.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an embodiment of the present invention.
FIG. 2 is a flowchart showing a method for manufacturing a fuel injection valve according to the embodiment.
FIG. 3 is a characteristic diagram in which a change characteristic of capacitance of a piezo actuator is displayed in semi-logarithm.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fuel injection valve 2 Control circuit 3 Polarization circuit 4 Pressure sensor 11 Fuel injection valve main body 12 Actuator 13 Needle valve 14 Nozzle body 15 End plate 16 Cap 17 Ball 18 Piston 19 Cylinder part 20 Seal ring 21 Pressure chamber 22 Disc spring 23 Injection Hole 24 Piston portion 25 Cylinder portion 26 Pressure chamber 27 Coil spring 28 Fuel chamber 29 Fuel supply port 30 Passage 31 Fuel passage 32 Plug body 33 Electromagnetic shut-off valve 35 Seal

Claims (7)

A fuel injection valve manufacturing apparatus that converts displacement of a piezo actuator into pressure and opens and closes a needle valve based on the pressure change,
Sealing means for sealing the fuel injection valve in a state where a predetermined pressure is introduced; pressure measuring means for measuring the internal pressure of the sealed fuel injection valve; and polarization voltage applying means for applying a polarization voltage to the piezoelectric actuator; And a control means for controlling the polarization voltage so that the measured internal pressure becomes a predetermined reference value. The fuel injection valve includes a needle valve that opens and closes a nozzle hole that is open at the tip, a piston portion that is connected to the needle valve in the injection valve and defines a fuel chamber and a pressure chamber, respectively, and a needle valve. A piezoelectric actuator that is located behind and expands or contracts the pressure chamber according to the applied voltage, and the fuel chamber is provided with a fuel supply port for supplying fuel from an external fuel supply system, and the fuel chamber, the pressure chamber, 2. The fuel injection valve manufacturing apparatus according to claim 1, wherein an orifice part is formed, and the pressure measuring means is configured to measure the pressure of the fuel chamber. 3. The control means includes means for determining that the fuel injection valve is defective when the polarization voltage exceeds a predetermined allowable value before the measured value of the internal pressure reaches the reference value in the process of adjusting the polarization voltage. An apparatus for manufacturing a fuel injection valve according to any one of claims 1 and 2. 3. The sealing device according to claim 2, wherein the sealing means includes a plug for closing the nozzle hole of the fuel injection valve from the outside, and a shutoff valve interposed in the middle of the fuel passage connected to the fuel supply port. Fuel injection valve manufacturing equipment. 5. The fuel injection valve manufacturing apparatus according to claim 1, wherein the reference value of the internal pressure is set to be at least 2% larger than the operating pressure value of the fuel injection valve. The fuel injection valve manufacturing apparatus according to any one of claims 1 to 4, wherein the reference value of the internal pressure is set to be 7% or more larger than the operating pressure value of the fuel injection valve. A method of manufacturing a fuel injection valve in which a displacement of a piezo actuator is converted into pressure, and a needle valve is opened and closed based on the pressure change. The fuel injection valve is sealed by introducing a predetermined pressure into the fuel injection valve A method for manufacturing a fuel injection valve, wherein a polarization voltage is applied to a piezo actuator while measuring an internal pressure, and the polarization voltage is adjusted so that the internal pressure reaches a predetermined reference value. .

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