JP3758325B2 - Fuel injection valve adjusting device and manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for adjusting a fuel injection valve 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 unique piezoelectric characteristic by applying a polarization voltage according to the material during manufacture, but this characteristic depends on factors such as manufacturing error and differences in Young's modulus inherent in the element. Variations occur. An error in the component accuracy or assembly accuracy of the fuel injection valve is added to the variation in the characteristics, so that individual differences occur in the fuel injection characteristics in the fuel injection valve using the piezoelectric actuator.
[0004]
[Means for Solving the Problems]
In the first invention, a hydraulic pressure chamber is defined at one end of the piezoelectric actuator, and the needle valve is opened and closed based on a change in pressure of the hydraulic pressure chamber when a driving voltage is applied to the piezoelectric actuator. As shown in FIG. 1, as a fuel injection valve adjustment device,
A measurement mechanism b having a hydraulic chamber a having the same dimensions as the fuel injection valve;
Pressure loading means c for loading the hydraulic pressure chamber a with an initial pressure corresponding to the use of a fuel injection valve;
Voltage applying means e for applying a driving voltage to the piezo actuator d;
Displacement measuring means f for measuring a displacement ΔL of the piezoelectric actuator when a voltage is applied in the initial pressure load state;
Volume calculating means g for calculating the initial volume V of the hydraulic chamber in the initial pressure load state;
Volume change amount calculating means h for calculating a volume change amount ΔV of the hydraulic chamber based on the displacement ΔL;
There is provided an adjustment length calculation means i for calculating a length correction amount by the shim of the piezo actuator so that the ratio between the calculated hydraulic chamber volume V and the volume change amount ΔV becomes a predetermined reference value.
[0005]
The adjusting device may include a determination unit that determines that the actuator is defective when the ratio between the hydraulic chamber initial volume V and the volume change amount ΔV deviates from a predetermined allowable value.
[0006]
According to a second aspect of the present invention, a hydraulic chamber is defined on one end side of the piezo actuator, and the needle valve is opened and closed based on a change in pressure of the hydraulic chamber when a driving voltage is applied to the piezo actuator. A method for manufacturing a fuel injection valve, comprising:
When assembling a piezo actuator to the fuel injection valve,
At least the dimension L1 of the actuator assembly of the fuel injection valve, the length L0 of the piezoactuator when the hydraulic chamber is loaded with an initial pressure equivalent to that when using the fuel injection valve, and the driving voltage applied to the piezoactuator in the pressure load state Measuring the displacement ΔL of the piezo actuator in a state of applying
Calculating the initial volume V of the hydraulic chamber from the assembly portion dimension L1, the actuator length L0, and the hydraulic chamber cross-sectional area S;
Calculating a volume change amount ΔV of the hydraulic chamber when the actuator is displaced from the displacement ΔL and the hydraulic chamber cross-sectional area S;
Calculating a target length L of the piezoelectric actuator such that a ratio between the initial volume V and the volume change amount ΔV becomes a predetermined reference value;
And calculating the thickness of the shim interposed in the piezo actuator from the difference between the target length L and the actual length L0.
[0007]
The fuel injection valve includes a main body in which a piezo actuator is accommodated and a nozzle that is connected to the tip of the piezo actuator and in which a needle valve is accommodated. A differential pressure chamber as a hydraulic pressure chamber is defined by a piston portion that is slidably fitted into the cylinder portion, and a nozzle is provided at a cylinder portion formed in the nozzle and a needle valve rear end portion. A back pressure chamber is defined by a piston portion that is slidably fitted to the nozzle cylinder portion, and an elastic body that biases the needle valve in a valve closing direction is provided, and the differential pressure chamber and the back pressure chamber are provided. Is configured to open and close the needle valve based on changes in the fuel pressure in the differential pressure chamber and the back pressure chamber that are communicated with each other via a passage and fuel is introduced and the piezoelectric actuator expands and contracts. Can be applied.
[0008]
[Action / Effect]
In the fuel injection valve configured to open and close the needle valve based on the pressure change of the hydraulic chamber when the piezo actuator expands and contracts, the fuel injection characteristic depends on the pressure change Δp, and the injection characteristic varies with different Δp. Become. That is, the desired fuel injection characteristic can be obtained by adjusting the piezo actuator so that Δp becomes a predetermined specified value.
[0009]
The change in pressure Δp of the hydraulic chamber is expressed as follows, where V is the volume of the hydraulic chamber before displacement of the piezo actuator in use and ΔV is the volume change of the hydraulic chamber when the actuator is displaced. Is proportional to the ratio of ΔV.
[0010]
Δp = k · ΔV / V (where k is a constant)
Therefore, as in each of the above-described inventions, ΔV / V is obtained, and the desired fuel injection characteristic can be obtained with certainty by using the shim to correct the actuator length obtained so that it becomes the reference value.
[0011]
Further, when the ratio between the hydraulic chamber volume V and the volume change amount ΔV deviates from a predetermined allowable value, for example, this results in that the target length L0 of the actuator becomes shorter than the actual length L. This is equivalent to the case where the limit of the thickness of the shim for adjustment is exceeded or the result of exceeding the limit of the shim thickness for adjustment. It is possible to know the failure of the actuator before incorporating it into the valve.
[0012]
On the other hand, in the second invention, in the process of actually assembling the fuel injection valve, not only the actual length of the piezoelectric actuator but also the dimension of the assembly portion on the fuel injection valve side is measured to calculate the pressure chamber volume. Therefore, a more accurate adjustment result can be obtained.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, an example of a fuel injection valve to which the present invention can be applied will be described with reference to FIG.
[0014]
In the figure, the fuel injection valve 1 has an actuator 12 accommodated in a cylindrical main body 11, and a nozzle body 14 in which a needle valve 13 is accommodated at the distal end of the main body 11. ing.
[0015]
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.
[0016]
A shim 32 for adjusting the mounting length of the actuator 12 is interposed between the actuator 12 and the piston 18 so as to obtain an appropriate injection characteristic. The main point of the present invention is how to adjust the thickness of the shim 32, which will be described in detail later.
[0017]
A differential pressure chamber 21 as a hydraulic pressure chamber is defined in front of the piston 18 and the cylinder portion 19, and the piston 18 is moved backward by the tension of the disc spring 22 accommodated in the differential pressure chamber 21. Is being energized.
[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 as an elastic body in the back pressure chamber 26 defined behind the piston portion 24, and the needle valve 13 is biased 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 from a fuel system (not shown) is supplied to the fuel chamber 28 through a fuel supply port 29. Is done. Further, the back pressure chamber 26 behind communicates with the differential pressure chamber 21 behind the 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]
Next, the operation of the fuel injection valve 1 when a drive signal is supplied to the actuator 12 will be described. In this fuel injection valve, a signal in the extension direction (for example, a signal voltage of about 400 V) is supplied to the actuator 12 during non-injection. At this time, the actuator 12 extends to keep the volume of the differential pressure chamber 21 small. In this case, the pressure of the fuel supplied to the fuel chamber 28 also acts on the back pressure chamber 26 via the sliding gap between the needle valve piston portion 24 and the cylinder portion 25. The front-rear pressure is balanced, so the needle valve 13 is held closed by the tension of the spring 27.
[0022]
When a contraction direction signal (for example, a signal voltage of 0 V) is supplied from this state, the actuator 12 and the piston portion 18 quickly contract to the initial position, so that the differential pressure chamber 21 expands its volume and decreases the pressure. This pressure drop is immediately transmitted to the back pressure chamber 26 via the passage 30. At this time, since the sliding gap between the needle valve piston portion 24 and the cylinder portion 25 acts as an orifice, the pressure in the back pressure chamber 26 is increased. The pressure change in the fuel chamber 28 is delayed with respect to the decrease, 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 displaced backward against the spring 27, and the nozzle hole 23 is opened to perform fuel injection.
[0023]
When a signal in the expansion direction is supplied 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 chambers 21 and 26, so that the needle valve 13 is closed. Displacement in the direction ends the fuel injection. 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 and the tension of the spring 27.
[0024]
By the way, in such a fuel injection valve, the actuator is caused by the length of the piezo actuator 12 in a state where the fuel pressure is applied to the differential pressure chamber 21, the actuator displacement during driving, the dimensional error of each part of the fuel injection valve, and the like. As described above, the differential pressure generated in the differential pressure chamber 21 at the time of expansion / contraction becomes different, which causes variations in characteristics of individual fuel injection valves.
[0025]
Therefore, in the present invention, the piezo actuator is adjusted during or before incorporation into the fuel injection valve so that the differential pressure (Δp) is constant. Next, a configuration for performing such adjustment will be described.
[0026]
In FIG. 3, reference numeral 12 denotes a piezoelectric actuator to be measured, and reference numeral 40 denotes a measurement mechanism. The measurement mechanism 40 includes a base portion 41 that supports one end portion of the piezo actuator 12, a measurement piston 42 that is provided at the other end portion of the piezo actuator 12, and a measurement cylinder that is provided to face the base portion 41. 43 etc.
[0027]
Specifically, as shown in FIG. 3A, the measurement cylinder 43 is formed with a cylindrical cylinder portion 45 into which the measurement piston 42 is fitted, and the cylinder portion 45 is measured via a seal ring 46. The piston 42 fits oil-tightly and freely in a sliding manner. The inner diameter of the cylinder portion 45 or the outer diameter of the measurement piston 42 is formed to have the same dimensions as the differential pressure chamber 21 of the fuel injection valve, and a hydraulic pressure chamber 47 is defined therebetween. In this case, a disc spring 22 is interposed in the hydraulic pressure chamber 47 in order to make the conditions the same as those of the fuel injection valve of FIG.
[0028]
A pressure measuring hole 48 communicating with the hydraulic pressure chamber 47 is formed in the measuring cylinder 43, and a pressure sensor 49 is oil-tightly fitted in the middle of the measuring hole 48. Further, the measuring cylinder 43 is provided with a displacement sensor 50 as a displacement measuring means downward so as to face a flange portion 42a formed on the outer peripheral portion of the measuring piston 42.
[0029]
In this measuring mechanism, the dimensions of each part are measured in a state in which the pressure during use of the fuel injection valve is loaded on the hydraulic pressure chamber 47. In this case, as described above, the hydraulic pressure chamber 47 has a sealed structure as the pressure load means. In addition, while measuring the pressure in the hydraulic chamber 47 by the pressure sensor 49, the measuring cylinder 43 is pressed toward the base portion 41 through a compression mechanism (not shown) until the pressure becomes a pressure in use. Yes. However, instead of doing this, a means for variably adjusting the hydraulic pressure by a pump or the like is connected to the hydraulic pressure chamber 47 so that the hydraulic pressure can be adjusted to the operating pressure while the measuring cylinder 43 is fixed. Things may be applied.
[0030]
In the fuel injection valve shown in FIG. 2, the operating pressure means that the actuator 12 is contracted from the pressure (design fuel pressure) in the differential pressure chamber 21 when the piezo actuator 12 is extended and the needle valve 13 is closed. This is a value obtained by subtracting the differential pressure (design differential pressure = Δp) generated in the differential pressure chamber 21 when the needle valve 13 is opened.
[0031]
Next, a procedure for determining the thickness of the shim 32 (see FIG. 2) that can obtain a predetermined injection characteristic, that is, the differential pressure Δp, using this measurement mechanism will be described.
[0032]
3A shows a free state in which no pressure is applied to the hydraulic chamber 47, and the actuator 12 at this time has an unloaded length Lf. From this state, the measuring cylinder 43 is pressed as described above, and a pressure during use is applied to the hydraulic pressure chamber 47. The actuator 12 is compressed by the action of this pressure via the measuring piston 42, and its length becomes L0 (see FIG. 3B).
[0033]
In this compressed state, when the drive voltage is not applied to the actuator 12 (initial state), the initial volume V of the hydraulic pressure chamber 47 is set to the position of the measuring cylinder 43, the initial length L0 of the actuator 12, and the known hydraulic pressure chamber cutoff. It is calculated from the area S and the like.
[0034]
Next, a drive voltage (400 V) is applied to the actuator 12 while the position of the measurement cylinder 43 is fixed. By applying this drive voltage, the actuator 12 expands to a length L400 (see (c) of FIG. 3). The difference between the lengths L400 and L0 is the displacement ΔL. In this case, the displacement ΔL is directly detected by the displacement sensor 50.
[0035]
The volume change amount ΔV of the hydraulic chamber 47 is calculated by multiplying the detected hydraulic chamber cross-sectional area S by ΔL detected in this way, and the ratio ΔV / V between this and the initial volume V is obtained. Since the ratio ΔV / V correlates with the differential pressure Δp generated in the hydraulic pressure chamber (differential pressure chamber 21) of the fuel injection valve as described above, the reference determined based on the design values of the ratio ΔV / V and Δp. When there is a deviation from the reference value, the actuator 12 is subjected to length correction so that the hydraulic chamber volume V changes in a direction to compensate for the deviation. It is done. That is, this correction length is the thickness of the shim 32 to be applied to the actuator 12.
[0036]
If the correction amount (thickness of the shim) obtained in this way becomes negative, or a condition that exceeds the adjustment limit by the shim can be determined from the value of the ratio ΔV / V. Thus, the defect can be found before the actuator 12 is actually incorporated into the fuel injection valve.
[0037]
Next, a fuel injection valve manufacturing method in which the injection characteristics of the piezo actuator 12 are appropriately set during the assembly process based on the same method as described above will be described with reference to the flowchart shown in FIG.
[0038]
In this manufacturing method, first, the dimension L1 (see FIG. 2) of the actuator assembly portion of the fuel injection valve is measured. The dimensions of each part of the injection valve, such as the outer diameter (hydraulic pressure chamber cross-sectional area) and thickness of the piston 18 and the thickness of the end plate 15, are known, but more accurate adjustment can be performed by measuring these dimensions.
[0039]
Next, the length L0 when the actuator 12 is loaded with the pressure during use, the length L400 when the drive voltage is applied, or the displacement ΔL are measured. This is measured in advance using a measuring apparatus as shown in FIG. 3 or measured in the same manner as in the case of the apparatus with the actuator 12 incorporated in the injection valve body 11.
[0040]
Next, the initial volume V of the hydraulic chamber is determined from the assembly portion dimension L1, the actuator length L0, the hydraulic chamber sectional area S, and the hydraulic chamber when the actuator is displaced from the displacement ΔL and the hydraulic chamber sectional area S. Is calculated.
[0041]
The subsequent steps are the same as those described with reference to FIG. 3, and the length correction amount of the piezo actuator, that is, the thickness of the shim so that the ratio ΔV / V between the initial volume V and the volume change amount ΔV becomes a predetermined reference value. A fuel injection valve that exhibits appropriate injection characteristics is obtained by interposing the shim 32 having the thickness between the actuator 12 and the piston portion 18.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a first invention.
FIG. 2 is a cross-sectional view showing an embodiment of a fuel injection valve to which the present invention can be applied.
FIG. 3 is a schematic configuration diagram showing an embodiment of an adjusting mechanism of the present invention.
FIG. 4 is a flowchart showing an embodiment of the second invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fuel injection valve 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 Differential pressure chamber 22 Belleville spring 23 Injection hole 24 Piston part 25 Cylinder part 26 Back pressure chamber 27 Coil spring 28 Fuel chamber 29 Fuel supply port 30 Passage 31 Fuel passage 32 Shim 40 Measuring mechanism 41 Base portion 42 Measuring piston 43 Measuring cylinder 45 Cylinder portion 46 Seal ring 47 Hydraulic chamber 48 Pressure measuring hole 49 Pressure sensor 50 Displacement sensor

Claims (4)

A fuel injection valve adjusting device that defines a hydraulic pressure chamber at one end of a piezoelectric actuator and opens and closes a needle valve based on a pressure change in the hydraulic pressure chamber when a drive voltage is applied to the piezoelectric actuator Because
A measurement mechanism having a hydraulic chamber of the same dimensions as the fuel injection valve;
Pressure loading means for loading the hydraulic pressure chamber with an initial pressure equivalent to when a fuel injection valve is used;
Voltage applying means for applying a driving voltage to the piezoelectric actuator;
A displacement measuring means for measuring a displacement ΔL of the piezoelectric actuator when a voltage is applied in the initial pressure load state;
Volume calculating means for calculating the initial volume V of the hydraulic chamber in the initial pressure load state;
Volume change amount calculating means for calculating a volume change amount ΔV of the hydraulic chamber based on the displacement ΔL;
Adjustment length calculating means for calculating a length correction amount by a shim of the piezo actuator so that a ratio between the calculated hydraulic chamber volume V and the volume change amount ΔV becomes a predetermined reference value. Adjustment device for fuel injection valve. 2. The fuel injection valve adjusting device according to claim 1, further comprising a determination unit that determines that the actuator is defective when the ratio between the hydraulic chamber volume V and the volume change amount ΔV deviates from a predetermined allowable value. 3. . A method of manufacturing a fuel injection valve in which a hydraulic chamber is defined at one end of a piezoelectric actuator, and a needle valve is opened and closed based on a change in pressure of the hydraulic chamber when a driving voltage is applied to the piezoelectric actuator. Because
When assembling a piezo actuator to the fuel injection valve,
At least the dimension L1 of the actuator assembly of the fuel injection valve, the length L0 of the piezoactuator when the hydraulic chamber is loaded with an initial pressure equivalent to that when using the fuel injection valve, and the driving voltage applied to the piezoactuator in the pressure load state Measuring the displacement ΔL of the piezo actuator in a state of applying
Calculating the initial volume V of the hydraulic chamber from the assembly portion dimension L1, the actuator length L0, and the hydraulic chamber cross-sectional area S;
Calculating a volume change amount ΔV of the hydraulic chamber when the actuator is displaced from the displacement ΔL and the hydraulic chamber cross-sectional area S;
Calculating a target length L of the piezoelectric actuator such that a ratio between the initial volume V and the volume change amount ΔV becomes a predetermined reference value;
And a step of calculating a thickness of a shim interposed in the piezo actuator from a difference between the target length L and the actual length L0. The fuel injection valve is composed of a main body in which a piezo actuator is accommodated and a nozzle which is connected to the tip of the piezo actuator and in which a needle valve is accommodated. A differential pressure chamber as a hydraulic pressure chamber is defined by a piston portion slidably fitted in the cylinder portion, and the nozzle is provided at a cylinder portion formed in the nozzle and a needle valve rear end portion. A back pressure chamber is defined by a piston portion that is slidably fitted into the nozzle cylinder portion, and an elastic body that biases the needle valve in the valve closing direction is provided. The differential pressure chamber and the back pressure chamber are It is configured that the needle valve is driven to open and close based on a change in fuel pressure in the differential pressure chamber and the back pressure chamber due to expansion and contraction of the piezo actuator, while being communicated with each other through a passage. The fuel injection according to claim 3 The method of production.

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