JP2002155789A - Piezo actuator drive circuit and fuel injection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine an electrostatic capacity of a piezo-stack at a high accuracy without using an energization inductor to the piezo-stack and receiving an influence of an internal inductance of the piezo-stack in a piezo-actuator driving circuit. SOLUTION: An A. C. Voltage is applied to a piezo-stack 3A from an A.C. power source 19 at a frequency of several points and a CPU 22 operates an electrostatic capacity of the piezo-stack 3A based on a frequency characteristic of a piezo-stack current flowing in the piezo-stack 3A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezo actuator drive circuit and a fuel injection device.

[0002]

2. Description of the Related Art A piezo actuator utilizes the piezoelectric action of a piezoelectric material such as PZT. A piezo stack, which is a capacitive element, expands or contracts by charging and discharging to generate a pressing force to operate a piston or the like. For example, a fuel injection device for an internal combustion engine is known in which a piezo actuator is used to switch between opening and closing a fuel injector.

A piezo stack has a structure in which ceramic layers and electrode layers are alternately stacked, and is electrically equivalent to a ceramic capacitor. Generally, the capacitance of a capacitive element including a piezo stack greatly increases as the temperature rises.
FIG. 8 shows a temperature characteristic of a piezo stack mounted on the injector, and shows a large temperature dependence in which the capacitance increases by 200% at around 120 ° C. with respect to the capacitance at 20 ° C. . For this reason, the charging speed fluctuates, the valve opening timing of the injector fluctuates in response to the fuel injection command, and the adjustment accuracy of the injection amount is not always sufficient. The supply energy E is E = (1/2) CV
² (= (１ ／) Q ² / C) and includes the capacitance C as a parameter, the voltage V across the piezo stack
Even if the charge amount Q is accurately controlled, the supply energy E may fluctuate, and the valve opening operation of the injector may become unstable, or the excessive charge amount may cause the valve portion to be worn.

[0004] In Japanese Patent No. 2773585, a DC power supply is used.
That have an inductor in the current path to the piezo stack.
In the piezoelectric actuator drive circuit, the energization path is
DC voltage lower than the voltage for driving the piezo stack using
Transient to the current path by applying
Time T0 until the current flows and shifts to the equilibrium state
Measure the inductance of the inductor as L0
T0 = (L0 * Cp) ^1/2To find the capacitance Cp
You.

[0005]

However, the technique disclosed in Japanese Patent No. 2773585 uses a current limiting inductor in the middle of an energizing path, and it is assumed that the inductance L0 always takes a constant value. The capacitance Cp is calculated. Further, the internal inductance of the piezo stack is not considered. For this reason, if the demand for high precision for the fuel injection control is further increased, it cannot always be said that it is sufficient.

The present invention has been made in view of the above circumstances,
An object of the present invention is to provide a piezo actuator drive circuit and a fuel injection device that can accurately determine the capacitance of a piezo stack and reflect the result to control the piezo stack.

[0007]

According to the first aspect of the present invention, in a piezo actuator drive circuit that switches between charging and discharging of a piezo stack and controls expansion and contraction of the piezo stack, an AC voltage is applied to the piezo stack. A power supply means for applying a current having a predetermined size that does not expand and contract so as to sweep the frequency, and flowing a current for measurement to the piezo stack, and a static electricity of the piezo stack based on a plurality of the currents for measurement having different applied frequencies. And a calculating means for calculating the capacity.

The equivalent circuit of the piezo stack includes an inductance component in addition to a capacitance component, and is a series circuit of these components. The frequency characteristics of the piezo stack are defined by the values of these components. Therefore, the capacitance can be calculated from a plurality of current values having different applied frequencies irrespective of the inductance component. In addition, since no inductor outside the piezo stack is used, there is no calculation error. Thereby, the piezo actuator can be appropriately controlled.

According to a second aspect of the present invention, in the piezo actuator driving circuit for controlling the expansion and contraction of the piezo stack by switching between charging and discharging of the piezo stack, the piezo stack is set to a predetermined current value at which the piezo stack does not expand and contract. A power supply unit for flowing a current and a calculation unit for calculating a capacitance of the piezo stack based on a voltage between both ends of the piezo stack before and after a predetermined time elapses are provided.

The equivalent circuit of the piezo stack includes an inductance component in addition to a capacitance component, and is a series circuit of these components. When a constant current is passed through the piezo stack, the induced electromotive force due to the inductance component becomes zero, and the voltage between both ends of the piezo stack changes linearly at a speed inversely proportional to the magnitude of the capacitance component. Therefore, the capacitance can be calculated regardless of the inductance component of the piezo stack. In addition, since no inductor outside the piezo stack is used, there is no calculation error. Thereby, the piezo actuator can be appropriately controlled.

According to a third aspect of the present invention, in the configuration of the first or second aspect of the invention, the calculating means is set so as to calculate the internal resistance of the piezo stack together with the capacitance.

In the case of the configuration of the first aspect of the present invention, since the resistance component constituting the equivalent circuit of the piezo stack also defines the frequency characteristic, the internal resistance of the piezo stack can also be calculated. The actuator can be more appropriately controlled.

Further, in the case of the configuration according to the second aspect of the present invention, since the voltage between both ends of the piezo stack has a voltage drop due to a resistance component as an offset amount, the internal resistance of the piezo stack can also be calculated. Thus, the piezo actuator can be more appropriately controlled.

According to a fourth aspect of the present invention, there is provided an injector having a fuel injection nozzle having a nozzle portion for fuel injection and outputting, by a piezo actuator, a pressing force for operating a valve element for switching between fuel injection and stop. And a driving circuit for driving the piezo actuator according to any one of claims 1 to 3. Further, according to the fifth aspect of the present invention, a configuration is provided in which a correction means is provided for correcting a fuel injection parameter calculated according to an operating state of the engine.

The capacitance and internal resistance of the piezo stack are
Even if there is variation or fluctuation, it is possible to know accurately, so that highly accurate fuel injection can be performed. In addition, since the fuel injection parameter calculated according to the operating state of the engine can be properly corrected in the fuel injection control of the injector, accurate fuel injection according to the operating state can be performed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 shows the configuration of a piezo actuator drive circuit according to the present invention. The piezo actuator drive circuit is applied to a control device of a fuel injection device of a common rail type four-cylinder diesel engine, and the overall configuration of the fuel injection device will be described later. Piezo actuator drive circuit 1 as the control device
Is a DC-DC converter 111 that generates a DC voltage of several tens to several hundreds of volts by power supply (+ B) from a vehicle-mounted battery, and a buffer capacitor 112 connected in parallel to its output terminal.
Constitutes a DC power supply 11 and the piezo stacks 3A, 3A.
Outputs charging voltages for B, 3C, and 3D. DC-DC
The converter 111 is a general step-down chopper type circuit.
When the switching element 1112 is turned on, the inductor 111
1 to store the energy in the switching element 1112
From the inductor 1111 that generates a back electromotive force when the buffer capacitor 112 is turned off via the diode 1113
Is charged. The buffer capacitor 112 is formed of a capacitor having a relatively large capacitance to some extent.
A substantially constant voltage value is maintained even when the 3D charging operation is performed.

The buffer capacitor 112 of the DC power supply 11
A first power supply path 12a for supplying power to the piezo stacks 3A to 3D via the inductor 13 is provided in the power supply path 12a between the buffer capacitor 112 and the inductor 13 in series with the first switching element 14a.
Is interposed. The first switching element 14a has M
The parasitic diode (hereinafter, referred to as a first parasitic diode) 141 a is constituted by an OSFET and is connected so as to be reversely biased with respect to a voltage between both ends of the buffer capacitor 112. Further, the inductor 13 and the piezo stacks 3A to 3D form a second energization path 12b. This energization path 12b has a second switching element 14b connected to a connection midpoint between inductor 13 and first switching element 14a, and includes inductor 13, piezo stacks 3A to 3D, and second switching element 14b. A closed circuit is formed. Second switching element 14
b is also formed of a MOSFET, and its parasitic diode (hereinafter, referred to as a second parasitic diode) 141b is connected so as to be reverse-biased with respect to the voltage between both ends of the buffer capacitor 112.

The energization paths 12a and 12b are common to the piezo stacks 3A to 3D, and the piezo stacks 3A to 3D to be driven can be selected as follows. Each of the piezo stacks 3A to 3D is connected in series with a switching element (hereinafter, appropriately referred to as a selective switching element) 15A, 15B, 15C, 15D, 15E, 15
F, and the first type of selection switching elements 15A to 15D are connected to the piezo stack 3 respectively.
A to 3D are connected in one-to-one correspondence, and the selection switching elements 15A to 15D corresponding to the pie stacks 3A to 3D of the injectors of the injection cylinders are turned on.

In the second type of selective switching elements 15E and 15F, the selective switching element 15E is common to the piezo stack 3A and the piezo stack 3B.
The selection switching element 15F is commonly connected to the piezo stack 3C and the piezo stack 3D. The second type of selection switching elements 15E and 15F are two piezo stacks including the piezo stacks 3A to 3D even if the selection switching elements 15A to 15D cause an uncontrollable state in any of the piezo stacks 3A to 3D. 3A to 3D are separated from the piezo actuator drive circuit 1 to ensure the operation of the remaining two piezo stacks 3A to 3D (limp form).

Each of the selective switching elements 15A to 15F uses a MOSFET, and its parasitic diode (hereinafter, referred to as a selective parasitic diode) 151A, 151
B, 151C, 151D, 151E, and 151F are connected to the buffer capacitor 112 so as to be reverse biased.

The piezo stack 3A and the piezo stack 3B have a switching element 16 for switching measurement.
Via E, piezo stack 3C and piezo stack 3D
In this configuration, a voltage is applied from an AC power supply 19 serving as a power supply unit via a switching element 16F for measurement switching. The AC power supply 19 is a power supply such as a voltage controlled oscillator (VCO) having a variable application frequency. The amplitude of the output of the AC power supply 19 is
The voltage value is set to an extremely small voltage value, for example, about 1 V as compared with several tens of volts which is an applied voltage at the time of 3D expansion / contraction driving. Accordingly, the piezo stacks 3A to 3D do not expand and contract due to voltage application, and operate with the same electrical characteristics as during expansion and contraction even with an alternating current in which a voltage is applied in a phase opposite to that during expansion and contraction.

The piezo stacks 3A to 3D are mounted on each of the injectors 4 for switching between fuel injection and stop of the injectors 4 (FIGS. 2 and 3) provided in each cylinder, as described later.

Switching elements 14a, 14b, 15A
A control signal is input from the controller 21 to each of the gates to 15F, 16E, and 16F, and as described above, one of the selection switching elements 15A to 15D is turned on to select the piezo stack 3A to 3D to be driven. At the same time, a pulse-like control signal is input to the gates of the switching elements 14a and 14b and the switching element 1
4a and 14b are turned on and off, and the piezo stacks 3A to 3D
, And charge control and discharge control.

A relatively low-resistance resistor 17E is commonly connected in series to the piezo tact 3A and the piezo tact 3B.
However, the same resistor 17F as the resistor 17E is provided in series for the piezo tact 3C and the piezo tact 3D. The voltage between both ends is inputted to the controller 21, and the charging current of the piezo stacks 3A to 3D is detected.

A resistor 18 having a relatively low resistance is provided in series with the second switching element 14b. The voltage between both ends is inputted to the controller 21, and the discharge current of the piezo stacks 3A to 3D is detected.

Further, both ends of the piezo stacks 3A to 3D (hereinafter referred to as piezo stack voltages) are inputted to the controller 21 and detected.

At the time of charge control, the controller 21 sets the ON period and the OFF period of the first switching element 14a as follows, and outputs a control signal for the first switching element 14a. That is, the first switching element 14a is turned on, and a gradually increasing charging current flows through the first current path 12a. When the charging current reaches a preset current value, the switching element 14a is turned off and an off period starts. At this time, since the back electromotive force generated in the inductor 13 is forward-biased with respect to the second parasitic diode 141b, a flywheel current that gradually decreases in the second conduction path 12b flows due to the energy accumulated in the inductor 13, The charging of the piezo stacks 3A to 3D proceeds. When the charging current becomes 0, the first switching element 14a is turned on again to enter an ON period, and this is repeated (multiple switching method). When the piezo stack voltage reaches a preset voltage, the switching element 14a is fixed to OFF, and the charging is completed.

During the discharge control, the ON period and the OFF period of the second switching element 14b are set as follows, and a control signal for the second switching element 14b is output. That is, the second switching element 14b is turned on, and a gradually increasing discharge current flows through the second conduction path 12b. When the discharge current reaches a preset current value, the switching element 14b is turned off and an off period starts. At this time, a large back electromotive force is generated in the inductor 13, and the flywheel current is caused to flow through the first current path 12 a by the energy stored in the inductor 13, and the energy is recovered by the buffer capacitor 112. When the discharge current becomes 0, the second switching element 14b is turned on again, and this is repeated. When the piezo stack voltage reaches 0, the switching element 14b is fixed to off, and the discharge is completed.

The controller 21 receives an injection signal from a CPU 21 which controls the entire fuel injection control, which will be described later, and thereby performs charge control and discharge control. The injection signal is a binary signal consisting of “L” and “H” corresponding to the injection period, and the piezo stack 3A
3D is started, and the piezo stacks 3A to 3D are discharged at the fall of the injection signal.

Further, the controller 21 activates the AC power supply 19 in response to a command from the CPU 21, and the piezo stack 3
The application frequency to A to 3D is set to a predetermined frequency, and the current detected by the resistors 17E and 17F at that time (hereinafter, referred to as a piezo stack current) is taken in. The applied frequency can be set within a predetermined range by changing a control signal to the AC power supply 19.

FIG. 2 shows the configuration of a common rail type fuel injection device for a diesel engine having a fuel injector 4 on which the piezo stacks 3A to 3D are mounted, and FIG. 3 shows the structure of the injector 4. . In the example shown, the piezo stack 3A is mounted, but the injectors on which the piezo stacks 3B to 3D are mounted have the same structure. The number of injectors 4 corresponding to the number of cylinders of the diesel engine is provided for each cylinder (only one injector 4 is shown in the figure), and fuel is supplied from a common common rail 54 that communicates via a supply line 55. Fuel is injected from the injector 4 into the combustion chamber of each cylinder at an injection pressure substantially equal to the fuel pressure in the common rail 54 (hereinafter, common rail pressure). Common rail 5
4 is a high-pressure supply pump 53
And stored at high pressure.

The fuel supplied from the common rail 54 to the injector 4 is used not only for injection into the combustion chamber, but also as a control oil pressure for the injector 4 and the like, and is supplied from the injector 4 through a low-pressure drain line 56 to a fuel tank. Reflux to 51.

The pressure sensor 57 is provided on the common rail 54 and detects the common rail pressure. Based on the detection result, the CPU 21 controls the metering valve 52 to adjust the amount of fuel pressure fed to the common rail 54, and Is controlled so as to have an appropriate injection pressure according to operating conditions known from other sensor inputs or the like.

As shown in FIG. 3, the injector 4 is a rod-shaped body, and is attached so that the lower part in the figure penetrates a combustion chamber wall (not shown) of the engine and projects into the combustion chamber. The injector 4 includes a nozzle unit 4a, a back pressure control unit 4b, and a piezo actuator 4c in this order from the bottom.

The needle 4 is provided in the main body 404 of the nozzle portion 4a.
21 is slidably held at its rear end, and the needle 421 sits on or separates from an annular seat 4041 formed at the tip of the nozzle body 404. Needle 42
High-pressure fuel is introduced from the common rail 54 into the outer peripheral space 405 at the distal end of the first through the high-pressure passage 401, and fuel is injected from the injection hole 403 when the needle 421 is unseated. The fuel pressure from the high-pressure passage 401 acts on the annular step surface 4211 of the needle 421 in the lift direction (upward).

The high pressure passage 401 is located behind the needle 421.
A fuel as a control oil is introduced from the through an in-orifice 407 to form a back pressure chamber 406 for generating a back pressure of the needle 421. This back pressure acts on the rear end surface 4212 of the needle 421 in the seating direction (downward) together with the spring 422 provided in the back pressure chamber 406.

The back pressure is switched by a back pressure control unit 4b, and the back pressure control unit 4b is driven by a piezo actuator 4c having the piezo stack 2A. The injector having the piezo stacks 2B to 2D has the same structure.

The back pressure chamber 406 has an out orifice 40
9 and is always in communication with the valve chamber 410 of the back pressure control unit 4b. The valve chamber 410 has a ceiling surface 4101 formed in an upwardly conical shape, and the top of the ceiling surface 4101 has a low-pressure chamber 4101.
Connected to 11. The low pressure chamber 411 communicates with a low pressure passage 402 communicating with the drain line 56.

The bottom surface 4102 of the valve chamber 410 has a high pressure passage 4
A high pressure control passage 408 branching from 01 is open.

A ball 423 having a lower portion cut horizontally is disposed in the valve chamber 410. The ball 423 is a valve body that can move up and down. When the ball 423 descends, the cut surface serves as a valve seat bottom (hereinafter, referred to as a high pressure side seat) 4 as a valve seat.
102, the valve chamber 410 is cut off from the high-pressure control passage 408, and when ascending, the valve chamber 410 is seated on the above-mentioned ceiling surface (hereinafter, referred to as a low-pressure side seat) 4101 to shut off the valve chamber 410 from the low-pressure chamber 411. As a result, when the ball 423 descends, the back pressure chamber 410 moves out of the orifice 409 and the valve chamber 4
The pressure is communicated with the low-pressure chamber 411 via 10, the back pressure of the needle 421 is reduced, and the needle 421 is separated. On the other hand, when the ball 423 rises, the back pressure chamber 406 is cut off from the low pressure chamber 411 and communicates only with the high pressure passage 401, so that the back pressure of the needle 421 rises and the needle 421 is seated.

The ball 423 is a piezo actuator 4c.
Is pressed and driven. The piezo actuator 4c is
A vertical hole 412 formed vertically above the low-pressure chamber 411.
Two pistons 424 and 425 having different diameters are slidably held, and a piezo stack 3A is disposed above the large-diameter piston 425 on the upper side with the vertical direction extending and contracting.

The large-diameter piston 425 is kept in contact with the piezo stack 3A by a spring 426 provided below the large-diameter piston 425, so that the large-diameter piston 425 is vertically displaced by the same amount as the amount of expansion and contraction of the piezo stack 3A.

The space defined by the lower small-diameter piston 424, the large-diameter piston 425, and the vertical hole 412 facing the ball 423 is filled with fuel to form a displacement expansion chamber 413, which extends the piezo stack 3A. Large piston 4
When the fuel is moved downward and presses the fuel in the displacement expansion chamber 413, the pressing force is transmitted to the small-diameter piston 424 via the fuel in the displacement expansion chamber 413. Here, small diameter piston 4
24 has a smaller diameter than the large-diameter piston 425,
The amount of extension of the piezo stack 3A is expanded and converted into displacement of the small-diameter piston 424.

At the time of fuel injection, first, the piezo stack 3
When A is charged and the piezo stack 3A expands, the small-diameter piston 424 descends and pushes down the ball 423. As a result, the ball 423 moves to the low pressure side
1 and seats on the high-pressure side seat 4102 and the back pressure chamber 406 communicates with the low pressure passage 402, so that the fuel pressure in the back pressure chamber 406 decreases. Thereby, the needle 4
The force acting on the seat 21 in the unseating direction is more dominant than the force acting in the seating direction, the needle 421 is unseated, and fuel injection is started.

On the other hand, when the injection is stopped, the piezo stack 3A is contracted by the discharge of the piezo stack 3A to release the pushing force to the ball 423. At this time, the inside of the valve chamber 410 is at a low pressure, and the high pressure fuel pressure acts on the bottom surface of the ball 423 from the high pressure control passage 408, so that the upward fuel pressure acts on the ball 423 as a whole. are doing. The release of the pressing force on the ball 423 releases the ball 423 from the high-pressure side seat 4102 and again seats on the low-pressure side seat 4101 to cause the valve chamber 4
Since the fuel pressure at 10 rises, the needle 421 is seated and injection stops.

In the fuel injection device of the present invention, in the fuel injection control by the CPU 22, high-precision fuel injection can be realized by reflecting the fluctuation of the capacitance of the piezo stacks 3A to 3D. The control will be described. FIG. 4 is a flowchart showing the details of the fuel injection control. In step S101, the piezo stacks 3A to
It is determined whether it is necessary to calculate a 3D capacitance or the like. The capacitance calculation request may be generated, for example, every time a predetermined time elapses, or may be generated depending on the operating state of the vehicle, such as when an ignition switch is turned on.

If it is necessary to calculate the capacitance or the like, a command signal is output to the controller 21 in step S102, and the controller 21 is operated as follows. The measurement switching elements 16E and 16F corresponding to the piezo stacks 3A to 3D to be measured and the selection switching elements 15A to 15D corresponding to 3A to 3D are turned on. Then, measurement voltages are sequentially applied to the piezo stacks 3A to 3D from the AC power supply 19 at several frequencies within a predetermined range. Each time a voltage having a different frequency is applied, the controller 21 takes in the piezo stack current with the resistor 17E or 17F.

FIG. 5 shows an equivalent circuit of the piezo stacks 3A to 3D. At this time, the behavior of the piezo stack current I follows the following equation (1), where V is the piezo stack voltage and Z is the impedance. Where C is the capacitance and Rs
Is an internal resistance, and Ls is an internal inductance.
Ω = 2πf where f is the output frequency of the AC power supply 19
It is.

V = | Z | × I = ｛(Rs) ² + (ωLs−1 / ωC) ² ｝ ^1/2 × I (1)

Since the magnitude of the piezo stack current I peaks at the resonance frequency f0 (= (Ls × C) ^1/2 / 2π) as shown in FIG. 6, the piezo stack current I taken in at several frequencies is obtained. Is stored as the piezo stack current I at resonance and the resonance frequency f0. At this time, equation (2) holds. V = Rs × I (2)

Next, the piezo stack current I is detected at a frequency fL sufficiently lower than the resonance frequency f0,
Remember. At this time, equation (3) holds. V ≒ ｛(Rs) ² + (1 / 2πfLC) ² ｝ ^1/2 × I (3)

The piezo stack 3 is supplied from the AC power supply 19.
A to 3D applied to the piezo stacks 3A to 3D have an internal resistance Rs and an internal inductance L.
The range of the temperature fluctuation of the capacitance C is experimentally estimated in advance in consideration of s, and the resonance frequency f0 can be specified with a certain degree of accuracy in such temperature fluctuation, and the resonance frequency f0 is sufficiently determined from the resonance frequency f0. Set so that the lower frequency is given. Therefore, several points including the fluctuation range of the resonance frequency f0 and one point lower than the resonance frequency f0 are set.

In step S103, the capacitance C and the internal resistance Rs are obtained from the relationship between (2) and (3) based on the piezo stack current value taken in. This is stored until there is a next measurement request (step S101) and the data is updated. Then, the process proceeds to step S104. In addition,
If it is not necessary to calculate the capacitance C or the like in step S101, steps S102 and S103 are skipped.

In step S104, fuel injection parameters such as a basic injection timing and a basic injection amount are calculated based on the accelerator opening, the engine speed, and the like.

In step S105, the piezo stacks 3A to 3A are determined based on the capacitance C and the internal resistance Rs.
A correction value of a fuel injection parameter such as an injection timing and an injection amount due to the variation of the capacitance C and the internal resistance Rs of D is obtained.

An example of the correction of the fuel injection parameter will be described. The injection signal output from the CPU 22 to the controller 21 defines the charging timing of the piezo stacks 3A to 3D at the time of fuel injection at the beginning and the discharging timing at the end. Changes to affect the response of the lift operation of the ball 423 to the back pressure chamber 40.
The timing at which the pressure of No. 6 reaches the pressure at which the needle 421 can open the valve comes before or after. On the other hand, for example, when the peak value of the charging current is controlled to be constant by the multiple switching method as in the present embodiment, the energy supply speed to the piezo stacks 3A to 3D decreases as the capacitance C increases. This is because the piezo stack voltage, which is the energy supplied to the piezo stacks 3A to 3D by the unit charge, decreases. Therefore, the correction is made so that the output timing of the injection signal is advanced as the capacitance C is larger.

Further, since the internal resistance Rs is correspondingly lost, the speed of supplying energy to the piezo stacks 3A to 3D is reduced. The correction is made so that the output timing of the injection signal is advanced as the internal resistance Rs is larger.

In step S106, a correction value of the fuel injection parameter is obtained based on other conditions such as the fuel temperature.

Then, a final fuel injection parameter is calculated based on the correction values obtained in steps S105 and S106 (step S107), an injection signal is output to the controller 21 based on the fuel injection parameter, and fuel injection is executed. Is performed (step S108).

According to the piezo actuator drive circuit 1, the electrostatic capacity of the piezo stacks 3A to 3D is reduced without using the inductor 13 and without being affected by the inductance of the inductor 13 or the internal inductance Ls of the piezo stacks 3A to 3D. Capacitance C and internal resistance Rs
Is obtained, the correction by these is properly performed, and highly accurate fuel injection can be realized.

The current is detected by the resistor 1 for charge control.
Although the configuration is simplified by using 7E and 17F,
A resistor dedicated for measuring capacitance or the like may be connected in series to the AC power supply 19 to form a measurement circuit together with the piezo stacks 3A to 3D only when measuring capacitance or the like.

At a predetermined frequency fH which is higher than the resonance frequency f0, the piezo stack current I
Is detected, the equation (4) is obtained, so that the internal inductance Ls is obtained. Therefore, the piezo stack 3A is formed by the resonance action of the inductor 13 and the piezo stacks 3A to 3D.
In the case of a resonance type charging circuit that charges .about.3D, more accurate injection control can be realized by correcting the internal inductance Ls as well. V ≒ ｛(Rs) ² + (2πfH Ls) ² ｝ ^1/2 × I (4)

Further, in the present embodiment, the calculation load is reduced by calculating based on the current value at the resonance point and the frequency range distant from the resonance point. However, the piezo stack current is detected under a plurality of frequencies to obtain the equation. The capacitance C based on (1),
Of course, the internal resistance Rs and the like may be calculated.

(Second Embodiment) FIG. 7 shows a piezo actuator driving circuit according to another embodiment of the present invention. First
In the configuration of the embodiment, the power supply means is replaced with another configuration. In the figure, portions that operate substantially the same as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment. The following description focuses on the differences from the embodiment.

The piezo actuator drive circuit 1A
The piezo stacks 3A to 3D are provided with a constant current power supply 19A which is a power supply unit for supplying a constant current to the piezo stacks 3A to 3D. The controller 21A is basically the same as that of the first embodiment, and performs charge control and discharge control based on the injection signal. Also, CP
The constant current power supply 19A is operated by a command from the U22A to supply a constant current to the piezo stacks 3A to 3D, and the detection signal of the piezo stack voltage at the start of energization and after a lapse of a predetermined time is held. The signal that defines the predetermined time is given as, for example, a rectangular wave whose length is set to the predetermined time from the CPU 22A.

The CPU 22A determines the capacitance C and the internal resistance R based on the two piezo stack voltage detection signals.
get s. That is, the piezo stacks 3A to 3D to be measured are charged by the operation of the constant current power supply 19A for the predetermined time, and the piezo stack voltage is increased from 0V. On the other hand, the piezo stack voltage Vi at the start of the predetermined time and the piezo stack voltage Vf at the end of the predetermined time are fetched. The calculation is performed as follows based on the piezo stack voltage Vf. In the equation, ΔT is a predetermined time.

Assuming that the piezo stack current is i and the piezo stack voltage is V within the predetermined time, the following equation (5) is obtained.
Holds. V = Ls × di / dt + Rs × i + (1 / C) × ∫idt (5)

Since i = constant, di / dt = 0, ∫
Since idt = i × t, and focusing on the beginning and end of the predetermined time, the equations (6-1) and (6-2) are obtained.

Vi = Rs × i (6-1) Vf = Rs × i + (1 / C) × i × ΔT (6-2)

From these two equations, the capacitance C and the internal resistance Rs of the piezo stacks 3A to 3D are calculated.

Also in this embodiment, the capacitance C and the internal resistance Rs can be accurately obtained regardless of the internal inductance of the inductor 13 and the piezo stacks 3A to 3D.
In addition, a constant current is applied to the piezo stacks 3A to 3D for 2
Since it is only necessary to take in the piezo stack voltage V twice, the calculation load is light.

In each of the above embodiments, the internal resistance Rs is also determined to realize extremely high-precision fuel injection. However, since the internal resistance Rs has a small temperature variation compared to the capacitance C, it can be easily obtained. The correction for the internal resistance Rs may be omitted.

In the case where the amount of charge of the piezo stack is specified by the piezo stack voltage as in the present embodiment or the amount of charge is specified, the supplied energy varies greatly depending on the capacitance. It is also possible to correct the final piezo stack voltage and the charge amount reached by charging according to the calculated capacitance so that As a result, the supplied energy is properly adjusted,
Wear of the ball 423 and the high-pressure side seat 4102 can be prevented.

Although the present invention has been described with reference to a configuration in which the piezo stack outputs the pressing force of the ball for increasing or decreasing the back pressure of the needle, the present invention is not necessarily limited to this configuration. The present invention can also be applied to a configuration that drives a needle. Further, the present invention can be applied not only to a fuel injection device of an internal combustion engine but also to another device having a piezo actuator.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first piezo actuator drive circuit to which the present invention is applied.

FIG. 2 is a configuration diagram of a fuel injection device for an internal combustion engine having a fuel injector equipped with a piezo actuator driven by the piezo actuator drive circuit.

FIG. 3 is a sectional view of the injector.

FIG. 4 is a flowchart showing a procedure for setting a fuel injection parameter in the piezo actuator drive circuit.

FIG. 5 is an equivalent circuit diagram of a piezo stack mounted on the injector.

FIG. 6 is a diagram showing a frequency characteristic of a piezo stack current at the time of measuring a capacitance or the like of the piezo actuator drive circuit.

FIG. 7 is a circuit diagram of a second piezo actuator drive circuit to which the present invention is applied.

FIG. 8 is a graph showing the temperature dependence of the capacitance of the piezo stack.

[Explanation of symbols]

1, 1A Piezo actuator drive circuit 11 DC power supply 111 DC-DC converter 112 Buffer capacitor 12a, 12b Current supply path 13 Inductor 14a First switching element 141a Parasitic diode 14b Second switching element 141b Parasitic diode 15A, 15B, 15C, 15D Selection switching element 15E, 15F Selection switching element 16E, 16F Measurement switching element 17E, 17F Resistor 18 Resistor 19 AC power supply (power supply means) 19A Constant current power supply (power supply means) 21, 21A Controller 22, 22A CPU (calculation means) 3A, 3B, 3C, 3D Piezo stack 4 Injector 4a Nozzle unit 4b Back pressure control unit 4c Piezo actuator 423 Ball (valve element)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 41/09 H01L 41/08 P // F02M 51/06 U

Claims (5)

[Claims] In a piezo actuator drive circuit for controlling the expansion and contraction of a piezo stack by switching between charging and discharging of the piezo stack, an AC voltage is applied to the piezo stack so that the piezo stack is swept at a certain size and the frequency is not expanded or contracted. Apply
Piezo actuator drive, comprising: a power supply means for flowing a current for measurement through a piezo stack; and a calculation means for calculating a capacitance of the piezo stack based on a plurality of currents for measurement having different applied frequencies. circuit. 2. A piezo actuator drive circuit for controlling the expansion and contraction of the piezo stack by switching between charging and discharging of the piezo stack, a power supply means for supplying a constant current to the piezo stack at a preset current value at which the piezo stack does not expand and contract; A piezo actuator drive circuit, comprising: calculation means for calculating a capacitance of the piezo stack based on a voltage between both ends of the piezo stack before and after a predetermined time elapses. 3. The piezo actuator drive circuit according to claim 1, wherein the calculation means is configured to calculate the internal resistance of the piezo stack together with the capacitance. 4. An injector having a nozzle portion for fuel injection, an injector for outputting a pressing force for operating a valve body for switching between fuel injection and stop by a piezo actuator, and driving the piezo actuator. 3
A fuel injection device, comprising: the piezo actuator drive circuit according to any one of the preceding claims. 5. The fuel injection device according to claim 4, wherein
A fuel injection device comprising a correction unit that corrects a fuel injection parameter calculated according to an operating state of an engine.