JP4345226B2 - Piezo actuator driving circuit and fuel injection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric actuator drive circuit and a fuel injection device.
[0002]
[Prior art]
The piezo actuator uses a piezoelectric action of a piezoelectric material such as PZT, and a piezo stack, which is a capacitive element, expands or contracts due to charge / discharge, and linearly moves a piston or the like. For example, a fuel injection device for an internal combustion engine is known in which an on-off valve of a fuel injection injector is switched by a piezo actuator.
[0003]
A piezo actuator drive circuit for driving a piezo actuator includes, for example, a first energization path from a DC power source to a piezo stack via a switching element and an inductor, and an inductor bypassing the DC power source and the switching element. And a second energization path for energizing the piezo stack, a charging current that gradually increases during the ON period of the switching element flows through the first energization path, and the switching current flows through the second energization path. A charging current that gradually decreases during the off period of the element flows by the flywheel action. By repeatedly turning on and off the switching element, the charging current repeatedly increases and decreases gradually, the amount of charge of the piezo stack increases, and the voltage across the piezo stack increases stepwise. This is known as a multiple switching method, and when the charge amount reaches a predetermined target charge amount, the switching element is fixed to OFF and the charging is terminated.
[0004]
There is a battery that allows the amount of charge to be variable and the amount of expansion and pressing force of the piezo stack to be obtained as required. In Japanese Examined Patent Publication No. 6-12101, as an example applied to a fuel injection device for a common rail internal combustion engine, the structure of an injector for injecting fuel is opened, and the pressure of the fuel supplied from the common rail to the needle in the nozzle is opened. In a fuel injection device that is urged in the direction and the piezo stack opens and opens the needle indirectly through the fuel pressure in the pressurized chamber, the piezo stack is charged according to the detected fuel pressure in the common rail. A device that controls the amount and optimizes the pressing force to the needle is disclosed. The end of charging is determined by, for example, detecting the voltage across the piezo stack and determining whether or not this voltage has reached the target voltage as the target charge amount, and fixing the switching element to OFF.
[0005]
[Problems to be solved by the invention]
By the way, when the switching element is fixed to OFF, the inductor stores energy according to the magnitude of the charging current at that time. It becomes an error for the quantity. This error fluctuates because the magnitude of the charging current when the charge amount of the piezo stack reaches the target charge amount changes when the constants of the components constituting the piezo actuator drive circuit change due to environmental changes or the like.
[0006]
The error in the amount of charge becomes the largest when the charging current reaches the peak value and when the switching element is fixed off. Therefore, as a measure for suppressing the error in the charge amount, it is conceivable to suppress the peak value of the charging current by advancing the timing for switching the switching element from the on period to the off period.
[0007]
However, when the target charge amount is controlled according to the fuel pressure in the common rail as in the technique described in Japanese Patent Publication No. 6-12101, the average charge current is reduced by suppressing the peak value, and the target charge amount is reduced. There is a problem that the charging time becomes long when a large value is taken.
[0008]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a piezo actuator driving circuit capable of performing charging control in an appropriate charging time while ensuring necessary charging accuracy.
[0009]
[Means for Solving the Problems]
In invention of Claim 1, Used for injectors of fuel injection devices for internal combustion engines A piezo stack provided in the piezo actuator has a first energization path for energizing from a DC power source through an inductor, and the energization path gradually increases during an ON period of a switching element that is provided in the middle and repeats ON / OFF. Let the charging current flow,
There is a second energization path for energizing the piezo stack from the inductor, bypassing the DC power supply and the switching element, and a charging current that gradually decreases during the OFF period of the switching element is caused to flow through the energization path by the flywheel action. ,
The charging current is repeated Predetermined Control means for controlling on / off of the switching element so as to take a peak value, and fixing the switching element to off when the charge amount of the piezo stack reaches a target charge amount set by an external input. In the multi-switching piezo actuator drive circuit provided,
The control means, the smaller the target charge amount, The length of the on period of the switching element is reduced, The timing for switching from the on period to the off period is set so that the peak value becomes smaller.
[0010]
As the target charge amount is smaller, the charge current is reduced, and the energy held in the inductor at the time when the switching element is fixed off is reduced, and the charge amount error is reduced. Thereby, the error ratio with respect to the charge amount finally charged to the piezo stack can be kept small.
[0011]
On the other hand, as the target charge amount increases, the charge current increases, and the battery can be charged to the target charge amount quickly. Note that the charging current when the switching element is fixed to off is relatively large, but the target charge amount itself is large, so the error rate with respect to the charge amount finally charged in the piezo stack is not so large. The required charging accuracy can be ensured.
[0012]
As in the invention according to claim 2, the control means includes a first signal corresponding to the charging current and Define the peak value A comparison means for comparing the second signal according to the target charge amount;
When the first signal reaches the second signal, a control signal output prohibiting means for prohibiting the output of the control signal for turning on the switching element and switching the control signal during the off period can be provided.
[0013]
Alternatively, as in the invention according to claim 3, the control means generates a first signal that rises according to the elapsed time of the on period;
With the first signal Define the peak value A comparison means for comparing the second signal according to the target charge amount;
Control signal output prohibiting means for prohibiting output of a control signal for turning on the switching element and switching in the off period when the first signal exceeds the second signal is provided.
[0014]
In invention of Claim 4, the nozzle part for the injection of the high pressure fuel supplied from a common rail,
A valve body for switching between fuel injection and stop, and a valve body on which the pressure of the high-pressure fuel acts for opening / closing operation thereof;
A piezo actuator that outputs a pressing force that operates the valve body against the high-pressure fuel pressure;
Pressure detecting means for detecting the fuel pressure in the common rail;
A piezo actuator drive circuit according to any one of claims 1 to 3, which drives the piezo actuator.
The control means sets the target charge amount to be larger as the detected fuel pressure in the common rail is higher.
[0015]
The pressing force capable of operating the valve body against the fuel pressure in the common rail can be controlled to an appropriate level without excess or deficiency. Further, unnecessary heat generation of the piezo actuator drive circuit is avoided.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
1 and 2 show the configuration of a piezoelectric actuator drive circuit to which the present invention is applied. The piezo actuator drive circuit 1 has a configuration in which the drive control circuit 19 controls the magnitude of the charging current in accordance with the target charge amount in the charge control in the circuit configuration of the multiple switching system. Prior to the description of FIG. 1, an overall configuration of a fuel injection device for a common rail type four-cylinder diesel engine having a piezo actuator drive circuit 1 will be described.
[0017]
FIG. 3 shows the configuration of the fuel injection device. The number of injectors 4 corresponding to the number of cylinders of the diesel engine is provided corresponding to each cylinder (only one injector 4 is shown in the figure), and fuel is supplied from a common common rail 54 communicated 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). The fuel in the fuel tank 51 is pumped to the common rail 54 by the high-pressure supply pump 53 and stored at a high pressure.
[0018]
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 control hydraulic pressure of the injector 4 and returns to the fuel tank 51 from the injector 4 via a low-pressure drain line 56. It is supposed to be.
[0019]
A pressure sensor 57, which is a pressure detection means, is provided on the common rail 54 and detects the common rail pressure. Based on the detection result, the ECU 58 controls the metering valve 52 to adjust the amount of fuel pumped to the common rail 54. The pressure is controlled so as to be an appropriate injection pressure according to the operating condition known from other sensor inputs. Further, the ECU 58 calculates the fuel injection timing and the injection amount based on the detection signal such as the crank angle, and switches between opening and closing the injector 4 according to this, and injects fuel from the injector 4 for a predetermined period. Let me.
[0020]
FIG. 4 shows the structure of the injector 4. The injector 4 is a rod-like body, and is attached so that a lower portion in the drawing passes through a combustion chamber wall (not shown) of the engine and protrudes into the combustion chamber. The injector 4 includes a nozzle portion 4a, a back pressure control portion 4b, and a piezo actuator 4c in order from the bottom.
[0021]
A needle 421 is slidably held at the rear end portion in the main body 404 of the nozzle portion 4 a, and the needle 421 is seated on or separated from an annular sheet 4041 formed at the front end portion in the nozzle main body 404. High pressure fuel is introduced from the common rail 54 into the outer peripheral space 405 at the tip of the needle 421 through the high pressure passage 401, and fuel is injected from the injection hole 403 when the needle 421 is lifted. 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).
[0022]
A fuel as control oil is introduced from the high-pressure passage 401 through the in-orifice 407 behind the needle 421, and a back pressure chamber 406 for generating a back pressure of the needle 421 is formed. This back pressure acts on the rear end surface 4212 of the needle 421 in the seating direction (downward) together with the spring 422 disposed in the back pressure chamber 406.
[0023]
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 provided with the piezo stack 3A.
[0024]
The back pressure chamber 406 always communicates with the valve chamber 410 of the back pressure control unit 4b through the out orifice 409. The valve chamber 410 has a conical shape with a ceiling surface 4101 facing upward, and is connected to the low pressure chamber 411 at the top of the ceiling surface 4101. The low pressure chamber 411 communicates with the low pressure passage 402 that leads to the drain line 56.
[0025]
A high pressure control passage 408 branched from the high pressure passage 401 is opened on the bottom surface 4102 of the valve chamber 410.
[0026]
In the valve chamber 410, a ball 423 whose lower portion is cut horizontally is disposed. The ball 423 is a valve body that can move up and down. When lowered, the ball 423 sits on the valve chamber bottom surface (hereinafter referred to as a high-pressure side seat) 4102 as a valve seat with the cut surface, and shuts off the valve chamber 410 from the high-pressure control passage 408. When ascending, the valve chamber 410 is blocked from the low-pressure chamber 411 by sitting on the ceiling surface (hereinafter referred to as a low-pressure side seat) 4101 as a valve seat. Thus, when the ball 423 is lowered, the back pressure chamber 410 communicates with the low pressure chamber 411 through the out orifice 409 and the valve chamber 410, the back pressure of the needle 421 decreases, and the needle 421 is lifted. On the other hand, when the ball 423 is raised, the back pressure chamber 406 is cut off from the low pressure chamber 411 and communicates only with the high pressure passage 401, the back pressure of the needle 421 rises, and the nozzle needle 421 is seated.
[0027]
The ball 423 is pressed and driven by the piezo actuator 4c. In the piezo actuator 4c, two pistons 424 and 425 having different diameters are slidably held in a vertical hole 412 formed in the vertical direction above the low pressure chamber 411, and the piezo stack 3A is disposed above the upper large-diameter piston 425. Are arranged with the up-down direction as the expansion / contraction direction.
[0028]
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, and is displaced up and down by the same amount as the expansion and contraction of the piezo stack 3A.
[0029]
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. The expansion of the piezo stack 3A causes a large diameter. When the piston 425 is displaced downward and presses the fuel in the displacement expansion chamber 413, the pressing force is transmitted to the small diameter piston 424 through the fuel in the displacement expansion chamber 413. Here, since the small diameter piston 424 has a smaller diameter than the large diameter piston 425, the extension amount of the piezo stack 3A is expanded and converted into the displacement of the small diameter piston 424.
[0030]
The displacement expansion chamber 413 communicates with the low pressure passage 402 through a check valve (not shown) so that sufficient fuel is always filled. The check valve is provided with the direction from the low pressure passage 402 toward the displacement expansion chamber 413 as a forward direction, and closes when the large-diameter piston 425 is pressed by the extension of the piezo stack 3A so as to confine the fuel in the displacement expansion chamber 413. It has become.
[0031]
At the time of fuel injection, first, the piezo stack 3A is charged and the piezo stack 3A is extended, so that the small-diameter piston 424 descends and pushes the ball 423 down. As a result, the ball 423 lifts from the low-pressure side seat 4101 and sits on the high-pressure side seat 4102 so that the back pressure chamber 406 communicates with the low pressure passage 402, so that the fuel pressure in the back pressure chamber 406 decreases. As a result, the force acting on the needle 421 in the seating direction becomes more dominant than the force acting on the seating direction, and the needle 421 is lofted to start fuel injection.
[0032]
In contrast, when the injection is stopped, the piezo stack 3A is contracted by the discharge of the piezo stack 3A, and the pressing force to the ball 423 is released. At this time, the inside of the valve chamber 410 is at a low pressure, and high pressure fuel pressure is applied to the bottom surface of the ball 423 from the high pressure control passage 408, so that upward fuel pressure is applied to the ball 423 as a whole. is doing. Then, by releasing the pushing force to the ball 423, the ball 423 is lifted from the high pressure side seat 4102 and seated again on the low pressure side seat 4101 to increase the fuel pressure in the valve chamber 410, so that the needle 421 is seated and injected. Stops.
[0033]
Next, the piezo actuator drive circuit 1 will be described. The piezoelectric actuator drive circuit 1 is connected in parallel to an in-vehicle battery 111, a DC-DC converter 112 that constitutes a step-down chopper circuit and generates a DC voltage of several tens to several hundreds V from the battery 111, and an output terminal thereof. A DC power supply 11 is constituted by the buffer capacitor 113, and a voltage for charging the piezo stacks 3A, 3B, 3C, 3D is output. The buffer capacitor 113 is configured with a relatively large capacitance, and maintains a substantially constant voltage value even when the piezo stacks 3A to 3D are charged. The piezo stacks 3B to 3D are substantially the same as the piezo stack 3A shown in FIG. 4, and are mounted on the remaining three injectors 4 in a one-to-one correspondence.
[0034]
A first energization path 12a for energizing the piezoelectric stacks 3A to 3D from the buffer capacitor 113 of the DC power supply 11 via the inductor 13 is provided. In the energization path 12a, these are connected in series between the buffer capacitor 113 and the inductor 13. A first switching element 14 is interposed. The first switching element 14 is composed of a MOSFET, and the parasitic diode 141 is connected so as to be reverse-biased with respect to the voltage across the buffer capacitor 113.
[0035]
The inductor 13 and the piezo stacks 3 </ b> A to 3 </ b> D form a second energization path 12 b that bypasses the DC power supply 11 and the first switching element 14, and the energization path 12 b is connected to the inductor 13 and the switching element 14. It has the 2nd switching element 15 connected to a midpoint. The second switching element 15 is also composed of a MOSFET, and the parasitic diode 151 is connected so as to be reverse-biased with respect to the voltage across the buffer capacitor 113.
[0036]
The energization paths 12a and 12b are common to each of the piezo stacks 3A to 3D, and the piezo stacks 3A to 3D as driving objects can be selected as follows. That is, each of the piezo stacks 3A to 3D is connected in series with switching elements (hereinafter referred to as selective switching elements) 16A, 16B, 16C, 16D in a one-to-one relationship, and the piezo stack of the injector 4 of the injection cylinder. 16A to 16D corresponding to 3A to 3D are turned on. MOSFETs are used as the selection switching elements 16A to 16D. The parasitic diodes 161A, 161B, 161C, 161D are connected to the buffer capacitor 113 so as to be reverse-biased.
[0037]
Further, the drive control circuit 19 includes a voltage across the resistor 17 having a small resistance value connected in series to the piezo stacks 3 </ b> A to 3 </ b> D and a resistor having a small resistance value connected in series to the second switching element 15. The voltage between both ends of the device 18 is inputted, and the charging current and discharging current of the piezo stacks 3A to 3D are known. The drive control circuit 19 is input with the voltage across the piezo stacks 3A to 3D (hereinafter referred to as piezo stack voltage) as the amount of charge.
[0038]
A control signal is input from the drive control circuit 19 to each of the gates of the switching elements 14, 15, 16A to 16D. As described above, any of the selection switching elements 16A to 16D is turned on to drive the piezo stack 3A to be driven. -3D is selected, and a drive signal, which is a pulsed control signal, is input to the gates of the switching elements 14 and 15 to turn the switching elements 14 and 15 on and off, and charge control and discharge control of the piezo stacks 3A to 3D Is supposed to do. In charge control and discharge control, based on the charge current and discharge current detected by the resistors 17 and 18 and the piezo stack voltage, an injection signal from the CPU 58a and a common rail pressure detection signal (hereinafter referred to as a common rail pressure signal). ).
[0039]
The injection signal is a binary signal composed of “H” and “L”, and becomes “H” substantially corresponding to the period during which fuel injection is to be performed.
[0040]
Hereinafter, the drive control circuit 19 will be described focusing on the circuit configuration for charging the piezo stacks 3A to 3D.
[0041]
The drive control circuit 19 generates a drive signal input to the gate of the switching element 14 by the drive signal generation circuit 21. The drive control circuit 19 includes a first comparator 22 to which a common rail pressure signal and a voltage signal obtained by dividing a piezo stack voltage by resistors 25 and 26 (hereinafter referred to as a piezo stack voltage signal) are input. A binary signal indicating whether the piezo stack voltage is higher or lower than the target voltage is output. This binary signal is “H” when the piezo stack voltage is lower than the target voltage. The output signal of the comparator 22 is input to the AND gate circuit 211 of the drive signal generation circuit 21. The drive signal of the switching element 14 is an output signal of the AND gate circuit 211, and the switching element 14 is allowed to be turned on only when the piezo stack voltage is lower than the target voltage. That is, the target charging voltage of the piezo stacks 3A to 3D is given according to the common rail pressure signal, and as shown in FIG. 5, the higher the common rail pressure is on the higher pressure side than the later-described injector valve opening voltage, the higher the target voltage.
[0042]
Further, a second comparator 23 is provided to which a voltage across the resistor 17 (hereinafter referred to as a charging current detection signal) and a reference voltage (hereinafter referred to as a lower limit signal) output from the reference voltage generator 27 are input. And outputs a binary signal indicating whether the charging current detection signal is higher or lower than the lower limit signal. This binary signal is “H” when the charging current detection signal is lower than the lower limit signal. The output signal of the comparator 23 is input to the AND gate circuit 213 of the drive signal generation circuit 21 together with the injection signal, and the output signal of the AND gate circuit 213 is input to the set terminal of the flip-flop circuit 212. Therefore, the comparison signal between the charging current detection signal and the lower limit signal is input to the set terminal of the flip-flop circuit 212 only while the injection signal is output.
[0043]
In addition, a third comparator 24 for inputting the charging current detection signal as the first signal and the common rail pressure signal as the second signal is provided, and whether the charging current detection signal is higher than the common rail pressure signal. Outputs a low binary signal. This binary signal is “H” when the charge current detection signal is higher than the common rail pressure signal. The output signal from the comparator 24 is input to the reset terminal of the flip-flop circuit 212.
[0044]
In the drive signal generation circuit 21, the output (Q) of the flip-flop circuit 212 is input to the AND gate circuit 211 together with the output signal of the comparator 22.
[0045]
Therefore, until the piezo stack voltage reaches the target voltage, that is, during the charging period, the AND gate circuits 211 and 213 are operated so that the driving signal from the driving signal generating circuit 21 is charged. A flip-flop with the output of the comparator 23 that is a comparison signal between the current detection signal and the lower limit signal as a set signal and the output of the comparator 24 that is a comparison signal between the charge current detection signal and the common rail pressure signal as a reset signal This is equivalent to the output (Q) of the circuit 212.
[0046]
That is, when the switching element 14 is turned on, a charging current flows through the energization path 12a. When the charging current during this ON period rises at a rate approximately proportional to the difference between the buffer capacitor voltage and the piezo stack voltage and reaches a predetermined value defined by the magnitude of the common rail pressure signal, The output becomes “H”, the flip-flop circuit 212 is reset, the switching element 14 is turned off and the off period starts with the predetermined value as a peak value. During the off period, the parasitic diode 151 of the second switching 15 is forward biased with respect to the induced electromotive force generated in the inductor 13, and a charging current that gradually decreases due to the energy accumulated in the inductor 13 is generated in the second energization path 12 b. When the flywheel action flows and this reaches a lower limit value, the output of the comparator 23 becomes “H”, the flip-flop circuit 212 is set, the switching element 14 is turned on again, and the ON period starts.
[0047]
When the piezo stack voltage reaches the target voltage, the output of the comparator 22 becomes “L” and the switching element 14 is fixed off.
[0048]
FIG. 6 is a timing chart showing the operating state of each part of the piezo actuator drive circuit 1. The first half is when the common rail pressure is high, and the second half is when the common rail pressure is low. The (−) input of the comparator 24 that defines the peak value of the charging current compared with the charging current signal is a signal having a magnitude proportional to the common rail pressure. If the common rail pressure is high, the charging current has a high peak value. As a result, the average charging current increases and the piezo stack voltage quickly reaches the target voltage. On the other hand, if the common rail pressure is low, the charging current has a low peak value, and the amount of charge when the switching element 14 is turned on / off once is small. Therefore, the ratio of the error to the final piezo stack voltage caused by the flywheel current that flows after the switching element 14 is fixed off can be kept small even on the low-pressure side of the common rail pressure. Note that, on the high-pressure side of the common rail pressure, the error becomes relatively large because the peak current is large, but the ratio to the final piezo stack voltage is not so large, and charging accuracy is substantially ensured. .
[0049]
Moreover, the following effect is produced by setting the target voltage according to the common rail pressure. FIG. 5 shows the lowest piezo stack voltage at which the piezo actuator 4c generates a pressing force that allows the ball 423 seated on the low pressure side seat 4101 to lift from the low pressure side seat 4101 against the fuel pressure in the valve chamber 410. (Injector valve opening voltage) is also shown. Since the fuel pressure in the valve chamber 410 is higher as the common rail pressure is higher, the ball opening voltage is higher as the common rail pressure is higher. The target voltage needs to be higher than the injector valve opening voltage. If the target voltage is higher than necessary, the impact when the ball 423 is seated on the high-pressure side seat 4102 increases, and if the target voltage is low, the target voltage is separated from the low-pressure side seat 4101. The seat may not be stable. An appropriate pressing force can be applied to the ball 423 by setting the target voltage to be higher than the ball opening voltage and according to the common rail pressure. Further, unnecessary heat generation of the piezo actuator drive circuit 1 is avoided.
[0050]
Note that the discharge control of the piezo stacks 3A to 3D is performed by turning on and off the second switching element 15 in the same manner as in the conventional device, supplying a gradually increasing discharge current to the second energization path 12b during the on period, and the first during the off period. A gradually decreasing discharge current is supplied to the energization path 12a. In the off period, charges are collected from the piezo stacks 3A to 3D to the buffer capacitor 113. The switching of the switching element 15 is turned off when the discharge current detected by the resistor 18 reaches a predetermined value, and turned on when the discharge current reaches zero.
[0051]
(Second Embodiment)
FIG. 7 shows a configuration of a piezo actuator drive circuit of a fuel injection device according to a second embodiment of the present invention. In the present embodiment, the drive control circuit of the piezo actuator drive circuit is replaced with another configuration in the first embodiment. In the drawing, the same reference numerals as those in the first embodiment denote the same operations as in the first embodiment. Therefore, the difference from the first embodiment will be mainly described.
[0052]
The drive control circuit 19A of the piezo actuator drive circuit 1A has the same basic configuration as that of the first embodiment, and controls the peak value of the charging current with another configuration.
[0053]
The output signal of the comparator 24 is input to the reset terminal of the flip-flop circuit 212 that defines the switching timing of the switching element 14 from the on period to the off period. The comparator 24 uses the common rail pressure signal as the (−) input as in the first embodiment, but the output signal of the ramp wave generation circuit 28 is input as the (+) input.
[0054]
The ramp wave generation circuit 28 is configured such that the constant current power supply 281 charges the calculation capacitor 282, and increases the voltage across the calculation capacitor 282 as an output signal of the ramp wave generation circuit 28 at a constant speed.
[0055]
The calculation capacitor 282 is provided with a transistor 283 in parallel, and the calculation capacitor 282 is rapidly discharged when it is turned on. The transistor 283 is turned on / off by the output signal of the NOT gate circuit 284 that receives the drive signal of the switching element 14. That is, the voltage across the operation capacitor rises linearly with respect to time during the on period of the switching element 14 and takes 0 V during the off period of the switching element 14.
[0056]
In the present embodiment, during the charging control period, when the charging current decreases to the lower limit value and the output signal of the drive signal generation circuit 21 becomes “H”, the charging current starts to increase and the transistor 283 is turned off to perform the calculation. The voltage across the capacitor rises from 0V. When the voltage across the operation capacitor reaches the common rail pressure signal, the output signal of the comparator 24 becomes “H” and the ON period ends. As described above, the voltage across the computing capacitor rises in proportion to the elapsed time after the start of the on-period, so the larger the common rail pressure signal, the longer the on-period. That is, if the common rail pressure is high, the peak value of the charging current is high as in the first half of FIG. 8, and if the common rail pressure is low, the peak value of the charging current is low as in the second half of FIG.
[0057]
Thereby, similarly to 1st Embodiment, charging control can be performed by appropriate charging time, ensuring required charging precision.
[0058]
(Third embodiment)
FIG. 9 shows the configuration of a piezo actuator drive circuit of a fuel injection device according to a third embodiment of the present invention. This embodiment is obtained by replacing the drive control circuit of the piezo actuator drive circuit with another configuration in the first embodiment. In the figure, the same reference numerals as those in the first embodiment denote the same operations as those in the first embodiment. Therefore, the difference from the first embodiment will be mainly described.
[0059]
The drive control circuit 19B of the piezo actuator drive circuit 1B has the same basic configuration as that of the first embodiment, and the common rail pressure signal input to the comparators 22 and 24 is detected not by the CPU 58a but by the detection signal of the common rail pressure sensor 57. Is configured to output the amplifier 29.
[0060]
In the present embodiment, as in the first embodiment, high-precision charging control can be realized by increasing the resolution when the common rail pressure is low and the target charging voltages of the piezo stacks 3A to 3D are low.
[0061]
In each of the embodiments described above, the piezo stack voltage is used as an indicator of the amount of charge, but it is needless to say that the amount of electric power or the amount of charge supplied to the piezo stack may be used as an indicator.
[0062]
Further, the common rail pressure signal is not given in proportion to the common rail pressure, but may be given in a curve according to the characteristics of the injector valve opening voltage in the figure.
[0063]
The present invention can be applied not only to a piezo actuator for fuel injection control of an injector, but also to driving a piezo actuator used for other purposes as long as the target charge amount is variable.
[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 main part circuit diagram of the piezo actuator driving circuit;
FIG. 3 is a configuration diagram of a fuel injection device for an internal combustion engine having a fuel injection injector on which a piezo actuator driven by the piezo actuator drive circuit is mounted.
FIG. 4 is a cross-sectional view of the injector.
FIG. 5 is a graph illustrating the operation of the piezo actuator drive circuit.
FIG. 6 is a timing chart showing the operation of each part of the piezo actuator drive circuit.
FIG. 7 is a main part circuit diagram of a second piezo actuator driving circuit to which the present invention is applied;
FIG. 8 is a timing chart showing the operation of each part of the piezo actuator drive circuit.
FIG. 9 is a main part circuit diagram of a third piezo actuator driving circuit to which the present invention is applied;
[Explanation of symbols]
1,1A, 1B Piezo actuator drive circuit
11 DC power supply
111 battery
112 DC-DC converter
113 Buffer capacitor
12a, 12b energization route
13 Inductor
14 First switching element
141 Parasitic diode
15 Second switching element
151 Parasitic diode
16A, 16B, 16C, 16D Selective switching element
161A, 161B, 161C, 161D Parasitic diode
17, 18 resistors
19, 19A, 19B Drive control circuit (control means)
212 Flip-flop circuit (control signal output prohibiting means)
24 comparator (comparison means)
28 Ramp wave generation circuit (signal generation means)
3A, 3B, 3C, 3D Piezo stack
4 Injector
4a Nozzle part
4b Back pressure control unit
4c Piezo actuator
54 Common rail
57 Common rail pressure sensor (pressure detection means)
58 ECU
58a CPU

Claims (4)

A piezo stack provided in a piezo actuator used for an injector of a fuel injection device of an internal combustion engine has a first energization path for energizing from a DC power source through an inductor, and the energization path is provided in the middle of the energization path. A charging current that gradually increases during the ON period of the switching element that repeats ON / OFF flows,
There is a second energization path for energizing the piezo stack from the inductor, bypassing the DC power supply and the switching element, and a charging current that gradually decreases during the OFF period of the switching element is caused to flow through the energization path by the flywheel action. ,
The switching element is turned on / off so that the charging current repeatedly takes a predetermined peak value, and the switching element is turned off when the charge amount of the piezo stack reaches a target charge amount set by an external input. A plurality of switching type piezo actuator driving circuits comprising control means fixed to
The control means is set such that the smaller the target charge amount , the shorter the on-period of the switching element, and the timing for switching from the on-period to the off-period is the timing at which the peak value becomes smaller. A piezoelectric actuator drive circuit characterized by that. 2. The piezo actuator driving circuit according to claim 1, wherein the control means compares a first signal corresponding to a charging current with a second signal corresponding to the target charge amount that defines the peak value. When,
A piezo actuator drive circuit comprising control signal output prohibiting means for prohibiting output of a control signal for turning on the switching element and switching to the off period when the first signal reaches the second signal. 2. The piezo actuator driving circuit according to claim 1, wherein the control means generates a first signal that rises according to an elapsed time of the ON period;
A comparison means for comparing the first signal with a second signal corresponding to the target charge amount that defines the peak value ;
A piezo actuator drive circuit comprising control signal output prohibiting means for prohibiting output of a control signal for turning on the switching element and switching to the off period when the first signal exceeds the second signal. A nozzle for injecting high-pressure fuel supplied from a common rail;
A valve body for switching between fuel injection and stop, and a valve body on which the pressure of the high-pressure fuel acts for opening / closing operation thereof;
A piezo actuator that outputs a pressing force that operates the valve body against the high-pressure fuel pressure;
Pressure detecting means for detecting the fuel pressure in the common rail;
A piezo actuator driving circuit according to any one of claims 1 to 3, which drives the piezo actuator.
The fuel injection device is characterized in that the control means is set so that the target charge amount increases as the detected fuel pressure in the common rail increases.

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