JP4183376B2 - 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 driving circuit for driving a piezo actuator includes, for example, a first energization path to a piezo stack that energizes the piezo stack via an inductor from a DC power source, the inductor, the piezo stack, and a diode in series. A first charging current that gradually increases during the ON period of the switching element that repeats ON / OFF provided in the middle flows through the first energizing path, and the second energizing path is connected to the second energizing path. A second charging current that gradually decreases as a flywheel current flows in the energization path of, while the switching element is off. The amount of charge in the piezo stack increases with the number of on / off cycles, and the voltage across the piezo stack increases. This is known as a multiple switching scheme.
[0004]
FIG. 15 shows a typical example of piezo stack charge control in a piezo actuator drive circuit. The switching element control circuit turns off the switching element when the piezo stack current reaches a preset current value IpPEAK, and the piezo stack current is When 0, the switching element is turned on. Therefore, assuming that the average current during the charging period is I and the length of the charging period is t, the charge amount Q = I × t. Here, since the waveform of the charging current is a substantially triangular wave, the average current I can be expressed as IpPEAK / 2 using the current value (hereinafter referred to as peak current value) IpPEAK, and charging is performed with a constant current as a whole. . Further, assuming that the electrostatic capacity of the piezo stack is C, the voltage across the piezo stack V = Q / C, and the energy E = (1/2) CV supplied to the piezo stack ² (= (1/2) Q ² / C), the voltage V across the piezo stack rises in proportion to the length t of the charging period, and the energy E supplied to the piezo stack rises in a quadratic curve.
[0005]
[Problems to be solved by the invention]
By the way, the configuration of the injector is configured such that the pressure of the fuel supplied from the common rail to the needle in the nozzle is urged in the valve closing direction, and the piezo stack indirectly presses and drives the needle through the fuel pressure in the pressurizing chamber. In the fuel injection device that is designed to open, the higher the fuel pressure in the common rail, the more the piezo stack that opposes this needs to output a larger pressing force. However, in Japanese Patent Publication No. 6-12101, There has been proposed an apparatus in which the amount of charge supplied to the piezo stack is controlled in accordance with the detected fuel pressure in the common rail to optimize the pressing force on the needle. A piezo actuator drive circuit used for controlling the amount of charge supplied to the piezo stack using the fuel pressure in the common rail as an input is required to be able to control charging more precisely.
[0006]
In general, the capacitance of a capacitive element including a piezo stack greatly increases with an increase in temperature. For example, in the temperature range of -20 to 160 ° C., the inductance only changes by a few percent in an inductor or the like, whereas in a piezo stack, the capacitance changes by several times in the temperature range. Indicates. Therefore, for example, even if the charge amount Q is accurately controlled, as described above, the voltage V and the supply energy E across the piezo stack include the capacitance C as a parameter. The voltage V across the piezo stack and the supply energy E vary greatly in inverse proportion to the capacitance C.
[0007]
In JP-A-11-31755, the capacitance of a piezo stack is monitored by monitoring the behavior of the voltage across the piezo stack and the extension amount of the piezo stack during charging, and reflecting the result in the operation of the switching element. It is described that absorbs the temperature dependence of. For example, the times tc1 and tc2 until the voltage V across the piezo stack reaches a predetermined value Vth are V = I × tc1 / C in the case of the time tc1 from the respective expressions of the charge Q and the voltage V across the piezo stack. In the case of the time tc2, V = I × tc2 / C. Therefore, even if the capacitance C of the piezo stack fluctuates due to temperature fluctuations, it is fed back to the set value of the peak current value IpPEAK. Can respond.
[0008]
However, the technique described in Japanese Patent Laid-Open No. 11-31755 greatly increases the calculation burden and increases the cost.
[0009]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a piezo actuator driving circuit and a fuel injection device capable of controlling a piezo stack with high accuracy without an excessive calculation burden.
[0010]
[Means for Solving the Problems]
According to the first aspect of the present invention, the piezo stack provided in the piezo actuator has a first energization path for energizing from the DC power source through the inductor, and the energization path is provided in the middle and repeatedly turned on and off. A first charging current that gradually increases during the ON period of the switching element;
The inductor, the piezo stack, and a diode have a second energizing path connected in series, and a charging current that gradually decreases by a flywheel action during the off period of the switching element flows through the energizing path,
In a multi-switching type piezo actuator drive circuit having a control means for increasing the amount of charge of the piezo stack according to the number of on / off times by controlling on / off of the switching element,
The control means sets the length of the ON period of the switching element during charging to a predetermined ON period length. At the same time, the off period is set to end when the charging current becomes zero and to enter the next on period. Control is performed so that the peak value of the charging current in one cycle of on / off gradually decreases with time.
[0011]
As charging of the piezo stack proceeds, the voltage across the piezo stack increases, so that the voltage applied to the inductor gradually decreases during the ON period of the switching element. As a result, the induced electromotive force is also gradually reduced, so that the gradient of the current flowing through the inductor in the ON period, that is, the gradient of the charging current to the piezo stack is also reduced as the piezo stack is charged. In the present invention, by making the ON period constant, the peak value of the charging current in one ON / OFF cycle decreases as charging progresses. That is, as the charging of the piezo stack proceeds, the charging current generally decreases while taking a triangular waveform, contrary to the voltage across the piezo stack.
[0012]
Here, if the capacitance of the piezo stack increases, this acts in a direction to suppress the rate of increase of the voltage across the piezo stack. The effect of the suppression direction on the increase rate of the voltage across the piezo stack acts to suppress the decrease rate of the voltage applied to the inductor, and thus acts to suppress the overall decrease rate of the charging current. . Since this acts in the direction of increasing the charging speed of the piezo stack, even if the capacitance of the piezo stack increases, the rate of increase in the voltage across the piezo stack is not significantly suppressed.
[0013]
As a result, even with respect to the overall charging current, even if the capacitance of the piezo stack increases, the rate of decrease is not significantly suppressed.
[0014]
In addition, the suppression action of the voltage rise rate across the piezo stack acts in a direction to decrease the energy supply speed to the piezo stack, and the charge current reduction suppression action in a direction to increase the energy supply speed to the piezo stack. Since they act, they cancel out, and the time profile of the supplied energy becomes substantially constant regardless of the fluctuation of the capacitance of the piezo stack.
[0015]
Therefore, the supply energy to the piezo stack can be suitably controlled in an open loop without detecting a change in the capacitance of the piezo stack and feeding back to the charge control.
[0016]
According to the invention of claim 2, in the configuration of the invention of claim 1, there is provided current detection means for detecting a charging current when the switching element is switched from the on period to the off period,
In the charging control of the piezo stack performed at a predetermined time set in advance, the control means sets the detected charging current to a preset current value at least for the first ON period, and the switching element at that time The on-period length is reset according to the length of the on-period.
[0017]
The gradient of the charging current in the on period varies depending on the inductance of the inductor, but the length of the on period is such that the charging current at the end of the first on period, that is, the peak value of the charging current becomes the preset current value. Therefore, the overall charging current profile over time is substantially constant regardless of the inductance of the inductor. Therefore, the temporal profile of the voltage across the piezo stack and the energy supplied to the piezo stack is also substantially constant. Thereby, the charge characteristic resulting from the individual difference of an inductor can be reduced.
[0018]
In invention of Claim 3, 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;
The piezo actuator drive circuit according to claim 1 or 2 that drives the piezo actuator.
[0019]
A common rail type fuel injection device can be constructed to supply energy for fuel injection / stop switching control to the piezo stack with high accuracy and simple open loop control regardless of changes in the environmental temperature or the like.
[0020]
According to a fourth aspect of the invention, in the configuration of the third aspect of the invention, there is provided pressure detecting means for detecting the fuel pressure in the common rail,
And, the piezo actuator drive circuit, the charge amount of the piezo stack is configured to be variable,
The control means sets so that the amount of charge of the piezo stack increases as the detected fuel pressure in the common rail increases.
[0021]
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.
[0022]
According to a fifth aspect of the present invention, in the configuration of the fourth aspect of the present invention, the DC power supply is configured such that an output voltage is variable,
The control means controls the DC power supply and sets the output voltage of the DC power supply to be higher as the detected fuel pressure in the common rail is higher.
[0023]
The higher the output voltage of the DC power supply, the larger the charging current, and the amount of charge of the piezo stack increases.
[0024]
According to a sixth aspect of the present invention, in the configuration of the fourth aspect of the invention, the control means sets the switching element so that the OFF period of the switching element becomes shorter as the detected fuel pressure in the common rail is higher.
[0025]
In the off period, the charging suspension period is provided after the charging current is reduced to 0 according to the length of the off period. Therefore, when the off period is shortened, the average charging current increases and the amount of charge of the piezo stack increases.
[0026]
According to a seventh aspect of the present invention, in the configuration of the fourth aspect of the invention, there is provided a current detecting means for detecting a charging current when the switching element is switched from the on period to the off period.
In the charging control of the piezo stack, the control means is configured such that the detected charging current is a command current value during the first on period, and the on period length is determined according to the length of the on period of the switching element at that time. Will be reset
In addition, the command current value is set to be larger as the detected fuel pressure in the common rail is higher.
[0027]
Since the average charging current increases as the on-period length increases, the amount of charge in the piezo stack increases.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 shows a configuration of a piezo actuator drive circuit to which the present invention is applied. The piezo actuator drive circuit is applied to a fuel injection device of a common rail type four-cylinder diesel engine. The overall configuration of the fuel injection device will be described later. The piezo actuator driving circuit 1 includes a DC power supply 11 by an in-vehicle battery 111, a DC-DC converter 112 that generates a DC voltage of several tens to several hundreds V from the battery 111, and a buffer capacitor 113 connected in parallel to the output terminal thereof. And outputs voltages for charging the piezo stacks 2A, 2B, 2C, and 2D. In the DC-DC converter 112, an inductor 1121 and a switching element 1122 are connected in series with the battery 111, and the energy accumulated in the inductor 1121 when the switching element 1122 is turned on generates a back electromotive force due to the energy when the switching element 1122 is turned off. The capacitor 113 is charged from the generated inductor 1121 through the diode 1123. The buffer capacitor 113 has a relatively large capacitance, and maintains a substantially constant voltage value even when the piezo stacks 2A to 2D are charged.
[0029]
A first energization path 12a for energizing the piezo stacks 2A to 2D from the buffer capacitor of the DC power supply 11 via the inductor 13 is provided, and the energization path 12a is connected between the buffer capacitor 113 and the inductor 13 in series with these. One switching element 14 is interposed. The first switching element 14 is composed of a MOSFET, and the parasitic diode (hereinafter referred to as the first parasitic diode) 141 is connected so as to be reverse-biased with respect to the voltage across the buffer capacitor 113. The inductor 13 and the piezo stacks 2 </ b> A to 2 </ b> D form a second energization path 12 b, and the energization path 12 b is a second switching connected to the midpoint of connection between the inductor 13 and the first switching element 14. The element 15 is included, and a closed circuit is formed by the inductor 13, the piezo stacks 2 </ b> A to 2 </ b> D, and the second switching element 15. The second switching element 15 is also composed of a MOSFET, and its parasitic diode (hereinafter referred to as second parasitic diode) 151 is connected so as to be reverse-biased with respect to the voltage across the buffer capacitor 113.
[0030]
The energization paths 12a and 12b are common to each of the piezo stacks 2A to 2D, and the piezo stacks 2A to 2D as driving objects can be selected as follows. That is, switching elements (hereinafter referred to as selective switching elements) 16A, 16B, 16C, and 16D are connected to each of the piezo stacks 2A to 2D in a one-to-one relationship, and the piezo stacks 2A to 2D of the injectors of the injection cylinders. The selection switching elements 16A to 16D corresponding to are turned on. MOSFETs are used as the selection switching elements 16A to 16D, and the parasitic diodes (hereinafter referred to as selection parasitic diodes) 161A, 161B, 161C, 161D are connected to the buffer capacitor 113 so as to be reverse-biased. .
[0031]
As will be described later, the piezo stacks 2A to 2D are mounted on the injectors 4 for switching between fuel injection and stop of the injectors 4 (FIGS. 2 and 3) provided in each cylinder.
[0032]
Control signals are respectively input from the control circuit 18 to the gates of the switching elements 14, 15, 16A to 16D. As described above, any of the selective switching elements 16A to 16D is turned on to drive the piezo stacks 2A to 2A to be driven. While 2D is selected, a pulsed control signal is input to the gates of the switching elements 14 and 15 to turn on and off the switching elements 14 and 15 to perform charge control and discharge control of the piezo stacks 2A to 2D. ing.
[0033]
Further, an injection signal from an ECU (described later) that controls the entire fuel injection control (described later) is input to the control circuit 18. The injection signal is a binary signal consisting of “L” and “H” corresponding to the injection period, and the control circuit 18 starts charging the piezo stacks 2A to 2D at the rising edge of the injection signal, and at the falling edge of the injection signal. The stacks 2A to 2D are discharged.
[0034]
Also, the voltage across the resistor 17 connected in series with each of the piezo stacks 2A to 2D is input to the control circuit 18 to detect the charging current and discharging current of the piezo stacks 2A to 2D. It is supposed to be.
[0035]
FIG. 2 shows the configuration of a common rail fuel injection device for a diesel engine having a fuel injection injector 4 on which the piezo stacks 2A to 2D are mounted. FIG. 3 shows the structure of the injector 4. Although the illustrated example has a piezo stack 2A mounted thereon, any piezo stack 2A to 2D has the same structure. 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.
[0036]
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.
[0037]
The pressure sensor 57 is provided on the common rail 54 and detects the common rail pressure. Based on the detection result, the ECU 3 controls the metering valve 52 to adjust the amount of fuel pumped to the common rail 54, and the common rail pressure is detected by other sensors. Control is performed so as to obtain an appropriate injection pressure in accordance with the operating condition known by input or the like.
[0038]
As shown in FIG. 3, the injector 4 is a rod-like body, and is attached so that the lower portion in the drawing penetrates the 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.
[0039]
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 distal end portion of 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 separated. 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).
[0040]
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.
[0041]
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 2A. The injector provided with the piezo stacks 2B to 2D has the same structure.
[0042]
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.
[0043]
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.
[0044]
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. As a result, when the ball 423 is lowered, the back pressure chamber 410 communicates with the low pressure chamber 411 via the out orifice 409 and the valve chamber 410, the back pressure of the needle 421 decreases, and the needle 421 is separated. 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, and the back pressure of the needle 421 rises and the needle 421 is seated.
[0045]
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 2A is disposed above the upper large-diameter piston 425. Are arranged with the up-down direction as the expansion / contraction direction.
[0046]
The large-diameter piston 425 is kept in contact with the piezo stack 2A 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 2A.
[0047]
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 2A 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 2A is expanded and converted into the displacement of the small-diameter piston 424.
[0048]
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 is closed when the large-diameter piston 425 is pressed by the extension of the piezo stack 2A so as to confine the fuel in the displacement expansion chamber 413. It has become.
[0049]
At the time of fuel injection, first, the piezo stack 2A is charged and the piezo stack 2A expands, whereby the small-diameter piston 424 descends and pushes down the ball 423. As a result, the ball 423 is separated from the low-pressure side seat 4101 and seated 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 seated and fuel injection is started.
[0050]
On the contrary, when the injection is stopped, the piezo stack 2A is contracted by the discharge of the piezo stack 2A, 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. The release of the pressing force on the ball 423 causes the ball 423 to be separated from the high-pressure side seat 4102 and seated on the low-pressure side seat 4101 again to increase the fuel pressure in the valve chamber 410, so that the needle 421 is seated and injected. Stops.
[0051]
The charging control of the control circuit 18 will be described. The control circuit 18 sets the ON period and the OFF period of the first switching element 14 as follows, and outputs a control signal for the first switching element 14. In other words, the on period is set to be constant, and the off period is set so that the first switching element 14 is turned on and the next on period is entered when the charging current becomes zero. The control signal is output during a time set in advance by timer control, and the first switching element 14 is repeatedly turned on and off at a number of times corresponding to the time.
[0052]
FIG. 4 shows the change with time of the charging current Ip. During the ON period of the switching element 14, charging gradually increases from the buffer capacitor 113 to the piezo stacks 2A to 2D through the inductor 13 to the first energizing path 12a. In the off-period of the switching element 14, the induced electromotive force generated in the inductor 13 becomes a forward bias with respect to the second parasitic diode 151, and the charging current that gradually decreases in the second energizing path 12b by the flywheel action. Flows. Here, the resonance frequency of the circuit including the inductor 13 and the piezo stacks 2A to 2D is sufficiently higher than the on / off frequency of the first switching element 14, and the waveform can be regarded as a triangle.
[0053]
Here, the peak value (peak current) IpPEAK of the charging current in one cycle of on / off is the current at the end of the on period, and is output voltage of the DC power supply 11 (hereinafter referred to as DC power supply output voltage), that is, between both ends of the buffer capacitor 113. When the voltage is VDC-DC, the piezo stack voltage is Vp, the length of the on period is TON, and the inductance of the inductor 13 is L, IpPEAK = (VDC-DC-Vp) × TON / L. In the equation, the DC power supply output voltage VDC-DC can be regarded as constant as described above.
[0054]
As shown in FIG. 5, the piezo stack voltage Vp has an initial value of 0 when charging of the piezo stacks 2A to 2D is started and shows a chronological profile that gradually increases with time. The voltage (VDC-DC-Vp) applied to the inductor 13 gradually decreases as the piezo stacks 2A to 2D are charged. As a result, the induced electromotive force of the inductor 13 gradually decreases, and the gradient of the charging current Ip during the ON period also decreases as the charging of the piezo stacks 2A to 2D proceeds. In the present invention, by setting the ON period to be constant, the charging current shows a temporal profile that decreases in reverse to the piezo stack voltage Vp as a whole while taking a triangular waveform.
[0055]
Here, since the piezo stack voltage Vp is inversely proportional to the capacitance C of the piezo stacks 2A to 2D, if the capacitance C increases, this acts in a direction to suppress the rising speed of the piezo stack voltage Vp.
[0056]
This action in the direction of suppressing the increase rate of the piezo stack voltage Vp acts in a direction in which the decrease in the voltage applied to the inductor 13 during the ON period of the switching element 14 is mitigated, and the overall decrease rate of the charging current Ip. Acts in the direction of suppressing This acts in the direction of increasing the charge supply speed to the piezo stacks 2A to 2D, and thus in the direction of increasing the piezo stack voltage Vp. Therefore, depending on the increase in the capacitance of the piezo stacks 2A to 2D, the piezo stack voltage The temporal profile of Vp does not change much.
[0057]
On the other hand, since the piezo stack voltage Vp does not change greatly due to the increase in capacitance of the piezo stacks 2A to 2D, the time profile of the charging current Ip does not change much.
[0058]
Moreover, this small influence on the piezo stack voltage Vp and the charging current Ip due to the increase in the capacitance of the piezo stacks 2A to 2D has the following properties. That is, the amount of energy supplied per unit time by charging to the piezo stacks 2A to 2D is represented by the product of the piezo stack voltage Vp and the charging current Ip, and the direction for suppressing the increase rate of the piezo stack voltage Vp is the unit. The direction in which the amount of energy supplied per time is reduced, and the direction in which the decrease in the charging current Ip is mitigated is the direction in which the amount of energy supplied per unit time is increased. . Therefore, it is possible to further suppress the energy supply amount per unit time from being dependent on the variation in the capacitance of the piezo stacks 2A to 2D due to the variation in the environmental temperature or the like.
[0059]
6 (A), 6 (B), and 6 (C), respectively, in the present fuel injection device, the piezo stack current Ip, the piezo stack voltage Vp, The change over time of the stored energy E is seen. As described above, the piezo stack voltage Vp has a gradually increasing time profile, and the piezo stack current Ip has a gradually decreasing time profile. The supply energy E has a time profile that increases substantially linearly.
[0060]
Then, as is known by comparing FIGS. 6 (A) to 6 (C), even if the capacitance C of the piezo stacks 2A to 2D increases, the piezo stack voltage Vp is slightly reduced. The charging current Ip is slightly reduced and the supply energy E is almost unchanged.
[0061]
Therefore, by simply controlling the charging time of the piezo stacks 2A to 2D to be constant, the energy supplied to the piezo stacks 2A to 2D can be reduced even if the capacitance C of the piezo stacks 2A to 2D changes without the Ford back control. Can be a constant value.
[0062]
Further, the discharge of the piezo stacks 2A to 2D is performed by turning on and off the switching element 15 so that a discharge current flows through the path of the piezo stacks 2A to 2D, the inductor 13 to the second switching element 15 to the selected parasitic diode 161 during the on period. In the off period, a discharge current flows through the path of the piezo stacks 2A to 2D, the inductor 13 to the first parasitic diode 141 to the buffer capacitor 113, and the charge, and thus the energy held by the piezo stack 2A, is recovered in the buffer capacitor 113. Is done.
[0063]
(Second Embodiment)
As described above, the temperature of the inductor 13 is relatively smaller than that of the piezo stacks 2A to 2D, but actual inductance may vary due to individual differences. In view of this point, the present embodiment further improves the accuracy of the supply energy control to the piezo stacks 2A to 2D. FIG. 7 shows the piezo actuator drive of the fuel injection device according to the second embodiment of the present invention. A circuit configuration is shown. In the figure, the same reference numerals as those in the first embodiment operate in the same manner as in the first embodiment, and therefore, differences from the first embodiment will be mainly described.
[0064]
The present embodiment is the same as the configuration of the first embodiment except for the piezo actuator driving circuit, and the difference from the first embodiment will be mainly described.
[0065]
The control circuit 18A of the piezo actuator driving circuit 1A does not perform the initial on-period for starting the charging of the piezo stacks 2A to 2D with a preset length, but the charging current Ip detected by the resistor 17. Is set to enter an off period when the current value reaches a preset current value. Then, a time from when the switching element 14 is turned on until the preset current value is reached is calculated, and this time is defined as the length TON of the subsequent ON period.
[0066]
Thereby, even if the inductance of the inductor 13 varies, it is absorbed by the length of the ON period of the first switching element 14, and the initial value of the peak current IpPEAK is unified to the preset current value. Thereby, the charging characteristics can be substantially uniformed.
[0067]
8A, 8B, and 8C show the behavior of the piezo stack current Ip, the piezo stack voltage Vp, and the supply energy E of the piezo stacks 2A to 2D by varying the inductance L of the inductor 13. On the other hand, when the inductance L is large, the ON period becomes long, but the temporal profile is constant for the piezo stack voltage Vp, the charging current Ip, and the supply energy E to the piezo stacks 2A to 2D.
[0068]
Thus, even if the inductor 13 has a variation in the inductance L, it can be absorbed and the charge control of the piezo stacks 2A to 2D can be performed with high accuracy.
[0069]
In the present embodiment, the ON period length TON is set to be extended every time the piezo stack is extended. However, the timing can be set as appropriate only when the ignition switch is turned on or only when the battery is replaced.
[0070]
(Third embodiment)
FIG. 9 shows a configuration of a piezo actuator drive circuit of a fuel injection device according to a third embodiment of the present invention. In the configuration of the first embodiment, the control circuit is replaced with another configuration. In the figure, the same reference numerals as those in the first embodiment operate in the same manner as in the first embodiment, and therefore, differences from the first embodiment will be mainly described. The basic setting of the control circuit 18B of the piezo actuator drive circuit 1B is the same as that of the first embodiment, and the capacitance of the piezo stacks 2A to 2D is changed by making the length of the ON period of the switching element 14 constant. Even so, fluctuations in supply energy are suppressed. The control circuit 18B controls the output voltage of the DC power supply 11 with the common rail pressure detected by the pressure sensor 57 (FIG. 2) as pressure detection means as an input. The output voltage of the DC power source 11 is set based on the on / off frequency of the element 1122. Here, as the common rail pressure is higher, the on / off frequency of the switching element 1122 is increased so that the output voltage of the DC power supply 11 becomes higher.
[0071]
Since IpPEAK = (VDC-DC-Vp) .times.TON / L as described above, the peak current IpPEAK increases by increasing the output voltage VDC-DC of the DC power supply 11. As shown in FIG. The energy increase rate of 2A to 2D can be increased. Thereby, energy according to the common rail pressure can be supplied to the piezo stacks 2A to 2D.
[0072]
In the injector 4, when the ball 423 is lifted, a pressing force is required to overcome the force by which the fuel pressure in the high-pressure control passage 408 pushes the ball 423 upward. Therefore, if the common rail pressure is high, the piezo stacks 2A to 2D must generate a large pressing force. On the other hand, if the common rail pressure is low, the pressing force is excessive depending on the amount of charge. Further, since the pressing force required for the ball 423 to lift is changed by the common rail pressure, the time required for the pressing force of the piezo stacks 2A to 2D to reach the required pressing force varies, and the timing at which the ball 423 starts to lift is affected. As a result, the fuel injection timing and the injection amount vary.
[0073]
According to the present fuel injection device, the higher the common rail pressure, the more energy is supplied. Therefore, if the common rail pressure is high, the ball 423 can be stably brought into a lift state by supplying sufficient energy, and abnormal injection or the like can be avoided. it can. On the other hand, if the common rail pressure is low, it is possible to supply appropriate energy corresponding to the common rail pressure. Also, if the pressing force of the piezo stacks 2A to 2D required to lift the ball 423 is high because the common rail pressure is high, the supply energy rises faster, and the ball 423 starts to be lifted at a predetermined time regardless of the common rail pressure. Is done. Thereby, the timing at which the ball 423 starts to lift can be aligned.
[0074]
(Fourth embodiment)
FIG. 11 shows the configuration of a piezo actuator drive circuit of a fuel injection device according to the fourth embodiment of the present invention. In the configuration of the third embodiment, the control circuit is replaced with another configuration. In the figure, since the same reference numerals as those in the third embodiment operate in the same manner as in the third embodiment, the differences from the third embodiment will be mainly described. In the third embodiment, the appropriate energy amount control corresponding to the common rail pressure is performed by changing the output voltage of the DC power supply 11, but this embodiment performs the proper energy supply control by another method. The basic setting of the control circuit 18C is the same as that of the first to third embodiments, and the capacitance C of the piezo stacks 2A to 2D is changed by making the length of the ON period of the switching element 14 constant. Even the supply energy fluctuation is suppressed. Then, the control circuit 18C provides a time delay for turning on the switching element 14 after the charging current becomes zero, and the charging current flows during the period from the end of charging by the flywheel current to the turning on of the switching element 14. There is no charging rest period. Here, the higher the common rail pressure, the shorter the off period and the shorter the charging suspension period.
[0075]
As shown in FIG. 12, as the length of the charging suspension period is longer, the overall charging current is reduced, and the rate of increase in the supply energy is reduced. Thereby, an effect substantially equivalent to 3rd Embodiment can be acquired.
[0076]
(Fifth embodiment)
FIG. 13 shows a configuration of a piezo actuator drive circuit of a fuel injection device according to a fifth embodiment of the present invention. In the configuration of the third embodiment, the control circuit is replaced with another configuration. In the figure, since the same reference numerals as those in the third embodiment operate in the same manner as in the third embodiment, the differences from the third embodiment will be mainly described. The control circuit 18D of the piezo actuator drive circuit 1D has basically the same configuration as the control circuit 18A of the second embodiment, and the time TON until the initial value of the peak current IpPEAK of the energization current of the switch element 14 is reached. It is set to repeat thereafter, and the initial value of the peak current IpPEAK is set according to the detected common rail pressure. That is, the initial value of the peak current IpPEAK is set so as to change according to the common rail pressure, such that the initial value is large when the common rail pressure is high and small when the common rail pressure is low. The same effect as that of the appropriate energy supply control by the configuration can be obtained.
[0077]
FIG. 14 shows the experimental results of the input energy to the piezoelectric actuators 2A to 2D with respect to the initial value of the peak current IpPEAK. By increasing the peak current IpPEAK, the energy of the piezoelectric actuators 2A to 2D after 150 μs increases approximately linearly. Thus, if the initial value of IpPEAK is set according to the common rail pressure, the charging energy corresponding to the common rail pressure can be obtained.
[0078]
The supply energy of the piezo stacks 2A to 2D may be gradually increased substantially continuously with respect to the common rail pressure, or the common rail pressure and the charging time may be divided into a plurality of stages and corresponded one to one.
[0079]
Also, in order to set the energy supplied to the piezo stack according to the common rail pressure, the piezo actuator drive circuit may be configured so that the energy supplied to the piezo stack is variable in addition to the third and fourth embodiments. Can be used.
[0080]
In each of the above embodiments, the injector includes a back pressure control unit that increases or decreases the pressure in the back pressure chamber, and the ball is pressed and driven via the hydraulic pressure in the displacement expansion chamber. The present invention is not limited to this, and can also be applied to the structure described in Japanese Patent Publication No. 6-12101, in which the piezo stack is configured to drive the needle via hydraulic pressure.
[0081]
The present invention can be applied not only to a piezoelectric actuator for controlling fuel injection of an injector but also to driving a piezoelectric actuator used for other purposes.
[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 injection injector equipped with a piezoelectric actuator driven by the piezoelectric actuator drive circuit.
FIG. 3 is a cross-sectional view of the injector.
FIG. 4 is a diagram showing a change with time of a charging current of the piezoelectric actuator driving circuit.
FIG. 5 is a diagram showing a change with time of each part of the piezoelectric actuator driving circuit;
6A, 6B, and 6C are graphs showing the operation of the piezoelectric actuator drive circuit in which the capacitance of the piezoelectric stack of the piezoelectric actuator is different.
FIG. 7 is a circuit diagram of a second piezo actuator drive circuit to which the present invention is applied.
FIGS. 8A, 8B, and 8C are graphs showing operations of the piezo actuator drive circuit in which inductances of inductors constituting the piezo actuator drive circuit are different from each other. FIGS.
FIG. 9 is a circuit diagram of a third piezo actuator driving circuit to which the present invention is applied.
FIG. 10 is a diagram showing a change with time of each part of the piezo actuator driving circuit.
FIG. 11 is a circuit diagram of a fourth piezo actuator drive circuit to which the present invention is applied.
FIG. 12 is a diagram showing a change with time of each part of the piezo actuator driving circuit;
FIG. 13 is a circuit diagram of a fifth piezo actuator drive circuit to which the present invention is applied.
FIG. 14 is a graph illustrating the operation of the piezo actuator drive circuit.
FIG. 15 is a diagram illustrating the operation of a representative example of a conventional piezo actuator driving circuit.
[Explanation of symbols]
1,1A, 1B, 1C, 1D Piezo actuator drive circuit
11 DC power supply
111 battery
112 DC-DC converter
113 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 resistors
2A, 2B, 2C, 2D Piezo stack
3 ECU
18, 18A, 18B, 18C, 18D Control circuit (control means)
4 Injector
4a Nozzle part
4b Back pressure control unit
4c Piezo actuator
423 Ball (valve)
54 Common rail
57 Pressure sensor (pressure detection means)

Claims (7)

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. A first charging current is passed,
The inductor, the piezo stack, and a diode have a second energizing path connected in series, and a charging current that gradually decreases by a flywheel action during the off period of the switching element flows through the energizing path,
In a multi-switching type piezo actuator drive circuit having a control means for increasing the amount of charge of the piezo stack according to the number of on / off times by controlling on / off of the switching element,
The control means sets the length of the on-period of the switching element at the time of charging to a predetermined on-period length, and sets the off period to the next on-period as the end when the charging current becomes zero. A piezo actuator drive circuit characterized by controlling so that the peak value of the charging current in one cycle of on / off gradually decreases with time. The piezo actuator driving circuit according to claim 1, further comprising a current detection means for detecting a charging current when the switching element switches from an on period to an off period,
In the charging control of the piezo stack performed at a predetermined time set in advance, the control means sets the detected charging current to a preset current value at least for the first ON period, and the switching element at that time A piezoelectric actuator driving circuit set so that the on-period length is reset according to the length of the on-period. 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;
A fuel injection apparatus comprising: the piezoelectric actuator driving circuit according to claim 1 or 2 that drives the piezoelectric actuator. The fuel injection device according to claim 3, further comprising pressure detecting means for detecting fuel pressure in the common rail,
And, the piezo actuator drive circuit, the charge amount of the piezo stack is configured to be variable,
The fuel injection device, wherein the control means is set so that the charge amount of the piezo stack increases as the detected fuel pressure in the common rail increases. The fuel injection device according to claim 4, wherein the DC power supply is configured such that an output voltage is variable.
The control means controls the DC power supply, and sets the output voltage of the DC power supply to be higher as the detected fuel pressure in the common rail is higher. 5. The fuel injection device according to claim 4, wherein the control means is set such that an OFF period of the switching element is shortened as the detected fuel pressure in the common rail is higher. 5. The fuel injection device according to claim 4, further comprising current detection means for detecting a charging current when the switching element is switched from an on period to an off period,
In the charging control of the piezo stack, the control means is configured such that the detected charging current is a command current value during the first on period, and the on period length is determined according to the length of the on period of the switching element at that time. Will be reset
The fuel injection device is set such that the command current value increases as the detected fuel pressure in the common rail increases.

Images