JPH01264575A - Driver device for piezoelectric element - Google Patents

Abstract

PURPOSE:To improve reliability by providing a driver circuit with a detecting means detecting the quantity of charges charged to a piezoelectric element and controlling the output voltage of the driver circuit in response to the detection of the detecting means. CONSTITUTION:A piezoelectric element 10 is used for a fuel injection valve for an internal combustion engine, and injects fuel into a combustion chamber. The element 10 is connected to a variable voltage power 40 by a charging circuit including a first switching element 42 composed of a thyristor and a first coil 44 in a drive for the piezoelectric element 10. The first coil 44 forms a resonance circuit to the capacity of the piezoelectric element 10, and generates resonance currents. A capacitor 46 for detecting voltage is arranged in series with the piezoelectric element 10 to the charging circuit, and a voltage detecting means 48 is provided. A discharge circuit is formed to the piezoelectric element 10, and said circuit is constituted of a second switching element 50 consisting of a thyristor and a second capacitor 52 for resonance. The first and second switching elements 42, 50 are trigger-controlled by a trigger circuit 54 by a controller 56.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive device for a piezoelectric element that can be used as an actuator for mechanical devices and the like.

[Conventional technology]

Piezoelectric elements have the property of expanding and contracting in response to applied voltage, and are therefore suitable for use as high-speed actuators. It has been proposed to use such a piezoelectric element in, for example, a fuel injection device for an internal combustion engine. The feature of this publication is the piezoelectric element drive device, which uses a constant voltage power source and a switching element to charge and discharge the piezoelectric element alternately.The piezoelectric element is Since it expands when it is charged and contracts when it is discharged, the operation of the actuator composed of the piezoelectric element can be controlled by controlling the opening and closing of the switching element.Also, the amount of displacement of the piezoelectric element driven by a constant voltage power supply can be controlled by controlling the opening and closing of the switching element. is recognized to vary with temperature,
For example, Japanese Patent Application Laid-Open No. 1877-1989 discloses that in order to correct this, a piezoelectric element whose displacement changes in an increasing function with respect to temperature and a piezoelectric element whose displacement changes in a decreasing function with respect to temperature are used in combination. is disclosed.

[Problem to be solved by the invention]

When a piezoelectric element is used as an actuator, a large number of thin plate-shaped piezoelectric elements are often stacked in the axial direction to form one piston-shaped stacked pair unit. Therefore,
As described above, it is easy to combine (laminate) thin plate-shaped piezoelectric elements having different temperature characteristics, and therefore it is possible to correct the amount of displacement of the piezoelectric elements that changes depending on the temperature.

However, in reality, it is quite difficult to prepare thin plate-shaped piezoelectric elements with constant temperature characteristics that change in an increasing function (current function) with respect to temperature, manage them in groups, and combine them. There is a problem in that the resulting products vary widely.

The present invention focuses on the fact that changes in the amount of displacement due to temperature of a piezoelectric element are caused by changes in internal capacitance value due to temperature of the piezoelectric element, and the amount of displacement of the piezoelectric element is kept constant by detecting the amount of charge charged in the piezoelectric element. It is an object of the present invention to provide a piezoelectric element driving device that can maintain the following characteristics.

[Means to solve the problem]

A piezoelectric element driving device according to the present invention includes a variable voltage power source for applying a driving voltage to a piezoelectric element, a switching element disposed between the piezoelectric element and the variable voltage power source, and a charge amount of the piezoelectric element. The present invention is characterized by comprising a detection means for detecting the voltage, and a control means for controlling the output voltage of the variable voltage power supply according to the output of the detection means.

[For production]

The internal capacitance value of the piezoelectric element in the usage state is estimated based on the output of the detection means that detects the amount of charge charged in the piezoelectric element.

Once the internal capacitance value is known, the output voltage of the variable voltage power source is controlled to obtain a constant displacement amount of the piezoelectric element.

〔Example〕

Examples will be described below with reference to the drawings.

The piezoelectric element 10 schematically shown in FIG.
It can be used in a fuel injection valve 12 of an internal combustion engine as shown in the figure. The fuel injection valve 12 has an injection port 14 at one end.
The housing 16 includes a needle valve 18 that can open and close the injection port 14.
is located. A fuel passage 20 is provided to communicate with the injection port 14 . The fuel passage 20 is connected to an external fuel supply source (not shown) so that the fuel supply source can supply fuel at a constant high pressure. Therefore, when the needle valve 18 opens the injection port 14, the fuel is injected into the combustion chamber at high pressure.

A cylinder 22 is formed in the housing 16 .

The upper end of the needle valve 18 has a larger diameter and forms a piston 24 that is slidable on a cylinder 22. It should be noted that the needle valve 18 and the piston 22 may be formed as separate seals and can be appropriately connected to each other.

The piezoelectric element 10 is formed by laminating a large number of thin plate-shaped piezoelectric elements in the axial direction to form one piston-shaped laminated pair unit, and is supported between upper and lower caps 26 and 28. ing. The upper cap 26 abuts the upper wall of the housing 16 and the lower cap 28 is slidable with the cylinder 22. That is, the piezoelectric element 10 can move the lower cap 28 when it expands and contracts in response to voltage supply. Lead wires 30, 32 are provided for supplying drive voltage to the piezoelectric element 10.

Inside the cylinder 22, a piston 24 and a lower cap 2
A hydraulic chamber 34 is formed between the cylinder 8 and the cylinder 8. Also, piston 2
A disc spring 36 for return is disposed below 4. Therefore, when the piezoelectric element 10 expands in response to high voltage, it pushes the piston 24 through the lower cap 28 and the hydraulic fluid in the hydraulic chamber 34, thereby closing the needle valve 18. Further, when the piezoelectric element 10 contracts in response to an O or negative voltage, the piston 24 is pushed up by the spring force of the disc spring 36, thereby opening the needle valve 18.

Referring to FIG. 1, a variable voltage power source 4o is provided to apply a driving voltage to the piezoelectric element 10.

The piezoelectric element 10 is connected to a variable voltage power supply 40 by a charging circuit including a first switching element 42 made of Cyrisk and a first coil 44. In this charging circuit, the first switching element 42 and the first coil 44 are on the positive side of the variable voltage power supply 40 than the piezoelectric element 10, and turn on the first switching element 42 (applying a trigger to the gate). They are arranged so that current flows in the direction of arrow A. The first coil 44 is for forming a resonant circuit for the capacitance of the piezoelectric element 10, and generates a sine wave resonant current.

This sinusoidal resonant current changes from 0 to the positive side when the first switching element 42 is turned on, and when it passes the peak on the positive side and becomes 0 again, the first switching element 42 is turned off. Therefore, at this time, the piezoelectric element 10
The capacitance held by is charged with electric charge.

In the charging circuit, a voltage detection capacitor 46 is arranged in series with the piezoelectric element 10. Voltage detection means 48 are connected at positions before and after the voltage detection capacitor 46, and read changes in voltage.

Since the voltage detection capacitor 46 has a fixed relationship with the capacitance of the piezoelectric element 10, the voltage detection means 48 therefore detects the voltage across the piezoelectric element 10.

The amount of charge is the product of voltage and capacitance value, and piezoelectric element 1
Since the capacitance value of 0 is constant, if you know the voltage, you can know the amount of charge.

Furthermore, a discharge circuit is formed for the piezoelectric element 10.

A second switching element 50 made of Cyrisk and a second resonance coil 52 are arranged in this discharge circuit. The second switching element 50 is arranged so that a discharge current flows in the direction of arrow B. Second switching element 5
When 0 is turned on, the charge stored in the piezoelectric element 10 is discharged, and a resonant current flows through the second coil 52.

Also in this case, the second switching element 50 is turned off at the point where the resonant current flows by one peak of the sine wave.

The first switching element 42 and the second switching element 50 are supplied with a trigger current from a trigger circuit 54.

A control device (εC1) 56 is provided. This control device 5G receives signals a, b, etc. from a sensor that detects, for example, the rotation speed and load of the internal combustion engine, and causes a trigger circuit 54 to
At the same time, a control signal is sent to the variable voltage power source 40 in response to a detection signal from the voltage detection means 48, so that the drive voltage of the piezoelectric element 10 can be feedback-controlled in accordance with the amount of charge charged in the piezoelectric element 10.

The control device 56 is configured as a microcomputer,
A known central processing unit (CP) with calculation and control functions
U) and the read-on memory that stores the program (
ROM> and random access memory (RAM) 7 for storing data and the like.

FIG. 3 is a flowchart showing fuel injection control performed at predetermined time intervals by the control device 56 when the piezoelectric element 10 is used as an actuator for the fuel injection valve 12 shown in FIG. FIG. 4 is a flowchart that is executed at predetermined time intervals in order to control the drive voltage of the variable voltage power supply 40 in response to the detection signal of the voltage detection means 48. Figure 5 (9) is a timing chart for explaining the operation of Figures 3 and 4, with the trigger (first
switching element 42 and second switching element 5
0), VPZT (piezoelectric element 1
0) and VC (voltage between the terminals of the voltage detection capacitor 46).

Referring to FIG. 3, in step 60, the fuel injection timing is determined based on signals a, b, etc. from the sensor that detects the rotation speed and load of the internal combustion engine, and if YES, step 6
Proceed to step 1 to perform fuel injection processing. In this case, the fuel injection timing in step 60 is given by the fuel injection start timing and the fuel injection end timing, and when the fuel injection start timing is detected in step 60, the trigger current is applied to the second switching element 50 in step 61. It is designed to supply This corresponds to time A in FIG. Before time A in FIG. 5, the piezoelectric element 10 is charged with a reference voltage of, for example, 500 volts, and the discharging circuit in FIG. 1 is activated by turning on the second switching element 50. When closed, the piezoelectric element 10 discharges, and the voltage between the terminals increases to 1200
It is supposed to be a bolt. Looking at this in the operation of the fuel injection valve 12 in FIG. 2, when the piezoelectric element 10 is charged before time A, the piezoelectric element 10 is in an extended state, and therefore the needle valve 18 is closed. ing. When the piezoelectric element 10 is discharged to a point in time, the piezoelectric element 10 contracts;
Then, the needle valve 18 opens as described above. Note that the second switching element 50 is automatically turned off when the discharge current reaches D.

Referring to FIG. 3, when the fuel injection end timing is detected in step 60, a trigger current is supplied to the first switching element 42 in step 61. This corresponds to time B in FIG.

Then, the piezoelectric element 10 is charged, the piezoelectric element 10 is expanded, and as a result, the needle valve 18 is closed. The piezoelectric element 10 is maintained in a charged state until the next discharge.

Referring to FIG. 3, after the fuel injection process, step 62
to determine whether fuel injection has ended. Fifth
At the time point shown in the figure, the determination in step 62 becomes YES, and the process proceeds to step 63, where the counter CT is set to a predetermined value and the delay flag f-- DLY is set to 1. The counter CT and the delay flag fDLY are used in the voltage control shown in FIG. 4, which is executed in a separate routine. Note that when the answer in step 60.64 is NO, there is no process related to fuel injection.

Referring to FIG. 4, in the voltage control routine, it is determined in step 70 whether the delay flag fnLV is set to 1, and if YES (time B1 in FIG.
Or in D), proceed to step 71. In step 71, the counter CT is decremented by 1, and in step 7
Proceeding to step 2, it is determined whether the contents of the counter CT have become O.

When the answer is YES, that is, when a predetermined time CT has elapsed after the end of fuel injection (see FIG. 5), the process advances to step 73 and the delay flag f is set. Reset LY to 0.

Therefore, the process proceeds to step 74 and the detection voltage V is determined. A-D conversion and import. Next, proceeding to step 76, the detection voltage V
. It is determined whether or not is equal to the reference voltage VREF, and if no, the process proceeds to step 76. Note that if the answer in step 70 is NO, if the answer is NO in step 72, the answer in step 75 is
If the answer is NO, the process proceeds to step 79, where the voltage V to be output that has been stored up to that point is set. U7 is used to control variable voltage power supply 40. Note that when the internal combustion engine is started, the output voltage is V due to initialization processing. UT is the reference voltage V
iEp.

In step 76, the detection voltage V is detected. is the reference voltage VR
It is determined whether it is larger than EF, and if YES, the process proceeds to step 77 and the output voltage VOt+T is corrected to decrease by ΔV. If no, the process proceeds to step 78 where the output voltage V is determined. The LIT is corrected to increase by ΔV. Finally, in step 79, the output voltage V is set. The variable voltage power supply 40 is controlled by the LIT.

Referring to FIG. 5, the detected voltage V at a predetermined time CT after time B. In the example, the detection voltage V is sampled. is higher than the reference voltage VREF (5 volts). This corresponds to the fact that the voltage VPZT between the terminals of the piezoelectric element 10 is higher than the reference voltage (500 volts). Even if the output voltage of the power supply is maintained constant, such things may occur due to changes in the usage conditions of the piezoelectric element 10 (temperature changes of the fuel injection valve 12 as ambient conditions, heat generation of the piezoelectric element ID itself, etc.). In the present invention, the voltage vpzt between the terminals of the piezoelectric element IO is kept constant by feedback-controlling the output voltage of the power supply. In FIG. 5, the detection voltage V. is higher than the reference voltage VREF (5 volts), so the output voltage V. LIT is corrected to decrease by ΔV, so that the inter-terminal voltage vpzT of the piezoelectric element 10 at the next charging time (time point D) approaches the reference voltage (500 volts).

In this example, the detection voltage V. The sampling is performed with a delay of a predetermined time CT from fuel injection.

The purpose of this is to perform sampling after the charging operation has stabilized, and the reading operation of the voltage detection means 48 may be delayed. In addition, in the flowchart of FIG. 4, the detection voltage V. The data is taken only once, but multiple samples are taken at an appropriate point before the next discharge to calculate the average value or the integral value. You can also do that.

FIG. 6 is a diagram showing a second embodiment in which the amount of charge charged in the piezoelectric element 10 is detected by measuring the peak value of the charging current. The charging and discharging circuit for piezoelectric element 10 is substantially the same as that in FIG. In the second embodiment,
The first coil 57 is for measuring the peak value of the charging current.
The peak current holding means 57a is arranged in relation to the resonant coil 44 of the charging circuit so that the peak current holding means 57a can hold the peak of the induced current generated in the resonant coil 44 with respect to the voltage during charging of the piezoelectric element 10. It has become. Control unit (ECU) 56 is peak current holding means 57
In response to the signal a, the variable piezoelectric #40 is controlled, and after the current detection is completed, a reset signal is sent to the peak current holding means 57H, so that a new detected value is obtained every time fuel is injected.

FIG. 7 is a diagram illustrating the operation of the second embodiment.

The fuel injection timing is between time A and time B as in the first embodiment, and when the first switching element 42 is turned on at time B, charging of the piezoelectric element 10 is started. At the same time, an induced current flows through the measurement coil 57, and this
It is indicated by H. The peak of the detected current is held as IPH in the peak current holding means 57a. At a subsequent time point Q, the peak current holding means 57a is reset.

FIG. 8 shows a third embodiment of the present invention, in which an integrating means 57b is provided in place of the peak current holding means 57a of the second embodiment. In FIG. 9, the output power of the integrating means 57b is shown as INT, which can also give the peak of the induced current flowing through the measuring coil 57. The peak or integral value of the induced current flowing through the measurement coil 57 is a value representative of the state of charge, and by knowing the peak or integral value, the amount of charge charged in the piezoelectric element 10 can be determined.

〔Effect of the invention〕

As described above, according to the present invention, a drive circuit using a variable voltage power source for a piezoelectric element is provided with a detection means for detecting the amount of charge charged in the piezoelectric element, and the variable voltage is adjusted according to the output of the detection means. Since a control means is provided to control the output voltage of the voltage power source, the amount of displacement of the piezoelectric element can be maintained constant even under the influence of temperature, etc., thereby increasing the reliability of the equipment and equipment to which it is applied. effect can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing a first embodiment of a piezoelectric element drive device according to the present invention, Fig. 2 is a diagram showing a fuel injection valve using the piezoelectric element of Fig. 1, and Fig. 3 is a diagram showing a fuel injection valve using the piezoelectric element of Fig. 1. A flowchart showing the control of fuel injection of the fuel injection valve, FIG. 4 is a flowchart showing the control of the variable voltage power supply for driving the piezoelectric element, which is carried out together with the control of the fuel injection valve of FIG.
5 is an explanatory diagram of the operation of the piezoelectric element drive device of FIG. 1 with reference to FIGS. 3 and 4, FIG. 6 is a block diagram showing the second embodiment of the present invention, and FIG. FIG. 8 is a configuration diagram showing a third embodiment of the present invention, and FIG. 9 is an explanatory diagram of the operation of the piezoelectric element drive device of FIG. 8. 10... piezoelectric element, 40... variable voltage power supply,
42.50... Switching element, 44.52... Resonance coil, 46... Voltage detection capacitor.

Claims (1)

[Claims] A variable voltage power supply for applying a driving voltage to the piezoelectric element, a switching element disposed between the piezoelectric element and the variable voltage power supply, a detection means for detecting the amount of charge charged in the piezoelectric element, and the detection means. A piezoelectric element driving device comprising: control means for controlling the output voltage of the variable voltage power supply according to the output of the means.