JPH06140682A - Driving circuit for piezoelectric element - Google Patents

Abstract

PURPOSE:To secure elongation length being stable to temperature and materialize a driving circuit at low cost by detecting the temperature without using temperature sensor, concerning the driving circuit for a piezoelectric element used for the fuel injection value of an internal combustion engine. CONSTITUTION:A capacitor 14 is provided in parallel with PZT 11. The voltage across the capacitor 14 is supplied to a voltage detecting circuit 16b through an amplifier 16a. The voltage detecting circuit 16b detects the voltages V1 and V2 across the capacitor 14 before and after charge. A charge calculating circuit 17 calculates the charge Q which has shifted from the capacitor 14 to PZT 11, based on V1 and V2. A temperature calculating circuit 18 calculates the temperature T of PZT 11, based on V1 and V2. A power source voltage control circuit 19a and a power source voltage compensating circuit 19 set the output voltage of a DC-DC converter 15, based on Q and T.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element drive circuit, and more particularly to a piezoelectric element drive circuit used as an on-off valve actuator for a fuel injection valve of an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, a piezoelectric element has a storage capacity similar to a capacitor, and when a voltage is applied across the element,
It is known to be an element that expands and contracts according to the stored charge. Because of its excellent piezoelectric effect, it is used in various actuators, for example, it is used as an actuator that opens and closes a fuel injection valve of a vehicle-mounted internal combustion engine.

When a piezoelectric element is used to open and close a fuel injection valve, variations in the expansion and contraction length cause variations in the fuel injection amount. Therefore, it is required to drive the piezoelectric element so that a constant charge is always charged. However, the capacitance of the piezoelectric element has a temperature dependency, and increases as the temperature of the piezoelectric element rises.

Therefore, when the piezoelectric element is charged with a constant voltage, the higher the element temperature, the more the electric charge is charged in the piezoelectric element, and the higher the temperature, the larger the expansion / contraction length. That is, in order to charge the piezoelectric element with a constant electric charge, it is necessary to lower the charging voltage as the temperature of the piezoelectric element rises, and it is necessary to detect the piezoelectric element temperature by some method.

Japanese Unexamined Patent Publication No. 64-69756 discloses a device in which a temperature sensor is attached to a piezoelectric element and the temperature of the piezoelectric element is measured by the temperature sensor. According to this device, the capacitance of the piezoelectric element at that temperature can be obtained based on the temperature measured by the temperature sensor, and an appropriate charging voltage can be set for the capacitance.

Therefore, according to the drive circuit described in the above publication, even if the temperature of the piezoelectric element fluctuates, the amount of charge charged in the piezoelectric element does not fluctuate, and the expansion / contraction length thereof does not fluctuate. . Therefore, even when the piezoelectric element is used in a portion where the environmental temperature frequently changes, such as a fuel injection valve of an on-vehicle internal combustion engine, a stable expansion / contraction length can be ensured regardless of temperature changes.

[0007]

However, in the above-mentioned conventional device, it is necessary to provide a temperature sensor for measuring the temperature of the piezoelectric element at an appropriate portion, separately from the circuit for driving the piezoelectric element. Therefore, when the above-mentioned conventional device is used as the drive circuit of the piezoelectric element, there is a problem that the cost increase due to the attachment of the temperature sensor cannot be avoided.

The present invention has been made in view of the above points, and paying attention to the fact that the amount of charge charged in the piezoelectric element changes with the temperature change of the piezoelectric element, regardless of the temperature sensor. An object of the present invention is to provide a piezoelectric element drive circuit which can secure a stable expansion / contraction length with respect to temperature and can be realized at low cost by performing temperature detection.

[0009]

FIG. 1 shows a principle diagram of a piezoelectric element drive circuit that achieves the above object.

Reference numeral 1 in FIG. 1 indicates a piezoelectric element. The charging system 10 for the piezoelectric element 1 includes an inductor 2 that forms a series LC circuit with the piezoelectric element 1, a switch circuit 3 that controls a current flowing in the series LC circuit, and a power supply-side capacitor that is connected in parallel with the series LC circuit. 4 and a power source 5.

The switch circuit 3 intermittently supplies a current to the piezoelectric element 1. The charging system 10 charges the piezoelectric element 1 at a voltage higher than the charging voltage of the power source side capacitor 4 by utilizing the transient characteristic of the series LC circuit.

The voltage across the power source side capacitor 4 is supplied to the capacitor voltage detecting means 6, and the voltage across the power source side capacitor 4 at the start of charging the piezoelectric element 1 and the power source side capacitor at the end of the charging of the piezoelectric element 1. 4 and the voltage across both terminals are detected.

The charge calculating means 7 calculates the amount of charge charged in the piezoelectric element 1 based on the voltage across the power source side capacitor 4 detected by the capacitor voltage detecting means 6.

The temperature calculating means 8 calculates the temperature of the piezoelectric element 1 based on the voltage across the power source side capacitor 4 detected by the capacitor voltage detecting means 6.

The power supply voltage control means 9 controls the output voltage of the power supply 5 on the basis of the charge charge calculated by the charge calculation means 7 and the temperature of the piezoelectric element 1 calculated by the temperature calculation means 8.

[0016]

In the piezoelectric element drive circuit having the above structure, when the switch circuit 3 is turned off to interrupt the current flowing through the piezoelectric element 1, the current flows from the power source into the power source side capacitor 4. Therefore, the voltage across the capacitor 4 on the power supply side in the steady state is equal to the output voltage of the power supply 5.

When the switching circuit 3 is turned on and the charging of the piezoelectric element 1 is started, a current flows from the power source 5 to the piezoelectric element 1 via the inductor 2 and is stored in the power source side capacitor 4. The electric charge is also discharged in the direction of the piezoelectric element 1.

When the charging of the piezoelectric element 1 progresses and the voltage across the piezoelectric element 1 approaches the output voltage of the power supply 5, the current flowing through the charging system 10 tends to decrease. Then,
A counter electromotive force is generated in the inductor 2 in the direction in which the current continues to flow. Therefore, even if the voltage across the piezoelectric element 1 reaches the output voltage of the power supply 5, the current continues to flow in the charging system 10, the piezoelectric element 1 is charged to a voltage higher than the output voltage of the power supply 5, and the charging ends. To do.

The power supply side capacitor 4 supplements the electric charge charged in the piezoelectric element 1 with a discharge that cannot be covered by the current from the power supply 5. At this time, the electric charge flowing from the power supply 5 is smaller than the electric charge flowing from the power supply side capacitor 4. Therefore, the piezoelectric element 1
The amount of electric charge charged to the power source 1 corresponds to the amount of electric charge discharged from the power source side capacitor 1.

The voltage across the piezoelectric element 1 before the start of charging is equal to the output voltage of the power source 5, the voltage across the piezoelectric element 1 decreases as the charging progresses, and reaches a minimum value at the end of charging. . Therefore, the difference between the voltage across the power source side capacitor 4 at the start of charging the piezoelectric element 1 and the voltage across the power source side capacitor 4 at the end of the charging of the piezoelectric element 1 causes the piezoelectric element 1 to be charged. The value corresponds to the amount of charge.

The amount of electric charge charged in the piezoelectric element 1 is a value determined by the voltage across the power source side capacitor 4 at the start of charging the piezoelectric element 1 and the electrostatic capacity of the piezoelectric element 1. . That is, the capacitance of the piezoelectric element 1, that is, the temperature of the piezoelectric element 1 is determined by the voltage across the capacitor 4 on the power source side at the start of charging and the amount of charge charged in the piezoelectric element 1, that is, before and after charging. It is a value determined by the difference in voltage across the power supply side capacitor 4.

By the way, the capacitor voltage detecting means 6
Detects the voltage across the power source side capacitor 1 before and after charging the piezoelectric element 1, and supplies the detected value to the charge calculating means 7 and the temperature calculating means 8. And
The charge calculating unit 7 and the temperature calculating unit 8 calculate the voltage across the power source side capacitor 4 before and after the piezoelectric element 1 is charged, the amount of charge charged in the piezoelectric element 1 and the temperature of the piezoelectric element 1. The charge amount and the temperature are calculated based on the relationship.

The power supply voltage control means 9 sets the output voltage of the power supply 5 so that the charge amount calculated by the charge calculation means 7 approaches a target charge amount, and the temperature calculation means 8 calculates the output voltage. The output voltage of the power supply 5 is corrected so as to cancel the variation of the electrostatic capacitance of the piezoelectric element 1 based on the temperature of the piezoelectric element 1.

[0024]

FIG. 2 is a block diagram showing the configuration of an embodiment of a piezoelectric element drive circuit according to the present invention.

In the figure, reference numeral 11 indicates lead zirconate titanate (PZT) which is a piezoelectric element in the circuit of this embodiment. The PZT 11 has a structure in which a large number of thin plate piezoelectric elements are laminated, and when a voltage is applied to the bipolar terminals, the PZT 11 expands in the longitudinal direction by the piezoelectric effect. In addition, when the voltage application is stopped, it immediately contracts to the original length.

As described above, the PZT 11 has excellent responsiveness due to the piezoelectric effect. Further, the PZT 11 is known to exhibit an accurate displacement according to the amount of charged electric charge, and has conventionally been used for the fuel injection valve 30 of an in-vehicle internal combustion engine as shown in FIG.

The structure of the fuel injection valve 30 to which the PZT 11 of this embodiment is applied will be described below.

In FIG. 3, reference numeral 31 indicates a housing of the fuel injection valve 30, and a fuel injection port 32 is provided at one end thereof. A needle valve 33 that can open and close the injection port 32 is arranged in the housing 31.

A fuel passage 34 is provided so as to be able to communicate with the injection port 32. The fuel passage 34 is connected to an external fuel supply source (not shown), and the fuel is always supplied to the fuel injection valve 30 at a constant high pressure. Therefore, when the needle valve 33 opens the injection port 32, the fuel passage 34
The fuel supplied to the internal combustion engine is injected into the combustion chamber of the internal combustion engine at a constant high pressure.

A cylinder 35 is formed inside the housing 31. A piston 36, PZT 11, which is formed integrally with the needle valve 33 and is slidable in the cylinder 35, and caps 37, 38 for holding the piston from above and below are housed in the cylinder 35. Here, the upper cap 37 contacts the upper wall of the housing 31,
The lower cap 38 can slide in the cylinder 35.

Therefore, when the PZT 11 receives the voltage supply and expands and contracts, the lower cap 38 slides in the cylinder 35 as the PZT 11 expands and contracts. The fuel injection valve 30 is provided with lead wires 39 and 40 for applying a voltage for driving the PZT 11.

By the way, a hydraulic chamber 41 is formed in the cylinder 35 between the piston 36 integrally formed with the needle valve 33 and the lower cap 38. Also,
A disc spring 42 for returning is arranged below the piston 36.

Accordingly, when the PZT 11 receives the charging voltage and extends, the piston 36 is pressed through the hydraulic oil in the lower cap 38 and the hydraulic chamber 41. When the piston 36 is pressed, the needle valve 33 closes the injection port 32 and the fuel supply is stopped. When the PZT 11 discharges electric charge and contracts, the disc spring 42 pushes back the piston 36 and the injection port 32 communicates with the fuel passage 36, so that fuel is injected again.

As described above, the PZT 11 of this embodiment is used for the actuator that opens and closes the fuel injection valve 30, and the operating environment temperature frequently and drastically fluctuates and expands and contracts with high accuracy. Is required.

The configuration of the drive circuit shown in FIG. 2 will be described in detail below as an example of the drive circuit satisfying such requirements.

In FIG. 2, reference numeral 12 indicates an inductor which is connected in series with the PZT 11 and constitutes a serial LC circuit.
A thyristor 13 corresponding to a switch circuit is provided between the PZT 11 and the inductor 12. The thyristor 13 is driven by a charge / discharge control circuit 21 described later, controls the current flowing into the PZT 11, and controls the PZT 11.
The reverse flow of current from T11 to the inductor 12 is cut off.

Reference numeral 14 is an electrolytic capacitor having an electrostatic capacity C ₁ corresponding to a power source side capacitor, which is the PZT 11,
The series LC circuit including the inductor 12 and the thyristor 13 is connected in parallel to the DC-DC converter 15. The DC-DC converter 15 corresponds to the power supply in the circuit of this embodiment and can change the output voltage according to an external command.

Further, a capacitor voltage detection circuit 16b is connected to both polar terminals of the capacitor 14 via an amplifier 16a. This capacitor voltage detection circuit 16b is
A charge timing signal indicating the start of charging the PZT 11 is supplied from the control circuit 21 described later. Then, the voltage across the capacitor 14 at that time is fetched as the charging start voltage V ₁ of the PZT 11.

Thyristor 1 for charging the PZT 11
When 3 is turned on, I in FIG. _PZTAs shown
In addition, a current flows through the PZT 11 via the inductor 12.
Put in. This I_PZTIs mainly charged in the capacitor 14
Charge flowed into the PZT 11 via the inductor 12.
It is a thing.

When I _PZT flows into PZT 11, PZT
As shown in FIG. 4B, the charge 11 is charged with the charge Q _PZT corresponding to the integrated value of I _PZT . Therefore, PZT11
The voltage V _PZT between the two becomes larger in proportion to Q _PZT , and eventually becomes equal to the output voltage of the DC-DC converter 15.

Thus, the voltage across the PZT 11 is DC
If the output voltage of the −DC converter 15 becomes equal to the output voltage, there is no potential difference between the two, so that the inflow of charges into the PZT 11 should end at that point. However, as described above, between the PZT 11 and the DC-DC converter 15, the inductor 12 that generates the counter electromotive force in the direction of suppressing the current change is arranged.

Therefore, the current (I
_{When PZT} ) decreases, an electromotive force is generated in the inductor 12 in a direction to keep the current flowing, and PZT1
1 continues to be supplied with electric charges. Therefore, the voltage across the PZT 11 at the end of charging is higher than the output voltage of the DC-DC converter 15. Then, the reverse flow of electric charges is blocked by the thyristor 13, and the PZT 11 is held in a state of being charged to a high voltage.

By the way, there is a limit to the current that the DC-DC converter 15 can flow. Therefore, when a large amount of charge transfer is required instantaneously as in the case of charging the _{PZT 11} , as shown in FIG. 4C, the current saturates at the start of charging (time t ₁ ) and the I _PZT The shortfall for the requested amount is
It is supplemented by the discharge from the capacitor 14.

Therefore, as shown in FIG.
11 from the start to the end of charging (time t
₁ to time t ₂ ) The voltage across the capacitor 14 continues to decrease and reaches the minimum value at the end of charging the PZT 11. Then, after that, as the electric charges are supplied from the DC-DC converter 15 again, the voltage across the terminals gradually increases.

The capacitor voltage detection circuit 16b monitors the voltage across the capacitor 14, and when the voltage across the capacitor 14 becomes the lowest (time t ₂ in FIG. 4D), the voltage across the capacitor 14 is terminated. Take in as voltage V ₂ . Then, the charging start voltage V ₁ and the charging end voltage V ₂ thus detected are supplied to the charge calculation circuit 17 and the temperature calculation circuit 18.

As described above, the charge Q _PZT stored in the _{PZT 11} is supplied to the DC-DC converter 15 during the charging period.
Is the total of the charges flowing out of the capacitor and the charges flowing out due to the discharge of the capacitor 14. However, the current that the DC-DC converter 15 can flow is a smaller value than the current that the capacitor 14 can instantaneously flow when discharging. Also, P
The electrostatic capacity of ZT11 is sufficiently smaller than the electrostatic capacity of the capacitor 14, and the charging of PZT11 is practically instantaneously terminated.

[0047] Therefore, the charge amount Q _PZT stored in PZT11, can be substantially it is possible to approximate the amount of charge flowing out from the capacitor 14, represented as _{Q PZT ≒ C 1 * (V} 1 -V 2) . Charge amount calculating circuit 17 performs a calculation of the Q _PZT Using this characteristic, and supplies the calculated value to the power supply voltage control circuit 19a.

The power supply voltage control circuit 19a compares the value supplied from the charge amount calculation circuit 18 with the target charge amount to be charged in the _PZT 11, and sets DC- to a value such that Q _PZT approaches the target value. The reference value of the output voltage value of the DC converter 15 is set.

In the conventional drive circuit, Q _PZT is generally detected by integrating I _PZT . Therefore, a current detecting sensor such as a pickup coil and an integrating circuit are required in the drive circuit. On the other hand, the drive circuit of the present embodiment calculates Q _PZT based on the fluctuation of the voltage across the capacitor 14 as described above. For this reason, it is not necessary to provide a current detection sensor, an integrator, or the like, and the configuration of the drive circuit can be simplified as compared with the related art.

By the way, the electrostatic capacitance C of PZT11
_As shown in FIG. 5 (A), _PZT has temperature dependence, and when the temperature T _{PZT of PZT 11} rises, it tends to increase accordingly. Therefore, in the drive circuit shown in FIG. 2, assuming that the output voltage of the DC-DC converter 15, that is, the charging voltage V ₁ is constant, PZT1
As the temperature rises by 1, the charge Q _PZT charged in the _{PZT 11} increases in one charge.

That is, the charging start voltage V₁Is constant
For example, the voltage V at the end of charging₂Is the temperature T of PZT11_PZTof
It will be represented by a function. FIG. 5B shows these.
V₁, V ₂And T_PZTIt shows the relationship with₁, V₂
T for a combination of_PZTShows that is uniquely determined
is doing. Temperature calculation circuit 1 in the drive circuit of this embodiment
8 uses this relationship to determine the temperature T of the PZT 11._PZTCalculate
And supplies the value to the power supply voltage correction circuit 19b.
It

The power supply voltage correction circuit 19b, based on the temperature T _PZT of the _PZT 11 detected by the temperature detection circuit 18,
DC-DC set by the power supply voltage control circuit 19a
The output voltage value of the converter 15 is corrected.

As described above, the temperature T _{PZT of the PZT 11}
If the same voltage is used for charging, PZT
The charge Q _{PZT of} 11 increases. On the other hand, the PZT 11 is an element that exhibits accurate expansion and contraction according to the amount of charge. Therefore, in order to drive the PZT 11 with a constant expansion and contraction regardless of the temperature, it is necessary to make the charging voltage follow the fluctuation of the temperature of the PZT 11.

Therefore, in the drive circuit of the present embodiment, the correction voltage ΔV ₁ for canceling the change of the electrostatic capacitance C _{PZT in} the power supply voltage correction circuit 19b is calculated based on the map shown in FIG. 5C. It is determined from T _PZT detected by the temperature calculation circuit 18 and added as a correction to V ₁ set by the power supply voltage control circuit.

As described above, according to the drive circuit of this embodiment, the temperature T of the PZT 11 can be adjusted without using the temperature sensor.
_{The PZT} can be detected, and the charge Q _PZT charged in the _{PZT 11} can be detected without using a current sensor or an integrating circuit. Then, based on these T _PZT and Q _PZT , feedback control of the output voltage of the DC-DC converter 15 is performed to charge the charge Q of the PZT 11.
_{The PZT} can be accurately maintained near the target value.

In FIG. 2, reference numerals 22 and 23 denote PZT11.
2 shows an inductor and a thyristor for discharging the charge Q _PZT charged in the first place. Like the inductor 12 on the charging side, the inductor 22 forms a series LC circuit with the PZT 11 and has an action of excessively discharging the PZT 11.

Further, the thyristor 23 corresponds to a switch circuit on the discharge side, is turned on when receiving a discharge signal from the charge / discharge control circuit 21, and is turned on from the PZT 11 to the inductor 2.
Pass current in three directions.

The charging / discharging control circuit 21 alternately turns on the charging side thyristor 13 and the discharging side thyristor 23 at predetermined intervals to cause the PZT 11 to repeat charging / discharging. That is, the PZT 11 expands and contracts in a cycle in which the charge / discharge control circuit 21 issues a charge / discharge signal. Therefore, the fuel injection valve 3 shown in FIG.
From 0, fuel is injected from when the discharge signal is issued from the charge / discharge control circuit 21 until the next charge signal is issued.

FIG. 6 is a diagram showing a configuration of an example in which the circuit of the above embodiment is realized by using a microcomputer. In the present embodiment, in the block diagram shown in FIG. 2, capacitor voltage detection circuit 16b, charge calculation circuit 17, temperature calculation circuit 18, power supply voltage control circuit 19a, power supply voltage correction circuit 1
9b, the charge / discharge control circuit 21 is a microcomputer 50
It is realized in. The same components as those in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 6, the microcomputer 50 is A
Input port 51 with built-in / D converter, output port 52, read only memory (ROM) 53, random access memory (RAM) 54, central processing unit (CPU)
55, and a common bus 56 connecting them to each other.

The input port 51 includes an air flow meter 61 for detecting the amount of air flowing into the internal combustion engine, a water temperature sensor 62 for detecting the cooling water temperature of the internal combustion engine, a throttle sensor 63 for detecting the accelerator opening, and an engine speed. Output terminals of the rotation speed sensor 64 and the like for detection are connected, and also an output terminal of an amplifier 16a for amplifying the voltage across the capacitor 14 is connected.

Further, the output port 52 is connected to the input terminals of the charge-side and discharge-side thyristors 13 and 23 and the DC-DC converter 15, and the charge signal, the discharge signal and the output voltage command signal are supplied to the respective terminals. is doing.

The microcomputer 50 calculates the amount of fuel to be supplied to the internal combustion engine by processing the data supplied from the various sensors 61 to 64 according to the program stored in the ROM 53. Then, the fuel injection valve 30 shown in FIG.
In order to inject the fuel into the internal combustion engine, the time TAU during which the fuel injection port 32 is opened, that is, the time TAU during which the PZT 11 is contracted is calculated.

Then, according to the TAU, charge / discharge signals are alternately supplied to the thyristors 13 and 23. Therefore, the PZT 11 is in a contracted (discharged) state for a predetermined time TAU.

On the other hand, the ROM 53 also stores a program for keeping the expansion / contraction length of the PZT 11 constant and suppressing variations in the fuel injected when the fuel injection valve 30 is open. The operation of executing this program will be described below with reference to the flowchart of FIG.

When this routine is started, first PZT1
Check whether the charge of 1 is started (step 10)
1). Here, if the charging has not been started yet, the processing is ended as it is, and the charging is waited for.

The thyristor 13 is turned on and the PZT11
When charging starts, go to step 102
The voltage V across the capacitor 14 at
Pressure V ₁(See FIG. 4D).

After the read V ₁ is temporarily stored in the RAM 54, the process proceeds to step 103 and the change in the voltage V across the capacitor 14 is monitored. Then, the above steps 101 to 103 are performed until V starts to increase as compared with the time of the previous routine.
Is repeatedly executed (from time t ₁ to time in FIG. 4D).
t ₂ ).

Then, the discharge of the capacitor 14 is finished,
When the both-end voltage V starts to increase, it is determined that the charging of the PZT 11 is completed (time t ₂ in FIG. 4D), and V at that time is read as the charging completion voltage V ₂ of the PZT 11 (step 104). .

As described above, the charge Q _PZT charged in the _{PZT 11} is almost equal to the charge flowing out from the capacitor 14. Therefore, at the current charging voltage, how much charge is P
Q _PZT ≈ to know if ZT11 is charged
C ₁ (V ₁ −V ₂ ) is calculated (step 105).

Then, the Q obtained in the above step 105
_PZTIs compared with the target charge amount, and Q _PZT> Target charge amount,
If this is the case, the voltage at the start of charging this time was too high.
_PZT<If the target charge amount, then the voltage at the start of charging this time is low
It is judged that it has passed, and the next charging start voltage V₁The reference value of
Calculate (step 106).

Next, at step 107, in order to correct the change in the electrostatic capacity of the PZT 11, the temperature T of the PZT 11 is adjusted.
Detects _PZT . As described above, T _PZT is a value uniquely determined by V ₁ and V ₂ . Further, in the ROM 53 of this embodiment, V ₁ and V ₂ are stored together with various programs.
And a map (see FIG. 5B) showing the relationship between T _PZT and T _PZT are stored. Therefore, in step 107, T _PZT is read from the map shown in FIG. 5B using V ₁ and V ₂ detected in steps 102 and 104 described above.

The ROM 53 is further provided with a correction voltage ΔV ₁ for canceling the change in the electrostatic capacitance C _PZT due to the change in T _PZT.
It also stores a map (see FIG. 5C) related to the above.
Therefore, in the present embodiment, the above step 107 is performed.
When T _PZT is obtained in Fig. 5 (C), based on that value.
The correction voltage ΔV ₁ is obtained from the map shown in (step 108).

Then, the next charging start voltage V ₁ is set by adding the correction voltage ΔV ₁ to the reference value of the charging start voltage V ₁ obtained in step 106, and the DC-DC from the output port 52 is set. It is supplied to the converter 15 (step 109), and the process is terminated.

As described above, according to the drive circuit of this embodiment, the feedback control for keeping the charge amount of the PZT 11 constant can be executed without providing the temperature sensor, the current sensor, the integrating circuit, or the like. Variations in the behavior of the PZT 11 due to temperature changes can also be corrected.

Therefore, the circuit can be simplified and the cost can be reduced as compared with the conventional piezoelectric element drive circuit, and the precision of control and the high reliability of control can be improved with the abolition of a circuit having a large detection error such as an integrating circuit. It can be sexualized.

In the above embodiment, the charging start voltage V ₁ is detected by detecting the timing at which the thyristor 13 is turned on, and the charging is started when the capacitor 14 is discharged and the voltage V at both ends starts to increase. Although the voltage V ₂ at the end is detected, the voltage across the capacitor 14 may be sequentially monitored and the maximum value and the minimum value may be used as V ₁ and V ₂ .

[0078]

As described above, according to the present invention, a temperature sensor is not necessary for detecting the temperature of the piezoelectric element, and the electric current flowing into the piezoelectric element is detected for detecting the charge charged in the piezoelectric element. There is no need for a current sensor and an integrator circuit to integrate this current.

Therefore, the structure is simplified as compared with the conventional piezoelectric element drive circuit, the cost can be reduced, and the reliability of the circuit can be improved and the control accuracy can be improved.
Therefore, the piezoelectric element drive circuit according to the present invention has a feature that it is suitable for a piezoelectric element drive circuit that is required to be able to drive a piezoelectric element with a stable expansion / contraction length regardless of environmental temperature and to be realized at low cost. Have

[Brief description of drawings]

FIG. 1 is a principle diagram of a drive circuit for a piezoelectric element according to the present invention.

FIG. 2 is a block diagram showing a configuration of an embodiment of a piezoelectric element drive circuit according to the present invention.

FIG. 3 is a front cross-sectional view showing the configuration of a fuel injection valve using a PZT as a power source, which is used in the drive circuit of this embodiment.

FIG. 4 is a waveform of a current or the like in a main part when the PZT is charged by the drive circuit of the present embodiment.

FIG. 5 is a diagram showing a relationship between temperature and capacitance of PZT used in this example.

FIG. 6 is a diagram showing a configuration of an example in which a drive circuit for a piezoelectric element according to the present invention is realized by using a microcomputer.

FIG. 7 is a flowchart showing an example of processing executed by a piezoelectric element drive circuit realized using a microcomputer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Piezoelectric element 2, 12, 22 Inductor 3, 13, 23 Thyristor 4 Power supply side capacitor 5 Power supply 6 Capacitor voltage detection means 7 Charge calculation means 8 Temperature calculation means 9 Power supply voltage control means 10 Charging system 11 PZT 14 Capacitor 15 DC-DC Converter 16a Amplifier 16b Capacitor voltage detection circuit 17 Charge calculation circuit 18 Temperature detection circuit 19a Power supply voltage control circuit 19b Power supply voltage correction circuit 21 Charge / discharge control circuit 50 Microcomputer

Claims (1)

[Claims] 1. A charging system for a piezoelectric element includes an inductor that forms a series LC circuit with the piezoelectric element, and a switch circuit that controls a current flowing through the series LC circuit, and a power supply connected in parallel with the series LC circuit. A driving circuit for a piezoelectric element that has a side capacitor and applies a charging voltage higher than the voltage across the power source side capacitor to the piezoelectric element when the piezoelectric element is charged by utilizing the transient characteristics of the series LC circuit. In, the capacitor voltage detecting means for detecting the voltage across the power source side capacitor at the start of charging the piezoelectric element and the voltage across the power source side capacitor at the end of charging the piezoelectric element, and the capacitor voltage detecting means. Charge calculating means for calculating the charge charged in the piezoelectric element based on the detected voltage across the power source side capacitor; Temperature calculating means for calculating the temperature of the piezoelectric element based on the voltage across the power source side capacitor detected by the capacitor voltage detecting means, the charge calculated by the charge calculating means, and the temperature calculating means. A drive circuit for a piezoelectric element, comprising: a power supply voltage control means for controlling a power supply voltage of a charging system for the piezoelectric element based on temperature.