JPH06153537A - Piezoelectric element driving circuit - Google Patents

Abstract

PURPOSE:To prevent the amount of extension of a piezoelectric element from being changed by variations in temperature of the piezoelectric element and periodic variations of a driving signal. CONSTITUTION:A switching power supply circuit 11 switches a first switching means SW by a supplied switching pulse, so that an outputted D.C. voltage is controlled. A piezoelectric element 12 is connected to a capacitor C2 which is charged by an output from the switching power supply circuit 11 via second switching means S1 and S2. Here, a duty ratio of a switching pulse corresponds to a frequency of a driving signal in such a manner that it becomes larger as the frequency becomes large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element driving circuit, and more particularly to a circuit for driving a piezoelectric element used as an actuator.

[0002]

2. Description of the Related Art Piezoelectric elements such as PZT (lead zirconate titanate) are generally used as actuators for fuel injection valves of internal combustion engines.

Conventionally, as disclosed in Japanese Patent Laid-Open No. 60-237869, a piezoelectric element drive circuit for boosting an output voltage of a DC-DC converter as a power supply circuit by an LC resonance circuit and applying the boosted voltage to both ends of a piezoelectric element. is there.

[0004]

In the above conventional circuit,
When the temperature and the driving cycle of the piezoelectric element fluctuate, the amount of energy charged in the piezoelectric element changes, which causes a change in the amount of expansion of the piezoelectric element due to charging, which is not constant.

The present invention has been made in view of the above points,
An object of the present invention is to provide a piezoelectric element drive circuit that prevents the expansion amount of the piezoelectric element from changing due to temperature fluctuations of the piezoelectric element and cycle fluctuations of the driving signal by making the duty ratio of the switching pulse correspond to the frequency of the driving signal. And

[0006]

A piezoelectric element drive circuit according to the present invention is a switching power supply circuit for controlling an output DC voltage by switching a first switching means with a supplied switching pulse, and an output of the switching power supply circuit. And a piezoelectric element connected to the capacitor via a second switching means, and the piezoelectric element is obtained by periodically switching the second switching means in synchronization with a drive signal. In a piezoelectric element drive circuit that charges and discharges a capacitor, the duty ratio of a switching pulse that switches the first switching means is set to increase as the frequency of a drive signal that switches the second switching means increases. Let

[0007]

In the present invention, since the duty ratio of the switching pulse is made to correspond to the frequency of the drive signal, the charging energy per time of the piezoelectric element is substantially constant even if the temperature of the piezoelectric element and the drive cycle change. Since the charging energy per charge is substantially constant, the amount of expansion of the piezoelectric element can be constant.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a circuit diagram of an embodiment of the circuit of the present invention.

In the figure, 10 is a battery, and the output voltage of this battery 10 is stabilized by an electric field capacitor C1 and supplied to a DC-DC converter 11.

DC-DC as a switching power supply circuit
The converter 11 includes a transformer T1 and a switching element SW (first switching means) that intermittently supplies a current from the battery 10 to the primary coil L1 of the transformer T1.
It is composed of diodes D1 and D2 that rectify the current induced in the secondary coil L2 of the transformer T1, and the electric field capacitor C is formed by the output of the DC-DC converter.
2 is charged and stabilized.

The connection point between the capacitor C2 and the diode D1 is connected to one end of the capacitive piezoelectric element 12 through the charging inductor L3 and the thyristor S1 connected in series to the charging inductor L3, and the other end of the piezoelectric element is connected to the diode D2 of the capacitor C2. It is connected to the connection point with. In addition, the piezoelectric element 12
The two ends are connected to each other through a thyristor S2 and a discharging inductor L4 connected in series with the thyristor S2. The thyristors S1 and S2 form second switching means.

On the other hand, the terminal 15 is connected to the electronic control circuit shown in FIG.
A drive signal as shown in FIG. This drive signal is, for example, a signal instructing fuel injection during the L level period.
The ignition circuit 16 detects the falling edge and the rising edge of the drive signal and generates the ignition signals shown in FIGS. 2B and 2C, respectively.
Supply to thyristors S1 and S2 respectively.

As a result, the thyristor S1 is shown in FIG.
During the H level period of the ignition signal, the output voltage of the DC-DC converter is boosted by the resonance circuit formed by the inductor L3 and the piezoelectric element 12, and the piezoelectric element 12 is charged.

Further, the thyristor S2 conducts during the H level period of the ignition signal of FIG. 2C, the piezoelectric element 12 is discharged by the resonance circuit formed by the inductor L4 and the piezoelectric element 12, and both ends of the piezoelectric element 12 are discharged. The inter-child voltage drops to a negative voltage.

The drive signal from the terminal 15 is supplied to the F / V conversion circuit 17, where a signal having a voltage proportional to the frequency of the drive signal is generated and supplied to the pulse width variable circuit 18. The variable pulse width circuit 18 generates a switching pulse having a constant frequency and a duty ratio as shown in FIG. 3 with respect to the signal voltage from the F / V conversion circuit 17, and supplies it to the switching element SW. The switching element SW conducts during the H level period of this switching pulse.

Here, in order to make the charging energy per one time of the piezoelectric element 12 constant, the energy per unit time proportional to the frequency of the drive signal 15 is set to DC-D.
It may be supplied to the primary side of the C converter 11. Also DC
Since the energy supplied to the primary side of the DC converter 11 is approximately proportional to the duty ratio of the switching pulse that the switching element SW conducts, it is approximately proportional to the frequency of the drive signal and the duty ratio of the switching pulse is determined. The charging energy per charge of the piezoelectric element can be made constant regardless of the temperature change of the piezoelectric element and the fluctuation of the driving cycle. The characteristic shown in FIG. 3 is not linear because the energy supplied to the primary side of the DC-DC converter is not completely proportional to the duty ratio of the switching pulse and is corrected.

Since the duty ratio of the switching pulse is made to correspond to the frequency of the drive signal as described above, the charge energy per time of the piezoelectric element is substantially constant even if the temperature of the piezoelectric element and the drive cycle change. You can
Since the charging energy per one time is substantially constant, the amount of expansion of the piezoelectric element can be constant.

Instead of providing the F / V conversion circuit 17 and the pulse width variable circuit 18, an electronic control circuit for generating a drive signal generates a switching pulse having a duty ratio corresponding to the frequency of the drive signal to generate a switching element. You may supply to SW.

[0019]

As described above, according to the piezoelectric element drive circuit of the present invention, the duty ratio of the switching pulse is made to correspond to the frequency of the drive signal, and the piezoelectric element is driven by the temperature change of the piezoelectric element and the cycle change of the drive signal. It is possible to prevent the elongation from changing, which is extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram of a circuit of the present invention.

FIG. 2 is a signal timing chart of each part of FIG.

FIG. 3 is a characteristic diagram of a pulse width variable circuit.

[Explanation of symbols]

 10 Battery 11 DC-DC Converter 12 Piezoelectric Element 16 Firing Circuit 17 F / V Converter Circuit 18 Pulse Width Variable Circuit

Claims (1)

[Claims] 1. A switching power supply circuit for controlling an output DC voltage by switching a first switching means by a supplied switching pulse, a capacitor charged by an output of the switching power supply circuit, the capacitor and a second capacitor. A piezoelectric element drive circuit comprising: a piezoelectric element connected via a switching means; and charging and discharging the piezoelectric element by periodically switching the second switching means in synchronization with a drive signal, A piezoelectric element drive circuit, wherein a duty ratio of a switching pulse for switching the first switching means is made to increase as a frequency of a drive signal for switching the second switching means increases.