JP2773585B2 - Piezo element drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art A piezoelectric element such as PZT (lead zirconate titanate) is generally used as an actuator for a fuel injection valve of an internal combustion engine.

The applicant of the present application has previously disclosed in Japanese Patent Application No. 4-177125 the charge amount of a piezoelectric element, and controlled the power supply voltage so that the charge amount matches the target charge amount. We proposed a piezoelectric element drive circuit that changes the initial value according to the temperature of the piezoelectric element.

[0004]

However, since the relationship between the temperature of the piezoelectric elements and the capacitance is different for each piezoelectric element, there is a problem that an optimum initial value of the power supply voltage cannot be supplied to all the piezoelectric elements. Was.

[0005] The present invention has been made in view of the above points,
By applying a small voltage to the piezoelectric element and calculating the capacitance and internal resistance of the piezoelectric element, it is possible to apply an initial voltage of an optimal value specific to the piezoelectric element, and from the first injection to the fuel injection valve. An object of the present invention is to provide a piezoelectric element drive circuit capable of injecting an accurate amount of fuel.

[0006]

FIG. 1 shows the principle of the present invention. The control means M1 controls the voltage applied to the piezoelectric element M3 for driving the fuel injection valve M2 to control the state of the piezoelectric element such as the amount of charge or the amount of charge energy of the piezoelectric element M3.

[0007] The charging means M4 charges the piezoelectric element M3 by applying a small voltage to the extent that the fuel injection valve M2 does not inject fuel.

The calculating means M5 calculates the capacitance and the internal resistance of the piezoelectric element M3 from the charging time by the charging means M4 and the power supply voltage change width or charged amount before and after charging.

[0009]

In the present invention, the capacitance and internal resistance of the piezoelectric element are calculated before fuel injection, and the initial value of the power supply voltage applied to the piezoelectric element is determined based on the calculated value. The fuel is not injected at the time of calculation, and an accurate amount of fuel injection according to the characteristics of each piezoelectric element can be performed from the initial injection.

[0010]

FIG. 2 is a circuit diagram showing an embodiment of the circuit of the present invention.

In FIG. 1, reference numeral 10 denotes a battery. The output voltage of the battery 10 is supplied to a DC-DC converter 11.

DC-DC as a switching power supply circuit
The converter 11 includes a transformer, a switching element that intermittently supplies current from the battery 10 to the primary coil of the transformer, and a diode that performs full-wave rectification of the current induced in the secondary coil of the transformer. -D
The power supply capacitor C2 is output by the output of the C converter 11.
Is charged and stabilized.

The positive output terminal of the DC-DC converter 11 is connected to one end of a capacitive piezoelectric element 14 through a charging inductor 12 and a thyristor 13 connected in series with the charging inductor 12, and the other end of the piezoelectric element 14 is connected to a DC-DC Converter 11
Is connected to the negative output terminal of Also, the piezoelectric element 12
Are connected through a thyristor 15 and a discharging inductor 16 connected in series to the thyristor 15.

The thyristors 13 and 15 are configured to be switching-controlled by an ignition circuit (not shown) connected to the gates. When one is on, the other is off, and the thyristors 13 and 15 alternately repeat on and off. The switching is controlled as follows.

When the thyristor 13 is on, the charge of the power supply capacitor C 2 is applied to the piezoelectric element 14 through the charging inductor 12 and the thyristor 13. That is, when the thyristor 13 is turned on, the current I ₁ flows in the direction shown in the figure, and the piezoelectric element 14 which is a capacitive load due to resonance.
High voltage V _P from the supply voltage V ₀ is stored in.

Thereafter, when the thyristor 15 is turned on, the charge of the piezoelectric element 14 is discharged through the thyristor 15 and the discharging inductor 16. Therefore, when the thyristor 15 is ON, the discharge current flows through the thyristor 15 and the discharge inductor, terminal voltage V _P of the piezoelectric element 14 by the overshoot is reduced to a negative voltage.

On the other hand, a current detector 20 provided between the positive output terminal of the DC-DC converter 11 and the charging inductor 12 outputs a current i ₁ flowing into the charging inductor 12.
Is detected and supplied to the control unit 21. The voltage detector 22
It detects the voltage across V ₀ which capacitor C2, the voltage detector 23 is supplied to each control unit 21 detects the terminal voltage V _P of the piezoelectric element 14. The control unit 21 controls the current i ₁ and the voltage V ₀
, The duty ratio of the switching pulse of the DC-DC converter 11 is varied, and the electric energy output per unit time is controlled to be constant.

Here, the fuel injection valve driven by the piezoelectric element 14 has a voltage V ₀ of 20 although there are some errors due to each piezoelectric element as shown by a solid line, a broken line and a dashed line in FIG.
Fuel is injected when the voltage exceeds 0 V, and no fuel is injected when the voltage is 200 V or less. The internal resistance R _P and the capacitance C _P of the equalization circuit of the piezoelectric element 14 shown in FIG. 4 this piezoelectric element 14 is pre-charged fuel injection valve does not work at start by using for example the following voltage 100V and Calculated, and based on this, D
An initial value of the output voltage of the C-DC converter 11 is calculated.

FIG. 5 shows a flowchart of one embodiment of the initial value determining process executed by the control unit 21. This process is started at the time of starting.

[0020] In the figure, it sets the output voltage of the DC-DC converter 11 at step S1 to a low voltage below V ₁ 100 V. Next, in step S2, the charging thyristor 13 is turned on, and in step S3, the current I ₁ or the voltage V ₀ is measured. In step S4, the equivalent circuit C _P ,
To calculate the R _P.

Due to the conduction of the thyristor 13, the voltage V ₀ across the capacitor C2 changes as shown in FIG. 6A, the current I ₁ flowing through the inductor changes as shown in FIG. The voltage V _P across the element 14 is shown in FIG.
It changes as shown in (C). The transient inductance L ₀ of the inductor 12 is determined by the internal resistance R _P and the capacitance C _P of the capacitance C ₀ and the piezoelectric element 14 of the capacitor C2. L ₀ and C ₀ are known, and a time T ₀ until the voltage V ₀ changes from V ₁ to V ₂ , or until the current I ₁ flows to become 0, or until the voltage _VP becomes stable.
Since is determined by ^{_{(L 0 C P) 1/}} 2, can now calculate the electrostatic capacitance C _P. Further, it calculates the internal resistance R _P from one of the minimum value V _2, or the maximum value I ₃ of the current I _1, or the voltage V _P of the stable value V ₃ of the voltage V _0.

[0022] At next step S5 from the capacitance C _P of the piezoelectric element 14 by using a map shown in FIG. 7 to calculate the initial value of the supply voltage.

Thereafter, it is determined in step S6 whether a signal for instructing fuel injection is supplied or not. While the signal is being supplied, the piezoelectric element 14 is charged in step S7 to activate the fuel injection valve. The fuel injection is performed by driving, and when the supply of the signal stops thereafter, the piezoelectric element 14 is discharged to stop the fuel injection, and the process returns to step S6.

[0024] To determine the initial power supply voltage applied to the piezoelectric element 14 on the basis thus calculates the capacitance C _P of the piezoelectric element 14 prior to fuel injection and the internal resistance R _P thereto, piezoelectric No fuel injection is performed when calculating the characteristics of the element 14, and an accurate amount of fuel injection according to the characteristics of each piezoelectric element can be performed from the first injection.

In addition, when calculating C _P and R _P , it is possible to judge whether a circuit is short-circuited, disconnected, or a piezoelectric element has a poor characteristic, thereby performing fail-safe. Further measures the piezoelectric element state such as voltage V _P at the time of fuel injection DC-D
The output voltage of the C converter 11 can be varied.

Further, for example, by executing the processing of FIG. 5 at the time of fuel cut or the like, it becomes possible to analyze the contents of the trouble when the trouble occurs.

[0027]

As described above, according to the piezoelectric element driving circuit of the present invention, by applying a small voltage to the piezoelectric element and calculating the capacitance and the internal resistance of the piezoelectric element, the optimum characteristic peculiar to the piezoelectric element is obtained. It is possible to apply an initial voltage of an appropriate value, and it is possible to inject a correct amount of fuel with the fuel injector from the first injection, which is extremely useful in practical use.

[Brief description of the drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a circuit configuration diagram of the circuit of the present invention.

FIG. 3 is a characteristic diagram of a fuel injection valve.

FIG. 4 is an equivalent circuit diagram of a piezoelectric element.

FIG. 5 is a flowchart of an initial value setting process.

FIG. 6 is a signal waveform diagram of each part in FIG. 2;

FIG. 7 is a diagram showing a map of initial values.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Battery 11 DC-DC converter 12 Charging inductor 13, 15 Thyristor 14 Piezoelectric element 16 Discharge inductor 21 Control part

Continuation of the front page (56) References JP-A-63-72381 (JP, A) JP-A-2-103970 (JP, A) JP-A-3-50360 (JP, A) JP-A-63-97854 (JP) , A) JP-A-63-183250 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F02D 41/00-41/40 H01L 41/09

Claims (1)

(57) [Claims] 1. A piezoelectric element drive circuit for controlling a voltage applied to a piezoelectric element for driving a fuel injection valve to control a state of the piezoelectric element such as a charge amount or a charge energy amount of the piezoelectric element. Charging means for charging by applying a small voltage such that the injection valve does not inject fuel; charging time by the charging means; and a power supply voltage change width or charge amount before and after charging; A piezoelectric element drive circuit, comprising: calculation means for calculating capacitance and internal resistance.