JP2853119B2 - Piezo actuator drive circuit - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a piezo actuator drive circuit, and more particularly, to a piezo actuator drive circuit suitable for in-vehicle use and which can be reduced in size and cost. [Prior art] Recent advances in ceramic technology are remarkable. Piezo actuators that use the piezoelectric electrostrictive effect of ceramic ferroelectrics are also entering the field of actuators that move objects, making use of their agile response. For example, an apparatus disclosed in Japanese Patent Application Laid-Open No. Sho 59-18249 for controlling the injection rate of a diesel engine has been proposed. As a driving circuit for driving such a piezo actuator, a DC that generates the high voltage necessary for driving from a battery
-A combination of a DC converter and a switching element such as a transistor can be considered from the conventional circuit technology. However, in such a method, there is a problem that a large and expensive high withstand voltage / large capacity capacitor, a large number of expensive high withstand voltage switching elements, a large inductor or a large transformer are required. As a configuration for solving this problem, there is a piezo actuator driving circuit as disclosed in Japanese Patent Application Laid-Open No. 50-36833. The piezo actuator drive circuit has a configuration including two inductors and switching means for charging and discharging. [Problems to be Solved by the Invention] However, in the piezo actuator driving circuit disclosed in Japanese Patent Application Laid-Open No. 50-36833, since the load at the time of discharging is only the inductor, the peak current of the switching means for discharging is reduced. In order to limit, the inductance of the inductor needs to be increased, and the energy capacity of the inductor also needs to be increased. Therefore, the piezoelectric actuator drive circuit also needs to increase the size of the inductor. Furthermore, due to the large inductance, only a small current flows immediately after the discharge switching means is turned on, and it takes time for the voltage across the piezo actuator to fall (it takes time to discharge), and the piezo The control response of the actuator is deteriorated. Further, since there is a portion where the voltage across the piezoelectric actuator suddenly changes and falls, the operating sound of the piezoelectric actuator cannot be suppressed low. [Means for Solving the Problems] A piezo actuator driving circuit according to the present invention is a piezo actuator driving circuit to which a piezo electrostriction effect is applied, wherein a piezo charging means for charging the piezo actuator at a predetermined charging timing, Piezo discharging means for discharging the piezo actuator at a predetermined timing, the piezo charging means includes a first inductor for converting energy from a power supply into magnetic energy, and a magnetic field which is magnetically coupled to the first inductor. A second inductor coupled to convert the magnetic energy of the first inductor into electric energy to charge the piezo actuator, and charging switching means mounted in series with the first inductor, wherein the piezo discharging means Is a series connection of the second inductor and a resistor. The gist of the invention is that a continuation is included in a discharge circuit of the piezo actuator, and a discharge switching means is provided in series with the piezo actuator and the second inductor. [Operation] In the piezo actuator drive circuit of the present invention, the energy from the power supply is converted into magnetic energy by the first inductor, and the magnetic energy is again converted into electric energy by the second inductor magnetically coupled to the first inductor. And charges the piezo actuator to high pressure.
This energy conversion is performed by the charging switching means. Thereafter, when the discharge switching means is activated at a predetermined timing, the piezo actuator is discharged via the second inductor. Driving a piezo actuator based on such a principle eliminates the need for a high withstand voltage, large capacity capacitor, etc.
Circuit size and cost can be reduced. Also, by providing a resistor in series with the second inductor in the discharge circuit, the peak current of the discharge switching means can be reduced without increasing the inductance of the second inductor, and the energy capacity of the second inductor can be reduced. Can be limited without making it bigger. Embodiment Hereinafter, a piezo actuator driving circuit according to the present invention will be described in detail with reference to an embodiment shown in the drawings. FIG. 1 is an overall configuration diagram applied to a fuel injection rate control device as one embodiment of the present invention. In the figure, 1 is a Bosch type distribution type fuel injection pump, 11 is a plunger,
The fuel is pushed to the left in the figure by a face cam (not shown) to make the fuel in the high-pressure chamber 12 high pressure, and the fuel is injected from the nozzle 2 into the combustion chamber of a diesel engine (not shown). Reference numeral 3 denotes a piezo actuator applied to the high pressure chamber 12 and utilizing the piezo electrostriction effect. The piezo actuator 3 has a configuration as disclosed in, for example, Japanese Patent Application Laid-Open No. 59-18249. Reference numeral 4 denotes an operating state detecting means, which is a rotational speed detector 41 for detecting the rotational speed of the diesel engine, an engine load detector 42 for detecting the load on the diesel engine, such as an accelerator sensor, and detecting the temperature of the cooling water of the diesel engine. And outputs a signal from the cooling water temperature detector 43 to the microcomputer 5. Reference numeral 5 denotes a microcomputer, a CPU 51 and a memory 5
2. Built-in timer 53, A / D converter 54, etc. The microcomputer 5 has a function of calculating a charge voltage and a calculation of a discharge timing. In the present embodiment, the amount of charge to be charged in advance to the piezo actuator 3 is divided into a plurality of times. Also, it has a function of calculating the number of times of charging. Reference numeral 6 denotes a piezo driving circuit, which has a function of piezo charging means and piezo discharging means, an inductor 61A for converting electric energy of a battery (not shown) into magnetic energy, an FET 62 for switching a current of the inductor 61A,
Varistor 6 prevents overvoltage from being applied to the drain of T62
3.When the drain voltage of FET62 becomes negative voltage,
An inductor that magnetically couples with the inductor 61A, discharges magnetic energy obtained by the inductor 61A as electric energy, and charges the piezo actuator to a high voltage.
61B, a transistor 65 for discharging the high voltage generated in the piezo actuator, a varistor 66 for preventing an abnormally high voltage from being applied to the collector of the transistor 65, and a resistor 67 for limiting the current flowing through the transistor 65 and protecting the transistor 65 When charging the piezo actuator, the resistance 67
And diodes 68 and 69 for bypassing the transistor 65 respectively. FIG. 2 is a schematic diagram showing a means for calculating the charging voltage. The target charging voltage 100 is calculated according to a signal from the rotation speed detector 43 or the like by a three-dimensional map interpolation calculation programmed in the microcomputer 5. Since the data of the three-dimensional map to be subjected to the interpolation calculation is based on the standard for the diesel engine, it cannot be said unconditionally. However, as will be described later, the voltage for pre-charging the piezo actuator 3 and the injection stop period after the pilot injection are as follows. Due to the proportional relationship, when the cooling water temperature is low, the ignition delay of the pilot injection is large, so the charging voltage is increased, and the horsepower is more important than the noise of the diesel engine as the rotation speed and load become higher. Therefore, it is desirable to use map data that reduces the charging voltage. FIGS. 3A, 3B, 3C, and 3D are timing charts showing the operation of the piezo drive circuit 6 when the piezo actuator is charged. First FET62 begins to flow current in the inductor 61A becomes the "ON" state, after time _{T ON, I M = V B} × T ON / L A ...... (1) comprising a current I _M flows (here, V _B : Battery voltage, L _A :
Inductor 61A inductance). Then, the FET 62 is turned “OFF”, and the magnetic energy of the inductor 61A is transferred to the inductor 6A magnetically tightly coupled to the inductor 61A.
Released from 1B, current I _B flows through a path of the diode 69 → inductor 61B → diode 68 → the piezoelectric actuator 3 (FIG. (C)), the piezoelectric actuator 3 is charged. Here, the time T _ON is determined by the equation (1) in which the current I _M
Arbitrarily adjusted to a constant value that does not exceed the rated current of. After a lapse of the time T _{OFF, the} FET 62 is _{turned on} again, and the charging of the piezo actuator 3 is repeated N times. Here, the time T _OFF may be equal to or longer than the time required for all the magnetic energy by the inductor 61A to be transferred to the piezo actuator 3 via the inductor 61B. At this time, the voltage V _P across the piezo actuator 3 is C _P : Equivalent capacitance of the piezo actuator. The number N of times of charging should be determined so that the voltage _VP between both ends and the target charging voltage 100 described with reference to FIG. 2 are equal to or close to each other. For example, as shown in FIG.
The microcomputer 5 may be programmed to perform one-dimensional map interpolation by 0. Here, the data of the one-dimensional map may be obtained experimentally or may be obtained by mapping equation (2). In FIG. 4, the interpolation result is rounded up and the number of times of charging is set to an integer value. By setting the turns ratio N _B / N _A of the magnetically coupled inductors 61 A and 61 _B to N _B / N _A >> 1, the FET 62 can be a low breakdown voltage element. FIG. 5 is a schematic diagram showing a means for calculating the discharge timing. The discharge timing is obtained by performing a one-dimensional map interpolation calculation according to a signal from the rotation speed detector 41. As will be described later, the pilot injection amount decreases as the discharge timing is advanced to the advanced side. The map data used for map interpolation cannot be said unconditionally because it is based on diesel engine conformity standards,
As the engine speed increases, the horsepower is more important than the noise, so that it is desirable to shift the discharge timing to the advanced side in order to reduce the pilot injection amount. Needless to say, the discharge timing may be corrected according to signals from the engine load detector 42, the coolant temperature detector 43, and the like. FIG. 6 shows the operation of the piezo drive circuit 6 during piezo discharge. When the discharge time determined as described above is reached, the sixth
The transistor 65 is turned “ON” as shown in FIG. Then piezo actuator 3 → resistor 67 → inductor 61B →
Current I _B flows through a path of the transistor 65 (FIG. (C)),
As shown in FIG. 3B, the voltage across the piezo actuator 3 drops sharply. When the transistor 65 is turned OFF when the voltage between both ends of the piezo actuator 3 becomes OV, the current of the inductor 61B instantaneously becomes 0, so that the current flows through the inductor 61A magnetically coupled to the inductor 61B. Flows and energy is regenerated in the battery. In the present embodiment, the resistor 67 and the inductor 61B connected in series are used as a discharge load for the following reason. (1) Eliminate the resistor 67 (OΩ) and load the inductor
If only to 61B, necessary to increase the inductance L _B of the inductor 61B to limit the peak current of the transistor 65 occurs, also the energy capacity of the inductor 61B also must be greater, the inductor 61B becomes large. Furthermore, since the inductor L _B becomes large, only a small current flows immediately after the transistor 65 is turned “ON”.
It takes time for the voltage between both ends of the piezo actuator 3 to decrease, and the characteristics of the pilot injection deteriorate during high-speed rotation. (2) If the discharge load is only the resistance 67, the transistor
In order to limit the peak current of 65, it is necessary to increase the resistance value of the resistor 67, and the discharge voltage decreases in proportion to the decrease in the voltage across the piezo actuator 3, so that the discharge takes time, and The characteristics of the pilot injection deteriorate. On the other hand, if the resistor 67 and the inductor 61B are arranged in series in the discharge path as shown in FIG.
B can be reduced in size, and the average current can be increased while the peak current flowing through the transistor 65 is suppressed, so that the voltage across the piezo actuator 3 can be quickly reduced. This is shown in FIG. Figure 7 shows the waveform of the voltage V _P of the discharge current I _B and the piezoelectric actuator when changing the load of the discharge, FIG. (A), (b) If the load of the discharge resistor 67 only (C) and (d) show the case where the discharge load is only the inductor 61B.
(F) shows the case where the discharge load is a series connection of the resistor 67 and the inductor 61B. Inductance of the resistance value and an inductor 61B of the resistor 67 is in this example are matched as the magnitude of the current I _B does not exceed 4 amps. From the figure, it can be seen that high-speed discharge without increasing to a load of the discharge and the series connection of resistor 67 and an inductor 61B peak value of the discharge current during I _B. As a result, the piezo actuator can operate at high speed, and the pilot characteristics at high speed rotation can be improved. (3) From the same figure, the discharge load is changed by the resistor 67 and the inductor.
When connected in series of 61B (FIG (e), (f)) piezoactuator voltage V _P of the has changed most smoothly, operating noise during this result piezo actuator discharge is suppressed. Next, the overall operation of the fuel injection rate control device of this embodiment will be described with reference to the timing chart shown in FIG. 8th
FIG. 7A shows the lift state of the plunger 11. First, when the plunger descends and reaches a point irrelevant to the fuel injection, the FET 62 repeats the "ON" state and the "OFF" state (FIG. 3 (b)) to gradually charge the piezo actuator 3 (charging). Voltage: _VP ). In this figure, the number of times of charging is four, but this number is predetermined by the means described with reference to FIG. 4 from the target charging voltage 100 obtained by the charging voltage calculating means. Thereafter, when the plunger starts to lift again, the pressure in the high-pressure chamber 12 also increases according to the plunger lift amount as shown in FIG. At the same time, the voltage across the piezo actuator 3 further rises due to the charge generated by itself as shown in FIG. Then, when the pressure in the high-pressure chamber 12 becomes equal to or higher than the nozzle opening pressure, the injection is started as shown in FIG. Thereafter, when the discharge timing previously obtained by the discharge timing calculation means has been reached (point), the transistor 65 is turned "ON" as shown in FIG. 3C, and the electric charge generated in the piezo actuator 3 is discharged. . At this time, the piezo actuator 3 contracts by an amount corresponding to the falling voltage V _P ′, the pressure in the high-pressure chamber 12 drops, and the injection stops once, and pilot injection is formed as shown in FIG. Here, it is understood from this principle that the pilot injection amount decreases when the discharge timing is advanced. Thereafter, when the plunger 11 further lifts, the pressure in the high-pressure chamber 1 increases again, and injection (main injection) is started. Here, the larger the voltage change amount (V _P ′) at the time of discharge of the piezo actuator 3, the larger the piezo actuator 3 shrinks, the larger the decrease width of the pressure in the high-pressure chamber 12, and the second injection is delayed, It can be seen that the injection stop period becomes longer. Thereafter, the injection of the fuel is stopped by governor means (not shown), the main injection is formed, and one cycle of the fuel injection is completed. As described in detail above, according to the present embodiment, both the injection amount of the pilot injection and the injection stop period can be adjusted to optimal values. A point to be noted in this embodiment is that the charging of the piezo actuator 3 is performed a plurality of times. The effect of this will be described below. The voltage that can be stored in the piezo actuator 3 in one charge
V _P1 is expressed by the following equation. C _P : equivalent capacity of the piezo actuator, I _M : current flowing through the inductor in advance, L _A : inductance of the inductor 61A. In the equation (3), in order to make _VP1 a high voltage, the current I
It is necessary to increase the or inductance L _A to increase the _M. In order to increase the current I _M , the FET 62 must be of a large current type, which is expensive and large. Further, when the inductance L _A is increased assuming that current can flow I _M, inductor 61A is large. Therefore, in this embodiment, the charging of the piezo actuator 3 is divided into a plurality of times, so that a relatively small
High voltage charging of the piezo actuator is realized by the FET 62 with a relatively small current capacity of 61A. Note that the number of charging times is multiple times in the present embodiment, when it is desired to the injection stop period relatively long, i.e., performs a charge a plurality of times for when you want to relatively increase the value of the voltage V _P, since the time the value of the voltage V _P smaller performed even fully charged in the above-described miniature inductors 61A and FET62 even once the charging times may be one time charge number in this case, When it is not necessary to charge the battery in advance, the number of times of charging may be zero. As another embodiment, FIG. 9 shows a case where a load at the time of discharging is a parallel connection of the second inductor 61B and the resistor 67 in the piezo drive circuit 6 '. When the piezo actuator is charged, the transistor 65 is "OFF", and no current flows through the diodes 70, 71 and the resistor 67, and the operation is the same as in FIG. When the transistor 65 is turned “ON” at the time of discharging the piezoelectric actuator, the path of the piezoelectric actuator → the inductor 61B → the diode 70 → the transistor 65 and the path of the piezoelectric actuator → the resistor 67 → the diode 71 → the transistor 65 are simultaneously conducted and discharged. The waveform of the current I _P and the voltage V _P of the piezoelectric actuator in this case 10
Shown in the figure. FIG. 10 shows a transistor as in FIG.
In order to protect 65 and the like, the value of the resistor 67 and the inductance of the inductor 61B are matched so that the peak value of the current does not exceed 4 amps, for example. As shown in the figure, when the discharge load is a parallel connection of the resistor and the inductor, the time required for the discharge can be further reduced as compared with the case where the resistor and the inductor are connected in series. However, when transistor 65 is turned “ON”,
Also, when the voltage of the piezo actuator becomes OV and the transistor 65 is turned “OFF”, the current I _P flowing through the piezo actuator changes suddenly at two places, so that the discharge load is more intense than in the case where the resistor and inductor are connected in series. The smoothness is lost, and the operation sound of the actuator is slightly increased. Therefore, when high-speed operation of the piezo actuator is required, the discharge load is connected in parallel with the resistor and the inductor. When quiet operation of the piezo actuator is required, the discharge load is connected in series with the resistor and the inductor. It is desirable. [Effects of the Invention] As described in detail above, according to the piezo actuator drive circuit of the present invention, the following effects can be obtained. (1) An expensive and large DC-D by switching the current to the first inductor using a charging switching element
The piezo actuator can be charged to a high voltage by the second inductor magnetically coupled to the first inductor without using a C converter or the like. By including the switching element, the current flowing through the discharge switching element can be limited, and at the same time, the second
Energy can be regenerated from the first inductor magnetically coupled to the first inductor to the battery. Also, by providing a resistor in series with the second inductor in the discharge circuit, the peak current of the switching means for discharging can be reduced without increasing the inductance of the second inductor, and the energy capacity of the second inductor can be reduced. Since the second inductor can be suppressed without increasing the size, the second inductor can be miniaturized, and at the same time, the discharge can be speeded up and the operation noise of the piezo actuator can be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an overall configuration diagram of an embodiment in which the present invention is applied to a pilot injection device for a diesel engine, and FIG. 2 is a schematic diagram showing means for calculating a charging voltage in the embodiment of FIG. FIG. 3, (a), (b), (c), (d) are timing charts showing the charging operation of the piezo drive circuit, FIG. 4 is a schematic diagram showing the relationship between the charging circuit and the target charging voltage, FIG. 5 is a schematic diagram showing a means for calculating a discharge timing, FIG. 6 is a timing chart showing a discharge operation of a piezo drive circuit, and FIG. 7 shows a relationship between a discharge load, a discharge current, and a voltage of a piezo actuator. FIG. 8 is a timing chart showing the operation of the entire pilot injection device, FIG. 9 is an overall configuration diagram of another embodiment in which the present invention is applied to a pilot injection device for a diesel engine, and FIG. 10 is FIG. Implementation of Of a timing chart showing the discharge operation of the piezoelectric driving circuit. 1 ... injection pump, 3 ... piezo actuator, 4 ... operating state detecting means, 5 ... microcomputer, 6, 6 '...
Piezo drive circuit, 61A ... first inductor, 61B ... second
Inductor, 62… FET, 65… Transistor, 67… Resistance, 68,70,71 …… Diode.

Continued on the front page (72) Inventor Shigekatsu Uchida 1 Toyota Town, Toyota City Toyota Motor Corporation (72) Inventor Fumiaki Kobayashi 1 Toyota Town Toyota City Toyota Motor Corporation (56) References JP JP-A-50-36833 (JP, A) JP-A-61-46441 (JP, A) JP-A-61-268871 (JP, A) Fully open JP-A-48-33925 (JP, U) (58) Fields investigated (Int .Cl. ⁶ , DB name) F02D 41/00-41/40

Claims (1)

(57) [Claims] In a piezo actuator driving circuit applying a piezo electrostriction effect, the piezo actuator driving circuit includes a piezo charging unit that charges the piezo actuator at a predetermined charging timing, and a piezo discharging unit that discharges the charged piezo actuator at a predetermined timing. The piezo charging means,
The first to convert energy from the power supply to magnetic energy
And a second inductor that is magnetically coupled to the first inductor, converts magnetic energy by the first inductor into electric energy, and charges the piezo actuator, and is mounted in series with the first inductor. Switching means for charging, wherein the piezo discharging means includes a series connection of the second inductor and a resistor in a discharging circuit of the piezo actuator, and is mounted in series with the piezo actuator and the second inductor. Piezo actuator drive circuit, characterized in that it comprises discharge switching means.