JP2003299371A - Piezo actuator driving circuit and fuel injector - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain an improvement in the failsafe function of a piezo actuator driving circuit of a multiple switching system. <P>SOLUTION: A current detection means 38b is provided in the mid of an energization path 33a for charging piezo stacks 127A-127D by a capacitor 32, and determines it as a short-circuit failure if a detected current exceeds a threshold by a controller 212. Unlike an LC resonance system exchanging all charges stored between the capacitor and the piezo stack, a short circuit does severe damage to the multiple switching system. By immediately detecting the short- circuit failure, therefore, the severe damage can be prevented. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric actuator drive circuit and a fuel injection device.

[0002]

2. Description of the Related Art A piezo actuator uses the piezoelectric action of a piezoelectric material such as PZT and is applied to, for example, a fuel injection device of an internal combustion engine, and an injector for fuel injection switches between injection and stop of fuel injection. The one used as a means is known. A piezo actuator expands by charging a piezo stack, which is a capacitive element, and discharges when it contracts. This is a type of actuator that energizes only when the piezo stack is expanded and contracted.

A drive circuit of a piezo actuator uses a capacitor for storing charge for charging the piezo stack and one of the capacitor and the piezo stack as a supply source, and an electric charge via an inductor for current limitation. And an energization path for moving the. In the case of being applied to a fuel injection device, for example, a piezo stack is charged from a capacitor to start fuel injection, and electric charges are collected from the piezo stack to the capacitor at a predetermined timing to stop fuel injection. Therefore, during fuel injection, there is a non-conduction state between the piezoelectric stack and the capacitor. Unlike the solenoid type that has been conventionally used for controlling the opening and closing of the injector, the energized state of the solenoid is maintained by maintaining the energization of the solenoid, and during this period, the injection is significantly different from that of the solenoid type. .

As a configuration of a piezo actuator drive circuit, there is one in which an LC resonance circuit is formed by a capacitor, a piezo stack and an inductor in Japanese Patent Laid-Open No. 2001-157472 (LC resonance system).

Further, in Japanese Unexamined Patent Publication No. 10-308542, there is provided a first type energizing path as an energizing path in which a gradually increasing current flows through an inductor when the switching element is repeatedly turned on and off. There is also a configuration in which a second type energization path in which a gradually decreasing current flows through the inductor is formed during the OFF period of the switching element (multiple switching method). L
Whereas the C-resonance method only exchanges energy (charge) by simply vibrating the behavior of current and voltage depending on the circuit constant, the multiple-switching method controls switching elements. The amount of charge of the piezo stack is flexible, and there is a possibility that the piezo actuator can be applied to various uses.

[0006]

However, in comparison with the LC resonance method in which all charges are discharged and received between the piezo stack and the capacitor, in the multiple switching method, a sufficient charge is stored in the capacitor. Therefore, it is necessary to supply only a predetermined amount of electric charges to the piezo stack, which complicates the configuration and control contents of the piezo actuator drive circuit.

Therefore, the piezoelectric actuator drive circuit is required to have higher practical value.
For example, in the LC resonance type, even if the switch that opens and closes the energization path after the start of charging or discharging is in the ON state and becomes uncontrollable (ON failure), the piezo actuator drive circuit and the piezo stack are particularly damaged. Although it is hardly received, the behavior of current and voltage is different in the switching type depending on the on / off state of the switching element, so if the switching element may not operate as instructed, the piezo actuator drive circuit or piezo stack Are subject to particularly significant damage, but none are capable of fault detection with a simple configuration.

The present invention has been made in view of the above circumstances,
It is an object of the present invention to provide a piezo actuator driving circuit having high practical value.

[0009]

According to a first aspect of the present invention, a capacitor for storing energy for driving a piezo stack mounted on a piezo actuator and one of the capacitor and the piezo stack are used as a supply source. ,
And a current-carrying path for moving charges through the inductor,
As the current-carrying path, a first-type current-carrying path in which a current that gradually increases in the inductor flows while the switching element is turned on and off is repeated,
A second type of energization path in which a gradually decreasing current flows through the inductor during the OFF period of the switching element is formed, and the piezo actuator is charged and discharged by the control means that controls the switching element. The drive circuit is provided with a current detecting means for detecting a current flowing in the energizing path, and the control means is configured to judge a short circuit failure when the current detected by the current detecting means exceeds a preset threshold value. Set to.

Unlike the LC resonance type, an overcurrent is caused by a current flowing through the energizing path due to an ON failure in which a switching element that opens and closes the energizing path remains uncontrolled and a short circuit of some or all of the inductors. This causes, for example, the piezo stack to be excessively charged, resulting in an excessive rise in the voltage between both terminals of the piezo stack. Therefore, by monitoring the current flowing through the energization path, it is possible to promptly know the occurrence of the failure. This improves practicality.

According to a second aspect of the present invention, in the configuration of the first aspect of the invention, as the piezo stack, a plurality of piezo stacks can be connected with a common energization path, and the selection switch controlled by the control means. The piezo stack connected to the energization path can be selected from the plurality of piezo stacks, and the control means turns off the selection switch when the short-circuit failure is detected, and the energization is performed. Set to open the route.

It is possible to easily stop charging and discharging and prevent damage to the piezo actuator drive circuit and the piezo stack.

According to a third aspect of the invention, in the configuration of the first or second aspect of the invention, a voltage detecting means for detecting the voltage of the energizing path is provided on the piezo stack side with respect to the switching element, and the control means is provided. When the short-circuit failure is determined and the first detection condition is that the voltage detected when the switching element is off is equal to or lower than a preset threshold value, the energizing path causes the supply source to switch the piezoelectric element. The charge is collected as a stack to collect the charge in the capacitor, and the charge collection is prohibited when the detected voltage is the second determination condition equal to or higher than a preset threshold value.

When it is determined that the short-circuit fault has occurred, the higher the voltage of the energizing path on the piezo stack side than the switching element, the more the ON fault of the switching element or the short-circuit fault of the inductor occurs as the mode of the short-circuit fault. There is a high probability that In this case, if the charge is normally recovered from the piezo stack to the capacitor, the ON failure of the switching element may cause conduction between the capacitor and the inductor, or the inductor may not function to limit the current. Therefore, if an attempt is made to flow a gradually increasing current from the piezo stack as the supply source in the current path of piezo stack-inductor-ground, the non-grounded side terminal of the capacitor will be grounded, and the capacitor will be connected between both terminals. There is a risk of short circuit. Alternatively, if there is a short circuit fault in the inductor, the piezo stack will short circuit. In the present invention, if the detected voltage is equal to or higher than the threshold value, normal charge recovery is not performed, so that such a short circuit of the capacitor or the piezo stack can be prevented in advance.

According to a fourth aspect of the invention, in the configuration of the third aspect of the invention, the threshold value of the detection voltage is set to a voltage between both terminals of the capacitor, and the control means is turned off. At this time, when the second determination condition is satisfied, the failure mode is set to determine that the switching element is on-failed.

When it is determined that a short-circuit failure has occurred, the switching element in the energization path from the capacitor is turned off as a countermeasure, but the detection voltage still reaches the voltage between both terminals of the capacitor. This is the case of an ON failure. Therefore, by setting the threshold value of the detection voltage to a voltage between both terminals of the capacitor,
The failure mode can be specified as an ON failure of the switching element.

According to a fifth aspect of the invention, in the structure of the third or fourth aspect of the invention, an emergency discharge path is formed for discharging the electric charge of the capacitor through the inductor and bypassing the piezo stack to the ground side. Along with
An emergency discharge switch for opening and closing the emergency discharge path is provided on the emergency discharge path.

As described above, even in the case of a short circuit failure in which normal charge collection is impossible, the charge can be discharged to the ground side by turning on the emergency discharge switch. The emergency discharge switch may be configured to operate under the control of the control means so that electric charge is automatically discharged at a predetermined timing after it is determined that a short circuit has occurred, or an operation at a repair shop or the like. Alternatively, manual operation may be used.

According to a sixth aspect of the present invention, in the structure of the first to fifth aspects of the invention, the capacitor is charged by a power source section controlled by the control means, and the control means is When it is determined that the short circuit has occurred, the operation of the power supply unit is set to stop.

By preventing new electric energy from being input to the capacitor, damage to the piezo actuator drive circuit and the piezo stack can be suppressed to a minimum.

According to a seventh aspect of the present invention, a capacitor for storing energy for driving the piezo stack mounted on the piezo actuator, and one of the capacitor and the piezo stack are used as a supply source, and a charge is supplied via an inductor. And an energizing path for moving the energizing path,
By repeating ON / OFF of the switching element, a first type energization path in which a gradually increasing current flows in the inductor during the ON period of the switching element, and a second type in which a gradually decreasing current flows in the inductor during the OFF period of the switching element In the piezo actuator drive circuit in which the energization path of the piezo stack is formed and the control means for controlling the switching element charges and discharges the piezo stack, a voltage for detecting the voltage of the non-grounded side terminal of the piezo stack. A detection means is provided, and the control means is set to judge that the piezo stack has failed when the voltage detected during the charge holding period after the completion of charging of the piezo stack is smaller than a preset threshold value. To do.

If the piezo stack is normal, the voltage is substantially constant during the charge holding period after completion of charging, whereas if the charge leaks due to a partial short circuit of the piezoelectric ceramic layer of the piezo stack, the voltage drops. To do. Therefore, such a failure of the piezo stack is known from the drop in voltage.

According to an eighth aspect of the present invention, a capacitor that stores energy for driving the piezo stack mounted on the piezo actuator, and one of the capacitor and the piezo stack are used as a supply source, and a charge is charged via an inductor. And an energizing path for moving the energizing path,
By repeating ON / OFF of the switching element, a first type energization path in which a gradually increasing current flows in the inductor during the ON period of the switching element, and a second type in which a gradually decreasing current flows in the inductor during the OFF period of the switching element And a current detecting means for detecting a current flowing in the current-carrying path in the piezo-actuator drive circuit in which the control means for controlling the switching element charges and discharges the piezo stack. The control means measures the time until the detected current reaches a preset current value immediately after the start of charging of the piezo stack, and when the measurement time is out of a predetermined range, the piezo Set to determine whether there is an apparent capacity abnormality of the stack or a temperature abnormality of the piezo stack.

The behavior of the current depends on the piezo stack and the inductor.
Depending on the circuit constant of the
It depends on the capacity used. Piezo stack here
The apparent capacity of a piezo stack is equivalent to a capacitor
E = (1/2) CV as the value ²(E: To the piezo stack
Energy input, C: Apparent piezo stack
C obtained from the relationship of capacity, V: voltage of piezo stack)
That is (hereinafter, simply referred to as capacity). And capacity
Is susceptible to temperature. Therefore, the current aging
From file profile to piezo stack capacity abnormality
Abnormal temperature of the battery is known.

Here, the time taken until a predetermined current value is obtained immediately after the start of charging the piezo stack is measured as an index of the current aging profile, so that the implementation is easy.

According to a ninth aspect of the invention, an injector for actuating a needle for opening and closing a nozzle hole for injecting fuel by a piezo actuator, and a means for driving the piezo actuator are provided for driving a piezo stack mounted on the piezo actuator. Has a capacitor that stores energy, and a conducting path that moves electric charge through an inductor from one of the capacitor and the piezo stack as a supply source, and the switching element is repeatedly turned on and off as the conducting path. As a result, a gradually increasing current flows through the inductor during the ON period of the switching element.
And a second type energization path in which a gradually decreasing current flows through the inductor during the OFF period of the switching element, and the control means for controlling the switching element charges the piezo stack. And a piezo actuator drive circuit for discharging, and a fuel injection having a command means for instructing the control means the charge timing of the piezo stack and the length of the charge holding period corresponding to the fuel injection timing and injection amount. In the device, the piezo actuator drive circuit is provided with current detection means for detecting a current flowing in the energization path, and the command means sets the detected current in advance immediately after the start of charging of the piezo stack. Measure the time until a predetermined current value is reached, and based on the measured time, charge the piezo stack and Set so as to correct the length of the charging holding period.

The sliding resistance of the movable member forming the injector is affected by the temperature change, and the operating characteristics of the injector change. On the other hand, as described above, the time until the detected current reaches a predetermined current value set in advance changes according to the temperature of the piezo stack that can be regarded as the temperature of the injector,
This is temperature information far corresponding to the injector temperature as compared with the cooling water temperature and the like. Therefore, the fuel injection can be performed with high accuracy by correcting the charge timing and the charge holding period of the piezo stack according to the measured time.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 2 shows the configuration of a common rail type fuel injection device for a diesel engine to which the present invention is applied. Injectors 1 for the number of cylinders of the diesel engine are provided corresponding to each cylinder (only one injector 1 is shown in the illustrated example), and are supplied with fuel from a common common rail 26 that communicates via a supply line 27, Fuel is injected from the injector 1 into the combustion chamber of each cylinder at an injection pressure substantially equal to the fuel pressure in the common rail 26 (hereinafter referred to as common rail pressure). The fuel in the fuel tank 23 is sent under pressure to the common rail 26 by the high-pressure supply pump 25 and stored at high pressure.

Further, the fuel supplied from the common rail 26 to the injector 1 is used not only for injection into the combustion chamber but also as a control hydraulic pressure for the injector 1 and the like. The fuel is passed from the injector 1 through the low pressure drain line 28 to the fuel tank. It returns to 23.

A piezo actuator drive circuit 21 for driving the piezo actuator mounted on each injector 1 is provided. The piezo actuator drive circuit 21 is controlled by the ECU 22, and the injector 1 of the selected cylinder injects fuel. The ECU 22 is mainly composed of a microcomputer and controls not only the piezoelectric actuator drive circuit 21 but also each part of the fuel injection device. For example, a detection signal from a pressure sensor (not shown) provided on the common rail 26 or the like. Based on the above, the metering valve 24 is controlled to adjust the pressure feed amount of fuel to the common rail 26 to adjust the common rail pressure. In addition, the ECU 22
A detection signal such as a fuel temperature and an engine oil temperature, and various signals such as a crank angle are input to the.

FIG. 3 shows the structure of the injector 1.
The injector 1 is a rod-shaped body, and is attached such that the lower portion in the drawing penetrates a not-illustrated combustion chamber wall of the engine and projects into the combustion chamber. The injector 1 includes a nozzle portion 1a, a back pressure control portion 1b, and a piezo actuator 1c in order from the bottom.
Has become.

A needle 121 is slidably held at its rear end in a sleeve-shaped main body 104 of the nozzle portion 1a, and the needle 121 is seated on an annular seat 1041 formed at the tip of the nozzle main body 104 or Move away.
High-pressure fuel is introduced from the common rail 54 into the outer peripheral space 105 at the tip of the needle 121 through the high-pressure passage 101, and fuel is injected from the injection hole 103 when the needle 121 is lifted. The needle 121 has an annular step surface 1211.
Further, the fuel pressure from the high pressure passage 101 acts in the lift direction (upward).

Behind the needle 121 is the high pressure passage 101.
The fuel as the control oil is introduced from the above through the in-orifice 107, and the back pressure chamber 106 that generates the back pressure of the needle 121 is formed. This back pressure acts on the rear end surface 1212 of the needle 121 in the seating direction (downward) together with the spring 122 arranged in the back pressure chamber 106.

The back pressure is increased / decreased by the back pressure control unit 1b, and the back pressure control unit 1b is driven by the piezo actuator 1c having the piezo stack 127.

The back pressure chamber 106 is the out orifice 10
9 is always in communication with the valve chamber 110 of the back pressure control unit 1b. In the valve chamber 110, a ceiling surface 1101 is formed in an upward conical shape, and a low pressure port 110a communicating with the low pressure chamber 111 is opened at the top of the ceiling surface 1101.
The low pressure chamber 111 has a low pressure passage 1 communicating with the drain line 56.
It communicates with 02. A high pressure port 110b communicating with the high pressure passage 101 via the high pressure control passage 108 is opened on the bottom surface of the valve chamber 110.

Inside the valve chamber 110, a ball 123 whose lower portion is horizontally cut is arranged. The ball 123 is a valve body that can move up and down, and when it descends, the cut surface causes the valve chamber bottom surface (hereinafter, referred to as a high pressure side seat) 1 as a valve seat to operate.
The high pressure port 110b is seated on the valve 102 to close the valve chamber 110 from the high pressure control passage 108, and when rising, the high pressure port 110b is seated on the ceiling surface (hereinafter referred to as the low pressure side seat) 1101 as a valve seat and the low pressure port 110a. The valve chamber 110 is shut off from the low pressure chamber 111 by closing. As a result, when the ball 123 descends, the back pressure chamber 106
Through the out-orifice 109 and the valve chamber 110 to the low pressure chamber 1
11, the back pressure of the needle 121 is reduced, and the needle 121 is separated. On the other hand, when the ball 123 rises, the back pressure chamber 106 is shut off from the low pressure chamber 111, and the high pressure passage 10 is blocked.
The back pressure of the needle 121 rises, and the needle 121 is seated.

The ball 123 is a piezo actuator 1c.
Is driven by pressing. The piezo actuator 1c
Vertical hole 112 formed vertically above the low-pressure chamber 111
Two pistons 124, 125 having different diameters are slidably held, and a piezo stack 127 is arranged above the large-diameter piston 125 on the upper side with the up-down direction as the expansion / contraction direction.

The large-diameter piston 125 is kept in contact with the piezo stack 127 by a spring 126 provided therebelow, and is displaced in the vertical direction by the same amount as the expansion and contraction amount of the piezo stack 127.

The space defined by the lower small-diameter piston 124, the large-diameter piston 125, and the vertical hole 112, which face the ball 123, is filled with fuel to form a displacement expansion chamber 113, and the piezo stack 127 extends. When the large-diameter piston 125 is displaced downward to press the fuel in the displacement magnifying chamber 113, the pressing force is transmitted to the small-diameter piston 124 via the fuel in the displacement magnifying chamber 113. Here, since the small-diameter piston 124 has a smaller diameter than the large-diameter piston 125, the extension amount of the piezo stack 127 is expanded and converted into the displacement of the small-diameter piston 124.

At the time of fuel injection, first, the piezo stack 1
27 is charged and the piezo stack 127 expands, whereby the small diameter piston 124 descends and pushes down the ball 123. As a result, the ball 123 moves the low pressure side seat 1
Since the back pressure chamber 106 communicates with the low pressure passage 102 by lifting from 101 and seating on the high pressure side seat 1102, the fuel pressure in the back pressure chamber 106 decreases. As a result, the force acting on the needle 121 in the seating direction becomes more dominant than the force acting on the seating direction, and the needle 121 is seated to start fuel injection.

On the contrary, to stop the injection, the discharge of the piezo stack 127 causes the piezo stack 127 to shrink and the ball 12
Release the pushing force to 3. At this time, the inside of the valve chamber 110 has a low pressure, and the high pressure fuel passage acts on the bottom surface of the ball 123 from the high pressure control passage 108.
An upward fuel pressure acts on the ball 123 as a whole. When the pressing force to the ball 123 is released, the ball 123 is separated from the high-pressure side seat 1102 and is seated on the low-pressure side seat 1101 again to increase the fuel pressure in the valve chamber 110, so that the needle 121 is seated and injected. Stops.

FIG. 1 shows the structure of the piezoelectric actuator drive circuit 21. For convenience of description, the piezo stack 127 will be appropriately referred to as a piezo stack 127A, a piezo stack 127B, a piezo stack 127C, and a piezo stack 127D corresponding to the four cylinders. The piezo actuator drive circuit 21 includes a charge / discharge circuit unit 211 that charges and discharges the piezo stacks 127A to 127D, a controller 212 that is a control unit that controls the piezo stacks 127A to 127D, and is connected to the piezo stacks 127A to 127D by a wire harness (not shown). To be done.

The charging / discharging circuit section 211 is used for the onboard battery 3
For charging the piezo stacks 127A to 127D, which has a DC-DC converter 31 which is a power supply unit that generates a direct current voltage of several tens to several hundreds of V by power feeding of 0, and a capacitor 32 connected in parallel to its output end. Output the voltage. DC-
The DC converter 31 can employ, for example, a general boost chopper type circuit. The capacitor 32 is composed of a capacitor having a sufficiently large electrostatic capacity (several hundred μF), and
The voltage value is kept substantially constant even during the charging operation to 7A to 127D.

From the capacitor 32 to the piezo stack 127
A to 127D is provided with a first energization path 33a which is a first type energization path for energizing via the inductor 34. The first energization path 33a is provided between the capacitor 32 and the inductor 34 in series with the first energization path 33a. The switching element 35 of FIG. The first switching element 35 is a MOS
The FET is composed of a parasitic diode (hereinafter, referred to as a first parasitic diode) 351 and is connected so that the voltage between both terminals of the capacitor 32 becomes reverse bias.

In addition, the inductor 34 and the piezo stack 1
27A-127D form the 2nd electricity supply path 33b which is a 2nd type electricity supply path. This energizing path 33b
Has a second switching element 36 connected to the midpoint of connection between the inductor 34 and the first switching element 35. The second energization path 33b bypasses the capacitor 32, and the inductor 34 and the piezo stack 127A to
A closed circuit passing through 127D and the second switching element 36 is formed. The second switching element 36 is also MO
It is composed of SFET and its parasitic diode (hereinafter referred to as the second diode).
361 (referred to as a parasitic diode) is connected such that the voltage between both terminals of the capacitor 32 is reverse biased.

The energization paths 33a and 33b are common to the piezo stacks 127A to 127D, and the selection switches 37A, 37B, 37C and 37D are connected in series with the piezo stacks 127A to 127D in a one-to-one correspondence. . Piezo stack 12 of injector 1 of injection cylinder
Selection switching element 37A corresponding to 7A to 127D
~ 37D is turned on, the piezo stack 127A ~
The energization paths 33a and 33b are selectively formed at 127D.

The selection switches 37A to 37D are MOSF.
ET is used, and its parasitic diodes (hereinafter referred to as selective parasitic diodes) 371A, 371B, 371.
C and 371D are connected so that the voltage between both terminals of the capacitor 32 is reverse biased.

Control signals are input from the controller 212 to the respective gates of the switching elements 35 and 36 and the selection switches 37A to 37D. As described above, one of the selection switches 37A to 37D is turned on to drive the piezo. The stacks 127A to 127D are selected, the switching elements 35 and 36 are turned on / off, and the piezoelectric stacks 127A to 127D are charged and discharged.

Between the selection switches 37A to 37D and the ground, a resistor 38b is shared by the selection switches 37A to 37D.
Is provided. The voltage between both terminals, that is, the voltage at point b in the figure is input to the controller 212, and the piezo stack 12
A charging current of 7A to 127D is detected.

A resistor 38c is provided in series with the second switching element 36. The voltage between both terminals, that is, the voltage at point c in the figure is input to the controller 212, and the discharge current of the piezo stacks 127A to 127D is detected.

Further, the piezo stack 1 of the inductor 34
Between the terminals on the 27A to 127D side and the ground, resistors 381a and 381b, which are connected in series and have a high resistance value, are provided.
The divided voltage, that is, the voltage at the point a in the figure is input to the controller 212, and the voltage between both terminals of the piezo stacks 127A to 127D is detected.

An emergency discharge path 42 is formed in parallel with the resistors 381a and 381b, and as will be described later in detail, the capacitor 32 and the piezo stacks 127A to 127A.
The electric charge of 127D is discharged to the ground side.
A resistor 44 and a diode 45 are connected in series to the emergency discharge path 42, as well as an emergency discharge switch 43 that opens and closes the emergency discharge path 42. The resistor 44 is for adjusting the time constant at the time of discharging charges. The diode 45 is for preventing backflow, has the inductor 34 side as a cathode, and the direction in which the current flows from the inductor 34 side to the ground side is the forward direction.

The emergency discharge switch 43 is a MOSF.
ET is used, and its parasitic diode (hereinafter, referred to as discharge parasitic diode) 431 is connected so that the voltage of the capacitor 32 becomes reverse bias.

A control signal is input from the controller 212 to the gate of the emergency discharge switch 43.

The controller 212, which is the control means,
According to the command signal from the CU 22 and the various detection signals of the charging / discharging circuit unit 211, a control signal is output to the charging / discharging circuit unit 211, an abnormality of the charging / discharging circuit unit 211 is detected, and an abnormality determination signal IJF1 is sent to the ECU 22. , IJF2
Is output. In addition, a discharge inhibit signal described later is generated, and the piezoelectric stack 12 is generated under a certain condition.
The execution of the charge recovery from 7A to 127D to the capacitor 32 is prohibited.

As a command signal input from the ECU 22,
The injection signal, the cylinder selection signal, and the charging period signal are input. The injection signal is the piezo stack 127A to 127D.
Is a binary signal composed of "L" and "H", which defines the charging time and the discharging time of. The injection period is substantially defined by the output timing and length of the injection signal. The cylinder selection signal is for selecting the piezo stack 127A to 127D to be charged, which corresponds to the injection cylinder. The charge period signal defines the length of the charge period of the piezo stacks 127A to 127D, that is, the charge amount.

Each piezo stack 127A-127
Resistors 41A, 41B, 41 are connected in parallel to D, respectively.
C and 41D are provided, and the piezo stacks 127A to 127D are always discharged little by little even after completion of charging. The resistors 41A to 41D are for fail safe,
The piezo stack 127A to 127D cannot be energized due to the disconnection of the wiring cable or the like, and the piezo stack 127A to 127A
When the normal charge recovery from 27D to the capacitor 32 is no longer possible, the charge holding state that allows the needle 121 to be in the lifted state does not continue for a predetermined time or longer. Further, the resistors 41A to 41D eliminate the electric charges generated by the pyroelectric effect. Therefore, the resistors 41A to 4A
The 1D resistance value is set in consideration of the longest injection time and the like.

FIG. 4 shows an operating state of the charging / discharging circuit section 211. The controller 212 outputs a predetermined control signal when the injection signal, the cylinder selection signal, and the charging period signal become “H”. The cylinder selection signal is for selecting the first cylinder and then for selecting the second cylinder. First, the first selection switch 37A corresponding to the first cylinder is turned on. The ON period of the selection switch 37A is until the discharge is completed.

When the injection signal and the charging period signal become "H" (t1), the controller 212 sets the ON period and the OFF period of the first switching element (hereinafter, appropriately referred to as a charging switch) 35 as follows. Then, the control signal is output to the charging switch 35. That is, the charging switch 3
5 is turned on, and a gradually increasing charging current is supplied to the first energization path 33a, which is the first type energization path whose source is the capacitor 32 (FIG. 5A). The on period is set to be constant. When the charging switch 35 is turned off, the counter electromotive force generated in the inductor 34 at this time is the second parasitic diode 3
Since it is forward biased with respect to 61, the energy accumulated in the inductor 34 causes the second energization path 33, which is the second type of energization path whose source is the capacitor 32.
A gradually decreasing flywheel current flows to b, and charging of the piezo stack 127A proceeds (FIG. 5 (B)). When the charging current reaches a threshold value set to approximately 0 in advance (hereinafter, appropriately referred to as 0A threshold value), the off period is ended, the charging switch 35 is turned on again to enter the on period, and this is repeated (multiplexing). Switching method). Charging current (signal at point b)
Flows in a substantially triangular waveform, and the voltage between both terminals of the piezo stack 127A (signal at a) rises in a stepwise manner.

When the charging period signal becomes "L" (t3), the control signal to the charging switch 35 is forced to fall, and the charging switch 35 is fixed to OFF. This completes charging. The piezo stack 127A expands by charging and presses and lifts the ball 123 via the displacement magnifying chamber 113.

The method of the present piezoelectric actuator drive circuit 211 in which the length of the ON period is constant is such that the energy input speed to the piezo stacks 127A to 127D is constant and the linearity is good, and the length of the charging period is long. Is the same, the amount of energy input to the piezo stacks 127A to 127D can be made substantially constant even if the capacities of the piezo stacks 127A to 127D change.

When the injection signal becomes "L" (t5
), The piezo stack 127A is discharged and the capacitor 3
Collect to 2. That is, the ON period and the OFF period of the second switching element (hereinafter, appropriately referred to as a discharge switch) 36 are set as follows, and the control signal is output to the discharge switch 36. That is, the discharge switch 36 is turned on, and a gradually increasing discharge current is supplied to the second energization path 33b, which is the second type energization path whose source is the piezo stack 127A (FIG. 6A). When the discharge current reaches a preset threshold value (hereinafter referred to as the upper limit current threshold value), the discharge switch 36 is turned off and the off period starts. At this time, a large counter electromotive force is generated in the inductor 34, and the inductor 3
The energy accumulated in 4 causes a flywheel current to flow through the first energization path 33a which is the first type energization path whose source is the piezo stack 127A, and the energy is recovered in the capacitor 32 (see FIG. B)). When the discharge current reaches the 0A threshold value, the discharge switch 36 is turned on again and this is repeated.

A threshold value in which the piezo stack voltage is set to approximately 0 (hereinafter, referred to as a 0V threshold value)
(T8), the discharge switch 36 is fixed to OFF,
The discharge of the piezo stack 127A is completed. The charge of the piezo stack 127A will be collected in the capacitor 32. And like this, the piezo stack 127A
Is discharged, the piezo stack 127A is contracted, the pressing force on the ball 123 by the fuel pressure in the displacement magnifying chamber 113 is released, and the ball 123 is seated.

Subsequently, at the predetermined crank angle, the injection signal and the charging period signal become "H" again, and the second
Cylinder selection signal for instructing the cylinder of "H" becomes "t" (t
1 '), the first and second energization paths 33a and 33b are formed in the piezo stack 127B. Similarly for the third and fourth cylinders, the piezo stack 127C, 12
7D is charged and discharged.

Next, a circuit portion of the controller 212 which detects an abnormality in the charge / discharge circuit section 211 and outputs the abnormality determination signals IJF1 and IJF2 to the ECU 22 will be described. FIG. 7 shows a circuit portion for generating the abnormality determination signal IJF1 and the discharge inhibition signal, and FIG. 8 shows its operating state. In the circuit portion, in addition to the injection signal, a charging voltage,
The timer threshold, overvoltage threshold, and large capacity threshold are input. In the following description, it is assumed that the selected cylinder is the first cylinder. That is, of the selection switches 37A to 37D, the description will be made assuming that the selection switch 37A is turned on.

The charging voltage is the voltage of the terminal on the piezo stack 127A side of the inductor 34, which is detected at point a.

The timer threshold value is a voltage signal for determining the elapse of time t4 described later.

Both the overvoltage threshold and the large capacity threshold are voltage abnormality determination thresholds that are compared with the charging voltage to determine the magnitude of the charging voltage. The overvoltage determination threshold value is a voltage signal whose magnitude is substantially equivalent to the voltage that can be regarded as the voltage of the capacitor 32. The large capacity threshold value is a threshold value for detecting when the capacity of the piezo stack 127A viewed from the charge / discharge circuit section 211 becomes abnormal and the charging voltage becomes insufficient. This is because the charging voltage is lowered due to the increase in the capacity of the piezo stack 127A in the case where the termination of charging is determined without depending on the magnitude of the piezo stack voltage as in the present embodiment.

The charge voltage is compared with the overvoltage threshold value or the large capacity threshold value selected by the switch 52 by the comparator 53. The switch 52 is switched and controlled by the output of the comparator 51. The output signal of the timer circuit 50 for counting the elapsed time from the rise of the injection signal and the timer threshold value are input to the comparator 51. When the elapsed time exceeds t4, the output of the comparator 51 becomes "L". Then, the overvoltage threshold is switched to the large capacity threshold.

The output of the comparator 53, which determines whether the charging voltage is greater than the voltage abnormality determination threshold value, and the output of the comparator 51, which outputs "L" when the elapsed time exceeds t4. And are input to the SR flip-flop 56 via the AND gate 54.

In the SR flip-flop 56, the output of the comparator 53 is inverted by the NOT gate 55 and input as the R input. The Q output of the SR flip-flop 56 serves as a discharge inhibition signal. It normally takes "L" and becomes "H" only when the charging voltage exceeds the overvoltage threshold during the period from the injection signal input to t4, and it is known that the charging voltage has risen excessively. . When the charge voltage drops and the output of the comparator 53 becomes "L", the discharge prohibition signal becomes "L". When the discharge prohibition signal becomes “H”,
The ECU 22 prohibits discharge. The reason for this will be described later.

On the other hand, in the D flip-flop 70, the injection signal is inverted and input by the NOT gate 58 as the CK input, and the output from the rising edge detection circuit 59 for detecting the rising edge of the injection signal is input as the CL input. is doing. The inverted output of the SR flip-flop 56 and the output of the comparator 53 are input to an AND gate 57, and the output of the AND gate 57 is a D flip-flop 70.
Is the D input. Therefore, until the start of discharge, if the charge voltage exceeds the threshold value of the large capacity, the IJF1 signal becomes “H” at the fall of the injection signal,
Next, the ejection signal rises and is held until the D flip-flop 70 is cleared. On the other hand, piezo stack 12
If the voltage of 7A does not rise during charging, or during the charge holding period (from when the charging period signal becomes "L" (t3) to when the injection signal becomes "L" (t5)), the charging voltage becomes If it falls and is below the large capacity threshold, the IJF1 signal remains "L". Also, the piezo stack 127
The IJF1 signal remains "L" even when A is overvoltage during charging.

FIG. 9 shows a circuit portion of the controller 212 which outputs the abnormality determination flag IJF2.
Shows the operating state. In addition to the injection signal, the charging voltage and the mask signal, the charging current, the energization start threshold value, the overcurrent threshold value and the 0V threshold value are input to the circuit portion.

The charging current is a signal known as the voltage at point b.

The mask signal takes an "H" value from the rising of the injection signal, that is, the start of charging the piezo stack 127A to the end of the off period substantially following the first on period of the charge switch 35. The circuit for generating this will be described later.

The energization start threshold is used to determine the magnitude of the charging current by comparing it with the charging current. It is set to be slightly higher than 0, and whether the charging switch is turned on and the charging current has started to increase gradually. It is a voltage signal for confirming whether or not.

The overcurrent threshold is determined by the conduction paths 33a, 33.
It is for determining whether or not an overcurrent has flown into b, and is set to a value that can determine an excessive value as a current value that reaches in the first ON period of the charging switch 35.

The 0V threshold value is used to determine the magnitude of the charging voltage by being compared with the charging voltage, and is set to be slightly higher than 0V, and is a voltage signal for confirming whether the discharge is completed. .

The comparator 6 compares the energization start threshold and the charging current.
It is compared with 0 and input to the AND gate 67. Comparator 6
The output of 0 is when the charging current exceeds the energization start threshold value.
It becomes "H".

Further, the charging current and the overcurrent threshold value are compared by the comparator 61, and the output thereof is input to the OR gate 65. In a normal state where the charging current does not exceed the overcurrent threshold, the output of the comparator 61 is "L". The injection signal is input to the OR gate 65 together with the output of the comparator 61 through the NOR gate 64, and while the injection signal is "H",
As long as the charging current does not exceed the overcurrent threshold, the output of the OR gate 65 is "L". The output of the OR gate 65 is S
It is input to the R flip-flop 68 as an R input.

The output of the OR gate 65 is also inverted by the NOT gate 66, and together with the output of the comparator 60 which determines whether the energization start threshold value is smaller than the charging current,
It is input to the AND gate 67. AND gate 6
The output of 7 rises when the charging current exceeds the energization start threshold after the injection signal becomes "H", and the inverted output of the SR flip-flop 68 becomes "L". The state of the inverted output is held at least until the injection signal becomes “L”. When the charging current again falls below the energization start threshold value at the end of the off period of the charging switch 35, the AND gate 6
The output of 7 becomes "L" again.

After the injection signal becomes "L", N
Another input of the OR gate 64 will determine the R and S inputs of the SR flip-flop 68. The other input of the NOR gate 64 is the output of the comparator 62 which compares the charging voltage with the 0V threshold,
It is inverted and input by the NOT gate 63, and when the charging voltage falls below the 0V threshold, the other input of the NOR gate 64 becomes “L”. Therefore, the charging voltage is 0V
While the voltage is above the threshold, the output of the NOR gate 64 is “L”, and the same state as before the injection signal is “L” is maintained. When the charging voltage is below the 0V threshold, the NOR gate is The output of 64 becomes "H", and the R input of the SR flip-flop 68 becomes "H". As a result, the inverted output of the SR flip-flop becomes "H".

Then, the inverted output of the SR flip-flop 68 and the mask signal are input to the OR gate 69, and the output becomes the abnormality determination signal IJF2. The abnormality determination signal IJF2 switches to "H" after the injection signal becomes "L", that is, when the charging voltage is below the 0V threshold, that is, when the piezoelectric stack 127A is substantially discharged. Yes, it becomes slower or faster depending on the discharge completion time of the piezo stack 127A.

After the charging current exceeds the energization start threshold value and the inverted output of the SR flip-flop 68 becomes "L", the charging current further rises and the charging current exceeds the overcurrent threshold value. If so, the output of the OR gate 65 becomes "H".
And the inverted output of the SR flip-flop 68 is "H".
Will return to. In the following description, the SR flip-flop 68 will be appropriately referred to as a failure determination F / F 68.

Next, FIG. 11 shows a circuit portion of the controller 212 which outputs the mask signal, and FIG.
Shows the operating state. The charging current, the energization start threshold value, and the injection signal are input to the circuit portion.

The comparator 7 compares the charging current and the energization start threshold value.
When the charging current exceeds the energization start threshold value, the output of the comparator 71 becomes "H". The output of the comparator 71 is input to the AND gate 72. AND gate 7
The output of 2 is input to the first D flip-flop 73 as a CK input. The first D flip-flop 73 constitutes a 2-bit counter together with the second D flip-flop 74. The inverted output of the second D flip-flop 74 of the upper bit serves as another input of the AND gate 72. Therefore, the output of the AND gate 72 is the output of the comparator 71 until the count value becomes "2".

An AND gate 75 is provided with the inverted output of the second D flip-flop 74 and the ejection signal as inputs, and the output thereof serves as a mask signal.

The injection signal is inverted by the NOT gate 76 and input to the D flip-flops 73 and 75 as CL input. When the injection signal falls, the D flip-flops 73 and 74 are cleared.

When the injection signal becomes "H" and the charging current is gradually increased and gradually decreased, the first and second D flip-flops are set each time the charging current exceeds the energization start threshold value. It is counted at 73 and 74. First, second
Since the inverted output of the D flip-flop 74 is "H" and the ejection signal is also "H", the mask signal starts with "H".

When the charging current exceeds the energization start threshold value for the second time, the inverted output of the second D flip-flop 74 becomes "L" and the mask signal also becomes "L".

Since the inverted output of the second D flip-flop 75 is input to the AND gate 72, the count is not performed thereafter and the mask signal is fixed at "L".

Therefore, the mask signal is "H" during the period from the rising of the injection signal until the charging current exceeds the energization start threshold value when the charging switch 35 is turned on for the second time.
It takes a value. If the charging switch 35 is not turned on for the second time, the mask signal remains "H" until the injection signal becomes "L" again.

In the ECU 22, the abnormality determination signal IJF1,
The presence or absence of abnormality is determined based on IJF2. FIG. 13 shows an operating state at the time of normal operation, and FIG. 14, FIG. 15, FIG.
7 shows the operating state when an abnormality occurs.

In FIG. 13 showing the operating state at the normal time,
Although the charging voltage rises with the progress of charging of the piezo stack 127A, it reaches an appropriate voltage value without exceeding the overvoltage threshold value and the charging is completed. Therefore, when the voltage abnormality determination threshold value becomes t4 at which the threshold value is switched to the large capacity threshold value, the voltage level determination (X) rises to "H". Since this is maintained even after t5 when the injection signal becomes "L", the abnormality determination signal IJF1 becomes "H" at the time of t5.

On the other hand, when the injection signal becomes "L", the discharge of the piezo stack 127A is started, the charge of the piezo stack 127A is collected in the capacitor 32, and the charging voltage decreases. Then, the charging voltage is 0
At t8 below the V threshold, the failure judgment F / F68
Becomes "H" and the abnormality determination signal IJF2 becomes "H". When the abnormality determination signal IJF2 switches from "L" to "H", it means that the discharge is completed.

If the range of t8 when the piezo stack 127A is properly charged and discharged is obtained in advance, the range is out of this range, and it can be considered that the discharge is completed too early. It is possible to set t9 at which it can be considered that discharge is completed too late. Since the discharge of the piezo stack 127A starts when the injection signal becomes "L", t7 and t9 are set with reference to t5 when the injection signal becomes "L". Since temperature information such as engine oil temperature is input to the ECU 22, t7 and t9 may be set based on this.

The ECU 22 determines that the abnormality determination signal IJF2 is normal if the abnormality determination signal IJF2 is "L" at time t7 and "H" at time t9. If the abnormality determination signal IJF2 is "H" at time t7 or "L" at time t9, it is determined to be abnormal. In the case of FIG. 13 which shows a normal state, it is "L" at the time of t7 and "H" at the time of t9.

A specific example in the case of an abnormality will be described. FIG. 14 and FIG. 15 show the short circuit of the charging / discharging circuit unit 211 or the piezo stacks 127A to 127D when the charging switch 35 is turned on. Note that FIG. 15 is shown in FIG.
It is an enlarged version of 4. Although the injection signal becomes "H" and the charging switch 35 is in the ON period, even if the control signal of the charging switch 35 becomes "L" after the ON period ends, the charging switch 35 has an ON failure. , The charging current continues to flow and rises further. When this exceeds the overcurrent threshold, the selection switch 37A for the first cylinder is turned off. As a result, even if the charging switch 35 has an on-failure, the energization paths 33a and 33b are not connected to the piezo stack 127A.
Then, the charging is stopped. If it is not cut off, the charging current will continue to rise as shown by the broken line in the figure, and such a situation can be reliably prevented by turning off the selection switch 37A. In addition, when the selection switch 37A of the first cylinder is turned off, the charge switch 35
Stop outputting control signals after the first time.

When the charging current exceeds the overcurrent threshold, the failure judgment F / F 68 becomes "H". This allows
At time t7, the ECU 22 can know that an abnormality that an overcurrent flows when the piezo stack 127A is charged has occurred.

When an abnormality that an overcurrent flows occurs, in addition to the ON failure of the charging switch 35, a short circuit failure of a part or all of the inductor 34, the piezo stack 1
A short circuit or the like between both terminals of 27A is conceivable, and such a case can be detected.

When the inductor 34 is partially short-circuited or the like, the charging voltage of the piezo stack 127A does not increase significantly only by turning it on for the first time. There is no problem in collecting the residual charge of the piezo stack 127A into the capacitor 32. However, when the charging switch 35 fails to turn on, the discharge switch 36 turns on to turn the capacitor 3 on.
2 to charge switch 35 to discharge switch 36 to resistor 38
A closed circuit from c to ground is formed. The resistor 38c is for detecting the discharge current and has a very small resistance value.
Will be short-circuited between both terminals.

When the charging switch 35 has an ON failure, the voltage at the terminal on the piezo stack 127A side of the inductor 34 detected at the point a becomes substantially the voltage of the capacitor 32 by turning off the selection switch 37A. Exceeds the overvoltage threshold which is the voltage abnormality determination threshold up to t4.
As a result, the discharge prohibition signal becomes "H", and the IJF
1 is held as "L".

When the controller 212 judges that a short-circuit failure has occurred and stops charging, and the discharge inhibition signal is "L", the controller 212 turns on / off the discharge switch 36 to recover the residual charge of the piezo stack 127A in the capacitor 32. .

On the other hand, if the discharge prohibition signal is "H", it is highly likely that the charging switch 35 has an ON failure, and therefore DC-
The operation of the DC converter 31 is stopped to prohibit charging of the capacitor 32 from the battery 30. Further, the emergency discharge switch 43 is turned on. As a result, the current is limited under the proper time constant of the resistor 44, and the piezo stack 127A and the capacitor 32 can be discharged to the ground side. As a result, it is possible to prevent the charge from being accumulated in the piezo stack 127A and the capacitor 32 in the abnormal state. Moreover, the piezo stack 127 is turned off until the selection switch 37A is turned off.
Since the injector 1 is charged to A, the injector 1 may be in the valve open state, that is, the injection state, but this state can be quickly eliminated.

Normally, the injector 1 is designed to exert a mechanical fail-safe function utilizing natural leakage of fuel from the displacement magnifying chamber 113, and is left open for a long time. Of course, the emergency discharge switch 43 may be manually operated at a repair shop or the like if the fuel injection during that time can be permitted.

The discharge inhibit signal is "H" when the charging voltage detected at the point a exceeds the abnormal voltage threshold value. However, in a normal state, the mask signal is the second time the charging switch 35 outputs the mask signal. When turned on, it becomes “L” (see FIG. 13)
Therefore, in the normal state, after t4, the discharge inhibit signal does not become "H" even if the charge voltage exceeds the abnormal voltage threshold value.

FIG. 16 shows the piezo stack 127 of the short circuit of the charge / discharge circuit section 211 or the piezo stack 127A.
This is when a part of the piezoelectric ceramic layer A is short-circuited. Even if the piezo stack 127A is normally charged, the charging period ends (t
3) After that, the charge leaks from the piezo stack 127A and the charge voltage gradually decreases.

Therefore, the residual charge at the start of discharge (t5) in the piezo stack 127A is smaller than that in the normal state, and the discharge period during which the discharge switch 36 is turned on and off is shortened. As a result, at the time of t7, the abnormality determination signal I
JF2 becomes "H" and IJF1 remains "L". As a result, the ECU 22 causes the piezo stack 127A
You can know the breakdown.

In FIG. 17, among the short-circuiting of the charge / discharge circuit section 211 or the piezo stacks 127A to 127D, the plurality of piezo stacks are simultaneously energized due to the ON failure of the selection switches 37A to 37D (hereinafter, the two cylinders simultaneous energization). That is the case). In the following description, when the piezo stack 127A corresponding to the first cylinder is being charged, the second
The description will be made assuming that the selection switch 37B corresponding to the cylinder No. has an ON failure, but the other combinations are substantially the same. When the two cylinders are energized simultaneously, the charging / discharging circuit section 2
Since the capacity of the piezo stack 127A when viewed from the 11 side increases, the charging speed decreases. In the case of the present embodiment in which the charge amount is controlled by the length of the charge period, the piezo stack 12
The charging voltage of 7 A does not fall within the predetermined voltage range, and is insufficient.

Therefore, at t4 when the abnormal voltage threshold value switches to the large capacity threshold value, the D input of the D flip-flop 57 becomes "L". Therefore, the abnormality determination signal IJF1 remains "L" even after t5 when the injection signal becomes "L". As a result, the ECU 22 can determine that the two cylinders are simultaneously energized. However, if the temperature representative of the engine such as the engine oil temperature is higher than a preset threshold value or the like, the ECU 22 does not determine whether the two cylinders are simultaneously energized.

The reason for this will be described. A capacitive element including a piezo stack generally has a large capacitance variation with temperature. FIG. 18 shows an example in which the temperature dependence of the capacity of the piezo stack used for the injector is investigated within the temperature range planned for a vehicle equipped with a diesel engine. The capacity is 2 at low temperature and at high temperature.
Different from double to triple.

Therefore, as described above, the abnormality determination signal IJ
Even if F1 is "L", it is not possible to distinguish whether it is due to simultaneous energization of two cylinders or an increase in capacity due to temperature rise. Therefore, if it is determined that the temperature is high compared with a preset threshold value or the like, it is not determined whether the two cylinders are simultaneously energized.

Of course, the piezo stacks 127A to 127D are controlled so that the temperature environment of the piezo stacks falls within a certain range.
If a measure such as heat radiation is taken, the abnormality determination signal I
When JF1 is “L”, it may be unconditionally determined that the two cylinders are simultaneously energized.

Since the discharging speed becomes slower together with the charging speed, the discharging completion time does not become so fast even if the charging voltage is low, and the discharging is completed at the same time as the normal time as shown in the figure. Therefore, the abnormality determination signal IJF2 is the same as that in the normal state.

The determination based on the abnormality determination signal IJF1 can also be applied to a partial short circuit of the piezoelectric ceramic layers of the piezo stacks 127A to 127D. That is, after the time t4 at which the voltage abnormality threshold value is switched to the large capacity threshold value and the charging voltage falls below the voltage abnormality threshold value before the injection signal becomes "L", the abnormality determination signal I
Since JF1 remains at "L", the piezo stack 127 can be selected depending on how the abnormal voltage threshold is taken after t4.
A partial short circuit of the piezoelectric ceramic layers A to 127D can be detected. In this case, the piezo stack 127A-1
The difference between the partial short-circuit of the piezoelectric ceramic layer of 27D and the simultaneous energization of two cylinders is that the abnormality determination signal IJF2 is "L" at t7 when the piezoelectric ceramic layers of the piezoelectric stacks 127A to 127D are partially short-circuited. Therefore, in the case of simultaneous energization of two cylinders, it is preferable to carry out since it is "H" at t7.

Although the present embodiment has been described for the case where the length of the ON period of the charging switch 35 is constant, the present invention is not necessarily limited to this.
The present invention can also be applied to a charging control method in which it is detected whether the charging current reaches a predetermined upper limit value during the ON period of the charging switch and the OFF period is entered when the charging current reaches the predetermined upper limit value.

(Second Embodiment) FIG. 19 shows a piezoelectric actuator drive circuit according to a second embodiment of the present invention. In this embodiment, the controller and the ECU are replaced in the configuration of the first embodiment, and the accuracy of fuel injection is improved. The substantially same parts as those in the first embodiment will be described with the same reference numerals. Controller 212A, ECU
22A has the same basic configuration as that of the first embodiment. The controller 212A determines that the output of the first D flip-flop 73 of the circuit portion (FIG. 11) for generating the mask signal is the ECU 22 as the first energization time measurement signal Tone.
Input to A.

The output of the first D flip-flop 73, which is the first energization time measurement signal Tone, is the charging switch 35 after the charging current exceeds the energization start threshold value when the charging switch 35 is turned on for the first time. It is a signal that becomes "H" until the charging current exceeds the energization start threshold value by the second turning on. Since the energization start threshold value is substantially 0 as described above, its length is substantially equal to that of the first charging switch 35.
Is the total time of the ON period and the OFF period that follows, and is the time from when the charging switch 35 is turned ON until the charging current reaches the energization start threshold value which is a predetermined current value set in advance.

The first energization time measurement signal Tone has the following properties. As mentioned above, the piezo stack 127A-
Since the charging of 127D is performed with the length of the ON period of the charging switch 35 being constant, the magnitude of the charging current reached during the ON period of the charging switch 35 is determined by the charging / discharging circuit unit 21.
It is determined by a constant of 1. Among the members forming the charging / discharging circuit unit 211, the injector 1 including the piezoelectric stacks 127A to 127D as a component is attached to the engine head, and therefore is placed in the most severe temperature environment. Therefore, the capacities of the piezo stacks 127A to 127D are greatly affected by temperature and fluctuate greatly.

As shown in FIG. 20, if the charging current reaching the ON period of the charging switch 35 is large, the length of the OFF period becomes long. Therefore, the piezo stacks 127A to 127A.
If the capacity of D is different, the first energization time measurement signal Ton
e changes. Therefore, the temperature fluctuation of the injector 1 is known from the first energization time measurement signal Tone. FIG. 21 shows an example of the relationship between the piezo stack 127 and the first energization time measurement signal Tone.

The ECU 22A is provided with a timer that starts counting at the rising edge of the first energization time measurement signal Tone, and determines the time until the falling edge of the first energization time measurement signal Tone. Time measurement signal T
Let one be the length.

Since the piezo stack 127 is a component of the injector 1, the temperature information obtained based on its capacity reflects the temperature of the injector 1 more accurately than the temperature of the engine oil or the like. Therefore, it is possible to obtain high-quality temperature information of the injector 1 without separately providing a sensor.

The length of the first energization time measurement signal Tone as the temperature information is used by the ECU 22A to correct the fuel injection timing and injection amount. Specifically, the output timing and length of the injection signal are corrected according to the length of the first energization time measurement signal Tone.

As a result, the sliding resistance of the movable member such as the needle 121 of the injector 1 and the pistons 124, 125, the viscosity of the fuel in the injector 1, etc. change due to the temperature change, and the operating characteristics of the ball 123 and the needle 121 are changed. Even if the influence is exerted, the influence can be prevented from affecting the fuel injection timing and the fuel injection amount.

Here, as an index of the current aging profile, the time taken until a predetermined current value (approximately 0 A in the embodiment) is taken immediately after the start of charging of the piezo stacks 127A to 127D is measured. Is easy.

Incidentally, it is preferable that a map obtained beforehand based on experiments or the like is prepared for the correction amount, and this map is stored in the ROM of the ECU 22A.

The first energization time measurement signal Tone corresponds to the ON period and the OFF period of the charging switch 35, but may be a signal corresponding to only the OFF period, for example.

Further, the piezoelectric actuator drive circuit of the present invention can be applied not only to the fuel injection device but also to various devices.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a piezo actuator drive circuit of the present invention for driving a piezo actuator mounted on an injector of a fuel injection device to which the present invention is applied.

FIG. 2 is an overall configuration diagram of the fuel injection device.

FIG. 3 is a configuration diagram centering on an injector of the fuel injection device.

FIG. 4 is a first timing chart showing an operating state of the piezo actuator driving circuit.

5 (A) and 5 (B) are each a diagram showing a state in which a piezo stack constituting the piezo actuator is being charged,
It is a figure which shows the operating state of the said piezo actuator drive circuit.

6 (A) and 6 (B) are diagrams respectively showing a state in which a piezo stack constituting the piezo actuator is discharged.
It is a figure which shows the operating state of the said piezo actuator drive circuit.

FIG. 7 is a circuit diagram of a first circuit portion of the piezo actuator driving circuit.

FIG. 8 is a timing chart showing an operating state of the circuit portion.

FIG. 9 is a circuit diagram of a second circuit portion of the piezo actuator driving circuit.

FIG. 10 is a timing chart showing an operating state of the circuit portion.

FIG. 11 is a circuit diagram of a third circuit portion of the piezo actuator driving circuit.

FIG. 12 is a timing chart showing an operating state of the circuit portion.

FIG. 13 is a second timing chart showing an operating state of the piezo actuator driving circuit.

FIG. 14 is a third timing chart showing an operating state of the piezoelectric actuator drive circuit.

FIG. 15 is a fourth timing chart showing an operating state of the piezo actuator driving circuit.

16 is an enlarged view of a part of FIG.

FIG. 17 is a fifth timing chart showing an operating state of the piezo actuator driving circuit.

FIG. 18 is a graph illustrating the operation of the piezoelectric actuator drive circuit.

FIG. 19 is an overall configuration diagram of a second fuel injection device to which the present invention has been applied.

FIG. 20 is a view for explaining the operation of the piezo actuator drive circuit that constitutes the fuel injection device.

FIG. 21 is a graph illustrating the operation of the piezoelectric actuator drive circuit.

[Explanation of symbols]

1 injector 1a nozzle part 1b back pressure control part 1c piezo actuator 103 injection hole 121 needles 127, 127A, 127B, 127C, 127D piezo stack 21,21A piezo actuator drive circuit 211 charge / discharge circuit part 212, 212A controller (control means) 22 , 22A ECU (command means) 30 Battery 31 DC-DC converter (power supply unit) 32 Capacitor 33a Energizing path 33b Energizing path 34 Inductor 35 Charging switch (switching element) 36 Discharging switch (switching element) 37A, 37B, 37C, 37D selection Switches 381a, 382a Resistors (voltage detection means) 38b, 38c Resistors (current detection means) 41A, 41B, 41C, 41D Resistors 42 Emergency discharge path 43 Emergency discharge switches Fourth resistor 45 diode

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01L 41/083 H01L 41/08 P F term (reference) 3G066 BA31 BA46 CC01 CC05U CD26 CE27 CE29 3G301 HA02 JB02 JB03 JB09 LB11 LC05 LC10 NE23 PG02B PG02Z 5H680 BB13 DD23 DD27 DD37 DD95 EE21 FF24 FF30 FF38 GG02

Claims (9)

[Claims] 1. A capacitor for accumulating energy for driving a piezo stack mounted on a piezo actuator, and an energizing path for moving electric charge through an inductor with one of the capacitor and the piezo stack as a supply source. As a current-carrying path, a first kind of current-carrying path in which a current that gradually increases in the inductor flows during the ON period of the switching element by repeating ON / OFF of the switching element, and the inductor during the OFF period of the switching element. In a piezo actuator drive circuit in which a second type energization path through which a gradually decreasing current flows is formed, and the piezo stack is charged and discharged by the control means that controls the switching element, a current flowing through the energization path Is provided with a current detection means for detecting, Exceeds the threshold current detected by the flow detecting means is preset, as well as determining that a failure occurs, the piezoelectric actuator drive circuit, characterized in that the set to determine the manner of a short circuit failure malfunction. 2. The piezo actuator drive circuit according to claim 1, wherein a plurality of piezo stacks can be connected as the piezo stack with a common energizing path, and the plurality of piezo stacks are connected by a selection switch controlled by the control means. The piezo stack connected to the energization path can be selected from among the piezo stacks, and when the control means determines that the short-circuit fault has occurred, the selection switch is turned off to open the energization path. Piezo actuator drive circuit set as described above. 3. The piezo actuator drive circuit according to claim 1, further comprising a voltage detection unit that detects a voltage of the energization path on the piezo stack side with respect to the switching element, the control unit comprising: A first voltage whose detected voltage is equal to or lower than a preset threshold value when the short-circuit failure is determined.
In the case of the second judgment condition of the second judgment condition, the current supply path allows the charge to be collected in the capacitor using the supply source as the piezo stack, and the detected voltage is equal to or higher than a preset threshold value. Sometimes, a piezo actuator drive circuit set to prohibit the charge recovery. 4. The piezo actuator drive circuit according to claim 3, wherein the threshold value of the detection voltage is set to a voltage between both terminals of the capacitor, and the control means controls the switching element when the switching element is off. A piezo actuator drive circuit set such that when the determination condition 2 is satisfied, the failure mode is determined to be an ON failure of the switching element. 5. The piezo actuator drive circuit according to claim 3, wherein an emergency discharge path for discharging the electric charge of the capacitor through the inductor and bypassing the piezo stack to the ground side is formed. A piezo actuator driving circuit having an emergency discharge switch for opening and closing the emergency discharge path in the emergency discharge path. 6. The piezoelectric actuator drive circuit according to claim 1, wherein the capacitor is
A piezo actuator drive circuit configured to be charged by a power supply unit controlled by the control unit, wherein the control unit is set to stop the operation of the power supply unit when the short-circuit failure is determined. 7. A capacitor for accumulating energy for driving a piezo stack mounted on a piezo actuator, and an energizing path for moving electric charge through an inductor with one of the capacitor and the piezo stack as a supply source. As a current-carrying path, a first kind of current-carrying path in which a current that gradually increases in the inductor flows during the ON period of the switching element by repeating ON / OFF of the switching element, and the inductor during the OFF period of the switching element. A second type energization path through which a gradually decreasing current flows is formed, and a piezo actuator drive circuit that switches between charging and discharging of the piezo stack by a control means that controls the switching element, wherein the piezo stack is not grounded. A voltage detecting means for detecting the voltage of the side terminal is provided, The means is set to judge that the piezo stack has failed when the voltage detected in the charge holding period after the completion of charging of the piezo stack is smaller than a preset threshold value. Actuator drive circuit. 8. A capacitor for storing energy for driving a piezo stack mounted on a piezo actuator, and an energization path for moving electric charge through an inductor, with one of the capacitor and the piezo stack as a supply source. As a current-carrying path, a first kind of current-carrying path in which a current that gradually increases in the inductor flows during the ON period of the switching element by repeating ON / OFF of the switching element, and the inductor during the OFF period of the switching element. In a piezo actuator drive circuit in which a second type energization path through which a gradually decreasing current flows is formed, and the piezo stack is charged and discharged by the control means that controls the switching element, the current flows through the energization path. A current detection unit for detecting a current is provided, and the control unit is Immediately after the charging of the zo stack is started, the time until the detected current reaches a predetermined current value set in advance is measured, and when the measured time is out of the predetermined range, the apparent capacity abnormality or piezo of the piezo stack is measured. A piezo actuator drive circuit, which is set so as to determine that the temperature of the stack is abnormal. 9. An injector for actuating a needle for opening and closing a nozzle hole for injecting fuel by a piezo actuator, and a condenser for driving the piezo actuator, the capacitor storing energy for driving a piezo stack mounted on the piezo actuator. And a current-carrying path for moving charges through the inductor with one of the capacitor and the piezo stack as a supply source, and the switching element is turned on and off by repeating the on-off of the switching element as the current-carrying path. A first type energization path in which a gradually increasing current flows in the inductor during a period and a second type energization path in which a gradually decreasing current flows in the inductor during the off period of the switching element, and the switching element By the control means for controlling
A piezo actuator drive circuit for charging and discharging the piezo stack, and a command means for instructing the control means the charge timing of the piezo stack and the length of the charge holding period corresponding to the fuel injection timing and injection amount. A fuel injection device having, wherein the piezo actuator drive circuit is provided with a current detection means for detecting a current flowing in the energization path, the command means, immediately after the start of charging the piezo stack, the detected current is Fuel injection characterized by measuring a time until a predetermined current value set in advance is set and correcting the charging timing and the charge holding period of the piezo stack based on the measured time. apparatus.