JP2002276502A - Piezo actuator driving circuit, and fuel injection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve monitor accuracy of voltage across a piezo stack and to allow discharge of the piezo stack that cannot be discharged due to disconnection or the like of a conducting wire. SOLUTION: Monitor wires 43A to 43D different from the conducting wires 41A to 41D are connected to terminals on non-ground side of the piezo stacks 127A to 127D, and a monitor signal of the voltage across each piezo stack is taken into controller 39, and thus voltage decrease of the conducting wires 41A to 41D during discharge control is prevented from affecting the monitor signals. Resistors 38A to 38D are connected to the piezo stacks 127A to 127D in parallel via the monitor wires 43A to 43D, and switches 39A to 39D are turned on to make discharge current flow from the piezo stacks 127A to 127D to the resistors 38A to 38D.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezo actuator drive circuit and a fuel injection device.

[0002]

2. Description of the Related Art A piezo actuator utilizes the piezoelectric action of a piezoelectric material such as PZT. A piezo stack, which is a capacitive element, expands or contracts by charging and discharging, and linearly moves a piston or the like. For example, in a fuel injection device for an internal combustion engine, there is known a fuel injection device in which switching of an opening / closing valve of an injector for fuel injection is performed by a piezo actuator. The piezo actuator drive circuit for driving the piezo actuator includes a charge / discharge circuit unit for supplying current to the piezo stack, and a control unit for controlling a charge / discharge current, a charge amount, and the like. In addition, a current-carrying wire that connects the charge / discharge circuit unit and the piezo stack and allows a charge current and a discharge current to flow is provided.

As a configuration of a charge / discharge circuit, a multiple switching type is known. This is because a first energizing path for charging a piezo stack from an electric storage buffer capacitor via an inductor is formed, and a second energizing path for bypassing the buffer capacitor by a diode is formed. By repeatedly opening and closing the first energizing path, a charging current that gradually increases through the first energizing path flows through the piezo stack during the ON period of the switching element, and the energy accumulated in the inductor during the OFF period of the switching element. The charging current is gradually supplied to the piezo stack through the second energization path while consuming. The discharge is performed by turning on and off another switching element to cause a discharge current in the opposite direction to flow through both energization paths.

The charging and discharging of the piezo stack are performed while monitoring the voltage between both ends. For example, when the voltage reaches a target voltage, the charging is completed. The detection of the voltage between both ends of the piezo stack is performed using the connection terminal with the current-carrying wire as a detection point.

As a fuel injection device, there is known a common rail type fuel supply system in which fuel pressurized by a high pressure supply pump is stored in a common rail and fuel is supplied from the common rail to an injector. Some use fuel as control oil for the injector.

[0006]

When the piezo stack is charged, the voltage between both ends of the piezo stack rises and the monitor voltage at the connection terminal also rises.
The detection voltage fluctuates, causing a detection error. FIG. 7 shows a monitor voltage from charge to discharge in the circuit of the multiple switching method. The switching element is turned on and off, and the charge current and the discharge current repeat the gradual increase and decrease as described above. The monitor voltage will fluctuate.

[0007] The piezo stack is a capacitive element as described above, and maintains a charge holding state even when charging is completed and the switching element is fixed to off. For this reason, if the conduction failure between the piezo stack and the charging / discharging circuit unit occurs due to the disconnection of the energizing wire or the like after the charging is completed, the discharging becomes impossible. This causes a problem that the fuel injection device cannot stop the fuel injection.

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 drive circuit and a fuel injection device which can monitor a voltage between both ends of a piezo stack with high accuracy with a simple configuration, and can discharge even when an energizing wire is disconnected. I do.

[0009]

According to the first aspect of the present invention, a charging / discharging circuit for charging and discharging a piezo stack mounted on a piezo actuator, and charging / discharging while monitoring a voltage between both ends of the piezo stack. In a piezo actuator driving circuit having a control unit for controlling energization of a piezo stack by a circuit unit and an energizing wire for connecting a charging / discharging circuit unit and the piezo stack and flowing a charging current and a discharging current, the piezoelectric stack is not grounded Side terminal,
A detection wire different from the current-carrying wire is connected, a monitor signal of the voltage between both ends of the piezo stack is taken into the charge / discharge circuit section, and a resistor is connected in parallel with the piezo stack via the detection wire to connect the piezo stack. And a fail-safe switch for opening and closing the discharge circuit.

Since no charging current or the like flows through the detection wire, the voltage between both ends of the piezo stack can be detected with high accuracy. Moreover, even if the normal discharge of the piezo stack becomes impossible, the piezo stack can be forcibly discharged using the detection wire by turning on the fail-safe switch means. At the time of this discharge, the control load is light since the fail-safe switch means is simply switched on.

According to the second aspect of the present invention, the fuel injection device includes a nozzle portion having a needle for opening and closing the injection hole, a high-pressure fuel stored in a common rail being supplied, and injecting the fuel from the injection hole. A back pressure chamber in which fuel is introduced from the common rail to generate back pressure of the needle, and a valve body disposed in the valve chamber interposed between the back pressure chamber and the low pressure source, and the port on the low pressure source side can be closed. And a back pressure increasing / decreasing means for reducing the pressure in the back pressure chamber as the lift amount of the valve body increases, and a piezo stack for pressing and driving the valve body. An injector having a piezo actuator for increasing the lift amount of the valve body as the amount increases is provided, and a piezo actuator driving circuit according to claim 1 for driving the piezo actuator.

With a simple configuration, the voltage between both ends of the piezo stack can be monitored with high accuracy, and discharge can be performed even when the conducting wire is disconnected.

According to a third aspect of the present invention, in the configuration of the second aspect of the present invention, the control unit switches the valve body between a seated state and a full lift state in response to a fuel injection command. An energization control for opening and closing the needle is executed, and in response to a command to reduce the fuel pressure in the common rail, the fail-safe switch means is turned on in advance before charging the piezo stack, and the needle is kept in a seated state. Is set to execute the energization control for bringing the valve body into the lift state.

At the time of energization control in response to the pressure-reducing command, if the piezo stack is charged to a charge amount that allows the valve body to be in a lift state (hereinafter, referred to as a half-lift) while the needle is in the seated state, then the piezo stack will naturally After a predetermined time from the progress of the discharge, the charge amount falls below the lower limit charge amount that can maintain the half lift. Since the discharge pattern of the piezo stack is determined by the time constant defined by the resistor and the piezo stack, the common rail pressure must be reduced by simply charging the piezo stack and using the time during which the half-lift state is maintained by charging as a unit. Can be.

According to a fourth aspect of the present invention, in the configuration of the third aspect of the present invention, a plurality of the injectors and the non-grounded conducting wires are provided in common with the charge / discharge circuit section,
Each energizing wire is provided with a switch means for selecting an injector to be connected to the charge / discharge circuit section, and in the energization control for the pressure reduction command, the control section turns on the failsafe switch means in advance and then turns on Switch the switch means for selection, and sequentially move the piezo stack,
Set to charge.

When the pressure reduction request is large, it is necessary to put a plurality of injectors in a half-lift state. in this case,
If the energization control for the pressure reduction command is to be performed by a common charge / discharge circuit section for a plurality of injectors, simply switching the injector connected to the charge / discharge circuit section will cause the piezo stack to be charged sequentially while switching the injectors. It is necessary to discharge while switching the injector again. On the other hand, in the present invention, since the discharge of the piezo stack is performed automatically, the control load does not become too heavy even if the number of injectors is large.

[0017]

FIG. 2 shows the construction of a common rail fuel injection system for a diesel engine to which the present invention is applied. As many injectors 1 as the number of cylinders of the diesel engine are provided for each cylinder (only one injector 1 is shown in the figure), and the fuel is supplied from a common common rail 54 that communicates via a supply line 55. 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 54 (hereinafter referred to as the common rail pressure). The fuel in the fuel tank 51 is supplied to the common rail 54 by the high-pressure supply pump 5.
3 and stored at high pressure.

The fuel supplied to the injector 1 from the common rail 54 is used not only for injection into the combustion chamber, but also as a control oil pressure for the injector 1 and the like, and is supplied from the injector 1 through a low-pressure drain line 56 to a fuel tank. Reflux to 51.

The CPU 61 constitutes a piezo actuator drive circuit 2 for driving a piezo actuator mounted on each injector 1 together with the drive unit 3, and determines a fuel injection timing and an injection amount based on a detection signal such as a crank angle. Calculate and issue an injection command corresponding to this.
The injection command is output to the drive unit 3 as an injection signal. The injection signal is a binary signal consisting of “H” and “L”, and causes the injector 1 to inject fuel for a predetermined period.

The CPU 61 controls the injection pressure so as to be appropriate according to the operating conditions known from other sensor inputs or the like. A pressure sensor 63 is provided on the common rail 54, and a detection signal of the common rail pressure is supplied to the AD converter 6.
2 and is input to the CPU 61. CP
U61 controls the metering valve 52 based on the common rail pressure to adjust the amount of fuel fed to the common rail 54. Also, when a sudden reduction of the common rail pressure is required, CP
U61 issues a pressure reduction command, and returns fuel as control oil for the injector 1 to the fuel tank 51 to reduce the common rail pressure as described later.

FIG. 3 shows the structure of the injector 1.
The injector 1 is a rod-shaped body, and is attached so that a lower part in the figure penetrates a combustion chamber wall (not shown) of the engine and protrudes into the combustion chamber. The injector 1 includes a nozzle unit 1a, a back pressure control unit 1b, and a piezo actuator 1c in this order from the bottom.
It has become.

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

Behind the needle 121, the high pressure passage 101
A fuel as a control oil is introduced from the through an in orifice 107 to form a back pressure chamber 106 for generating a back pressure of the needle 121. This back pressure acts on the rear end surface 1212 of the needle 121 together with the spring 122 provided in the back pressure chamber 106 in a seating direction (downward).

The back pressure is increased or decreased by a back pressure controller 1b, and the back pressure controller 1b is driven by a piezo actuator 1c having the piezo stack 127.

The back pressure chamber 106 has an out orifice 10
9 and is always in communication with the valve chamber 110 of the back pressure control unit 1b. The valve chamber 110 has a ceiling surface 1101 formed in an upwardly conical shape, and a low-pressure port 110 a communicating with the low-pressure chamber 111 is opened at the top of the ceiling surface 1101.
The low pressure chamber 111 is a low pressure passage 1 leading to the drain line 56.
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.

In the valve chamber 110, a ball 123 whose lower part is cut horizontally is provided. The ball 123 is a valve body that can move up and down. When the ball 123 descends, the cut surface serves as a valve seat bottom (hereinafter, referred to as a high-pressure side seat) 1 as a valve seat.
By closing the high pressure port 110b while sitting on the valve 102, the valve chamber 110 is isolated from the high pressure control passage 108, and when ascending, the valve chamber 110 is seated on the ceiling surface (hereinafter, referred to as a low pressure side seat) 1101 as the valve seat and the low pressure port 110a. Is closed to shut off the valve chamber 110 from the low-pressure chamber 111. Thereby, when the ball 123 descends, the back pressure chamber 106
Is the low pressure chamber 1 through the out orifice 109 and the valve chamber 110
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 isolated from the low pressure chamber 111 and the high pressure passage 10 is closed.
1, the back pressure of the needle 121 increases, and the needle 121 is seated.

The ball 123 is a piezo actuator 1c
Is pressed and driven. The piezo actuator 1c
A vertical hole 112 formed vertically above the low-pressure chamber 111.
Two pistons 124 and 125 having different diameters are slidably held, and a piezo stack 127 is disposed above the large-diameter piston 125 on the upper side with the vertical direction extending and contracting.

The large-diameter piston 125 is kept in contact with the piezo stack 127 by a spring 126 provided below the large-diameter piston 125, so that the large-diameter piston 125 is vertically displaced by the same amount as the piezo stack 127 expands and contracts.

The space defined by the lower small-diameter piston 124 facing the ball 123, the large-diameter piston 125, and the vertical hole 112 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 and presses the fuel in the displacement expansion chamber 113, the pressing force is transmitted to the small-diameter piston 124 via the fuel in the displacement expansion chamber 113. Here, since the small-diameter piston 124 has a smaller diameter than the large-diameter piston 125, the amount of extension of the piezo stack 127 is expanded and converted to 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 to the low-pressure side seat 1.
The lifter 101 lifts the seat and sits on the high-pressure side seat 1102 so that the back pressure chamber 106 communicates with the low pressure passage 102, so that the fuel pressure in the back pressure chamber 106 decreases. As a result, the force acting on the needle 121 in the unseating direction is more dominant than the force acting on the needle 121 in the seating direction, and the needle 121 is unseated and fuel injection is started.

On the other hand, when the injection is stopped, the piezo stack 127 is contracted by the discharge of the piezo stack 127 to reduce the ball 12.
Release the pushing force to 3. At this time, the pressure in the valve chamber 110 is low, and the high pressure fuel pressure 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 on the ball 123 is released, the ball 123 separates from the high-pressure seat 1102 and sits on the low-pressure seat 1101 again, and the fuel pressure in the valve chamber 110 rises. Stops.

Also, depending on the charge amount of the piezo stack 127, the ball 123
Lifts (half-lifts), the fuel recirculates from the valve chamber 110 to the fuel tank 51, and rapidly reduces the common rail pressure.

FIG. 1 shows a configuration of a piezo actuator driving circuit 2 for charging and discharging the piezo stack 127. For convenience of explanation, the piezo stack 1
27 corresponds to four cylinders, a piezo stack 127A,
The piezo stack 127B, the piezo stack 127C, and the piezo stack 127D are represented. The drive unit 3 of the piezo actuator drive circuit 2 includes a charge / discharge circuit unit 3a that charges and discharges the piezo stacks 127A to 127D, and a controller 39 that is a control unit that controls the charge / discharge circuit unit 3a.
Piezo stack 1 with wire harness 4
27A to 127D.

The charge / discharge circuit section 3a includes a wire harness 4
, Each wire 41A, 41B, 41C, 41D, 42a,
Connection terminals 301A, 301B, 301C, 301 to which the wire ends of 42b, 43A, 43B, 43C, 43D are connected.
D, 302a, 302b, 303A, 303B, 303
C, 303D. Connection terminals 301A to 301
D is for energization, and the piezo stacks 127A to 127A
D is provided in one-to-one correspondence. Connection terminal 303
A to 303D are for monitoring, and the piezo stack 12
7A to 127D are provided in one-to-one correspondence. The connection terminals 302a and 302b are common to the power supply and the monitor, while the connection terminal 302a is connected to the piezo stack 127A,
127B, the other 302b is the piezo stack 12
7C and 127D are provided in common. The common connection terminals 302a and 302b are on the ground side (hereinafter, referred to as common terminals).

The wire harness 4 is a connection terminal 3 for conducting electricity.
Current-carrying wires 41A-41 connected to 01A-301D
D and the monitor wires 43A to 43D connected to the monitor connection terminals 303A to 303D are connected to the piezo stack 1.
27A to 127D are provided in one-to-one correspondence,
The conducting wires 41A to 41D and the monitor wires 43A to 43D
43D line ends correspond to the corresponding piezo stack 127
A to 127D are connected to non-grounded terminals. This is because the conducting wires 41A to 41D and the monitor wires 43A to
43D, the connection pin of the connector on the wire harness 4 side may be separate and electrically connected to the terminal on the non-ground side of the piezo stack 127A to 127D in the connector on the injector 1 side. Power supply wires 41A to 41D and monitor wires 43 in the side connector.
A structure that conducts with A to 43D may be used. Also, wires 42 connected to the common terminals 302a and 302b
a and 42b are piezo stacks 127A to 127, respectively.
The D side is bifurcated, and the corresponding two piezo stacks 127A, 127B and 127C, 127C, 1
27D.

The charging / discharging circuit section 3a is a DC-D which generates a DC voltage of several tens to several hundreds of volts by power supply (+ B) of a vehicle-mounted battery.
The DC converter 31 and the buffer capacitor 312 connected in parallel to the output terminal of the C converter 311 constitute the DC power supply 31, and output a voltage for charging the piezo stacks 127A to 127D. The DC-DC converter 311 is a general boost chopper type circuit, and stores energy in the inductor 3111 when the switching element 3112 is turned on.
When the switching element 3112 is turned off, the buffer capacitor 312 is charged via the diode 3113 from the inductor 3111 that generates the back electromotive force. The buffer capacitor 312 has a sufficiently large capacitance,
A substantially constant voltage value is maintained even when the piezo stacks 127A to 127D are charged.

Buffer capacitor 312 of DC power supply 31
3 to the piezo stack 127A to 127D
A first energizing path 32a for energizing via 3 is provided, and a first switching element 34a is interposed between the buffer capacitor 312 and the inductor 33 in series with the first energizing path 32a. The first switching element 34a is formed of a MOSFET, and a parasitic diode (hereinafter, referred to as a first parasitic diode) 341a is connected so as to be reversely biased with respect to a voltage between both ends of the buffer capacitor 312. Further, the inductor 33 and the piezo stacks 127A to 127D are connected to the second current path 32b.
Is formed. This energization path 32b is connected to the inductor 3
3 and a second switching element 34b connected to a connection midpoint between the first switching element 34a and a closed circuit including the inductor 33, the piezo stacks 127A to 127D and the second switching element 34b. .
The second switching element 34b is also formed of a MOSFET, and a parasitic diode (hereinafter, referred to as a second parasitic diode) 341b is connected so as to be reverse-biased with respect to a voltage between both ends of the buffer capacitor 312.

The power supply paths 32a and 32b are common to the piezo stacks 127A to 127D, and the piezo stacks 127A to 127D side is the wire harness 4. The current supply paths 32a and 32b are
the piezo stack 12 of the inductor 33 which is the output terminal
Connection terminals 3 for branching at terminals on the side of 7A to 127D
It extends from 01A to 301D. The current paths 32a, 32 between the inductor 33 and the connection terminals 301A to 301D
In b, switching elements (hereinafter, appropriately referred to as selection switching elements) 35A, 35B, 3
5C and 35D are provided. Selective switching element 35
A to 35D are piezo stacks 127A to 127, respectively.
D is connected in series with D in a one-to-one correspondence, and the piezo stacks 127A to 127D of the injector 1 of the injection cylinder are provided.
Are turned on. The current supply paths 32a and 32b are selectively formed in the piezo stacks 127A to 127D.

MOSFETs are used for the selection switching elements 35A to 35D, and their parasitic diodes (hereinafter, referred to as selective parasitic diodes) 351A, 351
B, 351C and 351D are buffer capacitors 312
Are connected so as to be reverse-biased.

Switching elements 34a, 34b, 35A
Control signals are input to the respective gates of the selectors 35A to 35D from the controller 39, and as described above, any one of the selection switching elements 35A to 35D is turned on to select the piezo stacks 127A to 127D to be driven, and to perform switching. A pulse-like control signal is input to the gates of the elements 34a and 34b, and the switching elements 34a and
4b on and off, and the piezo stacks 127A to 127D
, And charge control and discharge control.

The common ground-side connection terminals 302a, 302
Resistors 36E and 36F are provided between b and the ground. The voltage between both ends is inputted to the controller 39, and the charging current of the piezo stacks 127A to 127D is detected.

A resistor 36G having a relatively low resistance is provided in series with the second switching element 34b. The voltage between both ends is input to the controller 39 and the piezo stack 12
The discharge currents of 7A to 127D are detected.

Lines 37A, 37B, 37C for taking the potentials of the connection terminals 303A to 303D into the controller 39 are connected to the connection terminals 303A to 303D for monitoring.
37D is formed. The potentials of the connection terminals 303A to 303D are voltages at both ends of each of the piezo stacks 127A to 127D (hereinafter, referred to as piezo stack voltages), and the controller 39 monitors the piezo stack 12
7A to 127D are controlled.

Also, connection terminals 303A to 30A for monitoring
Between the 3D and the ground, the resistors 38A, 38 connected in series corresponding to the connection terminals 303A to 303D in one-to-one correspondence.
B, 38C, 38D and switching elements (hereinafter, appropriately referred to as fail-safe switching elements) 39A, 39B, 3 which are switching means for fail-safe.
9C and 39D are interposed. Switching element 39
Control signals are input from the controller 39 to the bases of A to 39D.

At the time of charging control, the controller 39 sets the ON period and the OFF period of the first switching element 34a as follows, and outputs a control signal for the switching element 34a. That is, the switching element 34a is turned on and a gradually increasing charging current flows through the first current path 32a.
When the charging current reaches the preset upper limit current value, the switching element 34a is turned off and the off period starts. At this time, since the back electromotive force generated in the inductor 33 is forward-biased with respect to the parasitic diode 341b of the second switching element 34b, the flywheel that gradually decreases to the second current path 32b due to the energy stored in the inductor 33 A current flows, and charging of the piezo stacks 127A to 127D proceeds. When the charging current reaches the lower limit current value (approximately 0), the first switching element 34a is turned on again to enter the ON period, and this is repeated (multiple switching method). When the piezo stack voltage reaches a preset voltage, the switching element 34a is fixed to OFF, and the charging is completed. Thereby, the piezo stacks 127A to 127
D extends and presses and lifts the ball 123 via the displacement expansion chamber 113.

In the discharge control, the ON period and the OFF period of the second switching element 34b are set as follows, and a control signal for the second switching element 34b is output. That is, the second switching element 34b is turned on, and a gradually increasing discharge current flows through the second current path 32b. When the discharge current reaches a preset current value (hereinafter, referred to as an upper limit current value), the switching element 34b is turned off and an off period starts. At this time, a large back electromotive force is generated in the inductor 33, and the flywheel current flows through the first current path 32 a by the energy stored in the inductor 33, and the energy is recovered by the buffer capacitor 312. When the discharge current reaches the lower limit current value (substantially 0), the second switching element 34b is turned on again, and this is repeated. And
When the piezo stack voltage reaches 0, the switching element 3
4b is fixed off, and the discharge is completed. By discharging the piezo stacks 127A to 127D in this manner, the piezo stacks 127A to 127D are contracted and the pressing force of the displacement expansion chamber 113 on the ball 123 due to the fuel pressure is released, and the ball 123 is seated.

The controller 39 causes the piezo stacks 127A to 127D to charge and discharge at predetermined times according to various control signals from the CPU 61 constituting the control section 6a. An injection signal that defines a charging time and a discharging time is input as such a control signal. The injection signal is a binary signal composed of “L” and “H”, and the piezo stacks 127A to 127
D starts charging, and the falling piezo stack 127
A to 127D are discharged. Therefore, the injection period is defined by the output timing and length of the injection signal.

Further, a target voltage setting signal proportional to a target piezo stack voltage (hereinafter, referred to as a target voltage), which is a target charge amount, is input as a control signal, and the controller 39 causes the piezo stack voltage to reach the target voltage. Then, the switching element 34a is fixed off as described above. The target voltage setting signal is set as follows for the injection command. FIG. 4 shows that the ball 123 lifts and the valve chamber 11
Relationship between a piezo stack voltage at which fuel starts to leak from 0 (hereinafter, referred to as a leak start voltage), a piezo stack voltage at which the ball 123 is fully lifted and the needle 121 is lifted and injected (hereinafter, referred to as an injection start voltage), and a common rail pressure. The leak start voltage and the injection start voltage increase as the common rail pressure increases. CPU
Reference numeral 61 stores the correspondence between the target voltage slightly higher than the injection start voltage and the common rail pressure as a map or the like in the ROM, and sets the target voltage for the injection command based on this. As the target voltage, a sufficient piezo stack voltage capable of fully lifting the ball 123 is given. At this time, a higher target voltage is applied as the common rail pressure is higher, so that appropriate charging can be performed without excess or deficiency for the ball 123 to fully lift.

In response to the pressure reduction command, the CPU 61 determines the charging timing and the target voltage of the piezo stacks 127A to 127D as follows, and reduces the common rail pressure. In FIG. 4 described above, the range between the leak start voltage and the injection start voltage is the range of the voltage at which the ball 123 can be half-lifted, and the correspondence between the target voltage and the common rail pressure is stored as a map or the like within this range. Then, based on this, the target voltage for the pressure reduction command is set. Note that a target common rail pressure (hereinafter, referred to as a target pressure) in the pressure reduction command is calculated by the CPU 61 based on the engine operating state, and output to the controller 39.

The target voltage in the injection command and the pressure reduction command is
Instead of the map, the piezo stack voltage may be given by a function formula corresponding to the common rail pressure.

Further, a control signal for selecting a cylinder to be controlled is also output from the CPU 61, and according to the control signal, the piezo stacks 127A to 127 corresponding to the selected one of the selected switching elements 35A to 35D are selected.
D's are turned on.

FIG. 5 is a flowchart showing fail-safe control for wire breakage and the like. When charge control of the piezo stacks 127A to 127D is performed first (step S11), a monitor voltage of the piezo stack voltage taken in from the lines 37A to 37D is used. Is determined (step S12). If the monitor voltage has risen, it is determined that the monitoring of the piezo stack voltage is normally performed, and the normal control process is executed (step S13).
That is, the piezo stacks 127A to 127D are charged until the monitor voltage reaches the target voltage. Then, when the monitor voltage reaches the target voltage, the first switching element 34a is fixed to OFF as described above, and the charging is completed. Monitor wire 43 for taking in monitor voltage
Since no charging current flows through A to 43D, the piezo stack voltage can be monitored without being affected by the impedance of the monitor wires 43A to 43D. Thereby, the piezo stack voltage can be set to the target voltage with high accuracy.

Then, the state of charge of the piezo stacks 127A to 127D is held until the injection signal falls, and when the injection signal falls, the process proceeds to step S14, where the discharge control of the piezo stacks 127A to 127D is executed.

Next, it is determined whether or not the monitor voltage has decreased (step S15). If the monitor voltage decreases, it is determined that the discharge is normally performed without disconnection or the like of the conducting wires 41A to 41D, and the discharge control by the second switching element 34b is continued, and the electric charge is reduced. Collected in the buffer capacitor 312.

If the monitor wires 43A to 43D are disconnected, the monitor voltage does not increase even if the charging control of the piezo stacks 127A to 127D is executed (step S).
12). In this case, the process skips step S13 and proceeds to step S14, where the piezo stacks 127A to 127D
Is stopped and the control is forcibly switched to the discharge control.

In the charged state, the current-carrying wires 41A-41
If D is disconnected or the like, the discharge is not actually performed even if the discharge control is performed (step S14), and the monitor voltage does not decrease (step S15). In this case, the switching elements 39A to 39D connected to the piezo stacks 127A to 127D whose voltage does not decrease are turned on (step S1).
6). By turning on the switching elements 39A to 39D, the piezo stacks 127A to 127D and a resistor (hereinafter, appropriately referred to as a fail-safe resistor) 38 are provided.
The circuit consisting of A to 38D is closed, and the discharge current of the piezo stacks 127A to 127D is reduced by the resistors 38A to 38D.
Flows to Thus, it is possible to prevent a problem that the ball 123 is quickly seated and the injector 1 keeps injecting fuel.

As described above, the wires 43A to 43D for monitoring the piezo stack voltage are connected to the piezo stack 127A.
-127D also functions as a wire for forcibly discharging, so that the wires 43A to 43D are not limited to monitoring the piezo stack voltage, and have high practical value. Moreover, as described above, the monitor wires 43A-
Since no charging current or discharging current flows through 43D, the piezo stack voltage can be monitored with high accuracy.

The fail-safe switching elements 39A to 39D are piezo stacks 127A to 127D.
Are provided in a one-to-one correspondence with the wire 41A.
Due to disconnection of ~ 41D, some piezo stacks 127A ~
When 127D becomes incapable of discharging, fuel can be injected by other normal piezo stacks 127A to 127D except for the part of the piezo stacks 127A to 127D that have become incapable of discharging, thereby realizing a limp home. it can.

FIG. 6 shows a flow chart of the energization control (pressure reduction control in the figure) in response to the common rail pressure reduction command. It is determined whether the pressure reduction control has been completed based on whether the common rail pressure has reached the target pressure (step S2).
1) If the target pressure has not been reached, the fail-safe switching elements 39A to 39D of all cylinders are turned on (step S22).

Next, the target voltage of the piezo stack 1 of the first cylinder in the pressure reduction control is calculated, and the piezo stack 12 is operated.
7A to 127D are charged and boosted to the target voltage (step S23).

Thus, the high-pressure fuel is returned to the fuel tank 51 in the injector 1 of the first cylinder.

Next, the calculation of the target voltages of the piezo stacks 127B to 127D of the second, third and fourth cylinders and the charging of the piezo stacks 127B to 127D in the pressure reduction control are executed while sequentially switching the cylinder selection switching elements 35B to 35D. (Steps S24, S25, S2
6). After the calculation of the target voltage of the piezo stack 127D of the fourth cylinder and the execution of the charging of the piezo stack 127D,
It returns to step S21. If the common rail pressure has not reached the target pressure, the procedure from step S22 is repeated again.

In this pressure reduction control, the piezo stack 127A
To 127D, the second switching element 34b
The piezo stack 127A-12 by turning on and off
Piezo stack 1 of next cylinder without 7D discharge
The charging of 27A to 127D starts. Then, even after charging is completed, current flows from the piezo stacks 127A to 127D to the resistors 38A to 38D connected in parallel with the piezo stacks 127A to 127D, so that the amount of stored electricity decreases and the piezo stack voltage increases toward the leak start voltage. It is going down. The time constant that defines the decreasing speed at this time is a piezo stack 127A.
To 127D and the resistance of resistors 38A to 38D.

Thus, the ball 123 is seated again from the injector 1 of the first cylinder whose charging time is earlier.

As described above, it is only necessary to turn on the fail-safe switching elements 39A to 39D in advance in response to the pressure-reducing command, and the discharge control becomes unnecessary, so that the high-pressure fuel is recirculated from the injector 1 in a plurality of cylinders. Does not require the operation of the second switching element 34b,
The number of operations of the selection switching 35A to 35D can be reduced. As a result, the control burden is also reduced.

Thus, the wires 43A to 43D
Can increase the implementation value.

Note that the timing at which the ball 123 sits after completing the half lift is not arbitrarily set but is defined by the time constant and the like. The time constant and the like are set in consideration of, for example, the following. The injector 1 shown in FIG. 3 includes a mechanical fail-safe mechanism that gradually closes the valve after a certain period of time, even if the state is maintained forever after the piezo stack 127 is charged to allow fuel injection.
That is, the injector 1 compresses and pressurizes the fuel in the displacement expansion chamber 113 by the extension of the piezo stack 127, and generates a pressing force for pressing the ball 123. The fuel pressure is generated when the ball 123 is in the lift state. The pressure is such that it can withstand the upward urging force acting on the ball 123.
For this reason, the pressurized fuel in the displacement expansion chamber 113 leaks little by little from the sliding portions of the pistons 124 and 125 to the low-pressure section such as the low-pressure chamber 111, and the lift of the ball 123 is reduced, so that the pressure increases from the back-pressure chamber 106. The flow rate of the fuel flowing into the low-pressure chamber 111 decreases, whereby the back pressure gradually increases. At the end, the needle 121 sits and the fuel injection stops. Therefore, the half lift duration is set to be shorter than this time.

In this embodiment, only the monitor wires that are electrically connected to the non-ground side terminals of the piezo stack are provided. However, the monitor wires that are electrically connected to the ground side terminals of the piezo stack are also provided, and the piezo stack is further provided. The stack voltage can be monitored with high accuracy.

The fail-safe switching elements 39A to 39D are connected to the piezo stacks 127A to 127D.
Are provided in a one-to-one correspondence with each other, but a single fail-safe switching element is commonly used for the resistors 38A to 38D, and a diode is connected in series with each resistor. A one-to-one correspondence may be provided so that the direction from the resistor to the ground side is the forward direction. In this case, when the fail-safe switching element is turned on, injection cannot be substantially performed in the other cylinders during that time, but the piezo stacks 127A to 127 in which discharge is disabled cannot be performed.
The fuel injection of the injector 1 equipped with the fuel injection stop is stopped by the mechanical fail-safe mechanism, and after the engine stops, the fail-safe switching element is turned on to discharge the piezo stacks 127A to 127D which cannot be discharged. I do. This discharge may be set to be performed by a special command input to the CPU from the outside at a repair shop or the like.

Although this embodiment has been described as applied to a fuel injection device for an internal combustion engine, the present invention can be applied to an apparatus having a piezo actuator.

Further, in the present embodiment, not only the problem such as the continuous injection of fuel from the injector 1 can be prevented as described above, but also the piezo stacks 127A to 127A
The energizing wire is broken while 7D is in the charge holding state,
When the disconnection is detected by some abnormality detecting means and the engine is stopped and repair is to be performed, the piezo stack 12
Since the electric charges held in 7A to 127D can be reliably removed, there is an additional effect that safety at the time of repair can be secured.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a piezo actuator driving 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 centered on an injector of the fuel injection device.

FIG. 4 is a graph illustrating control in a CPU constituting the fuel injection device.

FIG. 5 is a first flowchart showing control in the fuel injection device.

FIG. 6 is a second flowchart showing control in the fuel injection device.

FIG. 7 is a graph showing the operation of a conventional piezo actuator drive circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Injector 1a Nozzle part 1b Back pressure control part (back pressure increasing / decreasing means) 1c Piezo actuator 110 Valve room 110a Low pressure port 123 Ball (valve element) 127, 127A, 127B, 127C, 127D Piezo stack 2 Piezo actuator drive circuit 3 Drive unit 3a Charge / discharge circuit unit 35A, 35B, 35C, 35D Switching element for selection (switch means for selection) 38A, 38B, 38C, 38D Fail-safe resistor (resistor) 39A, 39B, 39C, 39D Fail-safe Switching element (fail-safe switch means) 39 Controller 4 Wire harness 41A, 41B, 41C, 41D Current supply wire 43A, 43B, 43C, 43D Monitor wire (detection wire) 6 Control unit 61 CPU

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 41/083 H01L 41/08 P 41/09 U

Claims (4)

[Claims] 1. A charge / discharge circuit for charging and discharging a piezo stack mounted on a piezo actuator, and a control for controlling energization of the piezo stack by the charge / discharge circuit while monitoring a voltage between both ends of the piezo stack. A piezo actuator drive circuit having a unit and a current-carrying wire that connects the charge / discharge circuit unit and the piezo stack and allows a charging current and a discharge current to flow, wherein a terminal on the non-ground side of the piezo stack has another Connect the detection wire to capture the monitor signal of the voltage between both ends of the piezo stack into the control unit, and connect the resistor in parallel with the piezo stack via the detection wire to discharge the piezo stack discharge current to the resistor Piezoactuator having a switch circuit for fail-safe for opening and closing the discharge circuit. Over motor drive circuit. 2. A nozzle portion having a needle for opening and closing an injection hole, wherein a high-pressure fuel stored in a common rail is supplied, and the fuel is injected from the injection hole. A back pressure chamber for generating back pressure, and a valve body disposed in a valve chamber interposed between the back pressure chamber and the low pressure source so that the port on the low pressure source side can be closed. Back pressure increasing / decreasing means for reducing the pressure in the back pressure chamber as the amount increases, and a piezo stack for pressing and driving the valve element, the lift amount of the valve element increases as the charge amount of the piezo stack increases. A fuel injection device comprising: an injector having a piezo actuator for increasing the size; and the piezo actuator driving circuit according to claim 1 for driving the piezo actuator. 3. The fuel injection device according to claim 2, wherein
In response to a fuel injection command, the control unit performs an energization control to open and close the needle by switching the valve body between a seated state and a full lift state, and to issue a fuel pressure reduction command in the common rail. On the other hand, prior to charging the piezo stack, the fail-safe switch means is turned on in advance, and it is set so as to execute energization control for setting the valve body in the lift state while the needle is in the seated state. Characteristic fuel injection device. 4. The fuel injection device according to claim 3, wherein
A plurality of the injectors and the non-ground side energizing wires are provided in common with the charging / discharging circuit unit, and each energizing wire is provided with a switch means for selecting an injector to be connected to the charging / discharging circuit unit; In the energization control for the pressure reduction command, after previously turning on the fail-safe switch means,
A fuel injection device which is set so as to sequentially charge a piezo stack by switching a switch means for selection to be turned on.