JP3765282B2 - Piezo actuator driving circuit and fuel injection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a piezoelectric actuator drive circuit and a fuel injection device.
[0002]
[Prior art]
The piezo actuator uses a 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 used as a means for switching between fuel injection and its stop in a fuel injection injector. Things are known. The piezo actuator is discharged when the piezo stack, which is a capacitive element, expands by charging and contracts. This is an actuator that is energized only when the piezo stack is extended and contracted.
[0003]
The drive circuit of the piezo actuator moves a charge between the capacitor for storing the charge for charging the piezo stack and the capacitor and the piezo stack through one of the supply sources via the current limiting inductor. And an energization path. In the fuel injection device, for example, the fuel injection is started by charging the piezo stack from the capacitor, the charge is recovered from the piezo stack to the capacitor at a predetermined timing, and the fuel injection is stopped. Accordingly, during fuel injection, the piezo stack and the capacitor are in a non-conductive state. Conventionally, unlike the solenoid type used for injector opening / closing control, the energized state of the solenoid is maintained by continuing energization to the solenoid, and during that time, the injection is possible. .
[0004]
As a configuration of a piezo actuator drive circuit, Japanese Patent Application Laid-Open No. 2001-157472 has a configuration in which an LC resonance circuit is formed by a capacitor, a piezo stack, and an inductor (LC resonance method).
[0005]
Japanese Patent Laid-Open No. 10-308542 discloses a first type energization path through which a current that gradually increases in the inductor during an on period of the switching element when the switching element is repeatedly turned on and off. There is also a configuration in which a second type energization path through which a gradually decreasing current flows in the inductor during the off period is formed (multiple switching method). The LC resonance type simply exchanges energy (charge) by simply oscillating the current and voltage behavior determined by the circuit constants, while the multiple switching type has the control of the switching element. 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]
[Problems to be solved by the invention]
However, in comparison with the LC resonance method, in which all charges are discharged and received between the piezo stack and the capacitor, the multiple switching method has a sufficient amount of charge stored in the capacitor. It is necessary to supply only the piezoelectric stack to the piezo stack, and the configuration and control contents of the piezo actuator drive circuit are complicated.
[0007]
For this reason, a more practical value is required for the piezoelectric actuator drive circuit. For example, in the case of the LC resonance type, even if the switch that opens and closes the energization path after charging or discharging starts and becomes uncontrollable (ON failure), the piezo actuator drive circuit and the piezo stack are particularly damaged. In contrast to the switching type, the behavior of the current and voltage differs depending on the switching element on / off state, so if the switching element may not operate as commanded, the piezo actuator drive circuit and piezo stack However, there is nothing that can perform failure detection with a simple configuration.
[0008]
The present invention has been made in view of the above circumstances, and an object thereof is to provide a piezoelectric actuator driving circuit having high practical value.
[0009]
[Means for Solving the Problems]
  According to the first aspect of the present invention, the electric charge is transferred through the inductor by using a capacitor that stores energy for driving the piezo stack mounted on the piezo actuator and one of the capacitors and the piezo stack as a supply source. A first energization path through which an increasing current flows in the inductor during the on period of the switching element, and an off period of the switching element. A piezoelectric actuator driving circuit in which a second type of energization path through which a gradually decreasing current flows is formed in the inductor, and the piezo stack is charged and discharged by a control unit that controls the switching element;
  Providing a current detection means for detecting a current flowing in the energization path;
  The control means is set so that a short-circuit failure is determined when the current detected by the current detection means exceeds a preset threshold value.
  Furthermore, provided on the piezo stack side with respect to the switching element, a voltage detection means for detecting the voltage of the energization path,
  When the control means determines that the short-circuit fault has occurred and the voltage detected when the switching element is off is a first determination condition that is not more than a preset threshold value, Charge collection for collecting the charge in the capacitor using the piezo stack as a source is allowed, and the charge collection is set to be prohibited when the detected voltage is a second determination condition equal to or higher than a preset threshold value.
[0010]
[Means for Solving the Problems]
  Unlike the LC resonance type, the current flowing through the energization path becomes an overcurrent due to an on-failure in which the switching element that opens and closes the energization path becomes uncontrollable while the switching element is in an on state or a short circuit of part or all of the inductor. For example, this may cause excessive charging of the piezo stack, resulting in an excessive increase in the voltage between both terminals of the piezo stack. Therefore, by monitoring the current flowing through the energization path, it is possible to quickly know the occurrence of a failure. This improves the practicality.
  When the short-circuit fault is determined, the higher the voltage of the energization path on the piezo stack side than the switching element, the more the short-circuit fault mode is the on-failure of the switching element or the short-circuit fault of the inductor. The probability is high. In this case, if normal charge recovery from the piezo stack to the capacitor is performed, the capacitor and the inductor are in conduction due to the ON failure of the switching element, or the inductor does not act to limit the current. Therefore, when a current that gradually increases through the current path from the piezo stack to the inductor to the ground is supplied from the piezo stack as a supply source, the terminal on the non-ground side of the capacitor is grounded, and the capacitor is connected between both terminals. There is a risk of short circuit. Alternatively, if the inductor is short-circuited, the piezo stack is short-circuited. In the present invention, if the detection voltage is equal to or higher than the threshold value, normal charge recovery is not performed, and thus it is possible to prevent such a short circuit of the capacitor or the piezo stack.
[0011]
According to a second aspect of the 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 A piezo stack connected to the energization path can be selected from a plurality of piezo stacks,
If it is determined that the short-circuit failure has occurred, the control unit is set to turn off the selection switch and open the energization path.
[0012]
Simply, charging and discharging can be stopped to prevent damage to the piezo actuator drive circuit and the piezo stack.
[0015]
  Claim3In the described invention, the claims1 or 2In the configuration of the invention, the threshold value of the detection voltage is substantially set to a voltage between both terminals of the capacitor,
  When the second determination condition is satisfied when the switching element is off, the control means is set so that the failure mode is determined as an on-failure of the switching element.
[0016]
If a short-circuit failure is determined, the switching element in the energization path with the capacitor as the source is turned off as a countermeasure, but the detected voltage still reaches the voltage between both terminals of the capacitor. This is the case. Therefore, by setting the threshold value of the detection voltage to approximately the voltage between both terminals of the capacitor, the failure mode can be specified as an ON failure of the switching element.
[0017]
  Claim4In the described invention, the claims1 to 3In the configuration of the invention, 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, and the emergency discharge path includes the emergency discharge path. An emergency discharge switch that opens and closes the path is provided.
[0018]
As described above, even in the case of a short circuit failure in which normal charge recovery 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, and after it is determined that a short-circuit failure has occurred, the charge may be automatically discharged at a predetermined timing, or may be operated at a repair shop or the like. As a precondition, manual operation may be used.
[0019]
  Claim5In the described invention, claims 1 to4In the configuration of the invention, the capacitor is charged by a power supply unit controlled by the control means,
  The control means is set so as to stop the operation of the power supply unit when it is determined that the short circuit failure has occurred.
[0020]
By preventing electric energy from being newly input to the capacitor, damage to the piezoelectric actuator drive circuit and the piezoelectric stack can be minimized.
[0021]
  Claim6In the described invention,In the configuration of the invention of claims 1 to 5,
  The voltage detection means detects the voltage of the non-ground side terminal of the piezo stack,
  The control means is set so as to determine that the piezo stack has failed when a voltage detected in a charge holding period after completion of charging of the piezo stack is smaller than a preset threshold value.
[0022]
If the piezo stack is normal, the voltage is substantially constant during the charge holding period after completion of charging. On the other hand, if the charge leaks due to a partial short circuit of the piezoelectric ceramic layer of the piezo stack, the voltage decreases. Therefore, the failure of the piezo stack is known from the voltage drop.
[0023]
  Claim7In the described invention, a capacitor that accumulates energy for driving a piezo stack mounted on a piezo actuator, and a current-carrying path that moves charge between the capacitor and the piezo stack via one of the supply sources, As the energization path, a first type of energization path through which a current that gradually increases in the inductor during the on period of the switching element flows by repeatedly turning on and off the switching element, and the inductor during the off period of the switching element. In a piezo actuator driving 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 for controlling the switching element,
  Providing a current detection means for detecting a current flowing in the energization path;
  The control means includesImmediately after starting to charge the piezo stack, measure the time until the detected current takes a predetermined current value set in advance,Means for detecting the apparent capacity of the piezo stack or the temperature of the piezo stack based on the measurement time.
[0024]
  The behavior of the current varies depending on the circuit constants of the piezo stack and the inductor, but particularly varies depending on the apparent capacity of the piezo stack. The apparent capacity of the piezo stack here is equivalent to E = (1/2) CV with the piezo stack equivalent to a capacitor.²It is C obtained from the relationship of (E: energy input to the piezo stack, C: apparent capacity of the piezo stack, V: voltage of the piezo stack) (hereinafter simply referred to as capacity). And the capacity is susceptible to temperature. Therefore, from the current profile over timeThe capacity of the piezo stack and the temperature of the piezo stack are known, and furthermore, the capacity abnormality of the piezo stack and the temperature abnormality of the piezo stack can be known based on the information.
[0025]
Here, as the index of the current aging profile, the time until a predetermined current value is obtained immediately after the start of charging of the piezo stack is measured, so that the implementation is easy.
[0026]
  Claim8In the described invention, an injector for operating a needle for opening and closing a nozzle hole for injecting fuel by a piezo actuator;
  As means for driving the piezo actuator,
  A capacitor that stores energy for driving the piezo stack mounted on the piezo actuator, and a current-carrying path that moves charge through an inductor with one of the capacitor and the piezo stack as a supply source, By repeating ON / OFF of the switching element as the energization path, a first type energization path through which a current that gradually increases in the inductor during the ON period of the switching element and a current that gradually decreases in the inductor during the OFF period of the switching element flow. A piezo actuator driving circuit in which a second type of energization path is formed and the piezo stack is charged and discharged by a control means for controlling the switching element;
  A fuel injection device having command means for instructing the charging timing and the length of the charge holding period of the piezo stack corresponding to the fuel injection timing and the injection amount to the control means;
  In the piezoelectric actuator drive circuit,
  Providing a current detection means for detecting a current flowing in the energization path;
  The command means measures the time until the detected current takes a predetermined current value set in advance immediately after starting the charging of the piezo stack, and based on the measured time, the charging timing and the charging of the piezo stack Set to correct the length of the retention period.
[0027]
  The sliding resistance of the movable member constituting 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 takes a predetermined current value that is set in advance varies depending on the temperature of the piezo stack, which can be regarded as the temperature of the injector, and is much higher than the injector temperature. Corresponding temperature information. Therefore, fuel injection can be performed with high accuracy by correcting the charging time of the piezo stack and the length of the charge holding period according to the measured time.
  According to the tenth aspect of the present invention, the electric charge is transferred through the inductor by using a capacitor for storing energy for driving the piezo stack mounted on the piezo actuator and one of the capacitor and the piezo stack as a supply source. A first energization path through which an increasing current flows in the inductor during the on period of the switching element, and an off period of the switching element. In the piezo actuator driving circuit in which a second type energization path through which a gradually decreasing current flows is formed in the inductor, and the piezo stack is charged and discharged by the control means for controlling the switching element,
  Provided with voltage detection means for detecting the voltage of the energization path on the piezo stack side than the switching element,
  The control means;Detected by the voltage detection meansCharging the piezo stackWhen the voltage exceeds a preset threshold,Set to determine that there is an overvoltage abnormality in the piezo stack.
  Thereby, it can be determined that the charging voltage has increased excessively.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 2 shows the configuration of a common rail fuel injection device for a diesel engine to which the present invention is applied. The number of injectors 1 corresponding to the number of cylinders of the diesel engine is provided corresponding to each cylinder (only one injector 1 is shown in the figure), and the fuel is supplied from a common common rail 26 communicated 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 the common rail pressure). The fuel in the fuel tank 23 is pumped to the common rail 26 by a high pressure supply pump 25 and stored at a high pressure.
[0029]
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 control hydraulic pressure of the injector 1 and returns to the fuel tank 23 from the injector 1 via the low-pressure drain line 28. It is supposed to be.
[0030]
A piezo actuator driving circuit 21 for driving the piezo actuators 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 or the like, and controls each part of the fuel injection device in addition to the piezo actuator drive circuit 21. For example, a detection signal from a pressure sensor (not shown) provided on the common rail 26, for example. Based on the control, the metering valve 24 is controlled to adjust the amount of fuel pumped to the common rail 26 to adjust the common rail pressure. Further, the ECU 22 receives detection signals such as fuel temperature and engine oil temperature and various signals such as crank angle.
[0031]
FIG. 3 shows the structure of the injector 1. The injector 1 is a rod-like body, and is attached so that a lower portion in the drawing penetrates a combustion chamber wall (not shown) of the engine and protrudes 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.
[0032]
A needle 121 is slidably held at its rear end in a sleeve-like body 104 of the nozzle portion 1a, and the needle 121 is seated on or separated from an annular sheet 1041 formed at the tip of the nozzle body 104. . 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. Fuel pressure from the high-pressure passage 101 acts on the annular step surface 1211 of the needle 121 in the lift direction (upward).
[0033]
Fuel as control oil is introduced from the high-pressure passage 101 through the in-orifice 107 behind the needle 121, and a 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 together with the spring 122 disposed in the back pressure chamber 106 in the seating direction (downward).
[0034]
The back pressure is increased or decreased by a back pressure control unit 1 b, and the back pressure control unit 1 b is driven by a piezo actuator 1 c including the piezo stack 127.
[0035]
The back pressure chamber 106 is always in communication with the valve chamber 110 of the back pressure control unit 1b through an out orifice 109. The valve chamber 110 has a conical shape with the ceiling surface 1101 facing upward, and a low pressure port 110 a communicating with the low pressure chamber 111 is opened at the top of the ceiling surface 1101, and the low pressure chamber 111 communicates with the drain line 56. It communicates with the low pressure passage 102. A high-pressure port 110 b communicating with the high-pressure passage 101 through the high-pressure control passage 108 is opened at the bottom surface of the valve chamber 110.
[0036]
In the valve chamber 110, a ball 123 whose lower portion is cut horizontally is disposed. The ball 123 is a vertically movable valve body. When the ball 123 is lowered, the ball 123 is seated on a valve chamber bottom surface (hereinafter, referred to as a high pressure side seat) 1102 as a valve seat with the cut surface, thereby closing the high pressure port 110b. Is shut off from the low pressure chamber 111 by being seated on the ceiling surface (hereinafter referred to as a low pressure side seat) 1101 as a valve seat and closing the low pressure port 110a. . As a result, when the ball 123 is lowered, the back pressure chamber 106 communicates with the low pressure chamber 111 via the out orifice 109 and the valve chamber 110, the back pressure of the needle 121 decreases, and the needle 121 is separated. On the other hand, when the ball 123 is raised, the back pressure chamber 106 is cut off from the low pressure chamber 111 and communicates only with the high pressure passage 101, the back pressure of the needle 121 rises and the needle 121 is seated.
[0037]
The ball 123 is pressed and driven by the piezo actuator 1c. In the piezo actuator 1c, two pistons 124 and 125 having different diameters are slidably held in a vertical hole 112 formed in the vertical direction above the low pressure chamber 111, and the piezo stack 127 is disposed above the large-diameter piston 125 on the upper side. Are arranged with the up-down direction as the expansion / contraction direction.
[0038]
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 and is displaced in the vertical direction by the same amount as the amount of expansion and contraction of the piezo stack 127.
[0039]
A space defined by the lower small-diameter piston 124, the large-diameter piston 125, and the vertical hole 112 facing the ball 123 is filled with fuel to form a displacement expansion chamber 113. The expansion of the piezo stack 127 increases the diameter. When the piston 125 is displaced downward to press the fuel in the displacement expansion chamber 113, the pressing force is transmitted to the small diameter piston 124 through 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 extension amount of the piezo stack 127 is expanded and converted into the displacement of the small-diameter piston 124.
[0040]
At the time of fuel injection, first, the piezo stack 127 is charged and the piezo stack 127 is extended, whereby the small-diameter piston 124 is lowered to push down the ball 123. As a result, the ball 123 lifts from the low pressure side seat 1101 and is seated 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 seating direction becomes more dominant than the force acting on the seating direction, and the needle 121 is seated and fuel injection is started.
[0041]
On the contrary, when the injection is stopped, the piezo stack 127 is reduced by the discharge of the piezo stack 127 and the pushing force to the ball 123 is released. At this time, the inside of the valve chamber 110 is at a low pressure, and high pressure fuel pressure is applied to the bottom surface of the ball 123 from the high pressure control passage 108, so that upward fuel pressure is applied to the ball 123 as a whole. is doing. Then, by releasing the pushing force to the ball 123, the ball 123 is separated from the high pressure side seat 1102 and is seated again on the low pressure side seat 1101, and the fuel pressure in the valve chamber 110 is increased. Stops.
[0042]
FIG. 1 shows the configuration of the piezo actuator drive circuit 21. For convenience of explanation, the piezo stack 127 is appropriately represented as piezo stack 127A, piezo stack 127B, piezo stack 127C, and 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 controls the piezo stacks, and the like, and is connected to the piezo stacks 127A to 127D by a wire harness (not shown). Is done.
[0043]
The charging / discharging circuit unit 211 includes a DC-DC converter 31 that is a power supply unit that generates a DC voltage of several tens to several hundreds V by power supplied from the vehicle-mounted battery 30, and a capacitor 32 connected in parallel to the output terminal thereof. Then, the voltage for charging the piezo stacks 127A to 127D is output. The DC-DC converter 31 can employ, for example, a general boost chopper type circuit. The capacitor 32 has a sufficiently large capacitance (several hundred μF), and maintains a substantially constant voltage value even when the piezo stacks 127A to 127D are charged.
[0044]
A first energization path 33 a that is a first type of energization path for energizing the piezo stacks 127 </ b> A to 127 </ b> D from the capacitor 32 via the inductor 34 is provided, and the energization path 33 a is provided between the capacitor 32 and the inductor 34. Are connected in series with the first switching element 35. The first switching element 35 is composed of a MOSFET, and a parasitic diode (hereinafter referred to as a first parasitic diode) 351 is connected so that the voltage between both terminals of the capacitor 32 is reverse biased.
[0045]
The inductor 34 and the piezo stacks 127A to 127D form a second energization path 33b that is a second type of energization path. The energization path 33 b includes a second switching element 36 connected to a connection midpoint between the inductor 34 and the first switching element 35. The second energization path 33 b bypasses the capacitor 32 to form a closed circuit that passes through the inductor 34, the piezo stacks 127 </ b> A to 127 </ b> D, and the second switching element 36. The second switching element 36 is also composed of a MOSFET, and a parasitic diode (hereinafter referred to as a second parasitic diode) 361 is connected so that the voltage between both terminals of the capacitor 32 is reverse biased.
[0046]
The energization paths 33a and 33b are common to each of the piezo stacks 127A to 127D, and selection switches 37A, 37B, 37C, and 37D are connected to the piezo stacks 127A to 127D in a one-to-one correspondence. The selection switching elements 37A to 37D corresponding to the piezo stacks 127A to 127D of the injector 1 of the injection cylinder are turned on, and the energization paths 33a and 33b are selectively formed in the piezo stacks 127A to 127D.
[0047]
MOSFETs are used for the selection switches 37A to 37D, and the parasitic diodes (hereinafter referred to as selection parasitic diodes) 371A, 371B, 371C, and 371D are connected so that the voltage between both terminals of the capacitor 32 is reverse biased. ing.
[0048]
Control signals are respectively input from the controller 212 to the gates of the switching elements 35 and 36 and the selection switches 37A to 37D. As described above, any of the selection switches 37A to 37D is turned on to drive the piezo stacks 127A to 127A to be driven. While 127D is selected, the switching elements 35 and 36 are turned on and off to charge and discharge the piezo stacks 127A to 127D.
[0049]
A resistor 38b is provided between the selection switches 37A to 37D and the ground in common with the selection switches 37A to 37D. The voltage between both terminals, that is, the voltage at point b in the figure is input to the controller 212, and the charging currents of the piezo stacks 127A to 127D are detected.
[0050]
The second switching element 36 is provided with a resistor 38c in series. The voltage between both terminals, that is, the voltage at point c in the figure, is input to the controller 212, and the discharge currents of the piezo stacks 127A to 127D are detected.
[0051]
Further, resistors 381a and 381b having high resistance values connected in series are provided between the terminals of the inductor 34 on the piezo stack 127A to 127D side and the ground. The divided voltage, that is, the voltage at 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.
[0052]
Further, an emergency discharge path 42 is formed in parallel with the resistors 381a and 381b, and the electric charge of the capacitor 32 and the piezo stacks 127A to 127D is discharged to the ground side as will be described in detail later. In addition to the emergency discharge switch 43 that opens and closes the emergency discharge path 42, a resistor 44 and a diode 45 are connected in series. The resistor 44 is for adjusting a time constant at the time of discharging electric charges. The diode 45 is for preventing a backflow, the inductor 34 side is a cathode, and the direction in which current flows from the inductor 34 side to the ground side is the forward direction.
[0053]
The emergency discharge switch 43 is a MOSFET, and its parasitic diode (hereinafter referred to as a discharge parasitic diode) 431 is connected so that the voltage of the capacitor 32 is reverse-biased.
[0054]
A control signal is input from the controller 212 to the gate of the emergency discharge switch 43.
[0055]
The controller 212 serving as a control means outputs a control signal to the charge / discharge circuit unit 211 and detects an abnormality in the charge / discharge circuit unit 211 in accordance with a command signal from the ECU 22 and the various detection signals of the charge / discharge circuit unit 211. The abnormality determination signals IJF1 and IJF2 are output to the ECU 22. In addition, a discharge prohibition signal, which will be described later, is generated, and execution of charge recovery from the piezo stacks 127A to 127D to the capacitor 32 is prohibited under certain conditions.
[0056]
As command signals input from the ECU 22, an injection signal, a cylinder selection signal, and a charging period signal are input. The injection signal defines the charging timing and discharging timing of the piezo stacks 127A to 127D, and is a binary signal composed of “L” and “H”. The injection period is substantially defined by the output timing and length of the injection signal. The cylinder selection signal is used to select the piezo stack 127A to 127D to be charged corresponding 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.
[0057]
Each of the piezo stacks 127A to 127D is provided with resistors 41A, 41B, 41C, and 41D in parallel, and discharges little by little from the piezo stacks 127A to 127D even after the completion of charging. Resistors 41A to 41D are for fail-safe use, and cannot be energized due to disconnection of wiring cables of the piezo stacks 127A to 127D, and normal charge recovery from the piezo stacks 127A to 127D to the capacitor 32 becomes impossible In addition, the state where the needle 121 is in a lift state that can be brought into the lifted state does not continue for a predetermined time or longer. Further, the resistors 41A to 41D eliminate generated charges due to the pyroelectric effect. Therefore, the resistance values of the resistors 41A to 41D are set in consideration of the longest injection time and the like.
[0058]
FIG. 4 shows the operating state of the charge / discharge circuit unit 211. The controller 212 outputs a predetermined control signal when the injection signal, the cylinder selection signal, and the charging period signal become “H”. It is assumed that the cylinder selection signal is for selecting the first cylinder and subsequently 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.
[0059]
When the injection signal and the charging period signal become “H” (t 1), the controller 212 sets the ON period and the OFF period of the first switching element (hereinafter referred to as a charging switch as appropriate) 35 as follows: A control signal is output to the charging switch 35. That is, the charging switch 35 is turned on, and a gradually increasing charging current is passed through the first energization path 33a which is the first type energization path with the capacitor 32 as a supply source (FIG. 5A). The on period is set constant. When the charging switch 35 is turned off, the back electromotive force generated in the inductor 34 at this time is forward biased with respect to the second parasitic diode 361, so that the capacitor 32 is supplied from the energy stored in the inductor 34. A gradually decreasing flywheel current flows through the second energization path 33b, which is the second type of energization path, and charging of the piezo stack 127A proceeds (FIG. 5B). When the charging current reaches a threshold value set to approximately 0 in advance (hereinafter referred to as 0A threshold as appropriate), the off period ends, the charging switch 35 is turned on again and the on period starts, and this is repeated (multiple Switching method). The 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 stepwise.
[0060]
When the charge period signal becomes “L” (t3), the control signal to the charge switch 35 is forcibly lowered to fix the charge switch 35 to OFF. This completes charging. The piezo stack 127 </ b> A is extended by charging and presses and lifts the ball 123 through the displacement expansion chamber 113.
[0061]
The method of the piezo actuator driving circuit 211 in which the length of the ON period is constant has a constant energy input speed to the piezo stacks 127A to 127D, and has a good linearity, and the charging period has the same length. If it exists, even if the capacity | capacitance of the piezo stacks 127A-127D changes, it has the characteristics that the input energy amount to the piezo stacks 127A-127D can be made substantially constant.
[0062]
When the injection signal becomes “L” (t 5), the piezo stack 127 A is discharged and collected in the capacitor 32. That is, an on period and an off period of a second switching element (hereinafter, appropriately referred to as a discharge switch) 36 are set as follows, and a 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 caused to flow through the second energization path 33b, which is a second type of energization path that is supplied from the piezo stack 127A (FIG. 6A). When the discharge current reaches a preset threshold value (hereinafter referred to as an upper limit current threshold value), the discharge switch 36 is turned off to enter an off period. At this time, a large back electromotive force is generated in the inductor 34, and the first energization path which is the first type energization path using the flywheel current as a supply source from the piezoelectric stack 127 </ b> A by the energy accumulated in the inductor 34. The energy is collected in the capacitor 32 (FIG. 6B). When the discharge current reaches the 0 A threshold, the discharge switch 36 is turned on again, and this is repeated.
[0063]
When the piezo stack voltage reaches a predetermined threshold value (hereinafter referred to as 0V threshold value as appropriate) set to approximately 0 (t8), the discharge switch 36 is fixed to OFF, and the discharge of the piezo stack 127A is completed. . The charge of the piezo stack 127A is collected by the capacitor 32. Then, by discharging the piezo stack 127A in this way, the piezo stack 127A is reduced, the pressing force applied to the ball 123 by the fuel pressure in the displacement expansion chamber 113 is released, and the ball 123 is seated.
[0064]
Subsequently, at the predetermined crank angle, the injection signal and the charging period signal are again set to “H”, and the cylinder selection signal indicating the second cylinder is set to “H” (t1 ′). First and second energization paths 33a and 33b are formed. Similarly, the piezo stacks 127C and 127D are charged and discharged in the same manner for the third and fourth cylinders.
[0065]
Next, a circuit portion of the controller 212 that detects an abnormality of the charge / discharge circuit unit 211 and outputs the abnormality determination signals IJF1 and IJF2 to the ECU 22 will be described. FIG. 7 shows a circuit portion that generates the abnormality determination signal IJF1 and the discharge inhibition signal, and FIG. 8 shows the operating state thereof. In addition to the injection signal, a charging voltage, a timer threshold value, an overvoltage threshold value, and a large capacity threshold value are input to the circuit portion. In the following description, it is assumed that the selected cylinder is the first cylinder. That is, the description will be made assuming that the selection switch 37A is turned on among the selection switches 37A to 37D.
[0066]
The charging voltage is a voltage at the terminal on the piezo stack 127A side of the inductor 34 detected at point a.
[0067]
The timer threshold value is a voltage signal for determining the elapse of time t4 described later.
[0068]
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 is a voltage signal having a magnitude corresponding to a voltage that can be substantially regarded as the voltage of the capacitor 32. The large capacity threshold value is a threshold value for detecting when an abnormality occurs in the capacity of the piezo stack 127A viewed from the charge / discharge circuit section 211 side and the charging voltage is insufficient. This is because, in the case of determining the end of charging without depending on the magnitude of the piezo stack voltage as in the present embodiment, the charging voltage decreases due to an increase in the capacity of the piezo stack 127A.
[0069]
The charging voltage is compared with the overvoltage threshold or the large capacity threshold selected by the switch 52 by the comparator 53. The switch 52 is controlled to be switched by the output of the comparator 51. The comparator 51 receives the output signal of the timer circuit 50 that counts the elapsed time from the rise of the injection signal and the timer threshold value. When the elapsed time exceeds t4, the output of the comparator 51 is "L". Thus, the overvoltage threshold is switched to the large capacity threshold.
[0070]
The output of the comparator 53 that determines whether or not the charging voltage is larger than the voltage abnormality determination threshold value and the output of the comparator 51 that outputs "L" when the elapsed time exceeds t4 are ANDed. The signal is input to the SR flip-flop 56 through the gate 54.
[0071]
In the SR flip-flop 56, the output of the comparator 53 is inverted by a NOT gate 55 as an R input. The Q output of the SR flip-flop 56 is used as a discharge inhibition signal. It is known that it is “L” at normal time 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 increased excessively. . When the charging voltage decreases and the output of the comparator 53 becomes “L”, the discharge inhibition signal becomes “L”. When the discharge inhibition signal becomes “H”, the ECU 22 inhibits discharge. The reason for this will be described later.
[0072]
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 that detects the rising edge of the injection signal is input as the CL input. . The inverted output of the SR flip-flop 56 and the output of the comparator 53 are input to the AND gate 57, and the output of the AND gate 57 is the D input of the D flip-flop 70. Therefore, if the charging voltage exceeds the large capacity threshold until the start of discharging, the IJF1 signal becomes “H” at the fall of the injection signal, and then the injection signal rises and the D flip-flop 70 Holds until cleared. On the other hand, when the voltage does not increase when the piezo stack 127A is charged, or during the charge holding period (between the charge period signal becomes “L” (t3) and the injection signal becomes “L” (t5)). If the charging voltage drops below the large capacity threshold, the IJF1 signal remains “L”. Further, the IJF1 signal remains “L” even when the piezo stack 127A is overcharged during charging.
[0073]
FIG. 9 shows a circuit portion of the controller 212 that outputs the abnormality determination flag IJF2, and FIG. 10 shows its operating state. In addition to the injection signal, charging voltage, and mask signal, a charging current, an energization start threshold, an overcurrent threshold, and a 0 V threshold are input to the circuit portion.
[0074]
The charging current is a signal known as the voltage at point b.
[0075]
The mask signal takes an “H” value from the rise of the injection signal, that is, from the start of charging of the piezo stack 127A to the end of the off period that substantially follows the on period of the first charge switch 35, and generates this. The circuit that performs this will be described later.
[0076]
The energization start threshold is compared with the charging current to determine the magnitude of the charging current, and is set slightly higher than 0 to check whether the charging switch is turned on and the charging current starts to increase gradually. It is a voltage signal for
[0077]
The overcurrent threshold value is used to determine whether or not an overcurrent has flowed through the energization paths 33a and 33b, and is a value that can determine an excessive value as the current value reached in the first on-period of the charging switch 35. Set to
[0078]
The 0V threshold value is compared with the charging voltage to determine the magnitude of the charging voltage, and is set to be slightly higher than 0V, and is a voltage signal for confirming whether or not the discharging is completed.
[0079]
The energization start threshold value and the charging current are compared by the comparator 60 and input to the AND gate 67. The output of the comparator 60 becomes “H” when the charging current exceeds the energization start threshold.
[0080]
The charging current and the overcurrent threshold value are compared by the comparator 61, and the output is input to the OR gate 65. When 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 through the NOR gate 64 together with the output of the comparator 61. While the injection signal is “H”, unless the charging current exceeds the overcurrent threshold, The output of the OR gate 65 is “L”. The output of the OR gate 65 is input to the SR flip-flop 68 as the R input.
[0081]
The output of the OR gate 65 is also inverted by the NOT gate 66 and input to the AND gate 67 together with the output of the comparator 60 that determines whether or not the energization start threshold value is smaller than the charging current. The output of the AND gate 67 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”. If the charging current again falls below the energization start threshold at the end of the off period of the charging switch 35, the output of the AND gate 67 becomes “L” again.
[0082]
Further, after the injection signal becomes “L”, the R input and S input of the SR flip-flop 68 are determined by another input of the NOR gate 64. As another input of the NOR gate 64, the output of the comparator 62 that compares the charging voltage with the 0V threshold value is inverted and input by the NOT gate 63, and when the charging voltage falls below the 0V threshold value. The other input of the NOR gate 64 becomes “L”. Therefore, while the charging voltage exceeds the 0V threshold, the output of the NOR gate 64 is “L” and changes in the same state as before the injection signal becomes “L”, and the charging voltage is 0V threshold. The output of the NOR gate 64 becomes “H” and the R input of the SR flip-flop 68 is set to “H”. As a result, the inverted output of the SR flip-flop becomes “H”.
[0083]
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” after the charge voltage falls below the 0V threshold, that is, when the piezo stack 127A is substantially discharged. Yes, depending on the discharge completion timing of the piezo stack 127A, it may be delayed or accelerated.
[0084]
In addition, 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 increases and the charging current exceeds the overcurrent threshold value. The output of the OR gate 65 becomes “H”, and the inverted output of the SR flip-flop 68 returns to “H”. In the following description, the SR flip-flop 68 is appropriately referred to as a failure determination F / F 68.
[0085]
Next, FIG. 11 shows a circuit portion of the controller 212 that outputs the mask signal, and FIG. 12 shows its operating state. The charging current, energization start threshold value, and injection signal are input to the circuit portion.
[0086]
The charging current and the energization start threshold value are compared by the comparator 71. 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. The output of the AND gate 72 is input to the first D flip-flop 73 as a CK input. The first D flip-flop 73 and the second D flip-flop 74 constitute a 2-bit counter. The inverted output of the second D flip-flop 74 of the upper bit is 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”.
[0087]
An AND gate 75 is provided with the inverted output of the second D flip-flop 74 and the injection signal as inputs, and its output is a mask signal.
[0088]
Further, the injection signal is inverted by the NOT gate 76 and inputted as the CL input to the D flip-flops 73 and 75. When the injection signal falls, the D flip-flops 73 and 74 are cleared.
[0089]
Thus, when the injection signal becomes “H” and the charging current repeatedly increases and decreases gradually, each time the charging current exceeds the energization start threshold value, the first and second D flip-flops 73 and 74 It is counted with. Initially, since the inverted output of the second D flip-flop 74 is “H” and the injection signal is also “H”, the mask signal starts with “H”.
[0090]
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”.
[0091]
Since the inverted output of the second D flip-flop 75 is input to the AND gate 72, no counting is performed thereafter, and the mask signal is fixed to “L”.
[0092]
Therefore, the mask signal takes an “H” value during a period from when the injection signal rises to when the charging current exceeds the energization start threshold by the second turn-on of the charging switch 35. 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.
[0093]
The ECU 22 determines the presence or absence of an abnormality based on the abnormality determination signals IJF1 and IJF2. FIG. 13 shows a normal operating state, and FIGS. 14, 15, 16, and 17 show an operating state when an abnormality occurs.
[0094]
In FIG. 13 showing the normal operating state, the charging voltage increases as the charging of the piezo stack 127A progresses. However, the charging reaches an appropriate voltage value without exceeding the overvoltage threshold and the charging is completed. Therefore, at time t4 when the voltage abnormality determination threshold value switches 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 t5.
[0095]
On the other hand, when the injection signal becomes “L”, the discharge of the piezo stack 127A is started, the electric charge of the piezo stack 127A is collected by the capacitor 32, and the charging voltage is lowered. Therefore, when the charging voltage becomes t8 below the 0V threshold, the failure determination F / F 68 becomes “H” and the abnormality determination signal IJF2 becomes “H”. When the abnormality determination signal IJF2 switches from “L” to “H”, the discharge is completed.
[0096]
Here, if the range of t8 when the piezo stack 127A is properly charged and discharged is determined in advance, t7 can be regarded as being too early to complete the discharge, and the discharge completion is out of the range. It is possible to set t9 which can be regarded as being too late. Since the discharge of the piezo stack 127A is started when the injection signal becomes "L", t7 and t9 are set based on t5 when the injection signal becomes "L". Since temperature information such as the engine oil temperature is input to the ECU 22, t7 and t9 may be set based on this information.
[0097]
The ECU 22 determines that the abnormality determination signal IJF2 is normal if it is "L" at time t7 and "H" at time t9. Further, if the abnormality determination signal IJF2 is “H” at the time t7 or “L” at the time t9, it is determined that there is an abnormality. In the case of FIG. 13 showing the normal time, it is “L” at time t7 and “H” at time t9.
[0098]
A specific example when an abnormality occurs will be described. FIGS. 14 and 15 show the short circuit of the charge / discharge circuit unit 211 or the piezo stacks 127A to 127D when the charge switch 35 is turned on. FIG. 15 is an enlarged view of FIG. When the injection signal becomes “H” and the charging switch 35 is turned on, the charging switch 35 is turned on even if the on period ends and the control signal of the charging switch 35 becomes “L”. 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 is on-failed, the energization paths 33a and 33b are disconnected from the piezo stack 127A, so that charging is stopped. If not interrupted, 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. Note that the output of the second and subsequent control signals of the charging switch 35 is stopped when the selection switch 37A of the first cylinder is turned off.
[0099]
When the charging current exceeds the overcurrent threshold, the failure determination F / F 68 becomes “H”. As a result, at time t7, the ECU 22 can know that an abnormality has occurred in which an overcurrent flows during charging of the piezo stack 127A.
[0100]
As a case where an abnormality in which 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, a short circuit between both terminals of the piezo stack 127A, and the like are possible. Can also be detected.
[0101]
Further, in the case of a partial short-circuit of the inductor 34 or the like, the charging voltage of the piezo stack 127A is not greatly increased only by the first turn-on. There is no problem in collecting the remaining charge in the capacitor 32. However, when the charging switch 35 is in an on-failure, the closed circuit of the capacitor 32 to the charging switch 35 to the discharging switch 36 to the resistor 38c to the ground is formed by turning on the discharging switch 36. Since the resistor 38c is for detecting a discharge current and has a very small resistance value, the capacitor 32 is short-circuited between both terminals.
[0102]
When the charging switch 35 is in an on-failure state, 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. The overvoltage threshold, which is the voltage abnormality determination threshold, is exceeded. As a result, the discharge inhibition signal becomes “H”, and IJF1 is held at “L”.
[0103]
If the controller 212 determines that a short circuit failure has occurred and stops charging and the discharge inhibition signal is “L”, the controller 212 turns the discharge switch 36 on and off to collect the remaining charge in the piezo stack 127A in the capacitor 32.
[0104]
On the other hand, if the discharge inhibition signal is “H”, the charging switch 35 is highly likely to be on-failed, so that the operation of the DC-DC converter 31 is stopped and charging from the battery 30 to the capacitor 32 is prohibited. Further, the emergency discharge switch 43 is turned on. Thus, the current is limited under an appropriate 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 electric charge from being stored in the piezo stack 127A and the capacitor 32 in an abnormal state. In addition, since the piezo stack 127A is charged before the selection switch 37A is turned off, the injector 1 may be in a valve open state, that is, an injection state, but this state can be quickly resolved. it can.
[0105]
In general, the injector 1 exhibits a mechanical fail-safe function that utilizes natural fuel leakage from the displacement expansion chamber 113 and does not remain open for a long time. Therefore, as long as the fuel injection during that time can be permitted, the emergency discharge switch 43 may be manually performed at a repair shop or the like.
[0106]
The discharge prohibition signal is “H” when the charging voltage detected at point a exceeds the voltage abnormality threshold, but in a normal state, the mask signal is turned on when the charging switch 35 is turned on for the second time. Since it becomes “L” (see FIG. 13), the discharge prohibition signal does not become “H” even if the charging voltage exceeds the voltage abnormality threshold after t4 under normal conditions.
[0107]
FIG. 16 shows the short circuit of the charge / discharge circuit unit 211 or the piezo stack 127A when the piezoelectric ceramic layer of the piezo stack 127A is partially short-circuited. Even if the piezo stack 127A is normally charged, due to the partial short circuit of the piezoelectric ceramic layer, the charge leaks from the piezo stack 127A and the charging voltage gradually decreases after the end of the charging period (t3).
[0108]
Therefore, the residual charge at the start of discharge (t5) in the piezo stack 127A is less than that at the normal time, and the discharge period during which the discharge switch 36 is turned on / off is also shortened. As a result, the abnormality determination signal IJF2 is already “H” at time t7, and IJF1 remains “L”. Thereby, the ECU 22 can know the failure of the piezo stack 127A.
[0109]
FIG. 17 shows a case where a plurality of piezo stacks are simultaneously energized (hereinafter referred to as 2-cylinder simultaneous energization) due to an on failure of the selection switches 37A to 37D among the short circuits of the charge / discharge circuit unit 211 or the piezo stacks 127A to 127D. belongs to. In the following description, it is assumed that the selection switch 37B corresponding to the second cylinder is in an on failure when the piezo stack 127A corresponding to the first cylinder is charged. However, the other combinations are substantially the same. is there. In the case of two-cylinder simultaneous energization, the capacity of the piezo stack 127A as viewed from the charge / discharge circuit section 211 side increases, so the charging speed decreases. In the case of the present embodiment in which the amount of charge is controlled by the length of the charging period, the charging voltage of the piezo stack 127A does not fall within the predetermined voltage range and is insufficient.
[0110]
Therefore, at the time t4 when the voltage abnormality threshold is switched to the large capacitance threshold, the D input of the D flip-flop 57 becomes “L”. For this reason, even after the time t5 when the injection signal becomes “L”, the abnormality determination signal IJF1 remains “L”. As a result, the ECU 22 can determine that two cylinders are energized simultaneously. However, if the temperature representing 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 or not two cylinders are energized simultaneously.
[0111]
The reason for this will be described. A capacitive element including a piezo stack generally varies greatly in capacitance with temperature. FIG. 18 shows an example in which the temperature dependence of the capacity of a piezo stack used in an injector is investigated within a temperature range expected by a vehicle equipped with a diesel engine. The capacity is 2 at low and high temperatures. It is three to three times different.
[0112]
For this reason, as described above, even if the abnormality determination signal IJF1 is “L”, it cannot be distinguished whether it is due to simultaneous energization of two cylinders or an increase in capacity due to a temperature rise. Therefore, if it is determined that the temperature is higher than a preset threshold value or the like, it is not determined whether or not two cylinders are energized simultaneously.
[0113]
Of course, if measures such as heat dissipation are taken for the piezo stacks 127A to 127D so that the temperature environment of the piezo stack is within a certain range, when the abnormality determination signal IJF1 is “L”, the two cylinders are unconditionally used simultaneously. It is also possible to determine that the power is on.
[0114]
In addition, since the discharge rate becomes slow with the charge rate, even when the charge voltage is low, the discharge completion time is not so fast, and the discharge is completed at the same time as the normal time as shown in the figure. For this reason, the abnormality determination signal IJF2 is not different from the normal time.
[0115]
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 t4 when the voltage abnormality threshold is switched to the large capacity threshold, if the charging voltage falls below the voltage abnormality threshold before the injection signal becomes “L”, the abnormality determination signal IJF1 is also generated in this case. Since it remains “L”, a partial short circuit of the piezoelectric ceramic layers of the piezo stacks 127A to 127D can be detected by taking a voltage abnormality threshold after t4. In this case, a distinction between partial short-circuiting of the piezoelectric ceramic layers of the piezo stacks 127A to 127D and simultaneous energization of two cylinders is made when the abnormality determination signal IJF2 is “ In contrast to “L”, in the case of simultaneous energization of two cylinders, it is preferable to perform this because “H” at t7.
[0116]
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, and the charging current is predetermined during the on period of the charging switch. It can also be applied to a charge control system that detects whether or not the upper limit value is reached and enters the off period when the upper limit value is reached.
[0117]
(Second Embodiment)
FIG. 19 shows a piezoelectric actuator drive circuit according to the second embodiment of the present invention. In the present embodiment, the controller and the ECU are replaced in the configuration of the first embodiment, and high accuracy of fuel injection is achieved. Parts that are substantially the same as those in the first embodiment will be described with the same numbers. The basic configuration of the controller 212A and the ECU 22A is the same as that of the first embodiment. The controller 212A is configured such that the output of the first D flip-flop 73 of the circuit portion that generates the mask signal (FIG. 11) is input to the ECU 22A as the first energization time measurement signal Tone.
[0118]
The output of the first D flip-flop 73 serving as the first energization time measurement signal Tone is the second time after the charging switch 35 is turned on for the first time and the charging current exceeds the energization start threshold value. This is a signal that becomes “H” until the charging current exceeds the energization start threshold value when ON. Since the energization start threshold is substantially zero as described above, the length is substantially the total time of the on period of the first charge switch 35 and the subsequent off period, and the charge switch 35 is turned on. Until the charging current reaches an energization start threshold value which is a predetermined current value set in advance.
[0119]
The first energization time measurement signal Tone has the following properties. As described above, since the charging of the piezo stacks 127A to 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 the charge / discharge circuit portion. It is determined by the constant of 211. Among the members constituting the charge / discharge circuit unit 211, the injector 1 having the piezo stacks 127A to 127D as constituent parts is placed in the engine head, and thus is placed in the most severe temperature environment. For this reason, the capacity of the piezo stacks 127A to 127D varies greatly due to the influence of temperature.
[0120]
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 longer. Therefore, if the capacitances of the piezo stacks 127A to 127D are different, the first energization time measurement is performed. The signal Tone changes. Therefore, the temperature fluctuation of the injector 1 is known by 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.
[0121]
In the ECU 22A, a timer that starts counting at the rise of the first energization time measurement signal Tone is provided to obtain the time until the fall of the first energization time measurement signal Tone, which is obtained as the first energization time measurement signal. The length is Tone.
[0122]
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 by the engine oil temperature or the like. Therefore, it is possible to obtain high-quality temperature information of the injector 1 without separately providing a sensor.
[0123]
The length of the first energization time measurement signal Tone as the temperature information is used for correcting the fuel injection timing and the injection amount in the ECU 22A. Specifically, the output timing and length of the injection signal are corrected according to the length of the first energization time measurement signal Tone.
[0124]
Thereby, the sliding resistance of the movable members such as the needle 121 and the pistons 124 and 125 of the injector 1 and the viscosity of the fuel in the injector 1 change due to the temperature change, which affects the operation characteristics of the ball 123 and the needle 121. However, it is possible to prevent the influence from affecting the fuel injection timing and the injection amount.
[0125]
Here, as the index of the current aging profile, the time 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, so that the implementation is easy. is there.
[0126]
As for the correction amount, a map obtained based on experiments or the like is prepared in advance and stored in the ROM of the ECU 22A.
[0127]
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.
[0128]
The piezo actuator drive circuit of the present invention is not limited to the fuel injection device, and can be applied to various devices.
[Brief description of the drawings]
FIG. 1 is a circuit diagram of a piezo actuator drive circuit of the present invention that drives 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 drive circuit.
FIGS. 5A and 5B are diagrams showing an operating state of the piezo actuator drive circuit when charging a piezo stack constituting the piezo actuator, respectively.
FIGS. 6A and 6B are diagrams illustrating an operating state of the piezo actuator driving circuit when a piezo stack constituting the piezo actuator is discharged, respectively.
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 the operating state of the piezo actuator drive circuit.
FIG. 15 is a fourth timing chart showing an operating state of the piezo actuator drive circuit.
16 is an enlarged view of a part of FIG.
FIG. 17 is a fifth timing chart showing the operating state of the piezo actuator drive circuit.
FIG. 18 is a graph illustrating the operation of the piezo 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 a piezo actuator drive circuit constituting the fuel injection device.
FIG. 21 is a graph illustrating the operation of the piezo actuator drive circuit.
[Explanation of symbols]
1 Injector
1a Nozzle part
1b Back pressure control unit
1c Piezo actuator
103 nozzle hole
121 needle
127, 127A, 127B, 127C, 127D Piezo stack
21,21A Piezo actuator drive circuit
211 Charge / discharge circuit
212, 212A Controller (control means)
22, 22A ECU (command means)
30 battery
31 DC-DC converter (power supply)
32 capacitors
33a Current path
33b Current path
34 Inductor
35 Charge switch (switching element)
36 Discharge switch (switching element)
37A, 37B, 37C, 37D selection switch
381a, 382a Resistor (voltage detection means)
38b, 38c resistors (current detection means)
41A, 41B, 41C, 41D Resistor
42 Emergency discharge path
43 Emergency discharge switch
44 resistors
45 diodes

Claims (9)

A capacitor that stores energy for driving the piezo stack mounted on the piezo actuator, and a current-carrying path that moves charge through an inductor with one of the capacitor and the piezo stack as a supply source, By repeating ON / OFF of the switching element as the energization path, a first type energization path through which a current that gradually increases in the inductor during the ON period of the switching element and a current that gradually decreases in the inductor during the OFF period of the switching element flow. In a piezo actuator drive circuit in which a second type energization path is formed and the piezo stack is charged and discharged by a control means for controlling the switching element,
Current detection means for detecting a current flowing in the energization path ;
Provided with voltage detection means for detecting the voltage of the energization path on the piezo stack side than the switching element ,
When the current detected by the current detection means exceeds a preset threshold value, the control means determines that a failure has occurred, determines the failure mode as a short-circuit failure , and determines the short-circuit failure. In this case, when the voltage detected by the voltage detecting means is a first determination condition that is equal to or lower than a preset threshold value, the charge recovery for recovering the charge to the capacitor by using the supply path as the piezo stack by the energization path The piezoelectric actuator drive circuit is set to prohibit the charge recovery when the detected voltage is a second determination condition equal to or greater than a preset threshold value . The piezo actuator drive circuit according to claim 1, wherein a plurality of piezo stacks can be connected as a piezo stack with a common energization path, and a selection switch controlled by the control means includes a plurality of piezo stacks. From this, it is possible to select a piezo stack connected to the energization path,
A piezoelectric actuator drive circuit in which the control means is set to turn off the selection switch and open the energization path when it is determined that the short-circuit failure has occurred. The piezoelectric actuator drive circuit according to claim 1 or 2 , wherein the threshold value of the detection voltage is set to a voltage between both terminals of the capacitor.
A piezo actuator drive circuit in which the control means is set so that the failure mode is determined to be an on-failure of the switching element when the second determination condition is satisfied when the switching element is off . 4. The piezo actuator drive circuit according to claim 1 , 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. The piezoelectric actuator drive circuit is provided with an emergency discharge switch for opening and closing the emergency discharge path . The piezoelectric actuator drive circuit according to any one of claims 1 to 4, wherein the capacitor is charged by a power supply unit controlled by the control means.
A piezo actuator drive circuit configured to stop the operation of the power supply unit when the control means is determined to be the short-circuit failure . In the piezo actuator drive circuit according to any one of claims 1 to 5,
The voltage detection means detects the voltage of the non-ground side terminal of the piezo stack,
The piezo actuator drive circuit set so that the control means determines that the piezo stack has failed when the voltage detected in the charge holding period after completion of charging of the piezo stack is smaller than a preset threshold value. . A capacitor that stores energy for driving the piezo stack mounted on the piezo actuator, and a current-carrying path that moves charge through an inductor with one of the capacitor and the piezo stack as a supply source, By repeating ON / OFF of the switching element as the energization path, a first type energization path through which a current that gradually increases in the inductor during the ON period of the switching element and a current that gradually decreases in the inductor during the OFF period of the switching element flow. In a piezo actuator driving circuit in which a second type energization path is formed and the piezo stack is charged and discharged by the control means for controlling the switching element,
Providing a current detection means for detecting a current flowing in the energization path;
The control means measures the time until the detected current takes a predetermined current value set in advance immediately after charging of the piezo stack, and based on the measured time, the apparent capacity or piezo stack of the piezo stack is measured. A piezoelectric actuator drive circuit comprising means for detecting the temperature of the stack . An injector that operates a piezo actuator to open and close a nozzle hole for injecting fuel; and
As means for driving the piezo actuator,
A capacitor that stores energy for driving the piezo stack mounted on the piezo actuator, and a current-carrying path that moves charge through an inductor with one of the capacitor and the piezo stack as a supply source, By repeating ON / OFF of the switching element as the energization path, a first type energization path through which a current that gradually increases in the inductor during the ON period of the switching element and a current that gradually decreases in the inductor during the OFF period of the switching element flow. A piezo actuator driving circuit in which a second type of energization path is formed and the piezo stack is charged and discharged by a control means for controlling the switching element;
A fuel injection device having command means for instructing the charging timing and the length of the charge holding period of the piezo stack corresponding to the fuel injection timing and the injection amount to the control means;
In the piezoelectric actuator drive circuit,
Providing a current detection means for detecting a current flowing in the energization path;
The command means measures the time until the detected current takes a predetermined current value set in advance immediately after starting the charging of the piezo stack, and based on the measured time, the charging timing and the charging of the piezo stack A fuel injection device set to correct the length of the holding period. A capacitor that stores energy for driving the piezo stack mounted on the piezo actuator, and a current-carrying path that moves charge through an inductor with one of the capacitor and the piezo stack as a supply source, By repeating ON / OFF of the switching element as the energization path, a first type energization path through which a current that gradually increases in the inductor during the ON period of the switching element and a current that gradually decreases in the inductor during the OFF period of the switching element flow. In a piezo actuator drive circuit in which a second type energization path is formed and the piezo stack is charged and discharged by a control means for controlling the switching element,
Provided with voltage detection means for detecting the voltage of the energization path on the piezo stack side than the switching element,
The piezo actuator is characterized in that the control means is set so that an overvoltage abnormality of the piezo stack is determined when a charging voltage of the piezo stack detected by the voltage detection means exceeds a preset threshold value. Driving circuit.

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