JP4306133B2 - Fuel injection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to pressure reduction control of fuel pressure in a como rail of a fuel injection device.
[0002]
[Prior art]
A common rail type fuel injection device stores fuel boosted by a high pressure supply pump in a common rail and supplies the fuel from the common rail to an injector for fuel injection.
[0003]
Although there are various configurations of the injector, the needle that opens and closes the nozzle hole of the nozzle portion is raised and lowered by increasing or decreasing the back pressure to switch between injection and stop, and the back pressure is obtained from the fuel from the common rail There is something. The back pressure is increased or decreased by the following means. That is, a valve body is provided between a back pressure chamber in which fuel is introduced from a common rail and generates a back pressure and a low pressure source such as a fuel tank, and a valve body for opening and closing a port on the low pressure source side in the valve chamber When the valve body is lifted, the back pressure chamber communicates with the low pressure source to reduce the back pressure. As a result, the needle is lifted and fuel injection is started. As the back pressure increasing / decreasing means having the valve chamber and the valve body, a two-way valve or a three-way valve can be used.
[0004]
As an actuator for driving a valve body, a piezo actuator using a piezoelectric action of a piezoelectric material such as PZT has recently been considered. In the piezo actuator, a piezo stack that expands and contracts due to charging and discharging generates a pressing force. For example, the piezo stack extends by charging, and the port is closed to drive the valve body to lift it from the valve seat.
[0005]
[Problems to be solved by the invention]
By the way, in the common rail type fuel injection device, the fuel pressure in the common rail is controlled by adjusting the pumping amount of the fuel to the common rail so as to obtain the optimal injection pressure corresponding to the operation condition together with the fuel injection control. However, if the operating condition suddenly changes from a condition requiring high injection pressure (high pressure and high load) to a condition requiring relatively low pressure injection pressure (low pressure and low load), the fuel pressure in the common rail cannot be reduced. If fuel is injected in this pressure state, noise may be generated or exhaust may be deteriorated. Therefore, it is necessary not only to reduce the pumping amount of the common rail, but also to positively discharge high-pressure fuel from the common rail.
[0006]
As described above, in the configuration in which the injector uses the fuel from the common rail as the control oil, the valve body is lifted with the needle seated to reduce the fuel pressure in the common rail, and the fuel in the back pressure chamber is released. (JP 2000-161170 A). The back pressure of the needle in the closed state is sufficiently higher than the pressure at which the needle can be opened, and the seating state is maintained even if the back pressure is reduced to some extent. On the other hand, if the valve body is brought into a lift state (half lift) that does not reach the full lift as in the needle opening / closing control, the amount of decrease in the pressure in the back pressure chamber is small. Therefore, the fuel in the common rail is returned to the fuel tank through the injector and the fuel pressure in the common rail is reduced by setting the valve body to a half lift within the range where the back pressure of the needle does not fall below the needle openable pressure. become.
[0007]
In order to realize the half lift of the valve body when the injector is mounted with the piezo actuator, it is charged to a charge level that can withstand the fuel pressure in the valve chamber equal to the fuel pressure in the common rail in order to lift the valve body from the seated state. On the other hand, it is necessary not to exceed a charge amount (injection start charge amount) at which the needle lifts and fuel injection starts.
[0008]
However, when the valve body is in the seated state, the area of the pressure receiving surface of the valve body where the fuel pressure in the valve chamber acts in the lift direction is small, and the fuel pressure in the valve chamber is approximately equal to the fuel pressure in the common rail, so it acts in the seating direction. The unbalanced pressure is overwhelmingly dominant. On the other hand, once the valve body is lifted, the fuel pressure in the valve chamber decreases and the pressure receiving surface of the valve body where the fuel pressure acts in the lift direction increases, so that the force acting in the seating direction acts in the lift direction. The unbalanced pressure state is relieved.
[0009]
This relaxation of the unbalanced pressure state acts in a direction that promotes the extension of the piezo stack, so the charge amount that the valve body lifts and the fuel starts to return from the back pressure chamber to the fuel tank (leak start charge amount) The lift amount of the valve body is relatively large only by slightly exceeding, and there is not much difference between the leakage start charge amount and the injection start charge amount.
[0010]
For this reason, when depressurizing the common rail by half lift of the valve body, it is necessary to charge the piezo stack with high accuracy with respect to the target charge amount.
[0011]
As a configuration of a piezo actuator driving circuit for driving a piezo actuator, there is a multiple switching type configuration. This includes a first energization path for energizing the piezo stack from the capacitor via the switching element and the inductor, and a second energization path for energizing the piezo stack by bypassing the capacitor and the switching element. In the energization path, a charging current that gradually increases during the ON period of the switching element flows, and in the second energization path, a charging current that gradually decreases during the OFF period of the switching element flows by a flywheel action. . This takes a substantially triangular waveform in which the charging current gradually increases and decreases in response to one on / off of the switching element. When the switching element is repeatedly turned on and off, the charge amount of the piezo stack increases toward the target charge amount. For example, the length of one ON / OFF period is 5 μs and the peak value of the charging current is 20 to 30 A.
[0012]
Here, the larger the charging current, the larger the amount of energy supplied to the piezo stack per unit time, and the more likely the charging amount error is. In particular, in the case of the multiple switching method, charging is performed even during the off period of the switching element, and charging control is disabled during this period. Since the supply energy in this off period is defined by the peak value of the charging current, the larger the peak value, the more likely the charge amount error will occur. Therefore, if the charging accuracy is to be increased, the charging current is reduced. If the multiple switching method is used, the length of the ON period is shortened to suppress the peak value of the charging current. It is sufficient to reduce the energy supplied to the battery.
[0013]
However, if the peak value of the charging current is set to about 5 A, for example, the length of the ON period becomes about 1 μs, and a switching speed of about 500 kHz is required. It is disadvantageous.
[0014]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a fuel injection device capable of charging a piezo stack with high accuracy with respect to a target charge amount in pressure reduction control of common rail pressure.
[0017]
[Means for Solving the Problems]
  Claim1In the described invention, the nozzle has a needle for opening and closing the nozzle hole, and a high-pressure fuel stored in the common rail is supplied to inject the fuel from the nozzle hole, and the fuel is introduced from the common rail and the needle is A back pressure chamber for generating back pressure; 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 lowering the pressure of the back pressure chamber as the amount increases, and a piezo stack that presses and drives the valve body, and the amount of lift of the valve body increases as the amount of charge of the piezo stack increases. An injector with an increasing piezo actuator;
  An energization means having an energization path for energizing the piezo stack and charging and discharging the piezo stack;
  In response to a fuel injection command, the energization means is operated with a charge amount that the valve body can be fully lifted as a target charge amount, and in response to a fuel pressure reduction command in the common rail, the needle is seated. A fuel injection device having control means for operating the energization means with a charge amount that the valve body lifts as a target charge amount;
  Connected in parallel with the piezo stackFor depressurization that can be charged and discharged through the energization path.A capacitor,
  A pressure reducing switch means for switching between connection and disconnection of the capacitor and the piezo stack,
  The control means;
  The depressurization switch unit is controlled together with the energization unit, and the depressurization switch unit is turned on in the energization control for the depressurization command.The charging current is distributed to the piezo stack and the capacitorSet as follows.
[0018]
During decompression control, a decompression capacitor is connected in parallel to the piezo stack to be charged, so that the charging current is dispersed. Since the piezo stack is equivalent to suppressing the charging current, it is possible to charge the target charge amount that can be half lifted with high accuracy.
[0019]
  Claim2In the described invention, the nozzle has a needle for opening and closing the nozzle hole, and a high-pressure fuel stored in the common rail is supplied to inject the fuel from the nozzle hole, and the fuel is introduced from the common rail and the needle is A back pressure chamber for generating back pressure; 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 lowering the pressure of the back pressure chamber as the amount increases, and a piezo stack that presses and drives the valve body, and the amount of lift of the valve body increases as the amount of charge of the piezo stack increases. An injector with an increasing piezo actuator;
  A buffer capacitor for temporarily storing electric charge to be supplied to the piezo stack;
  A power supply for charging the buffer capacitor;
  A charging switch means for switching between opening and closing a charging path of the piezo stack,
  A switch means for discharging that switches between opening and closing a discharge path of the piezo stack,
  Control means for controlling a power supply, a switch means for charging and a switch means for discharging, and for the fuel injection command, the charge switch with the charge amount that the valve body can be fully lifted as a target charge amount Control means for operating the charging switch means with a charge amount that the valve body is lifted while the needle is seated as a target charge amount in response to a command to reduce the fuel pressure in the common rail. In a fuel injection device having
  The control means;
  In the energization control with respect to the pressure reduction command, the charging switch means and the discharging switch means are alternately turned on and off, and the voltage across the buffer capacitor is more than the voltage across the piezo stack corresponding to the target charge amount at the time of control against the pressure reduction command. Discharge until low voltage value,
  When the voltage across the buffer capacitor reaches the voltage value, the charging switch means is fixed to ON, and the piezo stack is set to be charged to the target charge amount together with the buffer capacitor by the power supply.
[0020]
During decompression control, the valve element is lifted by charging the piezo stack with the power supply. At this time, since the buffer capacitor is connected in parallel to the piezo stack to be charged, the charging current is dispersed. Since the piezo stack is equivalent to suppressing the charging current, it is possible to charge the target charge amount that can be half lifted with high accuracy.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
(First form)
  FIG. 2 shows the present invention.The basis of1 shows a configuration of a common rail fuel injection device of a diesel engine. 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 fuel is supplied from a common common rail 54 communicated via a supply line 55. The 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 pumped to the common rail 54 by the high-pressure supply pump 53 and stored at a high pressure.
[0022]
The fuel supplied from the common rail 54 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 51 from the injector 1 via a low-pressure drain line 56. It is supposed to be.
[0023]
The CPU 31 calculates the fuel injection timing and the injection amount based on the detection signal such as the crank angle, and injects the fuel from the injector 1 for a predetermined period.
[0024]
  Further, the CPU 31 performs control so as to obtain an appropriate injection pressure according to the operating conditions known from other sensor inputs. The pressure sensor 32 is provided on the common rail 54, and the detection signal of the common rail pressure is the CPU.31Is entered. CPU31Controls the metering valve 52 based on the common rail pressure to adjust the fuel pumping amount to the common rail 54. In addition, when the common rail pressure needs to be suddenly reduced, the CPU 31 generates a pressure reduction command internally, performs energization control different from that at the time of fuel injection on the piezo actuator drive circuit 2, and controls the injector 1 as will be described later. The fuel as oil is returned to the fuel tank 51 to reduce the common rail pressure.
[0025]
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.
[0026]
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).
[0027]
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).
[0028]
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.
[0029]
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.
[0030]
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.
[0031]
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.
[0032]
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.
[0033]
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.
[0034]
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.
[0035]
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.
[0036]
Further, as will be described later, the injector 1 lifts the ball 123 while the needle 121 is seated to return the fuel to the fuel tank 51, and is also used for sudden pressure reduction of the common rail pressure.
[0037]
When the piezo stacks 127A to 127D are unable to discharge due to disconnection of the energizing cable 4 connecting the piezo stacks 127A to 127D and the piezo actuator drive circuit 2, the fuel injection period specified by the injection signal of the injector 1 ends. Even if the fuel continues to be injected, the injector 1 shown in FIG. 3 has a mechanical fail-safe mechanism that closes the valve when the piezo stack 127 remains in a charged state for a certain time. 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 that presses the ball 123. When the ball 123 is in the lifted state, the fuel pressure is The pressure can resist the upward biasing 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 portion such as the low pressure chamber 111 and the lift amount of the ball 123 decreases, and the back pressure chamber 106 The flow rate of the fuel that flows into the low pressure chamber 111 decreases, and as a result, the back pressure gradually increases. Finally, the needle 121 is seated and the fuel injection stops.
[0038]
FIG. 1 shows the configuration of a piezo actuator drive circuit 2 that charges and discharges the piezo stack 127. For convenience of explanation, the piezo stack 127 is appropriately represented as the piezo stack 127A, the piezo stack 127B, the piezo stack 127C, and the piezo stack 127D in order from the # 1 cylinder corresponding to the four cylinders. The piezo actuator drive circuit 2 includes a drive circuit body 2a that is an energization unit and a controller 28 that is a control unit thereof.
[0039]
The drive circuit main body 2a includes a DC power supply 21 by a DC-DC converter 211 that generates a DC voltage of several tens to several hundreds V by power supply (+ B) of the in-vehicle battery, and a buffer capacitor 212 connected in parallel to the output terminal thereof. And the voltage for charging the piezo stacks 127A to 127D is output. The DC-DC converter 211 is a general step-up chopper type circuit, and stores energy in the inductor 2111 when the switching element 2112 is turned on, and generates a back electromotive force when the switching element 2112 is turned off, via the diode 2113. Thus, the buffer capacitor 212 is charged. The switching element 2112 is turned on / off based on the voltage across the current detection resistor 2114.
[0040]
The buffer capacitor 212 has a sufficiently large capacitance, and maintains a substantially constant voltage value even when the piezo stacks 127A to 127D are charged.
[0041]
A first energization path 22a is provided through the inductor 23 from the buffer capacitor 212 of the DC power source 21 to the piezo stacks 127A to 127D. A switching element 24a for charging is interposed. The charging switching element 24 a is formed of a MOSFET, and the parasitic diode (hereinafter referred to as a first parasitic diode) 241 a is connected so as to be reverse-biased with respect to the voltage across the buffer capacitor 212. Further, the inductor 23 and the piezo stacks 127A to 127D form a second energization path 22b. The energization path 22b includes a discharge switching element 24b connected to a midpoint of connection between the inductor 23 and the charging switching element 24a, and includes a closed circuit including the inductor 23, the piezo stacks 127A to 127D, and the discharging switching element 24b. Is forming. The discharging switching element 24b is also formed of a MOSFET, and the parasitic diode (hereinafter referred to as a second parasitic diode) 241b is connected so as to be reverse-biased with respect to the voltage across the buffer capacitor 212.
[0042]
The energization paths 22a and 22b are common to each of the piezo stacks 127A to 127D, and the piezo stacks 127A to 127D as driving objects can be selected as follows. Each of the piezo stacks 127A to 127D is connected in series with switching elements (hereinafter referred to as selective switching elements as appropriate) 25A, 25B, 25C, 25D, 25E, and 25F. Among these, the first type selection switching elements 25A to 25D are connected to the piezo stacks 127A to 127D in a one-to-one correspondence, and the piezo stacks 127A to 127D connected to the selected switching elements 25A to 25D are turned on. The current paths 22a and 22b are connected.
[0043]
The second type selection switching elements 25E and 25F are connected in common to the piezo stack 127A of the # 1 cylinder injector and the piezo stack 127B of the # 2 cylinder injector # 1. , Switching between permitting and prohibiting energization to the # 2 cylinder group (bank), and the selective switching element 25F is common to the piezo stack 127C of the # 1 cylinder injector 1 and the piezo stack 127D of the # 4 cylinder injector 1 To switch between enabling and disabling energization of the # 3 and # 4 cylinder groups (banks). By providing the second type of selective switching elements 25E and 25F, for example, even if the energized cables connected to the positive electrodes of the piezo stacks 127A to 127D are grounded, the selective switching elements 25E and By turning off 25F, it is possible to ensure the operation of the other bank (limp form).
[0044]
MOSFETs are used for the selection switching elements 25A to 25F, and the parasitic diodes (hereinafter referred to as selection parasitic diodes) 251A, 251B, 251C, 251D, 251E, and 251F are reversely biased with respect to the buffer capacitor 212. It is connected to the.
[0045]
Control signals are input from the controller 28 to the gates of the switching elements 24a, 24b, and 25A to 25F. As described above, any of the selective switching elements 25A to 25D is turned on to drive the piezo stacks 127A to 127D to be driven. Is selected, and a pulsed control signal is input to the gates of the charging switching element 24a and the discharging switching element 24b to turn on and off the switching elements 24a and 24b, and charge control and discharge control of the piezo stacks 127A to 127D. Is supposed to do.
[0046]
Also, a relatively low resistance resistor 27E is provided in series with the piezo stack 127A and the piezo stack 127B, and a resistor 27F that is the same as the resistor 27E is provided in series with the piezo stack 127C and the piezo stack 127D. is there. The voltage between both ends is input to the controller 28, and the charging currents of the piezo stacks 127A to 127D are detected.
[0047]
The second switching element 24b is provided with a resistor 27G having a relatively low resistance in series. The voltage between both ends is input to the controller 28, and the discharge currents of the piezo stacks 127A to 127D are detected.
[0048]
The controller 28 is input with the voltage across the piezo stacks 127A to 127D (hereinafter referred to as piezo stack voltage) as the charge amount.
[0049]
Further, a target voltage setting signal proportional to a target piezo stack voltage (hereinafter referred to as a target voltage) that is a target charge amount is input to the controller 28. The target voltage setting signal is set so that a sufficient piezo stack voltage that allows the ball 123 to be fully lifted is applied to the injection command. In response to the pressure reduction command, a piezo stack voltage is set so that the ball 123 can be lifted while the needle 121 is seated.
[0050]
At the time of charge control, the controller 28 sets the ON period and the OFF period of the first switching element 24a as follows, and outputs a control signal for the first switching element 24a. That is, the first switching element 24a is turned on and a gradually increasing charging current is caused to flow through the first energization path 22a. When the charging current reaches the preset upper limit current value, the switching element 24a is turned off and the off period starts. At this time, since the back electromotive force generated in the inductor 23 is forward biased with respect to the parasitic diode 241b of the second switching element 24b, the flywheel gradually decreases to the second energization path 22b by the energy accumulated in the inductor 23. 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 24a is turned on again to enter the on period, and this is repeated. When the piezo stack voltage reaches the target voltage, the switching element 24a is fixed to be off, and the charging is completed. By charging the piezo stacks 127 </ b> A to 127 </ b> D in this way, the piezo stacks 127 </ b> A to 127 </ b> D are extended to press and lift the ball 123 through the displacement expansion chamber 113.
[0051]
In the discharge control, the ON period and the OFF period of the second switching element 24b are set as follows, and a control signal for the second switching element 24b is output. That is, the second switching element 24b is turned on to allow a gradually increasing discharge current to flow through the second energization path 22b. When the discharge current reaches a preset current value (hereinafter referred to as an upper limit current value), the switching element 24b is turned off and an off period starts. At this time, a large back electromotive force is generated in the inductor 23, and the flywheel current is caused to flow through the first energization path 22 a by the energy accumulated in the inductor 23 and the energy is recovered in the buffer capacitor 212. When the discharge current reaches the lower limit current value (approximately 0), the second switching element 24b is turned on again, and this is repeated. When the piezo stack voltage reaches 0, the switching element 24b is fixed off, and the discharge is completed. By discharging the piezo stacks 127A to 127D in this way, the piezo stacks 127A to 127D are contracted, the pressing force to the ball 123 by the fuel pressure in the displacement expansion chamber 113 is released, and the ball 123 is seated.
[0052]
In this way, the energization paths 22a and 22b become charging paths to the piezo stacks 127A to 127D by opening / closing operation of the charging switching element 24a, and become discharging paths to the piezo stacks 127A to 127D by opening / closing operation of the discharging switching element 24b. .
[0053]
Charge / discharge timing setting signals T1, T2, T3, and T4 for defining the charging timing and discharging timing of the piezo stacks 127A to 127D are input from the CPU 31 to the controller 28. The charging / discharging timing setting signals T1 to T4 are binary signals composed of “L” and “H”, and charging of the piezo stacks 127A to 127D is started at the rising edge, and the piezo stacks 127A to 127D are discharged at the falling edge. . The charge / discharge timing setting signals T1 to T4 define an injection period for the injection command (hereinafter, the charge / discharge timing setting signal is referred to as an injection signal). The injection signals T1 to T4 are output from the CPU 31 to the controller 28 for each cylinder, and the corresponding selection switching elements 25A to 25D are turned on during the output period.
[0054]
Further, a decompression signal PD is inputted as a control signal from the CPU 31 to the controller 28, and decompression control described later is executed. The decompression signal PD is a binary signal composed of “L” and “H”.
[0055]
The controller 28 includes a comparator, various logical operation circuits, and the like.
[0056]
FIG. 4 is a timing chart showing the operation of each part of the piezo actuator drive circuit 2 when the normal injection control and the decompression control are executed by the CPU 31. With this, the operation of the fuel injection device together with the setting of the controller 28 and the CPU 31 is shown. explain. The first half of the timing chart is for normal injection control, and the second half is for pressure reduction control.
[0057]
In the first half of the timing chart, the decompression signal PD is not input, and the controller 28 executes normal injection control. In the example shown in FIG. When the injection signal T1 of the # 1 cylinder is input, the selection switching element 25A corresponding to the # 1 cylinder is turned on at the rise, and the piezo stack 127A of the # 1 cylinder is connected to the energization paths 22a and 22b so that charging / discharging is possible. It becomes. This state continues until the injection signal T1 falls.
[0058]
Then, the charging of the piezo stack 127A is started with the rise of the injection signal T1 as a trigger. That is, when the charging switching element 24a is repeatedly turned on / off, a charging current flows, the piezo stack voltage rises, and the ball 123 reaches a target voltage at which full lifting is possible, charging is completed. Then, the discharge switching element 24b is repeatedly turned on / off by using the falling of the injection signal T1 as a trigger to cause a discharge current to flow, and the piezo stack voltage is lowered to return to the original state.
[0059]
Next, decompression control will be described. If the decompression signal PD is “H”, the selection switching element 25B for the # 2 cylinder in the same bank is turned on together with the selection switching element 25A for the cylinder at the rise of the injection signal T1 for the # 1 cylinder. Further, by this pressure reduction signal PD, the target voltage is switched to a voltage (lower pressure target voltage) at which the ball 123 can be half lifted while the needle 121 is seated, which is lower than that during normal injection control. Then, with the rise of the injection signal T1 as a trigger, the charging switching element 24a is turned on / off, and charging proceeds. The set value of the peak value of the charging current is the same as that during normal injection control.
[0060]
Accordingly, both the piezo stack 127A and the piezo stack 127B are charged by the common energization paths 22a and 22b. Here, since the charging current is distributed to the piezo stack 127A and the piezo stack 127B, the charging current of each of the piezo stacks 127A and 127B is halved compared to the normal injection control.
[0061]
The rise of the piezo stack voltage that rises once when the charging switching element 24a is turned on / off is as follows. En is the energy supplied to the piezo stack by turning on and off the charging switching element 24a once, CPZT is the capacitance of the piezo stack, VPZT1 is the piezo stack voltage before and after turning on and off the charging switching element 24a once, If the latter is VPZT2, the following equation (1) is obtained.
en = (1/2) CPZT (VPZT2²−VPZT1²) ... (1)
[0062]
When charging a plurality (n) of piezo stacks, equation (2) is obtained.
en = n * (1/2) CPZT (VPZT2²−VPZT1²) ... (2)
[0063]
Here, if en = 20 mJ, CPZT = 10 μF, and VPZT1 = 100 V, the voltage rise width ΔVPZT (= VPZT2−VPZT1) when the piezo stack is charged is ΔVPZT = 18.3 V when there is one piezo stack. On the other hand, when there are two piezo stacks, ΔVPZT = 9.5V. In this way, it is possible to suppress the voltage rise width, and charging can be performed with high accuracy.
[0064]
Thereby, it is possible to charge the target voltage during decompression with high accuracy without lowering the peak value of the charging current and turning on and off the charging switching element 24a at high speed. When the injection signal T1 falls, the selective switching elements 25A and 25B are turned off, and discharge control is performed to discharge both the piezo stacks 127A and 127B to return to the original state.
[0065]
In addition, since the fuel can be released to the fuel tank 51 by both the # 1 and # 2 cylinder injectors 1, the pressure reduction speed is high. Thereby, even if the pressure reduction range from the current common rail pressure to the target pressure is large, the common rail pressure can be reduced with a high response.
[0066]
The same applies to the third and fourth cylinders. When the decompression signal is input and the injection signal T3 for the # 3 cylinder is input, the piezo stacks 127C and 127D for the # 3 and # 4 cylinders are charged. Thus, the piezo stacks 127C and 127D can be charged to the target voltage during decompression with high accuracy.
[0067]
Compared to the case where only one piezo stack is charged at the time of pressure reduction control, it is possible to charge with high accuracy as described above, despite performing control that is substantially unchanged. The remarkable effect is that the pressure can be reduced quickly.
[0068]
In addition, what is necessary is just to increase the number of the injectors 1 made into a half lift state, when charge with higher precision is required. That is, if the decompression signal PD is in the input state, the selection switching elements 25C and 25D for the # 3 and # 4 cylinders may be turned on so that the charging current is also distributed to the piezo stack 127C and the piezo stack 127D. In addition, in the region where the common rail pressure is low, the pressure acting on the ball 123 is low, and the target voltage during pressure reduction control is low for half lift. In the region where the piezo stack voltage is low, the increase width of the piezo stack voltage is increased by turning on and off the charging switching element 24a once. Therefore, the lower the common rail pressure, the more the number of cylinders to be half lifted and the higher the accuracy. .
[0069]
(Second Embodiment)
  FIG. 5 shows a piezo actuator drive circuit constituting the fuel injection device according to the second embodiment of the present invention. In the figure,First formThe same number is attached to the parts that operate substantially the same asFirst formThe difference will be mainly described. In the figure, the piezo stack of # 1 and # 2 cylinders and the corresponding selective switching elements are omitted.
[0070]
The piezo actuator drive circuit 2A is provided with a depressurizing capacitor 29, and can be charged and discharged through energization paths 22a and 22b. The depressurizing capacitor 29 is connected in series with a switching element 26 as depressurizing switch means, and is switched on and off by a control signal from the controller 28A. When the injection signal T1 is input while the pressure reducing signal PD is in the input state, the control signal is output together with the control signal to the selection switching element 25A for the # 1 cylinder during the output period.
[0071]
The decompression switching element 26 is connected in a direction in which the parasitic diode 261 is reverse-biased with respect to the buffer capacitor voltage. When the depressurizing switching element 26 is turned on, the depressurizing capacitor 29 is connected in parallel with the selected piezo stacks 127A to 127D.
[0072]
In the first embodiment, in the first embodiment, the selection switching element of the piezo stack for the cylinders in the same bank is turned on during the output period of the decompression signal in the first embodiment, whereas in the present embodiment, the switching element 26 is turned on as described above. Except for being turned on, it is basically the same as that of the first embodiment.
[0073]
  ThisFirst formSimilarly, at the time of decompression control, the charging current is distributed to the selected piezo stack 127A and the decompression capacitor 29, and the charging current is suppressed in the piezo stack 127A. Can be charged.
[0074]
In addition, since the target voltage at the time of pressure reduction control is low in the region where the common rail pressure is low as described above, a plurality of pressure reduction capacitors are provided, and a pressure reduction switching element is provided corresponding to each pressure reduction capacitor, It is also possible to increase the capacity other than the piezo stack at the time of pressure reduction control and increase the accuracy by turning on more pressure reduction switching elements in the region where the common rail pressure is lower.
[0075]
(Third embodiment)
  FIG. 6 shows a piezo actuator drive circuit constituting a fuel injection device according to the third embodiment of the present invention.First formIn the figure, the control setting of the switching element or the like executed by the controller at the time of pressure reduction control is changed.First formThe same number is attached | subjected to the part which carries out substantially the same operation | movement, and it demonstrates centering on difference with 1st Embodiment.
[0076]
FIG. 7 is a timing chart showing the state of each part during pressure reduction control. When the injection signal T1 rises while the pressure reducing signal PD is input, first, as described above, the selective switching element 25A for the # 1 cylinder is turned on, and the charging switching element 24a and the discharging switching element 24b are alternately turned on / off. To do. Each on-time etc. is set as follows. In other words, each of the ON periods is set to a predetermined length set in advance. First, in the ON period and the OFF period of the charging switching element 24a, the charging current I having a triangular waveform is the same as in the normal injection control._{# 1}Flows and the piezo stack 127A is charged. And charging current I_{# 1}Becomes substantially 0, the ON period of the discharge switching element 127B is entered. The on period and the off period of the discharge switching element 24b are the triangular discharge current I as in the normal injection control._{# 1}Flows and the piezo stack 127A is discharged. And the discharge current I_{# 1}Becomes substantially 0, the charging switching element 24a is turned on again to enter the on period, and this is repeated.
[0077]
During this time, the piezo stack voltage V_{# 1}Repeatedly rises and falls, and does not reach a voltage at which the ball 123 can lift (in the figure, VPZT during decompression). The buffer capacitor 212 consumes energy by Joule heat by repeatedly charging and discharging the piezo stack 127A, and the buffer capacitor voltage V_DC-DCGradually decreases.
[0078]
This buffer capacitor voltage V_DC-DCReaches a predetermined threshold voltage V1 set in advance, the switching elements 24a and 24b are turned off and on, and only the charging switching element 24a is fixed on.
[0079]
Now, the buffer capacitor voltage V_DC-DCAfter reaching the threshold voltage V1, only the charging switching element 24a is fixed on, so that the charge moves from the buffer capacitor 212 to the piezo stack 127A, and the buffer capacitor voltage V_DC-DCAnd piezo stack voltage V_{# 1}Become the same voltage. Since the capacitance of the buffer capacitor 212 is sufficiently larger than the capacitance of the piezo stack 127A, these voltages having the same voltage value are not much different from the threshold voltage V1. Here, by setting the threshold voltage V1 to a value lower than the target voltage VPZT at the time of pressure reduction control, the buffer capacitor voltage V after the charging switching element 24a is fixed on is set._DC-DCAnd piezo stack voltage V_{# 1}Is also lower than the target voltage VPZT during pressure reduction control. In the illustrated example, V1> 0, but 0V may be used.
[0080]
Buffer capacitor voltage V_DC-DCAnd piezo stack voltage V_{# 1}, The switching element 2112 of the DC-DC converter 211 starts to be turned on / off, and the buffer capacitor 212 and the piezo stack 127A are charged. Piezo stack voltage V_{# 1}When the voltage reaches the target voltage VPZT during pressure reduction control, the charging switching element 24a is fixed to OFF and the charging of the piezo stack 127A is completed. Since the piezo stack 127A and the buffer capacitor 212 connected in parallel are charged from the DC-DC converter 211, the charging current is distributed to the piezo stack 127A and the buffer capacitor 212, and the charging current I in the piezo stack 127A is distributed._{# 1}Is suppressed, and the piezo stack 127A can be charged to the target voltage during pressure reduction control with high accuracy. The DC-DC converter 211 continues to operate thereafter to charge only the buffer capacitor 212 to prepare for the next normal fuel injection control.
[0081]
Similarly to the above embodiments, the discharge of the piezo stack 127A is turned off at the fall of the injection signal, and the selective switching element 25A is turned off, and the discharge switching element 24b is turned on / off to discharge the piezo stack 127A.
[0082]
Note that the amount of charge of the piezo stack may be an index that is not the piezo stack voltage but the amount of power supplied to the piezo stack.
[0083]
The injector is configured such that the driving force generated by the piezo stack is transmitted to the ball via the fuel pressure in the displacement expansion chamber. However, the present invention has a single piston that is pressed by the piezo stack without the displacement expansion chamber. The present invention can also be applied to a fuel injection device including an injector configured to directly press and drive a ball.
[Brief description of the drawings]
[Figure 1]First1 is a circuit diagram of a piezo actuator driving circuit that constitutes a fuel injection device and drives a piezo actuator mounted on an injector for fuel injection. FIG.
FIG. 2 is an overall configuration diagram of the fuel injection device.
FIG. 3 is a cross-sectional view of the injector.
FIG. 4 is a timing chart showing the operation of the piezo actuator drive circuit.
FIG. 5 is a circuit diagram of a piezo actuator driving circuit constituting the second fuel injection device of the present invention.
FIG. 6 is a circuit diagram of a piezo actuator drive circuit constituting a third fuel injection device of the present invention.
FIG. 7 is a timing chart showing the operation of the piezo actuator drive circuit.
[Explanation of symbols]
  1 Injector
  1a Nozzle part
  1b Back pressure control unit (back pressure increasing / decreasing means)
  1c Piezo actuator
  110 Valve chamber
  110a Low pressure port
  123 Ball (valve)
  127, 127A, 127B, 127C, 127D Piezo stack
  2,2A, 2B Piezo actuator drive circuit
  2a Drive circuit body (energization means)
  211 DC-DC converter (power supply)
  212 Buffer capacitor
  22a, 22b energization path (charge path, discharge path)
  23 Inductor
  24a Switching element for charging (switching means for charging)
  24b Switching element for discharging (switching means for discharging)
  25A, 25B, 25C, 25D, 25E, 25F Selection switching element (switching means for selection)
  26 Switching element for pressure reduction (switching means for pressure reduction)
  28, 28A, 28B Controller (control means)
  29 Depressurizing capacitor
  31 CPU

Claims (2)

A nozzle having a needle that opens and closes the nozzle hole, is supplied with high-pressure fuel stored in a common rail, and injects the fuel from the nozzle hole, and fuel is introduced from the common rail to generate a back pressure of the needle The valve body is disposed in a back pressure chamber and 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, and the lift amount of the valve body is increased. And a back pressure increasing / decreasing means for decreasing the pressure of the back pressure chamber according to the present invention, and a piezo actuator having a piezo stack that presses and drives the valve body and increasing the lift amount of the valve body as the charge amount of the piezo stack increases. An injector with
An energization means having an energization path for energizing the piezo stack and charging and discharging the piezo stack;
In response to a fuel injection command, the energization means is operated with a charge amount that the valve body can be fully lifted as a target charge amount, and in response to a fuel pressure reduction command in the common rail, the needle is seated. A fuel injection device having control means for operating the energization means with a charge amount that the valve body lifts as a target charge amount;
A pressure reducing capacitor connected in parallel with the piezo stack and capable of being charged and discharged by the energization path;
A pressure reducing switch means for switching between connection and disconnection of the capacitor and the piezo stack,
The control means;
The depressurization switch means is controlled together with the energization means, and in the energization control with respect to the depressurization command, the depressurization switch means is turned on and the charging current is set to be distributed to the piezo stack and the capacitor. A fuel injection device. A nozzle having a needle that opens and closes the nozzle hole, is supplied with high-pressure fuel stored in a common rail, and injects the fuel from the nozzle hole, and fuel is introduced from the common rail to generate a back pressure of the needle The valve body is disposed in a back pressure chamber and 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, and the lift amount of the valve body is increased. And a back pressure increasing / decreasing means for decreasing the pressure of the back pressure chamber according to the present invention, and a piezo actuator having a piezo stack that presses and drives the valve body and increasing the lift amount of the valve body as the charge amount of the piezo stack increases. An injector with
A buffer capacitor for temporarily storing electric charge to be supplied to the piezo stack;
A power supply for charging the buffer capacitor;
A charging switch means for switching between opening and closing a charging path of the piezo stack,
A switch means for discharging that switches between opening and closing a discharge path of the piezo stack,
Control means for controlling a power supply, a switch means for charging and a switch means for discharging, and for the fuel injection command, the charge switch with the charge amount that the valve body can be fully lifted as a target charge amount Control means for operating the charging switch means with a charge amount that the valve body is lifted while the needle is seated as a target charge amount in response to a command to reduce the fuel pressure in the common rail. In a fuel injection device having
The control means;
In the energization control with respect to the pressure reduction command, the charging switch means and the discharging switch means are alternately turned on and off, and the voltage across the buffer capacitor is more than the voltage across the piezo stack corresponding to the target charge amount at the time of control against the pressure reduction command. Discharge until low voltage value,
The fuel is characterized in that when the voltage across the buffer capacitor reaches the voltage value, the charging switch means is fixed to ON and the piezo stack is charged to the target charge amount together with the buffer capacitor by a power supply. Injection device.

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