JP4615967B2 - Piezo injector drive device - Google Patents

Description

  The present invention relates to a drive device for a piezo injector that performs charge control and discharge control of the piezo element so as to drive a piezo injector that is a fuel injection valve including the piezo element as an actuator.

  In the piezo injector, a piezo actuator in which a laminated body (piezo stack) in which a large number of piezoelectric elements are stacked is expanded and contracted by a piezoelectric effect is applied to, for example, a fuel injection injector in a common rail fuel injection device of a diesel engine. The piezo actuator is a capacitive load, and can be switched between an expanded state and a contracted state by charging and discharging. In the piezo injector, the valve opening and closing are switched by the expansion and contraction operation of the piezo actuator.

  FIG. 10 shows a cross-sectional configuration of the piezo injector.

  The piezo injector is provided with a cylindrical needle storage portion 52 at the tip of its body 50. The needle storage section 52 stores a nozzle needle 54 that can be displaced in the axial direction. The nozzle needle 54 is seated on an annular needle seat portion 56 formed at the distal end portion of the body 50, thereby blocking the needle storage portion 52 from the outside (combustion chamber of the internal combustion engine), while from the needle seat portion 56. By separating, the needle storage portion 52 is communicated with the outside. The nozzle needle 54 is supplied with high-pressure fuel supplied from a common rail (not shown) to the high-pressure fuel passage 58 to the needle storage portion 52.

  The back side of the nozzle needle 54 (the side opposite to the side facing the needle seat portion 56) faces the back pressure chamber 60. Fuel from the high pressure fuel passage 58 is supplied to the back pressure chamber 60 through the orifice 64. Further, the back pressure chamber 60 is provided with a needle spring 62 that pushes the nozzle needle 54 toward the needle seat portion 56 side.

  The back pressure chamber 60 can communicate with the low pressure fuel passage 72 via the balance three-way valve 66. The balance three-way valve 66 is pushed to the rear side (upward in the drawing) of the body 50 by the valve spring 70. The three-way valve 66 is seated on the annular valve seat portion 74 by the force exerted by the valve spring 70, thereby blocking the low pressure fuel passage 72 and the back pressure chamber 60, and the force exerted by the valve spring 70. The low pressure fuel passage 72 and the back pressure chamber 60 are communicated with each other by being displaced toward the tip side of the body 50 against this.

  The surface of the three-way valve 66 on the valve seat 74 side faces the tip of the valve piston 78. On the other hand, the rear side of the valve piston 78 faces the tip of the piezo piston 80. A displacement expansion chamber 82 is defined by the valve piston 78, the piezo piston 80, and the inner peripheral surface of the body 50. The displacement expansion chamber 82 has a reduced diameter portion so that the diameter of the rear side of the body 50 is larger than that of the front end side of the body 50, and two columnar spaces are connected in series. The displacement expansion chamber 82 is filled with an appropriate fluid such as fuel.

  On the other hand, the piezo piston 80 is pushed to the rear of the body 50 by a piezo spring 84. Further, the piezo piston 80 is connected to a piezo element 86 having a piezo stack on the rear side of the body 50 and functioning as an actuator. Incidentally, the back surface of the piezo element 86 facing the piezo piston 80 is fixed to the body 50.

  Therefore, when no current is supplied to the piezo element 86 and the piezo element 86 is in the contracted state, the piezo piston 80 is positioned behind the body 50 by the piezo spring 84. At this time, since the valve piston 78 does not displace the three-way valve 66 toward the front end side of the body 50, the back pressure chamber 60 and the low-pressure fuel passage 72 are blocked by the three-way valve 66. For this reason, the nozzle needle 54 is pushed toward the distal end side of the body 50 by the fuel pressure (common rail pressure) in the back pressure chamber 60 and the needle spring 62 and is in a state of being seated on the needle seat portion 56 (valve closed state).

  On the other hand, when current is supplied to the piezo element 86 and the piezo element 86 is in the extended state, the piezo piston 80 moves to the front end side of the body 50 against the force of the piezo spring 84. As a result, the valve piston 78 displaces (opens) the three-way valve 66 toward the distal end side of the body 50, so that the back pressure chamber 60 communicates with the low pressure fuel passage 72. As a result, the pressure of the fuel in the back pressure chamber 60 decreases, and the force that the high pressure fuel in the needle housing portion 52 pushes the nozzle needle 54 to the rear of the body 50 causes the fuel in the back pressure chamber 60 and the needle spring 62 to move. If it becomes larger than the force which pushes the nozzle needle 54 to the front of the body 50 more than predetermined, the nozzle needle 54 will be in the state (valve open state) separated from the needle seat part 56. FIG.

  According to the above configuration, the nozzle needle 54 can be controlled to be opened / closed through charging / discharging of the piezo element 86, and consequently, fuel injection can be controlled.

  By the way, energy is stored in the piezo element 86 until the force at which the piezo element 86 is extended by charging the piezo element 86 exceeds the force pushing the piezo piston 80 to the rear side of the body 50 by the piezo spring 84 or the like. . On the other hand, when the piezo element 86, the piezo piston 80, and the three-way valve 66 start to be displaced, the piezo element 86 and the piezo piston 80 become a generally well-known spring-mass vibration system and perform natural vibration. Here, if the charging speed of the piezo element 86 is fast, that is, the natural frequency is large, a large amount of energy is stored in the piezo element 86 before the three-way valve 66 starts to be displaced, and a large vibration may occur. . Since the generated natural vibration is transmitted to the body 50 that fixes the piezo element 86, a large noise may occur in the injector.

  On the other hand, in order to reduce the noise, it is conceivable to reduce the energy supplied to the piezo element 86 and to reduce the drive energy supply speed. However, if the energy to be supplied is reduced, problems such as unstable operation of the injector arise. Further, when the energy supply rate is lowered, it may be difficult to repeat a plurality of injections in a short time, and the responsiveness that is a merit of the piezo injector may be sacrificed. In particular, in a diesel engine or the like that performs pilot injection and main injection, such a problem is serious because a reduction in responsiveness makes it difficult to shorten the interval between pilot injection and main injection.

  Incidentally, as a conventional charge control of the piezo element 86, there is one described in Patent Document 1, for example.

In addition, not only the piezo injector shown in FIG. 10 but also a piezo injector that is a fuel injection valve provided with a piezo element as an actuator, such a situation in which noise may be generated when driving the piezo injector is generally common. It has become.
JP-A-11-317551

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide a drive device for a piezo injector capable of suitably suppressing noise while ensuring responsiveness.

  In the following, means for achieving the above object and its effects are described.

  In the means 1, in the piezo injector drive device for performing charge control and discharge control of the piezo element so as to drive a piezo injector which is a fuel injection valve including the piezo element as an actuator, when performing charge control of the piezo element, Control means for performing control to increase the energization amount of the piezoelectric element after limiting the energization amount to the initial stage of energization is provided.

  As described above, by restricting the energization amount to the piezo element at the beginning of energization, it is possible to avoid excessive energy accumulation in the piezo element or the like before the piezo injector is opened. For this reason, when the piezo element is displaced, vibration transmitted from the piezo element to the other part of the piezo injector can be reduced, and noise can be suitably suppressed. Further, by increasing the energization amount after the limiting control, it is possible to avoid delaying the valve opening operation of the piezo injector, in other words, it is possible to ensure the responsiveness of the piezo injector. Therefore, according to the means 1, it is possible to suitably suppress noise while ensuring responsiveness.

  The control related to the restriction and increase may be performed, for example, such that the total amount of energization during a predetermined period from the start of energization is smaller than the total amount of energization during the same period as the predetermined period immediately after the predetermined period has elapsed. .

  In addition, the inventors' experiments have revealed that it is desirable that the period for performing the limiting control is approximately “1/3” of the period for performing the charging control.

  The means 2 further comprises a current path in which power of the power feeding means is supplied to the piezo element via a coil in the means 1, and a charge switch that controls opening and closing of the current path, and the control means includes the charge switch The charging control of the piezo element is performed by a periodic on / off operation.

  When the electric power of the power feeding means is supplied to the piezo element via the coil, the current flowing through the coil and the piezo element is an alternating current. For this reason, in order to supply the rectified current to one terminal of the piezo element, it is desirable to periodically turn on and off the charging switch. Thereby, the current supplied to the piezo element via the coil has a substantially triangular waveform. For this reason, according to the means 2, energy can be supplied to the piezo element by giving such a pulsed direct current a plurality of times.

  Incidentally, it is desirable that the period of the ON operation is not more than “¼” of the AC cycle. Thereby, the current amount increases during the ON operation period, and a current having a triangular waveform in which the current amount decreases when the OFF operation is performed is supplied to the piezo element.

  The term “periodic” as used herein means that the ON operation and the OFF operation are repeated, and this does not include the meaning that the ON operation time and the OFF operation time are constant each time. To do.

  Further, in the configuration of the means 2, the limitation and the increase after the lapse of the predetermined period are performed, for example, by making the energization amount of each period of the predetermined period smaller than the energization amount of each period after the lapse of the predetermined period. Also good. Here, instead of the energization amount of each cycle after the lapse of the predetermined period, the energization amount of one cycle immediately after the lapse of the predetermined period may be used.

  In means 3, in means 2, the control means monitors the energization amount to the piezo element accompanying the periodic on / off operation, and controls so that the monitored energization amount does not exceed a predetermined threshold value. By doing so, the above restriction was made.

  In the means 3, the energization amount can be controlled by limiting the energization amount to be monitored so as not to exceed a predetermined threshold.

  In the means 4, in the means 3, the control means monitors the energization amount to the piezo element accompanying the periodic on / off operation, and controls so that the monitored energization amount does not exceed a predetermined threshold value. In addition, the control for increasing the energization amount is performed by increasing the predetermined threshold value.

  If the on-operation time is long, not only may an excessive current be accumulated in the piezo element and generate a loud noise, but a drive circuit (such as the current circuit of the means 2) that drives the piezo element may be damaged by the excessive current. Etc. In this regard, in the above configuration, since the energization amount monitored even after shifting from the limiting control to the increasing control is limited so as not to exceed a predetermined threshold value, the charging switch is preferably damaged. Can be dealt with. In addition, at this time, the energization amount can be appropriately limited at the beginning of energization start and the energization amount can be appropriately set thereafter by increasing the predetermined threshold value after the above-described control for limiting the energization at the beginning of energization start. Can be increased.

  In means 5, in the means 2, when the control means performs control to increase the time for performing one on operation more than when performing the limiting control when performing the periodic on / off operation. Was made longer.

  According to such setting, it becomes easy to increase the integral value of the triangular waveform current described in the means 2 after the limiting control. For this reason, it becomes easy to increase the energization amount of the piezo element after the control for limiting the above.

  In the means 6, in the means 5, the control means generates a reference signal for performing the circumferential on / off operation, and is used for one on operation designated by the reference signal. The time for performing the control for increasing the time is longer than that for performing the limiting control.

  In the above configuration, the charging switch is turned on / off based on the reference signal. In addition, since the time for one on operation is set in the above-described manner, the reference signal can increase the energization amount thereafter while limiting the energization amount at the beginning of energization. In this way, if a reference signal in which the amount of energization is limited or the amount of energization is appropriately set in advance is used, the above-described limiting control and subsequent control can be performed even by open control.

  In means 7, in means 2, the restriction means performs control to increase the ratio of the on operation time to the off operation time in one cycle of the on / off operation as compared with the restriction control. The time is getting bigger.

  By increasing the ratio of the on operation time to the off operation time in one cycle of the on / off operation, it is possible to increase the energization amount in one cycle. For this reason, in the said structure, the energization amount of one period of ON / OFF operation can be increased after the control to restrict | limit.

  Means 8. In the means 3, 4 or 7, the control means is means for generating a reference signal for performing the periodic on / off operation, and means for performing the on / off operation of the charging switch based on the reference signal. It was made to comprise with.

  According to the means 8, the on / off operation can be easily performed. That is, in the configuration of the means 3 or 4, the reference signal can be set simply, for example, as a periodic signal having a regular time series in which the ON operation time and the OFF operation time are unchanged. In such a setting, the on-operation time and the off-operation time are set so that the on-operation time is optimal after the predetermined period has elapsed and the off-operation time in the predetermined period is not excessively long. It is desirable. Further, in the configuration of the means 7, the on / off operation pattern is set in advance by the reference signal, so that the control mode becomes complicated, such as variably setting the operation mode based on the monitoring of the current flow state in the current path. You can avoid that.

  In any one of the means 1 to 8, as with the means 9, the restriction means may restrict the energization amount at the beginning of energization to "8 to 10A".

  In the means 10, in order to drive a piezo injector that is a fuel injection valve having a piezo element as an actuator, in the piezo injector drive device that performs charge control and discharge control of the piezo element, when performing charge control of the piezo element, The energy supplied to the piezo element is controlled to increase after being limited to the initial stage of the energy supply.

  In this way, by temporarily limiting the energy supplied to the piezo element from the start of supply, it is possible to avoid excessive energy being stored in the piezo element or the like before the valve opening of the piezo injector is started. For this reason, the vibration transmitted to the piezo injector when the piezo element is displaced can be reduced, and the noise can be suitably suppressed. Furthermore, it is possible to avoid delaying the valve opening operation of the piezo injector by increasing the supplied energy after the limiting control, in other words, to ensure the responsiveness of the piezo injector. Therefore, according to the means 10, it is possible to suitably suppress noise while ensuring the responsiveness.

  In any one of the means 1 to 10, as in the case of the means 11, the period during which the limiting control is performed may be “34 μs” or more.

  As a result, the level of noise generated in the piezo injector can be effectively reduced. This period is set to “47 μs” or more when the predetermined threshold is “8A”, and is set to “50 μs” or more when the predetermined threshold is “10A”. It is desirable that the interpolation value be between 47 μs ”and“ 50 μs ”.

  In the means 12, in any one of the means 1 to 11, the piezo injector includes a three-way valve for communicating and blocking between a high pressure fuel passage to which high pressure fuel is supplied and a low pressure fuel passage for returning the fuel to the fuel tank. In addition, when the three-way valve is opened by extension of the piezo element, a fuel injection port is opened and fuel is injected, and during the period of performing the limiting control, the opening of the three-way valve is Until when it is supposed to start.

  According to the above configuration, since the energization amount is limited until it is assumed that the opening of the three-way valve is started, excessive energy is stored in the piezo element until the opening of the three-way valve is started. This can be suitably avoided.

(First embodiment)
Hereinafter, a first embodiment in which a piezo injector drive device according to the present invention is applied to a piezo injector drive device mounted on an in-vehicle diesel engine will be described with reference to the drawings.

  FIG. 1 shows the overall configuration of the present embodiment. As shown in FIG. 1, the piezo injector drive device according to the present embodiment performs charge control and discharge control of the piezo elements Pa and Pb to drive the piezo injectors PIa and PIb. The electronic control device 30 that has a device and the like and controls the diesel engine and the driver unit 1 are configured. Incidentally, electric power is supplied from the battery B to the driver unit 1 and the electronic control unit 30.

  The piezo injectors PIa and PIb have the structure shown in FIG. On the other hand, the piezo elements Pa and Pb include a laminated body (piezo stack) formed by laminating a plurality of piezoelectric elements, and function as an actuator by expanding and contracting due to the piezoelectric effect. Specifically, the piezo elements Pa and Pb are capacitive loads, which expand when charged and contract when discharged. Then, the piezoelectric injectors PIa and PIb are opened in accordance with the extending operation of the piezoelectric elements Pa and Pb, and fuel is injected into each cylinder. On the other hand, as the piezo elements Pa and Pb are reduced, the piezo injectors PIa and PIb are closed to stop fuel injection.

  Next, the driver unit 1 will be described. The power supplied from the battery B is first supplied to the DC / DC converter 2 which is a booster circuit. The DC / DC converter 2 is configured as a series connection body of a coil 2c and a charge switch 2s formed of an N-channel MOS (Metal Oxide Semiconductor) transistor, one terminal of which is on the battery B side and the other terminal. Are connected to the ground side. Incidentally, in the figure, a diode 2d is a parasitic diode formed by forming an N-channel transistor, and its anode side is connected to the ground side and its cathode side is connected to the coil 2c side. The DC / DC converter 2 is configured to turn on / off the charging switch 2s so that the voltage of the battery B (for example, “12V”) is changed to a high voltage (for example, “for example” “for charging control of the piezo elements Pa and Pb”. 200-300V ").

  The boosted voltage of the DC / DC converter 2 is applied to the capacitor 6 via the diode 4. The capacitor 6 has one terminal connected to the cathode side of the diode 4 and the other terminal grounded. When the boosted voltage of the DC / DC converter 2 is applied to the capacitor 6, the capacitor 6 stores electric charges to be supplied to the piezo elements Pa and Pb. Incidentally, it is desirable that the capacitor 6 has a capacitance (for example, about “several hundred μF”) such that the voltage hardly changes depending on the supply of electric charge for one charge operation to the piezo elements Pa and Pb.

  The terminal side of the capacitor 6 that is at a high potential, that is, the cathode side of the diode 4 is the terminal side that is at the high potential of the piezo elements Pa and Pb via a series connection body of the charge switch 10 and the charge / discharge coil 12. It is connected to the. And the terminal side used as the low electric potential of the piezoelectric elements Pa and Pb is earth | grounded via the serial connection body which consists of selection switch 14a, 14b and resistance 16a, 16b, respectively. Here, the charge switch 10 is composed of an N-channel MOS transistor. In the figure, a diode 10d is a parasitic diode formed by forming a transistor, and has an anode connected to the charge / discharge coil 12 side and a cathode connected to the diode 4 side. The selection switches 14a and 14b are each composed of an N-channel MOS transistor. In the figure, diodes da and db are parasitic diodes formed by forming these transistors, and their anodes are connected to the ground side and their cathodes are connected to the piezoelectric elements Pa and Pb side, respectively.

  One terminal of the discharge switch 18 is connected between the charge switch 10 and the charge / discharge coil 12, and the other terminal of the discharge switch 18 is grounded. Here, the discharge switch 18 is formed of an N-channel MOS transistor. Incidentally, in the figure, the diode 18d is formed by forming this transistor, and its anode is connected to the ground side, and its cathode is connected to the charge switch 10 and charge / discharge coil 12 side.

  On the other hand, the controller 20 is dedicated hardware for operating the charge switch 10 and the discharge switch 18 based on a command from the electronic control unit 30. Incidentally, in order to drive the charge switch 10 and the discharge switch 18 at high speed, in this embodiment, a signal is output from the controller 20 to the charge switch 10 and the discharge switch 18 via a driver (not shown). This driver is preferably supplied with power from the terminal side of the capacitor 6 at a high potential.

  Next, charging control and discharging control of the piezo elements Pa and pb performed by the electronic control device 30 and the controller 20 will be described.

  FIG. 2 is a time chart showing states of charge control and discharge control. 2A corresponds to the piezo element Pa in the drawing, which is a signal for designating the fuel injection timing and the injection period by setting its logical value to “H”. The transition of the injection signal IJTa which is a signal) is shown. 2B shows a control signal for selectively turning on one of the selection switches 14a and 14b by setting its logical value to “H” (in FIG. 2B, a control signal for the selection switch 14a). (Ex.). FIG. 2C shows a charge period signal that is a signal for designating the timing and period for charging the piezo elements Pa and Pb through the operation of the charge switch 10 by setting the logical value to “H”. It shows the transition. FIG. 2D shows a discharge period signal which is a signal for designating the timing and period for discharging the piezo elements Pa and Pb through the operation of the discharge switch 18 by setting the logical value to “H”. It shows the transition. FIG. 2E shows the transition of the potential on the terminal side, which is a high potential of the piezo elements Pa and Pb.

  In this series of controls, when an injection signal IJTa is input from the electronic control unit 30 to the controller 20 at time t1, the controller 20 performs the following processing. First, based on the injection signal IJTa, the charging period signal is generated in a mode that is logic “H” from time t1 to time t2, and a selection control signal is generated to selectively turn on the selection switch 14a. Output. Then, the charging switch 10 is turned on / off based on the generated charging period signal. The charging period signal may be generated by the electronic control device 30.

  Here, when the charge switch 10 is turned on, as shown in FIG. 3A, a closed loop circuit including a capacitor 6, a charge switch 10, a charge / discharge coil 12, a piezo element Pa, a selection switch 14a, and a resistor 16a. Is formed. Thereby, the electric charge of the capacitor 6 is charged in the piezo element Pa. On the other hand, after the charging switch 10 is turned on, the charging switch 10 is turned off. As shown in FIG. 3B, the diode 18d, the charging / discharging coil 12, the piezo element Pa, the selection switch 14a, the resistance A closed loop circuit 16a is formed. Thereby, the flywheel energy of the charge / discharge coil 12 is charged in the piezo element Pa.

  When the charging switch 10 is operated in the above-described manner, the piezo element Pa is charged, and the potential on the terminal side that becomes the high potential of the piezo element Pa increases. The closed loop circuit shown in FIG. 3A is a current path through which the power of the capacitor 6 is supplied via the charge / discharge coil 12, and the charge switch 10 has a function of controlling the opening and closing of the current path.

  On the other hand, when the injection signal IJTa becomes logic “L” at time t3 shown in FIG. 2, a discharge period signal is generated in a mode that becomes logic “H” from time t3 to time t4 and the discharge switch 18 is turned on / off. Manipulate.

  That is, when the discharge switch 18 is turned on, as shown in FIG. 4A, a closed loop circuit is formed by the discharge switch 18, the charge / discharge coil 12, the piezo element Pa, the selection switch 14a, and the resistor 14a. Thereby, the piezo element Pa is discharged. Further, after the discharge switch 18 is turned on, the discharge switch 18 is turned off. As shown in FIG. 4B, the capacitor 6, the diode 10d, the charge / discharge coil 12, the piezo element Pa, and the selection switch 14a. The closed loop circuit is formed by the resistor 16a. Thereby, the flywheel energy of the charge / discharge coil 12 is recovered by the capacitor 6 via the diode 10d.

  When the discharge switch 18 is operated in the above-described manner, the piezo element Pa is discharged, and the potential on the terminal side that becomes the high potential of the piezo element Pa is lowered.

  Then, the selection switch 14a is turned off at time t5 after the end of the discharge control period.

  In the embodiment described above, the charging / discharging control of the piezo elements Pa and Pb can be performed by performing the on / off operation of the charge switch 10 and the on / off operation of the discharge switch 18.

  However, depending on the on / off operation of the charging switch 10, the energy stored in the piezo elements Pa and Pb becomes excessive by the time the piezo injectors PIa and PIb are started to open, resulting in a large amount in the piezo injectors PIa and PIb. As described above, noise may occur.

  Therefore, in the present embodiment, when charging control of the piezo elements Pa and Pb is performed, the energization amount to the piezo elements Pa and Pb is controlled to be increased after being limited for a predetermined period from the start of energization. In this way, by restricting the energy supplied to the piezo elements Pa and Pb for a predetermined period from the start of energization, the piezo elements Pa and Pb have excessive energy before the piezo injectors PIa and PIb are opened. The noise of the piezo injectors PIa and PIb that are generated by being stored in the motor is suppressed. Further, by increasing the energization amount after the lapse of a predetermined period, the valve opening operation of the piezo injectors PIa and PIb is prevented from being delayed, and the responsiveness is ensured.

  Here, the energization control will be further described in detail with reference to FIG. FIG. 5A shows the transition of the injection signal. FIG. 5B is a reference signal for performing an on / off operation, and here, an example in which an on operation period is a logic “H” and an off operation period is a logic “L” is illustrated. FIG. 5C shows the transition of the actual on / off operation state of the charge switch 10 shown in FIG. FIG. 5D shows a current limiting mode. FIG. 5E shows the transition of the energization amount to the piezo elements Pa and Pb. FIG. 5 (f) shows the transition of the voltage on the terminal side at which the piezoelectric elements Pa and Pb become high potential.

  In the series of processing shown in FIG. 5, first, when an injection signal (IJTa, IJTb) is output from the electronic control unit 30 at time t11, the modes shown in FIGS. 2 (b) and 2 (c) above. The selector switches 14a and 14b are operated and a charge period signal is generated. And according to a charge period signal, the controller 20 performs the following processes. That is, the reference signal is generated to turn on / off the charging switch 10 during the charging period specified by the charging period signal. Here, the reference signal instructs periodic on operation and off operation by repeating logic “H” and logic “L”. In particular, the reference signal according to the present embodiment is set to have the same time that is the logic “H” in each cycle and the time that is the logic “L” in each cycle. Incidentally, here, “periodic” means repetition of logic “H” and logic “L”, in other words, repetition of ON operation and OFF operation. In this case, ON operation of each cycle It is not meant that time and off-time operations are equal.

  Further, the charging switch 10 is turned on / off based on the reference signal, and the current flowing through the resistors 16a and 16b shown in FIG. 1 is monitored. At time t12, when the monitored current value becomes equal to or greater than the predetermined threshold value Ith, the charging switch 10 is switched off even when the on operation is instructed by the reference signal. Specifically, the signal output to the charging switch 10 is generated based on the reference signal and the current monitoring result, so that the charging switch 10 is turned off when the monitored current value exceeds a predetermined threshold value Ith. Like that. Then, when the reference signal instructs to turn on again at time t13, the charging switch 10 is turned on again. Incidentally, in FIG. 5E, the energization amounts of the piezo elements Pa and Pb when not limited by the predetermined threshold value Ith are indicated by a one-dot chain line. Further, in FIG. 5 (f), the voltage on the terminal side at which the piezoelectric elements Pa and Pb become high potentials when not limited by the predetermined threshold value Ith is indicated by a broken line.

  Such processing, in other words, processing for limiting the monitored current value so as not to exceed the predetermined threshold value Ith, is performed over a predetermined period T during which it is desired to limit the energization amount to the piezoelectric elements Pa and Pb. Then, at time t14 after the predetermined period T has elapsed, the process of limiting the energization amount to the piezo elements Pa and Pb based on the predetermined threshold value Ith is ended. As a result, the energization amount to the piezo elements Pa and Pb is increased after the predetermined period T has elapsed.

  Here, the setting mode of the predetermined threshold Ith and the predetermined period T according to the present embodiment will be described.

  First, the setting mode of the predetermined threshold value Ith will be described. Regarding fuel injection control, there is a demand not only for avoiding noise problems of the piezo injectors PIa and PIb, but also for the fuel injection period. In other words, the appropriate fuel injection period is limited, and if this period is too long, it causes inconvenience in fuel injection control. For this reason, if the predetermined threshold value Ith is set to an extremely small value, the time for completing the fuel injection may exceed the allowable range and may be prolonged. It is conceivable to deal with this by increasing the energization amount after the control for limiting the energization amount to a very large amount, but in this case, the withstand voltage of the charge switch 10 is reduced. Not only can this cause problems, but it can also cause other noises in the high frequency range. For these reasons, it is desirable that the predetermined threshold value Ith is “8A” or more. On the other hand, when the predetermined threshold value Ith is a large value, the degree of decrease in the noise level when the predetermined period T is lengthened is reduced. For this reason, even if the energization amount is limited by the predetermined threshold value Ith, the noise level cannot be effectively reduced. For these reasons, it is desirable to set the predetermined threshold value Ith to “10 A” or less.

  FIG. 6 shows a relationship between a predetermined period T for limiting the current and a predetermined threshold value Ith used for limiting the current and the noise levels of the piezo injectors PIa and PIb. In FIG. 6, the horizontal axis represents a predetermined period T (μs), and the vertical axis represents a noise level (dB). The measured value of the relationship between the predetermined period T and the noise level under the condition where the predetermined threshold Ith is “8A” is indicated by a triangle mark, and the predetermined period T under the condition where the predetermined threshold is “10A” The measured values related to the noise level are indicated by square marks. Further, the measured value of the noise level when the predetermined threshold value is provided and the energization amount of the piezo elements Pa and Pb is not limited is indicated by the measurement point d1.

  As shown in FIG. 6, when the predetermined threshold value Ith is “8A”, the noise level starts to decrease from the time when the predetermined period T becomes “34 μs”, and the predetermined period T becomes “52 μs” or more. However, the noise level will not decrease. On the other hand, when the predetermined threshold value Ith is “10A”, the degree of reduction in the noise level increases from when the predetermined period T becomes “34 μs”, and when the predetermined period T becomes “44 μs” or more, the noise level decreases. The degree of is reduced.

  From the above, it is desirable to set the predetermined period T to “34 μs” or more so that the effect of reducing the noise level can be remarkably obtained by setting the predetermined period T.

  By the way, when the predetermined period T is lengthened, the degree of decrease in the noise level is small. Even if the predetermined period T is further shortened, a remarkable effect cannot be expected from the viewpoint of improving the noise level. On the other hand, among various required elements from the fuel injection control, the quick fuel injection is performed, in other words, the charging period of the piezoelectric elements Pa and Pb shown in FIG. Some require it. In view of the trade-off relationship between noise countermeasures and quick fuel injection, when the predetermined threshold Ith is “8A”, the predetermined period T is set to “52 μs” or more. Is not desirable. Further, when the predetermined threshold value Ith is “10A”, the noise level is lowered even if the predetermined period T is set to “52 μs” or more, but the predetermined threshold value Ith is set to “8A”. Even if the period T is lengthened, the noise level is not effectively lowered. In general, the degree of decrease in the noise level when the predetermined period T is lengthened becomes more prominent as the predetermined threshold value Ith is smaller. In view of such circumstances, it is desirable that the predetermined period T is not more than “52 μs”.

  From the two viewpoints described above, it is desirable that the predetermined threshold Ith is “8 to 10 A” and the predetermined period T is “34 to 52 μs”. In particular, when the predetermined threshold value Ith and the predetermined period T are set in this way, the noise level can be approximated to the noise level (approximately “90 dB”) of an existing electromagnetically driven injector.

  Here, in order to make the noise level substantially the same as that of the electromagnetically driven injector, the predetermined period T is further set to “47 μs” or more when the predetermined threshold value Ith is “8A”, and the predetermined threshold value Ith is set. When the value is “10 A”, it is desirable to set it to “50 μs” or more, and an interpolated value between “47 μs” and “50 μs” with respect to a predetermined threshold value Ith in the meantime.

  Incidentally, one of the merits of the piezoelectric injectors PIa and PIb is that the responsiveness is higher than that of the electromagnetically driven injector. For this reason, if the predetermined period T is excessively prolonged or the predetermined threshold value Ith is set to an excessively small value, the responsiveness is lowered and the characteristic superior to the responsiveness of the electromagnetically driven injector is lost. It can also be. In this regard, if the predetermined threshold value Ith and the predetermined period T are set as described above, the noise level is compared with that of the electromagnetically driven injector while ensuring good response as compared with the electromagnetically driven injector. Can be inferior.

  In addition, after the energization amount to the piezo elements Pa and Pb is limited by the predetermined threshold value Ith over the predetermined period T in the above-described mode, the piezo injectors PIa and PIb are increased by increasing the energization amount to the piezo elements Pa and Pb. The fully opened state (the fully open state of the nozzle needle 54 and the three-way valve 66) is quickly established. In order to perform such increase control quickly, it is desirable to set the reference signal so that the ON operation time is optimal after the predetermined period T has elapsed and the OFF operation time in the predetermined period T is not excessively long. .

  According to the embodiment described above in detail, the following effects can be obtained.

  (1) By restricting the energization amount to the piezo elements Pa and Pb over a predetermined period T, the piezo injectors PIa and PIb are opened (the nozzle needle 54 and the three-way valve 66 are opened, and the piezo piston 80 is displaced). It is possible to avoid that energy is excessively stored in the piezo elements Pa, Pb and the like before the start. For this reason, when the piezo injectors PIa and PIb start to open, vibrations transmitted to the piezo injectors PIa and PIb (vibrations associated with displacements of the piezo elements Pa and Pb) can be reduced, and therefore noise is preferable. Can be suppressed. Furthermore, it is possible to avoid delaying the valve opening operation of the piezo injectors PIa and PIb by increasing the energization amount after the lapse of the predetermined period T, in other words, to ensure the responsiveness of the piezo injectors PIa and PIb. it can.

  (2) The energization amount to the piezo elements Pa and Pb accompanying the periodic on / off operation is monitored over a predetermined period T, and the energization amount to be monitored is limited so as not to exceed the predetermined threshold value Ith. Thereby, it becomes possible to easily limit the energization amount during the predetermined period T.

  (3) The controller 20 generates a reference signal for performing a periodic on / off operation, and performs the on / off operation of the charging switch 10 based on the reference signal. In addition, at this time, the reference signal is a periodic signal having a regular time series in which the ON operation time and the OFF operation time are invariable. For this reason, the ON operation and the OFF operation can be performed with a simple configuration.

  (4) By setting the predetermined period T to “34 μs” or more, the noise level can be suitably reduced while ensuring the responsiveness of the piezoelectric injectors PIa and PIb.

  (5) By setting the predetermined threshold value Ith to “8 to 10 A”, it is possible to suitably reduce the noise level while ensuring the responsiveness of the piezoelectric injectors PIa and PIb.

(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  In the first embodiment, the energization amounts of the piezo elements Pa and Pb are monitored over a predetermined period T, and are limited so as not to exceed a predetermined threshold value Ith. On the other hand, in the present embodiment, during the charge control, the energization amounts of the piezo elements Pa and Pb are monitored so that this does not exceed the predetermined threshold value Ith, and the predetermined threshold value Ith is exceeded from the predetermined period T. Is set so that the value after the predetermined period T has a larger value.

  FIG. 7 shows the energization control of this embodiment. 7A shows the transition of the injection signal, FIG. 7B shows the reference signal, FIG. 7C shows the transition of the actual on / off operation state of the charging switch 10, and FIG. 7D shows the transition of the predetermined threshold value Ith, FIG. 7E shows the transition of the energization amount to the piezo elements Pa and Pb, and FIG. 7F shows the high potential of the piezo elements Pa and Pb. The voltage transition on the terminal side is shown.

  As shown in FIG. 7, when an injection signal is output from the electronic control unit 30 at time t21, the controller 20 performs a reference signal in the same manner as shown in FIGS. 5 (b) and 5 (c). And the charge switch 10 are operated. However, in the present embodiment, after the elapse of the predetermined period T, the predetermined threshold Ith is switched from the first value TH1 to the second value TH2 that is larger than the first value TH1. Here, the predetermined period T and the first value TH1 are set in the same manner as the predetermined period T and the predetermined threshold value Ith of the first embodiment. In addition, the second value TH2 is set to a value lower than a value that may cause damage to the circuits that drive the piezoelectric injectors PIa and PIb, such as damage to the charging switch 10 due to excessive current flowing.

  According to the present embodiment described above, the following effects can be obtained in addition to the effects (1) to (5) of the first embodiment.

  (6) By preventing the energization amounts of the piezo elements Pa and Pb from exceeding the second value TH2 after the predetermined period T has elapsed, the circuit that drives the piezo injectors PIa and PIb is prevented from being damaged. Can do.

(Third embodiment)
Hereinafter, the third embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  In the first embodiment, the energization amounts of the piezo elements Pa and Pb are monitored over a predetermined period T, and are limited so as not to exceed a predetermined threshold value Ith. On the other hand, in the present embodiment, the time for performing one on operation is set to be longer after the predetermined period T than the predetermined period T.

  FIG. 8 shows the energization control of this embodiment. 8A shows the transition of the injection signal, FIG. 8B shows the transition of the reference signal for periodically turning on / off the charging switch 10, and FIG. 8C shows the piezo. FIG. 8D shows changes in the energization amount to the elements Pa and Pb, and FIG. 8D shows changes in the voltage on the terminal side at which the piezoelectric elements Pa and Pb become high potentials. Incidentally, in this embodiment, open control is performed and the reference signal is a signal output to the charging switch 10.

  As shown in FIG. 8, when an injection signal is output from the electronic control unit 30 at time t31, the controller 20 generates a reference signal and operates the charging switch 10 based on the reference signal. However, in this embodiment, the time for performing one ON operation designated by the reference signal is set longer than the predetermined period T after the predetermined period T elapses. Further, even during the predetermined period T, the closer to the start of energization of the piezo elements Pa and Pb, the shorter the time for performing one on operation specified by the reference signal. In other words, the time tn for performing the ON operation in the n-th ON / OFF operation is set to satisfy “t (n)> t (n−1)”. Note that after the elapse of the predetermined period T, the reference signal is a signal having the same mode as that described in the first embodiment.

  Also according to the present embodiment described above, the effects (1), (4), and (5) of the first embodiment can be obtained.

(Fourth embodiment)
Hereinafter, the fourth embodiment will be described with reference to the drawings with a focus on differences from the first embodiment.

  In the first embodiment, the energization amounts of the piezo elements Pa and Pb are monitored over a predetermined period T, and are limited so as not to exceed a predetermined threshold value Ith. On the other hand, in the present embodiment, the ratio of the ON operation time to the OFF operation time in one cycle of the ON / OFF operation “(ON time) / (OFF time)” is a predetermined period T elapsed from the predetermined period T. Try to make the latter longer.

  FIG. 9 shows the energization control of this embodiment. 9A shows the transition of the injection signal, FIG. 9B shows the transition of the reference signal for turning on / off the charging switch 10, and FIG. 9 shows the transition to the piezo elements Pa and Pb. FIG. 9D shows the transition of the energization amount, and the transition of the voltage on the terminal side at which the piezoelectric elements Pa and Pb become high potentials. Incidentally, in this embodiment, open control is performed and the reference signal is a signal output to the charging switch 10.

  As shown in FIG. 9, when an injection signal is output from the electronic control unit 30 at time t41, the controller 20 generates a reference signal and operates the charging switch 10 based on this. However, in the present embodiment, the ratio of the on operation time to the off operation time in one cycle of the on / off operation specified by the reference signal is longer after the predetermined period T than the predetermined period T. To. In other words, the ratio rn of the on operation time to the off operation time in one cycle of the n-th on / off operation is set to be “r (n)> r (n−1)”. Note that after the elapse of the predetermined period T, the reference signal is a signal having the same mode as that described in the first embodiment.

  Also according to the present embodiment described above, the effects (1), (4), and (5) of the first embodiment can be obtained.

(Other embodiments)
The above embodiments may be implemented with the following modifications.

  In the first embodiment and the second embodiment, the reference signal is a signal that instructs the on time and the off time to be the same every time, but is not limited thereto. For example, the length of one cycle may be instructed to be longer after a predetermined period than the predetermined period. In this way, during the predetermined period, the energization amount to the piezo elements Pa and Pb becomes equal to or greater than the predetermined threshold value Ith, so that the off operation time in each cycle is excessively long even when the charging switch 10 is turned off. This can be avoided reliably. Furthermore, after the predetermined period has elapsed, it is possible to sufficiently secure the energization amount of each cycle.

  In the third embodiment, the time tn for performing the ON operation in the n-th ON / OFF operation is set to “t (n)> t (n−1)” only in the predetermined period. Not limited to this. For example, “t (n)> t (n−1)” may be satisfied even after the elapse of a predetermined period, and all ON operation times for the predetermined period may be the same.

  In the fourth embodiment, the ratio rn of the ON operation time to the OFF operation time in one cycle of the n-th ON / OFF operation is set to “r (n)> r (n− 1) ", but is not limited to this. For example, “r (n)> r (n−1)” may be satisfied even after the elapse of a predetermined period, and all the ratios in each period of the predetermined period may be the same.

  The controller 20 and the electronic control device 30 are configured as control means for controlling to increase the energization amount of the piezo element after limiting the energization amount to the piezo element for a predetermined period from the start of energization. It is not limited to what is done. That is, for example, all of such a series of controls may be performed by an electronic control device including a central processing unit. Further, the control means is not necessarily limited to performing the processing according to each of the embodiments and the modifications thereof by generating the reference signal.

  The setting mode of the predetermined threshold value Ith and the predetermined period T is not necessarily limited to that exemplified in the first embodiment. A period from when the energization is started to when the piezo injectors PIa and PIb are opened (preferably, a period until the three-way valve 66 starts to open) may be used. Further, as described above, there are various requirements regarding fuel injection control, and these are often mutually contradictory. For this reason, depending on the adjustment between the request elements, it may be desired to deviate from the predetermined threshold value Ith or the predetermined period T set in the aspect exemplified in the first embodiment. However, even in such a case, the energization amount to the piezo element is limited for a predetermined period from the start of energization, and then the control is performed to increase or the energy supplied to the piezo element is limited for a predetermined period from the start of energization. Thereafter, the noise level can be reduced by performing an increase control. Furthermore, the predetermined period T may be substantially “1/3” of the period during which charging control is performed.

  The piezo injectors PIa and PIb are not limited to those having the configuration illustrated in FIG. In short, any fuel injection valve having a piezo element as an actuator may be used. Specifically, the communication between the inside of the injector and the outside (combustion chamber) and the cutoff thereof may be controlled by expansion and contraction of the piezo element. Specifically, a three-way valve is provided for communicating and blocking between a high-pressure fuel passage to which high-pressure fuel is supplied and a low-pressure fuel passage for returning the fuel to the fuel tank, and the three-way valve is opened by extension of the piezo element. Thus, the outside (combustion chamber) and the inside of the piezo injector may be communicated to inject fuel. In this case, if one end of the piezo element is fixed to the body of the piezo injector, noise is likely to occur due to vibrations transmitted to the injector body when excessive energy is supplied to the piezo element. In particular, the application of the present invention is particularly effective.

  The drive circuit for driving the piezo elements Pa and Pb is not limited to that illustrated in FIG. For example, the charge switch 10 is not limited to the one having an N-channel MOS transistor. Further, the power supply means for supplying power to the piezo elements Pa and Pb via the charge / discharge coil 12 is not limited to the one that includes the capacitor 6, the DC / DC converter 2, and the battery B. For example, even if the capacitor 6 is not provided, it is possible to supply electric power of an appropriate voltage to the piezo elements Pa and Pb using the boosted voltage of the DC / DC converter 2. For example, if the voltage of the battery B is sufficiently high, the DC / DC converter 2 may not be provided.

  The piezo injectors PIa and PIb are not limited to fuel injection valves used in diesel engines, but may be fuel injection valves used in in-cylinder injection gasoline engines, for example.

BRIEF DESCRIPTION OF THE DRAWINGS The whole block diagram which shows 1st Embodiment which applied the drive device of the piezo injector concerning this invention to the drive device of the piezo injector with which a diesel engine is equipped. The time chart concerning charge / discharge control of the embodiment. The figure which shows the distribution | circulation aspect of the electric current at the time of charge control concerning the embodiment. The figure which shows the distribution | circulation aspect of the electric current at the time of the discharge control concerning the embodiment. The time chart which shows the charge control aspect concerning the embodiment. The graph for demonstrating the setting aspect of the threshold value and predetermined period concerning the embodiment. The time chart which shows the charge control aspect concerning 2nd Embodiment. The time chart which shows the charge control aspect concerning 3rd Embodiment. The time chart which shows the charge control aspect concerning 4th Embodiment. Sectional drawing which shows the structure of a piezo injector.

Explanation of symbols

  PIa, PIb ... Piezo injector, Pa, Pb ... Piezo element, B ... Battery, 2 ... DC / DC converter, 6 ... Capacitor, 10 ... Charge switch, 20 ... Controller, 30 ... Electronic control device.

Claims (11)

In a drive device for a piezo injector that performs charge control and discharge control of the piezo element in order to drive a piezo injector that is a fuel injection valve provided with the piezo element as an actuator,
The piezo injector includes a three-way valve for communicating and blocking between a high-pressure fuel passage to which high-pressure fuel is supplied and a low-pressure fuel passage for returning the fuel to the fuel tank, and the three-way valve is opened by the extension of the piezo element. By being valved, the fuel injection port is opened and fuel is injected,
Upon charging control of the piezoelectric element, the energy supplied to the piezoelectric element, was restricted with Tokima that is assumed to opening of the three-way valve is started, a control means for performing control to increase A drive device for a piezoelectric injector. 2. The driving device for a piezo injector according to claim 1, wherein the control means limits the energy to be supplied as a limitation of an energization amount to the piezo element. The drive device for a piezo injector according to claim 2,
A current path through which power of the power feeding means is supplied to the piezo element via a coil; and a charging switch for controlling the opening and closing of the current path,
The piezo injector drive device, wherein the control means performs charge control of the piezo element by periodically turning on and off the charge switch.   The control unit monitors the energization amount to the piezo element in accordance with the periodic on / off operation, and performs the above-described restriction by controlling the monitored energization amount so as not to exceed a predetermined threshold. Item 4. A piezo injector drive device according to Item 3.   The control means monitors the energization amount to the piezo element accompanying the periodic on / off operation, and controls the monitored energization amount so as not to exceed a predetermined threshold, and The drive device for a piezo injector according to claim 4, wherein the control for increasing the energization amount is performed by increasing the predetermined threshold value.   The control means, when performing the periodic on / off operation, makes the time for performing one on operation longer when performing control to increase the time than performing the limiting control. 4. A drive device for a piezo injector according to claim 3. The control means generates a reference signal for performing the periodic on / off operation, and performs control to limit the time of one on operation specified by the reference signal. drive of the piezo injector according to claim 6 wherein such person becomes long when performing control to increase than when. The control means is configured such that the ratio of the on operation time to the off operation time in one cycle of the on / off operation is greater when performing the control to increase than when performing the limiting control. A drive device for a piezo injector according to claim 3.   The control means comprises means for generating a reference signal for performing the periodic on / off operation, and means for performing an on / off operation of the charging switch based on the reference signal. Item 9. The drive device for a piezo injector according to item 4, 5 or 8. It said control means drives the piezo injector according to any one of claims 2-8 for limiting conductible initial stage of the energization amount to "8~10A".   11. The drive device for a piezo injector according to claim 10, wherein the period for performing the limiting control is “34 μs” or more.

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