JP2018003727A - Injection control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an injection control device capable of preventing damage to a discharging switch element due to an overcurrent when a short failure occurs in a charging switch element.SOLUTION: An injection control device 100 drives a piezo injector 110 with the charge/discharge operation of a piezoelectric element laminate 112. The injection control device 100 includes a common booster circuit 10, and a plurality of lines of driving circuits 30 each having a charging MOSFET 31 as the charging switch element and a discharging MOSFET 32 as the discharging switch element. When an overcurrent flowing in the charging MOSFET 31 is detected, the injection control device 100 sets the line of the discharging MOSFET 32 where the overcurrent flows, into an off-state.SELECTED DRAWING: Figure 2

Description

  The disclosure according to this specification relates to an injection control device that drives an injection valve.

  Generally, a plurality of injection valves provided in an internal combustion engine or the like are driven by a driving device as disclosed in Patent Document 1, for example. The drive device of Patent Document 1 includes a voltage booster circuit that generates a high voltage and a charge / discharge circuit that charges and discharges each piezoelectric actuator as a configuration for driving each piezoelectric actuator of a plurality of injection valves. The charging / discharging circuit includes a charging switch element that controls a current flowing through the piezoelectric actuator, and a discharging switch element that controls the discharge of charges accumulated in the piezoelectric actuator.

JP 2002-199748 A

  Now, in the driving device as in Patent Document 1, the charging switch element remains on for some accidental reason. When such a short circuit failure of the charging switch element occurs, if the discharging switch element is turned on in the discharging phase for discharging the charge of the piezoelectric actuator, an overcurrent is generated in the charging switch element and the discharging switch element. Can flow. As a result, the discharge switch element may be short-circuited due to an overcurrent, and may remain on.

  The present disclosure has been made in view of the above problems, and an object of the present disclosure is to provide an injection control device capable of preventing damage to a discharge switch element due to overcurrent even when a short-circuit failure occurs in the charge switch element. It is to provide.

  In order to achieve the above object, a disclosed first aspect is an injection control device that drives an injection valve (110) by charging / discharging a capacitive load (112), and each capacitive load of a plurality of injection valves. A common booster circuit (10) for generating a voltage to be supplied to the charging switch, a charging switch element (31) for controlling a current flowing in the capacitive load, and each capacitive load connected in series with the charging switch element A plurality of drive circuits (30) each having a discharge switch element (32) for controlling the discharge of the accumulated charge; an overcurrent detector (71) for detecting an overcurrent flowing through the charge switch element; When an overcurrent is detected by the overcurrent detection unit, the injection control device includes a switch control unit (60, 73) that turns off the discharge switch element of the system through which the overcurrent flows.

  In this aspect, when a short circuit failure occurs in the charging switch element in any of the drive circuits, an overcurrent flows through the charging switch element and the discharging switch element in the discharging phase of the capacitive load. When this overcurrent is detected by the overcurrent detection unit, the switch control unit turns off the discharge switch element of the system through which the overcurrent flows. According to the above control, even if a short failure occurs in the charging switch element, it is possible to prevent damage due to overcurrent of the discharging switch element.

  Note that the reference numbers in the parentheses merely show an example of a correspondence relationship with a specific configuration in an embodiment described later, and do not limit the technical scope at all.

It is a block diagram which shows the detail of the injection control apparatus by 1st embodiment, and each piezo injector. It is a figure for demonstrating the action | operation of the injection control apparatus at the time of a failure diagnosis. It is a figure which compares and shows the voltage change of the piezoelectric element laminated body when charging MOSFET is normal, and the voltage change of a piezoelectric element laminated body when charging MOSFET is short-circuited. It is a flowchart which shows the detail of the failure diagnosis process implemented with a microcomputer. It is a flowchart which shows the detail of the failure diagnosis process by 2nd embodiment.

  Hereinafter, a plurality of embodiments of the present disclosure will be described based on the drawings. In addition, the overlapping description may be abbreviate | omitted by attaching | subjecting the same code | symbol to the corresponding component in each embodiment. When only a part of the configuration is described in each embodiment, the configuration of the other embodiment described above can be applied to the other part of the configuration. Moreover, not only the combination of the configurations explicitly described in the description of each embodiment, but also the configuration of a plurality of embodiments can be partially combined even if they are not explicitly described, as long as there is no problem in the combination. And the combination where the structure described in several embodiment and the modification is not specified shall also be disclosed by the following description.

(First embodiment)
An injection control device 100 according to the first embodiment of the present disclosure shown in FIG. 1 is connected to a plurality of piezo injectors 110. The piezo injector 110 is installed in an internal combustion engine such as a diesel engine, for example. As an example, an injection control device 100 applied to a four-cylinder internal combustion engine is connected to four piezo injectors 110. The piezo injector 110 is formed with a number of injection holes for injecting fuel such as light oil. The piezo injector 110 functions as an injection valve that injects fuel directly into a combustion chamber of an internal combustion engine from a number of injection holes.

  Each piezo injector 110 has a piezoelectric element stack 112. The piezoelectric element laminate 112 is a laminate in which, for example, layers called PZT (PbZrTiO 3) and thin electrode layers are alternately stacked. The piezoelectric element laminate 112 is a capacitive load, and expands and contracts due to charge and discharge of electric charges due to the reverse piezoelectric effect that is a characteristic of the piezoelectric element. By the expansion and contraction operation of the piezoelectric element laminate 112, the injection hole of the piezo injector 110 is opened and closed.

  As described above, the injection control device 100 individually drives the plurality of piezo injectors 110 by charging and discharging each piezoelectric element stack 112. As a configuration for that purpose, the injection control device 100 includes a common booster circuit 10, a charge capacitor 20, a plurality of systems of drive circuits 30, a voltage monitoring resistor 40, an injector drive IC 60, and a microcomputer 70.

  The booster circuit 10 generates a high voltage to be supplied to each piezoelectric element stack 112 of each piezo injector 110 by boosting the voltage of a DC power supply VD such as a battery. The booster circuit 10 generates a voltage of, for example, several tens to several hundreds V and stores it in the charge capacitor 20. Even in the injection control device 100 including a plurality of drive circuits 30, the booster circuit 10 has a common configuration.

  The booster circuit 10 includes an inductance 11, a switch element 12, a diode 13, an overcurrent detection resistor 14, and the like. The inductance 11, the switch element 12, and the overcurrent detection resistor 14 are connected in series in this order from the DC power supply VD to the ground. The diode 13 is connected between a common connection point of the inductance 11 and the switch element 12 and one terminal of the charge capacitor 20. The forward direction of the diode 13 is a direction from the switch element 12 toward the charge capacitor 20.

  The charge capacitor 20 is charged by the booster circuit 10. The other terminal of the charge capacitor 20 is connected to the ground via the overcurrent detection resistor 14. A common connection point between the charge capacitor 20 and the diode 13 is branched into drive energization paths 21 and 22 that reach the respective drive circuits 30.

  According to the above configuration, when the booster circuit 10 performs on / off control of the switch element 12, that is, switching, the charge capacitor 20 is charged via the diode 13 by the induced voltage generated in the inductance 11. By appropriately switching the switch element 12, the voltage of the charge capacitor 20 is maintained at a predetermined voltage (hereinafter “common voltage”) Vcm.

  One drive circuit 30 and one voltage monitoring resistor 40 are provided for each piezo injector. One drive circuit 30, voltage monitor resistor 40, piezo injector 110, and the like constitute one system. For convenience, in the following description, each system shown in FIG. 1 is distinguished as one system S1 and two systems S2.

  Each drive circuit 30 of each system S1, S2 has a charge / discharge switching function for switching the charge phase and the discharge phase of each piezoelectric element laminate 112. Each drive circuit 30 is provided with a charging MOSFET 31, a discharging MOSFET 32, a current limiting coil 33, and the like.

  The charging MOSFET 31 and the discharging MOSFET 32 are n-channel field effect transistors. A feedback diode is added to the charging MOSFET 31 and the discharging MOSFET 32. The charging MOSFET 31 and the discharging MOSFET 32 are connected in series between the drive energization paths 21 and 22 and the ground. The discharging MOSFET 32 is disposed closer to the ground side (downstream side) than the charging MOSFET 31.

  The charging MOSFET 31 functions as a charging switch element that controls charging of the piezoelectric element stack 112. The charging MOSFET 31 is switched between an on state and an off state based on a control signal input from the injector drive IC 60. The charging MOSFET 31 controls the current flowing from the charge capacitor 20 to the piezoelectric element stack 112 in each drive circuit 30. When the charging MOSFET 31 is turned on, the common voltage Vcm (see FIG. 3) of the charge capacitor 20 is applied to the piezoelectric element laminate 112. As a result, the charge of the charge capacitor 20 moves to the piezoelectric element stack 112 and is stored in the piezoelectric element stack 112.

  A common connection point of the charging MOSFET 31 and the discharging MOSFET 32 is connected to the plus side of the piezoelectric element laminate 112 by an injector energization path 34. On the other hand, the discharge MOSFET 32 and the ground are connected to the negative side of the piezoelectric element laminate 112 by an injector energization path 35. The discharge MOSFET 32 is connected in parallel with the piezoelectric element laminate 112 by these injector energization paths 34 and 35.

  With the above connection, the discharge MOSFET 32 functions as a discharge switch element that controls the discharge of the piezoelectric element laminate 112. The discharge MOSFET 32 is switched between an on state and an off state based on a control signal input from the injector drive IC 60. The discharging MOSFET 32 controls the current flowing from the piezoelectric element stack 112 to the ground in each drive circuit 30. When the discharge MOSFET 32 is turned on, the charge accumulated in the piezoelectric element stack 112 is discharged to the ground.

  The current limiting coil 33 is provided in the injector energization path 34. The current limiting coil 33 limits the current flowing into the piezoelectric element stack 112 during the period when the piezoelectric element stack 112 is charged. Due to the function of the current limiting coil 33, even if the on / off control of the charging MOSFET 31 is performed, the inflow of the suddenly changed current into the piezoelectric element stack 112 is prevented.

  The voltage monitoring resistor 40 is a set of passive resistors arranged in parallel with the piezoelectric element laminate 112. Each end of the voltage monitoring resistor 40 is connected to each injector energization path 34, 35, respectively. The voltage monitoring resistor 40 is configured to monitor the voltage of the piezoelectric element laminate 112. The voltage between the set of passive resistors varies in synchronization with the voltage of the piezoelectric element stack 112. The voltage monitoring resistor 40 provides the microcomputer 70 with the voltage measured between the pair of passive resistors.

  The injector drive IC 60 is connected to, for example, the switch element 12 of the booster circuit 10, the charging MOSFET 31 and the discharging MOSFET 32 of each driving circuit 30, and the like. The injector drive IC 60 causes each switch element to perform switching by outputting a control signal to each switch element (12, 31, 32). Specifically, the injector drive IC 60 maintains the voltage of the charge capacitor 20 at the common voltage Vcm by the on / off control of the switch element 12. The injector drive IC 60 outputs a pulse-like control signal to the charging MOSFET 31 or the discharging MOSFET 32 based on the injection signal (see FIG. 3) acquired from the microcomputer 70. The charging MOSFET 31 and the discharging MOSFET 32 charge and discharge the piezoelectric element stack 112 by executing switching according to the control signal.

  In addition, the injector drive IC 60 can detect the overcurrent flowing through each drive circuit 30 by monitoring the potential between the charge capacitor 20 and the overcurrent detection resistor 14 (see FIG. 2). The injector drive IC 60 provides overcurrent detection information to the microcomputer 70 in real time.

  The microcomputer 70 is a processing unit that executes various arithmetic processes related to the control of the internal combustion engine. The microcomputer 70 includes a processor 70a, a RAM 70b, a storage medium 70c, a communication bus connecting these, and the like. As the storage medium 70c, a non-transitory tangible storage medium such as a flash memory is used. The storage medium 70c stores a drive control program for controlling the drive of the piezo injector 110, a failure diagnosis program for diagnosing a failure of the drive circuit 30, and the like. The microcomputer 70 causes the processor 70a to execute various programs.

  The microcomputer 70 calculates the fuel injection amount and the injection timing of each piezo injector 110 based on signals from various sensors by executing the drive control program. And the microcomputer 70 outputs the injection signal (refer FIG. 3) according to a calculation result toward the injector drive IC60. The injection signal is a rectangular wave signal corresponding to the injection period of each piezo injector 110.

  As an example, when the injection signal of one system S1 is output from the microcomputer 70 to the injector driving IC 60, the injector driving IC 60 starts switching of the charging MOSFET 31 of the one system S1 at the rising edge of the injection signal. Switching that is a charging operation of the charging MOSFET 31 is performed a specified number of times. On the other hand, during the period when the injection signal is input to the injector drive IC 60, the discharging MOSFET 32 is in the off state in which the energization is cut off. In such a charging phase, the piezoelectric element laminate 112 is charged by the charge capacitor 20, and fuel injection from each nozzle hole is started by the extension operation of the piezoelectric element laminate 112.

  When the injection signal of the one system S1 falls, the injector drive IC 60 starts switching of the discharging MOSFET 32 of the one system S1. Switching that is a discharge operation of the discharge MOSFET 32 is also performed a specified number of times. On the other hand, the charging MOSFET 31 is in an off state in which energization is interrupted. With such a discharge phase, discharge from the piezoelectric element stack 112 to the ground is started, and fuel injection from each nozzle hole is stopped by the contraction operation of the piezoelectric element stack 112.

  In addition, the microcomputer 70 can detect a failure in which the charging MOSFET 31 remains on (hereinafter, “short failure”) by executing the failure diagnosis program, and can stop the operation of the system in which the short failure has occurred. . As shown in FIG. 2, when a short failure occurs in the charging MOSFET 31, the terminal of the charge capacitor 20 is shorted to the ground in the discharging phase in which the discharging MOSFET 32 is turned on. As a result, an overcurrent (through current) flows through the drive energization path 22 in the charging MOSFET 31 and the discharging MOSFET 32. This overcurrent is a very large current with respect to the resistance of the discharging MOSFET 32. In FIG. 2, a case where a short-circuit failure occurs in the charging MOSFET 31 (see dot) of the two systems S2 among a plurality of systems will be described as an example.

  The microcomputer 70 constructs an overcurrent detection unit 71, a voltage acquisition unit 72, an injection signal control unit 73, a failure determination unit 74, and the like as functional blocks related to the failure diagnosis by executing the failure diagnosis program.

  The overcurrent detection unit 71 detects an overcurrent flowing through the charging MOSFET 31 based on detection information provided from the injector drive IC 60. As an example, a current of 40 amperes or more is detected as an overcurrent. In addition, the overcurrent detection unit 71 estimates a drive circuit 30 in which a short circuit failure may have occurred in the charging MOSFET 31. For example, when the overcurrent is detected when the discharge MOSFET 32 of the two systems S2 is turned on, the overcurrent detection unit 71 causes the short circuit of the charging MOSFET 31 of the two systems S2 to drive the two systems S2. It is estimated that an overcurrent has passed through 30.

  The voltage acquisition unit 72 acquires the voltage of the piezoelectric element stack 112 from the voltage detected by the voltage monitoring resistor 40 in each system. The voltage acquisition unit 72 acquires the voltage of the piezoelectric element stack 112 as the monitor voltage Vm at a specific determination timing (see FIG. 3). The monitor voltage Vm is used for a definite diagnosis (described later) of a short circuit failure when a short circuit failure of the charging MOSFET 31 is estimated by detecting an overcurrent.

  The injection signal control unit 73 cooperates with the injector drive IC 60 and performs control to turn off the discharge MOSFET 32 of the system through which the overcurrent flows based on the detection of the overcurrent by the overcurrent detection unit 71. Specifically, the injection signal control unit 73 outputs, to the injector drive IC 60, an injection signal of a system in which it is estimated that an overcurrent has flowed based on the detection of the overcurrent. As described above, the injector drive IC 60 switches the discharge MOSFET 32 to the OFF state, similarly to the normal drive control described above. The injection signal based on the detection of the overcurrent continues to be output until the failure determination unit 74 makes a definitive diagnosis that the charging MOSFET 31 is not a short circuit failure. Therefore, the discharging MOSFET 32 is held in the off state until the injection signal is turned off.

  In the above operation, the time from the detection of the overcurrent by the overcurrent detection unit 71 until the discharge MOSFET 32 is turned off (hereinafter referred to as “off switching time”) is preferably 10 μsec or less, and more preferably Set to 3 μs or less. More specifically, normally, the charging MOSFET 31 and the discharging MOSFET 32 are not turned on at the same time. If both the charging MOSFET 31 and the discharging MOSFET 32 are turned on, the overcurrent flowing through the MOSFETs 31 and 32 is defined as a through current. Then, when a through current flows through the discharge MOSFET 32, a time during which the discharge MOSFET 32 is short-circuited is defined as a failure time. The OFF switching time needs to be shorter than the failure time, and the specific time is 10 μsec. By such setting of the off-switching time, the injection signal control unit 73 turns off the discharging MOSFET 32 before 10 μsec has elapsed since the detection of the overcurrent.

  The failure determination unit 74 is in a state in which the charging MOSFET 31 has a short circuit failure based on the monitor voltage Vm acquired by the voltage acquisition unit 72 for the system (for example, 2 systems S2) in which the overcurrent is detected by the overcurrent detection unit 71. It is determined whether or not. As described above, when the injection signal is output based on the detection of the overcurrent, the injector drive IC 60 causes the charging MOSFET 31 to perform the charging operation, similarly to the normal drive control. The voltage of the piezoelectric element stacked body 112 rises to substantially the same value as the common voltage Vcm of the charge capacitor 20 by a plurality of times of switching accompanying the charging operation (see the middle stage in FIG. 3). Even if the charging MOSFET 31 is short-circuited, the voltage of the piezoelectric element laminate 112 rises to the common voltage Vcm (see the lower part of FIG. 3).

  The failure determination unit 74 acquires the monitor voltage Vm of the piezoelectric element stacked body 112 by the voltage acquisition unit 72 when a predetermined time (for example, 1 second) elapses from the start of the charging operation of the charging MOSFET 31. The failure determination unit 74 performs a definite diagnosis of a short failure by comparing the monitor voltage Vm with a determination voltage Vth that is a threshold set for failure determination.

  When the charging MOSFET 31 has not failed, the charging MOSFET 31 is turned off after the completion of the charging operation. As a result, the charging of the piezoelectric element laminate 112 by the charge capacitor 20 is correctly terminated, so that the voltage of the piezoelectric element laminate 112 gradually decreases due to natural discharge. Therefore, the monitor voltage Vm at the determination timing when a predetermined time has elapsed from the start of the charging operation is a value less than the determination voltage Vth (see the middle stage in FIG. 3).

  On the other hand, when the charging MOSFET 31 is short-circuited, the charging MOSFET 31 is not turned off, so that the charging of the piezoelectric element stack 112 by the charge capacitor 20 is continued even after the completion of the charging operation. As a result, the voltage of the piezoelectric element laminate 112 is maintained at a value that is substantially the same as the common voltage Vcm. Therefore, the monitor voltage Vm at the determination timing after a predetermined time has elapsed from the start of the charging operation is higher than the determination voltage Vth (see the lower part of FIG. 3).

  Based on the above principle, when the monitor voltage Vm is less than the determination voltage Vth, the failure determination unit 74 determines that the charging MOSFET 31 is not short-circuited (normal). On the other hand, failure determination unit 74 determines that charging MOSFET 31 has a short circuit failure when monitor voltage Vm is higher than determination voltage Vth. The determination voltage Vth is set to a value lower than the common voltage Vcm of the charge capacitor 20. As an example, the determination voltage Vth is set to a value of about 80 to 90% of the common voltage Vcm, for example.

  Details of a series of failure diagnosis processes executed by the microcomputer 70 will be described with reference to FIG. 2 based on FIG. The failure diagnosis process is started based on the start of the internal combustion engine and is repeatedly performed until the internal combustion engine is stopped.

  In S101, a process for detecting an overcurrent is performed, and the process proceeds to S102. In S102, it is determined whether or not an overcurrent has been detected in S101. If no overcurrent is detected, S101 and S102 are repeated. When an overcurrent is detected in S101, the process proceeds from S102 to S103.

  In S103, the system through which the overcurrent flows is specified, and an injection signal for the specified system is output to the injector drive IC 60, and the process proceeds to S104. Due to the injection signal output in S103, the transition to the discharge phase is interrupted, and the switching of the discharging MOSFET 32 to the off state and the charging operation of the charging MOSFET 31 are sequentially performed. As a result, the piezoelectric element laminate 112 is charged to the common voltage Vcm.

  In S104, it is determined whether or not a predetermined time has elapsed from the start of the charging operation of the charging MOSFET 31. When a predetermined time has elapsed, the process proceeds from S104 to S105. In S105, the monitor voltage Vm of the piezoelectric element laminate 112 when a predetermined time has elapsed is acquired, and the process proceeds to S106. In S106, the monitor voltage Vm acquired in S105 is compared with the determination voltage Vth, and the process proceeds to S107.

  As a result of the comparison in S106, if the monitor voltage Vm is less than the determination voltage Vth, the process proceeds from S107 to S108. In S108, it is determined that the charging MOSFET 31 is normal, and the failure diagnosis process is temporarily terminated. Based on the diagnosis result of S108, the injection signal turned on based on the detection of overcurrent is switched to the off state. The system in which the overcurrent is detected is released from the failure diagnosis state and returns to normal operation.

  On the other hand, if the result of the comparison in S106 is that the monitor voltage Vm is greater than or equal to the determination voltage Vth, the process proceeds from S107 to S109. In S109, it is determined that the short-circuit failure has occurred in the charging MOSFET 31, and the failure diagnosis process is temporarily terminated. According to the diagnosis result of S109, the failed drive circuit 30 is maintained in a state where the conduction of the discharging MOSFET 32 is cut off.

  In the first embodiment described so far, when a short-circuit failure occurs in the charging MOSFET 31 in the drive circuit 30 of any system, the charging MOSFET 31 and the discharging MOSFET 32 are excessive in the discharging phase of the piezoelectric element stack 112. Current flows. When this overcurrent is detected by the overcurrent detection unit 71, the injection signal control unit 73 and the injector drive IC 60 turn off the discharging MOSFET 32 of the system through which the overcurrent flows. According to the above control, even if a short failure occurs in the charging MOSFET 31, damage due to overcurrent of the discharging MOSFET 32 can be prevented.

  In addition, in the first embodiment, the failed drive circuit 30 is maintained in a state where the conduction of the discharge MOSFET 32 is cut off after the discharge MOSFET 32 is prevented from being damaged. As described above, the common voltage Vcm of the charge capacitor 20 can be applied to the piezoelectric element stack 112 of the piezo injector 110 through the normal drive circuit 30. As a result, the piezo injector 110 of the system in which the drive circuit 30 is normal can perform fuel injection based on normal drive control. Therefore, the injection control device 100 can continue the operation of the internal combustion engine although it is in an incomplete state.

  In the first embodiment, based on the detection of the overcurrent, after the discharge MOSFET 32 is once turned off, the failure determination unit 74 performs definite diagnosis of the short failure. When it is determined in the definite diagnosis that the charging MOSFET 31 is not short-circuited, the drive circuit 30 returns to normal operation.

  According to the above, when a temporary overcurrent due to noise or the like is detected, the drive circuit 30 can be smoothly returned to the normal operation although the operation is temporarily stopped. If the restoration to the normal operation is surely performed as described above, the overcurrent detection unit 71 can detect the overcurrent with high sensitivity so that no overcurrent detection omission occurs. As a result, a short circuit failure of the discharging MOSFET 32 due to an overcurrent can be prevented more reliably.

  Further, in the first embodiment, when the charging MOSFET 31 has a short circuit failure, the voltage of the piezoelectric element laminate 112 is maintained high. Therefore, if it is determined that there is an abnormality when the monitor voltage Vm is higher than the determination voltage Vth, the failure determination unit 74 can accurately determine a short-circuit failure of the charging MOSFET 31.

  On the other hand, when the charging MOSFET 31 is not short-circuited, the voltage of the piezoelectric element laminate 112 drops due to natural discharge. Therefore, if it is determined that the monitor voltage Vm is normal when the monitor voltage Vm is lower than the determination voltage Vth, the failure determination unit 74 can avoid erroneous determination of a short circuit failure with high accuracy.

  In addition, in the first embodiment, the off switching time from the detection of the overcurrent until the charging MOSFET 31 is turned off is set to 10 μsec or less so as to be less than the failure time due to the through current. By carrying out such rapid switching as described above, damage to the discharge MOSFET 32 due to overcurrent is more reliably prevented.

  In the first embodiment, the charging MOSFET 31 corresponds to the “charging switch element”, the discharging MOSFET 32 corresponds to the “discharging switch element”, and the injector drive IC 60 and the injection signal control unit 73 are the “switch control unit”. Is equivalent to. Further, the piezo injector 110 corresponds to an “injection valve”, and the piezoelectric element laminate 112 corresponds to a “capacitive load”.

(Second embodiment)
The second embodiment shown in FIG. 5 is a modification of the first embodiment. In the fault diagnosis process of the second embodiment, the process of comparing the monitor voltage Vm and the determination voltage Vth can be performed a plurality of times after the charging operation of the charging MOSFET 31 (see FIG. 2) of the system suspected of having a short fault. The failure determination unit 74 (see FIG. 2) determines that the charging MOSFET 31 is not short-circuited when the monitor voltage Vm drops below the determination voltage Vth even once. The details of the failure diagnosis process of the second embodiment will be described below with reference to FIGS. 2 and 3 based on the flowchart of FIG. In addition, the content of S201-S203 is substantially the same as the content of S101-S103 (refer FIG. 4) of 1st embodiment.

  The initial contents of S204 to S207 are substantially the same as the contents of S104 to S107 (see FIG. 4) of the first embodiment. When it is determined in the first S207 that the monitor voltage Vm is less than the determination voltage Vth, the process proceeds to S208, where it is determined that the charging MOSFET 31 is normal. On the other hand, if it is determined in S207 for the first time that the monitor voltage Vm is equal to or higher than the determination voltage Vth, the process proceeds to S209.

  In S209, it is determined whether or not the determination for comparing the monitor voltage Vm and the determination voltage Vth in S206 and S207 has been performed a predetermined number of times. If it is determined in S209 that the predetermined number of determinations have been completed, the process proceeds to S210. In S210, as in S109 of the first embodiment (see FIG. 4), it is determined that the charging MOSFET 31 is abnormal, and a series of failure diagnosis processing is terminated.

  On the other hand, if it is determined in S209 that the predetermined number of determinations has not been completed, the process returns to S204. In S204 after the negative determination in S209, the passage of a predetermined time is waited until the next determination timing. The second and subsequent determination timings are set after elapse of a predetermined time (for example, 1 second) with respect to the previous determination timing, for example. The interval of the determination timing may be constant, or may be adjusted gradually longer or shorter.

  If it is determined in S204 that the next determination timing has come due to the elapse of a predetermined time, the process proceeds to S205, and the latest monitor voltage Vm is acquired. In S206, the latest monitor voltage Vm is compared with the determination voltage Vth. When the latest monitor voltage Vm is less than the determination voltage Vth, the process proceeds from S207 to S208, and it is determined that the charging MOSFET 31 is normal. On the other hand, when the latest monitor voltage Vm is still equal to or higher than the determination voltage Vth, the process of obtaining the monitor voltage Vm at a predetermined interval and comparing it with the determination voltage Vth is repeated until the predetermined number of determinations are completed.

  In the second embodiment described so far, similarly to the first embodiment, the discharge MOSFET 32 can be prevented from being damaged by the control for turning off the discharge MOSFET 32 based on the detection of the overcurrent. In addition, in the second embodiment, the comparison between the monitor voltage Vm and the determination voltage Vth can be repeated a predetermined number of times. Therefore, a situation in which a definite diagnosis is made that a short-circuit failure has occurred even though the charging MOSFET 31 can operate normally is avoided. Note that the number of repetitions of the comparison determination can be adjusted as appropriate. For example, it may be set to about 10 times to ensure accuracy. Alternatively, it may be repeated several tens of times in order to reliably prevent erroneous determination of a short circuit failure.

(Other embodiments)
Although a plurality of embodiments have been described above, the present disclosure is not construed as being limited to the above-described embodiments, and can be applied to various embodiments and combinations without departing from the scope of the present disclosure. it can.

  In the second embodiment, the determination voltage Vth compared with the monitor voltage Vm is maintained at a constant value. However, in the process of repetition, adjustment such as gradually decreasing the determination voltage Vth or increasing the determination voltage Vth may be performed by the failure determination unit. Further, the failure determination unit may determine that the charging MOSFET is not short-circuited based on the determination that the monitor voltage Vm is less than the determination voltage Vth a plurality of times. With the above diagnostic method, the probability of erroneously diagnosing a charging MOSFET in an abnormal state as normal is reduced.

  In the above embodiment, the value of the overcurrent detected by the overcurrent detection unit can be changed as appropriate, and is preferably set based on the tolerance of the switch element 12 such as a discharge MOSFET. Moreover, in the said embodiment, although the electric potential by the overcurrent detection resistor for detecting an overcurrent was input into the injector drive IC, you may input into a microcomputer.

  In the above embodiment, MOSFETs are used as the charge switch element and the discharge switch element. However, the configuration of these switch elements is not limited to the MOSFET as in the above embodiment, and other field effect transistors or tri-state transistors, etc. , May be changed as appropriate.

  In the above-described embodiment, after provisional determination of a short circuit failure based on detection of overcurrent, it is officially determined whether or not there is a short circuit failure based on failure diagnosis. The processing contents of such failure diagnosis can be changed as appropriate. Moreover, if it is a form which does not need to restore | restore the system | strain stopped operation | movement based on temporary determination, failure diagnosis may not be implemented.

  The functional units for controlling the operation and diagnosing faults such as the booster circuit and the drive circuit can be provided by hardware and software different from the configurations of the injector drive IC and microcomputer of the above embodiment, or a combination thereof. Further, the number of piezo injectors driven by the injection control device may be changed as appropriate.

10 Booster Circuit, 30 Drive Circuit, 31 Charging MOSFET (Charge Switch Element), 32 Discharge MOSFET (Discharge Switch Element), 60 Injector Drive IC (Switch Control Unit), 71 Overcurrent Detection Unit, 72 Voltage Acquisition Unit 73 injection signal control unit (switch control unit) 74 failure determination unit 100 injection control device 110 piezo injector (injection valve) 112 piezoelectric element stack (capacitive load) Vm monitor voltage Vth determination voltage

Claims (7)

An injection control device that drives an injection valve (110) by charging and discharging a capacitive load (112),
A common booster circuit (10) for generating a voltage to be supplied to each capacitive load of the plurality of injection valves;
A charging switch element (31) for controlling a current flowing through the capacitive load, and a discharging switch element (in series) connected to the charging switch element in series to control the discharge of charges accumulated in each capacitive load ( 32), a plurality of drive circuits (30) each having
An overcurrent detector (71) for detecting an overcurrent flowing through the charging switch element;
A switch control unit (60, 73) for turning off the discharge switch element of the system through which an overcurrent flows when an overcurrent is detected by the overcurrent detection unit;
An injection control device comprising: The switch control unit causes the charging switch element to perform a charging operation for charging the capacitive load after the discharging switch element is turned off based on detection of an overcurrent by the overcurrent detection unit,
A voltage acquisition unit (72) for acquiring the voltage of the capacitive load as a monitor voltage (Vm) after the completion of the charging operation by the charging switch element;
The injection control apparatus according to claim 1, further comprising a failure determination unit (74) that determines whether or not the charging switch element is in a failed state based on the monitor voltage acquired by the voltage acquisition unit. .   The injection control according to claim 2, wherein the failure determination unit determines that the charging switch element has failed when the monitor voltage is higher than a determination voltage (Vth) set for failure determination. apparatus.   The injection control device according to claim 3, wherein the failure determination unit determines that the charging switch element is normal when the monitor voltage is lower than the determination voltage. The voltage acquisition unit repeatedly acquires the monitor voltage of the capacitive load after completion of the charging operation,
The failure determination unit determines that the charging switch element is not short-circuited when the monitor voltage repeatedly acquired by the voltage acquisition unit drops below the determination voltage even once. Or the injection control apparatus of 4. When the charging switch element and the discharging switch element are both turned on, an overcurrent flowing through the charging switch element and the discharging switch element is defined as a through current,
When the through current flows through the discharge switch element, the time when the discharge switch element fails is defined as a failure time.
6. The switch control unit according to claim 1, wherein the switch control unit turns off the discharge switch element before the failure time elapses after the overcurrent is detected by the overcurrent detection unit. Injection control device.   The injection according to any one of claims 1 to 6, wherein the switch control unit turns off the discharge switch element before 10 μsec elapses after the overcurrent is detected by the overcurrent detection unit. Control device.

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