JP6191496B2 - Fuel injection valve drive device - Google Patents

Description

  The present invention relates to a fuel injection valve driving device.

As a fuel injection valve (injector) for injecting fuel into each cylinder of an engine mounted on a vehicle, there is one that opens by energizing a coil.
An apparatus for driving this type of fuel injection valve includes a DCDC converter that boosts the battery voltage of a vehicle and charges a capacitor, and a control unit that operates the DCDC converter so that the charging voltage of the capacitor becomes a target voltage. In this type of device, at the start of driving of the fuel injection valve (at the start of the drive period), the opening of the fuel injection valve is accelerated by discharging from the capacitor to the coil of the fuel injection valve. After the end of the discharge, a constant current is passed from the battery voltage to the coil until the driving period ends (see, for example, Patent Document 1).

  In addition, in an engine mounted on a vehicle, in order to achieve highly efficient combustion for the purpose of reducing exhaust gas, a plurality of fuel injections by a fuel injection valve are performed during a single fuel injection period (for example, compression to combustion stroke) of a cylinder. There is a technology to be implemented once. The technique is called multistage injection, and the number of fuel injections performed in the multistage injection is called the number of injection stages (or simply, the number of stages).

  In the fuel injection valve driving apparatus that performs such multi-stage injection, energy is supplied (released) a plurality of times in a short time from the capacitor to the coil of the fuel injection valve. For this reason, the electrostatic capacity of the capacitor (hereinafter, also simply referred to as “capacitance”) requires, for example, the maximum number of stages of fuel injection in terms of engine control even if there is no charge since the start of multi-stage injection. It is set to a large value so that it can be implemented with accuracy.

JP 2013-160260 A

  Increasing the capacity of the capacitor increases the size of the capacitor and sometimes requires a plurality of capacitors. This leads to an increase in the size of the fuel injection valve drive device.

  Further, assuming that the capacitance of the capacitor is C and the charging voltage of the capacitor is V, energy stored in the capacitor (hereinafter also referred to as stored energy) is represented by “C × V × V / 2”. Therefore, the stored energy can be increased even if the charging voltage is increased. However, when the charging voltage is increased, the operating frequency of the DCDC converter increases, and therefore switching loss in the DCDC converter increases.

  Therefore, an object of the present invention is to realize a reduction in the capacity of a capacitor while suppressing a switching loss in a DCDC converter in a fuel injection valve driving device.

  According to a first aspect of the present invention, there is provided a fuel injection valve driving device comprising: a capacitor for storing energy to be discharged in a coil of a fuel injection valve; a DCDC converter for boosting a power supply voltage to charge the capacitor; Charging control means for operating the DCDC converter so as to become, a discharge switch for connecting the capacitor upstream of the coil in an energization path for flowing current to the coil, and driving of the fuel injection valve Discharge control means for supplying a discharge current for quickly opening the fuel injection valve from the capacitor to the coil by turning on the discharge switch at the start.

  Further, the fuel injection valve drive device includes a voltage changing unit, and the voltage changing unit controls the DCDC converter by the charge control unit according to the number of fuel injection stages to be performed by the fuel injection valve. The target voltage used for is changed. That is, in this fuel injection valve drive device, the target voltage (and hence the charging voltage) of the capacitor charging voltage is changed in accordance with the number of fuel injection stages to be performed.

  For this reason, there is no need to increase the capacity of the capacitor or to always set the target voltage of the charging voltage to a large value, and the number of multistage injection stages to be implemented from now on is large, and the energy stored in the capacitor is increased. Only when it has to be done can the charge voltage of the capacitor be increased to increase the stored energy. Therefore, it is possible to reduce the capacity of the capacitor (and hence downsize the fuel injection valve driving device) while suppressing the switching loss in the DCDC converter.

  In addition, the code | symbol in the parenthesis described in the claim shows the correspondence with the specific means as described in embodiment mentioned later as one aspect, Comprising: The technical scope of this invention is limited is not.

It is a block diagram showing the structure of the fuel-injection control apparatus (ECU) of embodiment. It is a time chart explaining operation | movement of a current control part. It is a flowchart showing a target voltage control process. It is explanatory drawing explaining the predetermined temperature TP in FIG. It is explanatory drawing explaining an accuracy guarantee minimum voltage. It is explanatory drawing explaining that valve closing delay time becomes long by the fall of a charging voltage. It is explanatory drawing explaining the effect | action of embodiment.

Hereinafter, a fuel injection control device as a fuel injection valve driving device of an embodiment will be described with reference to the drawings.
The fuel injection control device (hereinafter referred to as ECU) of the present embodiment has four fuel injectors for supplying fuel to each cylinder # 1 to # 4 of a multi-cylinder (4 cylinders in this example) engine mounted on a vehicle (automobile). An injector as a fuel injection valve is driven. Then, the ECU controls the fuel injection timing and the fuel injection amount to each of the cylinders # 1 to # 4 by controlling the energization start timing and the energization time to the coils of each injector. In this embodiment, the transistor (switching element) as a switch is, for example, a MOSFET, but may be another type of transistor such as a bipolar transistor or IGBT (insulated gate bipolar transistor).

  As shown in FIG. 1, the ECU 1 of the present embodiment includes a terminal 5 to which one end (upstream side) of the coil 2a of the injector 2 is connected, a terminal 7 to which the other end (downstream side) of the coil 2a is connected, A transistor T10 having one output terminal connected to the terminal 7 and a current detection resistor R10 connected between the other output terminal of the transistor T10 and the ground line are provided. The ground line is a reference potential (= 0V) line.

  In the injector 2, when the coil 2a is energized, a valve body (not-shown nozzle needle) (not shown) moves to the valve opening position (that is, opens), and fuel injection is performed. When the energization of the coil 2a is interrupted, the valve body returns to the original closed position (that is, closes), and fuel injection is stopped.

  FIG. 1 shows only one injector 2 corresponding to the n-th cylinder #n (n is any one of 1 to 4) out of the four injectors 2. In the following, the one injector 2 is shown. The driving will be described. Actually, the terminal 5 is a common terminal for the plurality of injectors 2. The terminal 7 and the transistor T10 are provided for each injector 2 (in other words, for each cylinder). The transistor T10 is a switch for selecting the injector 2 to be driven (in other words, the cylinder to be injected), and is also called a cylinder selection switch.

  The ECU 1 includes a transistor T11 as a constant current switch having one output terminal connected to a power supply line Lp to which a battery voltage (a voltage at the plus terminal of the in-vehicle battery) VB as a power supply voltage is supplied, and a transistor T11 A backflow prevention diode D11 having an anode connected to the other output terminal and a cathode connected to the terminal 5; a current return diode D12 having an anode connected to the ground line and a cathode connected to the terminal 5; And a capacitor C0 in which energy discharged in the coil 2a is stored, and a DCDC converter 21 as a charging circuit for boosting the battery voltage VB and charging the capacitor C0.

  The DCDC converter 21 includes a boosting coil L0 having one end connected to the power supply line Lp, a transistor T0 as a boosting switch provided in series on a path between the other end of the coil L0 and the ground line, The anode is connected to a current path connecting the resistor R0 for current detection provided between the transistor T0 and the ground line, and the other end of the coil L0 and the terminal on the coil L0 side (drain in this example) of the transistor T0. And a backflow prevention diode D0.

  The capacitor C0 is provided in series on the path between the cathode of the diode D0 and the ground line. The capacitor C0 is an aluminum electrolytic capacitor, for example, but may be another type of capacitor.

  In the DCDC converter 21, when the transistor T0 is turned on / off, a flyback voltage (back electromotive voltage) higher than the battery voltage VB is generated at the connection point between the coil L0 and the transistor T0. Capacitor C0 is charged through diode D0. For this reason, the capacitor C0 is charged with a voltage higher than the battery voltage VB.

  The ECU 1 further includes a transistor T12 as a discharge switch for connecting the positive electrode side of the capacitor C0 to the terminal 5, and an energy recovery diode D13 having an anode connected to the terminal 7 and a cathode connected to the positive electrode side of the capacitor C0. Then, the drive control circuit 23 that controls the transistors T0, T10, T11, and T12 and the voltage on the positive side of the capacitor C0 (that is, the charging voltage of the capacitor C0) VC are divided by a predetermined ratio and input to the drive control circuit 23. Two voltage dividing resistors R1, R2 to be performed, a temperature detection circuit 25 for detecting the temperature of the transistor T12, and a microcomputer (microcomputer) 27 are provided.

  The drive control circuit 23 is, for example, an IC, and controls the DCDC converter 21 (specifically, the transistor T0) and the current flowing in the coil 2a by controlling the transistors T10, T11, and T12 (hereinafter, referred to as the transistor T0). A current control unit 23b that controls the load voltage, and a target voltage control unit 23c that commands the target voltage VT of the charging voltage VC to the charge control unit 23a.

  The temperature detection circuit 25 includes, for example, a temperature detection diode provided near the transistor T12. The forward voltage of the diode (or a voltage obtained by amplifying the forward voltage) is used as the temperature of the transistor T12. The detected temperature detection signal is output to the drive control circuit 23. The temperature detection circuit 25 may be, for example, a circuit that divides a constant voltage by a thermistor and a resistor provided near the transistor T12. In this case, the constant voltage is divided by the thermistor and the resistor. This voltage becomes a temperature detection signal.

  Although not shown, the microcomputer 27 includes a CPU that executes a program, a ROM that stores a program, fixed data, and the like, a RAM that stores a calculation result by the CPU, and the like.

  Further, the microcomputer 27 receives a signal representing the engine speed NE, a signal representing the accelerator opening ACC by the vehicle driver, a signal representing the engine coolant temperature THW, and the like. Then, the microcomputer 27 generates an injection command signal for each cylinder based on the operating state of the engine detected by various input signals, and outputs it to the drive control circuit 23.

  The injection command signal means that the coil 2a of the injector 2 is energized (in other words, the injector 2 is opened) only when the level of the signal is the active level (for example, high in the present embodiment). . For this reason, the microcomputer 27 sets an energization period (which is also a drive period of the injector 2) to the coil 2a of the injector 2 for each cylinder based on the engine operation information, and only the energization period of the corresponding cylinder is set. It can be said that the injection command signal is set to high.

  The microcomputer 27 determines the number of stages of fuel injection to be performed based on the operating state of the engine. That the determined number of stages is 2 or more means that it is determined that multistage injection is to be performed, and that the determined number of stages is 1 does not perform multistage injection (that is, one stage that is non-multistage injection). Means that the injection is to be carried out.

  If the microcomputer 27 decides to perform the multi-stage injection, the multi-stage injection is performed from now before the timing of outputting the first (first stage) injection command signal for the multi-stage injection. Stage number information indicating the number of injection stages (for example, data of a plurality of bits indicating the number of injection stages) is output to the drive control circuit 23. Further, even when the microcomputer 27 decides to perform the first stage injection, the stage number information indicating that the number of injection stages is 1 is driven before the timing of outputting the injection command signal for the first stage injection. Output to the control circuit 23.

  On the other hand, in the drive control circuit 23, the charge control unit 23a detects the charge voltage VC of the capacitor C0 based on the voltage generated at the connection point between the voltage dividing resistors R1 and R2. Then, the charging control unit 23a turns on / off the transistor T0 of the DCDC converter 21 so that the detected charging voltage VC becomes the target voltage VT. The target voltage VT is higher than the battery voltage VB and is switched between two values by a target voltage control unit 23c described later.

  For example, when the charging control unit 23a determines that the charging voltage VC is equal to or lower than the lower limit (= VT−α) that is lower than the target voltage VT by a predetermined value (for example, 5% of VT) α, the charging voltage VC becomes the target voltage. Until it is determined that the voltage is equal to or higher than VT, on / off control of the transistor T0 is performed to charge the capacitor C0. In addition, as the on / off control of the transistor T0, the charge control unit 23a, for example, turns on the transistor T0 and then flows to the coil L0 via the current detected by the voltage generated in the resistor R0 (that is, the transistor T0). When the current reaches a predetermined value, the control of turning off the transistor T0 for a predetermined time and turning it on again is repeated.

  As will be described later, when energization of the coil 2a is started (when driving of the injector 2 is started), the current control unit 23b turns on the transistor T12 and discharges it from the capacitor C0 to the coil 2a. The unit 23a charges the capacitor C0 when discharging from the capacitor C0 to the coil 2a (hereinafter also simply referred to as discharge) is not performed. However, during the implementation period of multistage injection (see FIG. 5 or FIG. 7), the injection interval is shortened and the period in which discharge is not performed is also shortened. For this reason, for example, when multi-stage injection is performed, the charging control unit 23a starts the final stage from the timing at which discharge for the first stage injection is started (see t1 in FIG. 5 or FIG. 7). The capacitor C0 is not charged until the timing at which the discharge for injecting is completed (see t2 in FIG. 5 or FIG. 7).

Next, the operation of the current control unit 23b in the drive control circuit 23 will be described with reference to FIG.
As shown in FIG. 2, when the injection command signal S # n of the nth cylinder #n output from the microcomputer 27 is high, the current control unit 23b is in a state where the injection command signal S # n is high. Then, the transistor T10 corresponding to the injector 2 of the nth cylinder #n is turned on. In addition, when the injection command signal S # n becomes high, the current control unit 23b also turns on the transistor T12.

Then, the positive electrode side of the capacitor C0 is connected to the terminal 5, and the capacitor C0 is discharged to the coil 2a, and energization of the coil 2a is started by this discharge.
Then, after the transistor T12 is turned on, the current control unit 23b detects the load current (the current flowing through the coil 2a and the drive current of the injector 2) from the voltage generated in the resistor R10, and the load current is the discharge current. When the target maximum value ip (for example, 12A) is detected, the transistor T12 is turned off.

  In this way, at the start of energization of the coil 2a, the energy accumulated in the capacitor C0 is discharged to the coil 2a. In this example, the discharge current from the capacitor C0 to the coil 2a until reaching the target maximum value ip is a so-called peak current for quickly opening the injector 2. For example, a configuration in which the transistor T12 is turned on only for a predetermined time may be employed.

  Then, after turning off the transistor T12, the current control unit 23b turns on / off the transistor T11 so that the load current detected by the voltage generated in the resistor R10 becomes a constant current smaller than the target maximum value ip. Perform constant current control to turn off.

  More specifically, the current control unit 23b turns on the transistor T11 when detecting that the load current is lower than the lower threshold icL, and turns off the transistor T11 when detecting that the load current is higher than the upper threshold icH. Control is performed. The magnitude relationship among the lower threshold value icL, the upper threshold value icH, and the target maximum value ip is “ip> icH> icL” as shown in FIG.

  With such constant current control, when the load current decreases from the target maximum value ip and falls below the lower threshold value icL, the transistor T11 is repeatedly turned on / off, and the average value of the load current becomes equal to icH and icL. Is maintained at a constant current ic.

  Note that the constant current flowing through the coil 2a may be switched in two stages from the first constant current to the second constant current smaller than the first constant current. Further, when the transistor T11 is turned on, a current flows to the coil 2a from the power supply line Lp side through the transistor T11 and the diode D11. When the transistor T11 is turned off, the current flows back from the ground line side through the diode D12. Further, as shown in the second stage from the bottom in FIG. 2, for a while after the injection command signal S # n becomes high (specifically, until the coil current reaches the upper threshold icH), the transistor T11 Is turned on by the constant current control.

  Thereafter, when the injection command signal S # n from the microcomputer 27 changes from high to low, the current control unit 23b turns off the transistor T10 and ends the on / off control (constant current control) of the transistor T11. T11 is also kept off.

Then, energization to the coil 2a is stopped, the injector 2 is closed, and fuel injection by the injector 2 is completed.
Further, when the injection command signal S # n becomes low and both the transistor T10 and the transistor T11 are turned off, flyback energy is generated in the coil 2a, but the flyback energy (that is, remaining in the coil 2a). Energy) is recovered in the form of current to the capacitor C0 through the diode D13 forming the energy recovery path.

The injectors 2 other than the nth cylinder #n are also driven in the same procedure as described above.
Next, the target voltage control unit 23c in the drive control circuit 23 will be described.
The target voltage control unit 23 c performs the target voltage control process shown in FIG. 3 every time the above-described stage number information is output from the microcomputer 27 to the drive control circuit 23.

As shown in FIG. 3, the target voltage control unit 23c determines whether or not the injection stage number indicated by the stage number information output from the microcomputer 27 is equal to or greater than a predetermined value N (for example, 4) (S110).
When the target voltage control unit 23c determines that the number of injection stages is equal to or greater than the predetermined value N (S110: YES), the target voltage control unit 23c calculates the temperature of the transistor T12 based on the temperature detection signal from the temperature detection circuit 25. It is determined whether the temperature is equal to or higher than a predetermined temperature TP (for example, 30 ° C.) (S120). Since the voltage value of the temperature detection signal has a correlation with the temperature of the transistor T12, the target voltage control unit 23c compares the voltage value of the temperature detection signal with a predetermined threshold value, thereby determining the temperature of the transistor T12. You may determine whether it is more than predetermined temperature TP. For example, when the forward voltage of the temperature detection diode is a temperature detection signal, the voltage value of the temperature detection signal has a negative correlation with the temperature of the transistor T12. Therefore, in this case, the target voltage control unit 23c can be configured to determine that the temperature of the transistor T12 is equal to or higher than the predetermined temperature TP if the voltage value of the temperature detection signal is equal to or lower than the predetermined threshold.

  When the target voltage control unit 23c determines that the temperature of the transistor T12 is equal to or higher than the predetermined temperature TP (S120: YES), the charge control unit 23a uses the target voltage VT used for the control of the DCDC converter 21. Of the two types of the first voltage V1 and the second voltage V2, the larger second voltage V2 (for example, 55V) is set (S130).

  Further, when the target voltage control unit 23c determines that the number of injection stages is not equal to or higher than a predetermined value N (for example, 4) (S110: NO), or when it determines that the temperature of the transistor T12 is not equal to or higher than the predetermined temperature TP. (S120: NO), the target voltage VT is set to the smaller first voltage V1 (for example, 45V) of the first voltage V1 and the second voltage V2 (S140).

Next, the predetermined temperature TP used in the determination of S120 will be described with reference to FIG.
Although the charging voltage VC is applied to the transistor T12, as shown in FIG. 4, there is a correlation between the breakdown voltage and the temperature of the transistor T12, and the breakdown voltage decreases as the temperature decreases.

  Further, of the first voltage V1 and the second voltage V2 set as the target voltage VT of the charging voltage VC, the first voltage V1 is an assumed lowest temperature of the transistor T12 (a lowest temperature assumed in designing the ECU 1, For example, the voltage is smaller than the withstand voltage at −30 ° C.). For this reason, the first voltage V1 is smaller than the breakdown voltage of the transistor T12 in the entire temperature region assumed in designing the ECU 1. On the other hand, the second voltage V2 is a voltage that exceeds the breakdown voltage when the temperature of the transistor T12 is lower than the specific temperature TPa.

  For this reason, the predetermined temperature TP is set to a value equal to or higher than the specific temperature TPa (in the example of FIG. 4, it is set to a value larger than TPa). Therefore, when it is determined YES in S120 of FIG. 3 and the target voltage VT is set to the second voltage V2, it is possible to prevent the charging voltage VC (= V2) from exceeding the breakdown voltage of the transistor T12. .

Next, the effect of the ECU 1 will be described.
First, as shown in FIG. 5, when multistage injection is performed, discharge from the capacitor C0 to the coil 2a is performed at each stage of injection, and the charging voltage VC of the capacitor C0 decreases. In FIG. 5 and FIG. 7 to be described later, the period during which the load current is increasing is the period during which the discharge from the capacitor C0 to the coil 2a is performed (that is, the ON period of the transistor T12). Although illustration is omitted, when multi-stage injection of a plurality of cylinders is performed in parallel, the amount of decrease in the charging voltage VC is further increased.

  Then, as shown in FIG. 5, when the charging voltage VC decreases and becomes less than the predetermined accuracy guarantee minimum voltage Vmin, the valve closing delay time of the injector 2 is longer than a prescribed value required for engine control. It can be long. The valve closing delay time is the time from the falling timing of the injection command signal (change timing from high to low) to the closing timing at which the injector 2 actually closes, as shown in FIG. It is. The valve closing delay time becomes longer due to the delay of the valve closing timing.

  More specifically, as described above, when the injection command signal changes from high to low, the ECU 1 recovers the energy remaining in the coil 2a to the capacitor C0 through the diode D13. At the time of energy recovery, a path through which current flows is “downstream side of coil 2a → diode D13 → capacitor C0 → ground line → diode D12 → upstream side of coil 2a”. Then, by recovering energy from the coil 2a to the capacitor C0, the residual energy of the coil 2a is lost, and the injector 2 is quickly closed.

  At the time of this energy recovery, as shown in FIG. 6, the lower the voltage VL downstream of the coil 2a, the smaller the amount of current recovered from the coil 2a to the capacitor C0. As a result, the remaining energy of the coil 2a The time until disappearance becomes longer, and the valve closing delay time of the injector 2 becomes longer. The voltage VL on the downstream side of the coil 2a is the same as the charging voltage VC of the capacitor C0 if the forward voltage of the diode D13 is ignored. Therefore, the lower the charging voltage VC at the time of the falling of the injection command signal, the longer it takes for the energy of the coil 2a to disappear, and the longer the valve closing delay time of the injector 2.

  From the above, the capacity of the capacitor C0 and the target voltage VT of the charging voltage VC should be set so that the charging voltage VC is equal to or higher than the minimum voltage Vmin with guaranteed accuracy even when the multi-stage injection with the maximum number of stages is performed by design. It is.

  In order to realize this, either of increasing the capacitance of the capacitor C0 or increasing the charging voltage VC can be considered. This is because even if the capacity of the capacitor C0 is reduced, if the charging voltage VC is increased, the energy required for multistage injection can be stored in the capacitor C0. Specifically, if the capacity of the capacitor C0 is reduced, the amount of decrease in the charging voltage VC for each one-stage injection increases when multi-stage injection is performed, but the charge voltage VC before the start of multi-stage injection is increased. Thus, it is possible to prevent the charging voltage VC at the end of the final stage injection from being lower than the lowest accuracy guaranteed minimum voltage Vmin.

  Here, when the capacity of the capacitor C0 is increased, the size of the capacitor C0 is increased, and as a result, the ECU 1 is increased in size. For this reason, instead of reducing the capacity of the capacitor C0, it is conceivable to increase the target voltage VT of the charging voltage VC so that the charging voltage VC before the start of multistage injection increases.

  However, if the configuration in which the target voltage VT is always set to a large value is adopted, power is wasted when performing one-stage injection or when performing multi-stage injection with a small number of stages. That is, if the target voltage VT is set to a large fixed value, the operating frequency of the DCDC converter 21 increases even when the charging voltage VC does not need to be increased. Therefore, the switching loss in the DCDC converter 21 (specifically, the transistor T0 (Loss due to on / off) increases.

  Therefore, in the ECU 1, when the number of fuel injection stages to be performed is determined, the target voltage control unit 23c determines the target charging voltage VC according to the determined number of injection stages (that is, the number of fuel injection stages to be performed from now on). The voltage VT is changed.

  Specifically, when the injection stage number is less than a predetermined value N, the target voltage control unit 23c sets the target voltage VT to the smaller first voltage V1 (S140), and the injection stage number is equal to or greater than the predetermined value N. If so, the target voltage VT is set to the larger second voltage V2 (S130).

  The first voltage V1 is a value at which the charging voltage VC does not become less than the minimum accuracy guaranteed voltage Vmin if the number of fuel injection stages to be performed is less than the predetermined value N. On the other hand, the second voltage V2 is a value at which the charging voltage VC does not become less than the guaranteed minimum voltage Vmin even if the number of fuel injection stages to be performed is equal to or greater than the predetermined value N.

  For this reason, for example, as shown in FIG. 7, the number of injection stages of the next fuel injection is equal to or greater than a predetermined value N at time t0 after the previous fuel injection with the number of injection stages less than a predetermined value N (for example, 4). If it is determined in this example that it is 5), the target voltage control unit 23c increases the target voltage VT from the first voltage V1 to the second voltage V2. Then, the charging control unit 23a operates the DCDC converter 21 until the charging voltage VC increases from the first voltage V1 to the second voltage V2. That is, the capacitor C0 is additionally charged from the first voltage V1 to the second voltage V2. Since the multi-stage injection is performed in a state where the charging voltage VC is increased to the second voltage V2, the charging voltage VC is equal to or higher than the minimum voltage Vmin for which the accuracy is guaranteed even at the end of the fifth stage injection. Is ensured and, as a result, a specified valve closing delay time is realized.

  According to such an ECU 1, there is no need to increase the capacity of the capacitor C0 or to always set the target voltage VT of the charging voltage VC to a large value, and the number of injection stages of multistage injection to be performed from now on is large. Only when the energy stored in the capacitor C0 needs to be increased, the stored voltage can be increased by increasing the charging voltage VC. Therefore, it is possible to reduce the capacity of the capacitor C0 (and thus reduce the size of the ECU 1) while suppressing the switching loss in the DCDC converter 21.

  Further, the target voltage control unit 23c changes the target voltage VT according to not only the number of injection stages but also the number of injection stages and the temperature of the transistor T12. Specifically, the target voltage VT is increased when the number of injection stages is equal to or higher than the predetermined value N and the temperature of the transistor T12 is equal to or higher than the predetermined temperature TP (specifically, the first voltage is set). V1 is changed to a second voltage V2 larger than the first voltage V1). For this reason, when the target voltage VT is set to the second voltage V2, it is possible to prevent the charging voltage VC from exceeding the withstand voltage of the transistor T12.

  In the case where the temperature of the transistor T12 is lower than the predetermined temperature TP and the multi-stage injection with the injection stage number equal to or greater than the predetermined value N is performed, the charging voltage VC may be lower than the minimum accuracy guaranteed voltage Vmin. . However, it is considered that by performing the fuel injection, the temperature of the transistor T12 increases and becomes equal to or higher than the predetermined temperature TP. Therefore, it is very rare that the injection accuracy does not reach the accuracy required for engine control, and it is not considered to be a big problem.

As mentioned above, although embodiment of this invention was described, this invention can take a various form, without being limited to the said embodiment. The above-mentioned numerical values are also examples, and other values may be used.
As a modification, for example, when it is not necessary to consider that the charging voltage VC exceeds the withstand voltage of the transistor T12, the target voltage control unit 23c does not use the temperature of the transistor T12, but only according to the number of injection stages. It can be configured to change the voltage VT. Specifically, the determination in S120 in FIG. 3 can be deleted, and the target voltage control unit 23c can be configured to perform the process in S130 as it is when it is determined YES in S110 in FIG.

Further, the target voltage VT is not limited to two, and may be configured to be changed (switched) to any of three or more values.
Further, the data map for setting the target voltage VT using the number of injection stages and the temperature of the transistor T12 as parameters, and data indicating that the target voltage VT is increased as the number of injection stages is higher and the temperature is higher. The map may be stored in a memory, and the target voltage control unit 23c may be configured to set the target voltage VT based on the data map. In that case, only the number of injection stages may be used as a parameter for setting the target voltage VT.

  Further, the microcomputer 27 may be provided in a device outside the ECU 1. The drive control circuit 23 may be a microcomputer, and in that case, the drive control circuit 23 may be configured to have the function of the microcomputer 27.

The above modifications can be combined as appropriate.
In addition, the functions of one component in the above embodiment may be distributed as a plurality of components, or the functions of a plurality of components may be integrated into one component. Further, at least a part of the configuration of the above embodiment may be replaced with a known configuration having the same function. Moreover, you may abbreviate | omit a part of structure of the said embodiment as long as a subject can be solved. In addition, all the aspects included in the technical idea specified by the wording described in the claims are embodiments of the present invention.

  In addition to the ECU described above, the present invention can be implemented in various forms such as a system including the ECU as a constituent element, a program for causing a computer to function as the ECU, a medium storing the program, and a method for driving the fuel injection valve. It can also be realized.

  DESCRIPTION OF SYMBOLS 2 ... Injector (fuel injection valve), 2a ... Coil, C0 ... Capacitor, 21 ... DCDC converter, 23a ... Charge control part (charge control means), T12 ... Transistor (discharge switch), 23b ... Current control part (discharge control) Means), 23c... Target voltage control section (voltage changing means)

Claims (1)

A capacitor (C0) in which energy to be discharged is stored in the coil (2a) of the fuel injection valve (2);
A DCDC converter (21) for boosting a power supply voltage and charging the capacitor;
Charging control means (23a) for operating the DCDC converter so that the charging voltage of the capacitor becomes a target voltage;
A discharge switch (T12) for connecting the capacitor to the upstream side of the coil in the energization path for flowing current to the coil;
A discharge control means (23b) for supplying a discharge current for quickly opening the fuel injection valve from the capacitor to the coil by turning on the discharge switch at the start of driving of the fuel injection valve; ,
In a fuel injection valve drive device comprising:
The discharge switch is a transistor,
Temperature detecting means (25) for detecting the temperature of the discharging switch;
When the number of fuel injection stages to be performed by the fuel injection valve is equal to or greater than a predetermined value and the temperature detected by the temperature detection means is equal to or higher than a predetermined temperature, the charge control means is used for controlling the DCDC converter. the voltage changing means for the target voltage is increased (23c, S110~S140) comprise a, a,
A fuel injection valve driving device.

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