JPH0726701B2 - Solenoid valve drive circuit - Google Patents

Description

[Field of Industrial Application] The present invention relates to an electromagnetic valve for driving an electromagnetic valve operated by a vehicle-mounted power source, such as an electromagnetic valve of an electronically controlled fuel injection device or an anti-skid control device. It relates to a valve drive circuit.

"Prior Art" Recently, electronic control of automobiles has progressed, and various electronically controlled fuel injection devices have been developed for diesel engines and gasoline engines. In many of these devices, the fuel injection amount and the fuel injection timing are determined by controlling the valve opening period and valve closing period of the solenoid valve, or the valve opening timing and valve closing timing. For example, for gasoline engines, there are known electronic fuel injection systems. For a diesel engine, the fuel metering device shown in FIG. 8 has been invented,
The overflow of fuel is controlled by a solenoid valve (Japanese Patent Laid-Open No. 58-187).
537). That is, the amount of fuel injected into the engine through the nozzle is adjusted by controlling the overflow of the fuel pressurized by the plunger 23 that rotates and reciprocates by the face cam 22 with the solenoid valve 21. Further, as shown in FIG. 9, there is also an example in which a constant high pressure is applied to a classical injector and the lift of the needle is controlled by a solenoid valve (in this case, a three-way valve) (JP-A-59-165858). ). That is, when the solenoid valve (three-way valve) 31 is not energized, the port X and the port Y are connected, the high-pressure fuel is guided to the upper portion of the piston 33, and the pressure prevents the needle 32 from lifting. When the solenoid valve 31 is energized, the port X is closed and the port Y and the port Z are connected, so the pressure applied to the piston 33 is the port.
Leak to the low pressure side via Y and port Z. Therefore, the needle 32 is lifted by the fuel pressure and injects the fuel.

In the system as described above, the operation of the solenoid valves 21 and 31 is closely related to the fuel injection amount and the injection timing, and the on-delay and the off-delay of the solenoid valve depend on the control timing deviation and the fuel injection amount control accuracy. It will lead to the deterioration of. In particular, in a fuel injection system for a diesel engine, the fuel injection pressure is generally high, so the delay in the operation of the solenoid valve leads to a larger fuel injection amount error.

The present invention relates to a drive circuit for operating a solenoid valve at high speed in the system as described above, and is particularly applied to a fuel injection system for a diesel engine that requires high speed. However, the scope of application of the present invention is
Not only the fuel injection system for a diesel engine, but also an electronic fuel injection system and a vehicle control system such as an anti-skid control device can be expected to have excellent effects such as improved control accuracy.

Various drive circuits have been considered in order to move a solenoid valve that operates with a low-voltage battery for vehicle installation as a power source at high speed. Among them, in order to reduce the rise delay of the current due to the inductance L and the resistance R of the solenoid coil, a high voltage exceeding the battery voltage is generated, and that voltage is used when the valve is opened (pull-in) to achieve a fast drive current rise. And there is an example of realizing the quick opening of the solenoid valve. Furthermore, as seen in JP-A-59-85434,
There is an example in which a high voltage is generated intermittently before the operation of the solenoid valve in order to downsize the high voltage power supply and reduce the energy consumption.

FIG. 10 shows a block diagram of a conventional solenoid valve drive circuit using high voltage. The energy stored in the coil 41 is transferred to the capacitor 43 as high voltage storage means by controlling the transistor 42 to be turned on and off. Further, the detection circuit 44 detects the voltage accumulated in the capacitor 43,
Feedback control is performed to keep the accumulated high voltage constant. In such an example, since a high voltage is detected and feedback control is performed, the processing circuit is complicated. In addition, in applications such as engine control, the operation of the solenoid valve is generally synchronized with the engine speed, and the operation interval becomes longer in the low speed rotation range and at startup, so the accumulated high voltage is detected. It was gradually consumed by the voltage dividing resistance circuit of the part, and it was necessary to add energy as needed even after the target high voltage was once accumulated. Furthermore, when a capacitor is used as the energy storage means, generally, the temperature change of the capacitor and the change in capacitance due to aging are very large, and even if the charge voltage is controlled to be constant, the stored energy cannot be made constant. Also, as set forth in Japanese Patent Laid-Open No. 59-85434, if the charging is set to be performed by switching several times (2 to 4 times), the amount of energy to be stored in one charging becomes large and the charging voltage is changed. There was a problem that even if it was fed back, fine voltage control could not be performed.

[Problems to be Solved by the Invention] The present invention has been conceived in order to solve the above problems, and provides a solenoid valve drive circuit that can shorten the response delay of a solenoid valve and has a simple configuration. The purpose is to do.

"Means for Solving Problems" For the above purpose, according to the present invention, a high voltage generating means for applying a high voltage at the start of energization of a solenoid valve, a high voltage generating means exceeding a vehicle-mounted power supply voltage, and a solenoid valve are operated. The high voltage generating means includes a constant current circuit for flowing a constant current for holding a state and a switching circuit for controlling opening / closing of a solenoid valve, and the high voltage generating means stores a coil for temporarily storing energy and a high voltage. And a control circuit for transferring the energy stored in the coil to the high voltage storage means.The control circuit temporarily stores the energy in the coil when the current flowing in the coil reaches a set value. Energy
There is provided a solenoid valve drive circuit which operates so as to be transferred to the high-voltage storage means, and further performs this operation at least once before starting energization of the solenoid valve.

[Operation] According to the above configuration of the present invention, energy previously measured as a current value and stored in the coil is converted into a high voltage and stored in the capacitor, and is discharged when the valve is opened. Response delay is shortened. Moreover, since a constant current is passed through a coil with a small inductance variation to measure the energy and store the energy in the capacitor, there is little variation in the responsiveness of the solenoid valve even if the battery voltage or the operating environment of the system changes.

“Embodiment” According to the first embodiment of the present invention, the control circuit of the high voltage generating means is configured such that the current flowing through the coil is set to a set value as a timing for transferring the energy accumulated in the coil to the high voltage accumulating means. In addition to the above, there is provided a solenoid valve drive circuit characterized in that it is performed even when a set time has elapsed since the current started to flow through the coil. According to the first aspect, in a special case such as when the engine is started, it is possible to apply a voltage higher than the battery voltage to the solenoid valve even when the battery voltage significantly decreases.

According to a second embodiment of the present invention, the high voltage generating means generates a high voltage exceeding a battery voltage when all the solenoid valves are not energized. Provided. According to the second aspect, there is an advantage that the high voltage exceeding the battery voltage is surely stored in the high voltage storage means at the time of energizing the solenoid valve.

[Embodiment] Next, a first embodiment of the present invention will be described with reference to FIGS. 1 and 2.

In FIG. 1 (a), a block 10 is a high voltage generator, and a block 20 is a drive controller for the solenoid valve V and a block 30.
Is a constant current circuit unit for supplying the hold current IH after the pull-in of the solenoid valve V. The high voltage generator 10 includes a charge current control circuit 11 and a current detection circuit 12. A drive pulse τ for controlling ON / OFF of the solenoid valve V is applied to the terminal 1. A charge pulse PLS for operating the high voltage generator 10 is applied to the terminal 2. In the first embodiment, the drive pulse τ and the charge pulse PLS
Is output in an appropriate phase by the arithmetic unit 40 that calculates the fuel injection amount and fuel injection timing of the engine. That is,
Prior to the driving pulse τ, the high voltage generator 10 that receives the charge pulse PLS switches the current flowing through the coil L1 for temporarily storing energy,
A high voltage is generated in the capacitor C1 which is a high voltage storage means. As shown in the waveform of the charge voltage in FIG. 1B, in this embodiment, the voltage is boosted in two steps. The circuit and operation of the high voltage generator 10 are the main improvements of the present invention and will be described in detail later. In the drive control unit 20, when the drive pulse τ becomes a high voltage, the MOS field effect transistor FET1 becomes conductive. This field effect transistor
When the FET1 becomes conductive, the electric charge accumulated in high voltage in the capacitor C1 rapidly discharges through the diode D3, the solenoid valve V, the MOS field effect transistor FET1 and the resistor R1. Therefore, the current IV flowing through the solenoid valve V also rapidly. Reachs the rising peak current IP. When the discharge is completed, the current IV gradually decays and the preset hold current IH
Reach the level of. The level of this hold current IH is a level at which the attraction force sufficient to maintain the state after opening the valve can be generated, heat generation can be reduced, and when the MOS field effect transistor FET1 is off, the current decays sufficiently quickly. Is set to. After the peak current IP is attenuated to the hold current IH, a constant hold current is applied to hold the solenoid valve V.
IH is supplied to the solenoid valve V from the constant current circuit unit 30. This constant current circuit unit 30 detects the solenoid valve current IV by the resistor R1 and feeds it back, and a known chopper type (switching type) constant current circuit can be used, and the hold current IH
Is a solenoid valve V through diode D1 or diode D2.
Supplied. When the drive pulse τ becomes low potential, the MOS field effect transistor FET1 is turned off and the solenoid valve current IV is cut off. The constant voltage diode ZD1 is installed so as to absorb the flyback voltage generated by the solenoid valve V.

Next, a high voltage generator 10 which is a main improvement of the present invention will be described with reference to an embodiment shown in the drawings. FIG. 2 (a) shows the details of the first embodiment, in which the terminal 3 is connected to the positive terminal of the vehicle battery, the terminal 4 is connected to the negative terminal of the battery, and the circuit operation is performed. It becomes the ground level which is the reference potential. iC1 is a regulator for creating a constant voltage (8V) necessary for circuit operation, and for example, NEC three-terminal regulator μPC14308 can be used. Capacitors C2 and C
3 is inserted between the ground line and the input / output terminal of the regulator iC1 for removing ripples of the battery voltage and the constant voltage (8V).

A charge pulse PLS for operating the high voltage generator (10) shown in FIG. 2A is applied to the terminal 2. In the first embodiment, as shown in FIG. 2 (b), the solenoid valve drive pulse τ and the charge pulse PLS are output from the arithmetic unit ECU (not shown) in a relationship between time t1 and time t2. The times t1 and t2 are sufficiently shorter than the cycle of the solenoid valve drive pulse τ. The arithmetic unit that outputs two kinds of pulses, the solenoid valve drive pulse τ and the charge pulse PLS, having such a relationship can be easily configured by an analog circuit or a microcomputer.

The charge pulse PLS applied to the terminal 2 is transmitted to the NAND gate iC2 through the resistors R4 and R5. The level is limited by the diodes D5 and D6 at the connection point of the resistors R4 and R5 to prevent latch-up and malfunction of the NAND gate iC2. It is desirable that the NAND gate iC2 has hysteresis as an input characteristic. For example, TC40 manufactured by Tokyo Shibaura Electric Co., Ltd.
A Schmidt NAND gate such as 93 can be used. NAND gate
The charge pulse PLS inverted by iC2 is the NAND gate iC
It is inverted again at 3 and input to the clock terminal CK of the D-flip-flop iC4 (for example, TC-4013 manufactured by Tokyo Shibaura Electric). The D-flip-flop iC4 latches the state (high-level) connected to the D terminal at the rising edge of the pulse applied to the clock terminal CK. That is, the terminal of the D-flip-flop iC4 goes low at the rising edge of the charge pulse PLS, as shown in FIG. 2 (b). The signal output to the D-flip-flop iC4 is connected to the base of the transistor Tr1 via the resistor R6. The resistor R7 connects the base and emitter of the transistor Tr1 and stabilizes the on / off operation of the transistor Tr1. The emitter of the transistor Tr1 is connected to the ground line, and the collector terminal has a constant voltage (8V) via the resistor R8.
Connected to the line. The collector of the transistor Tr1 is connected to the MOS field effect transistor FET2 via the resistor R9.
It is also connected to the gate terminal of. The drain of the field effect transistor FET2 is connected to the coil L1 for temporarily storing energy, and the other terminal of the coil L1 is connected to the positive line of the battery. The source terminal of the field effect transistor FET2 is connected to the ground line via the coil L1, and the resistor R3 for detecting the current flowing through the field effect transistor FET2. Further, zener diodes ZD3 and ZD4 are added between the drain terminal of the field effect transistor FET2 and the ground in the direction of connecting the cathode to the train side. Further, the source terminal of the field effect transistor FET2 is connected to the negative input terminal of the comparator iC5 via the resistor R10. Also, the comparator i
The negative input terminal of C5 is pulled up to a constant voltage (8V) by the resistor R14, and the current level detected by the resistor R3 is raised to the operable input voltage range of the comparator iC5. The reference potential is input to the positive input terminal of the comparator iC5 via the resistor R13. The reference potential is created by dividing the voltage between the constant voltage line (8V) and ground with resistors R11 and R12, and a capacitor C4 for stabilization is added in parallel with the resistor R12. The resistor R15 that connects the output of the comparator iC5 and the positive input terminal and the capacitor C5 that is inserted between the positive input terminal and the negative input terminal provide hysteresis to prevent malfunction due to noise. That is, the comparator iC5 is composed of the coil L1 and the MOS field effect transistor F.
Charge current I CHG flowing through ET2 and current detection resistor R3
Is increased and the level of the negative input terminal becomes a constant current I _o that exceeds the reference potential, the output is inverted to the low level. The output of the comparator IC5 is connected to the first input of the NAND gate iC6, and the output of the NAND gate iC6 is the D-
It is connected to the clear terminal CL of the flip-flop iC4.

The rising of the charge pulse PLS triggers the D-latch of the D-flip-flop iC4, and the output of the D-flip-flop iC4 is inverted to the low level (FIGS. 2 (b)-(3)). When the terminal becomes low level, the transistor Tr1 does not flow the base current, so the collector-emitter is cut off, resulting in the field effect transistor FET2.
A high level (constant voltage source 8V) is applied to the gate of, and the drain and lease are electrically connected. Field effect transistor FET2
Is conducted, the charge current I CHG gradually rises in the path of the coil L1, the field effect transistor FET2 and the resistor R3 (FIG. 2 (b)-(4)). As the charge current I CHG increases, the voltage applied to the resistor R3 also increases,
The potential of the negative input terminal of iC5 rises. As a result, when the reference potential applied to the positive input terminal of the comparator iC5 is exceeded, the output of the comparator iC5 is inverted to the low level, the clear terminal of the D-flip-flop iC4 becomes the high level through the NAND gate iC6, and Q The terminal becomes high-level (Figs. 2 (b)-(3), (5)). as a result,
The base current of the transistor Tr1 flows and its transistor T
The r1 becomes conductive, the gate potential of the field effect transistor FET2 is dropped to the low level, and the field effect transistor FET2 is turned off. That is, the reference potential applied to the positive input terminal of the comparator iC5 is set to the set value by the current flowing through the coil L1.
If the output is inverted when iO is reached, a closed loop that turns off the field-effect transistor FET2 each time (1/2) LiO ² energy is stored in the coil L1 regardless of the battery voltage is created. be able to.

Next, after the field effect transistor FET2 is turned off, the coil
The control circuit that transfers the energy stored in L1 to the capacitor C1 that forms the high voltage storage means and its operation will be described. The anode of the thyristor TH1 is connected to the drain terminal of the field effect transistor FET2.
The cathode of H1 is a capacitor C1 as a high voltage storage means.
It is connected to the. A resistor R2, a zener diode ZD2, and a diode D4 are connected to the anode and gate terminal of the thyristor TH1 with the polarities shown in FIG. 2 (a). When the field effect transistor FET2 is turned off in the state where the energy of (1/2) LiO ² is accumulated in the coil L1, the coil L1 generates a high voltage due to the surge voltage. This high voltage has a sufficient level to trigger thyristor TH1 through resistor R2, zener diode ZD2, and diode D4. Thyristor TH by this trigger
1 is turned on, and the energy stored in the coil L1 is transferred to the capacitor C1 and stored as a high voltage. Further, the thyristor TH1 maintains the ON state until the energy of the coil L1 is exhausted, that is, while the current continues to flow from the coil L1 to the capacitor C1, and is automatically turned off when the current stops flowing. Further, by adopting the thyristor TH1, when the field effect transistor FET1 is turned on in FIG. 1 (a), that is, when the solenoid valve drive pulse τ is at a high level, the coil L1, the diode D3, the solenoid valve V, the field effect transistor FET1, It is possible to prevent an unintended current from flowing through the path of the resistor R1. This first
In this embodiment, by repeating the charge cycle a plurality of times (two times in this case), a larger amount of energy is stored in the capacitor C1 and a high voltage is generated (Fig. 2 (b)- (8)).

The basic configuration and operation of the high-voltage generator 10 in the first embodiment have been described above in detail. Further, in the present embodiment, even when the battery voltage drops, such as during start-up, or when the current detection feedback loop fails. In order to prevent the high voltage generation function from deteriorating, there is a protection function with a timed timer. That is, the output of the NAND gate iC3 is connected to the A trigger terminal of the monostable multivibrator iC7. This monostable multivibrator iC7 is a T by Shibaura Electric Co., Ltd.
C4528, etc. can be used, the output is inverted to the low level at the rising edge of the A trigger terminal, and thereafter the capacitor C6 and the resistor R1
The low level is maintained for a time determined by 6, and the diode D7, and the high level is restored (Fig. 2 (c)-
(6)). Further, the output of the monostable multivibrator iC7 is connected to the A trigger terminal of another monostable multivibrator iC8, and similarly, from the rising edge of the terminal of the monostable multivibrator iC7, the capacitor C7,
The output is set to the low level only during the period determined by the resistor R17 and the diode D8 (Fig. 2 (c)-(7)). The output terminal of the monostable multivibrator iC8 is connected to another input terminal of the NAND gate iC6. That is, in these circuits, for example, in a special case such as when starting the engine, when the battery voltage is significantly reduced and the constant current Io set in the coil L1 cannot be flowed due to the internal resistance of the coil L1 and the like. However, after the set time t ₃ , the field effect transistor FET2 is turned off to prevent the charge current I CHG from continuing to flow to the capacitor C1 and the stored energy is slightly reduced as compared with the normal operation. , Yet it is possible to apply a voltage higher than the battery voltage to the capacitor C1 and thus to the solenoid valve V,
The adverse effects can be minimized. It should be noted that the set time t ₃ is set to be sufficiently longer than the time to reach the set constant current Io at the normal battery voltage in consideration of the decrease in the battery voltage. Further, the time t ₃ is set to be smaller than the cycle t ₂ of the charge pulse PLS.

As described above, according to the first embodiment of the present invention, the high voltage energy that should be consumed when the solenoid valve V is pulled in (valve open) is accumulated while being measured in each cycle. Therefore, the response delay (valve opening delay) of the solenoid valve V can be significantly reduced, and the response characteristic independent of the battery voltage can be realized with a simple circuit configuration. Further, the operation of the solenoid valve V can be guaranteed without a problem even when the battery voltage is abnormally reduced by the time-limit circuit. Furthermore, if a capacitor with a small leakage current is used as the high-voltage storage means, the voltage drop due to discharge once the necessary energy is once charged is small and recharging is not necessary. As a result, undesired phase,
For example, the solenoid valve drive pulse τ is at a high level, and recharging cannot occur when the solenoid valve is energized.

Other Embodiments The number of charge pulses for generating a high voltage may be one or more, but if the number is small, a coil with a large inductance is required. Also, if the charge is divided into a large number of times, it takes time to complete the charge, so it is preferable to accumulate the required energy in two or three times.

Further, in the first embodiment, the circuit in which the MOS type field effect transistor is adopted as the power element is shown, but the same effect can be expected of course with the power transistor.

The capacitor C1 does not need to realize the required capacitance with one element, and a plurality of capacitors can be mounted in parallel. In addition, mounting a plurality of devices requires less current capacity.

Further, the capacitor C1 for accumulating high voltage is not inserted between the cathode of the thyristor TH1 and the ground, but is inserted between the cathode of the thyristor TH1 and the battery potential as in the second embodiment shown in FIG. You may.

As a third embodiment, as shown in FIG. 4 (a), the current flowing through the coil L1 is controlled to be constant by using the operational amplifier iC70, and the transistor Tr70 is controlled at any time when the current is controlled to be constant. It may be turned off. That is, the fourth
Charge pulse PLS applied to terminal 2 as shown in Figure (b)
When is turned on, the current control starts and the charge current I CH
Control G to constant current Io. After that, charge pulse PLS
The transistor Tr70 is turned off at the timing when is turned off, and the energy (1/2) L Io ² accumulated in the coil L1 is transferred to the capacitor C1. In this case, as indicated by a broken line in the charge current I CHG waveform of FIG. 4 (b), since the time to reach the constant current Io varies depending on the battery voltage, the arithmetic unit 40 that outputs a pulse has an appropriate pulse width. It is necessary to output the charged pulse PLS.

As a fourth embodiment, as shown in FIG.
It is conceivable to implement the protection function by the timed timer adopted in the embodiment in the arithmetic circuit. That is, as shown in FIG. 5 (b), the charge pulse PL is detected together with the loop for detecting that the charge current has reached the set constant current Io and turning off the field effect transistor FET2.
This is an example in which a protection circuit is added to turn off the field effect transistor FET2 even when S falls. Also in this case, as in the third embodiment, it is necessary to output the charge pulse PLS having an appropriate pulse width in the arithmetic unit for detecting the pulse.

In addition, as in the fifth embodiment shown in FIG.
It is also conceivable to provide the pulse generator 50 that outputs one or a plurality of pulses based on the drive pulse τ without inputting PLS from the arithmetic unit. Such a pulse generator
The 50 can be easily realized by combining a monostable multivibrator and a gate. In FIG. 6, a resistor R90 is inserted in parallel with a capacitor C1 forming a high voltage storage means. The resistor R90 is set so that discharge can be ignored in a normal electromagnetic valve operation cycle, and high voltage is gradually discharged when the system is stopped to ensure safety.

Further, as in the sixth embodiment shown in FIG. 7, a plurality of solenoid valves V
1, V2 ... VN can be controlled in the same way.

"Effects" As described above, the solenoid valve drive circuit of the present invention has the above-described configuration, so that the response delay of the solenoid valve can be shortened, the circuit configuration is simple, and the battery voltage and operating environment can be reduced. Even if the value changes, there is an excellent effect that there is little variation in the response of the solenoid valve.

[Brief description of drawings]

FIG. 1 (a) is a circuit diagram showing an electromagnetic valve drive circuit according to a first embodiment of the present invention, FIG. 1 (b) is a timing chart showing waveforms of respective parts of the first embodiment, and FIG. FIG. 2A is a circuit diagram showing details of the high voltage generator in the first embodiment, FIG. 2B is a timing chart for explaining the operation of the first embodiment in a normal state, and FIG. c) is a timing chart for explaining the protection function of the first embodiment, FIG. 3 is a circuit diagram showing the second embodiment in which the insertion position of the capacitor for accumulating a high voltage is changed, and FIG. FIG. 4A is a circuit diagram showing a third embodiment in which the configuration of the high voltage generator is changed, FIG. 4B is a timing chart showing the operation of the third embodiment, and FIG. FIG. 5B is a circuit diagram showing a fourth embodiment in which the configuration of the high voltage generator is changed, and FIG. A chart, FIG. 6 is a circuit diagram showing a fifth embodiment of the present invention, FIG. 7 is a circuit diagram showing a sixth embodiment, and FIGS. 8 to 10 are diagrams showing a conventional example. . 10: High voltage generator, 20: Drive controller, 30: Constant current circuit, L1: Coil C1: Capacitor V, V1, V2 …… VN: Solenoid valve IC7, IC8: Monostable multivibrator 11: Charge current control circuit 12: Current detection circuit

 ─────────────────────────────────────────────────── --Continued from the front page (56) Reference JP-A-57-203829 (JP, A) JP-A-59-220906 (JP, A) JP-A-60-50011 (JP, A) JP-A-59- 85434 (JP, A) JP 58-187537 (JP, A) JP 58-165858 (JP, A) JP 49-46582 (JP, B1)

Claims (3)

[Claims] 1. A solenoid valve drive circuit for controlling the opening and closing of at least one solenoid valve operated by an on-vehicle power supply, and a high voltage generating means for applying a high voltage at the start of energization of the solenoid valve, the high voltage generating means exceeding the on-vehicle power supply voltage. A constant current circuit for flowing a constant current for holding an operating state in the solenoid valve, and a switching circuit for controlling opening / closing of the solenoid valve, wherein the high voltage generating means includes a coil for temporarily storing energy. The high voltage storage means for storing a high voltage, and the energy stored in the coil is constituted by a control circuit that transfers the high voltage storage means, the control circuit, when the current flowing through the coil reaches a set value, Operate to transfer the energy temporarily stored in the coil to the high-voltage storage means, and perform this operation at least once before starting the energization of the solenoid valve. Solenoid valve drive circuit characterized by. 2. The control circuit of the high voltage generating means applies a current to the coil when the current accumulated in the coil is transferred to the high voltage accumulating means when the current flowing in the coil reaches a set value. The electromagnetic valve drive circuit according to claim (1), which is performed even after a set time has elapsed since the start. 3. The high voltage generating means generates a high voltage exceeding the battery voltage when all the solenoid valves are not energized, and the high voltage generating means according to claim (1) or (2). ) The solenoid valve drive circuit described in the item.