Signal output circuit and drive control method for electromagnetic valve

Abstract

To provide a signal output circuit for an electromagnetic valve, capable of preventing that the electromagnetic valve in a valve closed state is erroneously detected as becoming a valve open state, even in a case that the periodic pulsed electrification is performed to a solenoid coil.SOLUTION: A signal output circuit 40 of an electromagnetic valve 10 includes: a first smoothing circuit 110 for smoothing an input voltage Vi corresponding to a driving current flowing through a solenoid coil 30; a second smoothing circuit 120 having a second capacitor C2 and for smoothing the input voltage Vi; a comparator 130 for outputting an output signal So based on comparison between a first voltage V1 from the first smoothing circuit 110 and a second voltage V2 from the second smoothing circuit 120; and a discharging circuit 150 for discharging electric charges accumulated on the second capacitor C2.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a signal output circuit and a drive control method for a solenoid valve.

Background Art

[0002] Patent Document 1 discloses a diagnostic device for a solenoid valve. When power is supplied to the solenoid, initially the solenoid current increases. Thereafter, the solenoid current decreases and then increases again. Such reference characteristics of the waveform of the solenoid current are obtained in advance. When the waveform of the solenoid current detected during the operation of the solenoid valve changes with respect to the reference characteristics, it is diagnosed that the solenoid valve is deteriorated.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Conventionally, in order to reduce the power consumption of a solenoid valve, after the driving of the solenoid valve is started, the solenoid coil that drives the solenoid valve is energized in a periodic pulse shape. In the periodic pulse-shaped energization, an energized state in which a drive current flows through the solenoid coil and a non-energized state in which no drive current flows through the solenoid coil are alternately repeated. According to the diagnostic device for a solenoid valve disclosed in Patent Document 1, even if an abnormality occurs in which the solenoid valve remains in the valve-closed state without opening, an increase and decrease in the drive current similar to that at the time of valve opening can be detected by the periodic pulse-shaped energization. In that case, there is a problem that it is erroneously detected that the solenoid valve has opened.

[0005] An object of the present invention is to solve the above-described problems.

Means for Solving the Problems

[0006] A first aspect of the present invention is a signal output circuit for a solenoid valve, comprising: a first smoothing circuit having a first capacitor for smoothing an input voltage corresponding to a drive current flowing through a solenoid coil that drives the solenoid valve; a second smoothing circuit having a second capacitor for smoothing the input voltage and having a larger time constant than the first smoothing circuit; a first input terminal to which a first voltage obtained by smoothing the input voltage by the first smoothing circuit is input; a second input terminal to which a second voltage corresponding to a smoothed voltage obtained by smoothing the input voltage by the second smoothing circuit is input; a comparator having an output terminal for outputting an output signal based on a comparison between the first voltage and the second voltage; and a discharge circuit connected to the second capacitor for switching whether to discharge the charge stored in the second capacitor. The discharge circuit includes a first switching element and a discharge resistor connected in series.

[0007] A second aspect of the present invention is a method for driving and controlling a solenoid valve by a drive circuit having the signal output circuit for a solenoid valve according to the first aspect, the method comprising: a drive start step of turning on a second switching element connected to the solenoid coil to put the solenoid coil in an energized state in which the drive current flows through the solenoid coil in order to start driving the solenoid valve; a second off control of turning off the second switching element to put the solenoid coil in a non-energized state in which the drive current does not flow through the solenoid coil when a predetermined time has elapsed after the second on control is performed in the drive start step, and alternately repeating the second on control; a pulsed energization step of alternately repeating a first on control of turning on the first switching element to discharge the charge to the discharge circuit in the non-energized state and a first off control of turning off the first switching element in the energized state with respect to the first switching element; and a state change detection step of detecting a change in the state of the voltage, wherein the voltage changes from a first state in which the first voltage is higher than the second voltage to a second state in which the first voltage is lower than the second voltage based on the output signal. [Effect of the Invention]

[0008] According to the present invention, even when a periodic pulse current is applied to the solenoid coil, it is possible to prevent the electromagnetic valve in the valve-closed state from being erroneously detected as being in the valve-open state.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0010] FIG. 1 is a diagram illustrating a drive circuit 20 of an electromagnetic valve 10. The drive circuit 20 includes a power source E, a solenoid coil 30 that drives the electromagnetic valve 10, a signal output circuit 40 according to an embodiment of the present invention, and an amplifier 80.

[0011] When a drive current from the power source E flows through the solenoid coil 30, a magnetic force is generated. Due to this generated magnetic force, a movable iron core 10a in the electromagnetic valve 10 moves. When the movable iron core 10a moves, the electromagnetic valve 10 changes from the valve-closed state to the valve-open state. In the valve-closed state, the flow path from the input port to the output port of the electromagnetic valve 10 is blocked by the movable iron core 10a abutting against the valve seat. In the valve-open state, the flow path from the input port to the output port communicates because the movable iron core 10a is separated from the valve seat.

[0012] The drive circuit 20 has a current detection resistor Rs connected in series with the solenoid coil 30. One end of the current detection resistor Rs is connected to the ground. Note that the negative electrode of the power supply E is also connected to the ground. A signal output circuit 40 is connected to a position Pi to which the other end of the current detection resistor Rs is connected via an amplifier 80. Therefore, the input voltage Vi at the position Pi is input to the signal output circuit 40 via the amplifier 80. The input voltage Vi changes according to the drive current flowing through the solenoid coil 30.

[0013] The amplifier 80 is, for example, an operational amplifier. The input terminal of the amplifier 80 is connected to the position Pi. The output terminal of the amplifier 80 is connected to the signal output circuit 40. The amplifier 80 amplifies the input voltage Vi input from the input terminal to the amplifier 80. The input voltage Vi is amplified by the amplifier 80 and output from the output terminal of the amplifier 80. The amplified input voltage Vi is input to the signal output circuit 40. By providing the amplifier 80, the signal output circuit 40 can react sensitively to changes in the input voltage Vi.

[0014] The drive circuit 20 has a second switching element SW2 connected in series with the solenoid coil 30 and the current detection resistor Rs. When the second switching element SW2 is turned on, the solenoid coil 30 is in an energized state in which the drive current from the power supply E flows through the solenoid coil 30. When the second switching element SW2 is turned off, the solenoid coil 30 is in a non-energized state in which the drive current from the power supply E does not flow through the solenoid coil 30.

[0015] In the present embodiment, both the second on-control for turning on the second switching element SW2 and the second off-control for turning off the second switching element SW2 are performed by the signal output circuit 40. When the second switching element SW2 is a MOSFET, the signal output circuit 40 turns the gate voltage on or off via a MOSFET driver. When the gate voltage is on, the second switching element SW2 is turned on. When the gate voltage is off, the second switching element SW2 is turned off.

[0016] The drive circuit 20 has a diode Dc connected to both ends of the solenoid coil 30. The cathode of the diode Dc is connected to the position Pcp at one end of the solenoid coil 30. One end of the solenoid coil 30 and the cathode of the diode Dc are both connected to the positive electrode of the power supply E. The anode of the diode Dc is connected to the position Pcn at the other end of the solenoid coil 30. The other end of the solenoid coil 30 and the anode of the diode Dc are both connected to the ground via the second switching element SW2 and the current detection resistor Rs.

[0017] Similar to the solenoid coil 30, the diode Dc is connected in series with the second switching element SW2. When the second switching element SW2 is in the off state, the diode Dc and the solenoid coil 30 form a closed circuit Lc. When the second switching element SW2 changes from on to off, the induced current generated in the solenoid coil 30 transiently refluxes through the closed circuit Lc. The second switching element SW2 is not included in the closed circuit Lc. Therefore, the induced current is prevented from damaging the second switching element SW2. That is, the diode Dc protects the second switching element SW2.

[0018] The signal output circuit 40 includes a control unit 100, a first smoothing circuit 110, a second smoothing circuit 120, a voltage dividing resistor Rv, a comparator 130, a discharge circuit 150, and a diode Dd. The control unit 100 may not be included in the signal output circuit 40, but in this embodiment, the control unit 100 is included in the signal output circuit 40. The first smoothing circuit 110 and the second smoothing circuit 120 are both connected to the amplifier 80 at the position Ps on the output line from the output terminal of the amplifier 80.

[0019] The first smoothing circuit 110 has a first resistor R1 and a first capacitor C1. One end of the first resistor R1 is connected to the output terminal of the amplifier 80. The other end of the first resistor R1 is connected to the first input terminal M1 which is the inverting input terminal of the comparator 130. One end of the first capacitor C1 is connected to a position P1 between the other end of the first resistor R1 and the first input terminal M1 of the comparator 130. The other end of the first capacitor C1 is connected to the ground.

[0020] The first smoothing circuit 110 smoothes the input voltage Vi amplified by the amplifier 80. The first voltage V1 obtained by smoothing the input voltage Vi by the first smoothing circuit 110 is input to the first input terminal M1 of the comparator 130.

[0021] The second smoothing circuit 120 has a second resistor R2 and a second capacitor C2. One end of the second resistor R2 is connected to the output terminal of the amplifier 80 via the diode Dd. The other end of the second resistor R2 is connected to the second input terminal M2 which is the non-inverting input terminal of the comparator 130. One end of the second capacitor C2 is connected to a position P2 between the other end of the second resistor R2 and the second input terminal M2 of the comparator 130. The other end of the second capacitor C2 is connected to the ground. One end of the voltage dividing resistor Rv is connected to a position Pv between the above-mentioned position P2 and the second input terminal M2 of the comparator 130. The other end of the voltage dividing resistor Rv is connected to the ground.

[0022] The second smoothing circuit 120 smoothes the input voltage Vi amplified by the amplifier 80. The voltage dividing resistor Rv divides the smoothed voltage obtained by smoothing the input voltage Vi by the second smoothing circuit 120. That is, the smoothed voltage is divided by the voltage dividing resistor Rv according to the ratio of the resistance value of the voltage dividing resistor Rv to the sum of the resistance value of the voltage dividing resistor Rv and the resistance value of the second resistor R2. A second voltage V2 is obtained according to this smoothed voltage. The second voltage V2 obtained by dividing the smoothed voltage by the voltage dividing resistor Rv is input to the second input terminal M2 of the comparator 130.

[0023] The resistance value of the first resistor R1, the capacitance value of the first capacitor C1, the resistance value of the second resistor R2, and the capacitance value of the second capacitor C2 are determined in advance such that the time constant of the second smoothing circuit 120 becomes larger than the time constant of the first smoothing circuit 110. Note that the capacitance value of the second capacitor C2 is preferably larger than the capacitance value of the first capacitor C1. Thereby, the change in the second voltage V2 can be delayed more than the change in the first voltage V1. Also, the resistance value of the voltage dividing resistor Rv is preferably larger than the resistance value of the second resistor R2. Thereby, the state change described later regarding the magnitude relationship between the first voltage V1 and the second voltage V2 can be stably detected.

[0024] The discharge circuit 150 has a first switching element SW1 and a discharge resistor Rd connected in series. The discharge circuit 150 is connected across both ends of the second capacitor C2. When the first switching element SW1 is turned off, charge is accumulated in the second capacitor C2.

[0025] In a state where the first switching element SW1 is on, the second capacitor C2 and the discharge resistor Rd form a closed circuit Ld. When the first switching element SW1 changes from off to on, the charge accumulated in the second capacitor C2 is discharged by being consumed by the discharge resistor Rd. By determining the resistance value of the discharge resistor Rd to be small, the charge accumulated in the second capacitor C2 can be rapidly discharged.

[0026] The discharge circuit 150 can switch whether to discharge the charge accumulated in the second capacitor C2 by turning the first switching element SW1 on or off. The first on control for turning the first switching element SW1 on and the first off control for turning the first switching element SW1 off are both performed by the signal output circuit 40.

[0027] When the first switching element SW1 is a MOSFET, the signal output circuit 40 turns the gate voltage on or off via the MOSFET driver. When the gate voltage is on, the first switching element SW1 turns on. When the gate voltage is off, the first switching element SW1 turns off.

[0028] Note that the discharge resistor Rd may be disposed between the position P2 where the second resistor R2 and the second capacitor C2 of the second smoothing circuit 120 are connected and the second resistor R2. In that case, the discharge resistor Rd contributes to the smoothing of the input voltage Vi by the second smoothing circuit 120 together with the second resistor R2 and the second capacitor C2.

[0029] As described above, the diode Dd is disposed between the amplifier 80 and the second resistor R2. The cathode of the diode Dd is connected to the second resistor R2. The anode of the diode Dd is connected to the amplifier 80 and the first smoothing circuit 110. By disposing the diode Dd, as long as the first switching element SW1 is off, the second smoothing circuit 120 can function as a peak hold circuit capable of holding the peak value of the second voltage V2.

[0030] The comparator 130 has the first input terminal M1 and the second input terminal M2 described above, and an output terminal N. The output terminal N outputs an output signal So based on the comparison between the first voltage V1 input to the first input terminal M1 and the second voltage V2 input to the second input terminal M2 to the control unit 100.

[0031] The control unit 100 includes a processor such as a CPU (Central Processing Unit) or a GPU (Graphics Processing Unit), and a memory that stores a program executed by the processor. The control unit 100 may be realized by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array), or an electronic circuit including discrete devices.

[0032] The control unit 100 includes a switching control unit 182, a negation circuit 184, and a detection unit 186. The switching control unit 182 performs the second on-control and the second off-control on the second switching element SW2 described above. The switching control unit 182 further performs the first on-control and the first off-control on the first switching element SW1 described above.

[0033] In the present embodiment, as shown in FIG. 1, the control line extending from the switching control unit 182 branches at the position Pw, and each of the branched control lines heads toward the second switching element SW2 and the first switching element SW1. The negation circuit 184 is arranged on the control line between the position Pw and the first switching element SW1.

[0034] The switching control unit 182 alternately repeats the second off-control and the second on-control for the second switching element SW2. Thereby, the periodic pulse-like energization of the solenoid coil 30 is executed. The solenoid coil 30 repeats the energized state and the non-energized state.

[0035] The negation circuit 184 realizes the first on-control and the first off-control for the first switching element SW1 by inverting the phases of the second off-control and the second on-control for the second switching element SW2. In this way, the switching control unit 182 can alternately repeat the first on-control and the first off-control for the first switching element SW1. The first switching element SW1 and the second switching element SW2 do not turn on simultaneously.

[0036] The detection unit 186 is connected to the output terminal N of the comparator 130. The detection unit 186 acquires the output signal So output from the comparator 130. The detection unit 186 detects a change in the voltage state regarding the first voltage V1 and the second voltage V2 based on the acquired output signal So. The detection of the change in the voltage state that occurs for the first time after the start of driving the solenoid valve 10 can be associated with the detection of the valve open state of the solenoid valve 10, for example, by using an external device or the like. That is, the output signal So from the comparator 130 can be used to determine the valve open state of the solenoid valve 10. Specific examples of the change in the voltage state detected by the detection unit 186 based on the output signal So from the comparator 130 will be described below.

[0037] As described above, both the first smoothing circuit 110 and the second smoothing circuit 120 smooth the amplified input voltage Vi. As described above, the time constant of the second smoothing circuit 120 is larger than the time constant of the first smoothing circuit 110. Therefore, when the input voltage Vi rises according to time, the smoothing of the input voltage Vi by the second smoothing circuit 120 is delayed compared to the smoothing of the input voltage Vi by the first smoothing circuit 110.

[0038] In that case, the first voltage V1 input to the first input terminal M1 of the comparator 130 can be higher than the second voltage V2 input to the second input terminal M2. Therefore, for example, an output signal So indicating a Low level is output from the output terminal N of the comparator 130. The detection unit 186 detects that the first voltage V1 is higher than the second voltage V2 based on the output signal So indicating a Low level.

[0039] Also when the input voltage Vi decreases according to time, the smoothing of the input voltage Vi by the second smoothing circuit 120 is delayed compared to the smoothing of the input voltage Vi by the first smoothing circuit 110. In that case, the first voltage V1 input to the first input terminal M1 can be lower than the second voltage V2 input to the second input terminal M2. Therefore, for example, an output signal So indicating a High level is output from the output terminal N. The detection unit 186 detects that the first voltage V1 is lower than the second voltage V2 based on the output signal So indicating a High level.

[0040] Therefore, when the input voltage Vi rises and then falls according to time, the detection unit 186 can detect a change in the voltage state, based on the output signal So, from a first state where the first voltage V1 is higher than the second voltage V2 to a second state where the first voltage V1 is lower than the second voltage V2.

[0041] FIG. 2 is a diagram illustrating changes in the first voltage V1 and the second voltage V2 according to time when the solenoid valve 10 opens normally. In FIG. 2, changes in the output signal So, on / off changes of the first switching element SW1, and on / off changes of the second switching element SW2 are also illustrated.

[0042] To start driving the solenoid valve 10, the switching control unit 182 of the control unit 100 performs second on-control on the second switching element SW2 and first off-control on the first switching element SW1 at time T0. The second switching element SW2 turns on, and the first switching element SW1 turns off. Since a large amount of power is required to open the solenoid valve 10, periodic pulsed energization of the solenoid coil 30 is not performed. That is, continuous energization is performed on the solenoid coil 30.

[0043] After the driving of the solenoid valve 10 starts, both the first voltage V1 and the second voltage V2 rise. However, the smoothing of the second smoothing circuit 120 is delayed compared to the smoothing of the first smoothing circuit 110. Therefore, the rise of the second voltage V2 is slower than the rise of the first voltage V1. Since the first voltage V1 is higher than the second voltage V2, the comparator 130 outputs an output signal So indicating a Low level from the output terminal N. The detection unit 186 detects that the first voltage V1 is higher than the second voltage V2 based on the output signal So from the comparator 130. The solenoid valve 10 remains in the valve-closed state.

[0044] At time T1p after time T0, the first voltage V1 rises to the voltage value V1p. From time T0 to time T1p, the second voltage V2 also rises but is lower than the first voltage V1. When the solenoid valve 10 opens normally, at this time T1p, the movable iron core 10a in the solenoid valve 10 starts to move. That is, the solenoid valve 10 changes from the valve-closed state to the valve-open state. As the movable iron core 10a moves in the solenoid coil 30, the inductance increases, so the input voltage Vi decreases. After time T1p, the first voltage V1 decreases as the input voltage Vi decreases.

[0045] As described above, compared with the smoothing of the first smoothing circuit 110, the smoothing of the second smoothing circuit 120 is delayed. Therefore, the time T2p when the second voltage V2 changes from rising to falling is later than the above-mentioned time T1p. The second voltage V2 rises to the voltage value V2p at time T2p and then gradually decreases as the above-mentioned input voltage Vi decreases. The second smoothing circuit 120 can function as a peak hold circuit. Therefore, the decrease of the second voltage V2 is slower than the decrease of the first voltage V1. Therefore, at time Td after time T1p and time T2p, both the first voltage V1 and the second voltage V2 have decreased to the voltage value Vd.

[0046] From time T0 to time Td, the first state where the first voltage V1 is higher than the second voltage V2 continues. After passing time Td, it changes from the first state to the second state where the first voltage V1 is lower than the second voltage V2. Such a voltage state change occurs for the first time after the driving of the solenoid valve 10 starts. Since the output signal So changes from Low to High, the detection unit 186 detects this first state change. The detection of this first state change can be associated with the detection of the valve-open state of the solenoid valve 10, for example, by using an external device or the like.

[0047] At time T1b after time Td, the solenoid valve 10 fully opens and the movable iron core 10a stops moving. At time T1b, the first voltage V1 drops to the voltage value V1b. Since the inductance does not change after time T1b, the drop in the first voltage V1 stops at the voltage value V1b and the first voltage V1 starts to rise again. The time T2b when the second voltage V2 changes from dropping to rising is later than the above-mentioned time T1b. In the example shown in FIG. 2, at time Tu which is after time T1b and before time T2b, both the rising first voltage V1 and the dropping second voltage V2 show the voltage value Vu.

[0048] From time Td to time Tu, the second state where the first voltage V1 is lower than the second voltage V2 continues. When time Tu elapses, it changes from the second state to the first state where the first voltage V1 is higher than the second voltage V2. The output signal So changes from High to Low again. At time T2b after time Tu, the second voltage V2 drops to the voltage value V2b. The drop in the second voltage V2 stops at the voltage value V2b and the second voltage V2 starts to rise again like the first voltage V1. As described above, since the rise of the second voltage V2 is slower than the rise of the first voltage V1, the first state continues even after time T2b.

[0049] When the first voltage V1 rises to the voltage value V1m, it then maintains the voltage value V1m. When the second voltage V2 rises to the voltage value V2m, it then maintains the voltage value V2m. The voltage value V1m is equal to the voltage value obtained by amplifying the input voltage Vi by the amplifier 80. The voltage value V2m is equal to the divided voltage value of the voltage value obtained by amplifying the input voltage Vi by the amplifier 80 by the voltage dividing resistor Rv.

[0050] That is, due to the voltage dividing resistor Rv, the first state where the first voltage V1 is higher than the second voltage V2 is maintained. Therefore, the comparator 130 continues to output an output signal So indicating a Low level from the output terminal N.

[0051] When the electromagnetic valve 10 is in the valve-open state, since a large amount of power is not required, for the purpose of power-saving operation, this periodic pulsed energization is performed. Assume that the time when this periodic pulsed energization starts is the time Tc when a predetermined time Th has elapsed from the time T0. In the example shown in FIG. 2, the time Tc is after the time Tu. Along with the periodic pulsed energization starting at the time Tc, the switching control unit 182 alternately repeats the first off-control and the first on-control for the first switching element SW1. That is, the switching control unit 182 performs periodic pulsed energization for the solenoid coil 30.

[0052] In addition, when the detection unit 186 first detects a state change at the above-mentioned time Td, the switching control unit 182 may alternately repeat the second off-control and the second on-control for the second switching element SW2 before the predetermined time Th elapses. In that case, the switching control unit 182 may start periodic pulsed energization for the solenoid coil 30 after the standby time from the time Td has elapsed. The standby time is the time from the time Td to the time expected to elapse until the above-mentioned time T1b, and is determined in advance by experiments or the like.

[0053] In the example shown in FIG. 2, periodic pulsed energization starts at the time Tc. At the time Tc, the first voltage V1 rises to the voltage value V1m, and the second voltage V2 rises to the voltage value V2m. At the time Tc, the second switching element SW2 turns off, and then the second switching element SW2 repeats on and off. As shown in FIG. 2, after the time Tc, the phase of the on / off change of the first switching element SW1 and the phase of the on / off change of the second switching element SW2 are opposite to each other. Both the first voltage V1 and the second voltage V2 decrease and transition at a low voltage, and the power-saving operation of the electromagnetic valve 10 is achieved.

[0054] FIG. 3 is a diagram illustrating changes in the first voltage V1 and the second voltage V2 over time when the solenoid valve 10 does not open properly. Also illustrated in FIG. 3 are changes in the output signal So, on / off changes of the first switching element SW1, and on / off changes of the second switching element SW2.

[0055] To start driving the solenoid valve 10, the switching control unit 182 of the control unit 100 performs second on control on the second switching element SW2 and first off control on the first switching element SW1 at time T0. The second switching element SW2 turns on, and the first switching element SW1 turns off. As described above, at time T0, the solenoid coil 30 is not energized with a periodic pulse. The solenoid coil 30 is continuously energized.

[0056] After starting to drive the solenoid valve 10, both the first voltage V1 and the second voltage V2 increase. However, as described above, the increase in the second voltage V2 is slower than the increase in the first voltage V1. Since the first voltage V1 is higher than the second voltage V2, the comparator 130 outputs an output signal So indicating a Low level from the output terminal N. The detection unit 186 detects that the first voltage V1 is higher than the second voltage V2 based on the output signal So from the comparator 130. The solenoid valve 10 remains in the valve-closed state.

[0057] Thereafter, when the first voltage V1 and the second voltage V2 increase, the solenoid valve 10 should open. However, due to factors such as a low applied voltage from the power supply E or the fixed movement of the movable iron core 10a in the solenoid valve 10, the solenoid valve 10 may not open properly. When the solenoid valve 10 does not open, the input voltage Vi does not decrease. Therefore, the voltage drops of the first voltage V1 and the second voltage V2 do not occur.

[0058] The first state in which the first voltage V1 is higher than the second voltage V2 continues until time Tc arrives after a predetermined time Th has elapsed from time T0. Therefore, the comparator 130 continues to output an output signal So indicating a low level from the output terminal N. If the voltage dividing resistor Rv is not provided, the first state changes to a state in which the first voltage V1 and the second voltage V2 are equal. However, since the state does not change further to the second state in which the first voltage V1 is lower than the second voltage V2, it is not essential to provide the voltage dividing resistor Rv.

[0059] In this embodiment, in consideration of the possibility that the first state may change to the second state temporarily or multiple times due to noise or the like, the voltage dividing resistor Rv is provided to reduce this possibility. Therefore, when the solenoid valve 10 does not open, the voltage dividing resistor Rv makes it easier to maintain the first state. The voltage dividing resistor Rv reduces the risk of erroneously detecting a voltage state change that changes the first state to the second state, and the valve open state can be detected more accurately.

[0060] When time Tc arrives, periodic pulse current is started for the purpose of power saving operation. That is, the switching control unit 182 alternately performs the second OFF control and the second ON control on the second switching element SW2. When the second switching element SW2 changes from ON to OFF, the input voltage Vi decreases for the first time after the solenoid valve 10 starts to be driven. In this case, the problems that may occur in the conventional signal output circuit will be described below.

[0061] In a conventional signal output circuit, when the input voltage Vi drops, a voltage state change may occur in which the magnitude relationship between the two voltage values ​​input to the comparator is reversed due to a delay caused by smoothing the input voltage Vi. When this state change is detected for the first time after the solenoid valve 10 starts to be driven, the valve open state of the solenoid valve 10 may be detected, for example, by using an external device. In other words, there is a risk that the valve open state of the solenoid valve 10 may be erroneously detected due to the start of the periodic pulse-like current supply.

[0062] In this embodiment, this problem is solved. That is, in the signal output circuit 40 according to this embodiment, the above-described voltage state change does not occur triggered by the start of periodic pulse energization. The principle thereof will be described below.

[0063] At time Tc shown in FIG. 3, the first voltage V1 has risen to the voltage value V1m, and the second voltage V2 has risen to the voltage value V2m. Since the first state where the first voltage V1 is higher than the second voltage V2 is maintained, the comparator 130 continues to output an output signal So indicating a low level from the output terminal N. As described above, periodic pulse energization is started at time Tc. The switching control unit 182 alternately repeats the second off control and the second on control for the second switching element SW2, and alternately repeats the first on control and the first off control for the first switching element SW1.

[0064] After time Tc, the phase of the on / off change of the first switching element SW1 and the phase of the on / off change of the second switching element SW2 are opposite to each other. Therefore, at time Tc, the second switching element SW2 changes from on to off, and the first switching element SW1 changes from off to on. Since the first smoothing circuit 110 is provided, the first voltage V1 does not decrease rapidly and decreases gradually. Since the charge accumulated in the second capacitor C2 is rapidly discharged by the discharge circuit 150, the second voltage V2 decreases rapidly. Therefore, a voltage change in which the first voltage V1 becomes lower than the second voltage V2 does not occur.

[0065] Between time Tc and a subsequent time Tc1, the first voltage V1 decreases to the voltage value V11, and the second voltage V2 decreases to the voltage value V21. Since the charge accumulated in the second capacitor C2 is rapidly discharged, the second voltage V2 at time Tc1 is sufficiently lower than the first voltage V1. Also between time Tc and time Tc1, since the first state where the first voltage V1 is higher than the second voltage V2 is maintained, the comparator 130 continues to output an output signal So indicating a low level from the output terminal N.

[0066] As described above, after the start of driving the solenoid valve 10 at time T0, the detection unit 186 detects that the first voltage V1 is higher than the second voltage V2 based on the output signal So from the comparator 130. Also, as described above, between time Tc and time Tc1, the first voltage V1 remains higher than the second voltage V2, and no voltage change occurs in which the first voltage V1 becomes lower than the second voltage V2. Therefore, even when the solenoid coil 30 is energized in a periodic pulse shape, it is possible to prevent the solenoid valve 10 in the valve-closed state from being erroneously detected as being in the valve-open state.

[0067] At time Tc1, the second switching element SW2 changes from off to on, and the first switching element SW1 changes from on to off. Between time Tc1 and a subsequent time Tc2, the first voltage V1 rises to a voltage value V12, and the second voltage V2 rises to a voltage value V22. The rise of the second voltage V2 is slower than the rise of the first voltage V1.

[0068] Also between time Tc1 and time Tc2, since the first state in which the first voltage V1 is higher than the second voltage V2 is maintained, the comparator 130 continues to output an output signal So indicating a Low level from the output terminal N. The detection unit 186 still detects that the first voltage V1 is higher than the second voltage V2 based on the output signal So from the comparator 130.

[0069] At time Tc2, the second switching element SW2 changes from on to off again, and the first switching element SW1 changes from off to on again. Since the above-described voltage change does not occur even after time Tc2, the comparator 130 continues to output an output signal So indicating a Low level from the output terminal N even after time Tc2. That is, in the present embodiment, it is possible to prevent the valve-open state of the solenoid valve 10 from being erroneously detected when the periodic pulse-shaped energization starts.

[0070] 4 is a flowchart showing an example of a drive control process procedure of the drive circuit 20 of the solenoid valve 10. This process procedure is performed, for example, by the control unit 100 of the signal output circuit 40 executing a program stored in a memory. This process procedure is executed when a command to start driving the solenoid valve 10 is issued by a user of the solenoid valve 10 or the like.

[0071] When this process procedure is started, in step S1, the switching control unit 182 of the control unit 100 executes a second ON control for the second switching element SW2. This starts driving the solenoid valve 10. The switching control unit 182 measures the elapsed time using a timer circuit, a clock circuit, or the like.

[0072] In step S2, the switching control unit 182 determines whether or not a predetermined time Th has elapsed. If the result in step S2 is YES, the process proceeds to step S3. If the result in step S2 is NO, the process in step S2 is repeated.

[0073] In step S3, the switching control unit 182 applies a periodic pulse of current to the solenoid coil 30. That is, the switching control unit 182 alternately and repeatedly performs a second OFF control and a second ON control on the second switching element SW2, and alternately and repeatedly performs a first OFF control and a first ON control on the first switching element SW1. When the process of step S3 is completed, this process procedure ends.

[0074] As described above, when the first state change is detected by the detection unit 186 at time Td shown in Fig. 2, the switching control unit 182 may start supplying periodic pulsed current to the solenoid coil 30 before the lapse of a predetermined time Th. Fig. 5 is a flowchart showing another example of the drive control processing procedure of the drive circuit 20 of the solenoid valve 10. In Fig. 5, the same numbers are used for the processing steps common to Fig. 4, and the description of the processing steps will be omitted below.

[0075] If the result in step S2 is NO, this processing procedure proceeds to step S11. In step S11, based on the output signal So from the comparator 130, the detection unit 186 determines whether it has detected a change in the voltage state from a first state where the first voltage V1 is higher than the second voltage V2 to a second state where the first voltage V1 is lower than the second voltage V2. If the result in step S11 is YES, this processing procedure proceeds to step S12. If the result in step S11 is NO, this processing procedure returns to step S2.

[0076] In step S12, the switching control unit 182 determines whether a waiting time has elapsed since the voltage state change was detected in step S11. If the result in step S12 is YES, this processing procedure proceeds to step S3. If the result in step S12 is NO, the processing in step S12 is repeated.

[0077] In the present embodiment, as described above, at the time Tc when a predetermined time Th has elapsed from the time T0, the periodic pulse energization to the solenoid coil 30 is started. However, if the periodic pulse energization is not performed, the signal output circuit 40 may not have the first smoothing circuit 110 and the discharge circuit 150. In that case, the signal output circuit 40 includes the control unit 100, the second smoothing circuit 120, the voltage dividing resistor Rv, and the comparator 130. The first voltage V1 input to the first input terminal M1 of the comparator 130 is equal to the input voltage Vi amplified by the amplifier 80.

[0078] As described above, the voltage dividing resistor Rv divides the smoothed voltage obtained by smoothing the input voltage Vi by the second smoothing circuit 120. The second voltage V2 obtained by dividing the smoothed voltage is input to the second input terminal M2 of the comparator 130. Therefore, when the solenoid valve 10 does not open, the voltage dividing resistor Rv maintains the first state where the first voltage V1 is higher than the second voltage V2. The voltage dividing resistor Rv reduces the risk of erroneously detecting a change in the voltage state from the first state to the second state, and the valve open state can be detected more accurately.

[0079] Regarding the above disclosure, the following additional remarks are further disclosed.

[0080] (Appendix 1) The signal output circuit (40) of the solenoid valve (10) has a first capacitor (C1), and a first smoothing circuit (110) that smooths the input voltage (Vi) corresponding to the drive current flowing through the solenoid coil (30) for driving the solenoid valve; a second capacitor (C2), and a second smoothing circuit (120) that smooths the input voltage and has a larger time constant than the first smoothing circuit; a first input terminal (M1) to which a first voltage (V1) obtained by smoothing the input voltage by the first smoothing circuit is input; a second input terminal (M2) to which a second voltage (V2) corresponding to the smoothed voltage obtained by smoothing the input voltage by the second smoothing circuit is input; a comparator (130) having an output terminal (N) that outputs an output signal (So) based on a comparison between the first voltage and the second voltage; and a discharge circuit (150) connected to the second capacitor and configured to switch whether to discharge the charge accumulated in the second capacitor. The discharge circuit has a first switching element (SW1) and a discharge resistor (Rd) connected in series. With such a configuration, even when the solenoid coil is energized in a periodic pulse shape, it is possible to prevent the solenoid valve in the valve-closed state from being erroneously detected as being in the valve-open state.

[0081] (Appendix 2) In the signal output circuit of the solenoid valve according to Appendix 1, it is preferable that the capacitance of the second capacitor is larger than the capacitance of the first capacitor. With such a configuration, it is possible to delay the change in the second voltage more than the change in the first voltage.

[0082] (Appendix 3) In the signal output circuit of the solenoid valve according to Appendix 1, the signal output circuit may further include an amplifier (80) that amplifies the input voltage, and each of the first smoothing circuit and the second smoothing circuit may smooth the input voltage amplified by the amplifier. With such a configuration, the signal output circuit can respond sensitively to changes in the input voltage.

[0083] (Appendix 4) In the signal output circuit of the solenoid valve described in Supplementary Note 1, a voltage dividing resistor (Rv) for dividing the smoothing voltage may be further provided, and the second voltage may be obtained by dividing the smoothing voltage by the voltage dividing resistor. According to such a configuration, it is possible to maintain a first state in which the first voltage is higher than the second voltage. The risk that a state change of the voltage in which the first state changes to a second state in which the first voltage V1 is lower than the second voltage V2 is erroneously detected is reduced, and the valve open state can be detected more accurately.

[0084] (Supplementary Note 5) In the signal output circuit of the solenoid valve according to any one of Supplementary Notes 1 to 4, a detection unit (186) may be further provided that detects a state change of the voltage in which the first voltage changes from a first state higher than the second voltage to a second state lower than the second voltage based on the output signal. According to such a configuration, the detection of the voltage change can be associated with the detection of the valve open state of the solenoid valve.

[0085] (Supplementary Note 6) In the signal output circuit of the solenoid valve described in Supplementary Note 5, a switching control unit (182) may be further provided that performs a first on-control for discharging the charge to the discharge circuit by turning on the first switching element in a non-energized state in which the drive current does not flow through the solenoid coil, and a first off-control for turning off the first switching element in an energized state in which the drive current flows through the solenoid coil. According to such a configuration, when the solenoid coil changes from an energized state to a non-energized state, the charge accumulated in the second capacitor can be rapidly discharged.

[0086] (Supplementary Note 7) In the signal output circuit of the solenoid valve described in Supplementary Note 6, the switching control unit performs second on-control to turn on a second switching element (SW2) connected to the solenoid coil in order to put the solenoid coil in the energized state, and second off-control to turn off the second switching element in order to put the solenoid coil in the non-energized state. When a predetermined time (Th) has elapsed after the switching control unit performs the second on-control to start driving the solenoid valve, the switching control unit alternately repeats the second off-control and the second on-control for the second switching element, and alternately repeats the first on-control and the first off-control for the first switching element. The first switching element and the second switching element do not have to be turned on simultaneously. According to such a configuration, it is possible to realize power-saving operation of the solenoid valve while preventing the valve-open state of the solenoid valve from being erroneously detected.

[0087] (Supplementary Note 8) In the signal output circuit of the solenoid valve described in Supplementary Note 7, if the detection unit detects the state change before the predetermined time has elapsed after the switching control unit performs the second on-control, the switching control unit may alternately repeat the second off-control and the second on-control for the second switching element before the predetermined time has elapsed. According to such a configuration, when the solenoid valve is normally opened, a high power-saving effect can be obtained.

[0088] (Supplementary Note 9) In a method for driving and controlling a solenoid valve by a drive circuit (20) having a signal output circuit of the solenoid valve according to any one of Supplementary Notes 1 to 4, in order to put the solenoid coil in an energized state in which the drive current flows through the solenoid coil, a second on-control for turning on a second switching element connected to the solenoid coil is performed in a drive start step for starting the drive of the solenoid valve; when a predetermined time has elapsed after the second on-control is performed in the drive start step, a second off-control for turning off the second switching element is performed on the second switching element in order to put the solenoid coil in a non-energized state in which the drive current does not flow through the solenoid coil, and the second on-control are alternately repeated; for the first switching element, a first on-control for discharging the charge to the discharge circuit by turning on the first switching element in the non-energized state and a first off-control for turning off the first switching element in the energized state are alternately repeated in a pulsed energization step; and a state change detection step for detecting a state change of a voltage in which the first voltage changes from a first state higher than the second voltage to a second state lower than the second voltage based on the output signal. According to such a configuration, it is possible to realize a power-saving operation of the solenoid valve while preventing an incorrect detection of the valve-open state of the solenoid valve when the solenoid valve does not open normally.

[0089] (Supplementary Note 10) In the method for driving and controlling a solenoid valve according to Supplementary Note 9, when the state change is detected in the state change detection step before the predetermined time has elapsed after the second on-control is performed in the drive start step, the pulsed energization step is performed before the predetermined time has elapsed. According to such a configuration, the power-saving effect of the solenoid valve that has opened normally is further enhanced.

[0090] Note that the present invention is not limited to the above-described disclosure, and various configurations can be adopted without departing from the gist of the present invention.

Explanation of Reference Numerals

[0091] 10... Solenoid valve 20... Drive circuit 30... Solenoid coil 40... Signal output circuit 80... Amplifier 100... Control unit 110... First smoothing circuit 120... Second smoothing circuit 130... Comparator 150... Discharge circuit 182... Switching control unit 184... Inverting circuit 186... Detection unit

Claims

1. A first smoothing circuit having a first capacitor and smoothing an input voltage corresponding to a drive current flowing through a solenoid coil that drives a solenoid valve; A second smoothing circuit having a second capacitor, smoothing the input voltage, and having a larger time constant than the first smoothing circuit; A first input terminal to which a first voltage obtained by smoothing the input voltage by the first smoothing circuit is input, a second input terminal to which a second voltage corresponding to a smoothed voltage obtained by smoothing the input voltage by the second smoothing circuit is input, and a comparator having an output terminal that outputs an output signal based on a comparison between the first voltage and the second voltage; A discharge circuit connected to the second capacitor and switching whether or not to discharge the charge stored in the second capacitor; Comprising: The discharge circuit is a signal output circuit of a solenoid valve having a first switching element and a discharge resistor connected in series.

2. The signal output circuit of a solenoid valve according to claim 1, wherein the capacitance of the second capacitor is larger than the capacitance of the first capacitor.

3. The signal output circuit of a solenoid valve according to claim 1, further comprising an amplifier that amplifies the input voltage, wherein each of the first smoothing circuit and the second smoothing circuit smooths the input voltage amplified by the amplifier.

4. The signal output circuit of a solenoid valve according to claim 1, further comprising a voltage dividing resistor that divides the smoothed voltage, wherein the second voltage is obtained by dividing the smoothed voltage by the voltage dividing resistor.

5. The signal output circuit of a solenoid valve according to any one of claims 1 to 4, further comprising a detection unit that detects a change in voltage state in which the first voltage changes from a first state higher than the second voltage to a second state lower than the second voltage based on the output signal.

6. The signal output circuit of a solenoid valve according to claim 5, further comprising a switching control unit that performs a first on control for discharging the charge to the discharge circuit by turning on the first switching element in a non-energized state where the drive current does not flow through the solenoid coil, and a first off control for turning off the first switching element in an energized state where the drive current flows through the solenoid coil.

7. The signal output circuit of a solenoid valve according to claim 6, The switching control unit performs a second turn-on control to turn on a second switching element connected to the solenoid coil in order to put the solenoid coil in the energized state, and a second turn-off control to turn off the second switching element in order to put the solenoid coil in the non-energized state. When a predetermined time has elapsed after the switching control unit performs the second turn-on control to start driving the solenoid valve, the switching control unit alternately repeats the second turn-off control and the second turn-on control for the second switching element, and alternately repeats the first turn-on control and the first turn-off control for the first switching element. A signal output circuit of a solenoid valve in which the first switching element and the second switching element do not turn on simultaneously.

8. A signal output circuit of a solenoid valve according to claim 7, When the detection unit detects the state change before the predetermined time has elapsed after the switching control unit performs the second turn-on control, the switching control unit alternately repeats the second turn-off control and the second turn-on control for the second switching element before the predetermined time has elapsed. A signal output circuit of a solenoid valve.

9. A method for driving and controlling a solenoid valve by a drive circuit having a signal output circuit of a solenoid valve according to any one of claims 1 to 4, A drive start step of performing a second turn-on control to turn on a second switching element connected to the solenoid coil in order to put the solenoid coil in an energized state in which the drive current flows through the solenoid coil to start driving the solenoid valve. When a predetermined time has elapsed after the second turn-on control is performed in the drive start step, for the second switching element, a second turn-off control to turn off the second switching element in order to put the solenoid coil in a non-energized state in which the drive current does not flow through the solenoid coil, and the second turn-on control are alternately repeated, and for the first switching element, a first turn-on control to discharge the charge to the discharge circuit by turning on the first switching element in the non-energized state, and a first turn-off control to turn off the first switching element in the energized state are alternately repeated. A pulsed energization step. A state change detection step of detecting a state change of a voltage in which the first voltage changes from a first state higher than the second voltage to a second state lower than the second voltage based on the output signal. A method for driving and controlling a solenoid valve, comprising the above.

10. The method for driving and controlling a solenoid valve according to claim 9, If the state change is detected in the state change detection step before the predetermined time elapses after the second on-control is performed in the drive start step, the pulse energization step is performed before the predetermined time elapses. A method for driving and controlling a solenoid valve.

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