Signal output circuit for solenoid valve, and drive control method

Abstract

This signal output circuit (40) for a solenoid valve (10) comprises: a first smoothing circuit (110) which smooths an input voltage (Vi) corresponding to a drive current flowing through a solenoid coil (30); a second smoothing circuit (120) which has a second capacitor (C2) and smooths the input voltage; a comparator (130) which outputs an output signal (So) based on a comparison between a first voltage (V1) from the first smoothing circuit and a second voltage (V2) from the second smoothing circuit; and a discharge circuit (150) which discharges the charge accumulated in the second capacitor.

Description

Signal output circuit and drive control method for solenoid valve

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

[0002] Chinese Patent Publication No. 110998761 discloses a diagnostic device for a solenoid valve. When power is supplied to the solenoid, the solenoid current initially increases. Then, the solenoid current decreases and then increases again. Reference characteristics of the waveform of this solenoid current are obtained in advance. If the waveform of the solenoid current detected during operation of the solenoid valve changes from the reference characteristics, the solenoid valve is diagnosed as being deteriorated.

[0003] Conventionally, in order to reduce the power consumption of a solenoid valve, after the solenoid valve starts to operate, the solenoid coil that drives the solenoid valve is energized in a periodic pulse pattern. In the periodic pulse pattern, a current flows through the solenoid coil, and a non-current state in which no current flows through the solenoid coil is alternately repeated. According to a solenoid valve diagnostic device disclosed in Chinese Patent Application Publication No. 110998761, even if an abnormality occurs in which the solenoid valve does not open but remains in a closed state, the periodic pulse pattern allows the detection of an increase or decrease in the drive current similar to that when the valve is open. In this case, there is a problem that the solenoid valve may be erroneously detected as being in an open state.

[0004] The present invention aims to solve the above-mentioned problems.

[0005] 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 and 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 and smoothing the input voltage and having a larger time constant than the first smoothing circuit; a comparator having 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 the smoothed voltage obtained by smoothing the input voltage by the second smoothing circuit is input; and an output terminal to output an output signal based on a comparison between the first voltage and the second voltage; and a discharge circuit connected to the second capacitor and switching whether or not to discharge the charge accumulated in the second capacitor, wherein the discharge circuit has a first switching element and a discharge resistor connected in series.

[0006] A second aspect of the present invention is a drive control method for a solenoid valve using a drive circuit having a signal output circuit for a solenoid valve according to the first aspect, the method including: a drive start step of performing second on control to turn on a second switching element connected to the solenoid coil in order to bring the solenoid coil into a current-carrying state in which the drive current flows through the solenoid coil, in order to start driving the solenoid valve; and a second on control to turn on the second switching element connected to the solenoid coil in order to bring the solenoid coil into a current-carrying state in which the drive current does not flow through the solenoid coil, when a predetermined time has elapsed since the second on control was performed in the drive start step. The method includes a pulsed current supply step in which a second off control that turns off a switching element and the second on control are alternately repeated, and a first on control that turns on the first switching element in the non-conductive state to discharge the charge to the discharge circuit, and a first off control that turns off the first switching element in the conductive state, are alternately repeated; and a state change detection step in which a voltage state change is detected based on the output signal, in which the first 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.

[0007] According to the present invention, even when a periodic pulse of current is applied to the solenoid coil, it is possible to prevent a solenoid valve that is in a closed state from being erroneously detected as being in an open state.

[0008] The above objects, features and advantages will be easily understood from the following description of the embodiments, which will be described with reference to the accompanying drawings.

[0009] Fig. 1 is a diagram illustrating a drive circuit of a solenoid valve. Fig. 2 is a diagram illustrating changes in a first voltage and a second voltage over time when the solenoid valve opens normally. Fig. 3 is a diagram illustrating changes in a first voltage and a second voltage over time when the solenoid valve does not open normally. Fig. 4 is a flowchart showing an example of a processing procedure for drive control processing of a solenoid valve. Fig. 5 is a flowchart showing another example of a processing procedure for drive control processing of a solenoid valve.

[0010] 1 is a diagram illustrating a drive circuit 20 for a solenoid valve 10. The drive circuit 20 includes a power source E, a solenoid coil 30 that drives the solenoid 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. This generated magnetic force moves the movable iron core 10a inside the solenoid valve 10. As the movable iron core 10a moves, the solenoid valve 10 changes from a closed state to an open state. In the closed state, the movable iron core 10a abuts against the valve seat, blocking the flow path from the input port to the output port of the solenoid valve 10. In the open state, the movable iron core 10a moves away from the valve seat, opening the flow path from the input port to the output port.

[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 ground. The negative electrode of the power supply E is also connected to ground. The signal output circuit 40 is connected via an amplifier 80 to a position Pi to which the other end of the current detection resistor Rs is connected. Therefore, an input voltage Vi at the position Pi is input to the signal output circuit 40 via the amplifier 80. The input voltage Vi changes depending on 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 to the amplifier 80 from the input terminal. 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 sensitively respond 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 a conducting state in which a drive current from the power source E flows through the solenoid coil 30. When the second switching element SW2 is turned off, the solenoid coil 30 is in a non-conducting state in which the drive current from the power source E does not flow through the solenoid coil 30.

[0015] In this embodiment, 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 both performed by the signal output circuit 40. When the second switching element SW2 is a MOSFET, the signal output circuit 40 turns on or off the gate voltage via a driver for the MOSFET. 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 one end Pcp 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 pole of the power supply E. The anode of the diode Dc is connected to the other end Pcn of the solenoid coil 30. The other end of the solenoid coil 30 and the anode of the diode Dc are both connected to ground via a second switching element SW2 and a current detection resistor Rs.

[0017] The diode Dc is connected in series with the second switching element SW2, as is the solenoid coil 30. 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, an induced current generated in the solenoid coil 30 transiently circulates through the closed circuit Lc. The second switching element SW2 is not included in the closed circuit Lc. This prevents the induced current from damaging the second switching element SW2. In other words, the diode Dc protects the second switching element SW2.

[0018] The signal output circuit 40 has 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 does not have to 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 a position Ps on an output line extending 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 a 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 ground.

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

[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 a diode Dd. The other end of the second resistor R2 is connected to a 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 ground. One end of a 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 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 in accordance with the ratio of the resistance value of the voltage-dividing resistor Rv to the sum of the resistance values ​​of the voltage-dividing resistor Rv and the second resistor R2. A second voltage V2 is obtained in accordance with 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 values ​​of the first resistor R1, the capacitance values ​​of the first capacitor C1, the resistance values ​​of the second resistor R2, and the capacitance values ​​of the second capacitor C2 are determined in advance so that the time constant of the second smoothing circuit 120 is larger than the time constant of the first smoothing circuit 110. The capacitance value of the second capacitor C2 is preferably larger than the capacitance value of the first capacitor C1. This allows changes in the second voltage V2 to be delayed more slowly than changes in the first voltage V1. The resistance value of the voltage-dividing resistor Rv is also preferably larger than the resistance value of the second resistor R2. This allows stable detection of state changes, described below, related to the magnitude relationship between the first voltage V1 and the second voltage V2.

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

[0025] When the first switching element SW1 is in the on state, 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 stored in the second capacitor C2 is consumed by the discharge resistor Rd and is thereby discharged. By determining the resistance value of the discharge resistor Rd to be small, the charge stored 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 on or off the first switching element SW1. The first on control for turning on the first switching element SW1 and the first off control for turning off the first switching element SW1 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 on or off the gate voltage via a driver of the MOSFET. When the gate voltage is on, the first switching element SW1 is on. When the gate voltage is off, the first switching element SW1 is off.

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

[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, the second smoothing circuit 120 can function as a peak hold circuit that can hold the peak value of the second voltage V2 as long as the first switching element SW1 is off.

[0030] The comparator 130 has the above-mentioned first input terminal M1 and second input terminal M2, and an output terminal N. The output terminal N outputs an output signal So to the control unit 100 based on a 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.

[0031] The control unit 100 includes a processor such as a central processing unit (CPU) or a graphics processing unit (GPU), and a memory for storing programs executed by the processor. The control unit 100 may be realized by an integrated circuit such as an application specific integrated circuit (ASIC) or a field programmable gate array (FPGA), or an electronic circuit including discrete devices.

[0032] The control unit 100 includes a switching control unit 182, a NOT circuit 184, and a detection unit 186. The switching control unit 182 performs the second ON control and the second OFF control for the second switching element SW2 described above. The switching control unit 182 also performs the first ON control and the first OFF control for the first switching element SW1 described above.

[0033] 1, a control line extending from the switching control unit 182 branches at a position Pw, and the branched control lines respectively lead to the second switching element SW2 and the first switching element SW1. A NOT circuit 184 is disposed on the control line between the position Pw and the first switching element SW1.

[0034] The switching control unit 182 alternately performs second off control and second on control on the second switching element SW2, thereby energizing the solenoid coil 30 in a periodic pulse pattern. The solenoid coil 30 alternates between an energized state and a de-energized state.

[0035] The NOT circuit 184 inverts the phases of the second OFF control and the second ON control for the second switching element SW2, thereby realizing the first ON control and the first OFF control for the first switching element SW1. 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 are not turned ON at the same time.

[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 voltage state change related to the first voltage V1 and the second voltage V2 based on the acquired output signal So. The detection of the voltage state change that occurs for the first time after the solenoid valve 10 starts to be driven can be associated with the detection of the valve open state of the solenoid valve 10 by using, for example, an external device. In other words, 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 voltage state changes 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 increases over 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 this case, the first voltage V1 input to the first input terminal M1 of the comparator 130 may 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] Even when the input voltage Vi decreases over 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 this case, the first voltage V1 input to the first input terminal M1 may 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, if the input voltage Vi increases and then decreases over time, the detection unit 186 can detect, based on the output signal So, a change in the voltage state from a first state in which the first voltage V1 is higher than the second voltage V2 to a second state in which the first voltage V1 is lower than the second voltage V2.

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

[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 is turned ON and the first switching element SW1 is turned OFF. Because a large amount of power is required to open the solenoid valve 10, periodic pulsed current is not supplied to the solenoid coil 30. In other words, current is supplied to the solenoid coil 30 continuously.

[0043] After the solenoid valve 10 starts to operate, both the first voltage V1 and the second voltage V2 rise. However, the smoothing by the second smoothing circuit 120 is delayed compared to the smoothing by the first smoothing circuit 110. Therefore, the rise of the second voltage V2 is slower than the rise of the first voltage V1. Because 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, which is later than time T0, the first voltage V1 rises to a voltage value V1p. From time T0 to time T1p, the second voltage V2 also rises, but is lower than the first voltage V1. If the solenoid valve 10 opens normally, the movable iron core 10a inside the solenoid valve 10 begins to move at time T1p. That is, the solenoid valve 10 changes from a valve-closed state to a valve-open state. As the movable iron core 10a moves inside the solenoid coil 30, the inductance increases, causing the input voltage Vi to decrease. After time T1p, the first voltage V1 decreases as the input voltage Vi decreases.

[0045] As described above, the smoothing by the second smoothing circuit 120 is delayed compared to the smoothing by the first smoothing circuit 110. Therefore, time T2p, at which the second voltage V2 changes from increasing to decreasing, occurs later than the aforementioned time T1p. After the second voltage V2 increases to a voltage value V2p at time T2p, it gradually decreases in accordance with the aforementioned decrease in the input voltage Vi. The second smoothing circuit 120 can function as a peak hold circuit. Therefore, the decrease in the second voltage V2 is slower than the decrease in the first voltage V1. Therefore, at time Td, which is later than time T1p and time T2p, both the first voltage V1 and the second voltage V2 have decreased to a voltage value Vd.

[0046] From time T0 to time Td, the first state in which the first voltage V1 is higher than the second voltage V2 continues. After time Td has passed, the first state changes to a second state in which the first voltage V1 is lower than the second voltage V2. This voltage state change occurs for the first time after the solenoid valve 10 starts to be driven. The output signal So changes from low to high, and 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, which is later than time Td, the solenoid valve 10 is fully opened, and the movable core 10a stops moving. At time T1b, the first voltage V1 drops to a voltage value V1b. Because the inductance no longer changes after time T1b, the drop in the first voltage V1 stops at voltage value V1b, and the first voltage V1 starts to rise again. Time T2b, at which the second voltage V2 changes from a drop to an increase, is later than time T1b. In the example shown in FIG. 2 , at time Tu, which is later than time T1b and earlier than time T2b, the rising first voltage V1 and the falling second voltage V2 both show the voltage value Vu.

[0048] From time Td to time Tu, the second state in which the first voltage V1 is lower than the second voltage V2 continues. After time Tu, the second state changes to the first state in which 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 decreases to a voltage value V2b. The decrease in the second voltage V2 stops at voltage value V2b, and the second voltage V2 begins to increase again, similar to the first voltage V1. As described above, the increase in the second voltage V2 is slower than the increase in the first voltage V1, so the first state continues even after time T2b.

[0049] The first voltage V1 rises to a voltage value V1m and then maintains the voltage value V1m. The second voltage V2 rises to a voltage value V2m and 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 voltage value obtained by amplifying the input voltage Vi by the amplifier 80 divided by the voltage-dividing resistor Rv.

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

[0051] When the solenoid valve 10 is in the open state, a large amount of power is not required, and therefore, this periodic pulse-like energization is performed for the purpose of power-saving operation. The time at which this periodic pulse-like energization begins is assumed to be time Tc, which is a predetermined time Th after time T0. In the example shown in FIG. 2 , time Tc is after time Tu. Along with the periodic pulse-like energization that begins at time Tc, the switching control unit 182 alternately performs first off control and first on control on the first switching element SW1. In other words, the switching control unit 182 energizes the solenoid coil 30 in a periodic pulse-like manner.

[0052] When the detection unit 186 detects the first state change at the above-mentioned time Td, the switching control unit 182 may alternately perform the second off control and the second on control on the second switching element SW2 before the predetermined time Th has elapsed. In this case, the switching control unit 182 may start supplying periodic pulsed current to the solenoid coil 30 after a standby time has elapsed from the time Td. The standby time is the time from the time Td to the time when the above-mentioned time T1b is expected to have elapsed, and is determined in advance through experiments or the like.

[0053] In the example shown in FIG. 2 , periodic pulse current begins to flow at time Tc. At time Tc, the first voltage V1 rises to a voltage value V1m, and the second voltage V2 rises to a voltage value V2m. At time Tc, the second switching element SW2 turns off, and thereafter the second switching element SW2 repeatedly turns on and off. As shown in FIG. 2 , 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. Both the first voltage V1 and the second voltage V2 decrease and remain at low voltages, thereby achieving power-saving operation of the solenoid valve 10.

[0054] 3 is a diagram illustrating the changes in the first voltage V1 and the second voltage V2 over time when the solenoid valve 10 does not open normally. Also illustrated in FIG. 3 are the changes in the output signal So, the on / off changes of the first switching element SW1, and the 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 is turned ON, and the first switching element SW1 is turned OFF. As described above, at time T0, no periodic pulsed current is supplied to the solenoid coil 30. Instead, current is supplied to the solenoid coil 30 continuously.

[0056] After the solenoid valve 10 starts to operate, 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. Because 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 detector 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, the solenoid valve 10 may not open normally due to factors such as a low voltage applied from the power source E or the movable iron core 10a inside the solenoid valve 10 being stuck. If the solenoid valve 10 does not open, the input voltage Vi does not decrease. Therefore, a voltage drop in the first voltage V1 and the second voltage V2 does 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 since time T0. Therefore, the comparator 130 continues to output an output signal So indicating a low level from the output terminal N. Note that 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 a further change from that state to the second state in which the first voltage V1 is lower than the second voltage V2 does not occur, providing the voltage-dividing resistor Rv is not essential.

[0059] In this embodiment, considering the possibility that the first state may temporarily or multiple times change to the second state due to noise or the like, the voltage dividing resistor Rv is provided to reduce this possibility. Therefore, if 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 from the first state to the second state, and the valve open state can be detected more accurately.

[0060] When time Tc arrives, periodic pulse energization begins for the purpose of power saving operation. That is, the switching control unit 182 repeatedly performs second off control and 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, problems that can occur in conventional signal output circuits will be described below.

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

[0062] This embodiment solves this problem. That is, in the signal output circuit 40 according to this embodiment, the above-mentioned change in voltage state does not occur when the periodic pulse-like current starts to flow. The principle behind this will be explained below.

[0063] At time Tc shown in Fig. 3, the first voltage V1 rises to a voltage value V1m, and the second voltage V2 rises to a voltage value V2m. Because 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. As described above, periodic pulsed current flow begins at time Tc. The switching control unit 182 alternately performs second off control and second on control on the second switching element SW2, and alternately performs first on control and first off control on 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. Because the first smoothing circuit 110 is provided, the first voltage V1 does not decrease rapidly, but gradually. Because 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 the following time Tc1, the first voltage V1 drops to a voltage value V11, and the second voltage V2 drops to a voltage value V21. Because the charge stored in the second capacitor C2 is rapidly discharged, the second voltage V2 at time Tc1 is sufficiently lower than the first voltage V1. Even between time Tc and time Tc1, the first state in which the first voltage V1 is higher than the second voltage V2 is maintained, so the comparator 130 continues to output the output signal So indicating a low level from the output terminal N.

[0066] As described above, after the solenoid valve 10 starts to be driven 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, even 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 if periodic pulsed current is applied to the solenoid coil 30, it is possible to prevent the solenoid valve 10, which is 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 the 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] Between time Tc1 and time Tc2, the first state in which the first voltage V1 is higher than the second voltage V2 is maintained, and therefore the comparator 130 continues to output the output signal So indicating a low level from the output terminal N. Based on the output signal So from the comparator 130, the detection unit 186 continues to detect that the first voltage V1 is higher than the second voltage V2.

[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. The same transition occurs after time Tc2, so the voltage change described above does not occur. Therefore, even after time Tc2, the comparator 130 continues to output the output signal So indicating a low level from the output terminal N. In other words, in this embodiment, it is possible to prevent the start of periodic pulse-like current flow from being used as a trigger to erroneously detect the valve open state of the solenoid valve 10.

[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 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 processing procedure starts, in step S1, the switching control unit 182 of the control unit 100 executes second ON control for the second switching element SW2, thereby starting the drive of 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 a predetermined time Th has elapsed. If the answer is YES in step S2, the process proceeds to step S3. If the answer is NO in step S2, the process of step S2 is repeated.

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

[0074] As described above, when the detection unit 186 detects the first state change 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 predetermined time Th has elapsed. Fig. 5 is a flowchart showing another example of the drive control processing procedure for the drive circuit 20 of the solenoid valve 10. In Fig. 5, steps common to those in Fig. 4 are assigned the same numbers, and descriptions of those steps will be omitted below.

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

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

[0077] In this embodiment, as described above, periodic pulse current supply to the solenoid coil 30 begins at time Tc, which is a predetermined time Th after time T0. However, if periodic pulse current supply is not performed, the signal output circuit 40 does not need to include the first smoothing circuit 110 and the discharge circuit 150. In this 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 in which the first voltage V1 is higher than the second voltage V2. The voltage dividing resistor Rv reduces the risk of erroneously detecting a voltage state change that changes from the first state to the second state, and the valve open state can be detected more accurately.

[0079] In addition to the above disclosure, the following additional notes are disclosed.

[0080] (Note 1) A signal output circuit (40) of a solenoid valve (10) includes a first smoothing circuit (110) having a first capacitor (C1) and smoothing an input voltage (Vi) corresponding to a drive current flowing through a solenoid coil (30) that drives the solenoid valve, a second smoothing circuit (120) having a second capacitor (C2) and smoothing the input voltage and having a time constant larger than that of 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, and a second smoothing circuit (120) having a time constant larger than that of the first smoothing circuit. a comparator (130) having a second input terminal (M2) for receiving a second voltage (V2) corresponding to a smoothed voltage obtained by smoothing the input voltage, and an output terminal (N) for outputting 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 switching whether or not to discharge the charge stored in the second capacitor, the discharge circuit having a first switching element (SW1) and a discharge resistor (Rd) connected in series. With this configuration, even when a periodic pulse of current is applied to the solenoid coil, a solenoid valve in a valve-closed state can be prevented from being erroneously detected as being in an open state.

[0081] (Supplementary Note 2) In the signal output circuit for a solenoid valve described in Supplementary Note 1, it is preferable that the capacitance of the second capacitor is larger than the capacitance of the first capacitor. With this configuration, it is possible to delay a change in the second voltage compared to a change in the first voltage.

[0082] (Supplementary Note 3) The signal output circuit for a solenoid valve according to Supplementary Note 1 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 this configuration, the signal output circuit can respond sensitively to changes in the input voltage.

[0083] (Supplementary Note 4) The signal output circuit for the solenoid valve described in Supplementary Note 1 may further include a voltage dividing resistor (Rv) that divides the smoothed voltage, and the second voltage may be obtained by dividing the smoothed voltage by the voltage dividing resistor. With this configuration, it is possible to maintain a first state in which the first voltage is higher than the second voltage. This reduces the risk of erroneously detecting a voltage state change from the first state to a second state in which the first voltage V1 is lower than the second voltage V2, and allows for more accurate detection of the valve open state.

[0084] (Supplementary Note 5) The signal output circuit for a solenoid valve according to any one of Supplementary Notes 1 to 4 may further include a detection unit (186) that detects a voltage state change based on the output signal, where 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. With this 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) The signal output circuit for the solenoid valve described in Supplementary Note 5 may further include a switching control unit (182) that performs first on control to turn on the first switching element in a non-energized state where the drive current does not flow through the solenoid coil, thereby causing the discharge circuit to discharge the charge, and first off control to turn off the first switching element in a powered state where the drive current flows through the solenoid coil. With this configuration, the charge accumulated in the second capacitor can be rapidly discharged when the solenoid coil changes from a powered state to a non-energized state.

[0086] (Supplementary Note 7) In the signal output circuit for the solenoid valve described in Supplementary Note 6, the switching control unit performs a second on control to turn on a second switching element (SW2) connected to the solenoid coil to bring the solenoid coil into the energized state, and a second off control to turn off the second switching element to bring the solenoid coil into the de-energized state, and when a predetermined time (Th) has elapsed since the switching control unit performed the second on control to start driving the solenoid valve, the switching control unit alternately performs the second off control and the second on control on the second switching element and alternately performs the first on control and the first off control on the first switching element, so that the first switching element and the second switching element do not turn on simultaneously. With this configuration, it is possible to achieve power-saving operation of the solenoid valve while preventing erroneous detection of the valve open state of the solenoid valve.

[0087] (Supplementary Note 8) In the signal output circuit for a solenoid valve described in Supplementary Note 7, if the detection unit detects the state change before the predetermined time has elapsed since the switching control unit performed the second on control, the switching control unit may alternately repeat the second off control and the second on control on the second switching element before the predetermined time has elapsed. With this configuration, a high power saving effect can be achieved when the solenoid valve opens normally.

[0088] (Supplementary Note 9) A drive control method for a solenoid valve using a drive circuit (20) having a signal output circuit for a solenoid valve according to any one of Supplementary Notes 1 to 4, comprising: a drive start step for performing second on-control to turn on a second switching element connected to the solenoid coil in order to set the solenoid coil to a current-carrying state in which the drive current flows through the solenoid coil, in order to start driving the solenoid valve; and when a predetermined time has elapsed since the second on-control was performed in the drive start step, performing second on-control to turn on the second switching element in order to set the solenoid coil to a current-de-carrying state in which the drive current does not flow through the solenoid coil. and a pulsed energization step of alternately repeating a second off control that turns off a switching element and the second on control, and alternately repeating a first on control that turns on the first switching element in the de-energized state to discharge the charge to the discharge circuit and a first off control that turns off the first switching element in the energized state, and a state change detection step of detecting a voltage state change, based on the output signal, in which the first 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. With this configuration, it is possible to achieve power-saving operation of the solenoid valve while preventing erroneous detection of an open state of the solenoid valve when the solenoid valve does not open normally.

[0089] (Supplementary Note 10) In the method for controlling the drive of a solenoid valve according to Supplementary Note 9, if the state change is detected in the state change detection step before the predetermined time has elapsed since the second ON control was performed in the drive start step, the pulsed current application step is performed before the predetermined time has elapsed. With this configuration, the power saving effect of a solenoid valve that is normally opened is further improved.

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

Claims

1. A first smoothing circuit (110) having a first capacitor (C1) and smoothing an input voltage (Vi) corresponding to a drive current flowing through a solenoid coil (30) that drives a solenoid valve (10); a second smoothing circuit (120) having a second capacitor (C2) and smoothing the input voltage and having a time constant larger than that of the first smoothing circuit; a comparator (130) having 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, and an output terminal (N) to output 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 switching whether or not to discharge the charge accumulated in the second capacitor, The discharge circuit is a signal output circuit (40) for a solenoid valve, the signal output circuit (40) having a first switching element (SW1) and a discharge resistor (Rd) connected in series.

2. A signal output circuit for a solenoid valve as claimed in claim 1, wherein the capacity of the second capacitor is greater than the capacity of the first capacitor.

3. A signal output circuit for a solenoid valve as claimed in claim 1, further comprising an amplifier (80) for amplifying the input voltage, and each of the first smoothing circuit and the second smoothing circuit smoothes the input voltage amplified by the amplifier.

4. A signal output circuit for a solenoid valve as claimed in claim 1, further comprising a voltage dividing resistor (Rv) for dividing the smoothed voltage, and the second voltage is obtained by dividing the smoothed voltage by the voltage dividing resistor.

5. A signal output circuit for a solenoid valve as claimed in any one of claims 1 to 4, further comprising a detection section (186) for detecting a voltage state change based on the output signal, the voltage state changing 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.

6. A signal output circuit for a solenoid valve as described in claim 5, further comprising a switching control section (182) which 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 a powered state where the drive current flows through the solenoid coil.

7. A signal output circuit for a solenoid valve as described in claim 6, wherein the switching control section performs a second on control to turn on a second switching element (SW2) connected to the solenoid coil in order to bring the solenoid coil into the energized state, and a second off control to turn off the second switching element in order to bring the solenoid coil into the non-energized state, and when a predetermined time (Th) has elapsed after the switching control section performs the second on control to start driving the solenoid valve, the switching control section alternately performs the second off control and the second on control on the second switching element, and alternately performs the first on control and the first off control on the first switching element, and the first switching element and the second switching element are not turned on simultaneously.

8. A signal output circuit for a solenoid valve as described in claim 7, wherein, when the detection unit detects the state change before the predetermined time has elapsed since the switching control unit performed the second on control, the switching control unit alternately repeats the second off control and the second on control on the second switching element before the predetermined time has elapsed.

9. A method for controlling the drive of a solenoid valve using a drive circuit (20) having a signal output circuit for a solenoid valve as described in any one of claims 1 to 4, comprising: a drive start step in which a second on control is performed to start driving the solenoid valve, the second on control being performed to turn on a second switching element connected to the solenoid coil in order to place the solenoid coil in a current-carrying state in which the drive current flows through the solenoid coil; and a pulse-like current-carrying step in which, when a predetermined time has elapsed since the second on control was performed in the drive start step, a second off control is performed to turn off the second switching element in order to place the solenoid coil in a current-carrying state in which the drive current does not flow through the solenoid coil, and the second on control are alternately repeated, and, for the first switching element, a first on control is performed to turn on the first switching element in the current-carrying state to discharge the charge to the discharge circuit, and a first off control is performed to turn off the first switching element in the current-carrying state. a state change detection step of detecting a state change of a voltage, in which the first 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.

10. A method for controlling the drive of an electromagnetic valve as described in claim 9, wherein if the state change is detected in the state change detection step before the predetermined time has elapsed since the second on control was performed in the drive start step, the pulsed current step is performed before the predetermined time has elapsed.

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