Proportional solenoid valve opening control system

Abstract

Provided is a proportional solenoid valve opening control system capable of performing position correction of a movable iron core by electrical current correction control and obtaining a flow rate characteristic that becomes constant with respect to an increase in valve differential pressure. 【Solution means】A current control circuit that controls the supply current to the solenoid via a switching element that is ON-OFF controlled by a PWM signal has an amplitude detection unit that detects the amplitude value of a sawtooth current waveform formed by the current rise during the ON period and the current fall during the OFF period in one pulse period from the detected current value of the solenoid, and based on the detected amplitude value, a current correction amount calculation unit that calculates a correction current amount corresponding to the amount of current that cancels out the displacement amount between the current position of the movable iron core and the position of the movable iron core where the target command flow rate is obtained and adds it to the command signal.

Description

Technical Field

[0001] The present invention relates to a proportional solenoid valve opening control system that performs current correction control based on the position of a movable iron core estimated from the detected current amplitude of a solenoid in order to improve the flow rate reduction characteristics associated with changes in the valve differential pressure of a proportional solenoid valve.

Background Art

[0002] In a general hydraulic solenoid valve (solenoid valve), when the solenoid coil is de-energized, the valve spool is positioned in the closed state by the biasing force of a spring, and the movable iron core is attracted to the fixed iron core by the electromagnetic attraction force generated by energizing the solenoid coil. Accordingly, the valve spool is displaced in the valve opening direction.

[0003] In particular, a proportional solenoid valve attracts a movable iron core with an electromagnetic force proportional to the current flowing through the solenoid coil, and accordingly, a predetermined valve opening (opening area) is obtained by displacing the valve spool against the spring biasing force, and the flow rate of the target working fluid is achieved. Therefore, in a proportional solenoid valve, the position of the movable iron core and the valve spool is controlled so as to obtain an arbitrary valve opening by controlling the current to the solenoid. In a proportional solenoid, a thrust proportional to the energizing current to the coil is obtained as the output of the solenoid, but substantially, the position of the movable iron core is controlled by balancing the thrust of the solenoid and the resistance of the spring serving as a load.

[0004] As described above, since a proportional solenoid valve can arbitrarily control the opening of the valve from closed to fully open by controlling the current to the solenoid and can adjust it to a desired flow rate, it enables continuous flow rate adjustment that cannot be achieved by a general on / off solenoid valve that can switch between two states of open and closed. Therefore, it is effective for high-precision speed control. Accordingly, proportional solenoid valves are widely used for controlling various hydraulic drive devices in various construction and civil engineering machines including heavy machines such as crane trucks and excavator trucks, agricultural machines, and fishing machines such as the winching machines of fishing boat nets.

[0005] In addition, for current control of a proportional solenoid, it is common to use PWM (Pulse Width Modulation) control. PWM control obtains an output current with a desired waveform by controlling the ratio of the ON time to the OFF time in one cycle, that is, by modulating the pulse width.

[0006] The modulation of the pulse width is performed by controlling the timing of the ON-OFF switching of energization in a switching element. A transistor such as an FET (Field Effect Transistor) is used as the switching element. Therefore, in practice, a rectangular wave voltage with a modulated pulse width is applied to the solenoid coil. Since the current rises during the ON period and drops during the OFF period according to the rectangular wave, the control current to the solenoid is energized with a sawtooth-shaped current waveform.

[0007] Substantially, the conduction rate can be increased by increasing the pulse width of the ON time in one cycle, and the conduction rate can be decreased by decreasing the pulse width of the ON time. Such an ON-OFF ratio can obtain an arbitrary output between 0% and 100% conduction rate.

[0008] Therefore, in a proportional solenoid valve, for example, as shown in FIG. 9, in the current control circuit 50, from a command signal Os in which a command current value Oc is converted into a digital signal via an analog / digital converter 5, a predetermined PWM signal Ps with a modulated pulse width is generated by a PWM conversion unit 51 according to its level and output as a switching control signal. Then, ON-OFF switching control according to this PWM signal Ps is performed on a switching element 3 (FET) interposed between the solenoid 2 and the power supply, thereby obtaining a target current waveform, and a control current corresponding to the command current value Oc is supplied to the solenoid 2.

[0009] In such PWM control, a freewheeling diode is essential. As shown in FIG. 9, by connecting a freewheeling diode 4 across the solenoid 2, the current during OFF is diverted to prevent the generation of a back electromotive force.

[0010] The above current control circuit 50 can be configured by the CPU arithmetic unit of a one-chip microcomputer. A one-chip microcomputer is a microprocessor in which a CPU, a storage device (ROM·RAM), various input / output devices, a timer, an analog / digital converter, etc. are collectively mounted on a single integrated circuit (IC chip). By performing the processing of a specific function with only such a small one IC chip, and in recent years, due to price reduction, low power consumption and high performance, and miniaturization, the one-chip microcomputer is not only used for controlling the proportional solenoid valve as described above, but is generally used for controlling automation devices and electrical equipment in many fields.

[0011] As described above, a control current is supplied to the solenoid 2 by PWM control based on the command signal Os, the movable iron core and the valve spool are positioned by the attracting force corresponding to the control current, and the target flow rate corresponding to the command current value Oc is obtained at a predetermined valve opening degree.

[0012] However, the control current flowing through the solenoid 2 changes due to changes in the power supply voltage and the load resistance. Therefore, in order to suppress such changes, as shown in FIG. 9, in the current control circuit 50, the command current value is corrected by negative feedback based on the detected current value from the current detection unit 6 on the output side of the solenoid 2 by the negative feedback circuit 52, and it has generally been to enhance the stability of the control current.

[0013] Such a PWM control type proportional solenoid valve is used, for example, for continuous position control of actuators in various hydraulic devices as disclosed in Patent Documents 1 and 2.

Prior Art Documents

Patent Documents

[0014]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0015] In a proportional solenoid valve, not only the drive position control of the valve spool but also control for maintaining the target flow rate is necessary. That is, since it is required to keep the flow rate constant even when a change occurs in the valve differential pressure between the inflow side and the outflow side, the thrust generated at an arbitrary position of the valve spool and the movable iron core, that is, the suction force of the coil is controlled.

[0016] Normally, since the fluid force that increases as the valve differential pressure increases acts on the valve spool in the valve closing direction, by adjusting the spool shape and the biasing force by the spring, the amount of displacement of the valve spool by the fluid force (flow path opening area) and the flow rate that changes with the valve differential pressure are balanced to obtain a differential pressure-flow rate characteristic such that the flow rate remains constant with respect to a change in the valve differential pressure.

[0017] However, it has been difficult to keep the flow rate constant with respect to a change in the valve differential pressure over all flow rate and differential pressure regions only by adjusting the spool shape and the biasing force of the spring. Generally, in a design (spool design) with a characteristic that emphasizes the maximum flow rate to increase the maximum value of the flow rate with respect to the valve differential pressure, it is possible to make the characteristic of the flow rate with respect to the valve differential pressure in a relatively small flow rate range (differential pressure-flow rate characteristic) constant, but in a relatively large flow rate range, since the fluid force is too large with respect to the solenoid suction force, as shown in FIG. 10, the characteristic is such that the flow rate decreases as the valve differential pressure increases. That is, in a proportional solenoid valve that only opposes the biasing force by the spring, as shown in FIG. 11, since the energizing current to the proportional solenoid is constant, the amount of displacement of the movable iron core and the valve spool position in the valve closing direction due to the fluid force is greater than the increasing pressure of the flow rate accompanying the increase in the valve differential pressure, so the flow rate decreases as the differential pressure increases.

[0018] In addition, in a setting where the biasing force of the spring against the fluid force is increased, the displacement amount of the movable iron core and valve spool that can be changed by the attracting force of the proportional solenoid becomes small, so the maximum flow rate that the valve can originally pass through decreases. On the other hand, in the case of a valve having a valve spool position detection sensor, positioning control of the spool that emphasizes reproducibility is performed, and in order to set its gain high, it is controlled in a direction where spool displacement does not occur due to the fluid force, and it was not considered to make the flow rate constant by correcting the valve opening.

[0019] In a proportional solenoid valve, it is desirable to improve the characteristic of the flow rate decrease accompanying the increase in the valve differential pressure as described above. However, since it is a sensorless configuration without a valve spool position detection sensor, it was not possible to make the flow rate constant by electrically controlling the position of the movable iron core and valve spool and correcting the valve opening.

[0020] In view of the above problems, an object of the present invention is to perform position correction of a movable iron core and valve spool by electrical current correction control without causing an adverse effect of reducing the maximum flow rate of the valve even in a sensorless proportional solenoid valve, and to provide a proportional solenoid valve opening control system capable of obtaining a flow rate characteristic that is constant even when the valve differential pressure increases.

Means for Solving the Problems

[0021] In order to achieve the above object, in a proportional solenoid valve opening control system that achieves a target valve opening by controlling the current supplied from a power source to a solenoid for a proportional solenoid valve in which a valve spool is displaced together with a movable iron core by an electromagnetic attracting force proportional to the current supplied to the solenoid, and the flow rate of the working fluid is determined by the valve opening corresponding to the displacement, A switching element that controls the current supplied to the solenoid by turning on and off the power supply from the power source, and based on a command signal indicating a command current value corresponding to a target flow rate, outputs a switching control signal that commands the switching timing of the on / off operation of the switching element to the switching element, and a storage unit that stores instructions for processing executed by the current control circuit. The current control circuit A PWM conversion unit that generates, as the switching control signal, a PWM signal in which the on / off pulse width in one pulse period is adjusted to a duty ratio corresponding to the energization rate corresponding to the command current value from the command signal, and outputs the PWM signal to the switching element. It includes a negative feedback circuit that negatively feeds back the detected current value from the output side of the solenoid and adds the deviation from the command current value to the command signal for correction. It further includes a current correction circuit that obtains a correction current amount that cancels out the flow rate change accompanying the change in the valve differential pressure of the proportional solenoid valve and corrects the current to the solenoid. The current correction circuit An amplitude detection unit that detects the amplitude value of a sawtooth-like current waveform formed by the current rise during the ON period and the current fall during the OFF period in the one pulse period from the detected current value of the solenoid. Based on the detected amplitude value detected by the amplitude detection unit, it calculates and outputs a correction current amount corresponding to an electric current amount that cancels out the displacement amount between the current position of the movable iron core and the position of the movable iron core where the target command flow rate is obtained, and adds it to the command signal. It is characterized by having a current correction amount calculation unit.

[0022] The proportional solenoid valve opening degree control system according to the invention described in claim 2 is the proportional solenoid valve opening degree control system according to claim 1, wherein the current correction amount calculation unit Applying a characteristic function that is set in advance according to the correlation between the detected amplitude value and the amplitude value of the current waveform based on the PWM signal of the solenoid and the distance from the solenoid fixed core adsorption position of the movable iron core and stored in the storage unit to estimate the current position of the movable iron core, specifying the valve differential pressure at the current position, specifying the current value at the position of the movable iron core where the target command flow rate can be obtained in the valve differential pressure, and outputting the difference between the current value and the current value at the current position as the current correction amount.

[0023] The proportional solenoid valve opening degree control system according to the invention described in claim 3 is the proportional solenoid valve opening degree control system according to claim 1, wherein the current correction amount calculation unit outputs the difference between the detected amplitude value and the theoretical amplitude value at the time of no flow rate in the command current value as the correction current amount. The current correction circuit further includes a weighting unit that multiplies the current correction amount by a weighting factor that is set to be selectable in advance according to the change in the flow rate decrease rate accompanying the increase in the valve differential pressure and stored in the storage unit.

[0024] The proportional solenoid valve opening degree control system according to the invention described in claim 4 is the proportional solenoid valve opening degree control system according to claim 1, wherein the current control circuit is composed of a CPU arithmetic unit mounted on a one-chip microcomputer, and the storage unit is a storage device mounted on the one-chip microcomputer.

[0025] The proportional solenoid valve opening degree control system according to claim 5 is the proportional solenoid valve opening degree control system according to claim 1, wherein the amplitude detection unit Obtains an AC component with the DC component removed by differentiating the detection current signal obtained from the detection current value from the current detection unit via an analog / digital converter, smooths the pulse wave converted to DC by full-wave rectifying the AC component, and outputs an amplitude signal as a gently shaped waveform.

[0026] The proportional solenoid valve opening degree control system according to claim 6 is the proportional solenoid valve opening degree control system according to claim 1, wherein the amplitude detection unit obtains a pulse one-cycle signal indicating one cycle of the pulse in which the ON-OFF control of the switching element is performed from the PWM conversion unit, and from the detected current value of the solenoid obtained by the current detection unit, the maximum current value and the minimum current value in the pulse one-cycle section specified by the pulse one-cycle signal are specified, and the difference therebetween is calculated as the current amplitude of the PWM cycle.

Effect of the Invention

[0027] According to the present invention as well, in the proportional solenoid valve opening degree control system, a current control circuit that controls the current supplied to the solenoid of the proportional solenoid valve in a PWM control manner, based on the amplitude value of the sawtooth current waveform detected from the detected current value of the solenoid, calculates a current correction amount that cancels the displacement amount between the current position of the movable iron core and the position of the movable iron core where the target command flow rate can be obtained, and adds it to the command signal to correct the current supplied to the solenoid. Therefore, by correcting the current to the solenoid, it is possible to obtain a proportional solenoid valve that can suppress the increase and decrease of the flow rate accompanying the increase and decrease of the valve differential pressure and improve the flow rate characteristics with respect to the valve differential pressure to a constant flow rate.

[0028] In addition, since such current correction control provides a characteristic of a constant flow rate with respect to the valve differential pressure, it is also possible to simplify the structure of the valve spool and increase the maximum flow rate of the valve by increasing the fluid force. Furthermore, since it is possible to respond to the load behavior generated by the load fluctuation at the use site, an effect that the application range of the proportional solenoid valve according to the present invention becomes wider than before can also be expected.

Brief Description of the Drawings

[0029]

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Embodiments for Carrying Out the Invention

[0030] The proportional solenoid valve opening degree control system according to the present invention is a PWM control type proportional solenoid valve, in which a current control circuit for controlling the current supplied to the solenoid to achieve the target flow rate of the working fluid, in addition to the conventional negative feedback circuit, further includes a current correction circuit that corrects the current according to the displacement amount of the movable iron core position due to the increase or decrease of the valve differential pressure that causes a flow rate change in the proportional solenoid valve.

[0031] The current correction circuit in the present invention includes an amplitude detection unit that detects the amplitude value of a sawtooth-shaped current waveform based on the PWM signal from the detected current value of the solenoid, and based on the detected amplitude value detected by this amplitude detection unit, calculates and outputs a current correction amount that cancels out the displacement amount between the current position of the movable iron core and the position of the movable iron core where the target command flow rate is obtained, and adds it to the command signal. By this current correction circuit, it is possible to suppress the flow rate change accompanying the increase or decrease of the valve differential pressure, and it becomes possible to improve the flow rate characteristics with respect to the valve differential pressure to a constant flow rate.

[0032] The current supplied to the solenoid of the proportional solenoid valve becomes a sawtooth-shaped current waveform formed by the current rise during the ON period and the current fall during the OFF period by PWM control. However, the inventor of the present invention found that there is a correlation between the amplitude value of this sawtooth-shaped current waveform and the position of the movable iron core, and the relationship between this current amplitude and the position of the movable iron core does not change depending on the valve differential pressure. Therefore, by detecting the sawtooth-shaped current amplitude value from the detected current value on the output side of the solenoid, the current position of the movable iron core can be estimated, and by obtaining a current correction amount that cancels out the displacement amount between this current position and the position of the movable iron core where the target command flow rate is obtained, the inventor came up with the idea that the control current to the solenoid can be corrected, and thus the present invention was achieved.

[0033] That is, since the amplitude of the sawtooth current waveform is determined by the inductance of the solenoid, it changes due to the change in the magnetic path of the solenoid. As shown in FIG. 4, as the movable iron core approaches the adsorption position to the fixed iron core of the solenoid, the current amplitude value increases. Based on this characteristic, a characteristic function based on the correlation between the current amplitude value and the distance of the movable iron core from the fixed iron core adsorption position can be obtained in advance. Therefore, by using this characteristic function, the current position of the movable iron core at this time can be estimated from the detected amplitude value of the sawtooth current waveform detected from the detected current value on the output side of the solenoid.

[0034] On the other hand, not only the relationship between the current amplitude and the position of the movable iron core, but also the relationship characteristics between the flow rate and the valve differential pressure with respect to the position of the movable iron core with the current in the solenoid valve as an intermediate variable are obtained by experimental measurement in advance. Therefore, based on these relationship characteristics, if the current position of the movable iron core is specified, the valve differential pressure at that current position can also be specified. Furthermore, the position of the movable iron core at which the target command flow rate can be obtained at that valve differential pressure can also be specified.

[0035] Therefore, by obtaining the amount of current that cancels the displacement between the position of the movable iron core at which the target command flow rate is obtained and the current position as a correction amount, and adding the current correction amount to the command current value, the flow rate can be controlled to be constant. In this case, actually, based on the relationship characteristics known in advance for the solenoid valve as described above, the current value at the current position and the current value at the position of the movable iron core at which the target command flow rate is obtained can be specified respectively. Therefore, the current correction amount can be obtained by calculating the difference between the two current values.

[0036] Here, the correlation between the PWM-controlled sawtooth current amplitude value of the solenoid and the distance of the movable iron core from the fixed iron core adsorption position is shown in the graph of FIG. 5 with the measured data at different command current values of 0.8 A, 1 A, 1.2 A, and 1.4 A. In this graph, the distance of the movable iron core from the fixed iron core adsorption position (mm) is shown on the horizontal axis with respect to the effective value of the PWM current amplitude (A) on the vertical axis, and the direction in which the distance increases is the direction in which the flow rate decreases.

[0037] From the graph of FIG. 5, it can be seen that the correlation between the effective value of the current amplitude and the distance from the fixed core adsorption position of the movable core has a substantially similar characteristic function (the relationship between the current amplitude and the position) for each current value. Therefore, if such a characteristic function is preset and stored in the storage unit, it can be used in actual current correction control. In addition, the storage unit can also store the flow rate characteristics with respect to the valve differential pressure and the movable core position characteristics with respect to the valve differential pressure, etc., which are experimentally measured in advance for the solenoid valve, and these relational characteristics can also be used by the current correction amount calculation unit.

[0038] In the present invention, it is also possible to roughly obtain the current correction amount by simplifying the process of obtaining the above current correction amount. In this case, the position of the movable core at no flow rate in the state where the valve opening degree is determined only by the solenoid attraction force and the spring force opposing it at the command current value of the solenoid valve, that is, the position of the movable core at no flow rate, is regarded as the position of the movable core at which the target command flow rate can be obtained at the valve differential pressure at the current position of the movable core. Thus, the difference between the current values at both positions can be regarded as the difference between the amplitude values (current values) corresponding to both positions. Therefore, the current correction amount calculation unit of the present invention may calculate the difference between the detected amplitude value (current value) corresponding to the current position of the movable core and the theoretical amplitude value (current value) at no flow rate as the current correction amount.

[0039] Note that the current correction amount calculated as described above is made more appropriate by providing a weighting unit in the current correction circuit that adds to the command signal as the final correction amount a weighted value according to the reduction rate of the flow rate that decreases as the valve differential pressure increases, thereby optimizing the correction control.

[0040] This is because in a proportional solenoid valve, the displacement rate of the movable core accompanying the increase in the valve differential pressure, that is, the flow rate reduction rate may have a flow rate characteristic that is not constant. Therefore, if a weighting coefficient corresponding to different flow rate reduction rates is set in advance from the weighting function corresponding to this flow rate characteristic, by multiplying the appropriate weighting coefficient to the current correction amount, the correction amount finally added to the command signal is adjusted, and more appropriate and efficient current correction control becomes possible.

[0041] For example, in the flow rate characteristics (before correction) shown in FIG. 8, it can be seen that correction is not necessary during period X from the state where the valve differential pressure is zero to the pressure required to achieve the target flow rate. Therefore, until period X elapses while the movable iron core moves from the valve open position in the closing direction, "0" may be set as the weighting factor to be multiplied by the current correction amount.

[0042] And after the target flow rate is achieved and period X has elapsed, correction control is performed to keep the flow rate constant by adding a current correction amount corresponding to the decrease in the flow rate as the valve differential pressure increases as described above. However, after the target flow rate is reached, as the control current to the solenoid increases due to the correction, the displacement rate of the movable iron core and the decrease in the flow rate accompanying the increase in the valve differential pressure are suppressed after a certain period Y has elapsed. Therefore, if the weighting factor corresponding to period Y is set to "1" and the weighting factor corresponding to period Z where the displacement rate of the movable iron core and the flow rate decrease rate are small after period Y has elapsed is set to be larger than period Y, for example, "1.5", these weighting factors can be appropriately used in the actual current correction control.

[0043] By appropriately selecting and using each of the above weighting factors according to the change in the flow rate decrease rate, as shown in the predicted flow rate characteristics after correction in FIG. 8, the decrease in the flow rate accompanying the increase in the valve differential pressure is suppressed to an appropriate correction amount over periods Y and Z after the target flow rate is achieved, and the flow rate characteristics shown before correction are improved to substantially a constant flow rate characteristic.

[0044] Note that there are the following two types of amplitude detection units in the current correction circuit of the present invention depending on the detection method of the current amplitude value.

[0045] As the first amplitude detection unit, as shown in FIG. 6, a pulse one-cycle signal indicating a pulse one-cycle T in which ON-OFF control of a switching element is performed is acquired from the PWM conversion unit, and a detected current value of the solenoid is acquired from the current detection unit. The maximum current value M and the minimum current value n in the section of one cycle T are stored from the detected current value, and the difference between the two is obtained as the current amplitude of the PWM cycle.

[0046] Also, as the second amplitude detection unit, as shown in FIG. 7, the detected current value of the solenoid from the current detection unit is acquired as a detection current signal Cs via an analog / digital converter, and the detected current signal Cs is differentiated (S1) to remove the DC component, and the AC component ACc is full-wave rectified (S2) to obtain a pulse wave Pc converted to DC, and this pulse wave Pc is smoothed (S3) and output as an amplitude signal Ams.

[0047] The proportional solenoid valve opening control system according to the present invention having the above configuration can also be configured with a one-chip microcomputer, similar to the conventional current control system of a proportional solenoid valve. In this case, the current control circuit in the present invention can be configured in the CPU arithmetic unit of the one-chip microcomputer, and the storage device (ROM·RAM) of the one-chip microcomputer can be used as the storage unit for storing the above characteristic functions, weighting factors, etc. Therefore, since the hardware configuration is substantially the same as the conventional one except for the CPU arithmetic unit, there is almost no increase in cost compared to the conventional one.

Example

[0048] As an example of the present invention, the schematic configuration of the proportional solenoid valve opening control system 1 when configured with a one-chip microcomputer is shown in the circuit block diagram of FIG. 1. In this example, the case where the proportional solenoid valve is of the spring balance type, direct-acting valve spool type, and 3-position 4-port (pressure port P, cylinder ports A, B, return port T) type is taken as an example. In this proportional solenoid, the control direction is selected by energizing one of the two solenoids. In this example, the flow direction of P→B, A→T is used.

[0049] In the proportional solenoid valve opening control system 1 of this embodiment, there are a switching element 3 that controls the current supplied to the solenoid 2 by turning on and off the energization from the power supply, and based on a command signal Os in which a command current value Oc corresponding to a target flow rate is converted into a digital signal via an analog / digital converter 5, a current control circuit 10 that outputs a switching control signal for commanding the ON / OFF switching timing to the switching element 3.

[0050] In this embodiment, the current control circuit 10 is composed of a CPU arithmetic unit of a one-chip microcomputer. A freewheeling diode 4 is connected to both ends of the solenoid 2 to divert the current when it is OFF and prevent the generation of a back electromotive force. Also, an FET (field effect transistor) is used for the switching element 2.

[0051] Also, in the storage device (ROM·RAM) 30 of the one-chip microcomputer, not only the instructions of the process executed by the current control circuit 10 are stored, but also the characteristic function set in advance according to the correlation between the amplitude value of the sawtooth current waveform based on the PWM signal Ps of the solenoid 2 and the distance from the adsorption position of the movable iron core to the solenoid fixed iron core as shown in FIG. 5 above, and the characteristics showing the relationship between the flow rate and the valve differential pressure with respect to the position of the movable iron core with the current in the solenoid valve measured experimentally in advance as a mediating variable can also be stored.

[0052] In the current control circuit 10, in a PWM conversion unit 11 to which the command signal Os is input via an amplifier G, a PWM signal Ps in which the ON / OFF pulse width in one pulse period is adjusted to a duty ratio corresponding to the energization rate of the command current value Oc is generated and output as the switching control signal.

[0053] Also, a current detection unit 6 for detecting the current value is provided on the output side of the solenoid 2, and the current control circuit 10 is provided with a negative feedback circuit 12. By this negative feedback circuit 12, the detected current signal Cs obtained by converting the detected current value from the current detection unit 6 into a digital signal via the analog / digital converter 7 is smoothed and negatively fed back, and the deviation from the command signal Os is added to the command signal Os. As a result, a control current for suppressing changes in the energizing current due to power supply voltage fluctuations and load resistance changes is obtained for the solenoid 2.

[0054] And in this embodiment, the current control circuit 10 further includes a current correction circuit 20 that corrects the energization amount to the solenoid 2 so as to cancel out the flow rate change accompanying the change in the valve differential pressure.

[0055] The current correction circuit 20 includes an amplitude detection unit 21 that detects the amplitude value of a sawtooth current waveform based on the PMN signal from the detected current signal Cs and outputs it as a detected amplitude signal Ams, a theoretical amplitude output unit 22 that outputs the theoretical current amplitude value at the time of zero flow rate in the command current value as a theoretical amplitude signal Tms based on the command signal Os, and a current correction amount calculation unit 23 that outputs the difference obtained by comparing the detected amplitude signal Ams and the theoretical amplitude signal Tms as a current correction amount Ca.

[0056] In this embodiment, the amplitude detection unit 21 employs the detection method shown in FIG. 7 described above. That is, in the amplitude detection unit 21, the detected current signal Cs is differentiated (S1) to obtain an AC component ACc with the DC component removed, this AC component ACc is full-wave rectified (S2) to obtain a pulse wave Pc converted to DC, and then this pulse wave Pc is smoothed (S3) to obtain an amplitude signal Ams as a gently shaped waveform.

[0057] Also, in the current correction circuit 20 of the present embodiment, a weighting unit 24 is further provided that applies weighting corresponding to the flow rate change rate to the current correction amount Ca to obtain an appropriate correction amount CA. In this weighting unit 24, three types of weighting coefficients, "0", "1", and "1.5", which are set in advance corresponding to the flow rate characteristics shown in FIG. 8 and stored in the storage device 30, are used.

[0058] In the proportional solenoid valve opening control system 1 according to the present embodiment having the above configuration, the results of current correction control are shown in the graph diagrams of FIGS. 2 and 3. FIG. 2 plots the corrected flow rate (L / min) on the vertical axis with respect to the valve differential pressure (MPa) on the horizontal axis and shows it together with the flow rate characteristics before correction. FIG. 3 plots the corrected current (A) on the vertical axis with respect to the valve differential pressure (MPa) on the horizontal axis and shows the current correction amount with respect to the current value before correction.

[0059] As can be seen from the results shown in FIGS. 2 and 3, according to the current correction control of the present embodiment, an improvement in the valve differential pressure - constant flow rate characteristic was observed that was substantially consistent with the prediction shown in FIG. 8.

Explanation of Reference Numerals

[0060] 1: Proportional solenoid valve opening control system 2: Solenoid 3: Switching element 4: Commutating diode 5, 7: Analog / digital converter G: Amplifier 6: Current detection unit 10, 50: Current control circuit 11, 51: PWM conversion unit 12, 52: Negative feedback circuit 20: Current correction circuit 21: Amplitude detection unit 22: Theoretical amplitude calculation unit 23: Current correction amount calculation unit 24: Weighting unit

Claims

1. A proportional solenoid valve in which a valve spool is displaced together with a movable iron core by an electromagnetic attractive force proportional to the current passed through the solenoid, and the flow rate of a working fluid is determined by the valve opening corresponding to the displacement. In this proportional solenoid valve opening control system, a target valve opening is achieved by controlling the current passed from a power source to the solenoid, a switching element that controls a current supplied to the solenoid by turning on and off the current from the power source, a current control circuit that outputs a switching control signal that instructs the switching element on and off switching timing based on a command signal indicating a command current value corresponding to a target flow rate, and a memory unit that stores instructions for processing to be executed by the current control circuit; The current control circuit includes: a PWM conversion unit that generates a PWM signal as the switching control signal, the PWM signal being adjusted to a duty ratio such that an ON-OFF pulse width in one pulse period becomes a duty ratio corresponding to the command current value, and outputs the PWM signal to the switching element; a negative feedback circuit that negatively feeds back a detected current value from an output side of the solenoid and adds a deviation from the command current value to the command signal for correction, a current correction circuit for correcting a current to the solenoid by calculating a correction current amount for offsetting a change in flow rate caused by a change in the valve differential pressure of the proportional solenoid valve; The current correction circuit includes: an amplitude detection unit that detects an amplitude value of a sawtooth-shaped current waveform formed by a current rise during the ON period and a current drop during the OFF period in one pulse cycle from the detected current value of the solenoid; a current correction amount calculation unit that calculates and outputs a correction current amount corresponding to a current amount that offsets an amount of displacement between the current position of the movable core and a position of the movable core at which a target command flow rate is obtained, based on a detected amplitude value detected by the amplitude detection unit, and adds the correction current amount to the command signal.

2. The current correction amount calculation unit 2. The proportional solenoid valve opening control system according to claim 1, characterized in that a characteristic function, which is set in advance based on a correlation between an amplitude value of a current waveform based on a PWM signal of the solenoid and a distance of the movable core from a solenoid fixed core attraction position and is stored in the memory unit, is applied to the detected amplitude value to estimate a current position of the movable core and identify a valve differential pressure at the current position, a current value at a movable core position where a target command flow rate is obtained at the valve differential pressure is calculated, and a difference between the current value and the current value at the current position is output as the current correction amount.

3. the current correction amount calculation unit outputs a difference between the detected amplitude value and a theoretical amplitude value at no flow rate for the command current value as the correction current amount, 2. The proportional solenoid valve position control system according to claim 1, wherein the current correction circuit further comprises a weighting unit that multiplies the current correction amount by a weighting coefficient that is selectably set in advance in accordance with a change in a flow rate reduction rate accompanying an increase in the valve differential pressure and that is stored in the memory unit.

4. 2. The proportional solenoid valve opening control system according to claim 1, wherein the current control circuit is composed of a CPU calculation unit mounted on a one-chip microcomputer, and the memory unit is a memory device mounted on the one-chip microcomputer.

5. The amplitude detection unit 2. The proportional solenoid valve opening control system according to claim 1, characterized in that the detection current signal obtained from the current detection unit via an analog / digital converter is subjected to differentiation processing to obtain an AC component from which a DC component has been removed, and the AC component is full-wave rectified to convert the pulse wave into a DC component, which is then smoothed to output an amplitude signal having a gently shaped waveform.

6. The amplitude detection unit The proportional solenoid valve opening control system according to claim 1, characterized in that a pulse one-cycle signal indicating one pulse cycle during which the switching element is controlled ON-OFF is obtained from the PWM conversion unit, and a maximum current value and a minimum current value in a pulse one-cycle section specified by the pulse one-cycle signal are identified from the detected current value of the solenoid obtained by the current detection unit, and the difference between the maximum current value and the minimum current value is calculated as the current amplitude of the PWM cycle.

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