JP7594959B2 - Solenoid valve control device - Google Patents

Description

The present invention relates to a control device for a solenoid valve.

This type of solenoid valve is widely used in the fields of automobiles, construction machinery, industrial machinery, etc., as an interface between, for example, electrical circuits and hydraulic circuits. For example, in a hydraulic excavator, a construction machine, the travel of the lower traveling body, the rotation of the upper rotating body, the operation of the work front, etc. are performed by a hydraulic actuator, and the hydraulic actuator is driven by the supply of hydraulic oil according to the switching of a control valve. In a conventional hydraulic system, the operation of the operator is mechanically transmitted to the control valve, but in recent years, a configuration has been adopted in which the control valve is electrically driven and controlled by an electronic control unit based on the operation information of the operator and sensor information in order to operate the hydraulic excavator more accurately. To do this, the electrical signal from the electronic control unit needs to be converted into a hydraulic signal and transmitted to the control valve, and this role is performed by a solenoid proportional valve, which is a type of solenoid valve.

For example, in the case of a boom cylinder that tilts the boom on the work front, a load drive signal with a duty ratio corresponding to the amount of operation of the boom lever is generated by the electronic control unit and input to the solenoid of the electromagnetic proportional valve. The electromagnetic proportional valve switches hydraulic oil from the pilot hydraulic pump and inputs it to the pressure-receiving chamber of the control valve as pilot pressure. The control valve switches hydraulic oil from the main hydraulic pump and supplies it to the boom cylinder, which drives the boom cylinder in response to the operation of the boom lever to tilt the boom.

In conventional hydraulic systems, the boom lever and control valve are mechanically linked, so there is no operational delay between them. However, in a configuration equipped with an electromagnetic proportional valve as described above, if the control response of the electromagnetic proportional valve is poor, a delay occurs in switching the control valve and therefore in the movement of the boom in response to the operation of the boom lever, giving the operator the impression that the operational response is poor. Therefore, from the perspective of the operational response of the object to be operated, such as the boom, good control response is required of the electromagnetic proportional valve.

As a technology for improving the control response of an electromagnetic valve, for example, Patent Document 1 discloses a fuel injector control device. In this invention, in order to open the fuel injector quickly, a higher drive voltage is applied to the fuel injector when the fuel injector is opened, compared to normal operation after the valve is opened. In detail, as shown in FIG. 4 of Patent Document 1, when the timing for opening the fuel injector is reached, a high drive voltage is first applied to drive the fuel injector in the opening direction, and when the drive current reaches a preset peak current value Ipeak, the drive voltage is reduced to 0 or less, and when the drive current accordingly drops to a preset value 404, the drive current is kept close to the target holding current value 403 by turning the drive voltage ON and OFF at a low drive voltage. This type of current control is executed based on a profile preset based on the fuel injection amount.

International Publication No. 2019/044395

The technology in Patent Document 1, which is targeted at fuel injectors, allows the current control profile to be set based on very limited parameters such as the fuel injection amount. However, depending on the application and type of solenoid valve, a large number of parameters need to be reflected in the profile, and there are many cases in which this technology cannot be applied.

For example, in the electromagnetic proportional valve applied to the construction machinery described above, the target current command value to be supplied to the electromagnetic proportional valve is set based on operation information by the operator, such as boom tilt operation, or sensor information, such as the boom tilt angle and boom cylinder hydraulic pressure. In addition, this target current command value is fed back based on the load current value that actually flows through the electromagnetic proportional valve coil. Therefore, it is practically difficult to reflect such a wide variety of parameters in the profile, and a drastic solution has been desired for some time.

The present invention was made to solve these problems, and its purpose is to provide a control device for a solenoid valve that can improve the control response of the solenoid valve without the need to set a profile for current control in advance.

In order to achieve the above object, a control device for a solenoid valve of the present invention includes a load current detection circuit that detects a load current value flowing through a coil of a solenoid valve, a duty ratio calculation unit that calculates a duty ratio of a PWM signal for making the load current value coincide with a target current command value set for the solenoid valve and the load current value detected by the load current detection circuit, a PWM signal generation unit that generates the PWM signal based on the duty ratio calculated by the duty ratio calculation unit, and a load drive voltage supplied from a voltage source to boost the PWM signal generated by the PWM signal generation unit and output the PWM signal as a load drive signal. and a load drive circuit that supplies a voltage to a coil of a magnetic valve. The control device for a solenoid valve for a fluid circuit further comprises a load drive voltage switching circuit connected between the voltage source and the load drive circuit and capable of varying the load drive voltage supplied from the voltage source to the load drive circuit, a current value comparison unit that determines the load drive voltage to be supplied to the load drive circuit based on the target current command value and the load current value, and a load drive voltage switching signal generation unit that outputs a load drive voltage switching signal to the load drive voltage switching circuit, the load drive voltage switching signal representing a switch command to the load drive voltage determined by the current value comparison unit .

According to the control device for a solenoid valve of the present invention, it is possible to improve the control responsiveness of a solenoid valve for a fluid circuit without the need to set a profile related to current control in advance.

1 is a side view showing a hydraulic excavator equipped with a control device for a solenoid proportional valve according to an embodiment. FIG. 1 is an overall configuration diagram showing a hydraulic system of a hydraulic excavator. FIG. 2 is a control block diagram showing a control device for a solenoid proportional valve. FIG. 2 is a control block diagram showing the configuration of an electronic control unit in the control device. 5 is a flowchart showing a load drive voltage setting routine executed by a calculation processing unit for setting a load drive voltage. 11 is a time chart showing a control state when a target current command value CIn is increased from CI1 to CI2. 5 is a control block diagram corresponding to FIG. 4 and showing another example 1 in which the load drive voltage is switched between three stages. FIG. 6 is a flowchart showing a load drive voltage setting routine according to a first modification, which corresponds to FIG. 5 . FIG. 5 is a control block diagram corresponding to FIG. 4 and showing a second modified example in which a first voltage source and a second voltage source are provided as voltage sources. 6 is a flowchart corresponding to FIG. 5 and illustrating a second modified example in which a process for increasing and correcting the control gain G is added. 6 is a flowchart corresponding to FIG. 5 and showing another example 3 of switching the load drive Vpwm to a high speed side when an abnormality occurs in the hydraulic system.

Hereinafter, an embodiment in which the present invention is embodied in a control device for an electromagnetic proportional valve mounted on a hydraulic excavator will be described.
FIG. 1 is a side view showing a hydraulic excavator equipped with a control device for a proportional solenoid valve according to this embodiment, and first, the overall configuration of the hydraulic excavator will be described with reference to this figure.
A pair of left and right crawlers 3 are provided on a lower traveling structure 2 of the hydraulic excavator 1, and the crawlers 3 are driven by a traveling hydraulic motor 3a (shown in FIG. 2) to travel the hydraulic excavator 1. An upper rotating structure 4 is provided on the lower traveling structure 2 via a rotating device (not shown), and the upper rotating structure 4 is driven by a rotating hydraulic motor 4a (shown in FIG. 2) provided on the rotating device to rotate.

An articulated front work unit 5 is provided at the front of the upper rotating body 4, and the front work unit 5 is composed of a boom 6, an arm 7, and a bucket 8. The boom 6 is tilted by a boom cylinder 6a, the arm 7 is tilted by an arm cylinder 7a, and the bucket 8 is tilted by a bucket cylinder 8a.
A cab 10 for an operator is provided at the front of the upper rotating body 4, and a fuel tank 11 and a machine room 12 are provided behind the cab 10. A hydraulic power unit 13 (shown in FIGS. 2 and 3) is provided in the machine room 12, and this hydraulic power unit 13 drives the above-mentioned traveling and rotating hydraulic motors 3a, 4a and the cylinders 6a to 8a (hereinafter sometimes collectively referred to as hydraulic actuators) of the front work unit 5.

Figure 2 is an overall configuration diagram showing the hydraulic system of the hydraulic excavator 1, and Figure 3 is a control block diagram showing the control device for the solenoid proportional valve. The hydraulic power unit 13 is composed of an engine 14 as a power source, a pump unit 15 that is driven and rotated by the engine 14, a solenoid proportional valve 16 that controls the switching of hydraulic oil from the pump unit 15, and a control valve 17 that switches the hydraulic oil from the pump unit 15 based on the pilot pressure supplied from the solenoid proportional valve 16 to drive each hydraulic actuator. Note that although the solenoid proportional valve 16 and the control valve 17 are shown simplified in Figures 2 and 3, in reality they are provided corresponding to each hydraulic actuator.

To be more specific, an operating device 19 and various sensors 20 are connected to an electronic control unit 18 that controls the hydraulic power unit 13. The operating device 19 is an input device for operating the travel of the hydraulic excavator 1, the rotation of the upper rotating body 4, and the boom 6, arm, bucket, etc. of the work front 5. The various sensors 20 include, for example, a pressure sensor that detects the pressure of the hydraulic oil supplied to each hydraulic actuator in response to switching of the control valve 17, a position sensor that detects the stroke position of the cylinders 6a to 8a, and an angle sensor that detects the tilt angle of the boom 6, etc. Based on the operation information O_in from the operating device 19 and the sensor information S_in from the various sensors 20, the electronic control unit 18 calculates a load drive signal PWM as a control target value for each hydraulic actuator.

The pump unit 15 is composed of a pilot hydraulic pump and a main hydraulic pump (not shown), and the hydraulic oil discharged from the pilot hydraulic pump is supplied to each electromagnetic proportional valve 16 via the pump line 21. The electromagnetic proportional valve 16 is equipped with a solenoid 16a with a built-in coil, and is designed to operate according to the excitation of the coil. A load drive signal PWM is input from the electronic control unit 18 to the solenoid 16a of each electromagnetic proportional valve 16, and the opening of each electromagnetic proportional valve 16 is adjusted according to the excitation state of the coil by the load drive signal PWM. The pressure of the hydraulic oil supplied from the pilot hydraulic pump changes according to the opening of the electromagnetic proportional valve 16, and is input to the pressure receiving chamber of the control valve 17 as pilot pressure. In other words, the electromagnetic proportional valve 16 functions to convert the load drive signal PWM, which is an electrical signal, into pilot pressure, which is a hydraulic signal, and corresponds to the solenoid valve of the present invention.

Meanwhile, hydraulic oil discharged from the main hydraulic pump is supplied to each control valve 17 via pump line 22, and each control valve 17 switches the hydraulic oil from the main hydraulic pump according to the pilot pressure input to the pressure receiving chamber, and supplies it to the corresponding hydraulic actuator. This drives each hydraulic actuator, and the driving force of the actuator operates the crawler 3, upper rotating body 4, front work unit 5, etc., which are the objects to be operated. To enable the driving of such hydraulic actuators, the discharge pressure of the main hydraulic pump is set higher than the discharge pressure of the pilot hydraulic pump, which is used as a hydraulic signal.

The load drive signal PWM from the electronic control unit 18 is also input to the solenoid 16a of the electromagnetic proportional valve 16 provided in the pump unit 15, and the tilt angle of the main and pilot hydraulic pumps, and therefore the discharge volume of hydraulic oil, are adjusted.

FIG. 4 is a control block diagram showing the configuration of the electronic control unit 18 in the control device, in particular, and shows an excerpt of a portion corresponding to a single proportional solenoid valve 16.
As described above, the electronic control unit 18 is connected to the operation device 19, various sensors 20, and the solenoid proportional valve 16, as well as to a voltage source 24 such as an on-board battery. The electronic control unit 18 is made up of a calculation processing unit 25, a load drive circuit 26, a load drive voltage switching circuit 36, a voltage conversion circuit 37, and a load current detection circuit 27.

The overall processing flow within the electronic control unit 18 is as follows. The calculation processing unit 25 generates a PWM signal PWM_c based on the deviation CIn-ADn between the target current command value CIn of the solenoid proportional valve 16 calculated based on the operation information O_in from the operation device 19 and the sensor information S_in from the various sensors 20 and a voltage value (load current average value ADn described later) correlated with the current flowing through the solenoid proportional valve 16 input from the load current detection circuit 27, and outputs the PWM signal PWM_c to the load drive circuit 26. The voltage conversion circuit 37 boosts the voltage V1 supplied from the voltage source 24 to a higher voltage V2. In the following description, the voltage V1 is referred to as the normal processing voltage, and the voltage V2 is referred to as the high-speed processing voltage.

The normal processing voltage V1 and the high-speed processing voltage V2 are input to the load drive voltage switching circuit 36, which sets one of them as the load drive voltage Vpwm and outputs it to the load drive circuit 26. The load drive circuit 26 boosts the PWM signal PWM_c using the load drive voltage Vpwm, and supplies the generated load drive signal PWM to the solenoid proportional valve 16 to adjust the opening.

The above processing executed within the electronic control unit 18 will now be described in detail. First, the operation information O_in and the sensor information S_in are input to a target current command value calculation unit 29 of the arithmetic processing unit 25, and based on this information, the target current command value calculation unit 29 calculates a target current command value CIn and outputs it to a current value comparison unit 30. For example, with regard to the operation of the boom 6, a target current command value CIn for the solenoid proportional valve 16 of the boom cylinder 6a is calculated based on the amount of operation from the boom lever (not shown), which is one piece of operation information O_in.

Meanwhile, the current flowing through the solenoid 16a of the electromagnetic proportional valve 16 is detected as a load current value Ifb by the load current detection circuit 27, which converts the load current value Ifb into a voltage signal Vfb that can be acquired by the calculation processing unit 25 and outputs it to the load current acquisition unit 31 of the calculation processing unit 25. The load current acquisition unit 31 converts the voltage signal Vfb into a digital signal Vfb_D that can be processed by the calculation processing unit 25 and outputs it to the load current average value calculation unit 32. The load current average value calculation unit 32 averages the digital signal Vfb_D over one period of the carrier frequency of the PWM signal PWM_c to calculate the load current average value ADn (corresponding to the load current value of the present invention), and outputs it to the current value comparison unit 30 and the duty ratio calculation unit 33 as feedback information.

The calculation process of the target current command value CIn by the target current command value calculation unit 29 described above is performed in a cycle shorter than one period of the carrier frequency of the PWM signal PWM_c. Similarly, since the load current average value calculation unit 32 averages the digital signal Vfb_D over one period of the carrier frequency, the conversion process to the digital signal Vfb_D by the load current acquisition unit 31 is also performed in a cycle shorter than one period of the carrier frequency.

The current value comparison unit 30 selects either the normal processing voltage V1 or the high-speed processing voltage V2 as the load drive voltage Vpwm based on the deviation CIn-ADn between the target current command value CIn input from the target current command value calculation unit 29 and the load current average value ADn input from the load current average value calculation unit 32, generates a current comparison signal Com_i indicative of the selection result, and outputs it to the duty ratio calculation unit 33 and the load drive voltage switching signal generation unit 38.
FIG. 5 is a flowchart showing a load drive voltage setting routine executed by the current value comparison unit 30 in order to set the load drive voltage Vpwm. This routine is executed with one period of the PWM signal PWM_c as the control interval, for example.

When the routine starts, first in step S1, it is determined whether the deviation CIn-ADn between the target current command value CIn and the load current average value ADn is less than the load drive voltage switching threshold value Xv, and if the result is Yes (affirmative), the process proceeds to step S2. In this embodiment, a predetermined ratio to the target current command value CIn (meaning the error to the target current command value CIn, for example, 10%) is set as the load drive voltage switching threshold value Xv (corresponding to the switching threshold value of the present invention), which is previously stored as an internal variable in the current value comparison unit 30. In step S2, the normal processing voltage V1 is selected as the load drive voltage Vpwm, and in the following step S3, a current comparison signal Com_i representing the selection of the normal processing voltage V1 is output, and then the routine ends. Also, if the determination in step S1 is No (negative), the process proceeds to step S4. In step S4, the high-speed processing voltage V2 is selected as the load drive voltage Vpwm, and in the following step S3, a current comparison signal Com_i representing the selection of the high-speed processing voltage V2 is output.

A situation where the result of the No judgment in step S1 (CIn-ADn≧Xv) is reached is one where a target current command value CIn is set that is significantly larger (Xv or more) than the current load current average value ADn, and a rapid increase in the load drive signal PWM is required to make the load current average value ADn follow this target current command value CIn. In such a case, the high-speed processing voltage V2 is selected as the load drive voltage Vpwm, and as will be described in detail later, the rate of change of the load current value Ifb increases, resulting in a rapid increase in the load drive signal PWM.

As an example, if the load drive voltage switching threshold Xv is set to 10% of the target current command value CIn, when the target current command value CIn = 500mA, the load drive voltage switching threshold Xv = 50mA. In this case, if the load current average value ADn = 100mA, the deviation between the target current command value CIn and the load current average value ADn is CIn-ADn = 400mA, which is greater than the load drive voltage switching threshold Xv, and the high-speed processing voltage V2 is selected as the load drive voltage Vpwm.

As a result of feedback control based on the above conditions, when the load current average value ADn increases and reaches ADn = 490 mA, the deviation between the target current command value CIn and the load current average value ADn becomes CIn - ADn = 10 mA, which is less than the load drive voltage switching threshold value Xv, so the normal processing voltage V1 is selected as the load drive voltage Vpwm.

Returning to FIG. 4, the duty ratio calculation unit 33 receives the target current command value CIn from the target current command value calculation unit 29, the load current average value ADn from the load current average value calculation unit 32, and the current comparison signal Com_i from the current value comparison unit 30. Based on these values CIn, ADn, and Com_i, the duty ratio calculation unit 33 uses PID control or the like to calculate the duty ratio MVn of the PWM signal PWM_c for matching the load current average value ADn to the target current command value CIn. Basically, when the load current average value ADn is smaller than the target current command value CIn, the duty ratio MVn is increased compared to the previous control, and conversely, when the load current average value ADn is larger than the target current command value CIn, the duty ratio MVn is decreased compared to the previous control. The duty ratio calculation unit 33 also holds a predetermined control gain G, which defines the relationship between the amount of increase or decrease at this time and the absolute value |CIn-ADn| of the deviation CIn-ADn, as an internal variable, and applies this control gain G to the calculation process of the duty ratio MVn.

The duty ratio MVn calculated by the duty ratio calculation unit 33 is output to the PWM signal generation unit 35, which generates a PWM signal PWM_c corresponding to the duty ratio MVn and a preset carrier frequency and outputs it to the load drive circuit 26. Since the PWM signal PWM_c is a low voltage for calculation processing that depends on the power supply voltage of the calculation processing unit 25, it is boosted by the load drive circuit 26 to a voltage that can drive the solenoid proportional valve 16. For this reason, the load drive circuit 26 performs a switching operation to boost the PWM signal PWM_c to the load drive voltage Vpwm supplied from the load drive voltage switching circuit 36, and supplies it to the solenoid 16a of the solenoid proportional valve 16 as the load drive signal PWM.

The opening of the solenoid proportional valve 16 is adjusted according to the duty ratio MVn of the load drive signal PWM, the pilot pressure input to the pressure receiving chamber of the control valve 17 changes as described above, the hydraulic oil switched by the control valve 17 is supplied to the hydraulic actuator, and the hydraulic actuator is driven and controlled. Then, the load current value Ifb flowing through the solenoid 16a of the solenoid proportional valve 16 at this time is converted to a voltage signal Vfb by the load current detection circuit 27, converted to a digital signal Vfb_D by the load current acquisition unit 31, and averaged by the load current average value calculation unit 32, and is fed back to the current value comparison unit 30 as the load current average value ADn, and the process is repeated again in the above order.

On the other hand, the load drive voltage switching signal generating unit 38 generates a load drive voltage switching signal SW_v based on the current comparison signal Com_i input from the current value comparing unit 30, and outputs it to the load drive voltage switching circuit 36. When the current comparison signal Com_i indicates the selection of the normal processing voltage V1, it outputs a switching command to the normal processing voltage V1 as the load drive voltage switching signal SW_v, and when it indicates the selection of the high-speed processing voltage V2, it outputs a switching command to the high-speed processing voltage V2.

When the input load drive voltage switching signal SW_v is a command to switch to the normal processing voltage V1, the load drive voltage switching circuit 36 outputs the normal processing voltage V1 supplied from the voltage source 24 to the load drive circuit 26 as the load drive voltage Vpwm. When the input load drive voltage switching signal SW_v is a command to switch to the high-speed processing voltage V2, the load drive voltage switching circuit 36 outputs the high-speed processing voltage V2 supplied from the voltage conversion circuit 37 as the load drive voltage Vpwm to the load drive circuit 26. Then, based on this load drive voltage Vpwm, the PWM signal PWM_c is boosted by the switching operation of the load drive circuit 26, and the generated load drive signal PWM is supplied to drive the solenoid proportional valve 16.

Next, the control state of the control device of the solenoid proportional valve 16 configured as described above will be explained based on the time chart of Figure 6. The figure shows the control state when the target current command value CIn increases from CI1 to CI2, and is the control state that occurs when, for example, the boom lever is held at a predetermined operation amount and the tilt angle of the boom 6 changes in the upward or downward direction at a substantially constant speed (CIn = CI1), and then the operation amount of the boom lever is increased (CIn = CI2) to increase the tilt speed of the boom 6, and then the increased operation amount is maintained.

First, in period t1, a substantially constant value CI1 is set as the target current command value CIn, and the load current average value ADn is maintained near this target current command value CI1. In the above boom operation example, the control state at this time corresponds to a situation in which the tilt angle of the boom 6 is changing at a speed corresponding to the amount of operation of the boom lever. Since the deviation CIn-ADn at this time is substantially 0, that is, less than the load drive voltage switching threshold value Xv, a Yes determination is made in step S1 of Figure 5, and the normal processing voltage V1 is selected as the load drive voltage Vpwm.

A relatively low-voltage load drive signal PWM based on the normal processing voltage V1 is generated based on a duty ratio MVn calculated from the deviation CIn-ADn between the target current command value CIn and the load current average value ADn by applying a predetermined control gain G. At this time, the load current value Ifb flowing through the solenoid 16a of the solenoid proportional valve 16 follows the ON/OFF of the load drive signal PWM with a delay due to the influence of the coil provided in the solenoid 16a. That is, as shown in FIG. 6, when the load drive signal PWM is turned ON, the load current value Ifb increases at a predetermined rate of change, and when it is turned OFF, it decreases at a predetermined rate of change, and the load current average value ADn is calculated as the average value for one cycle. Therefore, the ratio between the increasing section and the decreasing section of the load current value Ifb in one cycle, and thus the direction of increase/decrease of the load current value Ifb in one cycle, is determined according to the duty ratio MVn.

The change in the load current value Ifb is influenced not only by the duty ratio MVn but also by the voltage of the load drive signal PWM. That is, when a low-voltage load drive signal PWM based on the normal processing voltage V1 is supplied to the solenoid proportional valve 16, the load current value Ifb increases and decreases gently, in other words, the load current value Ifb increases and decreases with a small rate of change. On the other hand, when a high-voltage load drive signal PWM based on the high-speed processing voltage V2 is supplied to the solenoid proportional valve 16, as shown in FIG. 6, the rate of change of the load current value Ifb on the decreasing side is the same as in the case of the normal processing voltage V1, but the rate of change on the increasing side is greater than in the case of the normal processing voltage V1.

When the target current command value CIn increases stepwise from CI1 to CI2, a transition occurs from period t1 to period t2, and the control state at this time corresponds to a situation in which the amount of operation of the boom lever is increased in the boom operation example described above. In the example of FIG. 6, the boom lever is operated at a timing that does not coincide with the processing timing of the calculation processing unit 25, so the control state by the calculation processing unit 25 does not change during the duration of period t2.

When the calculation processing unit 25 reaches the next processing timing, the process moves to period t3, and a PWM signal PWM_c is generated based on a predetermined carrier frequency and the duty ratio MVn calculated from the deviation CIn-ADn between the target current command value CIn and the load current average value ADn. Since the deviation CIn-ADn at this time exceeds the load drive voltage switching threshold value Xv, a No judgment is made in step S1 of FIG. 5, and the high-speed processing voltage V2 is selected as the load drive voltage Vpwm. Therefore, a high-voltage load drive signal PWM based on the high-speed processing voltage V2 is generated and supplied to the solenoid proportional valve 16.

In the duty ratio calculation unit 33, the duty ratio MVn is set to an increasing direction compared to the periods t1 and t2 in order to reduce the deviation CIn-ADn, but in addition, in this embodiment, the deviation CIn-ADn is quickly reduced by switching the load drive signal PWM to the high voltage side. As described above, when a high-voltage load drive signal PWM based on the high-speed processing voltage V2 is supplied to the solenoid proportional valve 16, the rate of change on the increasing side of the load current value Ifb becomes larger than in the case of the normal processing voltage V1. As a result, the load current value Ifb and therefore the load current average value ADn quickly increase following the target current command value CIn, and the deviation CIn-ADn quickly decreases to become less than the load drive voltage switching threshold value Xv.

Therefore, when the calculation processing unit 25 reaches the next processing timing and moves to period t4, the normal processing voltage V1 is selected as the load drive voltage Vpwm based on the judgment of Yes in step S1 of FIG. 5. During the duration of period t3, a slight overshoot occurs in the load current value Ifb and the load current average value ADn, but in period t4, the overshoot is suppressed by the decrease in the duty ratio MVn, and the load current average value ADn gradually approaches the target current command value CIn and is maintained in its vicinity. After that, the duty ratio MVn of the load drive signal PWM corresponding to the target current command value CI2 is maintained at a substantially constant value, and the load current value Ifb increases and decreases according to the ON/OFF of the duty ratio MVn. In the above boom operation example, the control state at this time corresponds to a state in which the boom lever operation amount after the increase is maintained.

The above explanation was for the case where the load drive signal PWM is increased in response to an increase in the target current command value CIn, but the same processing procedure as above is also adopted when the load drive signal PWM is decreased in response to a decrease in the target current command value CIn. However, in this case, since the deviation CIn-ADn is on the negative side, the load drive signal PWM equivalent to the normal processing voltage V1 continues to be generated based on the Yes judgment in step S1, and the load current value Ifb is controlled to increase and decrease gradually. This is also true for the other examples 1 to 3 described below.

In this way, in period t3, for example, this corresponds to an increase in the amount of operation of the boom lever during operation, so it is required to quickly speed up the tilting of the boom 6. The control situation at this time is in a transient state in which the load current average value ADn rapidly increases following the stepped increase in the target current command value CIn, so more quickly reflecting the deviation CIn-ADn between the target current command value CIn and the load current average value ADn in the load drive signal PWM leads to good control responsiveness of the solenoid proportional valve 16, and ultimately good operational responsiveness of the boom 6.

In this situation, in this embodiment, the load drive voltage Vpwm is switched to the high voltage side in response to an increase in the deviation CIn-ADn, and a high voltage load drive signal PWM is supplied to the solenoid proportional valve 16, so that the rate of change of the load current value Ifb to the increasing side becomes large. As a result, the load current value Ifb can be quickly increased following the target current command value CIn, and the deviation CIn-ADn can be quickly reduced, resulting in improved control responsiveness of the solenoid proportional valve 16. Therefore, for example, in the above boom operation example, the tilting of the boom 6 can be quickly accelerated in response to the operation of the boom lever, and the operational responsiveness can be improved.

At this time, the solenoid proportional valve 16 is in an operating state where it begins to move the stopped spool using the driving force of the solenoid to increase the opening. Due to the influence of the spool's inertial mass and sliding resistance, etc., there is a delay in the start of the spool's movement relative to the rising edge of the load drive signal PWM. This operational delay is reduced by increasing the voltage of the load drive signal PWM input to the coil, and this factor also contributes greatly to improving the control responsiveness of the solenoid proportional valve 16.

On the other hand, in periods t1 and t4, for example, this corresponds to a case where the boom lever is held at a predetermined operation amount, and the control situation at this time is an equilibrium state in which the target current command value CIn is set to a substantially constant value CI1, CI2, and the load current average value ADn is maintained near the target current command value CIn. Therefore, good operation responsiveness is not required of the boom 6, and therefore this can be regarded as a situation in which good control responsiveness is not required of the solenoid proportional valve 16.

In this embodiment, the load drive signal PWM is switched to the low voltage side in response to a decrease in the deviation CIn-ADn, so the rate of change when the load current value Ifb increases or decreases decreases. This reduces the control responsiveness of the solenoid proportional valve 16, but no adverse effects occur because good control responsiveness is not required in the first place. For example, in the boom operation example above, the operator does not get the impression that the operation responsiveness has deteriorated because the boom lever is held at a nearly constant operating amount.

In this manner, in a situation where control responsiveness is not required of the solenoid proportional valve 16, the load drive voltage Vpwm is switched to the low voltage side. This makes it possible to reduce the power consumption of the voltage source 24 compared to, for example, a case in which the high voltage side load drive voltage Vpwm is always selected from the viewpoint of control responsiveness. In addition, the load drive circuit 26 generates heat due to switching operations synchronized with the PWM signal PWM_c, but by switching the load drive voltage Vpwm to the low voltage side, the amount of heat generated can be reduced, improving the reliability of the control device.

As described above, according to the control device for the electromagnetic proportional valve 16 of this embodiment, in a situation where the control response of the electromagnetic proportional valve 16 is required, the high-speed processing voltage V2 is selected as the load drive voltage Vpwm when generating the load drive signal PWM, while in a situation where the control response of the electromagnetic proportional valve 16 is not required, the normal processing voltage V1 is selected as the load drive voltage Vpwm. This makes it possible to achieve both of the two conflicting requirements of improving the control response of the electromagnetic proportional valve 16 and reducing the power consumption of the voltage source 24 and the heat generation of the load drive circuit 26.

The above-mentioned effects can be achieved by a simple process of comparing the deviation CIn-ADn between the target current command value CIn and the load current average value ADn with the load drive voltage switching threshold value Xv, and switching the load drive voltage Vpwm when generating the load drive signal PWM according to the comparison result. That is, in the technology of Patent Document 1, which aims to improve control responsiveness like the present invention, a profile related to current control is preset to quickly open the fuel injector.

If this is replaced with the electromagnetic proportional valve 16 of this embodiment, it becomes necessary to set a profile for current control of the electromagnetic proportional valve 16, reflecting a wide variety of parameters such as the operation information O_in by the operator, the sensor information S_in, and feedback information of the load current value Ifb. However, this is difficult in reality, and even if it could be realized, it would require a great deal of effort to set the profile, which would result in an increase in manufacturing costs. According to this embodiment, such advance profile setting is no longer necessary, and as a result, the manufacturing costs of the control device for the electromagnetic proportional valve 16 can be reduced.

In contrast, in this embodiment, the load drive voltage Vpwm supplied to the load drive circuit 26 can be switched between a normal processing voltage V1 and a high-speed processing voltage V2, and one of them is selected as the load drive voltage Vpwm depending on the result of comparing the deviation CIn-ADn between the target current command value CIn and the load current average value ADn with the load drive voltage switching threshold value Xv.

For this reason, the control device of this embodiment can be implemented by only slightly modifying the specifications of the conventional control device that applies a single load drive voltage Vpwm. In detail, the control device can be implemented by simply adding a voltage conversion circuit 37 that boosts the voltage V1 from the voltage source 24 to voltage V2, and a load drive voltage switching circuit 36 that switches between voltages V1 and V2, as well as adding a simple calculation process (corresponding to the current value comparison unit 30 and the load drive voltage switching signal generation unit 38) that selects the load drive voltage Vpwm depending on the result of comparing the deviation CIn-ADn with the load drive voltage switching threshold value Xv, thereby achieving the various effects described above.

In the above embodiment, the load drive voltage Vpwm when generating the load drive signal PWM is switched between two stages: a normal processing voltage V1 and a high-speed processing voltage V2, but this is not limited to this. The load drive voltage Vpwm may be switched in multiple stages, and an embodiment in which it is switched in three stages will be described below as Alternative Example 1. Note that in Alternative Example 1 and Alternative Examples 2 and 3 described below, explanations that overlap with the embodiment will be omitted and differences will be described in detail.

[Modification 1]
7, this modification 1 includes a second voltage conversion circuit 41 in addition to the voltage conversion circuit 37. The second voltage conversion circuit 41 boosts the voltage V1 supplied from the voltage source 24 to a second high-speed processing voltage V3 higher than the high-speed processing voltage V2 boosted by the voltage conversion circuit 37, and outputs the second high-speed processing voltage V3 to the load drive voltage switching circuit 36. As a result, in this modification 1, the load drive voltage Vpwm is switched between three levels, and therefore the processing contents of the current value comparison unit 30, the load drive voltage switching signal generation unit 38, and the load drive voltage switching circuit 36 also differ from those of the embodiment.

The current value comparison unit 30 holds the first load drive voltage switching threshold Xv1 and the second load drive voltage switching threshold Xv2 as internal variables. The load drive voltage switching threshold Xv described in the embodiment corresponds to the second load drive voltage switching threshold Xv2, and the first load drive voltage switching threshold Xv1 is set to a larger value.

The current value comparison unit 30 executes the load drive voltage setting routine shown in FIG. 8, and first in step S11, it determines whether the deviation CIn-ADn between the target current command value CIn and the load current average value ADn is less than the first load drive voltage switching threshold value Xv1. If the determination is Yes, it proceeds to step S12, where it determines whether the deviation CIn-ADn is less than the second load drive voltage switching threshold value Xv2. If the determination is Yes, in step S13, it selects the normal processing voltage V1 as the load drive voltage Vpwm, and in the subsequent step S3, it outputs a current comparison signal Com_i indicating the selection of the normal processing voltage V1, and then ends the routine.

If the result of the determination in step S12 is No, the high-speed processing voltage V2 is selected as the load drive voltage Vpwm in step S15, and the process proceeds to step S14. If the result of the determination in step S11 is No, the second high-speed processing voltage V3 is selected as the load drive voltage Vpwm in step S16, and the process proceeds to step S14.

As an example, if the first load drive voltage switching threshold Xv1 is set to 20% of the target current command value CIn and the second load drive voltage switching threshold Xv2 is set to 10% of the target current command value CIn, when the target current command value CIn = 500mA, the first load drive voltage switching threshold Xv1 = 100mA and the second load drive voltage switching threshold Xv2 = 50mA. In this case, if the load current average value ADn = 100mA, the deviation between the target current command value CIn and the load current average value ADn is CIn-ADn = 400mA, and since the deviation CIn-ADn is equal to or greater than the first load drive voltage switching threshold Xv1, the second high-speed processing voltage V3 is selected as the load drive voltage Vpwm.

As a result of feedback control based on the above conditions, when the load current average value ADn increases and reaches ADn = 420 mA, the deviation between the target current command value CIn and the load current average value ADn becomes CIn-ADn = 80 mA, and the deviation CIn-ADn is less than the first load drive voltage switching threshold value Xv1 and greater than or equal to the second load drive voltage switching threshold value Xv2, so the high-speed processing voltage V2 is selected as the load drive voltage Vpwm.

Furthermore, as a result of feedback control based on the above conditions, when the load current average value ADn increases and reaches ADn = 490 mA, the deviation CIn-ADn = 10 mA between the target current command value CIn and the load current average value ADn, and the deviation CIn-ADn is less than the second load drive voltage switching threshold value Xv2, so the normal processing voltage V1 is selected as the load drive voltage Vpwm.

The current value comparison unit 30 then outputs a current comparison signal Com_i representing the load drive voltage Vpwm selected in this manner to the load drive voltage switching signal generation unit 38, which generates a load drive voltage switching signal SW_v based on the current comparison signal Com_i and outputs it to the load drive voltage switching circuit 36. Therefore, the load drive voltage Vpwm corresponding to the load drive voltage switching signal SW_v is input to the load drive circuit 26, the PWM signal PWM_c is boosted by the switching operation of the load drive circuit 26, and the load drive signal PWM generated thereby is supplied to drive the solenoid proportional valve 16.

Therefore, for example, in a situation where the amount of operation of the boom lever has increased as described in the embodiment based on FIG. 6, the second high-speed processing voltage V3 is first applied to quickly increase or decrease the load drive signal PWM, thereby improving the control responsiveness of the solenoid proportional valve 16. Then, when the deviation CIn-ADn between the target current command value CIn and the load current average value ADn has decreased to a certain extent, the high-speed processing voltage V2 is switched to, and the load drive signal PWM is increased more slowly.

When the operator first begins to increase the amount of operation of the boom lever, the operation of the hydraulic excavator 1 changes quickly due to the good control responsiveness of the solenoid proportional valve 16, giving the impression that the operational responsiveness is good. Then, as the impact on the operational responsiveness decreases with the decrease in the deviation CIn-ADn, the load drive voltage Vpwm decreases, so that it is possible to reduce the power consumption of the voltage source 24 and the amount of heat generated due to the switching operation of the load drive circuit 26. Therefore, compared to the above embodiment, it is possible to achieve a higher level of achievement of the two conflicting requirements.

In the above embodiment, in addition to the normal processing voltage V1 supplied from the voltage source 24, the normal processing voltage V1 is boosted to the high-speed processing voltage V2 by the voltage conversion circuit 37 and used as the load drive voltage Vpwm, but this is not limited to this. For example, as shown in FIG. 9, the voltage conversion circuit 37 may be omitted and instead a second voltage source 51 may be provided that supplies a high-speed processing voltage V2 higher than the normal processing voltage V1. In this case, the same effect as in the embodiment can be achieved. Of course, the same applies to the alternative example 1.

Furthermore, the function of the voltage conversion circuit 37 is not limited to boosting the voltage from the voltage source 24. For example, in the configuration shown in FIG. 4, a high-speed processing voltage V2 may be supplied from the voltage source 24, and this high-speed processing voltage V2 may be stepped down to a normal processing voltage V1 by the voltage conversion circuit 37 and used as the load drive voltage Vpwm. Also, in the configuration shown in FIG. 7, a second high-speed processing voltage V3 may be supplied from the voltage source 24, and this second high-speed processing voltage V3 may be stepped down to a high-speed processing voltage V2 by the voltage conversion circuit 37, and then stepped down to a normal processing voltage V1 by the second voltage conversion circuit 41, and used as the load drive voltage Vpwm.

In addition, in the above embodiment and modified example 1, the calculation processing unit 25 is configured with a microcomputer, FPGA (Field Programmable Gate Array), etc., and performs calculation processing with digital signals, but this is not limited to this as long as the configuration can achieve the desired control. For example, part or all of the calculation processing unit 25 may be configured as an analog circuit.

In the above embodiment and modified example 1, the load drive voltage switching threshold Xv is set as a predetermined ratio to the target current command value CIn, but this is not limited to this. For example, the load drive voltage switching threshold Xv may be switched depending on the pressure and viscosity of the hydraulic oil supplied to the solenoid proportional valve 16. If the pressure of the hydraulic oil increases, the spool of the solenoid proportional valve 16 becomes difficult to move due to the high pressure hydraulic oil, and if the viscosity of the hydraulic oil increases in cold regions, the spool of the solenoid proportional valve 16 also becomes difficult to move due to the high viscosity hydraulic oil, so in either case, the control responsiveness decreases.

Therefore, if either the pressure or viscosity of the hydraulic oil detected by the various sensors 20 is equal to or greater than a preset threshold, the load drive voltage switching determination value Xv may be lowered to forcibly switch the load drive voltage Vpwm to the high-speed processing voltage V2. This ensures the desired responsiveness of the solenoid proportional valve 16 even in situations where the hydraulic oil conditions have deteriorated.

In the above embodiment and Alternative Example 1, the load drive voltage Vpwm is switched between the normal processing voltage V1 and the high-speed processing voltage V2 in accordance with the deviation CIn-ADn, but the control gain G when calculating the duty ratio may also be switched. The purpose of this is to further improve the control responsiveness of the solenoid proportional valve 16, and will be described below as Alternative Example 2 based on the configuration of the embodiment shown in FIG. 4.

[Modification 2]
The current value comparison unit 30 executes a load drive voltage setting routine shown in Fig. 10. Steps S21 and S22 are added to the routine of Fig. 5 described in the embodiment, and when the high-speed processing voltage V2 is selected as the load drive voltage Vpwm in step S4, the process proceeds to step S21. In step S21, it is determined whether or not a predetermined time has elapsed since the normal processing voltage V1 was switched to the high-speed processing voltage V2, in other words, whether or not a predetermined time has elapsed since a situation in which a rapid increase in the load drive signal PWM is required based on the deviation CIn-ADn ≥ Xv has occurred. If the determination is No, the process proceeds to step S3 as in the embodiment, and a current comparison signal Com_i representing the selection of the high-speed processing voltage V2 is output. If the determination in step S21 is Yes, an increase correction of the control gain G based on a preset correction amount is determined in step S22, and the current comparison signal Com_i including the increase correction of the gain G is output in step S3.

As in the embodiment, the load drive voltage Vpwm is switched based on the current comparison signal Com_i, while the duty ratio calculation unit 33 to which the current comparison signal Com_i is input receives an increase correction of the gain G, increases the control gain G by a preset correction amount, and applies it to the calculation process of the duty ratio. As a result, even if the absolute value |CIn-ADn| of the deviation CIn-ADn between the target current command value CIn and the load current average value ADn is the same, a larger duty ratio MVn is calculated compared to the previous control. Therefore, in the above boom operation example, the control responsiveness of the solenoid proportional valve 16 is further improved at the beginning (within a specified time) when the operation amount of the boom lever starts to be increased, so that the operator can get the impression that the operation responsiveness is good.

In this second example, the control gain G is increased until a predetermined time has elapsed, but this is not limiting. For example, instead of a predetermined time, the control gain G may be increased until the deviation CIn-ADn=0, or instead of increasing the control gain G, the duty ratio may be maintained at 100% for a predetermined time. Also, the duty ratio may be maintained at 100% for a predetermined time by combining the increase in the control gain G with the increase in the control gain G.

In the above embodiment and variants 1 and 2, various effects are achieved by switching the load drive voltage Vpwm when generating the load drive signal PWM, but the function of switching the load drive voltage Vpwm can also be applied when an abnormality occurs in the hydraulic system (hereinafter, sometimes simply referred to as a system abnormality). Below, a case where this idea is applied to the hydraulic excavator 1 of the above embodiment will be described as variant 3.

[Modification 3]
This modification 3 is based on the following knowledge. When some abnormality occurs in the hydraulic system, it is not possible to expect an accurate operation of the operation target corresponding to the operation amount to the operating device 19. However, this kind of discrepancy between the two can be reduced by improving the control response of the solenoid proportional valve 16 by increasing the load drive voltage Vpwm. When the control response of the solenoid proportional valve 16 is improved, the control response of the control valve 17, which is switched in response to the input of pilot pressure from the solenoid proportional valve 16, is also improved. This is because the hydraulic actuator is supplied with hydraulic oil in response to the switching of the control valve 17, and therefore the control response of the hydraulic actuator is also improved.

Based on this knowledge, the routine of FIG. 11 is executed in the modified example 3. Compared to the routine of the embodiment shown in FIG. 5, the processing of step S0 is added, and this processing of step S0 is executed by the abnormality determination unit 61 shown in FIG. 3. The abnormality determination unit 61 determines the presence or absence of an abnormality in the hydraulic system in step S0.

An example of a system abnormality is hunting that occurs at the tip of the bucket 8 on the work front 5. The pressure of the hydraulic oil supplied to the bucket cylinder 8a fluctuates due to various factors, and hunting is a phenomenon in which the pressure fluctuation at this time coincides with the natural vibration frequency of the bucket 8, causing the tip of the bucket 8 to vibrate slightly.

To continue the explanation below by taking hunting of the bucket 8 as an example, the pressure of the hydraulic oil supplied to the bucket cylinder 8a can be detected, for example, by a pressure sensor 20 (one of various sensors, and hence hereinafter given the component number 20) attached to the control valve 17 that drives the bucket cylinder 8a. Therefore, in step S0, a determination process is performed based on the fluctuation state of the pressure detected by the pressure sensor 20. In more detail, it is determined that hunting is present when both of the following two requirements are met.
1) The waveform of the detected pressure fluctuation approximates a sine wave.
2) The fluctuation period of the detected pressure is within a judgment region that is preset with the natural frequency of the bucket 8 as the center.

If these requirements are not met and hunting is not present, and the result of the determination in step S0 in Fig. 11 is No, the process proceeds to step S1. In the subsequent processing, the load drive voltage Vpwm is switched between the high-speed side and the low-speed side based on a comparison between the deviation CIn-ADn and the load drive voltage switching threshold value Xv, as in the embodiment.
If both of these conditions are met, and hunting is detected and a Yes judgment is made in step S0, the high-speed processing voltage V2 is selected in step S4. Unless hunting is eliminated for some reason, a Yes judgment is made in step S0 and the processing in step S4 is continued. Therefore, even if the deviation CIn-ADn falls below the load drive voltage switching threshold Xv, the load drive voltage Vpwm is maintained on the high-speed side based on the judgment result in step S0.

As a result of the above processing, when hunting of the bucket 8 occurs, the control responsiveness of the electromagnetic proportional valve 16 is improved by switching to the high speed treatment voltage V2, and the control responsiveness of the control valve 17, which is switch-controlled by the pilot pressure from the electromagnetic proportional valve 16, is also improved. Furthermore, the control responsiveness of the hydraulic actuator to which hydraulic oil is supplied in response to the switching of the control valve 17 is also improved, making it possible to reduce adverse effects due to system abnormalities. For example, in the case of hunting occurring in the bucket 8 described above, the control responsiveness of the control valve 17 that supplies hydraulic oil to the bucket cylinder 8a is improved, thereby improving the control responsiveness of the bucket cylinder 8a, so hunting can be reduced and the bucket 8 can operate more normally.
In this modification 3, when a system abnormality occurs, the high speed processing voltage V2 is selected as the load drive voltage Vpwm based on the judgment in step S0, but instead, the load drive voltage switching threshold Xv in step S1 may be lowered. Even in this case, the high speed processing voltage V2 is selected, and the same effect can be achieved.

In addition, by implementing this modification example 3, phenomena such as hunting are reduced, making it difficult for the operator to notice the occurrence of an abnormality. Therefore, if it is determined in step S0 that an abnormality has occurred, the operator may be notified of this by a warning light, audio guidance, or the like. Based on the notification, the operator will recognize the occurrence of a system abnormality, and can take appropriate measures, such as halting operation of the hydraulic excavator 1 in the case of a serious abnormality.

In addition, in this modification example 3, hunting of the bucket 8 based on the pressure of the hydraulic oil supplied to the bucket cylinder 8a has been described as an example of a system abnormality, but this is not limited to this, and system abnormalities can be determined from various sensor information. For example, with respect to the hydraulic excavator 1, various system abnormalities occurring in the hydraulic excavator can be determined based on detection information such as pressure, position, angle, or inertia detected by the various sensors 20, and further based on information combining these. Then, when it is determined that an abnormality exists, the system abnormality can be mitigated by switching the load drive voltage Vpwm to the high speed side, as in this modification example.

Although the description of the embodiment is now complete, the aspects of the present invention are not limited to this embodiment. For example, in the above embodiment and Alternative Examples 1 to 3, the control device for the electromagnetic proportional valve 16 mounted on the hydraulic excavator 1 was embodied, but the solenoid valve of the present invention is not limited to this. Any solenoid valve that excites the solenoid coil by supplying a load drive signal PWM and continuously changes its opening degree can be modified as desired, and may be applied, for example, to a fuel injector for fuel injection provided on an engine. Furthermore, the target field is not limited to construction machinery, and the present invention can be applied as desired to solenoid valves used in various fields such as automobiles and industrial machinery.

In the above embodiment and each of the other examples, the load drive voltage Vpwm is selected from among a plurality of voltages V1 to V3 based on the result of comparing the deviation CIn-ADn between the target current command value CIn and the load current average value ADn with the load drive voltage switching thresholds Xv, Xv1, and Xv2, but this is not limited to this. For example, the voltage V1 from the voltage source 24 may be increased or decreased by a voltage conversion circuit to make it variable to an arbitrary voltage, while the current value comparison unit 30 may be configured to set the load drive voltage Vpwm steplessly according to the deviation CIn-ADn, and the load drive voltage Vpwm may be output from the voltage conversion circuit to the load drive circuit 26.

In addition, in the above embodiment and each of the other examples, the load drive voltage Vpwm is switched using the deviation CIn-ADn between the target current command value CIn and the load current average value ADn as an index, but this is not limited to this. Any index can be changed as long as it reflects the deviation state between the target current command value CIn and the load current average value ADn. For example, the relationship between the index and the load drive voltage Vpwm may be set in advance, and the load drive voltage Vpwm may be obtained from the index.

1. Hydraulic excavator (construction machinery)
3a Travel hydraulic motor (hydraulic actuator)
4a Swing hydraulic motor (hydraulic actuator)
6a Boom cylinder (hydraulic actuator)
7a Arm cylinder (hydraulic actuator)
8 Bucket 8a Bucket cylinder (hydraulic actuator)
16. Solenoid proportional valve (solenoid valve)
Reference Signs List 16a Solenoid 17 Control valve 24 Voltage source 26 Load drive circuit 27 Load current detection circuit 30 Current value comparison section 33 Duty ratio calculation section 35 PWM signal generation section 36 Load drive voltage switching circuit 37 Voltage conversion circuit 38 Load drive voltage switching signal generation section 41 Second voltage conversion circuit 51 Second voltage source 61 Abnormality determination section

Claims (10)

a load current detection circuit for detecting a load current value flowing through a coil of the solenoid valve;
a duty ratio calculation unit that calculates a duty ratio of a PWM signal for making the load current value coincide with the target current command value set for the solenoid valve and the load current value detected by the load current detection circuit, based on the target current command value set for the solenoid valve and the load current value detected by the load current detection circuit;
a PWM signal generating unit that generates the PWM signal based on the duty ratio calculated by the duty ratio calculating unit;
a load drive circuit that boosts the PWM signal generated by the PWM signal generation unit with a load drive voltage supplied from a voltage source and supplies the boosted PWM signal to a coil of the solenoid valve as a load drive signal;
In a control device for a solenoid valve,
a load drive voltage switching circuit connected between the voltage source and the load drive circuit and capable of varying the load drive voltage supplied from the voltage source to the load drive circuit;
a current value comparison unit that determines the load drive voltage to be supplied to the load drive circuit based on the target current command value and the load current value;
a load drive voltage switching signal generating unit that outputs a load drive voltage switching signal representing a switching command to the load drive voltage determined by the current value comparing unit to the load drive voltage switching circuit;
4. A control device for a solenoid valve for a fluid circuit, comprising: 2. The control device for an electromagnetic valve for a fluid circuit according to claim 1, wherein the current value comparison unit determines a larger value as the load drive voltage when the deviation between the target current command value and the load current value is large, compared to when the deviation is small. 3. The control device for a solenoid valve for a fluid circuit according to claim 1, wherein the duty ratio calculation unit increases the duty ratio of the PWM signal when the load drive voltage switching circuit switches the load drive voltage to an increasing side. 4. The control device for a solenoid valve for a fluid circuit according to any one of claims 1 to 3, characterized in that the solenoid valve is an electromagnetic proportional valve that inputs a pilot pressure to a pressure receiving chamber of a control valve in response to the load drive signal, switches hydraulic oil by the control valve in response to the pilot pressure, and drives a hydraulic actuator mounted on a construction machine. An abnormality determination unit that determines whether or not there is an abnormality in a system in which the solenoid valve is provided,
5. A control device for a solenoid valve for a fluid circuit as claimed in any one of claims 1 to 4, characterized in that the current value comparison unit determines a larger value as the load drive voltage when the abnormality determination unit determines that there is an abnormality in the system compared to when there is no abnormality. The hydraulic actuator is a bucket cylinder that tilts a bucket of a front work surface of the construction machine,
An abnormality determination unit that determines whether or not the bucket is hunting based on a pressure of the hydraulic oil supplied to the bucket cylinder,
5. The control device for a solenoid valve for a fluid circuit according to claim 4, wherein the current value comparison unit determines a larger value as the load drive voltage when the abnormality determination unit determines that hunting is occurring in the bucket compared to when the abnormality determination unit determines that hunting is not occurring. the load drive voltage switching circuit is configured to selectively supply a plurality of different load drive voltages to the load drive circuit;
the current value comparison section selects the load drive voltage to be supplied to the load drive circuit from the plurality of load drive voltages;
7. A control device for a solenoid valve for a fluid circuit according to claim 1, wherein the load drive voltage switching signal generating unit outputs the load drive voltage switching signal corresponding to the load drive voltage selected by the current value comparing unit to the load drive voltage switching circuit. 8. The control device for a solenoid valve for a fluid circuit according to claim 7, wherein the current value comparison unit compares the deviation between the target current command value and the load current value with a switching threshold, and selects a larger load drive voltage from the plurality of load drive voltages when the deviation is equal to or greater than the switching threshold compared to when the deviation is less than the switching threshold . A voltage conversion circuit for converting the voltage of the voltage source into a different voltage is further provided,
9. The control device for an electromagnetic valve for a fluid circuit according to claim 7 or 8, characterized in that the load drive voltage switching circuit is configured to selectively supply the voltage from the voltage source and the voltage converted by the voltage conversion circuit to the load drive circuit as the load drive voltage. The voltage source includes a plurality of voltage sources having different voltages,
9. The control device for an electromagnetic valve for a fluid circuit according to claim 7, wherein the load drive voltage switching circuit is configured to selectively supply voltages from the plurality of voltage sources to the load drive circuit as the load drive voltage.

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