JP2024047362A - Cylinder Unit - Google Patents

Abstract

[Problem] The present invention aims to provide a cylinder device that can suppress deterioration of the tracking performance for a target thrust even if the throttle coefficient of the first variable throttle valve or the second variable throttle valve changes. [Solution] The cylinder device A of the present invention includes a hydraulic cylinder 1 having a cylinder 2, a piston 3 that is movably inserted into the cylinder 2 and divides the inside of the cylinder 2 into two working chambers R1 and R2, a first flow path 4 and a second flow path 5 that are parallel to each other and communicate the working chambers R1 and R2, a first variable throttle valve 6 provided in the first flow path 4, a second variable throttle valve 7 provided in series in the second flow path 5, and a bidirectional discharge type pump 9 driven by a motor 8, a controller 11 that controls the first variable throttle valve 6, the second variable throttle valve 7, and the motor 8, a PID control unit 21, a proportional gain correction unit 24 that corrects the proportional gain, and a differential gain correction unit 25 that corrects the differential gain. [Selected Figure] Figure 7

Description

The present invention relates to a cylinder device.

A conventional cylinder device is, for example, applied to an active suspension interposed between the body and axle of a vehicle, and is specifically configured to include a cylinder, a piston movably inserted into the cylinder to divide the inside of the cylinder into two working chambers, a rod connected to the piston, a first flow path and a second flow path that communicate the two working chambers in parallel, a first variable throttle valve provided in the first flow path, a second variable throttle valve and a bidirectional discharge pump provided in series in the second flow path, a hydraulic cylinder having a motor that drives the pump, and a control device that controls the first variable throttle valve, the second variable throttle valve, and the motor (for example, see Patent Document 1).

When a conventional cylinder device is used as an active suspension, the cylinder is connected to one of the vehicle body and the axle, and the rod is connected to the other of the vehicle body and the axle. The pump is driven by a motor to generate thrust, thereby suppressing vibration of the vehicle body.

Furthermore, in conventional cylinder devices, when the hydraulic cylinder is forcibly extended or retracted by an external force, the hydraulic oil flowing through the second flow path rotates the pump, and the motor is used in the braking range to generate electricity and generate regenerative power. When the motor is used in the braking range in this way, the torque generated by the motor causes the pump to provide resistance to the flow of hydraulic oil. As a result, the hydraulic cylinder generates thrust that prevents the hydraulic cylinder from being extended or retracted by external forces.

JP 2009-196597 A

In conventional cylinder devices, the amount of hydraulic oil passing through the pump and the torque borne by the motor can be adjusted by adjusting the throttling coefficient of the first variable throttle valve and the throttling coefficient of the second variable throttle valve. Note that the throttling coefficient is the flow rate per unit time divided by the pressure, and a smaller throttling coefficient indicates that the resistance in the variable throttle valve increases.

When the motor is in a braking state, on a graph with motor torque on the vertical axis and motor rotation speed on the horizontal axis, the regenerative efficiency is maximized when the intersection of the torque output by the motor and the motor rotation speed (motor operating point) falls on a line (maximum regenerative efficiency line) that passes through the origin and has a slope half that of the line tangent to the short-circuit curve that shows the relationship between torque and rotation speed when the motor is short-circuited.

Therefore, in conventional cylinder devices, when the motor is in a braking state, the throttling coefficient of the first variable throttle valve and the throttling coefficient of the second variable throttle valve are adjusted so that the intersection of the torque output by the motor and the rotational speed of the motor is located on the line that maximizes regenerative efficiency.

In this way, in conventional cylinder devices, the throttling coefficients of the first and second variable throttle valves are controlled to position the motor's operating point on the line of maximum regenerative efficiency when the motor is in a braking state, aiming to maximize the regenerative efficiency of the motor. However, changing the throttling coefficients of the first and second variable throttle valves changes the characteristics of the cylinder device, resulting in a deterioration in the ability of the cylinder device's actual thrust to track the target thrust of the cylinder device.

The present invention aims to provide a cylinder device that can suppress deterioration of the tracking performance for the target thrust even if the throttling coefficient of the first variable throttle valve or the second variable throttle valve changes.

In order to achieve the above object, the cylinder device in the problem-solving means of the present invention includes a hydraulic cylinder having a cylinder, a piston movably inserted into the cylinder to divide the inside of the cylinder into two working chambers, a first flow path and a second flow path that are parallel to each other and communicate the working chambers, a first variable throttle valve provided in the first flow path, a second variable throttle valve provided in series in the second flow path, and a bidirectional discharge pump driven by a motor, and a controller that controls the first variable throttle valve, the second variable throttle valve, and the motor, and the controller has a PID control unit that performs PID compensation on the target thrust of the hydraulic cylinder to generate a current command to be applied to the motor, a proportional gain correction unit that corrects the proportional gain of the PID control unit, and a differential gain correction unit that corrects the differential gain of the PID control unit, and the proportional gain correction unit and the differential gain correction unit correct the proportional gain and the differential gain based on the throttle coefficient of the first variable throttle valve and the throttle coefficient of the second variable throttle valve, respectively.

With a cylinder device configured in this manner, even if the throttling coefficient of the first variable throttle valve and the throttling coefficient of the second variable throttle valve change, the proportional gain and differential gain used in the PID control unit are optimized to the throttling coefficient of the first variable throttle valve and the throttling coefficient of the second variable throttle valve at that time.

The controller in the cylinder device may also include an integral gain correction unit that corrects the integral gain of the PID control unit based on the bulk modulus of the liquid in the hydraulic cylinder. With a cylinder device configured in this way, even if the bulk modulus of the liquid changes and the characteristics of the cylinder device change, it is possible to suppress deterioration in the ability of the actual thrust of the hydraulic cylinder to follow the target thrust.

Furthermore, the controller in the cylinder device may have a proportional gain processing section that mitigates the change in the proportional gain corrected by the proportional gain correction section, and a differential gain processing section that mitigates the change in the differential gain corrected by the differential gain correction section, and the PID control section may generate a current command using the proportional gain processed by the proportional gain processing section and the differential gain processed by the differential gain processing section. According to the cylinder device configured in this manner, even if the throttling coefficient of the first variable throttle valve and the throttling coefficient of the second variable throttle valve change and the proportional gain and the differential gain are corrected, the sudden change in the proportional gain value and the differential gain value used in the PID control section is mitigated, and the sudden change in the current command output by the PID control section is also mitigated, so that the sudden change in the thrust of the hydraulic cylinder can also be mitigated.

Furthermore, the controller in the cylinder device may include a feedforward control unit that receives the input of the target thrust and determines an additional current command to be added to the current command determined by the PID control unit through feedforward control, and may generate a final current command that indicates the target current to be supplied to the motor by adding the current command determined by the PID control unit and the additional current command determined by the feedforward control unit. With a cylinder device configured in this way, the feedforward control unit, which does not feed back the actual thrust of the hydraulic cylinder, determines an additional current command that allows the thrust of the hydraulic cylinder to quickly follow the thrust command, taking into account the response delay of the hydraulic cylinder to the thrust command, and adds the additional current command to the current command of the PID control unit to generate the final current command, thereby improving the responsiveness to the target thrust without affecting the ability of the hydraulic cylinder to follow the target thrust.

As described above, the cylinder device of the present invention can suppress deterioration of the tracking performance for the target thrust even if the throttling coefficient of the first variable throttle valve or the second variable throttle valve changes.

FIG. 1 is a conceptual diagram of a cylinder device according to one embodiment. FIG. 2 is a model diagram showing the relationship between the flow rate and the differential pressure of the cylinder device in one embodiment. FIG. 3 is a graph showing the rotational speed of the motor as a function of the flow rate through the pump, and the torque of the motor as a function of the pressure difference (pressure loss) as the liquid passes through the pump. FIG. 4 is a diagram showing the range of the motor rotation speed and the torque that can be output. FIG. 5 is a diagram showing the configuration of the controller. FIG. 6 is a diagram showing the configuration of the throttle valve control section. FIG. 7 is a diagram showing the configuration of the thrust control unit.

The present invention will be described below based on the embodiment shown in the figures. As shown in FIG. 1, the cylinder device A in one embodiment is configured with a hydraulic cylinder 1 and a controller 11.

Each part of the cylinder device A will be described in detail below. As shown in FIG. 1, the hydraulic cylinder 1 is configured with a cylinder 2, a piston 3 movably inserted into the cylinder 2 to divide the cylinder 2 into two working chambers R1 and R2, a first flow path 4 and a second flow path 5 that are parallel to each other and communicate the working chambers R1 and R2, a first variable throttle valve 6 provided in the first flow path 4, a second variable throttle valve 7 provided in series in the second flow path 5, and a bidirectional discharge pump 9 driven by a motor 8, and the cylinder 2 is filled with liquid and sealed. The piston 3 is connected to a rod 10 that is movably inserted into the cylinder 2, and in the case of this hydraulic cylinder 1, the rod 10 protrudes from both ends of the cylinder 2, making it a so-called double-rod type cylinder device.

When the hydraulic cylinder 1 is applied to a vehicle, the cylinder 2 is connected to one of the sprung and unsprung members of the vehicle, and the rod 10 is connected to the other of the sprung and unsprung members, and is interposed between the sprung and unsprung members. When the hydraulic cylinder 1 is applied to a vehicle and used, the thrust it exerts suppresses vibrations of the vehicle body, which is the sprung member, and the vehicle wheels, which are the unsprung members.
In this specification, the hydraulic cylinder 1 is said to extend when the rod 10 moves upward in Fig. 1 relative to the cylinder 2 together with the piston 3, and conversely, the hydraulic cylinder 1 is said to contract when the rod 10 moves downward in Fig. 1 relative to the cylinder 2 together with the piston 3. Note that although the hydraulic cylinder 1 is configured as a double rod type in the illustrated example, it may be configured as a single rod type.

As described above, the cylinder 2 is divided by the piston 3 into an extension side working chamber R1 at the top in FIG. 1 and a compression side working chamber R2 at the bottom in FIG. 1, and each of the working chambers R1 and R2 is filled with a liquid such as hydraulic oil. The liquid may be other liquids such as water or an aqueous solution in addition to hydraulic oil. As described above, the hydraulic cylinder 1 is a double-rod type hydraulic cylinder, and even if the rod 10 moves up and down relative to the cylinder 2 together with the piston 3 in FIG. 1, the volume displaced by the rod 10 in the cylinder 2 does not change. Therefore, the hydraulic cylinder 1 does not have a reservoir to compensate for the volume of the rod 10 moving in and out of the cylinder 2, but may have an accumulator connected to the inside of the cylinder 2 to compensate for the volume change due to the temperature change of the liquid.

The pump 9 is set to a bidirectional discharge type, and may be, for example, a vane pump, gear pump, axial pump, or the like, equipped with a rotating shaft (not shown) that can suck in and discharge fluid by rotating the rotating shaft, and conversely, can forcibly drive the rotating shaft by the flow of fluid. Furthermore, the rotating shaft of the pump 9 is connected to the motor 8, which can be driven by electricity and can generate torque to suppress the rotation of the pump 9 when forcibly rotated by input from the pump 9 side. Various types of motors, whether DC or AC, such as brushless motors, induction motors, synchronous motors, etc., can be used.

The hydraulic cylinder 1 can expand and contract spontaneously and generate thrust in a desired direction by driving the pump 9 with the motor 8 to rotate and send liquid from the extension side working chamber R1 to the compression side working chamber R2, or from the compression side working chamber R2 to the extension side working chamber R1 through the second flow path 5. In addition, when the hydraulic cylinder 1 is forcibly expanded or contracted by an external input, the pump 9, to which the torque of the motor 8 is transmitted, applies resistance to the flow of liquid moving through the second flow path 5 from the extension side working chamber R1 to the compression side working chamber R2, or from the compression side working chamber R2 to the extension side working chamber R1, generating thrust in a direction that prevents expansion or contraction.

When the hydraulic cylinder 1 is forcibly extended or retracted, the motor 8 is forcibly driven via the pump 9 by the flow of liquid going back and forth through the second flow path 5, so that the kinetic energy of the liquid is converted into electrical energy by the motor 8, enabling power regeneration. The power regenerated by the motor 8 may be sent to an external device or stored in a storage battery.

In other words, the first variable throttle valve 6 is provided in the first flow path 4 that bypasses the pump 9 and communicates between the working chambers R1 and R2, and the second variable throttle valve 7 is provided in the second flow path 5 together with the pump 9. Therefore, the first variable throttle valve 6 is arranged in parallel with the second variable throttle valve 7 and the pump 9. The first variable throttle valve 6 and the second variable throttle valve 7 are capable of changing the throttle coefficient, which is the ratio of the passing flow rate to the pressure loss, by changing the opening degree and the valve passage length. Specifically, for example, various valves such as a variable choke and a variable orifice can be used, and the throttle coefficient can be changed by driving the valve body (not shown) with a drive source such as a solenoid or a motor. The drive source that changes the throttle coefficient in the first variable throttle valve 6 and the second variable throttle valve 7 is controlled by the controller 11.

Regarding the relative positioning of the pump 9 and the second variable throttle valve 7, the pump 9 may be disposed on either the working chamber R1 or the working chamber R2 side. In addition, the fluid filled in the cylinder 2 may be any fluid, such as oil, water, an aqueous solution, or gas.

Now, the hydraulic cylinder 1 configured in this way can function as an actuator that expands and contracts by itself when power is supplied from the controller 11 to the motor 8 to drive the pump 9, but conversely, when the hydraulic cylinder 1 is expanded or contracted by an external force, the torque of the motor 8 suppresses the rotation of the pump 9; that is, the motor 8 is used in the braking region to generate a torque in the opposite direction to the rotation direction of the pump 9, and the motor 8, the first variable throttle valve 6, and the second variable throttle valve 7 work together to generate a damping force. When the motor 8 is used in the braking region, the rotation speed and torque of the motor 8 can be controlled by adjusting the throttle coefficients of the first variable throttle valve 6 and the second variable throttle valve 7.

When the motor 8 is supplied with current to drive the pump 9, that is, when the motor 8 is used in the powering region to cause the hydraulic cylinder 1 to function as an actuator, the first variable throttle valve 6 is fully closed to prevent communication between the working chambers R1 and R2 via the first flow path 4, while the second variable throttle valve 7 is fully opened to prevent unnecessary resistance to the flow of liquid caused by the second variable throttle valve 7, resulting in energy loss.

Here, we will use the model diagram shown in Figure 2 to explain how to control the load (rotational speed and torque) of the motor 8 when the hydraulic cylinder 1 is extended or retracted by an external force. Note that the pump 9 provides resistance to the flow of liquid by the torque transmitted from the motor 8, causing pressure loss when the liquid passes through, so it can be treated as equivalent to a variable throttle valve. Therefore, in Figure 2, the motor 8 and pump 9 are shown as one variable throttle valve M.

Then, let ΔP be the pressure difference between one working chamber R1 and the other working chamber R2 when the hydraulic cylinder 1 is expanding or contracting, Q be the flow rate per unit time of the fluid flowing out of one working chamber R1 (hereinafter simply referred to as flow rate), C1 be the throttling coefficient which is the ratio of the flow rate q1 of the fluid passing through the first variable throttle valve 6 divided by the differential pressure (pressure loss) ΔP generated at the first variable throttle valve 6, C2 be the throttling coefficient which is the ratio of the flow rate q2 of the fluid passing through the second variable throttle valve 7 divided by the differential pressure (pressure loss) Δp2 generated at the second variable throttle valve 7, and C3 be the throttling coefficient which is the ratio of the flow rate q2 of the fluid passing through the variable throttle valve M consisting of the motor 8 and the pump 9 divided by the differential pressure (pressure loss) Δpm generated at the variable throttle valve M. Then, the following formula (1) is obtained.

Here, if we set C = C2 x C3/(C2 + C3), equation (1) can be written as equation (2) below.

Furthermore, since the total flow rate Q = q1 + q2 holds, and the pressure difference ΔP generated at the first variable throttle valve 6 is equal to the pressure difference generated across the entire variable throttle valve M consisting of the second variable throttle valve 7, motor 8, and pump 9, the following equation (3) holds.

Substituting equation (3) into equation (2) and summarizing, we get the following equation (4).

And, as can be seen from the above equation (4), if the flow rate Q and the differential pressure ΔP are not changed, the flow rate q2 can be changed by changing the restriction coefficient C1.

In other words, by adjusting the flow rate q1 in the first variable throttle valve 6 that bypasses the pump 9 by changing the throttle coefficient C1, the flow rate q2 passing through the variable throttle valve M can be changed. For example, when the first variable throttle valve 6 is shifted from a fully closed state to a fully open state, the flow rate q2 can be increased or decreased to increase or decrease the rotation speed of the motor 8.

Furthermore, the flow rate at the second variable throttle valve 7 and the variable throttle valve M is q2, the overall differential pressure is ΔP, the differential pressure (pressure loss) at the variable throttle valve M is Δpm, and the composite throttle coefficient C of the second variable throttle valve 7 and the variable throttle valve M is C = C2 x C3 / (C2 + C3) as described above, so by focusing only on the second variable throttle valve 7 and the variable throttle valve M, the following equation (5) is obtained.

And, as can be seen from the above equation (5), if the flow rate q2 and the differential pressure ΔP are not changed, the differential pressure Δpm in the variable throttle valve M can be changed by changing the throttling coefficient C2.

In other words, by changing the throttling coefficient C2, it is possible to change the differential pressure Δpm that occurs when the fluid passes through the pump 9. For example, when the second variable throttling valve 7 is shifted from a fully closed state to a fully open state, the differential pressure Δpm can be increased or decreased to increase or decrease the torque that must be borne by the motor 8.

The above will be explained with reference to the graph shown in FIG. 3, in which the rotation speed of the motor 8 corresponds to the flow rate of the pump 9 and the torque of the motor 8 corresponds to the differential pressure (pressure loss) when the fluid passes through the pump 9, with the flow rate Q and the differential pressure ΔP kept constant. By changing the throttling coefficient C2 of the second variable throttle valve 7, the torque to be borne by the motor 8 (burden torque) can be adjusted along the vertical axis, and by changing the throttling coefficient C1 of the first variable throttle valve 6, the rotation speed of the motor 8 can be adjusted along the horizontal axis. The burden torque of the motor 8 is the torque acting between the motor 8 and the pump 9, and can be regarded as the torque that needs to be applied from the motor 8 to the pump 9 in order for the cylinder device A to output the desired thrust. In this document, the term "burden torque" is used even when the hydraulic cylinder 1 is expanding and contracting spontaneously.

In detail, point a in FIG. 3 shows the relationship between the rotation speed and the load torque of the motor 8 when the second variable throttle valve 7 is fully open to maximize the throttle coefficient C2 and the first variable throttle valve 6 is fully closed to minimize the throttle coefficient C1; point b shows the relationship between the rotation speed and the load torque of the motor 8 when the second variable throttle valve 7 is fully open to maximize the throttle coefficient C2 and the first variable throttle valve 6 is fully open to maximize the throttle coefficient C1; point c shows the relationship between the rotation speed and the load torque of the motor 8 when the second variable throttle valve 7 is fully closed to minimize the throttle coefficient C2 and the first variable throttle valve 6 is fully closed to minimize the throttle coefficient C1; and point d shows the relationship between the rotation speed and the load torque of the motor 8 when the second variable throttle valve 7 is fully closed to minimize the throttle coefficient C2 and the first variable throttle valve 6 is fully open to maximize the throttle coefficient C1. That is, by changing the throttle coefficients C1 and C2 of the first variable throttle valve 6 and the second variable throttle valve 7, the rotation speed and load torque of the motor 8 can be adjusted within the range surrounded by points a, b, c, and d.

Specifically, when the intersection of the rotation speed and the load torque of the motor 8 (the operating point of the motor) is at point a, increasing the throttling coefficient C1 of the first variable throttle valve 6 can shift it toward point b, decreasing the throttling coefficient C2 of the second variable throttle valve 7 can shift it toward point c, and increasing the throttling coefficient C1 of the first variable throttle valve 6 and decreasing the throttling coefficient C2 of the second variable throttle valve 7 can shift it toward point d. In other words, by controlling the throttling coefficients of the first variable throttle valve 6 and the second variable throttle valve 7, it is possible to control the rotation speed and the load torque of the motor 8.

In the explanation of Figure 3, we assume that the flow rate Q and the differential pressure ΔP are constant, so there is no state in which the motor 8 is rotating despite its burden torque being 0, or in which there is a burden torque even though the rotation speed is 0. Therefore, the line connecting points b and d and the line connecting points d and c indicate the boundaries of the range in which the operating point of motor 8 can be, and the operating point of motor 8 will never be a value on these lines.

The range of the burden torque that can be output for any rotation speed of the motor 8 is the area shown by hatching surrounded by an output limit line z1 consisting of a straight line parallel to the horizontal axis in the first and second quadrants and a curved line connected to both ends of this line in the graph of the rotation speed torque coordinate system, in which the vertical axis is the burden torque and the horizontal axis is the rotation speed, as shown in Figure 4, and an output limit line z2 consisting of a straight line parallel to the horizontal axis in the third and fourth quadrants and a curved line connected to both ends of this line. The straight line in the output limit line indicates the upper limit of the burden torque of the motor 8, and is a boundary that occurs due to the current being limited by a current limiter (not shown) provided in the controller 11. The curved line in the output limit line also divides the burden torque region that can be output at the rotation speed at that time and the burden torque region that cannot be output, and is a boundary line determined by the characteristics of the power supply voltage (not shown), the induced power of the motor 8, etc. The sign of the torque in the forward direction of the motor 8 is positive and the sign of the torque in the reverse direction is negative, and the sign of the rotation speed when the motor 8 rotates in the forward direction is positive and the sign of the torque in the reverse direction is negative.

As can be seen from FIG. 4, the higher the rotational speed of the motor 8 in each quadrant, the lower the upper limit of the load torque that can be output. In other words, when the first variable throttle valve 6 is closed to block the first flow path 4 and the entire flow rate of the liquid passing through the working chambers R1 and R2 is passed to the pump 9, the higher the extension/contraction speed of the hydraulic cylinder 1 becomes, and the higher the rotational speed of the motor 8 becomes, and the smaller the load torque that can be output by the motor 8 becomes. Note that the dashed line shown in FIG. 4 is the maximum regenerative efficiency line that shows the relationship between the rotational speed and the load torque at which the regenerative efficiency is maximized, and the regenerative efficiency is maximized when the operating point of the motor 8 is on the maximum regenerative efficiency line.

In addition, in the second quadrant, where the rotation speed is negative and the burden torque is positive, and in the fourth quadrant, where the rotation speed is positive and the burden torque is negative, the motor 8 is operating in the braking region where power regeneration is possible, and in the first quadrant, where the rotation speed is positive and the burden torque is positive, and in the third quadrant, where the rotation speed is negative and the burden torque is negative, the motor 8 is operating in the powering region where power is consumed. Thus, the motor 8 is in a braking state when operating in the braking region, and in a powering state when operating in the powering region.

When motor 8 is operating in the braking region, and point g and point h in Figure 4 are compared, which are on the horizontal axis side of the maximum regenerative efficiency line, point h, which has a higher rotational speed, has a larger regenerative power of motor 8. The maximum regenerative efficiency line is a line that shows the relationship between the rotational speed of motor 8 and the torque that maximizes regenerative efficiency, and when the operating point of motor 8 is on the maximum regenerative efficiency line, the regenerative efficiency will be maximized at that rotational speed. Also, there is room to increase the regenerative power by increasing the rotational speed of motor 8.

Therefore, as shown in FIG. 5, the controller 11 of this embodiment includes a thrust control unit 20 for controlling the torque of the motor 8 to make the actual thrust of the hydraulic cylinder 1 follow the target thrust, as well as a throttle valve control unit 30 for increasing the regenerative power of the motor 8 independently of the thrust control unit 20.

First, the throttle valve control unit 30 will be described. As shown in FIG. 6, the throttle valve control unit 30 includes a first variable throttle valve control unit 31 that monitors the rotation speed and torque of the motor 8 and controls the first variable throttle valve 6, and a second variable throttle valve control unit 32 that controls the second variable throttle valve 7. If the motor 8 includes a sensor such as a resolver that can detect the rotation position of the rotor (not shown), the rotation speed of the motor 8 can be obtained from the rotation position information of the rotor detected by the sensor. If the motor 8 is a DC motor or a motor equivalent to a DC motor, the torque of the motor 8 is proportional to the current flowing through the motor 8, so the current can be regarded as the torque as it is. Since the motor control unit 40 includes a sensor that detects the current of the motor 8, the current value can be obtained from the motor control unit 40 and used as the torque of the motor 8.

The throttle valve control unit 30 may be provided with a sensor for detecting the rotation speed of the motor 8, and a sensor for detecting the torque of the motor 8 or a sensor for detecting the current of the motor 8. The throttle valve control unit 30 sequentially captures the rotation speed and torque of the motor 8 at a predetermined calculation period, and processes the captured rotation speed and torque by the first variable throttle valve control unit 31 and the second variable throttle valve control unit 32. The throttle valve control unit 30 processes the torque of the motor 8, but as described above, the current flowing through the motor 8 can be regarded as torque, so the current flowing through the motor 8 may be treated as torque and processed. The throttle valve control unit 30 monitors the rotation speed and torque of the motor 8 to grasp where the operating point of the motor 8 is located on the graph of the rotation speed and torque. The throttle valve control unit 30 then controls the throttling coefficients of the first variable throttle valve 6 and the second variable throttle valve 7 according to the operating state of the motor 8.

The first variable throttle valve control unit 31 includes a drive circuit for energizing the drive source of the first variable throttle valve 6, and when the motor 8 is operating in a braking state, performs regenerative control to reduce the throttling coefficient of the first variable throttle valve 6 so as to increase the rotation speed of the motor 8, and when the motor 8 is operating in a powered state, controls the throttling coefficient of the first variable throttle valve 6 to a preset initial value. The initial value is set to a value suitable for thrust control of the hydraulic cylinder 1 when the motor 8 is operating in a powered state. When the motor 8 is operating in a powered state, if the first variable throttle valve 6 has a large flow path, the liquid supplied from the pump 9 to the working chamber R1 or R2 will escape through the first flow path 4, so the initial value is preferably set to a minimum value so as to close the first variable throttle valve 6 or to minimize the opening.

The second variable throttle valve control section 32 includes a drive circuit for energizing the drive source of the second variable throttle valve 7, and basically maximizes the throttling coefficient of the second variable throttle valve 7 to control the flow area of the second variable throttle valve 7 to the maximum. The second variable throttle valve 7 prevents the passage of liquid discharged by the pump 9 and becomes a resistance when the hydraulic cylinder 1 operates as an actuator, so the second variable throttle valve control section 32 maximizes the throttling coefficient of the second variable throttle valve 7 when the operating point of the motor 8 is in the powering region and the motor 8 is operating in a powering state. Since the second variable throttle valve 7 provides resistance to the flow of liquid passing through the second flow path 5, the torque borne by the motor 8 can be increased or decreased by increasing or decreasing the throttling coefficient. Even when the operating point of the motor 8 is in the braking region and the operating state of the motor 8 is in the braking state, the second variable throttle valve control section 32 basically maximizes the throttle coefficient of the second variable throttle valve 7 and controls the flow path area of the second variable throttle valve 7 to the maximum, but increases the throttle coefficient of the second variable throttle valve 7 to reduce the torque borne by the motor 8 at the operating point so that the operating point of the motor 8 does not fall into a burden torque region that cannot be output. Simply put, since the upper limit of the torque that can be output at the rotational speed of the motor 8 (upper torque limit) is uniquely determined by the power supply voltage that drives the motor 8, the second variable throttle valve control section 32 may reduce the throttle coefficient of the second variable throttle valve 7 to reduce the torque borne by the motor 8 when the torque of the motor 8 reaches or exceeds a value obtained by subtracting a predetermined value from the upper torque limit at the rotational speed at that time. If you want to maximize the regenerative efficiency by placing the throttling coefficient of the second variable throttle valve 7 on the aforementioned maximum regenerative efficiency line, information on the actual thrust of the hydraulic cylinder 1 is required when calculating the throttling coefficient of the second variable throttle valve 7. Therefore, the throttle valve control unit 30 may obtain the actual thrust from the actual thrust detection unit 41 and calculate the throttling coefficient based on the actual thrust in addition to the rotation speed and torque.

As described above, the throttle valve control unit 30 monitors the rotation speed and torque of the motor 8, and controls the throttle coefficient of the second variable throttle valve 7 so that the operating point of the motor 8 does not fall into the burden torque region where output is not possible. When the operating state of the motor 8 is in a braking state, in order to increase the regenerative power, the throttle valve control unit 30 reduces the throttle coefficient of the first variable throttle valve 6, reduces the flow rate of the liquid passing through the first flow path 4, and increases the flow rate of the liquid flowing through the second flow path 5 in which the pump 9 is installed, thereby increasing the rotation speed of the motor 8. Note that, as described above, when the motor 8 is in a braking state, the throttle valve control unit 30 performs regenerative control to increase the regenerative power of the motor 8 by increasing the rotation speed of the motor 8, but regenerative control to increase the regenerative efficiency may also be performed by controlling the throttle coefficients of the first variable throttle valve 6 and the second variable throttle valve 7 by the first variable throttle valve control unit 31 and the second variable throttle valve control unit 32 so that the operating point of the motor 8 is located on the regenerative efficiency maximum line.

Next, as shown in FIG. 7, the thrust control unit 20 includes a PID control unit 21 and a feedforward control unit 22 that receive a thrust command indicating the target thrust of the hydraulic cylinder 1 from a higher-level control device and obtain a target current to be supplied to the motor 8 based on PID control, an adder unit 23 that adds the current commands output by the PID control unit 21 and the feedforward control unit 22 to generate a final current command indicating the target current of the motor 8, a proportional gain correction unit 24, a differential gain correction unit 25, and an integral gain correction unit 26 that respectively correct the proportional gain, differential gain, and integral gain used by the PID control unit 21 during PID compensation (proportional, integral, and differential compensation), a proportional gain processing unit 27 that processes the proportional gain corrected by the proportional gain correction unit 24, a differential gain processing unit 28 that processes the differential gain corrected by the differential gain correction unit 25, an integral gain processing unit 29 that processes the integral gain corrected by the integral gain correction unit 26, and a motor control unit 40 that receives the final current command generated by the adder unit 23, and feeds back the current flowing through the motor 8 to control the current flowing through the motor 8 to the target current.

In this embodiment, the hydraulic cylinder 1 is applied to a vehicle, and the upper control device determines the thrust to be generated in the hydraulic cylinder 1 primarily for the purpose of suppressing vibration of the vehicle body as a sprung member. The thrust command may be determined so as to enable not only reduction in vibration of the vehicle body but also reduction in vibration of the wheels as unsprung members. Furthermore, the thrust control unit 20 may detect vibration information of the vehicle body, or the vehicle body and wheels, in the vehicle, or receive this vibration information from the vehicle and determine the thrust command itself, rather than obtaining the thrust command from the upper control device.

Although not shown in detail, the PID control unit 21 has a proportional path that obtains a control deviation between the target thrust and the actual thrust of the hydraulic cylinder 1, and multiplies the control deviation by a proportional gain to perform proportional compensation, a proportional path that differentiates the control deviation and multiplies it by a differential gain to perform differential compensation, and a proportional path that integrates the control deviation and multiplies it by an integral gain to perform integral compensation, and outputs a value obtained by adding up the values processed in each of the three paths as a current command. The controller 11 has an actual thrust detection unit 41 that detects the actual thrust of the hydraulic cylinder 1, and the actual thrust of the hydraulic cylinder 1 detected by the actual thrust detection unit 41 is input to the thrust control unit 20 together with the target thrust. 7, the actual thrust detection unit 41 is configured to include, for example, a pressure sensor 41a that detects the pressure in the working chamber R1, a pressure sensor 41b that detects the pressure in the working chamber R2, and a calculation unit 41c that calculates the actual thrust generated by the hydraulic cylinder 1 by multiplying the difference between the pressures in the working chambers R1 and R2 by the pressure-receiving area of the piston 3. Since the actual thrust generated by the hydraulic cylinder 1 can be grasped by detecting the load applied to the rod 10, the actual thrust detection unit 41 may be a sensor that detects the load acting on the rod 10. Although not shown, the thrust control unit 20 may include, instead of the actual thrust detection unit 41, an actual thrust estimation unit that estimates the actual thrust of the hydraulic cylinder 1 rather than detecting the thrust actually output by the hydraulic cylinder 1. Instead of detecting the pressure and load described above, the actual thrust estimating unit may be an observer that detects state quantities of the hydraulic cylinder 1, such as the throttle coefficients of the first variable throttle valve 6 and the second variable throttle valve 7, the rotational speed of the motor 8, and torque, and estimates the actual thrust of the hydraulic cylinder 1 from the state quantities, or an observer that detects state quantities of a system in which the cylinder device A is mounted, such as the displacement and speed of the vehicle body, and estimates the actual thrust of the hydraulic cylinder 1 from the state quantities. The actual thrust estimating unit may also estimate the actual thrust of the hydraulic cylinder 1 from information from acceleration sensors attached to the vehicle body and the axles. In this way, the actual thrust estimating unit may estimate the actual thrust from sensor information used for purposes other than the control of the cylinder device A.

The throttle valve control unit 30 changes the throttle coefficients of the first variable throttle valve 6 and the second variable throttle valve 7, causing a change in the characteristics from the target thrust of the hydraulic cylinder 1 to the thrust of the hydraulic cylinder 1. Therefore, if the PID control unit 21 simply performs PID compensation by feeding back the actual thrust of the hydraulic cylinder 1 to generate a current command to control the motor 8, pressure fluctuations will occur before and after the first variable throttle valve 6 and the second variable throttle valve 7, causing the thrust of the hydraulic cylinder 1 to change suddenly, and the ability of the actual thrust of the hydraulic cylinder 1 to follow the thrust command will deteriorate.

The controller 11 of this embodiment is therefore equipped with a proportional gain correction unit 24 that corrects the proportional gain and a differential gain correction unit 25 that corrects the differential gain in response to changes in the throttling coefficients of the first variable throttling valve 6 and the second variable throttling valve 7 caused by the throttling valve control unit 30.

Here, assuming that the pressure receiving area of the piston 3 of the hydraulic cylinder 1 is _A0 , the viscous resistance of the motor 8 is Cm, the moment of inertia of the rotor of the motor 8 is Im, the torque constant of the motor 8 is Kt, the throttling coefficient of the first variable throttle valve 6 is fv1, the throttling coefficient of the second variable throttle valve 7 is fv2, the bulk elasticity coefficient of the liquid in the hydraulic cylinder 1 is _K0 , the displacement volume of the pump 9 is Vp, the initial volume of the working chambers R1, R2 of the hydraulic cylinder 1 is _V0 , and the Laplace operator is s, a transfer function G(s) from the current im given to the motor 8 of the hydraulic cylinder 1 to the actual thrust fa generated by the hydraulic cylinder 1 can be expressed by the following Equation 6.

Furthermore, if the proportional gain in the PID control unit 21 is Kp, the differential gain in the PID control unit 21 is Kd, and the integral gain in the PID control unit 21 is Ki, the transfer function C(s) of the PID control unit 21 can be expressed by the following equation 7.

Assuming that the current of the motor 8 controlled by the motor control unit 40 follows the current command without delay, the transfer function from the target thrust fa, cmd to the actual thrust fa of the hydraulic cylinder 1 is expressed by the following equation 8.

It can be seen from Equation 8 that the coefficients ^s2 and s in the denominator change with the throttle coefficient fv1 of the first variable throttle valve 6 and the throttle coefficient fv2 of the second variable throttle valve 7 as parameters. Therefore, it can be confirmed from Equation 8 that when the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 change under the control of the throttle valve control section 30, the transfer function of the system in the cylinder device A changes, and the responsiveness of the thrust of the hydraulic cylinder 1 to the target thrust changes.

On the other hand, the coefficient of ^s2 in the denominator of Equation 8 includes the derivative gain Kd, and the coefficient of s includes the proportional gain Kp. Therefore, by changing the values of the proportional gain Kp and the derivative gain Kd in accordance with changes in the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7, it is possible to suppress deterioration in the ability of the thrust of the hydraulic cylinder 1 to follow the target thrust, which is caused by changes in the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7.

The proportional gain correction unit 24 obtains information on the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7, and the PID control unit 21 obtains an optimal proportional gain for the values of the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 at that time from the values of the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7, and corrects the proportional gain of the PID control unit 21 to the obtained value. The differential gain correction unit 25 obtains information on the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7, and the PID control unit 21 obtains an optimal differential gain for the values of the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 at that time from the values of the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7, and corrects the differential gain of the PID control unit 21 to the obtained value.

In this way, the proportional gain and differential gain used by the PID control unit 21 are corrected to proportional gain and differential gain appropriate for the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 at that time, so when the PID control unit 21 obtains a current command from the target thrust and the actual thrust, even if the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 change, deterioration of the tracking ability of the actual thrust of the hydraulic cylinder 1 to the target thrust can be suppressed. Note that the throttle valve control unit 30 controls the first variable throttle valve 6 and the second variable throttle valve 7, and generates commands for adjusting the respective throttle coefficients of the first variable throttle valve 6 and the second variable throttle valve 7 and provides them to the drive sources of the first variable throttle valve 6 and the second variable throttle valve 7, so that the respective throttle coefficients of the first variable throttle valve 6 and the second variable throttle valve 7 can be grasped. Therefore, the proportional gain correction unit 24 and the differential gain correction unit 25 may obtain information on the throttling coefficient of the first variable throttle valve 6 and the throttling coefficient of the second variable throttle valve 7 from the throttle valve control unit 30. The proportional gain correction unit 24 and the differential gain correction unit 25 may also obtain information on each throttling coefficient by detecting the current supplied to the drive source of the first variable throttle valve 6 and the drive source of the second variable throttle valve.

The proportional gain correction unit 24 specifically uses a map for determining the proportional gain from the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 to determine the proportional gain that is optimal for the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 at that time. The differential gain correction unit 25 specifically uses a map for determining the differential gain from the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 to determine the differential gain that is optimal for the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 at that time.

In detail, first, the throttling coefficient of the first variable throttle valve 6 and the throttling coefficient of the second variable throttle valve 7 are set to predetermined values, and the proportional gain, differential gain, and integral gain of the PID control unit 21 for the hydraulic cylinder 1 are adjusted so that the actual thrust of the hydraulic cylinder 1 follows the target thrust, and the reference proportional gain, differential gain, and integral gain are obtained.

In this manner, the hydraulic cylinder 1 is controlled by the PID control unit 21 set to the reference proportional gain, differential gain, and integral gain, and target thrusts of various frequencies and a target thrust whose frequency gradually changes are provided to the PID control unit 21 to control the hydraulic cylinder 1. The actual thrust output is measured, a transfer function from the target thrust to the actual thrust of the cylinder device A is obtained, and the values of the coefficients ^s2 and s in the denominator of the transfer function are calculated.

Then, the throttling coefficient of the first variable throttle valve 6 and the throttling coefficient of the second variable throttle valve 7 are changed to grasp the change in the transfer function of the cylinder device A, and a proportional gain map is obtained for obtaining a proportional gain that is optimal for the throttling coefficient of the first variable throttle valve 6 and the throttling coefficient of the second variable throttle valve 7, and a differential gain map is obtained for obtaining a differential gain that is optimal for the throttling coefficient of the first variable throttle valve 6 and the throttling coefficient of the second variable throttle valve 7.

Using the proportional gain map obtained in this manner, the proportional gain correction unit 24 determines the optimal proportional gain for the PID control unit 21 from the throttling coefficient of the first variable throttle valve 6 and the throttling coefficient of the second variable throttle valve 7. The differential gain correction unit 25 also uses the differential gain map to determine the optimal differential gain for the PID control unit 21 from the throttling coefficient of the first variable throttle valve 6 and the throttling coefficient of the second variable throttle valve 7.

The proportional gain and differential gain in the PID control unit 21 are corrected to the proportional gain calculated by the proportional gain correction unit 24 and the differential gain calculated by the differential gain correction unit 25. Therefore, even if the throttling coefficient of the first variable throttle valve 6 and the throttling coefficient of the second variable throttle valve 7 change, the proportional gain and differential gain are optimized according to the change in each throttling coefficient, so that the actual thrust of the hydraulic cylinder 1 follows the target thrust with good responsiveness.

The proportional gain calculated by the proportional gain correction unit 24 and the differential gain calculated by the differential gain correction unit 25 may be immediately used by the PID control unit 21, but if the values of the proportional gain and the differential gain change suddenly, the current command generated by the PID control unit 21 may also change suddenly. Therefore, the thrust control unit 20 includes a proportional gain processing unit 27 that performs low-pass filter processing on the proportional gain calculated by the proportional gain correction unit 24 to mitigate the change in the proportional gain, and a differential gain processing unit 28 that performs low-pass filter processing on the differential gain calculated by the differential gain correction unit 25 to mitigate the change in the differential gain.

Thus, the thrust control unit 20 includes a proportional gain processing unit 27 that mitigates the change in the proportional gain calculated by the proportional gain correction unit 24, and a differential gain processing unit 28 that mitigates the change in the differential gain calculated by the differential gain correction unit 25, and the proportional gain value and the differential gain value in the PID control unit 21 are changed to the proportional gain value processed by the proportional gain processing unit 27 and the differential gain value processed by the differential gain processing unit 28. Therefore, even if the throttling coefficient of the first variable throttle valve 6 and the throttling coefficient of the second variable throttle valve 7 change and the proportional gain and the differential gain are corrected, the sudden change in the proportional gain value and the differential gain value used in the PID control unit 21 is mitigated, and the sudden change in the current command output by the PID control unit 21 is also mitigated, so that the sudden change in the thrust of the hydraulic cylinder 1 can also be mitigated.

The thrust control unit 20 of this embodiment includes an integral gain correction unit 26. In the above-mentioned formula 8, the bulk modulus _K0 of the liquid in the hydraulic cylinder 1 is included as a parameter of the coefficient e of the integral gain Kf. The bulk modulus _K0 of the liquid changes depending on the pressure of the liquid. Therefore, the integral gain correction unit 26 obtains information on the pressure in the cylinder 2 from the actual thrust detection unit 41, estimates the bulk modulus _K0 , obtains an integral gain that is optimal for the estimated bulk modulus _K0 , and corrects the integral gain in the PID control unit 21 to the obtained integral gain. For example, the integral gain correction unit 26 may obtain the bulk modulus _K0 using a formula for obtaining the bulk modulus _K0 from the pressure at the average temperature when the cylinder device A is used. In addition, the relationship between the temperature, pressure, and bulk modulus _K0 of the liquid may be mapped, and the integral gain correction unit 26 may detect the temperature of the liquid using a temperature sensor that detects the temperature of the liquid in the cylinder 2, and obtain the bulk modulus _K0 from the detected temperature and pressure by map calculation.

Then, the integral gain in the PID control unit 21 is corrected to the integral gain calculated by the integral gain correction unit 26. Therefore, even if the bulk modulus _K0 of the liquid changes and the characteristics of the cylinder device A change, the integral gain and the differential gain are optimized according to the change in the bulk modulus _K0 , so that the actual thrust of the hydraulic cylinder 1 follows the target thrust with good responsiveness.

The integral gain calculated by the integral gain correction unit 26 may be immediately used by the PID control unit 21, but if the values of the proportional gain and the differential gain suddenly change, the current command generated by the PID control unit 21 may also suddenly change. Therefore, the thrust control unit 20 is provided with an integral gain processing unit 29 that performs low-pass filter processing on the integral gain calculated by the integral gain correction unit 26 to mitigate the change in the integral gain.

In this way, the thrust control unit 20 includes an integral gain processing unit 29 that alleviates the change in the integral gain calculated by the integral gain correction unit 26, and the value of the integral gain in the PID control unit 21 is changed to the value of the integral gain processed by the integral gain processing unit 29. Therefore, even if the bulk modulus _K0 of the liquid changes and the integral gain is corrected, a sudden change in the value of the integral gain used in the PID control unit 21 is alleviated, and a sudden change in the current command output by the PID control unit 21 is also alleviated, so that a sudden change in the thrust of the hydraulic cylinder 1 can also be alleviated.

The bulk modulus _K0 is included as a parameter of the coefficients _s2 and s in the denominator in Equation 8. Therefore, the proportional gain correction unit 24 and the differential gain correction unit 25 may also obtain optimal proportional gains and differential gains in response to changes in the bulk modulus _K0 as well as the throttle coefficients of the first variable throttle valve 6 and the second variable throttle valve 7, and correct the proportional gains and differential gains. How to obtain the proportional gain and differential gain in response to changes in the bulk modulus _K0 may be determined by measuring changes in the transfer function when the value of the bulk modulus _K0 is changed, and creating a map that allows the proportional gain and differential gain to be optimally set.

As described above, in the cylinder device A of this embodiment, in addition to the PID control unit 21 in which the controller 11 receives the input of the target thrust and determines the current command to be output to the motor 8 through PID control, the cylinder device A also includes a proportional gain correction unit 24 that corrects the proportional gain based on the throttling coefficient of the first variable throttle valve 6 and the throttling coefficient of the second variable throttle valve 7, and a differential gain correction unit 25 that corrects the differential gain. Therefore, even if the throttling coefficients of the first variable throttle valve 6 and the second variable throttle valve 7 are changed by the throttling valve control unit 30, deterioration of the tracking ability of the hydraulic cylinder 1 to the target thrust can be suppressed.

The feedforward control unit 22 determines an additional current to be added to the current command determined by the PID control unit 21 in order to improve the responsiveness of the hydraulic cylinder 1 to the thrust command input from the upper control device. The feedforward control unit 22 determines an additional current that allows the thrust of the hydraulic cylinder 1 to quickly track the thrust command, taking into account the response delay of the hydraulic cylinder 1 to the thrust command. The feedforward control unit 22 does not feed back the actual thrust of the hydraulic cylinder 1, and therefore improves the responsiveness of the hydraulic cylinder 1 to the target thrust without affecting the tracking ability to the target thrust.

The adder 23 adds the current command calculated by the PID control unit 21 from the target thrust and the added current command calculated by the feedforward control unit 22 from the target thrust to generate a final current command indicating the target current to be supplied to the motor 8, and inputs the current command to the motor control unit 40.

The motor control unit 40, not shown in detail, includes a drive circuit that drives the motor 8, and a controller that feeds back the actual current of the motor 8 and drives the drive circuit based on the control deviation between the target current indicated by the current command input from the adder 23 and the actual current flowing through the motor 8 to perform PWM control of the motor 8. The motor control unit 40 controls the current of the motor 8 so that it follows the target current indicated by the current command according to the current command input from the adder 23. Note that the motor control unit 40 only needs to be provided with a drive circuit suitable for current control of the motor 8 depending on the type of the motor 8, and be able to control the current of the motor 8 according to the current command.

In addition, except for the pressure sensors 41a, 41b in the actual thrust detection unit 41, the drive circuit in the motor control unit 40, and the drive circuit in the throttle valve control unit 30, the hardware resources of the controller 11 include, although not shown in the figure, an interface for inputting signals of thrust commands, the rotational speed and torque (current) of the motor 8, and the pressure in the cylinder 2, a storage device such as a ROM (Read Only Memory) in which programs used for processing required to control the motor 8, the first variable throttle valve 6, and the second variable throttle valve 7 are stored, an arithmetic unit such as a CPU (Central Processing Unit) that executes processing based on the programs, and a storage device such as a RAM (Random Access Memory) that provides memory space for the CPU. Each part of the thrust control unit 20 and the throttle valve control unit 30 in the controller 11 can be realized by the execution of the programs by the CPU. Additionally, the controller 11 may be realized by an analog electronic circuit, instead of by a CPU executing the program.

As described above, the cylinder device A of this embodiment includes a hydraulic cylinder 1 having a cylinder 2, a piston 3 that is movably inserted into the cylinder 2 and divides the inside of the cylinder 2 into two working chambers R1 and R2, a first flow path 4 and a second flow path 5 that are parallel to each other and communicate the working chambers R1 and R2, a first variable throttle valve 6 provided in the first flow path 4, a second variable throttle valve 7 provided in series in the second flow path 5, and a bidirectional discharge type pump 9 driven by a motor 8, and the first variable throttle valve 6, the second variable throttle valve 7, and the motor 8. The controller 11 includes a PID control unit 21 that generates a current command to be given to the motor 8 by PID compensation of the target thrust of the hydraulic cylinder 1, a proportional gain correction unit 24 that corrects the proportional gain of the PID control unit 21, and a differential gain correction unit 25 that corrects the differential gain of the PID control unit 21. The proportional gain correction unit 24 and the differential gain correction unit 25 correct the proportional gain and the differential gain based on the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7, respectively. According to the cylinder device A configured in this manner, even if the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 change, the proportional gain and the differential gain used in the PID control unit 21 are optimized to the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 at that time. Therefore, according to the cylinder device A of this embodiment, even if the throttle coefficient of the first variable throttle valve 6 or the second variable throttle valve 7 changes, the deterioration of the tracking performance for the target thrust can be suppressed.

Furthermore, the controller 11 in the cylinder device A of this embodiment is equipped with an integral gain correction unit 26 that corrects the integral gain of the PID control unit 21 based on the bulk modulus _K0 of the liquid in the hydraulic cylinder 1. With the cylinder device A configured in this manner, even if the bulk modulus _K0 of the liquid changes and the characteristics of the cylinder device A change, it is possible to suppress deterioration in the ability of the actual thrust of the hydraulic cylinder 1 to follow the target thrust.

Furthermore, the controller 11 in the cylinder device A of this embodiment has a proportional gain processing unit 27 that mitigates the change in the proportional gain corrected by the proportional gain correction unit 24, and a differential gain processing unit 28 that mitigates the change in the differential gain corrected by the differential gain correction unit 25, and the PID control unit 21 generates a current command using the proportional gain processed by the proportional gain processing unit 27 and the differential gain processed by the differential gain processing unit 28. According to the cylinder device A configured in this manner, even if the throttling coefficient of the first variable throttle valve 6 and the throttling coefficient of the second variable throttle valve 7 change and the proportional gain and differential gain are corrected, the sudden change in the value of the proportional gain and the value of the differential gain used in the PID control unit 21 is mitigated, and the sudden change in the current command output by the PID control unit 21 is also mitigated, so that the sudden change in the thrust of the hydraulic cylinder 1 can also be mitigated.

The controller 11 in the cylinder device A of this embodiment is also equipped with a throttle valve control unit 30 that controls either or both of the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 so as to increase the regenerative power of the motor 8 when the motor 8 is in a braking state. With the cylinder device A configured in this manner, even if the throttle coefficient of the first variable throttle valve 6 or the second variable throttle valve 7 is changed, the control by the PID control unit 21 can suppress deterioration of the responsiveness of the hydraulic cylinder 1 to the target thrust, so that it is possible to both suppress the tracking ability of the hydraulic cylinder 1 and increase the regenerative power by the throttle valve control unit 30.

Furthermore, the controller 11 in the cylinder device A of this embodiment includes a feedforward control unit 22 that receives the input of the target thrust and determines an additional current command to be added to the current command determined by the PID control unit 21 through feedforward control, and generates a final current command that indicates the target current to be supplied to the motor 8 by adding the current command determined by the PID control unit 21 and the additional current command determined by the feedforward control unit 22. According to the cylinder device A configured in this manner, the feedforward control unit 22, which does not feed back the actual thrust of the hydraulic cylinder 1, determines an additional current command that allows the thrust of the hydraulic cylinder 1 to quickly follow the thrust command, taking into account the response delay of the hydraulic cylinder 1 to the thrust command, and adds the additional current command to the current command of the PID control unit 21 to generate a final current command, so that the responsiveness to the target thrust can be improved without affecting the ability of the hydraulic cylinder 1 to follow the target thrust.

Although the preferred embodiment of the present invention has been described in detail above, modifications, variations, and changes are possible without departing from the scope of the claims.

1: hydraulic cylinder, 2: cylinder, 3: piston, 4: first flow path, 5: second flow path, 6: first variable throttle valve, 7: second variable throttle valve, 8: motor, 9: pump, 11: controller, 21: PID control section, 22: feedforward control section, 24: proportional gain correction section, 25: differential gain correction section, 26: integral gain correction section, 27: proportional gain processing section, 28: differential gain processing section, 30: throttle valve control section, A: cylinder device, R1, R2: working chamber

Claims (4)

a hydraulic cylinder having a cylinder, a piston movably inserted into the cylinder to divide the inside of the cylinder into two working chambers, a first flow passage and a second flow passage arranged in parallel with each other and communicating the working chambers with each other, a first variable throttle valve provided in the first flow passage, a second variable throttle valve provided in series in the second flow passage, and a two-way discharge pump driven by a motor;
a controller for controlling the first variable throttle valve, the second variable throttle valve, and the motor,
the controller has a PID control unit that performs PID compensation on a target thrust of the hydraulic cylinder to generate a current command to be applied to the motor, a proportional gain correction unit that corrects a proportional gain of the PID control unit, and a differential gain correction unit that corrects a differential gain of the PID control unit,
the proportional gain correction unit and the differential gain correction unit respectively correct the proportional gain and the differential gain based on a throttle coefficient of the first variable throttle valve and a throttle coefficient of the second variable throttle valve. The controller:
2. The cylinder device according to claim 1, further comprising an integral gain correction unit that corrects an integral gain of the PID control unit based on a bulk modulus of the liquid in the hydraulic cylinder. The controller:
a proportional gain processing unit that reduces a change in the proportional gain corrected by the proportional gain correction unit;
a differential gain processing unit that reduces a change in the differential gain corrected by the differential gain correction unit,
The cylinder device according to claim 1 , wherein the PID control unit generates the current command by using a proportional gain processed by the proportional gain processing unit and a differential gain processed by the differential gain processing unit. 3. The cylinder device according to claim 1, wherein the controller has a feedforward control unit that receives an input of the target thrust and determines an additional current command to be added to a current command determined by the PID control unit through feedforward control, and generates a final current command that indicates a target current to be supplied to the motor by adding the current command determined by the thrust control unit and the additional current command determined by the feedforward control unit.

Images