JP2024053184A - Cylinder Unit - Google Patents

Abstract

[Problem] The present invention aims to provide a cylinder device capable of generating a stable thrust by preventing the motor and the cylinder device from exciting each other's vibrations and oscillating. [Solution] The cylinder device A includes a hydraulic cylinder 1 having a cylinder 2, a piston 3 that 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 arranged in parallel to 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 a controller 11 that controls the first variable throttle valve 6, the second variable throttle valve 7, and the motor 8, and when the motor 8 is in a braking state and the voltage command is saturated, the controller 11 controls one or both of the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7. [Selected Figure] Figure 5

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 pump is rotated by the hydraulic oil flowing through the second flow path, so the motor is used in the braking region, and 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. As described above, in conventional cylinder devices, in addition to when the motor is used in the powering region to actively extend or retract the hydraulic cylinder, the thrust generated by the cylinder device can be adjusted by controlling the torque generated by the motor even when the motor is used in the braking region.

JP 2009-196597 A

Here, the mechanical resonance frequency fm of the cylinder device can be expressed by the following Equation 1, where the throttling coefficient of the first variable throttle valve is fv1, the throttling coefficient of the second variable throttle valve is fv2, the bulk elasticity coefficient of the fluid is Ko, the displacement volume of the pump is Vp, the moment of inertia of the motor rotor is Im, and the initial volume of the upper and lower chambers is _V0 .

On the other hand, if the motor's electrical resonant frequency is fe, the winding resistance is R, the winding inductance is L, and the rotor's electrical angular speed is φ, then the resonant frequency can be expressed by the following equation 2. From equation 2, it can be seen that the motor's electrical resonant frequency fe changes according to the rotor's electrical angular speed φ, and the higher the motor's rotational speed, the higher the value of the resonant frequency fe.

When the motor rotation speed increases and the electrical resonant frequency fe approaches the mechanical resonant frequency fm, a vibration mode appears in which the two frequencies excite each other and cause oscillation, resulting in a phenomenon in which the thrust generated by the cylinder device becomes unstable and changes in an oscillatory manner. As disclosed in JP 2008-67581, this phenomenon is known to occur when all three conditions are met: the motor is in a braking state, the motor voltage command is in a saturated state, and the mechanical resonant frequency of the cylinder device and the electrical resonant frequency of the motor are close to each other.

However, as mentioned above, in conventional cylinder devices, there are many situations where the motor is used in the braking region due to expansion and contraction caused by external force. Therefore, in conventional cylinder devices, when the motor expands and contracts very quickly due to the action of an external force, the motor operates in a braking state, and the motor rotation speed increases, causing the value of the electrical resonance frequency fe to approach the value of the mechanical resonance frequency fm, creating a vibration mode in which the motor oscillates, and the generated thrust may fluctuate in an oscillatory manner.

The present invention aims to provide a cylinder device that can generate a stable thrust force by preventing the motor and cylinder device from exciting each other's vibrations and oscillating.

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. When the controller determines that the motor is in a braking state and the voltage command of the motor is saturated, it either reduces the rotational speed of the motor to reduce the electrical resonance frequency and simultaneously changes the mechanical resonance frequency of the cylinder device, or controls one or both of the throttling coefficient of the first variable throttle valve and the throttling coefficient of the second variable throttle valve so as to reduce one or both of the rotational speed and torque of the motor.

With a cylinder device configured in this way, by determining that the motor is in a braking state and that the motor voltage command is saturated, it is possible to determine that the motor may oscillate, and by lowering the motor rotation speed to lower the electrical resonance frequency while simultaneously changing the mechanical resonance frequency of the cylinder device, or by lowering one or both of the motor rotation speed and torque to return the motor to a controllable state, it is possible to prevent the motor and cylinder device from exciting each other's vibrations and causing oscillation, and generate a stable thrust.

The controller in the cylinder device may also include a braking state determination unit that determines whether the motor is in a braking state based on the motor's rotation speed and torque, and a saturation determination unit that determines whether the motor's voltage command is saturated based on the resultant vector length of the motor's q-axis voltage command and d-axis voltage command. With this cylinder device configured in this way, it is possible to accurately determine whether the motor's operating point is in the second or fourth quadrant in the braking state in the rotation speed torque coordinate system based on the motor's rotation speed and torque, and since the saturation of the motor's voltage command is determined based on the resultant vector length of the q-axis voltage command and the d-axis voltage command, it is possible to easily determine whether the motor's voltage command is saturated, and the conditions for executing oscillation prevention control can be accurately and easily determined.

As described above, the cylinder device of the present invention can prevent the motor and cylinder device from exciting each other's vibrations and oscillating, and generate a stable thrust.

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 oscillation prevention control section.

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 that is movably inserted into the cylinder 2 and divides 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 together with the piston 3 relative to the cylinder 2 upward in Fig. 1, and conversely, the hydraulic cylinder 1 is said to contract when the rod 10 moves together with the piston 3 relative to the cylinder 2 downward in Fig. 1. Note that although the hydraulic cylinder 1 is configured as a double rod type in the illustrated example, it may also 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 be a bidirectional discharge type, and may be, for example, a vane pump, gear pump, axial pump, or the like, that has a rotating shaft (not shown) and 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 in this embodiment is a three-phase brushless DC motor that can be driven by passing electricity, and when forcibly rotated by input from the pump 9 side, can generate electricity and generate torque that suppresses the rotation of the pump 9.

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, the differential pressure between one working chamber R1 and the other working chamber R2 when the hydraulic cylinder 1 is expanding or contracting is ΔP, the flow rate per unit time of the fluid flowing out from one working chamber R1 (hereinafter simply referred to as flow rate) is Q, the throttling coefficient 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, the throttling coefficient is C1, 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 is C2, and the throttling coefficient is the ratio of the flow rate q2 of the fluid passing through the variable throttle valve M consisting of the motor 8 and pump 9 divided by the differential pressure (pressure loss) Δpm generated at the variable throttle valve M, the following formula 3 is obtained.

Here, if we set C = C2 x C3/(C2 + C3), equation 3 can be written as equation 4 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 5 holds.

Substituting Equation 5 into Equation 4 and summarizing, we get Equation 6 below.

And, as can be seen from the above equation 6, 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 7 is obtained.

And, as can be seen from the above equation 7, 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 load torque that can be output for any rotation speed of the motor 8 is the area surrounded by a straight line j1 parallel to the horizontal axis in the first and second quadrants, curves k1 and k2 connected to the line j1, a straight line j2 parallel to the horizontal axis in the third and fourth quadrants, and curves k3 and k4 connected to the line j2 in the rotation speed torque coordinate system with the load torque on the vertical axis and the rotation speed on the horizontal axis, as shown in Figure 4. The straight lines j1 and j2 indicate the upper limit of the load torque of the motor 8, and are boundaries that arise due to the current being limited by a current limiter (not shown) provided in the controller 11. The curves k1, k2, k3, and k4 are also lines that separate the area of the load torque that the motor 8 can output at the rotation speed at that time from the area of the load torque that cannot be output, and are boundary lines determined by the characteristics of the voltage of the power supply not shown, the induced electromotive force of the motor 8, and the like. In FIG. 4, the torque of the motor 8 in the forward direction is positive and the torque in the reverse direction is negative, and the rotational speed of the motor 8 when rotating in the forward direction is positive and the torque in the reverse direction is negative.

As can be seen from Figure 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/retraction speed of the hydraulic cylinder 1, the higher the rotational speed of the motor 8 will be, and the smaller the load torque that can be output will be.

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, 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 it consumes power to power itself. Thus, the motor 8 is in a braking state when it is operating in the braking region, and in a powering state when it is operating in the powering region.

The line formed by the straight line j1 and the curves k1 and k2 connected to the straight line j1, and the line formed by the straight line j2 and the curves k3 and k4 connected to the straight line j2 indicate the output limit of the motor 8 in the rotational speed torque coordinate system, and indicate that the motor 8 is in an uncontrollable state when the operating point of the intersection of the rotational speed and torque of the motor 8 in the braking region of the second and fourth quadrants is in region X, which exceeds the output limit. Also, when the operating point of the motor 8 is in region Y, which is in the braking region and within the output limit, the motor 8 can generate the desired torque at the rotational speed at that time, and therefore indicates that the motor 8 is in a controllable state.

Here, as shown in FIG. 3, the rotation speed of the motor 8 can be reduced by increasing the throttling coefficient of the first variable throttle valve 6, and the torque borne by the motor 8 can be reduced by decreasing the throttling coefficient of the second variable throttle valve 7. Therefore, when the motor 8 is in the second and fourth quadrants and the motor 8 is in a braking state, and the operating point of the motor 8 exceeds the output limit and is in region X, the motor 8 cannot be controlled normally. By adjusting one or both of the throttling coefficients of the first variable throttle valve 6 and the second variable throttle valve 7, the rotation speed of the motor 8 is reduced to reduce the electrical resonance frequency and at the same time change the mechanical resonance frequency of the cylinder device A, or by reducing one or both of the rotation speed and torque of the motor 8 to return the motor 8 to a controllable state, it is possible to prevent the motor 8 and the cylinder device A from exciting each other's vibrations and oscillating, and generate a stable thrust in the cylinder device A. This means that in Equation 1, the mechanical resonance frequency fm of the cylinder device A can be changed by using the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 as parameters. As described above, by adjusting one or both of the throttle coefficients of the first variable throttle valve 6 and the second variable throttle valve 7, the rotation speed of the motor 8 can be reduced to reduce the electrical resonance frequency, and at the same time, the mechanical resonance frequency of the cylinder device A can be changed to prevent the motor 8 and the cylinder device A from exciting each other's vibration and oscillating. Also, although not described in detail, the damping ratio of the cylinder device A can be changed by combining the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 from the transfer function from the current input of the motor 8 to the thrust of the cylinder device A.

As shown in FIG. 5, the controller 11 includes a thrust control unit 20 that receives a thrust command indicating the target thrust of the hydraulic cylinder 1 from a higher-level control device and controls the motor 8, as well as an oscillation prevention control unit 30 that controls the throttling coefficient of the first variable throttle valve 6 and the throttling coefficient of the second variable throttle valve 7 to prevent oscillation of the motor 8.

The thrust control unit 20 includes a current command generating unit 21 that, upon receiving a thrust command indicating the target thrust of the hydraulic cylinder 1 from a higher-level control device, determines a target current to be supplied to the motor 8 and outputs a current command indicating the target current, a current loop 22 that, upon receiving the current command generated by the current command generating unit 21, generates a voltage command to control the current flowing through the motor 8 according to the target current by feeding back the current flowing through the motor 8, and a drive circuit 23 that supplies power to the motor 8 by inputting the voltage command from the current loop 22. In this embodiment, the hydraulic cylinder 1 is applied to a vehicle, and the higher-level control device determines the thrust to be generated in the hydraulic cylinder 1 mainly for the purpose of suppressing the vibration of the vehicle body as a sprung member. The thrust command may be determined so as to enable not only the reduction of the vibration of the vehicle body but also the reduction of the vibration of the wheels as unsprung members. The thrust control unit 20 may also determine a thrust command by itself, rather than obtaining a thrust command from a higher-level control device, by detecting vibration information of the vehicle body, or the vehicle body and wheels in the vehicle, or by receiving such vibration information from the vehicle.

The current command generating unit 21 performs a calculation process to, for example, feed back the actual thrust generated by the hydraulic cylinder 1, and perform PID (proportional integral differential) compensation for the control deviation between the target thrust commanded by the thrust command and the actual thrust, thereby determining a target current according to the torque to be output from the motor 8. In addition, the current command generating unit 21 performs vector control to control the motor 8 by decomposing into a q-axis current for generating torque and a d-axis current for generating magnetic flux regardless of the electrical angle of the rotor by converting three phases to two phases and converting fixed coordinates to rotating coordinates, thereby determining the q-axis current command iq ^* and the d-axis current command id ^* of the motor 8.

The actual thrust of the hydraulic cylinder 1 is input to the current command generating unit 20a from an actual thrust detecting unit 25 including a pressure sensor 25a for detecting the pressure in the working chamber R1, a pressure sensor 25b for detecting the pressure in the working chamber R2, and a calculation unit 25c for calculating the 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. The current command generating unit 21 may be configured in any manner as long as it can calculate a target current from the thrust command and generate a q-axis current command iq ^* and a d-axis current command id ^* . Since the thrust generated by the hydraulic cylinder 1 can be grasped by detecting the load applied to the rod 10, the actual thrust detecting unit 25 may be a sensor for detecting the load acting on the rod 10.

In addition, the thrust control unit 20 may be provided with an actual thrust estimation unit (not shown) that estimates the actual thrust of the hydraulic cylinder 1 instead of detecting the thrust actually output by the hydraulic cylinder 1, instead of the actual thrust detection unit 25. Instead of detecting the pressure and load described above, the actual thrust estimation unit may be an observer that detects state quantities of the hydraulic cylinder 1, such as the throttling coefficients of the first variable throttle valve 6 and the second variable throttle valve 7, the rotational speed of the motor 8, and the torque, and estimates the actual thrust of the hydraulic cylinder 1 from the state quantities, or an observer that detects state quantities of the 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. In addition, the actual thrust estimation unit may estimate the actual thrust of the hydraulic cylinder 1 from information from acceleration sensors attached to the vehicle body and the axle. In this way, the actual thrust estimation unit may estimate the actual thrust from sensor information used for purposes other than the control of the cylinder device A. The current command generation unit 21 may then feed back the actual thrust force estimated by the actual thrust force estimation unit to determine the target current.

The current loop 22 obtains information on the q-axis current iq and the d-axis current id of the motor 8 from information on at least two phases of the current flowing through the three-phase windings of the motor 8, and generates a q-axis voltage command Vq* by PID compensation of the q-axis current deviation between the q-axis current command iq ^* and the q-axis current iq, and generates a d-axis voltage command Vd ^* by PID compensation of the d-axis current deviation between the d-axis current command id ^* and the d-axis current id. The current loop 22 of this embodiment obtains the q-axis voltage command Vq ^* and the d-axis voltage command Vd ^* as current commands, and converts these two-phase voltage commands Vq ^* and Vd ^* into three-phase voltage commands Vu, Vv, and Vw of the actual U-phase, V-phase, and W-phase of the motor 8, and inputs ^them to the drive circuit 23. The current loop 22 also inputs the obtained q-axis voltage command Vq ^* and d-axis voltage command Vd ^* to the oscillation prevention control unit 30, which will be described later. In addition, the current loop 22 may perform PI compensation instead of PID compensation in the control path for obtaining the q-axis voltage command Vq ^* from the q-axis current command iq ^* and the control path for obtaining the q-axis voltage command Vd ^* from the q-axis current command id ^* .

In addition, since the controller 11 in the cylinder device A of this embodiment performs vector control of the motor 8, it may also perform control to improve the rotational speed torque characteristics, such as maximum torque control or field weakening control.

When the drive circuit 23 receives the three-phase voltage commands Vu, Vv, and Vw, it applies voltages to the three-phase windings of the motor 8 according to the duty ratios indicated by the voltage commands Vu, Vv, and Vw to PWM-drive the motor 8. The drive circuit 23 is equipped with a sensor that detects the current flowing through the three-phase windings of the motor 8, and inputs information on the current flowing through the windings of the motor 8, which is required for the processing of the current loop 22, to the current loop 22 as feedback. The current loop 22 obtains information on the current flowing through the windings of the motor 8 from the drive circuit 23, but may also be equipped with a separate sensor that detects the current flowing through the windings of the motor 8.

Next, the oscillation prevention control unit 30 controls the first variable throttle valve 6 and the second variable throttle valve 7 while monitoring the rotation speed, torque, and voltage command in the thrust control unit 20 of the motor 8. Regarding the rotation speed of the motor 8, if the motor 8 is equipped with a sensor such as a resolver capable of detecting the rotation position of the rotor (not shown), the rotation speed can be obtained from the rotation position information of the rotor detected by the sensor. The rotation speed of the motor 8 may also be estimated from the stroke displacement information of the suspension. Regarding the torque of the motor 8, since the motor 8 is a three-phase brushless DC motor, when the d-axis current is set to 0, the torque of the motor 8 is proportional to the q-axis current iq, so the q-axis current iq can be regarded as the torque as it is, and the q-axis current iq can be obtained from the current loop 22 and used as the torque of the motor 8. Note that the oscillation prevention control unit 30 may be equipped with a sensor that detects the rotation speed of the motor 8 and a sensor that detects the torque of the motor 8 or a sensor that detects the current of the motor 8 separately. The oscillation prevention control unit 30 sequentially takes in the rotation speed, torque, and voltage command of the motor 8 at a predetermined calculation cycle, and processes the taken-in rotation speed, torque, and voltage command. The oscillation prevention control unit 30 processes the torque of the motor 8, but as described above, the q-axis current iq flowing through the motor 8 can be regarded as torque, so the q-axis current iq of the motor 8 can be treated and processed as torque.

The oscillation prevention control unit 30 performs oscillation prevention control to prevent oscillation of the motor 8 by reducing the rotation speed or torque, or the rotation speed and torque, of the motor 8, on the condition that the operating state of the motor 8 is in a braking state and the current command generated by the current loop 22 is in a saturated state. On the other hand, when the motor 8 is in a powering state or in a braking state but the current command generated by the current loop 22 is not saturated and the conditions for performing oscillation prevention control are not met, even if the motor 8 is in a state where it can be normally controlled, if the flow path area of the first variable throttle valve 6 is large, the pressure difference between the working chamber R1 and the working chamber R2 becomes small, the thrust generated by the hydraulic cylinder 1 becomes small, and the energy consumed by the motor 8 becomes high. Therefore, when the conditions for performing oscillation prevention control are not met, the oscillation prevention control unit 30 basically fixes the throttling coefficient of the first variable throttle valve 6 to a first initial value, which is a minimum value or a very small value, regardless of the operating state of the motor 8, and controls the first variable throttle valve 6 to close or reduce the flow path area, thereby limiting the flow rate of the liquid passing through the first flow path 4 to zero or a very small amount. In addition, since the second variable throttle valve 7 is provided in series with the pump 9 in the second flow path 5 and acts as a resistance to the operation of the pump 9, when the conditions for performing oscillation prevention control are not met, the oscillation prevention control unit 30 sets the throttling coefficient of the second variable throttle valve 7 to the second initial value, which is the maximum value, so that the second variable throttle valve 7 does not obstruct the passage of the liquid discharged by the pump 9.

The oscillation prevention control unit 30 will be described in detail below. The oscillation prevention control unit 30 includes a filter processing unit 31 including a first filter 31a that removes components equal to or higher than the unsprung resonance frequency from the rotation speed of the motor 8 to output a filtered rotation speed, and a second filter 31b that removes components equal to or higher than the unsprung resonance frequency from the torque of the motor 8 to output a filtered torque, a braking state determination unit 32 that determines whether the motor 8 is in a braking state based on the filtered rotation speed and the filtered torque, a saturation determination unit 33 that determines whether the voltage command of the motor 8 is in a saturated state, a target throttle coefficient setting unit 34 that determines the target throttle coefficient of the first variable throttle valve 6 and the target throttle coefficient of the second variable throttle valve 7 based on the determination results of the braking state determination unit 32 and the saturation determination unit 33, and a drive circuit 35 that controls the current supplied to the drive source (not shown) of the first variable throttle valve 6 and the drive source (not shown) of the second variable throttle valve 7 upon receiving a command indicating the target throttle coefficient determined by the target throttle coefficient setting unit 34.

The filter processing unit 31 includes a first filter 31a that removes components of the rotation speed of the motor 8 that are equal to or higher than the unsprung resonance frequency band and outputs a filtered rotation speed, and a second filter 31b that removes components of the torque of the motor 8 that are equal to or higher than the unsprung resonance frequency band and outputs a filtered torque. The filter processing unit 31 processes the rotation speed and torque of the motor 8 that are input sequentially, and outputs signals of the filtered rotation speed and the filtered torque.

When the hydraulic cylinder 1 is used by being interposed between the vehicle body, which is the sprung member of the vehicle, and the wheels, which are the unsprung members, the hydraulic cylinder 1 expands and contracts due to the relative movement between the vehicle body and the wheels, and vibrations of the vehicle body and wheels are input to the hydraulic cylinder 1. The vibrations input to the hydraulic cylinder 1 also change the flow rate of liquid passing through the pump 9 in the second flow path 5, and the rotation speed and torque of the motor 8 also fluctuate. Therefore, high-frequency components in the resonant frequency band of the wheels and high-frequency noise are superimposed on the rotation speed and torque of the motor 8 before processing by the filter processing unit 31.

Therefore, if processing by the filter processing unit 31 is not performed, the operating point of the motor 8 will shift in an oscillatory manner at high frequencies, and hunting may occur in subsequent processing such as determining the operating state of the motor 8. For this reason, in this embodiment, the first filter 31a and the second filter 31b are bandpass filters that can extract the resonant frequency components of the sprung member. Since the resonant frequency band of the sprung member is approximately 1 Hz to 2 Hz, the first filter 31a and the second filter 31b are set to have characteristics that can extract components of 1 Hz to 2 Hz.

In this way, in the cylinder device A of this embodiment, the rotation speed and torque of the motor 8 are processed by the filter processing unit 30 to remove high-frequency components above the unsprung resonance frequency from the rotation speed and torque of the motor 8, so that the braking state of the motor 8 can be accurately grasped according to the vibration of the sprung member in the vehicle, and the throttling coefficient of the first variable throttle valve 6 and the throttling coefficient of the second variable throttle valve 7 can be appropriately controlled by the oscillation prevention control unit 30. Note that the first filter 31a and the second filter 31b in the filter processing unit 31 are filters that extract components in the sprung resonance frequency band, but they may be low-pass filters that can remove at least components above the unsprung resonance frequency band. In this way, even if the first filter 31a and the second filter 31b are low-pass filters that can remove components above the unsprung resonance frequency band, the vibration and noise of the unsprung member can be removed from the rotation speed and torque signals, so that the braking state of the motor 8 can be accurately grasped, and the oscillation prevention control unit 30 can appropriately control the first variable throttle valve 6 and the second variable throttle valve 7. By providing the first filter 31a and the second filter 31b in the filter processing unit 31, the braking state of the motor 8 can be grasped with high accuracy, but it is also possible to omit the first filter 31a and the second filter 31b.

Then, the braking state determination unit 32 determines whether the motor 8 is in a braking state based on the filtered rotation speed and the filtered torque. Specifically, the braking state determination unit 32 determines which quadrant in FIG. 4 the operating point of the motor 8 is in, based on the sign of the filtered rotation speed and the sign of the filtered torque, and determines whether the motor 8 is in a braking state or a powering state. After determining the operating state of the motor 8, the braking state determination unit 32 inputs the determination result to the target throttle coefficient setting unit 34.

In detail, when the filtered rotation speed is positive and the filtered torque is positive, that is, when the filtered rotation speed is ωf and the filtered torque is Tf, ωf ≧ 0 and Tf ≧ 0, the braking state determination unit 32 determines that the operating point of the motor 8 is in the powering region of the first quadrant in FIG. 4, and determines that the operating state of the motor 8 is a powering state in the first quadrant (powering determination).

In addition, when the filtered rotation speed is negative and the filtered torque is positive, that is, when ωf<0 and Tf≧0, the braking state determination unit 32 determines that the operating point of the motor 8 is in the braking region of the second quadrant in FIG. 4, and determines that the operating state of the motor 8 is in a braking state in the second quadrant (braking determination).

Furthermore, if the filtered rotational speed is negative and the filtered torque is negative, ωf<0 and Tf<0, the braking state determination unit 32 determines that the operating point of the motor 8 is in the powering region of the third quadrant in FIG. 4, and determines that the operating state of the motor 8 is in the powering state in the third quadrant (powering determination).

Then, when the filtered rotation speed is positive and the filtered torque is negative, that is, when ωf≧0 and Tf<0, the braking state determination unit 32 determines that the operating point of the motor 8 is in the braking region of the fourth quadrant in FIG. 4, and determines that the operating state of the motor 8 is in a braking state in the fourth quadrant (braking determination).

In this way, the braking state determination unit 32 determines whether the value of ωf is positive or negative and whether the value of Tf is positive or negative, and determines which of the four quadrants the operating point of the motor 8 falls into, and determines whether the operating state of the motor 8 is in a braking state or a powering state.

The saturation determination unit 33 determines whether the voltage command consisting of the q-axis voltage command Vq ^* and the d-axis voltage command Vd ^* obtained by the current loop 22 is saturated or not. Since a voltage exceeding the voltage of the power supply (not shown) that supplies power to the motor 8 cannot be applied to the windings of the motor 8, it is sufficient to determine whether the voltage command is saturated or not by comparing the voltage command with a saturation voltage based on the power supply voltage. If the saturation determination is performed using a three-phase voltage command input to the drive circuit 35, the saturation determination becomes troublesome. However, in the cylinder device A of this embodiment, the magnitude of the voltage command consisting of the q-axis voltage command Vq ^* and the d-axis voltage command Vd ^* can be grasped by the composite vector length of the q-axis voltage command Vq ^* and the d-axis voltage command Vd ^* , and since the q-axis and the d-axis are mutually orthogonal, the value of the composite vector length is also easy to calculate, and it is possible to immediately determine whether the voltage command is saturated or not by comparing the q-axis voltage command Vq ^* and the d-axis voltage command Vd ^* with the composite vector length and the saturation voltage.

Therefore, it is only necessary to compare the length of the resultant vector of the q-axis voltage command Vq ^* and the d-axis voltage command Vd ^* with the saturation voltage Vs to determine whether the voltage command is saturated or not.

Therefore, specifically, the saturation judgment unit 33 compares the squared value of the composite vector length of the q-axis voltage command Vq ^* and the d-axis voltage command Vd ^* obtained by the current loop 22 (Vq ^*2 + Vd ^*2 ) with the squared value of the saturation voltage Vs, and judges that the voltage command for the motor 8 is saturated (saturation judgment) if the squared value of the composite vector length exceeds the squared value of the saturation voltage Vs, and judges that the voltage command for the motor 8 is not saturated (non-saturation judgment) if the squared value of the composite vector length is equal to or less than the squared value of the saturation voltage Vs.

That is, saturation determination unit 33 determines that the voltage command is saturated if (Vq ^*2 + Vd ^*2 ) > ^Vs2 , and determines that the voltage command is not saturated if (Vq ^*2 + Vd ^*2 ) ≦ ^Vs2 . Note that the saturation voltage Vs, which is the basis for the above determination, may be a value obtained by multiplying the power supply voltage by 1/√2 when control is performed such that the inter-terminal voltages of the U-, V-, and W-phase windings can be increased to the voltage of a power supply not shown in the figure, or may be a value obtained by multiplying the power supply voltage by √6/4 when control is performed to apply a sinusoidal voltage to the U-, V-, and W-phase windings.

In this way, the square value of the resultant vector length of the q-axis voltage command Vq ^* and the d-axis voltage command Vd ^* , i.e., the sum (Vq ^*2 + Vd ^{*2) of the square value of the q-axis voltage command Vq* and the square value of the d-axis voltage command Vd* is compared with the square value of the saturation voltage Vs to determine whether the resultant vector length (Vq*2 + Vd*2 ) 1/2 of the q} -axis voltage command Vq ^* and the d-axis voltage command Vd ^* exceeds the saturation voltage Vs. This eliminates the need for root calculations for the calculation required for this determination, which contributes to shortening the calculation time. The saturation determination unit 33 then inputs the determination result to the target throttle coefficient setting unit 34.

When the braking state determination unit 31 determines that the operating state of the motor 8 is in a braking state and the saturation determination unit 33 determines that the voltage command of the motor 8 is saturated, the target throttle coefficient setting unit 34 reduces the rotation speed of the motor 8 to reduce the electrical resonance frequency and at the same time changes the mechanical resonance frequency of the cylinder device A, or reduces one or both of the rotation speed and torque of the motor 8 to return the motor 8 to a controllable state, thereby preventing oscillation of the cylinder device A. When the target throttle coefficient setting unit 34 determines that the motor 8 is in a powered state or non-saturated state, there is no risk of the thrust of the cylinder device A oscillating, so it does not perform oscillation prevention control, and controls the target throttle coefficient of the first variable throttle valve 6 to a first initial value and the flow area of the first variable throttle valve 6 to be minimum or extremely small, and controls the target throttle coefficient of the second variable throttle valve 7 to be maximum and the flow area of the second variable throttle valve 7 to be maximum. On the other hand, in the case of braking judgment and saturation judgment, the target throttle coefficient setting unit 34 cannot control the rotation speed and torque of the motor 8, and when the rotation speed of the motor 8 becomes high and the electrical resonance frequency approaches the mechanical resonance frequency, the motor 8 may oscillate. Therefore, the target throttle coefficient setting unit 34 performs oscillation prevention control to prevent oscillation. When preventing oscillation, the target throttle coefficient setting unit 34 increases the flow path area of the first variable throttle valve 6 to reduce the rotation speed of the motor 8, or reduces the flow path area of the second variable throttle valve 7 to reduce the load torque of the motor 8, or performs both. When the target throttle coefficient setting unit 34 performs oscillation prevention control to reduce the rotation speed of the motor 8, the electrical resonance frequency of the motor 8 decreases and moves away from the mechanical resonance frequency of the motor 8, which exists on the higher frequency side, and at the same time, the rotation speed of the motor 8 is reduced to reduce the electrical resonance frequency, thereby preventing the motor 8 and the cylinder device A from exciting each other's vibrations and oscillating, and a stable thrust can be generated. In addition, when the target throttle coefficient setting unit 34 performs oscillation prevention control to reduce the torque of the motor 8, the motor 8 can be controlled normally by placing the operating point of the motor 8 within the region Y where the motor 8 can be controlled, preventing the motor 8 and the cylinder device A from exciting each other's vibrations and oscillating, and generating a stable thrust in the cylinder device A. In addition, since the damping ratio of the cylinder device A can be changed by combining the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 from the transfer function from the current input of the motor 8 to the thrust of the cylinder device A, the damping ratio of the cylinder device A can be changed to prevent the motor 8 and the cylinder device A from exciting each other's vibrations and oscillating.

When controlling the throttle coefficient of the first variable throttle valve 6, when the judgment result of the braking state judgment unit 31 is a braking judgment and the judgment result of the saturation judgment unit 33 is a saturation judgment, the target throttle coefficient setting unit 34 sets the throttle coefficient of the first variable throttle valve 6 from the first initial value to a first predetermined value that can sufficiently reduce the rotation speed of the motor 8. Before the braking judgment and saturation judgment are made, the target throttle coefficient setting unit 34 changes the target throttle coefficient of the first variable throttle valve 6 from the first initial value to the first predetermined value when the braking judgment and saturation judgment are made. Also, after the braking judgment and saturation judgment are made and the target throttle coefficient of the first variable throttle valve 6 is set to the first predetermined value, when the judgment result becomes a powering judgment or a non-saturation judgment, the target throttle coefficient setting unit 34 changes the target throttle coefficient of the first variable throttle valve 6 from the first initial value to the first predetermined value. In addition, when the difference between the first initial value and the first predetermined value is large, when the target throttle coefficient of the first variable throttle valve 6 is changed from the first initial value to the first predetermined value or from the first predetermined value to the first initial value, the target throttle coefficient may suddenly change and the rotation speed of the motor 8 may suddenly change. Therefore, in the cylinder device A of this embodiment, a first mitigation processing unit 36 is provided after the target throttle coefficient setting unit 34 to process the target throttle coefficient of the first variable throttle valve 6 through a low-pass filter to mitigate the sudden change in the target throttle coefficient of the first variable throttle valve 6, thereby mitigating the sudden change in the rotation speed of the motor 8.

In addition, when controlling the throttling coefficient of the second variable throttle valve 6, the target throttling coefficient setting unit 34 sets the throttling coefficient of the second variable throttle valve 7 from the maximum to a second predetermined value that can sufficiently reduce the torque of the motor 8 as the target throttling coefficient of the second variable throttle valve 7 when the braking state determination unit 31 determines that the torque is being applied and the saturation determination unit 33 determines that the torque is being applied. Before the braking determination and saturation determination are reached, the target throttling coefficient setting unit 34 sets the target throttling coefficient of the second variable throttle valve 7 to the second initial value, so when the braking determination and saturation determination are reached, the target throttling coefficient setting unit 34 changes the target throttling coefficient of the second variable throttle valve 7 from the second initial value to the second predetermined value. In addition, after the braking determination and saturation determination are reached and the target throttling coefficient of the second variable throttle valve 7 is set to the second predetermined value, when the determination result becomes a powering determination or a non-saturation determination, the target throttling coefficient setting unit 34 changes the target throttling coefficient of the second variable throttle valve 7 from the second initial value to the second predetermined value. In addition, when the difference between the second initial value and the second predetermined value is large, when the target throttle coefficient of the second variable throttle valve 7 is changed from the second initial value to the second predetermined value or from the second predetermined value to the second initial value, the target throttle coefficient may suddenly change, causing a sudden change in the rotation speed of the motor 8. Therefore, in the cylinder device A of this embodiment, a second mitigation processing unit 37 is provided after the target throttle coefficient setting unit 34 to process the target throttle coefficient of the second variable throttle valve 7 through a low-pass filter to mitigate the sudden change in the target throttle coefficient of the second variable throttle valve 7, thereby mitigating the sudden change in the torque of the motor 8.

In addition, when a braking judgment and a saturation judgment are made, the target throttle coefficient setting unit 34 may increase the target throttle coefficient of the first variable throttle valve 6 and decrease the target throttle coefficient of the second variable throttle valve 7 to reduce both the rotational speed and torque of the motor 8, thereby moving the electrical resonance frequency of the motor 8 away from the mechanical resonance frequency and moving the operating point of the motor 8 into the controllable region Y to prevent oscillation of the motor 8.

When both the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 are changed, the target throttle coefficient setting unit 34 may set the target throttle coefficient of the first variable throttle valve 6 to a first target value greater than a predetermined first initial value, and may set the target throttle coefficient of the second variable throttle valve 7 to a second target value less than a predetermined second initial value, or may map combinations of the throttle coefficients of the first variable throttle valve 6 and the second variable throttle valve 7 that are optimal according to the rotation speed and torque values of the motor 8 when braking and saturation are determined, and use the map to determine the target throttle coefficients of the first variable throttle valve 6 and the second variable throttle valve 7 from the rotation speed and torque of the motor 8.

On the other hand, as described above, when the braking state determination unit 31 determines that the vehicle is in a powered state, or when the saturation determination unit 33 determines that the vehicle is not in a saturated state, the target throttle coefficient setting unit 34 sets the target throttle coefficient of the first variable throttle valve 6 to a first initial value to reduce the energy consumption of the motor 8, and sets the target throttle coefficient of the second variable throttle valve 7 to a second initial value to maximize the flow area of the second variable throttle valve 7 so as not to interfere with the operation of the pump 9.

In this way, the target throttle coefficient determined by the target throttle coefficient setting unit 34 is input to the drive circuit 35. The drive circuit 35 adjusts the throttle coefficient of the second variable throttle valve 7 by applying current to the drive source (not shown) of the first variable throttle valve 6 and the drive source (not shown) of the second variable throttle valve 7 so that the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 match the target throttle coefficient.

When controlling both the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7, the controller 11 controls the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7 according to the flowchart shown in FIG. 6. First, the controller 11 detects the rotation speed and torque of the motor 8 (step F1). Next, the controller 11 filters the rotation speed and torque of the motor 8 to obtain the filtered rotation speed and filtered torque (step F2).

Furthermore, the controller 11 judges whether the operating state of the motor 8 is a braking state from the filtered rotation speed and the filtered torque (step F3). Next, if the operating state of the motor 8 is a braking state, the controller 11 judges whether the voltage command required by the thrust control unit 20 that controls the motor 8 is saturated (step F4). Then, in the judgments of steps F3 and F4, if the operating state of the motor 8 is a braking judgment and the voltage command is a saturation judgment, the controller 11 sets the first predetermined value and the second predetermined value that reduce the rotation speed and torque of the motor 8 to the target throttling coefficient of the first variable throttle valve 6 and the target throttling coefficient of the second variable throttle valve 7, respectively, since the motor 8 is uncontrollable and there is a risk of the motor 8 oscillating (step F5). If the motor 8 is determined to be in a powered state in steps F3 and F4, or if the voltage command is determined to be non-saturated, the controller 11 sets the first initial value and the second initial value to the target throttle coefficient of the first variable throttle valve 6 and the target throttle coefficient of the second variable throttle valve 7, respectively, since there is no risk of the motor 8 oscillating in a controllable state (step F6). After setting the target throttle coefficients, the controller 11 performs low-pass filter processing on the target throttle coefficients of the first variable throttle valve 6 and the second variable throttle valve 7 in order to mitigate a sudden change in the target throttle coefficients (step F7). After low-pass filter processing on each target throttle coefficient, the controller 11 supplies current from the drive circuit 35 to the drive source of the first variable throttle valve 6 and the drive source of the second variable throttle valve 7, and controls the throttle coefficients of the first variable throttle valve 6 and the second variable throttle valve 7 to the corresponding target throttle coefficients (step F8).

The controller 11 repeatedly executes the above process to control the throttle coefficient of the first variable throttle valve 6 and the throttle coefficient of the second variable throttle valve 7.

In addition, except for the drive circuit 23 in the thrust control unit 20, the pressure sensors 25a, 25b in the actual thrust detection unit 25, and the drive circuit 35 in the oscillation prevention 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 storage space for the CPU. Each part of the thrust control unit 20 and the oscillation prevention 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 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 type pump 9 driven by a motor 8, and a controller 11 that controls the first variable throttle valve 6, the second variable throttle valve 7, and the motor 8. When the controller 11 determines that the motor 8 is in a braking state and the voltage command for the motor 8 is saturated, it either reduces the rotational speed of the motor 8 to reduce the electrical resonance frequency and simultaneously changes the mechanical resonance frequency of the cylinder device A, or controls one or both of the throttling coefficient of the first variable throttle valve 6 and the throttling coefficient of the second variable throttle valve 7 to reduce one or both of the rotational speed and torque of the motor 8.

According to the cylinder device A configured in this manner, by determining that the motor 8 is in a braking state and that the voltage command of the motor 8 is saturated, it is possible to grasp that the motor 8 may oscillate, and by lowering the rotation speed of the motor 8 to lower the electrical resonance frequency and at the same time changing the mechanical resonance frequency of the cylinder device A, or by lowering one or both of the rotation speed and torque of the motor 8 to return the motor 8 to a controllable state, it is possible to prevent the motor 8 and the cylinder device A from exciting each other's vibrations and oscillating. In this way, according to the cylinder device A of this embodiment, it is possible to prevent the motor 8 and the cylinder device A from exciting each other's vibrations and oscillating, and a stable thrust can be generated.

The controller 11 in the cylinder device A of this embodiment also includes a braking state determination unit 32 that determines whether the motor 8 is in a braking state based on the rotational speed and torque of the motor 8, and a saturation determination unit 33 that determines saturation of the voltage command of the motor 8 based on the composite vector length of the q-axis voltage command and the d-axis voltage command of the motor 8.

With the cylinder device A configured in this way, it is possible to accurately determine whether the operating point of the motor 8 is in the second or fourth quadrant in the braking state in the rotational speed torque coordinate system based on the rotational speed and torque of the motor 8. In addition, since the saturation of the voltage command of the motor 8 is determined based on the composite vector length of the q-axis voltage command and the d-axis voltage command, it is easy to determine whether the voltage command of the motor 8 is saturated, and the conditions for executing oscillation prevention control can be accurately and easily determined.

Furthermore, in the cylinder device A of this embodiment, the controller 11 is provided with a first mitigation processing unit 36 and a second mitigation processing unit 37 that mitigate a sudden change between the target throttling coefficient of the first variable throttle valve 6 and the target throttling coefficient of the second variable throttle valve 7. According to the cylinder device A configured in this manner, even if the target throttling coefficient of the first variable throttle valve 6 and the target throttling coefficient of the second variable throttle valve 7 are changed by the oscillation prevention control unit 30, the sudden change of each target throttling coefficient is mitigated, so that the thrust fluctuation of the cylinder device A can be suppressed. Note that the first mitigation processing unit 36 and the second mitigation processing unit 37 process the corresponding target throttling coefficient with a low-pass filter to mitigate a sudden change in the target throttling coefficient, but instead of low-pass filter processing, a process may be performed to gradually change the target throttling coefficient from the value before the change to the value after the change in a stepwise or continuous manner over time.

In addition, in the cylinder device A of this embodiment, the controller 11 is equipped with a first filter 31a that removes components equal to or higher than the unsprung resonance frequency of the vehicle from the rotation speed of the motor 8, a second filter 31b that removes components equal to or higher than the unsprung resonance frequency of the vehicle from the torque of the motor 8, and a braking state determination unit 32 that determines whether the motor 8 is in a braking state based on the filtered rotation speed and filtered torque. According to the cylinder device A configured in this manner, high-frequency components equal to or higher than the unsprung resonance frequency are removed from the rotation speed and torque of the motor 8, so that the braking state of the motor 8 can be accurately grasped according to the vibration of the sprung member in the vehicle, and the throttling coefficient of the first variable throttle valve 6 and the throttling coefficient of the second variable throttle valve 6 can be appropriately controlled.

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, 32: braking state determination unit, 33: saturation determination unit, A: cylinder device, R1, R2: working chamber

Claims (2)

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 to communicate the working chambers, 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, when determining that the motor is in a braking state and that a voltage command for the motor is saturated, reduces the rotational speed of the motor to reduce an electrical resonance frequency and at the same time changes a mechanical resonance frequency of the cylinder device, or controls one or both of the throttling coefficient of the first variable throttle valve and the throttling coefficient of the second variable throttle valve so as to reduce one or both of the rotational speed and torque of the motor. The controller:
a braking state determination unit that determines whether the motor is in a braking state based on a rotation speed and a torque of the motor;
2. The cylinder device according to claim 1, further comprising a saturation determination unit that determines saturation of the voltage command of the motor based on a composite vector length of a q-axis voltage command and a d-axis voltage command of the motor.

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