Electric hydraulic actuators and brake devices

Abstract

To provide an electrically-driven hydraulic actuator capable of securely discharging working fluid in the hydraulic actuator without using a solenoid valve.SOLUTION: An electrically-driven hydraulic actuator includes: a pump 7 using power of a motor 3; a hydraulic actuator 5 reciprocating between a first state and a second state while energized to become the first state; a reservoir 4; and a fluid circuit for controlling the hydraulic actuator by using a hydraulic pressure. The fluid circuit includes: a pressurization flow passage 201 for supplying fluid from the pump to the hydraulic actuator; a discharge flow passage 300 for discharging the fluid from the hydraulic actuator through an unloading valve 61 to the reservoir; a pilot flow passage 301 branched in the middle of the pressurization flow passage and supplying the fluid pressurized to a pilot pressure to the unloading valve; a mechanism 27 that generates the pilot pressure during an operation of the pump; and a check valve 26 for causing the fluid to pass from the pump only to a direction of a hydraulic cylinder. When the pump is operated, a transition to the second state is made, and when the pump is stopped, the state returns to the first state.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an electrohydraulic actuator and a brake device. [Background technology]

[0002] An electrohydraulic actuator comprises a pump (impeller pump, gear pump, etc.) operated by a motor, a hydraulic actuator operated by working fluid (hydraulic oil, etc.) pressurized by the pump, and a fluid circuit. The fluid circuit comprises a flow path for the working fluid that interconnects the pump, reservoir, and hydraulic actuator, and a valve mechanism interposed in the flow path for supplying the working fluid accumulated in the reservoir to the hydraulic actuator to operate the hydraulic actuator, and for discharging the working fluid from the hydraulic actuator in an operating state toward the reservoir.

[0003] A well-known example of an electrohydraulic actuator is an electrohydraulic cylinder, which uses a hydraulic cylinder as a hydraulic actuator. The fluid circuit (hydraulic circuit) of an electrohydraulic cylinder controls a pump powered by a motor and a valve mechanism installed in an appropriate location in the hydraulic circuit. This creates a flow path for hydraulic oil (the working fluid) through, for example, a reservoir, a pump, and a hydraulic cylinder. This fills the cylinder tube of the hydraulic cylinder with hydraulic oil, pushing the piston up. The tip of the piston rod is connected to some other mechanism to be operated, and the operation of the other mechanism is linked to the operation of the electrohydraulic cylinder. The piston is constantly biased downward by the restoring force of the other mechanism and a mechanism such as a spring (hereinafter referred to as the "biasing mechanism") included in the electrohydraulic cylinder. When the hydraulic circuit stops the supply of hydraulic oil to the cylinder tube and a flow path connecting the cylinder tube to the reservoir is formed, the biasing mechanism pushes the piston down.

[0004] Electric hydraulic cylinders are used, for example, in electric lifting machine brakes. When the electric hydraulic cylinder is energized and the piston rod is pushed up, a braking mechanism such as a drum brake or disc brake operates to release the brake pads. The braking mechanism is constantly biased by a spring or the like in the direction of returning to the braking state. When the power to the electric hydraulic cylinder is turned off, the hydraulic oil inside the hydraulic cylinder is discharged, and the biasing force of the braking mechanism presses the brake pads against the brake drum or brake disc. This places the brake device in a braking state. The hydraulic circuit of the electric hydraulic cylinder used in the electric lifting machine brake includes a solenoid valve and its control circuit. By controlling the opening and closing of the solenoid valve located at an appropriate position in the flow path, a flow path is formed for filling the hydraulic cylinder with hydraulic oil and returning the filled hydraulic oil to the reservoir.

[0005] Incidentally, electric hydraulic cylinders used in electric hydraulic booster brakes are disclosed as "electrohydraulic brake release devices" in, for example, the following Patent Documents 1 and 2. Also, the following Patent Document 3 discloses an "electric hydraulic actuator" and a "disc brake device" equipped with the electric hydraulic actuator. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 6322699 [Patent Document 2] Patent No. 6353036 [Patent Document 3] Patent No. 7262870 Summary of the Invention [Problem to be solved by the invention]

[0007] Generally, the hydraulic circuit of an electrohydraulic actuator has solenoid valves located at appropriate positions in the hydraulic fluid flow path. By controlling the opening and closing of appropriate solenoid valves, the hydraulic circuit can quickly switch between a flow path that directs hydraulic fluid pressurized by a pump to the hydraulic actuator and a flow path that forcibly discharges the hydraulic fluid from the hydraulic actuator and returns it to the reservoir. In this way, solenoid valves can operate the hydraulic circuit quickly and with high precision.

[0008] However, because solenoid valves require electricity, the hydraulic circuit cannot function properly if the power supply is interrupted. Furthermore, solenoid valves may malfunction due to ambient electrical noise. Therefore, when using an electrohydraulic actuator in an electric lifting device brake, the fluid circuit must be equipped with some kind of safety mechanism that reliably discharges the hydraulic fluid inside the actuator even in the event of a power outage or a malfunctioning solenoid valve. Daily maintenance and inspections are also required to ensure the safety mechanism operates reliably in an emergency. Therefore, electrohydraulic actuators tend to increase installation and maintenance costs due to the fluid circuit equipped with a solenoid valve.

[0009] Furthermore, power consumption increases when a solenoid valve is energized for a long period of time or when it is operated repeatedly at a high frequency. Higher power consumption also increases running costs. Furthermore, unlike motors, solenoid valves in electro-hydraulic actuators are in direct contact with the working fluid. Therefore, heat generated by increased power consumption can reduce the viscosity of the working fluid, potentially making it impossible to obtain the hydraulic pressure required to operate the hydraulic actuator. If a cooling mechanism or other device is provided in an electro-hydraulic actuator to combat heat generation, it becomes difficult to miniaturize the electro-hydraulic actuator and to provide it at a lower cost.

[0010] Therefore, the present invention has been made to solve the above-mentioned problems, and aims to provide an electro-hydraulic actuator equipped with a fluid circuit that can reliably discharge the working fluid inside the actuator without using a solenoid valve, and a brake device equipped with such an electro-hydraulic actuator. [Means for solving the problem]

[0011] To achieve the above object, the present invention provides: a motor that outputs rotational power; a pump operated by the rotational power of the motor; a hydraulic actuator operated by the hydraulic fluid pressurized by the pump; a reservoir for storing the working fluid; a fluid circuit for hydraulically controlling the operation of the hydraulic actuator; Equipped with the hydraulic actuator reciprocates between a first operating state and a second operating state in response to the hydraulic pressure of the supplied hydraulic fluid, and is constantly biased in a direction returning to the first operating state; The fluid circuit includes: a pressurizing flow path for supplying the hydraulic fluid pressurized by the pump to a hydraulic actuator; a pressure reducing flow path that connects the hydraulic actuator and the reservoir via an unloading valve in an openable and closable manner; a pilot flow path for supplying hydraulic oil pressurized to a pilot pressure to the unloading valve in order to close the pressure reduction flow path; a pilot pressure generating mechanism that generates the pilot pressure; a check valve interposed in the pressurizing flow path for allowing the working fluid to pass only in a forward direction from the pump toward the hydraulic actuator; Including, the pilot pressure generating mechanism generates the pilot pressure while the pump is operating; the pilot flow path branches off midway from the pump to the check valve in the pressurizing flow path and reaches the unloading valve, The pilot pressure is generated during operation of the pump, causing the pump to transition to the second operating state, and when the pump stops, the pilot pressure disappears, the pressure reduction flow path is opened, and the pump returns to the first operating state. It is an electrohydraulic actuator.

[0012] The electric hydraulic actuator may be configured such that a throttle mechanism constituting the pilot pressure generating mechanism and the check valve are disposed in this order along the pressurizing flow path from the pump to the hydraulic actuator. The throttle mechanism may be an orifice.

[0013] The check valve also serves as the pilot pressure generating mechanism, the check valve delivers the working fluid toward the hydraulic actuator when the working fluid supplied from the pump has a predetermined pilot pressure or higher. It may also be an electrohydraulic actuator.

[0014] The pilot pressure generating mechanism is composed of an unloading relief valve consisting of a parent valve and a child valve, and a throttle mechanism, the master valve has a throttle valve built in, a master valve primary port connected to the pilot flow path, a master valve secondary port connected to a flow path communicating with the reservoir, and a master valve pilot port communicating with the master valve primary port via the throttle valve, and also has a master valve spool that is urged upward by hydraulic pressure in the master valve primary port, and a master valve spring that urges the master valve spool downward, with a predetermined direction being the up-down direction; the child valve has a child valve primary port connected to the parent valve pilot port, a child valve secondary port connected to a flow path communicating with the reservoir via the throttle mechanism, and a child valve pilot port connected to a flow path from the check valve to the hydraulic actuator, and has, with a predetermined direction being a vertical direction, a valve element urged upward by hydraulic pressure in the child valve primary port, a child valve spool urged upward by hydraulic pressure in the child valve pilot port, and a child valve spring urges the valve element downward, The child valve distributes the hydraulic pressure P1 at the child valve primary port into hydraulic pressure P2 that presses the valve element upward and hydraulic pressure P3 that presses the child valve spool downward, with P2 > P3, and when the hydraulic pressure P1 reaches a predetermined cutout pressure, the valve element is pressed in one direction, opening the child valve primary port and the child valve secondary port to an unloaded state, The master valve spool is pressed upward by a pressure difference between the hydraulic pressure P1 on the master valve pilot port side, which is reduced as the slave valve enters the unloaded state, and the hydraulic pressure P5 on the master valve primary port side, thereby opening communication between the master valve primary port and the master valve secondary port, and the master valve enters an unloaded state. When the sub-valve is in an unloaded state, the unloaded state is maintained by the hydraulic pressure P4 at the sub-valve pilot port, When both the parent valve and the child valve are in the unloaded state, the hydraulic pressure P5 is maintained at the pilot pressure by the hydraulic pressure P1 generated by the passage resistance of the throttle mechanism and the hydraulic pressure generated by the parent valve spring urging the parent valve spool downward, and the hydraulic actuator is maintained in the second operating state by the hydraulic pressure P4. It may also be an electrohydraulic actuator.

[0015] The unloading relief valve may be an electrohydraulic actuator in which the master valve and the slave valve are attached to a metal block having a flow path for the working fluid, and the master valve and the slave valve are cartridges that are detachably attached to the metal block. The throttle mechanism may be interposed in the flow path formed in the metal block, and the unit may constitute the pilot pressure generating mechanism.

[0016] the fluid circuit includes a flow path that branches off from the pilot flow path, passes through a throttle mechanism, and reaches the reservoir; the throttle mechanism has a flow path resistance higher than the flow path resistance of the pilot pressure generating mechanism when the pump is operating, and eliminates residual pressure of the working fluid remaining in the flow path from the pump to the pilot pressure generating mechanism in the pressurizing flow path and in the pilot flow path when the pump is stopped. It may also be an electrohydraulic actuator.

[0017] In any of the electro-hydraulic actuators described above, the hydraulic actuator may be a direct-acting hydraulic actuator. The electro-hydraulic actuator may be configured such that the first operating state is reached when the piston of the direct-acting hydraulic actuator is at bottom dead center, and the second operating state is reached when the piston is at top dead center, and the piston is biased toward bottom dead center by an external mechanism connected to the tip of a piston rod. The electro-hydraulic actuator may also be configured such that the first operating state is reached when the piston of the direct-acting hydraulic actuator is at bottom dead center, and the second operating state is reached when the piston is at top dead center, and the electro-hydraulic actuator includes a spring mechanism that constantly biases the piston toward bottom dead center.

[0018] The scope of the present invention also includes a brake device equipped with an electric hydraulic actuator in which the hydraulic actuator is a direct-acting hydraulic actuator, and the brake device is equipped with a braking mechanism that presses or separates brake linings against both sides of a circular brake disc, the braking mechanism being constantly biased in the direction of a braking state, and when the electric hydraulic actuator is in the second operating state, the braking state of the brake disc is released, and when the electric hydraulic actuator is in the first operating state, the brake disc is in a braking state.

[0019] A brake device equipped with an electric hydraulic actuator in which the hydraulic actuator is a direct-acting hydraulic actuator can also be a brake device that includes a braking mechanism that presses or separates brake linings against both sides of a circular brake disc, and in which the braking mechanism releases the braking state of the brake disc when in the second operating state, and the brake disc is in a braking state when in the first operating state. [Effects of the Invention]

[0020] According to the present invention, there are provided an electro-hydraulic actuator having a fluid circuit that can reliably discharge the working fluid inside the actuator without using a solenoid valve, and a brake device having the electro-hydraulic actuator. Other advantages will become apparent from the following description. [Brief explanation of the drawings]

[0021] [Figure 1A] 1 is a diagram showing the appearance of an electrohydraulic actuator according to an embodiment; [Figure 1B] FIG. 2 is a diagram showing the internal configuration of a housing of the electrohydraulic actuator according to the embodiment. [Figure 2] 1B is a cross-sectional view taken along the line aa in FIG. 1A, showing the internal structure of the electrohydraulic actuator according to the embodiment. FIG. [Figure 3A] 1 is a diagram showing the appearance of a pump constituting an electrohydraulic actuator according to an embodiment. FIG. [Figure 3B] 1 is a diagram showing the internal structure of a pump that constitutes an electrohydraulic actuator according to an embodiment. FIG. [Figure 4] FIG. 1 is a diagram showing a hydraulic circuit of an electrohydraulic actuator according to an embodiment. [Figure 5A] 1 is a diagram showing a schematic structure of an unloading valve that constitutes the hydraulic circuit, showing a state in which the internal flow path of the unloading valve is open. FIG. [Figure 5B] 1 is a diagram showing a schematic structure of an unloading valve that constitutes the hydraulic circuit, showing a state in which an internal flow path of the unloading valve is closed. FIG. [Figure 6] FIG. 10 is a diagram showing a first modified example of a hydraulic circuit of an electrohydraulic actuator according to an embodiment. [Figure 7] FIG. 10 is a diagram showing a second modified example of the hydraulic circuit of the electrohydraulic actuator according to the embodiment. [Figure 8] 10A and 10B are diagrams for explaining the operation of a master valve of an unloading relief valve that constitutes a hydraulic circuit in a second modified example. [Figure 9] 10A and 10B are diagrams for explaining the operation of a sub-valve of an unloading relief valve that constitutes a hydraulic circuit in a second modified example. [Figure 10] 10 is a timing chart for explaining the operation of the hydraulic circuit in the second modified example. [Figure 11] FIG. 10 is a diagram showing the unloading relief valve unit in a second modified example, in which the parent valve and the child valve, which are configured as cartridges, are attached to a metal block. [Figure 12] 10A and 10B are diagrams illustrating other examples of the unloading relief valve. [Figure 13] FIG. 1 is a diagram showing a schematic structure of a hydraulic cylinder with a built-in spring that can be used in an electrohydraulic actuator according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] The following description will discuss embodiments of the present invention with reference to the accompanying drawings. In the drawings used in the following description, the same or similar parts are designated by the same reference numerals, and redundant explanations may be omitted. In some drawings, unnecessary reference numerals may be omitted.

[0023] ===Example=== <Electrohydraulic Actuator> One embodiment of the present invention is an electrohydraulic cylinder that uses a hydraulic cylinder, which is a direct-acting hydraulic actuator, as the hydraulic actuator. FIG. 1A is a diagram showing the appearance of an electrohydraulic actuator (hereinafter, sometimes referred to as a "thruster 1") according to a first embodiment, and FIG. 1B is a diagram showing the internal configuration of the housing of the thruster 1. As shown in FIG. 1A, the thruster 1 has a rectangular cylindrical exterior shape, and a clevis 11 is attached to one end face for securing the thruster 1 to other equipment. The tip side of a piston rod 52 of an internal hydraulic cylinder protrudes from the other end so as to be capable of reciprocating in the axial direction. A head 12 is attached to the tip of the piston rod 52 and is connected to a mechanism (hereinafter, sometimes referred to as an "external mechanism") that links the operation of the thruster 1. A hole 19 is formed in the head 12 for attaching the external mechanism.

[0024] If the direction of reciprocating motion of piston rod 52 is defined as the up-down direction, and the up-down direction of thruster 1 is defined as piston rod 52 protruding above thruster 1, thruster 1 has an overall structure in which an upper structure and a lower structure are connected via flattened rectangular cylindrical metal block 2 whose thickness direction is the up-down direction. The upper structure of thruster 1 is a housing (hereinafter sometimes referred to as the "upper housing") that is made up of the metal block (hereinafter sometimes referred to as the "connection block 2"), a hollow rectangular cylindrical cover (hereinafter sometimes referred to as the "upper cover 13"), and a metal plate (hereinafter sometimes referred to as the "upper cover plate 15") with an insertion hole 14 for piston rod 52, and the components and mechanisms that make up thruster 1 are housed within the housing. The lower structure comprises a housing (hereinafter sometimes referred to as the "lower housing") consisting of a connection block 2, a hollow rectangular cylindrical cover (hereinafter sometimes referred to as the "lower cover 16"), and a metal plate (hereinafter sometimes referred to as the "base plate 17") to which a clevis 11 is attached, and the components and mechanisms that make up the thruster 1 are also housed within this lower housing.

[0025] 1B, a motor 3 is installed in the lower housing of the thruster 1. The connection block 2 and the base plate 17 are connected via mounting bolts 18, and when the mounting bolts 18 are fastened, the lower cover is sandwiched between the connection block 2 and the base plate 17 to form the lower housing. The upper housing is formed when the mounting bolts 18 connecting the connection block 2 and the top cover plate 15 are fastened, and the upper cover is sandwiched between the connection block 2 and the base plate 17.

[0026] The space within the upper housing is largely occupied by a reservoir 4 filled with hydraulic oil. The reservoir 4 is a closed space formed by the upper surface of the connection block 2, a hollow cylindrical reservoir case 41 coaxially inscribed in the hollow rectangular cylindrical upper cover 13, and the lower surface of the upper cover plate 15. In the thruster 1 according to the embodiment, the reservoir 4 contains a cylindrical metal block (hereinafter sometimes referred to as the "manifold block 6") in which a hydraulic oil flow path is formed, a hydraulic cylinder 5, various valves (61, 62) arranged at appropriate locations in the hydraulic circuit, and the like. In addition, the lower end of a cylinder tube 51, which serves as the housing for the hydraulic cylinder 5, and the various valves (61, 62) are attached to the upper surface of the manifold block 6. Furthermore, a pump is installed in the space formed inside the manifold block 6.

[0027] The internal structure of the thruster 1 is shown in Figure 2. Figure 2 is a cross-sectional view taken along the line aa in Figure 1A. In Figure 2, part of the thruster 1 is shown hatched to make it easier to understand the internal structure of the thruster 1. The configuration and structure of the thruster 1 will be described below with reference to Figure 2.

[0028] A motor 3 is disposed within the lower housing, covered by a hollow cylindrical motor case 32. A motor shaft 31 has a rotation axis extending in the vertical direction and protrudes upward from the motor case 32. The lower end of the motor shaft 31 is supported by a bearing 33 using a ball bearing provided on the base plate 17.

[0029] A hole (hereinafter sometimes referred to as "communication hole 21") that connects the upper and lower surfaces of the connection block 2 is formed, and the upper end of the motor shaft 31 is inserted into this communication hole 21. Inside the connection block 2, a bearing 22 for the motor shaft 31 using a ball bearing is incorporated, and part of the flow path included in the hydraulic circuit is also formed.

[0030] In this embodiment, the pump 7 is an external gear pump, and the end of the motor shaft 31 is connected to the end of the pump drive shaft 71 within the connection block 2 via a connecting member 23. In this way, the connection block 2 functions to interconnect the structures above and below it. Note that the flow paths within the connection block 2 and manifold block 6 are formed by drilling holes (hereinafter sometimes referred to as "machined holes") from the outside of a solid metal block and sealing the openings of the machined holes with plugs, as shown in the dotted elliptical area 100 in Figure 2.

[0031] The upper and lower ends of a hollow cylindrical reservoir case 41 housed in the upper housing are sealed with O-rings or the like while abutting against the upper surface of the connection block 2 and the lower surface of the upper cover plate 15. This forms a reservoir 4 consisting of an enclosed space.

[0032] A cylindrical manifold block 6 disposed within the reservoir 4 is attached to the connection block 2, and has hydraulic fluid flow paths and a storage space 66 for the pump 7 formed therein. A circular recess 63 is formed in the upper surface of the manifold block 6, into which the lower end of a single-barrel hydraulic cylinder 5 is inserted. An opening (hereinafter sometimes referred to as "recess opening 64") that connects to the internal flow path is formed at the bottom of this recess 63, and a port 54 is provided at the lower end of the cylinder tube 51 of the hydraulic cylinder 5, through which hydraulic fluid flows in and out via this recess opening 64. An opening 65 that connects to the internal flow path and to which valves (61, 62) are attached is also formed in the upper surface of the manifold block 6. An opening (hereinafter sometimes referred to as "exhaust port") is also formed on an appropriate surface of the manifold block 6 for returning hydraulic fluid from the flow path to the reservoir 4. In the thruster 1 according to the first embodiment, exhaust ports (FIG. 1B, reference numerals 68a, 68b) corresponding to each valve (61, 62) are formed on the side surface of the manifold block 6. When the valves (61, 62) are attached to the manifold block 6, the valve mechanisms of the valves (61, 62) are installed in predetermined flow paths within the manifold block 6.

[0033] A cylindrically hollowed-out storage space 66 for the pump 7 is formed on the underside of the manifold block 6. The pump 7 is attached to the connection block 2 and placed in this storage space 66. A hydraulic oil intake port 72 opens on the side of the pump 7, perpendicular to the up-down direction, and a bell mouth 74 is attached to this opening via a coupling pipe 73. A suction filter 75 that filters out foreign matter from the hydraulic oil is attached to the open end of the bell mouth 74. An opening 67 that is cut into a rectangular shape is formed on the side of the cylindrical manifold block 6. This opening 67 communicates with the storage space 66 for the pump 7, and exposes the bell mouth 74 of the pump 7 to the outside of the manifold block 6 within the reservoir 4.

[0034] The structure of pump 7 is shown in Figures 3A and 3B. Figure 3A is a diagram showing the external appearance of pump 7, and Figure 3B is a diagram showing the internal structure of pump 7. As shown in Figure 3A, drive shaft 71 of pump 7 protrudes downward through shaft hole 174 formed in the bottom surface of a housing (hereinafter sometimes referred to as "pump case 171"). A discharge port 172 for hydraulic oil also opens in the bottom surface of pump case 171. Furthermore, pump case 171 is also formed with insertion holes 173 for bolts that penetrate in the vertical direction and attach it to connection block 2.

[0035] As shown in FIG. 3B, the pump case 171 is composed of a case main body 171a in which a storage space for gears (175a, 175b) is formed, and a cover portion 171b that covers the underside of the case main body 171a, and the case main body 171a and the cover portion 171b are integrally assembled with bolts or the like.

[0036] A gear (hereinafter referred to as drive gear 175a) that supports drive shaft 71 and a gear (hereinafter referred to as driven gear 175b) that meshes with drive gear 175a are housed within case body 171a. A pressure chamber (hereinafter referred to as "suction-side pressure chamber 176a") that communicates with suction port 72 and a pressure chamber (hereinafter referred to as "discharge-side pressure chamber 176b") that communicates with discharge port 172 are formed in the area where drive gear 175a and driven gear 175b mesh. When drive gear 175a rotates counterclockwise as viewed from below, hydraulic oil that has been sent from suction port 72 to suction-side pressure chamber 176a is sent to discharge-side pressure chamber 176b and then discharged from discharge port 172 via discharge-side pressure chamber 176b.

[0037] Returning to FIG. 2 , in the thruster 1, the pump 7 is fixed to the upper surface of the connection block 2 with bolts (not shown). A hydraulic oil inlet 24, which is one end of a flow path formed inside the connection block 2, opens on the upper surface of the connection block 2 at a position corresponding to the discharge port 172 of the pump 7. The other end of the flow path opens on the upper surface of the connection block 2 as a hydraulic oil outlet 25. When the manifold block 6 is attached to the connection block 2, the hydraulic oil inlet in the manifold block 6 corresponds to the position of the outlet 25 on the connection block 2, and the flow path in the connection block 2 and the flow path in the manifold block 6 are connected. A check valve (hereinafter sometimes referred to as a “check valve 26”) is attached to the hydraulic oil outlet 25 on the connection block 2 to prevent hydraulic oil discharged from the pump 7 from flowing back from the flow path on the manifold block 6 side to the flow path on the connection block 2 side. The basic configuration of the thruster 1 described above is almost the same as that of the electrohydraulic actuator described in Patent Document 3, but the hydraulic circuit of the thruster 1 according to the embodiment does not have a solenoid valve, and instead controls the operation of the hydraulic cylinder using a valve mechanism that operates hydraulically. The only electrically powered component included in the thruster 1 is the motor 3. The configuration of the hydraulic circuit included in the thruster 1 according to the embodiment and the operation of the thruster using this hydraulic circuit will be described below.

[0038] <Hydraulic circuit configuration> FIG. 4 shows a hydraulic circuit diagram of a thruster 1 according to an embodiment. As shown in FIG. 4, the hydraulic circuit includes a flow path (hereinafter sometimes referred to as a "pressurizing flow path 201") that guides hydraulic oil pressurized by a pump 7 to a port 54 of a cylinder tube 51 to push up a piston 53; a flow path (hereinafter sometimes referred to as a "pressure adjusting flow path 202") that adjusts the hydraulic pressure inside the cylinder tube 51 to a predetermined value (e.g., 50 bar) while maintaining the piston 53 at top dead center; and a flow path (hereinafter sometimes referred to as a "pressure reducing flow path 203") that forcibly discharges the hydraulic oil inside the cylinder tube 51 that has been pressurized by the pump 7 toward the reservoir 4. In the thruster 1 according to an embodiment, the piston 53 is constantly biased downward by an external mechanism connected to a head 12 at the tip of the piston rod 52 or a biasing mechanism 50 such as a spring attached to the thruster 1.

[0039] In this embodiment, the pressure adjustment flow path 202 is made up of a flow path 202a from the port 54 of the cylinder tube 51 to a branch point 60 to the relief valve 62, which also serves as part of the pressurization flow path 201, a flow path 202b from the branch point 60 to the relief valve 62, and a flow path 203c from the relief valve 62 to the reservoir 4. As shown in FIGS. 1B and 2, the main body of the relief valve 62 is attached to the manifold block 6. The relief valve 62 has a primary port 621 to which hydraulic oil is input and a secondary port 622 from which the input hydraulic oil is discharged, the primary port 621 being connected to the port 54 side of the cylinder tube 51, and the secondary port 622 being connected to the reservoir 4.

[0040] The pressure reduction flow path 203 is a flow path for returning the hydraulic oil in the cylinder tube 51 to the reservoir 4 via the unloading valve 61. Note that the unloading valve 61 used in the hydraulic circuit of the thruster 1 according to the embodiment operates to close the flow path between the primary port 611, into which the hydraulic oil flows from the port 54 of the cylinder tube 51, and the secondary port 612, which serves as an outlet for the hydraulic oil that has flowed into the primary port 611, when the hydraulic oil flowing into the pilot port 613 reaches a predetermined hydraulic pressure (for example, 5 bar) or higher. The unloading valve 61 opens and closes the flow path between the primary port 611 and the secondary port 612 depending on the hydraulic pressure of the hydraulic oil flowing into the pilot port 613.

[0041] The schematic structure of the unloading valve is shown in Figures 5A and 5B. Figures 5A and 5B show the unloading valve 61 installed in the manifold block 6, with Figure 5A showing the unloading state in which the flow path between the primary port 611 and the secondary port 612 (hereinafter sometimes referred to as the "internal flow path") is open, and Figure 5B showing the loading state in which the internal flow path is closed.

[0042] As shown in FIGS. 5A and 5B, unloading valve 61 includes a hollow cylindrical housing 610 and a cylindrical valve element 614 that is slidable in a liquid-tight manner along a cylindrical axis 617. A primary port 611 and a secondary port 612 that open to the side of housing 610 communicate with the interior of hollow housing 610. A pilot port 613 opens to one end face of hollow cylindrical housing 610. A female thread is formed on the inside of the other end face. Hydraulic pressure (indicated by the white arrow in the figure) for controlling the opening and closing of the internal flow path is applied to pilot port 613, and a pressure adjustment screw 615 for adjusting the hydraulic pressure (hereinafter sometimes referred to as "pilot pressure") required to close the internal flow path is threadedly attached to the female thread. More specifically, if the direction of cylindrical axis 617 is defined as the up-down direction and the up-down directions of unloading valve 61 are defined by assuming that pilot port 613 is provided at the lower end of housing 610, spring 616 is disposed between the lower end of pressure adjustment screw 615 and the upper end of cylindrical valve element 614, and the pilot pressure can be adjusted by adjusting the amount of threading of pressure adjustment screw 615. Of course, an unloading valve in which the pilot pressure is fixed so that it cannot be variably set may also be used.

[0043] A wide groove 618 is formed on the side of the cylindrical valve disc 614, circumferentially around the cylindrical axis 617 and extending in the direction of the cylindrical axis 617. As a result, the side of the valve disc 614 is separated from the inner surface of the housing 610 in the area where the groove 618 is formed, and the side of the valve disc 614 is in close contact with the inner surface of the housing 610 outside the area where the groove 618 is formed. When the hydraulic pressure at the pilot port 613 is lower than the pilot pressure, as shown in FIG. 5A , the biasing force of a spring 616 interposed between the pressure adjustment screw 615 and the valve disc 614 moves the valve disc 614 downward, positioning the wide groove 618 between the primary port 611 and the secondary port 612, thereby opening the internal flow path between the primary port 611 and the secondary port 612. As a result, as indicated by the solid arrow in FIG. 5A , hydraulic oil in the cylinder tube 51 is discharged through the unloading valve 61 to the reservoir 4.

[0044] On the other hand, when the oil pressure at pilot port 613 is equal to or higher than the pilot pressure, as shown in FIG. 5B, valve element 614 moves upward against the biasing force of spring 616, and the side of valve element 614 outside the formation area of ​​groove 618 comes into close contact with the inner surface of housing 610 in the area that includes the opening area of ​​secondary port 612, thereby closing the internal flow path.

[0045] In this embodiment, the main body of the unloading valve 61 is attached to the manifold block 6, and within the manifold block 6, there are formed flow paths (203a to 203c) that form part of a pressure reduction flow path 203, from the hydraulic cylinder 5 to a primary port 611 of the unloading valve 61, and a flow path 203d that connects the secondary port 612 to the reservoir 4. Also, as part of the pressure reduction flow path 203, there is formed a flow path 203f that is connected to a flow path 203e formed within the connection block 2 and continues to a pilot port 613. Note that hereinafter, in the pressure reduction flow path 203, the flow paths (203a to 203d) that extend from the port 54 of the hydraulic cylinder 5 to the reservoir 4 via the internal flow path of the unloading valve 61 will be referred to as a discharge flow path 300, and the flow paths (203e, 203f) that extend from the pump 7 to the pilot port 613 of the unloading valve 61 will be referred to as a pilot flow path 301.

[0046] The pressurizing flow path 201 is composed of a flow path 201a that runs from the inlet 24 in the connection block 2 through the check valve 26 to the outlet 25, and a flow path 201b that is connected to the outlet 25 in the manifold block 6 and runs to the port 54 of the hydraulic cylinder 5. Along the way of the flow path 201a in the connection block 2, a throttle mechanism 27 for adjusting the flow rate of hydraulic oil in the forward direction from the pump 7 to the port 54, and a check valve 26 for preventing backflow of hydraulic oil from the hydraulic cylinder 5 and allowing hydraulic oil to pass only in the forward direction, are arranged in this order. In this embodiment, the throttle mechanism 27 is an orifice that is a fixed throttle, and this throttle mechanism 27 functions as a mechanism for generating pilot pressure (hereinafter, may be referred to as a pilot pressure generating mechanism 20).

[0047] In the pressurizing flow path 201a in the connection block 2, the flow path from the pump 7 to the throttling mechanism 27 branches at the branch point 121, and the branched flow path 203e in the connection block 2 and the flow path 203f connected to the flow path 203e and leading to the pilot port 613 of the unloading valve 61 in the manifold block 6 become the above-mentioned pilot flow path 301.

[0048] <Thruster operation> Next, the operation of the thruster 1 according to the embodiment will be described. Here, the state in which the piston 53 of the hydraulic cylinder 5 of the thruster 1 is at the bottom dead center will be referred to as the first operating state, and the state in which the piston 53 is at the top dead center will be referred to as the second operating state. Below, the operation of the thruster 1 from the first operating state to the second operating state by turning on power and then turning off power to return to the first operating state will be described with reference to Figures 2 and 4.

[0049] When the thruster 1 according to the embodiment is powered on, the motor 3 is driven to operate the pump 7. The pump 7 continues to operate while power is supplied. While the pump 7 is operating, hydraulic oil in the reservoir 4 continues to be discharged toward the pressurization flow path 201. The hydraulic oil discharged from the pump 7 is guided to the pilot port 613 of the unloading valve 61 via the pilot flow path 301, and the throttle mechanism 27 pressurizes the hydraulic oil filled in the pilot flow path 301 to the pilot pressure. This closes the internal flow path of the unloading valve 61. As indicated by the black arrows in FIG. 2 , the hydraulic oil pressurized to the pilot pressure passes through the throttle mechanism 27 and check valve 26 of the pressurization flow path 201 toward the port 54 of the hydraulic cylinder 5 and is supplied into the cylinder tube 51.

[0050] Because hydraulic oil flowing through the check valve 26 toward the port 54 does not flow back toward the pump 7, as the pump 7 continues to operate, it fills the cylinder tube 51 and increases the hydraulic pressure therein. This causes the piston 53, which is at bottom dead center, to be pushed up against the biasing mechanism 50, which is driven by an external mechanism or the like. In other words, the thruster 1, which was in the first operating state, moves toward the second operating state. As long as power is supplied to the pump 7, the pump 7 continues to operate even after the piston 53 reaches top dead center. Therefore, the cylinder tube 51 continues to be pressurized even after the thruster 1 transitions to the second operating state. When the hydraulic pressure in the cylinder tube 51 exceeds the hydraulic pressure set in the relief valve 62, a flow path (hereinafter sometimes referred to as an "internal flow path") is formed between the primary port 621 and the secondary port 622 of the relief valve 62, and the hydraulic oil flowing from the pump 7 toward the port 54 is returned to the reservoir 4 from the outlet 68b via the relief valve 62. As a result, the pressure inside the cylinder tube 51 is adjusted to the pressure set in the relief valve 62, and the thruster 1 maintains the second operating state.

[0051] If the power is turned off at this point, the motor 3 stops, and the operation of pressurizing the hydraulic oil by the pump 7 also stops. The hydraulic pressure in the pilot flow path 301 disappears when the pump 7 stops, and almost simultaneously, the internal flow path of the unloading valve 61 opens, forming a discharge flow path 300 that runs from the port 54 to the reservoir 4. This causes the hydraulic pressure in the cylinder tube 51 to rapidly decrease. In addition, the piston 53 is pushed downward by the biasing force of the external mechanism, and the hydraulic oil in the cylinder tube 51 is quickly returned to the reservoir tank from the discharge port 68a via the discharge flow path 300. In this way, the thruster 1 returns to the first operating state.

[0052] As described above, the thruster 1 according to the embodiment reliably discharges hydraulic oil from the cylinder tube 51 toward the reservoir 4 and returns to the first operating state using only a hydraulically operated valve mechanism. Furthermore, the valve mechanism does not require electrical power, resulting in energy savings. Furthermore, a valve mechanism that does not require electrical power is less likely to generate heat, even when operated continuously or frequently, and the viscosity of the hydraulic oil does not decrease. Furthermore, if a brake device equipped with the thruster 1 according to the embodiment and operating in the first operating state is in a braking state, the brake device quickly enters the braking state as the thruster 1 returns to the first operating state in the event of a power outage. As a result, even if a power outage occurs during the operation of a moving device that is the target of braking, such as a crane, the moving device will not continue to operate due to inertia and will quickly stop. In other words, a brake device equipped with the thruster 1 according to the embodiment is highly safe. Of course, external electromagnetic noise will not cause the thruster 1 to malfunction.

[0053] ===Hydraulic circuit modification=== The hydraulic circuit of the thruster 1 according to the embodiment is not limited to that shown in Fig. 4. It can be modified as appropriate depending on the specifications and usage of the thruster 1, the performance required of the thruster 1, etc. Below, hydraulic circuits according to the following two modifications, the first and second modifications, will be given as modifications of the hydraulic circuit of the thruster 1 according to the embodiment.

[0054] <First Modification> In the hydraulic circuit of the thruster 1 according to the embodiment, stopping the pump 7 reduces the pilot pressure to zero, and opens the discharge flow path 300 via the unload valve 61. Note that in the above hydraulic circuit, depending on the type and mechanism of the pump 7, when the pump 7 is stopped, residual pressure from the hydraulic oil remaining in the flow path from the pump 7 to the check valve 26 may cause a slight delay in the timing at which the discharge flow path 300 opens relative to the timing at which the pump 7 is stopped.

[0055] For example, if the pump 7 is an impeller pump using rotary vanes, it is likely to operate in the opposite direction to pressurization even if there is residual pressure, and therefore the pilot pressure will quickly become zero when the pump 7 is stopped. On the other hand, if the pump 7 is an internal gear pump or an external gear pump as in the embodiment, there may be a slight delay in eliminating the residual pressure.

[0056] Therefore, as shown in the hydraulic circuit illustrated in FIG. 6 , a flow path 204 is provided that branches off from the pilot flow path 301 and leads to the reservoir 4 via a throttle mechanism 205 such as an orifice. The flow path resistance of the throttle mechanism 205 in the flow path 204 is set much higher than the flow path resistance of the throttle mechanism 27 in the pressurizing flow path 201. For example, if the load pressure of the hydraulic cylinder 5 is 20 Bar and the pilot pressure is 5 Bar when the pump 7 is operating, the differential pressure of the added throttle mechanism 205 becomes 20 Bar, which is the operating pressure of the pressurizing flow path 201. Because the flow path resistance of the added throttle mechanism 205 is set very high, only a small amount of hydraulic oil discharged from the operating pump 7 leaks from the added throttle mechanism 205 to the reservoir 4. Instead, most of the hydraulic oil flows toward the port 54 of the hydraulic cylinder 5 while generating pilot pressure by the pilot pressure generating mechanism 20. As a result, the pilot pressure in the pilot flow path 301 keeps the unloading valve 61 closed during operation of the pump 7.

[0057] On the other hand, the residual pressure when the pump 7 stops, i.e., the hydraulic pressure due to the hydraulic oil remaining in the flow path from the pump 7 to the check valve 26 in the pressurizing flow path 201 and in the pilot flow path 301, is extremely low, so almost no flow path resistance is generated by the throttle mechanism 205. In other words, the hydraulic oil that is the source of the residual pressure easily passes through the throttle mechanism 205, and the residual pressure quickly becomes zero. Therefore, in the hydraulic circuit shown in FIG. 6, regardless of the type or mechanism of the pump 7, the internal flow path of the unload valve 61 opens more quickly when the pump 7 stops, and the thruster 1 quickly returns to the first operating state.

[0058] In the hydraulic circuit shown in FIG. 6, the flow path 202c in the pressure adjustment flow path 202, which runs from the relief valve 62 to the reservoir 4, and the flow path 203d in the pressure reduction flow path 203, which runs from the unloading valve 61 to the reservoir 4, join together in the manifold block 6. However, as in the hydraulic circuit shown in FIG. 4, these flow paths (202c, 203d) may be formed separately.

[0059] <Second Modification> The thruster 1 according to the embodiment is configured to maintain the second operating state by continuously operating the pump 7. That is, even after transitioning to the second operating state, the pump 7 continues to discharge hydraulic oil at a hydraulic pressure required to raise the piston 53 against the biasing force of the spring 50 to return the hydraulic cylinder 5 to the first operating state. Therefore, in a thruster 1 with a larger biasing force of the spring 50, the motor 3 driving the pump 7 continues to operate under high load, making it more likely to become hot. This can cause deterioration of the hydraulic oil. Naturally, this also increases the power consumption of the motor 3. Therefore, as a second modification of the hydraulic circuit for the thruster 1 according to the embodiment, a hydraulic circuit that can reduce the power consumption of the motor 3 without placing a high load on the motor 3 even when a hydraulic cylinder 5 requiring a higher hydraulic pressure is used will be described below.

[0060] FIG. 7 shows a second modified example of the hydraulic circuit in the thruster 1. The hydraulic circuit shown in FIG. 7 is for illustrative purposes only, and does not include the connection block 2 or manifold block 6, which are related to the mechanical structure. In the hydraulic circuits of the thruster 1 shown in FIGS. 4 and 6, the pilot pressure generating mechanism 20 is configured with a throttle mechanism 27 and a check valve 26 connected in series along the pressurizing flow path 201. In the hydraulic circuit shown in FIG. 7, however, a pilot pressure generating mechanism 180 is connected in parallel to the pressurizing flow path 201. The pilot pressure generating mechanism 180 is configured with an unloading relief valve 80 consisting of a master valve 81 and a slave valve 82, and a throttle mechanism 83 consisting of an orifice or the like. For ease of understanding the operation of the thruster 1 and the hydraulic pressure at various points in the hydraulic circuit, FIG. 7 conveniently includes a hydraulic pressure gauge 181 that measures the discharge pressure Pa of the pump 7 and a hydraulic pressure gauge 182 that measures the hydraulic pressure Pb in the flow path from the check valve 26 to the hydraulic cylinder 5 along the pressurizing flow path 201. It should be noted that the hydraulic pressure Pb measured by the hydraulic pressure gauge 182 is substantially the hydraulic pressure inside the hydraulic cylinder 5, and therefore, hereinafter, the hydraulic pressure Pb may be referred to as the "cylinder pressure Pb."

[0061] Figure 8 shows the internal structure of the parent valve 81, and Figure 9 shows the internal structure of the child valve 82. Figures 8 and 9 are diagrams for explaining the operation of the parent valve 81 and child valve 82. The left side of Figures 8 and 9 shows the parent valve 81 and child valve 82 in a loaded state with the internal flow paths between the primary ports (811, 821) and secondary ports (812, 822) closed, and the right side shows the parent valve 81 and child valve 82 in an unloaded state with the internal flow paths open.

[0062] As shown in Fig. 8, the master valve 81 has a primary port 811 and a secondary port 812 that communicate with each other in an openable and closable manner via an internal flow path, and a pilot port (hereinafter sometimes referred to as "master valve pilot port 813") that discharges hydraulic oil that has flowed into the primary port 811 via a built-in throttle valve 814. Also, as shown in Fig. 9, the slave valve 82 has a primary port 821 and a secondary port 822 that communicate with each other in an openable and closable manner via an internal flow path, and a pilot port (hereinafter sometimes referred to as "slave valve pilot port 823") to which hydraulic oil is applied to control the opening and closing of the internal flow path. In Figs. 8 and 9, the direction of inflow and outflow of hydraulic oil is indicated by solid arrows, as in Fig. 5A, and the direction of application of hydraulic oil to open and close the valve is indicated by hollow arrows, as in Fig. 5B. As with the unloading valve 61 shown in Figures 5A and 5B, the ports (811-813, 821-823) of the parent valve 81 and the child valve 82 include ports (812, 813, 821, 822) with multiple openings. However, in Figures 8 and 9, for ports with multiple openings, the flow direction of hydraulic oil is shown for only one opening, in order to make it easier to understand the flow path of hydraulic oil.

[0063] First, the structure of the master valve 81 will be described in detail. As shown in Fig. 8, the master valve 81 is provided with a primary port 811 to which a discharge pressure Pa is applied at one end face of a hollow cylindrical housing 815, and a secondary port 812 communicating with the interior of the hollow cylinder and the master valve pilot port 813 are opened on the side face. A plug 816 is fitted to the other end face of the housing 815. Here, if the direction of the cylindrical axis 110 of the cylindrical housing 815 of the master valve 81 is defined as the up-down direction, and the up-down direction is defined by the fact that the primary port 811 is provided at the lower end side, then the housing 815 contains a cylindrical spool 817 that slides in the up-down direction, and a spring 818 that urges the spool 817 downward with a relatively weak pressure (e.g., equivalent to 5 Bar).

[0064] A flange-shaped head 817a is formed at the upper end of spool 817, and a seat 815a is formed inside casing 815 to support a lower surface 817b of head 817a, restricting downward movement of spool 817. The lower end of spool 817 is cylindrical with an outer diameter that fits closely to the inner surface of casing 815. The diameter narrows as it moves from the lower end to the upper portion, and the narrowed outer shape is maintained as it reaches head 817a. Therefore, a gap exists between the side of the cylindrical portion of spool 817 directly below head 817a and the inner surface of casing 815. A recess (hereinafter sometimes referred to as "lower recess 817c") that opens at the lower end is formed below spool 817, and the opening of lower recess 817c serves as primary port 811. The inner surface of lower recess 817c is shaped like a cone connected to the top of a cylinder. Meanwhile, a recess (hereinafter sometimes referred to as "upper recess 817d") having a cylindrical inner surface and an open upper end is formed above spool 817. Incidentally, a recess 816a that is open downward and has a top surface at the top is formed on the lower end side of plug 816, and spring 818 is interposed between the bottom surface of upper recess 817d of spool 817 and the top surface of recess 816a of plug 816.

[0065] The conical apex of lower recess 817c and the lower surface of upper recess 817d are connected via throttle valve 814, which is a thin tube-shaped flow path (orifice). Furthermore, a flow path (hereinafter sometimes referred to as "upper flow path 817e") that connects to the inside of upper recess 817d is formed in a cylindrical region of reduced diameter directly below head 817a of spool 817. Furthermore, a flow path (hereinafter sometimes referred to as "lower flow path 817f") that connects to the inside of lower recess 817c is formed in a region on the lower end side of spool 817 that is in close contact with the inner surface of housing 815. Spring 818 is interposed between the lower surface of plug 816 and the lower surface of upper recess 817d of spool 817.

[0066] Next, the structure of the sub-valve 82 will be described. As shown in Figure 9, sub-valve 82 has a hollow cylindrical sleeve 830 inserted into one end of a hollow cylindrical housing 824, and a cylindrical spool 825 that slides along the cylindrical axis 111 is inserted into the sleeve 830. Housing 824 contains a ball valve 826 that opens and closes as spool 825 slides, and a ball holder 828 that holds ball valve 826 and biases it with a spring 827 in a direction that attempts to return ball valve 826 to a closed state. The side of spool 825 is in close contact with the inner surface of sleeve 830, and the outer surface of sleeve 830 is in close contact with the inner surface of housing 824. There is a gap between the side of ball holder 828 and the inner surface of housing 824.

[0067] Here, the direction of the cylindrical axis 111 of the hollow cylindrical housing 824 of the sub-valve 82 is defined as the up-down direction, and the up-down direction of the sub-valve 82 is defined as the direction of the cylindrical axis 111 of the hollow cylindrical housing 824, with the sleeve 830 inserted into the lower end of the housing 824. The upper and lower ends of the sleeve 830 are open, with the upper opening having a smaller diameter than the lower opening. The edge of this smaller-diameter opening of the sleeve forms a seat portion 826a, which is the seat of the ball valve 826. The primary port 821 of the sub-valve 82 continues from the housing 824 to a space 829 formed within the sleeve 830 below the seat portion 826a of the ball valve 826. The spool 825 has a two-stage cylindrical shape, with the upper end being smaller in diameter than the lower end. The smaller-diameter upper cylindrical portion protrudes into the space 829 and abuts against the ball valve 826. This forms a space 829 around the upper cylindrical portion of the spool 825 to be filled with hydraulic oil. That is, above the space 829 in the sleeve 830, an opening of the seat portion 826a is formed, and below the space 829, an opening of a hollow portion through which the spool 825 is inserted is formed.

[0068] 9, in the above-mentioned space 829, the opening area S2 of the seat portion 826a in contact with the ball valve 826 is smaller than the area S1 in this space 829 where the hydraulic pressure acts on the spool 825, i.e., the opening area of ​​the lower end of the sleeve 830 (for example, S2 / S1 = 0.7). Therefore, the force pushing up the ball valve 826 by the hydraulic pressure of the hydraulic oil flowing into the primary port 821 and the force pushing down the spool 825 are not equal, and the force pushing up the ball valve 826 predominates. In the hydraulic circuit according to the modified example, the unloading relief valve 80 is configured by the parent valve 81 and the child valve 82 having the above-mentioned structure and the flow paths connected to these valves (81, 82). Furthermore, the unloading relief valve 80 and a throttle mechanism 83 interposed in the flow path from the secondary port 822 of the sub-valve 82 to the reservoir 4 constitute a pilot pressure adjustment mechanism 70.

[0069] Next, the operation of the hydraulic circuit in the second modified example will be described. Fig. 10 shows a timing chart illustrating changes in the discharge pressure Pa and cylinder pressure Pb accompanying the operation of the thruster 1. The horizontal axis of the chart in Fig. 10 represents the timing (T0 to T3) when the thruster 1 reaches a predetermined operating state, and the vertical axis represents the hydraulic pressure of the discharge pressure Pa and cylinder pressure Pb at the predetermined timing. In the chart shown in Fig. 10, power is applied to the motor 3 at T0 to operate the pump 7, and power to the motor 3 is cut off at T3 to stop the pump 7. Below, the operation of the hydraulic circuit shown in Fig. 7 will be described with reference to Figs. 8 to 10.

[0070] As shown in the hydraulic circuit of Figure 7, in the pressurizing flow path 201, the primary port 811 of the parent valve 81 is connected to the flow path from the pump 7 to the check valve 26, i.e., the pilot flow path 301. In addition, the parent valve pilot port 813 is connected to the child valve primary port 821. Therefore, the hydraulic pressure of the hydraulic oil flowing into the primary port 811 of the parent valve 81 becomes the discharge pressure Pa of the pump 7. In addition, the cylinder pressure Pb is applied to the child valve pilot port 823 of the child valve 82. For convenience, the hydraulic pressure applied to the primary port 821 of the child valve 82 will be referred to as the child valve control pressure Pc.

[0071] First, when the pump 7 is stopped, no discharge pressure Pa is applied to the primary port 811 of the master valve 81, and therefore the spool 817 is pressed down by the biasing force of the spring 818, and the lower surface 817b of the head 817a comes into contact with the upper surface of the seat 815a formed inside the housing 815. In this state, the upper flow path 827e and the master valve pilot port 813, and the lower flow path 817f and the secondary port 812 are all closed. On the other hand, no cylinder pressure Pb is applied to the slave valve pilot port 823 of the slave valve 82, and therefore the biasing force of the spring 827 keeps the ball valve 826 in contact with the seat 826a, and the primary port 821 and the secondary port 822 are closed.

[0072] When the pump 7 operates, the discharge pressure Pa of the pump 7 rises, as shown by the solid line in FIG. 10. Meanwhile, as shown by the dashed line in FIG. 10, the cylinder pressure Pb rises slightly later than the discharge pressure Pa due to the time lag between when the pump 7 starts discharging hydraulic oil (T0) and when the pressure reaches the hydraulic pressure (e.g., 5 bar) required to pass through the check valve 26 of the pressurizing flow path 201. Note that when the pump 7 operates, the hydraulic pressure required to maintain the unloading valve 61 in a loaded state is lower than the hydraulic pressure required to pass through the check valve 26. In other words, the unloading valve 61 maintains the loaded state by the hydraulic pressure applied to the pilot port 613 via the pilot flow path 301. As a result, the cylinder pressure Pb rises together with the discharge pressure Pa.

[0073] More specifically, when the pump 7 is operated, in the master valve 81, as shown by the dotted arrow in Figure 8, the hydraulic oil flows into the upper recess 817d via the throttle valve 814 and is discharged from the master valve pilot port 813 via the opening at the upper end of the upper recess 817d. The hydraulic oil discharged from the master valve pilot port 813 then flows into the primary port of the slave valve 82. The throttle valve 814 built into the master valve 81 reduces the discharge pressure Pa to approximately the same as the cylinder pressure Pb. That is, the cylinder pressure Pb is approximately equal to the slave valve control pressure Pc.

[0074] Meanwhile, in the sub-valve 82, the force of spring 827 urging ball valve 826 downward is dominant over the hydraulic pressure of the hydraulic oil flowing into primary port 821, so ball valve 826 remains closed. Therefore, discharge pressure Pa continues to rise. Also, as the discharge pressure Pa and cylinder pressure Pb rise, at time T1 when piston 53 begins to rise, the resistance of spring 50 temporarily slows the upward trend of discharge pressure Pa and cylinder pressure Pb. Thereafter, when cylinder pressure Pb overcomes the urging force of spring 50, piston 53, which was at bottom dead center, begins to move toward top dead center, and discharge pressure Pa and cylinder pressure Pb continue to rise.

[0075] The discharge pressure Pa and cylinder pressure Pb continue to rise even after the piston 53 reaches top dead center (e.g., Pa = 87 Bar, Pb = 82 Bar) and reach their maximum values ​​(e.g., Pa = 90 Bar, Pb = 85 Bar) at a certain point (T2). After that, the discharge pressure Pa begins to decrease rapidly, while the cylinder pressure Pb maintains its maximum value. At the point (T2) when the discharge pressure Pa and cylinder pressure Pb reach their maximum values, the sub-valve control pressure Pc ≈ 85 Bar pushes the ball valve 826 upward against the biasing force of the spring 818. As shown by the dotted arrow in Figure 9, the internal flow path between the primary port 821 and the secondary port 822 opens via the gap between the ball holder 828 and the inner surface of the housing 824, i.e., the unloaded state is reached. When the sub-valve 82 enters the unloaded state, the sub-valve control pressure Pc decreases.

[0076] Here, assuming that cylinder pressure Pb is not applied to the slave valve pilot port 823, there is a time lag between the increase / decrease trends of slave valve control pressure Pc and discharge pressure Pa due to the throttle valve 814 of the master valve 81. Therefore, at the moment when the slave valve 82 enters the unloaded state and the slave valve control pressure Pc decreases, a large pressure difference occurs between the high discharge pressure Pa and the slave valve control pressure Pc. Since the slave valve control pressure Pc also acts as a force to push down the spool 817 of the master valve 81, when the slave valve 82 enters the unloaded state, the above-mentioned pressure difference pushes up the spool 817 of the master valve 81, opening the primary port 811 and secondary port 812 of the master valve 81, and the master valve 81 also enters the unloaded state. However, at the next moment, the force pushing down the ball valve 826 by the spring 827 becomes dominant over the reduced slave valve control pressure Pc, causing the ball valve 826 to quickly close, and the slave valve 82 to enter the loaded state again. As a result, the child valve control pressure Pc increases, the spool 817 of the parent valve 81 is pushed down, and the parent valve 81 also returns to the loaded state. In other words, when the cylinder pressure Pb is not applied to the child valve pilot port 823, the unloading relief valve 80 functions as a relief valve consisting of the parent valve 81 and the child valve 82.

[0077] However, cylinder pressure Pb is applied to the child valve pilot port 823, and this cylinder pressure Pb is maintained by the check valve 26 interposed in the pressurized flow path 201 and the unloading valve 61, which is in a loaded state. For this reason, at the moment when the child valve control pressure Pc, which is also the hydraulic pressure in the space 829 inside the child valve 82, begins to decrease, the maximum cylinder pressure Pb is applied to the child valve pilot port 823. Then, in the space 829 inside the sleeve 830 of the child valve 82, where the hydraulic oil comes into contact with the ball valve 826 and the spool 825, as described above, due to the relationship in size between the area S1 of the spool 825 and the opening area S2 of the seat portion 826a (S1>S2), the child valve control pressure Pc acts so that the force pushing up the ball valve 826 is dominant. Therefore, the moment the child valve 82 enters the unloaded state and the child valve control pressure Pc becomes lower than the cylinder pressure Pb, the spool 825 is forced upward and slides due to the pressure difference between the high cylinder pressure Pb applied to the child valve pilot port 823 and the reduced child valve control pressure Pc, and the tip of the spool 825 abuts against the ball valve 826. The force caused by the upward sliding of the spool 817 then acts as an additional force to further urge the ball valve 826 upward. This maintains the child valve 82 in an unloaded state. When the child valve 82 enters the unloaded state, the parent valve 81 also enters the unloaded state, as described above. Naturally, the cylinder pressure Pb when the child valve 82 is maintained in the unloaded state is set to be higher than the cylinder pressure Pb (e.g., Pb = 82 Bar) when the piston 53 reaches top dead center and the thruster 1 enters the second operating state. If the sub-valve control pressure Pc when the sub-valve 82 transitions to the unloaded state is the cutout pressure Pco of the unloading relief valve 80 (≒maximum value of Pb), then the cylinder pressure Pb at which the unloaded state can no longer be maintained becomes the cut-in pressure Pci.

[0078] As described above, in the hydraulic circuit according to the second modified example, when the child valve 82 enters the unloaded state due to the child valve control pressure Pc, both the parent valve 81 and the child valve 82 maintain the unloaded state if the cylinder pressure Pb is greater than the cut-in pressure Pci. Furthermore, in the hydraulic circuit according to the second modified example, when the parent valve 81 and the child valve 82 both enter the unloaded state, a hydraulic pressure (e.g., 5 bar) equivalent to the force exerted by the spring 818 to press down on the spool 817 is applied to the primary port 811 of the parent valve 81, which is in the unloaded state. In addition, because the throttle mechanism 83 is interposed in the flow path from the secondary port 822 of the child valve 82 to the reservoir 4, a hydraulic pressure (e.g., 5 bar) is generated due to the resistance to passage through this throttle mechanism 83, and this hydraulic pressure acts as the child valve control pressure Pc, pressing down on the spool 817 of the parent valve 81. Therefore, in the hydraulic circuit according to the second modification, even if both the parent valve 81 and the child valve 82 continue to be in the unloaded state, the hydraulic oil on the primary port 811 side of the parent valve 81 is maintained at a hydraulic pressure (for example, 10 Bar) obtained by adding the hydraulic pressure corresponding to the passage resistance between the primary port 811 and the secondary port 812 of the parent valve 81 to the hydraulic pressure corresponding to the passage resistance of the throttle mechanism 83 connected to the secondary port 822 side of the child valve 82, as shown in FIG. 10 . Then, the hydraulic oil that passes through the throttle mechanism 83 from the secondary port 822 of the child valve 82 and the hydraulic oil discharged from the secondary port 812 of the parent valve flows toward the reservoir 4 and is discharged again from the pump 7. In other words, when the unloading relief valve 80 is in the unloaded state, the discharge pressure Pa of the pump 7 only needs to be sufficient to maintain the pilot pressure, and the pump 7 is driven at a low load. Meanwhile, the discharge flow path 300 leading to the reservoir 4 via the unloading valve 61 for the hydraulic oil in the hydraulic cylinder 5 is closed, and the check valve 26 prevents the hydraulic oil in the pressurizing flow path 201 leading from the pump 7 to the hydraulic cylinder 5 from flowing back toward the pump 7. Therefore, the cylinder pressure Pb maintains the hydraulic pressure required to maintain the second operating state.

[0079] Next, when the motor 3 is turned off and the pump 7 is stopped (T3), the discharge pressure Pa of the pump 7 disappears, and the pilot pressure also disappears. This opens the internal flow path of the unloading valve 61, and the hydraulic oil in the hydraulic cylinder 5 is returned to the reservoir 4 via the discharge flow path 300, causing a sudden decrease in pressure Pb. As the cylinder pressure Pb decreases, the hydraulic pressure applied to the sub-valve pilot port 823 of the sub-valve 82 also decreases, weakening the force pushing up the spool 825 against the downward biasing force of the spring 827. When the pressure Pb decreases to the cut-in pressure (e.g., 56 bar) (T4), the spring 827 pushes the spool 825 downward via the ball holder 828 and the ball valve 826. The ball valve 826 abuts against the seat portion 826a, closing the internal flow path between the primary port 821 and the secondary port 822.

[0080] Furthermore, hydraulic oil in the flow path from primary port 821 of child valve 82 via parent valve pilot port 813 and primary port 811 of parent valve 81 to pump 7 and in pilot flow path 301 is returned to reservoir 4 via throttle mechanism 205 arranged midway through flow path 204 connecting pump 7 with the discharge flow path, just like the hydraulic circuit according to the first modified example shown in Figure 6. This causes discharge pressure Pa to disappear more quickly. The above is the operation of the hydraulic circuit according to the second modified example.

[0081] In a real hydraulic circuit, hydraulic fluid leakage cannot be completely prevented, so the cylinder pressure Pb gradually decreases over time. However, in a typical usage scenario of the thruster 1, the duration of the second operating state is shorter than the time from when the thruster 1 reaches the second operating state until the second operating state can no longer be maintained due to a decrease in the cylinder pressure Pb over time. Therefore, the problem of the cylinder pressure Pb decreasing over time and the second operating state being unable to be maintained does not substantially occur. Of course, the duration of the second operating state can be extended by increasing the seal strength of various parts of the hydraulic circuit or increasing the number of sealed locations. Therefore, the seal strength of various parts and the number of sealed locations can be appropriately determined during the design phase of the hydraulic circuit depending on the duration of the second operating state required for the expected usage of the thruster 1. By further improving the manufacturing precision of the sub-valve 82, it is possible to set the cut-in pressure Pci of the sub-valve 82 to be equal to or greater than the pressure when the piston 53 of the hydraulic cylinder 5 reaches top dead center (e.g., 82 bar) and less than the cut-out pressure Pco (e.g., 85 bar). This allows the second operating state to be maintained regardless of whether or not there is a leakage of hydraulic oil.

[0082] As described above, the hydraulic circuit shown in FIG. 7 includes the unloading relief valve 80, which is composed of the master valve 81 and the slave valve 82, and the pilot pressure generating mechanism 180, which includes the throttle mechanism 83. Therefore, when the thruster 1 transitions to the second operating state, the discharge pressure Pa of the pump 7 is automatically adjusted to a low hydraulic pressure sufficient to maintain the pilot pressure of the unloading valve 61. This reduces the load on the motor 3 that drives the pump 7, even when the biasing force of the spring 50 is strong and it is necessary to increase the cylinder pressure Pb in the second operating state. This prevents deterioration of the hydraulic oil due to heat generated by the motor 3. This also reduces the time the motor 3 operates under high load, thereby reducing the power consumption of the motor 3. Furthermore, since conventional thrusters using electromagnetic valves consume power when the electromagnetic valves are turned on and off, the thruster 1 with the hydraulic circuit shown in FIG. 7 is more effective at reducing power consumption than conventional thrusters when the motor 3 is turned on and off intermittently and frequently.

[0083] <Master and slave valve cartridges> The hydraulic circuit in the second modified example described above includes an unloading relief valve 80 in which two individual valve mechanisms, a parent valve 81 and a child valve 82, are connected by a flow path. The flow path connecting the parent valve 81 and the child valve 82 may be configured using piping, but as shown in FIGS. 8 and 9, the parent valve 81 and the child valve 82 are plug-type valves each having a hollow cylindrical housing (815, 824), and are formed as cartridges that are replaceably inserted into and removed from a metal block having a flow path formed therein, similar to the manifold block 6 and the connection block 2, as with the unloading valve 61 shown in FIGS. 5A and 5B. Therefore, the unloading relief valve 80 may be configured as a unit in which the parent valve 81 and the child valve 82 are formed as cartridges, and the parent valve 81 and the child valve 82 are incorporated into a metal block having a flow path formed therein.

[0084] Figure 11 shows an unloading relief valve 80 unit 90 in which a parent valve 81 and a child valve 82 are combined into a cartridge. In addition to the parent valve 81 and the child valve 82, the unit 90 shown in Figure 11 also incorporates an insertable / removable unloading valve 61 and a throttle mechanism 83 (not shown) that constitutes the pilot mechanism 180. The throttle mechanism 83 is fitted into the flow path inside the metal block 91, similar to the check valve 26 incorporated into the connection block 2 of the thruster 1 shown in Figure 2.

[0085] As shown in FIG. 11 , the lower ends of the valves (61, 81, 82) are embedded in the metal block 91 so that the ports (611-613, 811-813, 821-823) of the valves (61, 81, 82) are located within the metal block 91. Note that in FIG. 11 , the valves (61, 81, 82) are shown in cross section to facilitate understanding of the embedded state of the valves (61, 81, 82). However, the actual embedded positions of the valves (61, 81, 82) in the front-to-back direction of the page may differ from one another in the front-to-back direction of the page. Furthermore, flow paths, such as a pilot flow path 301, that connect predetermined ports of the master valve 81, the slave valve 82, and the unload valve 61 are formed within the metal block 91. Note that the throttle mechanism 83 is inserted midway through the flow path that connects to the secondary port 822 of the slave valve 82. Of course, the metal block 91 constituting the unit 90 may be the manifold block 6 or the connection block 2.

[0086] The hydraulic circuit according to the second modification uses two valves, a parent valve 81 and a child valve 82, which are linked to each other, to achieve one function, the unloading relief valve 80. When performing maintenance (inspection, replacement, repair, adjustment, etc.) on either the parent valve 81 or the child valve 82, these cartridge-formed valves (81, 82) can be easily attached and detached individually from the metal block 91. On the other hand, when performing maintenance on the overall function of the unloading relief valve 80, the unit 90 can be removed from the thruster 1. Therefore, by configuring the parent valve 81 and the child valve 82 as cartridges and configuring the unloading relief valve 80 as a unit 90 in which the cartridge-formed parent valve 81 and the child valve 82 are attached to a metal block so that they can be inserted and removed, any type of maintenance can be flexibly handled, and maintenance costs can be reduced.

[0087] ===Other Examples=== The electrohydraulic actuator according to the present invention has been described above using an electrohydraulic cylinder (thruster 1) as an example, but it goes without saying that the present invention is not limited to the above example and can be modified in various ways without departing from the spirit of the invention. The above example has been described in detail to clearly explain the present invention, and the present invention is not necessarily limited to an embodiment having all of the described configurations. Furthermore, some of the configurations of the above embodiment can be added to, deleted from, or replaced with other configurations.

[0088] For example, in the hydraulic circuit shown in FIG. 4, outlets (68a, 68b) corresponding to the unloading valve 61 and the relief valve 62 are provided, but the flow paths (203d, 202c) passing through the unloading valve 61 and the relief valve 62, respectively, may join within the manifold block 6 and be discharged into the reservoir 4 from a single outlet.

[0089] In the pilot pressure generating mechanism 180 in the hydraulic circuit according to the second modification, the unloading relief valve 80 is composed of a separate parent valve 81 and a child valve 82. However, the parent valve 81 and the child valve 82 that constitute the unloading relief valve 80 may be integrally configured. FIG. 12 shows a pilot pressure generating mechanism 180 in which the parent valve 81, the child valve 82, and the throttle mechanism 83 are integrally configured. In FIG. 12, the same reference numerals are used to designate components corresponding to the parts and members shown in FIGS. 7 to 9. In addition, in FIG. 12, parts corresponding to the parent valve 81 and the child valve 82 are indicated by different hatching. Note that in the child valve 82 shown in FIG. 12, the valve disc 826 is conical rather than spherical. In any case, the form of the unloading relief valve 80 is not limited as long as the function and operation are the same.

[0090] Some or all of the flow paths constituting the hydraulic circuit may be formed using piping rather than being formed within a metal block such as the connection block 2 or the manifold block 6. Furthermore, the unloading valve 61 and the relief valve 62 do not have to be attached to the manifold block 6, and may be attached to the connection block 2 or inserted in the middle of the piping, for example. In any case, it is sufficient that the flow paths (201-203) corresponding to the hydraulic circuit shown in FIG. 4 are formed. Furthermore, the pump 7 is not limited to an external gear pump, and may be an internal gear pump, an impeller pump, or the like.

[0091] In the above embodiments, the throttle mechanism (27, 83, 205) is not limited to the orifice, which is a fixed throttle, but may be a throttle valve, which is a variable throttle. A throttle valve can variably adjust the flow rate by finely adjusting the opening of the valve element. For example, in the hydraulic circuits shown in FIGS. 4 and 6, when the pilot pressure set in the unloading valve 61 is not constant depending on the application or specifications of the thruster 1, the desired pilot pressure can be variably set. However, there are individual differences in the relationship between the adjustment amount of the opening and the actual opening of the valve element of each throttle valve.

[0092] On the other hand, an orifice, which is a fixed throttle, has little individual variation, and for thrusters 1 of the same model, as long as the throttle opening is specified, multiple orifices with the specified opening can be manufactured, eliminating the need to individually adjust the opening for multiple thrusters 1 of the same model. In this way, a thruster 1 using an orifice as a throttle mechanism can reduce the cost of adjusting the throttle opening. Furthermore, since an orifice has no moving parts, is highly reliable, and is cheaper than a throttle valve, it can also reduce the parts cost of the thruster 1. In any case, an appropriate throttle mechanism (27, 83, 205) can be adopted depending on the specifications of the thruster 1 and the performance required of the thruster 1.

[0093] In the thruster 1 according to the above embodiment, the piston 53 is constantly urged downward by a biasing mechanism 50, such as an external mechanism, connected to the head 12 at the tip of the piston rod 52 of the hydraulic cylinder 5. However, a spring that constantly urges the piston 53 downward may be incorporated into the cylinder tube 51. FIG. 12 shows an example of a hydraulic cylinder 105 in which a spring 150 is incorporated into the cylinder tube 51. Here, assuming that the axial direction of the piston rod 52 is the up-down direction and that the piston 53 is pushed upward when the pump 7 is operated, the up-down direction is defined. In the hydraulic cylinder 105 shown in FIG. 12, the piston 53 is not cylindrical but is disk-shaped with a rim 151 extending upward from its periphery, and a spring 150 having a helical axis in the axial direction of the piston rod 52 is disposed between the inner surface 152 at the upper end of the cylinder tube 51 and the upper surface 153 of the piston.

[0094] The hydraulic cylinder 5 in the thruster 1 according to the above embodiment is arranged so that the piston 53 moves back and forth in the vertical direction, but the hydraulic cylinder 5 can also be arranged so that it moves back and forth in a direction intersecting the motor shaft 31 (for example, a perpendicular direction).

[0095] In the hydraulic circuits shown in Figures 4 and 6, the pilot pressure generating mechanism 20 is composed of the throttle mechanism 27 and the check valve 26, but the pilot pressure generating mechanism 20 can also be composed of the check valve 26 alone. Specifically, the check valve 26 is configured to allow hydraulic oil to pass in the forward direction from the pump 7 toward the cylinder tube 51 at a low hydraulic pressure, while the function of the check valve 26 prevents hydraulic oil from flowing backward in the reverse direction from the cylinder tube 51 toward the pump 7. Therefore, a check valve 26 is used that allows hydraulic oil to pass in the forward direction when hydraulic oil pressure greater than the pilot pressure is applied in the forward direction. This allows the pilot pressure generating mechanism 20 to be composed of only the check valve 26.

[0096] If the pilot pressure generating mechanism 20 were to consist only of the check valve 26, the number of parts in the thruster 1 would be reduced, and it would be possible to provide the thruster 1 at a lower cost. However, because the pilot pressure required to operate the unloading valve 61 is a relatively large hydraulic pressure, the check valve 26, which prevents hydraulic oil from passing in the forward direction below this hydraulic pressure, would naturally be large. This would make it difficult to miniaturize the thruster 1. In any case, the configuration of the pilot pressure generating mechanism 20 may be determined appropriately depending on the manufacturing costs and specifications required for the thruster 1.

[0097] While the thruster 1 described above as an embodiment includes a hydraulic cylinder 5 as a hydraulic actuator, the hydraulic actuator need not necessarily be a direct-acting hydraulic actuator in which a moving part, such as a piston 53, reciprocates linearly, as in the hydraulic cylinder 5. For example, the hydraulic actuator may include a rotating moving part, such as a hydraulic actuator including a rotor that rotates by a predetermined angle hydraulically within a sealed stator. An electrohydraulic actuator including such a hydraulic actuator with a rotating moving part may be configured to reciprocate between a first operating state corresponding to the rotational angular position of the rotor when the stator is not pressurized with hydraulic oil, and a second operating state corresponding to the rotational angular position when the stator is filled with sufficiently pressurized hydraulic oil and the rotor has rotated a predetermined angle from the first operating state. An example of a biasing mechanism in an electrohydraulic actuator having a moving part that rotates by hydraulic pressure may be a helical spring that constantly biases the rotor to a rotational position corresponding to the first operating state.

[0098] Naturally, the working fluid in an electrohydraulic actuator is not limited to hydraulic oil, but may be water, air, steam, or any other fluid capable of generating hydraulic pressure for operating the hydraulic actuator. [Explanation of symbols]

[0099] 1 thruster (electric hydraulic actuator, electric hydraulic cylinder), 2 connecting blocks, 3 motors, 4 reservoirs, 5,105 hydraulic cylinders, 6 Manifold block, 7 Pump, 11 Clevis, 12 Head, 20,180 pilot pressure generating mechanism, 21 communication hole, 23 connecting member, 24 inlet, 25 Outlet, 26 Check valve, 27, 73, 205 Throttle mechanism, 31 motor shaft, 50 biasing mechanism, 51 cylinder tube, 52 piston rod, 53 piston, 54 (hydraulic cylinder 5) port, 61 unload valve, 62 relief valve, 68a, 68b discharge port, 80 unloading relief valve, 81 unloading relief valve parent valve, 82 Sub-valve of unloading relief valve, 150 Spring (biasing mechanism), 90 Unit including unload relief valve, 91 Metal block, 201 pressurizing flow path, 201a, 201b flow paths constituting the pressurizing flow path, 202 pressure adjustment flow path, 202a to 202c flow paths constituting the pressure adjustment flow path, 203 pressure reducing flow path, 203a to 203f, 301 pilot flow path constituting a pressure reducing flow path; 300 a discharge flow path constituting a pressure reducing flow path; 811 a primary port of a parent valve; 812 secondary port of parent valve, 813 pilot port of parent valve, 814 throttle valve, 815 Parent valve housing, 817 Parent valve spool, 818 Parent valve spring, 823 pilot port of sub-valve, 821 primary port of sub-valve, 822 secondary port of sub-valve; 824 housing of sub-valve; 825 spool of sub-valve; 826 Ball valve, 827 Sub-valve spring

Claims

1. a motor that outputs rotational power; a pump operated by the rotational power of the motor; a hydraulic actuator operated by the hydraulic fluid pressurized by the pump; a reservoir for storing the working fluid; a fluid circuit for hydraulically controlling the operation of the hydraulic actuator; Equipped with the hydraulic actuator reciprocates between a first operating state and a second operating state in response to the hydraulic pressure of the supplied hydraulic fluid, and is constantly biased in a direction returning to the first operating state; The fluid circuit includes: a pressurizing flow path for supplying the hydraulic fluid pressurized by the pump to a hydraulic actuator; a pressure reducing flow path that connects the hydraulic actuator and the reservoir via an unloading valve in an openable and closable manner; a pilot flow path for supplying hydraulic oil pressurized to a pilot pressure to the unloading valve in order to close the pressure reduction flow path; a pilot pressure generating mechanism that generates the pilot pressure; a check valve interposed in the pressurizing flow path for allowing the working fluid to pass only in a forward direction from the pump toward the hydraulic actuator; Including, the pilot pressure generating mechanism generates the pilot pressure while the pump is operating; the pilot flow path branches off midway from the pump to the check valve in the pressurizing flow path and reaches the unloading valve, During operation of the pump, the pilot pressure is generated, causing the pump to transition to the second operating state, and when the pump stops, the pilot pressure disappears, the pressure reduction flow path is opened, and the pump returns to the first operating state, a throttle mechanism constituting the pilot pressure generating mechanism and the check valve are arranged in this order in the pressurizing flow path from the pump to the hydraulic actuator. Electro-hydraulic actuator.

2. An electric hydraulic actuator as described in claim 1, wherein the throttling mechanism is an orifice.

3. A motor that outputs rotational power; a pump operated by the rotational power of the motor; a hydraulic actuator operated by the hydraulic fluid pressurized by the pump; a reservoir for storing the working fluid; a fluid circuit for hydraulically controlling the operation of the hydraulic actuator; Equipped with the hydraulic actuator reciprocates between a first operating state and a second operating state in response to the hydraulic pressure of the supplied hydraulic fluid, and is constantly biased in a direction returning to the first operating state; The fluid circuit includes: a pressurizing flow path for supplying the hydraulic fluid pressurized by the pump to a hydraulic actuator; a pressure reducing flow path that connects the hydraulic actuator and the reservoir via an unloading valve in an openable and closable manner; a pilot flow path for supplying hydraulic oil pressurized to a pilot pressure to the unloading valve in order to close the pressure reduction flow path; a pilot pressure generating mechanism that generates the pilot pressure; a check valve interposed in the pressurizing flow path for allowing the working fluid to pass only in a forward direction from the pump toward the hydraulic actuator; Including, the pilot pressure generating mechanism generates the pilot pressure while the pump is operating; the pilot flow path branches off midway from the pump to the check valve in the pressurizing flow path and reaches the unloading valve, During operation of the pump, the pilot pressure is generated, causing the pump to transition to the second operating state, and when the pump stops, the pilot pressure disappears, the pressure reduction flow path is opened, and the pump returns to the first operating state, The pilot pressure generating mechanism is composed of an unloading relief valve consisting of a parent valve and a child valve, and a throttle mechanism, the master valve has a throttle valve built in, a master valve primary port connected to the pilot flow path, a master valve secondary port connected to a flow path communicating with the reservoir, and a master valve pilot port communicating with the master valve primary port via the throttle valve, and also has a master valve spool that is urged upward by hydraulic pressure in the master valve primary port, and a master valve spring that urges the master valve spool downward, with a predetermined direction being the up-down direction; the child valve has a child valve primary port connected to the parent valve pilot port, a child valve secondary port connected to a flow path communicating with the reservoir via the throttle mechanism, and a child valve pilot port connected to a flow path from the check valve to the hydraulic actuator, and has, with a predetermined direction being a vertical direction, a valve element urged upward by hydraulic pressure in the child valve primary port, a child valve spool urged upward by hydraulic pressure in the child valve pilot port, and a child valve spring urges the valve element downward, The child valve distributes the hydraulic pressure P1 at the child valve primary port into hydraulic pressure P2 that presses the valve element upward and hydraulic pressure P3 that presses the child valve spool downward, with P2 > P3, and when the hydraulic pressure P1 reaches a predetermined cutout pressure, the valve element is pressed in one direction, opening the child valve primary port and the child valve secondary port to an unloaded state, The master valve spool is pressed upward by a pressure difference between the hydraulic pressure P1 on the master valve pilot port side, which is reduced as the slave valve enters the unloaded state, and the hydraulic pressure P5 on the master valve primary port side, thereby opening communication between the master valve primary port and the master valve secondary port, and the master valve enters an unloaded state. When the child valve is in an unloaded state, the unloaded state is maintained by the hydraulic pressure P4 at the child valve pilot port, When both the parent valve and the child valve are in the unloaded state, the hydraulic pressure P5 is maintained at the pilot pressure by the hydraulic pressure P1 generated by the passage resistance of the throttle mechanism and the hydraulic pressure generated by the parent valve spring urging the parent valve spool downward, and the hydraulic actuator is maintained in the second operating state by the hydraulic pressure P4. Electro-hydraulic actuator.

4. An electrohydraulic actuator according to claim 3, the unloading relief valve is an integrated unit in which the parent valve and the child valve are attached to a metal block in which a flow path for working fluid is formed, the parent valve and the child valve are cartridges configured to be detachable from the metal block; Electro-hydraulic actuator.

5. An electric hydraulic actuator as described in claim 4, wherein the throttling mechanism is interposed in the middle of a flow path formed within the metal block, and the unit constitutes the pilot pressure generating mechanism.

6. 2. The electrohydraulic actuator of claim 1, the fluid circuit includes a flow path that branches off from the pilot flow path, passes through a throttle mechanism, and reaches the reservoir; the throttle mechanism has a flow path resistance higher than the flow path resistance of the pilot pressure generating mechanism when the pump is operating, and eliminates residual pressure of the working fluid remaining in the flow path from the pump to the pilot pressure generating mechanism in the pressurizing flow path and in the pilot flow path when the pump is stopped. Electro-hydraulic actuator.

7. An electrohydraulic actuator according to any one of claims 1 to 6, the hydraulic actuator is a direct acting hydraulic actuator; The first operating state is reached when the piston of the direct acting hydraulic actuator is at bottom dead center; The second operating state is reached when the piston is at top dead center, The piston is biased in the direction of bottom dead center by an external mechanism connected to the tip of the piston rod. Electro-hydraulic actuator.

8. An electrohydraulic actuator according to any one of claims 1 to 6, the hydraulic actuator is a direct acting hydraulic actuator; The first operating state is reached when the piston of the direct acting hydraulic actuator is at bottom dead center; The second operating state is reached when the piston is at top dead center, A spring mechanism is provided to constantly bias the piston toward the bottom dead center. Electro-hydraulic actuator.

9. A brake device equipped with the electrohydraulic actuator according to claim 7, The brake mechanism presses or separates the brake linings against both sides of the disc-shaped brake disc. The braking mechanism is constantly biased in a direction to be in a braking state, When the electrohydraulic actuator is in the second operating state, the braking state of the brake disc is released, and when the electrohydraulic actuator is in the first operating state, the brake disc is in a braking state. Brake device.

10. A brake device equipped with the electrohydraulic actuator according to claim 8, The brake mechanism presses or separates the brake linings against both sides of the disc-shaped brake disc. When the braking mechanism is in the second operating state, the braking state of the brake disc is released, and when the braking mechanism is in the first operating state, the brake disc is in a braking state. Brake device.

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