Electro-hydraulic actuator and brake device

Abstract

This electro-hydraulic actuator is provided with: a pump (7) that uses a motor (3) as power; a hydraulic actuator (5) that is preloaded so as to be in a first state, and that reciprocates between the first state and a second state; a reservoir (4); and a fluid circuit that controls the hydraulic actuator using hydraulic pressure, the fluid circuit having: a pressurization flow path (201) that supplies fluid from the pump to the hydraulic actuator; a discharge flow path (300) for discharging the fluid from the hydraulic actuator to the accumulator via an unloading valve (61); a pilot flow path (301) that branches midway in the pressurization flow path and supplies the fluid pressurized to the pilot pressure to the unloading valve; a means (27) for generating pilot pressure during the operation of the pump; a check valve (26) that causes the fluid to pass only in the direction from the pump toward the hydraulic cylinder shifts to the second state when the pump performs an operation, and returns to the first state when the pump is stopped.

Description

Technical Field

[0001] The invention relates to an electro-hydraulic actuator and a brake device. Background Art

[0002] The electric hydraulic actuator has: a pump (impeller pump, gear pump, etc.) that uses an electric motor to perform an action; a hydraulic actuator that uses a working fluid (working oil, etc.) pressurized by the pump to perform an action; and a fluid circuit. The fluid circuit has: a flow path for the working fluid that connects the pump, the reservoir, and the hydraulic oil pressure actuator to each other; a valve mechanism that is installed in the middle of the flow path and is used to supply the working fluid stored in the reservoir to the hydraulic actuator to operate the hydraulic actuator, or to discharge the working fluid from the hydraulic actuator in an operating state to the reservoir.

[0003] In addition, as an electric hydraulic actuator, an electric hydraulic cylinder that uses a hydraulic cylinder as a hydraulic actuator is well known. The fluid circuit (hydraulic circuit) possessed by the electric hydraulic cylinder controls a pump that performs an action using the power of an electric motor and a valve mechanism provided at an appropriate location in the hydraulic circuit. For example, a flow path of working oil as a working fluid is formed in the order of a reservoir, a pump, and a hydraulic cylinder, and the cylinder barrel of the hydraulic cylinder is filled with working oil to push the piston. In addition, any other mechanism that will be the object of the action is connected to the front end of the piston rod so that the action of the other mechanism is linked to the action of the electric hydraulic cylinder. In addition, the piston is always preloaded in the downward direction by the restoring force of other mechanisms, springs and other mechanisms possessed by the electric hydraulic cylinder (hereinafter sometimes referred to as "preload mechanisms"). If the supply of working oil to the cylinder barrel is stopped through the hydraulic circuit, and a flow path connecting the cylinder barrel and the reservoir is formed, the piston is pressed down by the preload mechanism.

[0004] The electric hydraulic cylinder is used, for example, in an electric pressure feeder brake. The electric hydraulic cylinder performs an action in the following manner, that is, in the electric pressure feeder brake, if the electric hydraulic cylinder becomes energized and pushes the piston rod, the brake mechanism of the drum brake, disc brake, etc. releases the brake pad. The brake mechanism is always preloaded in the direction of returning to the braking state by a spring or the like. If the power supply of the electric hydraulic cylinder is cut off, the working oil in the hydraulic cylinder is discharged, and the brake pad is pressed against the brake drum and brake disc by the preload force of the brake mechanism. As a result, the brake device is in a braking state. In addition, the hydraulic circuit of the electric hydraulic cylinder used in the electric pressure feeder brake has a solenoid valve and its control circuit, and the solenoid valve arranged at an appropriate place in the flow path is opened and closed to control the opening and closing of the solenoid valve, thereby forming a flow path for filling the hydraulic cylinder with working oil or returning the filled working oil to the reservoir.

[0005] In addition, regarding the electric hydraulic cylinder used in the electric hydraulic pressure feeder brake, for example, the following Patent Documents 1 and 2 disclose it as an "electric hydraulic brake release device". In addition, the following Patent Document 3 discloses an "electric hydraulic actuator" and a "disc brake device" having the electric hydraulic actuator.

[0006] Patent Document 1: Japanese Patent No. 6322699

[0007] Patent Document 2: Japanese Patent No. 6353036

[0008] Patent Document 3: Japanese Patent No. 7262870 Summary of the invention

[0009] Generally, in the fluid circuit of the electric hydraulic actuator, a solenoid valve is arranged at an appropriate location of the flow path of the working fluid. By performing appropriate opening and closing control of the solenoid valve, the fluid circuit can quickly switch between the flow path for guiding the working fluid pressurized by the pump to the hydraulic actuator and the flow path for forcibly discharging the working fluid from the hydraulic actuator and returning it to the reservoir. As described above, the solenoid valve can cause the fluid circuit to perform operations at high speed and high precision.

[0010] However, the solenoid valve requires electricity, so when the power supply is stopped, the hydraulic circuit cannot operate normally. In addition, the solenoid valve may malfunction due to the surrounding electrical noise. Therefore, when the electric hydraulic actuator is used for the electric conveyor brake, it is necessary to have a fluid circuit with some kind of safety mechanism that can reliably discharge the working fluid in the actuator even in the event of a power outage or a malfunction of the solenoid valve. In order to ensure that the safety mechanism can operate reliably in an emergency, daily maintenance inspections are also necessary. Therefore, since the electric hydraulic actuator has a fluid circuit with a solenoid valve, the installation cost and the cost required for maintenance are likely to increase.

[0011] Furthermore, when the solenoid valve is continuously energized for a long time or repeatedly operated at a high frequency, the power consumption increases. If the power consumption increases, the operating cost increases. In addition, in the electro-hydraulic actuator, the solenoid valve is in direct contact with the working fluid, unlike the motor. Therefore, the viscosity of the working fluid decreases due to the heat generated by the increase in power consumption, and it is possible that the hydraulic pressure required for the operation of the hydraulic actuator cannot be obtained. As a countermeasure for heat generation, if a cooling mechanism or the like is provided in the electro-hydraulic actuator, it becomes difficult to miniaturize the electro-hydraulic actuator and it becomes difficult to provide the electro-hydraulic actuator more cheaply.

[0012] Therefore, the present invention has been made to solve the above-mentioned problems, and an object thereof is to provide an electro-hydraulic actuator having a fluid circuit capable of reliably discharging working fluid in the actuator without using a solenoid valve, and a brake device having the electro-hydraulic actuator.

[0013] The present invention for achieving the above-mentioned object is an electro-hydraulic actuator having:

[0014] a motor, which outputs rotational power;

[0015] a pump that is actuated by the rotational power of the motor;

[0016] a hydraulic actuator that performs an action using a working fluid pressurized by the pump;

[0017] a fluid reservoir storing the working fluid; and

[0018] a fluid circuit for controlling the action of the hydraulic actuator by hydraulic pressure,

[0019] The hydraulic actuator reciprocates between a first operating state and a second operating state according to the hydraulic pressure of the supplied working fluid, and is always biased in a direction to return to the first operating state.

[0020] The fluid circuit comprises:

[0021] a pressurizing flow path for supplying the working fluid pressurized by the pump to a hydraulic actuator;

[0022] a pressure reducing flow path which connects the hydraulic actuator and the accumulator via an unloading valve so as to be openable and closable;

[0023] a pilot flow passage for supplying hydraulic oil pressurized to a pilot pressure to the unloading valve in order to close the pressure reducing flow passage;

[0024] a pilot pressure generating mechanism, which is used to generate the pilot pressure; and

[0025] a check valve disposed in the middle of the pressurizing flow path and configured to allow the working fluid to pass only in a forward direction from the pump toward the hydraulic actuator;

[0026] The pilot pressure generating mechanism generates the pilot pressure during the operation of the pump.

[0027] The pilot flow path branches off midway from the pump to the check valve in the pressurizing flow path and reaches the unloading valve.

[0028] The pilot pressure is generated during the operation of the pump to enter the second operation state. When the pump is stopped, the pilot pressure disappears and the pressure reducing flow path is opened to return to the first operation state.

[0029] The electro-hydraulic actuator may be configured such that a throttle mechanism constituting the pilot pressure generating mechanism and the check valve are sequentially disposed in the middle of the pressurizing flow path from the pump to the hydraulic actuator. The throttle mechanism may be an orifice.

[0030] It can also be an electro-hydraulic actuator in which:

[0031] The check valve also serves as the pilot pressure generating mechanism.

[0032] The check valve sends the working fluid toward the hydraulic actuator when the working fluid supplied from the pump reaches a predetermined pilot pressure or higher.

[0033] It can also be an electro-hydraulic actuator in which:

[0034] The pilot pressure generating mechanism is composed of an unloading relief valve and a throttling mechanism, and the unloading relief valve is composed of a main valve and a sub-valve.

[0035] The mother valve has a built-in throttle valve, a mother valve primary port connected to the pilot flow path, a mother valve secondary port connected to the flow path connected to the reservoir, and a mother valve pilot port connected to the mother valve primary port via the throttle valve, and the specified direction is set as the up and down direction, and has a mother valve column preloaded upward by the hydraulic pressure at the mother valve primary port and a mother valve spring preloaded downward.

[0036] The sub-valve has a sub-valve primary port connected to the mother valve pilot port, a sub-valve secondary port connected to the flow path connected to the reservoir via the throttling mechanism, and a sub-valve pilot port connected to the flow path from the check valve to the hydraulic actuator, and the specified direction is set as the up and down direction, and has a valve body preloaded upward by the hydraulic pressure at the sub-valve primary port, a sub-valve valve column preloaded upward by the hydraulic pressure at the sub-valve pilot port, and a sub-valve spring preloading the valve body downward.

[0037] The sub-valve is set to P2>P3, so that the hydraulic pressure P1 at the primary port of the sub-valve is dispersed into the hydraulic pressure P2 that presses the valve body upward and the hydraulic pressure P3 that presses the sub-valve valve column downward, and if the hydraulic pressure P1 reaches the specified circuit-breaking pressure, the valve body is pressed in one direction, so that the primary port of the sub-valve and the secondary port of the sub-valve are opened and become an unloading state,

[0038] The mother valve utilizes the pressure difference between the hydraulic pressure P1 on the mother valve pilot port side and the hydraulic pressure P5 on the mother valve primary port side which is reduced in pressure accompanying the unloading state of the sub-valve to press the mother valve column upward so that the connection between the mother valve primary port and the mother valve secondary port is opened to become an unloading state.

[0039] If the sub-valve is in the unloaded state, the unloaded state is maintained by the hydraulic pressure P4 at the sub-valve pilot port.

[0040] If both the mother valve and the sub-valve are in the unloaded state, the hydraulic pressure P5 is maintained as the pilot pressure by utilizing the hydraulic pressure P1 generated by the resistance of the throttling mechanism and the hydraulic pressure generated by the mother valve spring pre-tightening the mother valve valve column downward, and the hydraulic pressure P4 is utilized to maintain the hydraulic actuator in the second action state.

[0041] It can also be an electro-hydraulic actuator in which:

[0042] The unloading relief valve is an integrated unit formed by installing the main valve and the sub-valve on a metal block forming a flow path of the working fluid, and the main valve and the sub-valve are box-type structures that can be attached and detached relative to the metal block. Alternatively, the throttling mechanism is sandwiched in the middle of the flow path formed in the metal block, and the unit constitutes the pilot pressure generating mechanism.

[0043] It can also be an electro-hydraulic actuator in which:

[0044] The fluid circuit has a flow path that branches from the pilot flow path and reaches the reservoir via a throttle mechanism.

[0045] The throttling mechanism has a flow resistance higher than the flow resistance of the pilot pressure generating mechanism when the pump is in operation, and eliminates the residual pressure of the working fluid remaining in the flow path from the pump to the pilot pressure generating mechanism and the pilot flow path in the pressurizing flow path when the pump stops.

[0046] The electric hydraulic actuator described in any one of the above, wherein the hydraulic actuator can be a direct-acting hydraulic actuator. Furthermore, it can also be set as the following electric hydraulic actuator, wherein when the piston of the direct-acting hydraulic actuator is at the bottom dead center, it becomes the first action state, and when the piston is at the top dead center, it becomes the second action state, and the piston is preloaded in the direction of the bottom dead center by an external mechanism connected to the front end of the piston rod. It can also be set as the following electric hydraulic actuator, wherein when the piston of the direct-acting hydraulic actuator is at the bottom dead center, it becomes the first action state, and when the piston is at the top dead center, it becomes the second action state, and it has a spring mechanism that always preloads the piston in the direction of the bottom dead center.

[0047] The scope of the present invention also includes a brake device, which has an electric hydraulic actuator that sets the hydraulic actuator as a direct-acting hydraulic actuator. The brake device has a braking mechanism that presses or isolates the brake friction linings on both sides of a circular brake disc, and the braking mechanism is always pre-tightened in the direction of becoming a braking state. When the electric hydraulic actuator is in the second action state, the braking state of the brake disc is released, and when it is in the first action state, the brake disc is put into a braking state.

[0048] A brake device having an electric hydraulic actuator with a hydraulic actuator that sets the hydraulic actuator as a direct-acting type can be set as the following brake device, which has a braking mechanism for pressing or isolating brake friction linings on both sides of a circular plate-shaped brake disc, and the braking mechanism releases the braking state of the brake disc when it is in the second action state, and puts the brake disc into a braking state when it is in the first action state.

[0049] Effects of the Invention

[0050] According to the present invention, there are provided an electro-hydraulic actuator having a fluid circuit capable of reliably discharging working fluid in the actuator without using an electromagnetic valve, and a brake device having the electro-hydraulic actuator. Other effects will become clear from the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1A It is a diagram showing the appearance of an electro-hydraulic actuator according to the embodiment.

[0052] Figure 1B It is a diagram showing the structure inside the housing of the electro-hydraulic actuator according to the embodiment.

[0053] Figure 2 yes Figure 1A 2 is a cross-sectional view taken along the arrow aa in FIG. 1 , and is a diagram showing the internal structure of the electric hydraulic actuator involved in the embodiment.

[0054] Figure 3A It is a diagram showing the appearance of a pump constituting the electric hydraulic actuator according to the embodiment.

[0055] Figure 3B It is a diagram showing the internal structure of a pump constituting the electric hydraulic actuator according to the embodiment.

[0056] Figure 4 It is a diagram showing a hydraulic circuit of the electric hydraulic actuator according to the embodiment.

[0057] Figure 5AIt is a diagram showing a schematic structure of a unloading valve constituting the above-mentioned hydraulic circuit, and shows a state in which an internal flow path of the unloading valve is open.

[0058] Figure 5B It is a diagram schematically showing the structure of a unload valve constituting the above-mentioned hydraulic circuit, and shows a state in which an internal flow path of the unload valve is closed.

[0059] Figure 6 It is a diagram showing a first modified example of the hydraulic circuit of the electric hydraulic actuator according to the embodiment.

[0060] Figure 7 It is a diagram showing a second modified example of the hydraulic circuit of the electric hydraulic actuator according to the embodiment.

[0061] Figure 8 It is a diagram for explaining the operation of the mother valve constituting the unloading relief valve of the hydraulic circuit in the second modified example.

[0062] Fig. 9 It is a diagram for explaining the operation of a sub-valve constituting an unloading relief valve of a hydraulic circuit in a second modified example.

[0063] Fig.10 It is a timing chart for explaining the operation of the hydraulic circuit in the second modification.

[0064] Fig.11 This is a diagram showing a unit of the unloading relief valve in which the mother valve and the sub-valve having a cassette structure are mounted on a metal block in a second modified example.

[0065] Fig.12 It is a diagram showing another example of the above-mentioned unloading relief valve.

[0066] Fig.13 This is a diagram showing a schematic structure of a hydraulic cylinder in which a spring is built in that can be used in the electric hydraulic actuator according to the embodiment. DETAILED DESCRIPTION

[0067] Cross-references of related applications

[0068] This application claims priority based on Japanese Patent Application No. 2023-095586 filed on June 9, 2023 and priority based on Japanese Patent Application No. 2024-016498 filed on February 6, 2024, and cites the contents thereof.

[0069] The embodiments of the present invention are described below with reference to the accompanying drawings. In addition, in the drawings used for the following description, the same or similar parts are sometimes marked with the same reference numerals and repeated descriptions are omitted. In addition, unnecessary reference numerals are sometimes omitted in the description according to the drawings.

[0070] ===Example===

[0071] <Electro-hydraulic actuator>

[0072] As one embodiment of the present invention, an electric hydraulic cylinder using a hydraulic cylinder as a direct-acting hydraulic actuator is exemplified. Figure 1A 1 is a diagram showing the appearance of an electro-hydraulic actuator (hereinafter sometimes referred to as a "thruster 1") according to a first embodiment. Figure 1B 1 is a diagram showing the structure inside the frame of the thruster 1. Figure 1A As shown, the thruster 1 has a square cylindrical appearance, and a hook 11 for fixing the thruster to other equipment is installed on one end surface. At the other end side, the front end side of the piston rod 52 of the built-in hydraulic cylinder protrudes in a manner that can reciprocate in the axial direction. A head 12 connected to a mechanism (hereinafter sometimes referred to as an "external mechanism") that is linked to the action of the thruster 1 is installed at the front end of the piston rod 52. In addition, a hole 19 for installing the external mechanism is formed in the head 12.

[0073] If the reciprocating direction of the piston rod 52 is set as the up-down direction, and the piston rod 52 is set as protruding upward from the thruster 1 to define each up-down direction in the thruster 1, the thruster 1 has an overall structure in which the upper structure and the lower structure are connected via a flat square cylindrical metal block 2 with the up-down direction as the thickness direction. The upper structure of the thruster 1 is contained in a frame (hereinafter sometimes referred to as an "upper frame") composed of the metal block (hereinafter sometimes referred to as a "connecting block 2"), a hollow square cylindrical cover (hereinafter sometimes referred to as an "upper cover 13"), and a metal plate having an insertion hole 14 for the piston rod 52 (hereinafter sometimes referred to as an "upper cover plate 15"), and the components and mechanisms constituting the thruster 1 are stored. The lower structure has a frame (hereinafter sometimes referred to as a "lower frame") composed of a connecting block 2, a hollow square cylindrical cover (hereinafter sometimes referred to as a "lower cover 16"), and a metal plate (hereinafter sometimes referred to as a "base plate 17") to which a hook 11 is installed. The lower frame also accommodates components and mechanisms that constitute the thruster 1.

[0074] like Figure 1B As shown, a motor 3 is provided in the lower frame of the thruster 1. The connecting block 2 and the base plate 17 are connected via mounting bolts 18 and are tightened by the mounting bolts 18, thereby clamping the lower cover between the connecting block 2 and the base plate 17 to form the lower frame. As for the upper frame, the upper cover is clamped between the connecting block 2 and the base plate 17 by tightening the mounting bolts 18 that connect the connecting block 2 and the upper cover plate 15, thereby forming the upper frame.

[0075] The space in the upper frame is mostly occupied by the reservoir 4 filled with hydraulic oil. The reservoir 4 is formed by a closed space formed by the upper surface of the connection block 2, the hollow cylindrical reservoir housing 41 inscribed coaxially with the hollow square cylindrical upper cover 13, and the lower surface of the upper cover plate 15. With regard to the thruster 1 involved in the embodiment, a cylindrical metal block (hereinafter sometimes referred to as "manifold block 6") forming a flow path for hydraulic oil, a hydraulic cylinder 5, and various valves (61, 62) arranged at appropriate locations in the hydraulic circuit are accommodated in the reservoir 4. In addition, the lower end side of the cylinder barrel 51 that becomes the housing of the hydraulic cylinder 5 and various valves (61, 62) are mounted on the upper surface of the manifold block 6. In addition, a pump is provided in the space formed inside the manifold block 6.

[0076] exist Figure 2 The internal structure of the thruster 1 is shown in FIG. Figure 2 yes Figure 1A In the aa direction cross-sectional view. In addition, Figure 2 In order to facilitate understanding of the internal structure of the thruster 1, a portion of the thruster 1 is shown using a cross-section line. Figure 2 The structure and construction of the thruster 1 will be described.

[0077] The motor 3 is arranged in the lower frame in a state covered by a hollow cylindrical motor housing 32. The motor shaft 31 has a rotation axis in the vertical direction and protrudes upward from the motor housing 32. The lower end of the motor shaft 31 is axially supported by a bearing 33 using a ball bearing provided on the base plate 17.

[0078] A hole (hereinafter sometimes referred to as "communication hole 21") that connects the upper surface and the lower surface is formed in the connection block 2, and the upper end side of the motor shaft 31 is inserted into the communication hole 21. A bearing 22 of the motor shaft 31 using a ball bearing is assembled inside the connection block 2, and a part of the flow path included in the hydraulic circuit is formed.

[0079] In this embodiment, the pump 7 is an external gear pump, and the front end of the motor shaft 31 is in the connection block 2 and connected to the front end of the pump drive shaft 71 via the connecting member 23. In this way, the connection block 2 has the function of connecting the upper and lower structures to each other. In addition, the flow paths in the connection block 2 and the manifold block 6 are as follows. Figure 2 As illustrated in the dotted ellipse region 100 in FIG. 1 , a hole (hereinafter sometimes referred to as a “processed hole”) is formed from the outside in a clean metal block and the opening of the processed hole is closed with a plug.

[0080] The upper and lower ends of the hollow cylindrical reservoir housing 41 housed in the upper frame body abut against the upper surface of the connection block 2 and the lower surface of the upper cover plate 15 and are sealed by an O-ring, etc. Thus, the reservoir 4 is formed as a closed space.

[0081] The cylindrical manifold block 6 disposed in the reservoir 4 is mounted on the connection block 2, and has a flow path for the working oil and a storage space 66 for the pump 7 formed therein. A circular recess 63 is formed on the upper surface of the manifold block 6, into which the lower end side of the single-cylinder hydraulic cylinder 5 is inserted, and an opening (hereinafter sometimes referred to as a "recess opening 64") communicating with the internal flow path is formed at the bottom of the recess 63, and a port 54 is provided at the lower end of the cylinder 51 of the hydraulic cylinder 5 for allowing the working oil to flow in and out through the recess opening 64. In addition, an opening 65 is formed on the upper surface of the manifold block 6, which is connected to the internal flow path and for the valves (61, 62) to be installed. In addition, an opening (hereinafter sometimes referred to as a "discharge port") for returning the working oil in the flow path to the reservoir 4 is formed on an appropriate surface of the manifold block 6. With regard to the thruster 1 involved in the first embodiment, discharge ports ( Figure 1B Furthermore, when the valves (61, 62) are mounted on the manifold block 6, the valve mechanisms of the valves (61, 62) are provided so as to be sandwiched in a predetermined flow path in the manifold block 6.

[0082] A storage space 66 for the pump 7 hollowed out in a cylindrical shape is formed on the lower surface side of the manifold block 6. The pump 7 is mounted on the connection block 2 and arranged in the storage space 66. The pump 7 has an opening 72 for the suction of the working oil at the side orthogonal to the up-down direction, and a tapered port (bell-mouth) 74 is mounted on the opening via a joint pipe 73. In addition, a suction filter 75 for filtering foreign matter in the working oil is mounted at the open end of the tapered port 74. Moreover, an opening portion 67 cut in a rectangular shape is formed on the side of the cylindrical manifold block 6. The opening portion 67 is connected to the storage space 66 of the pump 7, so that the tapered port 74 of the pump 7 is exposed to the outside of the manifold block 6 in the reservoir 4.

[0083] exist Figure 3A , Figure 3B The construction of the pump 7 is shown in FIG. Figure 3A 2 is a diagram showing the appearance of the pump 7. Figure 3B 7 is a diagram showing the internal structure of the pump 7. Figure 3A As shown, the driving shaft 71 of the pump 7 protrudes downward through the shaft hole 174 formed on the lower surface of the frame (hereinafter, sometimes referred to as the "pump housing 171"). In addition, a discharge port 172 for the working oil is opened on the lower surface of the pump housing 171. In addition, the pump housing 171 is also formed with an insertion hole 173 for a bolt that penetrates in the up-down direction and is used to mount the pump housing 171 on the connection block 2.

[0084] like Figure 3BAs shown, the pump housing 171 is composed of a housing body 171a forming a storage space for gears (175a, 175b) and a cover portion 171b covering the lower surface side of the housing body 171a. The housing body 171a and the cover portion 171b are assembled into one body using bolts or the like.

[0085] A gear (hereinafter referred to as the driving gear 175a) for axially supporting the driving shaft 71 and a gear (hereinafter referred to as the driven gear 175b) meshing with the driving gear 175a are built into the housing body 171a. A pressure chamber (hereinafter sometimes referred to as the "suction side pressure chamber 176a") connected to the suction port 72 and a pressure chamber (hereinafter sometimes referred to as the "discharge side pressure chamber 176b") connected to the discharge port 172 are formed in the area where the driving gear 175a and the driven gear 175b mesh. Moreover, if the driving gear 175a rotates counterclockwise as viewed from below, the pump 7 sends the working oil sent from the suction port 72 to the suction side pressure chamber 176a to the discharge side pressure chamber 176b side, and is discharged from the discharge port 172 via the discharge side pressure chamber 176b.

[0086] Back to Figure 2 In the thruster 1, the pump 7 is fixed to the upper surface of the connection block 2 by bolts (not shown). On the upper surface of the connection block 2, an inlet 24 for the working oil, which is one end of the flow path formed inside the pump 7, is opened at a position corresponding to the discharge port 172 of the pump 7. The other end of the flow path is opened on the upper surface of the connection block 2 as an outlet 25 for the working oil. If the manifold block 6 is installed on the connection block 2, the inlet of the working oil of the manifold block 6 corresponds to the position of the above-mentioned outlet 25 of the connection block 2, and the flow path of the connection block 2 is connected to the flow path of the manifold block 6. In addition, a check valve (hereinafter sometimes referred to as a "one-way valve 26") is installed at the outlet 25 of the working oil of the connection block 2 so that the working oil discharged from the pump 7 does not flow back from the flow path on the manifold block 6 side to the flow path on the connection block 2 side. In addition, the basic structure of the thruster 1 is roughly the same as the electric hydraulic actuator described in the above-mentioned patent document 3, but in the hydraulic circuit of the thruster 1 involved in the embodiment, there is no solenoid valve, and a valve mechanism that performs an action by hydraulic pressure is used to control the action of the hydraulic cylinder. In addition, the thruster 1 has only the motor 3 as an electric component. Next, the structure of the hydraulic circuit of the thruster 1 involved in the embodiment and the action of the thruster realized by the hydraulic circuit are described.

[0087] <Structure of hydraulic circuit>

[0088] exist Figure 4 FIG. 2 shows a hydraulic circuit diagram of the thruster 1 according to the embodiment. Figure 4As shown, the hydraulic circuit has: a flow path (hereinafter, sometimes referred to as "pressurization flow path 201") for guiding the working oil pressurized by the pump 7 to the port 54 of the cylinder 51 in order to push the piston 53; a flow path (hereinafter, sometimes referred to as "pressure adjustment flow path 202") for maintaining the piston 53 at the top dead center and adjusting so that the cylinder 51 has a predetermined hydraulic pressure (for example, 50 bar); and a flow path (hereinafter, sometimes referred to as "pressure reduction flow path 203") for forcibly discharging the working oil in the cylinder 51 pressurized by the pump 7 to the reservoir 4. In addition, in the thruster 1 involved in the embodiment, the piston 53 is always preloaded downward by an external mechanism connected to the head 12 at the front end of the piston rod 52 or a preload mechanism 50 such as a spring attached to the thruster 1.

[0089] In this embodiment, the pressure regulating flow path 202 is composed of a flow path 202a, a flow path 202b, and a flow path 202c. The flow path 202a is a flow path from the port 54 of the cylinder 51 to the branch point 60 which also serves as a part of the pressurizing flow path 201 and reaches the relief valve 62. The flow path 202b is a flow path from the branch point 60 to the relief valve 62. The flow path 203c is a flow path 203 from the relief valve 62 to the reservoir 4. Figure 1B , Figure 2 As shown, the main body of the relief valve 62 is mounted on the manifold block 6. The relief valve 62 has a primary port 621 for inputting hydraulic oil and a secondary port 622 for discharging the input hydraulic oil. The primary port 621 is connected to the port 54 side of the cylinder 51, and the secondary port 622 is connected to the reservoir 4.

[0090] The pressure reducing flow path 203 is a flow path for returning the working oil in the cylinder 51 to the reservoir 4 via the unloading valve 61. The unloading valve 61 used in the hydraulic circuit of the thruster 1 according to the embodiment operates in such a manner that, when the working oil flowing into the pilot port 613 reaches a predetermined hydraulic pressure (e.g., 5 bar) or more, the flow path between the primary port 611 through which the working oil flows from the port 54 of the cylinder 51 and the secondary port 612 which is the outflow port of the working oil flowing into the primary port 611 is closed. The unloading valve 61 opens and closes the flow path between the primary port 611 and the secondary port 612 according to the hydraulic pressure of the working oil flowing into the pilot port 613.

[0091] exist Figure 5A , Figure 5B The schematic structure of the unloading valve is shown in FIG. Figure 5A , Figure 5B The unloading valve 61 is shown in a state provided in the manifold block 6. Figure 5A The unloaded state is shown in which the flow path between the primary port 611 and the secondary port 612 (hereinafter, sometimes referred to as “internal flow path”) is opened. Figure 5BShows the load state with the internal flow path closed.

[0092] like Figure 5A , Figure 5B As shown, the unloading valve 61 contains a cylindrical valve body 614 that can slide along the cylinder axis 617 in a liquid-tight state in a hollow cylindrical frame 610. Moreover, the primary port 611 and the secondary port 612 opened on the side of the frame 610 are connected to the interior of the hollow frame 610. In addition, a pilot port 613 is opened on one end face of the hollow cylindrical frame 610. An internal thread is formed on the inner side of the other end face side. A hydraulic pressure (white hollow arrow in the figure) for controlling the opening and closing of the internal flow path is applied to the pilot port 613, and a pressure regulating screw 615 for adjusting the hydraulic pressure (hereinafter, sometimes referred to as "pilot pressure") required to close the internal flow path is screwed into the internal thread. More specifically, if the direction of the cylinder axis 617 is set to the up-down direction, and the pilot port 613 is set at the lower end of the frame 610 to define the up-down directions of the unloading valve 61, a spring 616 is arranged between the lower end of the pressure regulating screw 615 and the upper end of the cylindrical valve body 614, and the pilot pressure can be adjusted by adjusting the screw insertion amount of the pressure regulating screw 615. Of course, an unloading valve in which the pilot pressure is fixed and cannot be variably set can also be used.

[0093] A groove 618 is formed on the side of the cylindrical valve body 614, which rotates around the cylinder axis 617 and is wide in the direction of the cylinder axis 617. As a result, in the area where the groove 618 is formed, the side of the valve body 614 is separated from the inner surface of the frame 610, and outside the area where the groove 618 is formed, the side of the valve body 614 is in close contact with the inner surface of the frame 610. In addition, when the hydraulic pressure at the pilot port 613 is lower than the pilot pressure, as shown in FIG. Figure 5A As shown in FIG. 1 , due to the preload force of the spring 616 sandwiched between the pressure regulating screw 615 and the valve body 614, the valve body 614 moves downward, and the wide groove 618 becomes a position spanning between the primary port 611 and the secondary port 612, and the internal flow path between the primary port 611 and the secondary port 612 is opened. Figure 5A As shown by the black arrow in FIG. 8 , the hydraulic oil in the cylinder 51 is discharged toward the accumulator 4 via the unloading valve 61 .

[0094] On the other hand, when the hydraulic pressure at the pilot port 613 is equal to or higher than the pilot pressure, Figure 5B As shown, the valve body 614 moves upward against the preload of the spring 616, and the side surface of the valve body 614 outside the formation area of ​​the groove 618 is in close contact with the inner surface of the frame 610 in the area including the opening area of ​​the secondary port 612, and the internal flow path is closed.

[0095] In this embodiment, the main body of the unloading valve 61 is mounted on the manifold block 6, and a flow path (203a to 203c) from the hydraulic cylinder 5 to the primary port 611 of the unloading valve 61, which is a part of the pressure reducing flow path 203, and a flow path 203d communicating with the reservoir 4 from the secondary port 612 are formed in the manifold block 6. In addition, as a part of the pressure reducing flow path 203, a flow path 203f is formed which is connected to the flow path 203e formed in the connection block 2 and is continuous with the pilot port 613. In addition, hereinafter, in the pressure reducing flow path 203, the flow path (203a to 203d) from the port 54 of the hydraulic cylinder 5 to the reservoir 4 via the internal flow path of the unloading valve 61 is referred to as the discharge flow path 300, and the flow paths (203e, 203f) from the pump 7 to the pilot port 613 of the unloading valve 61 are referred to as the pilot flow path 301.

[0096] The pressurizing flow path 201 is composed of a flow path 201a, which is a flow path from the inlet 24 in the connection block 2 to the outlet 25 via the check valve 26, and a flow path 201b, which is a flow path connected to the outlet 25 in the manifold block 6 and reaches the port 54 of the hydraulic cylinder 5. In the middle of the flow path 201a in the connection block 2, in the forward direction from the pump 7 to the port 54, a throttle mechanism 27 for adjusting the flow rate of the hydraulic oil and a check valve 26 for preventing the backflow of the hydraulic oil from the hydraulic cylinder 5 and passing the hydraulic oil only in the forward direction are sequentially arranged. In this embodiment, the throttle mechanism 27 is an orifice serving as a fixed throttle, and the throttle mechanism 27 functions as a mechanism for generating a pilot pressure (hereinafter, sometimes referred to as a pilot pressure generating mechanism 20).

[0097] Moreover, in the pressurizing flow path 201a in the connecting block 2, the flow path from the pump 7 to the throttling mechanism 27 is branched at the branch point 121, and the branched flow path 203e in the connecting block 2 and the flow path 203f connected to the flow path 203e and reaching the pilot port 613 of the unloading valve 61 in the manifold block 6 become the above-mentioned pilot flow path 301.

[0098] <Thruster Operation>

[0099] Next, the operation of the thruster 1 according to the embodiment will be described. Here, in the thruster 1, the state in which the piston 53 of the hydraulic cylinder 5 is at the bottom dead center is referred to as the first operation state, and the state in which the piston 53 is at the top dead center is referred to as the second operation state. Figure 2 and Figure 4 , the operation of the thruster 1 is described, after the power supply to the thruster 1 in the first operation state is turned on to shift to the second operation state, and then the power supply is turned off to return to the first operation state.

[0100] Regarding the thruster 1 involved in the embodiment, if the power is turned on, the motor 3 is driven and the pump 7 is operated. While the power is supplied, the pump 7 continues to operate. When the pump 7 is in operation, the working oil of the reservoir 4 is continuously discharged toward the pressurizing flow path 201. In addition, the working 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 working oil filled in the pilot flow path 301 is pressurized to the pilot pressure by the throttle mechanism 27. As a result, the internal flow path of the unloading valve 61 is closed. In addition, as in Figure 2 As indicated by the black arrow in the figure, the hydraulic oil pressurized to the pilot pressure passes through the throttle mechanism 27 and the check valve 26 of the pressurizing flow path 201 toward the port 54 of the hydraulic cylinder 5 and is supplied into the cylinder tube 51 .

[0101] The hydraulic oil flowing toward the port 54 through the check valve 26 will not flow back to the pump 7 side, so if the pump 7 continues to operate, the hydraulic pressure in the cylinder 51 is increased while filling the cylinder 51. As a result, the piston 53 at the bottom dead center is pushed against the preload mechanism 50 such as an external mechanism. That is, the thruster 1 in the first operating state operates toward the second operating state. In addition, as long as the pump 7 is supplied with power, the piston 53 continues to operate even after reaching the top dead center, so the cylinder 51 continues to be pressurized even after the thruster 1 enters the second operating state. In addition, if the hydraulic pressure in the cylinder 51 is greater than the hydraulic pressure set in the relief valve 62, a flow path (hereinafter sometimes referred to as "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 returns to the reservoir 4 from the discharge port 68b via the relief valve 62. As a result, the pressure in the cylinder 51 is adjusted to the pressure set in the relief valve 62 , and the thruster 1 maintains the second operating state.

[0102] Here, if the power is turned off, the motor 3 stops, and the pressurization of the working oil by the pump 7 also stops. The hydraulic pressure in the pilot flow path 301 disappears at the time when the pump 7 stops, and almost simultaneously, the internal flow path of the unloading valve 61 is opened to form a discharge flow path 300 from the port 54 to the reservoir 4. As a result, the hydraulic pressure in the cylinder 51 is rapidly reduced. In addition, the piston 53 is pressed downward by the preload force of the external mechanism, and the working oil in the cylinder 51 quickly returns to the reservoir from the discharge port 68a via the discharge flow path 300. As a result, the thruster 1 returns to the first operating state.

[0103] Thus, in the thruster 1 according to the embodiment, only the valve mechanism that performs the action by hydraulic pressure can be used, and the working oil in the cylinder tube 51 can be reliably discharged to the reservoir 4, so that it can be restored to the first action state. In addition, the valve mechanism does not require electricity, so it saves electricity. In addition, even if the valve mechanism that does not require power is continuously operated or operated at a high frequency, it is not easy to generate heat, and the viscosity of the working oil will not be reduced. Moreover, if it is a brake device that becomes a braking state in the first action state with the thruster 1 according to the embodiment, the thruster 1 is restored to the first action state when the power is cut off, and the brake device quickly becomes a braking state. Therefore, even if a power outage occurs during the action of any movable device that becomes the braking object of the brake device, such as a crane, the movable device will not stop quickly due to inertia. That is, the brake device of the thruster 1 according to the embodiment has high safety. Of course, malfunction of the thruster 1 caused by external electromagnetic noise will not occur.

[0104] ===Modification of Hydraulic Circuit ===

[0105] The hydraulic circuit of the thruster 1 according to the embodiment is not limited to Figure 4 The specification and usage of the thruster 1 can be appropriately modified according to the performance required of the thruster 1. The following first and second modified examples of hydraulic circuits of the thruster 1 according to the embodiment are modifications of the hydraulic circuits.

[0106] <First Modification>

[0107] In the hydraulic circuit of the thruster 1 according to the embodiment, the pilot pressure becomes zero due to stopping the pump 7, and the discharge flow path 300 is opened via the unloading valve 61. In addition, in the above-mentioned hydraulic circuit, when the pump 7 stops, the residual pressure of the working oil remaining in the flow path from the pump 7 to the check valve 26 may slightly delay the opening timing of the discharge flow path 300 relative to the stop timing of the pump 7, depending on the type and mechanism of the pump 7.

[0108] For example, if the pump 7 is an impeller pump using rotary blades, even if there is residual pressure, it is easy to move in the opposite direction to the pressurization, so the pilot pressure becomes zero more quickly with the stop of the pump 7. On the other hand, when the pump 7 is an internal gear pump or an external gear pump as in the embodiment, the release of the residual pressure may be slightly delayed.

[0109] Therefore, if Figure 6As in the illustrated hydraulic circuit, a flow path 204 is provided which branches from the middle of the pilot flow path 301 and reaches the reservoir 4 via a throttling mechanism 205 such as an orifice, and the flow path resistance of the throttling mechanism 205 interposed in the flow path 204 is set to be much higher than the flow path resistance of the throttling mechanism 27 located in the middle of the pressurizing flow path 201. For example, when the load pressure of the hydraulic cylinder 5 is 20 Bar and the pilot pressure is 5 Bar when the pump 7 is in operation, the pressure difference of the additional throttling mechanism 205 becomes the working pressure of the pressurizing flow path 201, that is, 20 Bar. Furthermore, the flow path resistance of the additional throttling mechanism 205 is set to be very high, so that the flow rate of the working oil leaking from the additional throttling mechanism 205 to the reservoir 4 is small in the working oil discharged from the operating pump 7, and most of the working oil generates a pilot pressure through the pilot pressure generating mechanism 20 and flows toward the port 54 of the hydraulic cylinder 5. Thus, when the pump 7 is operating, the unloading valve 61 is maintained in a closed state by the pilot pressure in the pilot flow path 301 .

[0110] On the other hand, the residual pressure when the pump 7 stops, that is, the hydraulic pressure of the working oil remaining in the flow path from the pump 7 to the check valve 26 and the pilot flow path 301 in the pressurizing flow path 201 is extremely low, so there is almost no flow path resistance caused by the throttle mechanism 205. In other words, the working oil that is the source of the residual pressure easily passes through the throttle mechanism 205, and the residual pressure becomes zero more quickly. Figure 6 In the hydraulic circuit shown, regardless of the type and mechanism of the pump 7, as the pump 7 stops, the internal flow path of the unloading valve 61 is opened more quickly, and the thruster 1 returns to the first operating state at a higher speed.

[0111] In addition, Figure 6 In the hydraulic circuit shown in the figure, the flow path 202c from the relief valve 62 to the reservoir 4 in the pressure regulating flow path 202 and the flow path 203d from the unloading valve 61 to the reservoir 4 in the pressure reducing flow path 203 merge in the manifold block 6, but are not connected to each other. Figure 4 Similar to the hydraulic circuit shown, these flow paths (202c, 203d) are independently formed.

[0112] <Second Modification>

[0113] The thruster 1 involved in the embodiment is configured to maintain the second operating state by allowing the pump 7 to continue to operate. That is, after the pump 7 is switched to the second operating state, the working oil is continued to be discharged at the hydraulic pressure required to resist the preload force of the spring 50 used to restore the hydraulic cylinder 5 to the first operating state and to raise the piston 53. Therefore, in the thruster 1 in which the preload force of the spring 50 is large, the motor 3 that drives the pump 7 continues to operate at a high load, and thus easily becomes high temperature. Therefore, there is a possibility that the working oil will deteriorate. Of course, the power consumption of the motor 3 also increases. Therefore, below, as a second modified example of the hydraulic circuit in the thruster 1 involved in the embodiment, a hydraulic circuit that does not impose a high load on the motor 3 and can reduce the power consumption of the motor 3 can be cited.

[0114] exist Figure 7 A second modified example of the hydraulic circuit in the thruster 1 is shown in FIG. Figure 7 The hydraulic circuit shown is used to illustrate the structure and operation, and the connection block 2 and the manifold block 6 related to the mechanical structure are omitted. Figure 4 , Figure 6 In the hydraulic circuit of the thruster 1 shown in the figure, the pilot pressure generating mechanism 20 is constituted by the throttle mechanism 27 and the check valve 26 connected in series in the middle of the pressurizing flow path 201, but in Figure 7 In the hydraulic circuit shown, the pilot pressure generating mechanism 180 is connected in parallel with the pressurizing flow path 201. The pilot pressure generating mechanism 180 is composed of an unloading relief valve 80 and a throttle mechanism 83. The unloading relief valve 80 is composed of a main valve 81 and a sub-valve 82. The throttle mechanism 83 is composed of a throttle hole and the like. Figure 7 In order to facilitate understanding of the operation of the thruster 1 and the hydraulic pressure at various locations in the hydraulic circuit, the hydraulic circuit includes a hydraulic pressure gauge 181 for measuring the discharge pressure Pa of the pump 7 and a hydraulic pressure gauge 182 for measuring the hydraulic pressure Pb in the flow path from the check valve 26 to the hydraulic cylinder 5 in the pressurizing flow path 201. In addition, the hydraulic pressure Pb measured by the hydraulic pressure gauge 182 is substantially the hydraulic pressure in the hydraulic cylinder 5, and therefore, the hydraulic pressure Pb is sometimes referred to as "cylinder pressure Pb" hereinafter.

[0115] exist Figure 8 The internal structure of the mother valve 81 is shown in Fig. 9 The internal structure of the sub-valve 82 is shown in FIG. Figure 8 and Fig. 9 is a diagram for explaining the operation of the main valve 81 and the sub-valve 82. Figure 8 and Fig. 9On the left side of the paper, the state when the internal flow path between the primary port (811, 821) and the secondary port (812, 822) in the mother valve 81 and the sub-valve 82 is closed and in a loaded state is shown. On the right side of the paper, the mother valve 81 and the sub-valve 82 are shown when the internal flow path is open and in an unloaded state.

[0116] like Figure 8 As shown, the mother valve 81 has a primary port 811 and a secondary port 812 that are connected to each other through an internal flow path and can be freely opened and closed, and a pilot port (hereinafter sometimes referred to as "mother valve pilot port 813") that discharges the working oil flowing into the primary port 811 through a built-in throttle valve 814. Fig. 9 As shown, the sub-valve 82 has a primary port 821 and a secondary port 822 that are connected to each other through an internal flow path and can be freely opened and closed, and a pilot port (hereinafter sometimes referred to as a "sub-valve pilot port 823") that applies hydraulic pressure for controlling the opening and closing of the internal flow path. Figure 8 , Fig. 9 In, with Figure 5A Similarly, the outflow and inflow directions of the hydraulic oil are indicated by black arrows, which are Figure 5B Similarly, the direction of application of hydraulic pressure for opening and closing the valve is indicated by a white hollow arrow. Figure 5A , Figure 5B The unloading valve 61 shown in the figure is similar to the ports (811 to 813, 821 to 823), and also has ports (812, 813, 821, 822), and the ports (812, 813, 821, 822) have a plurality of openings, but Figure 8 , 9 In order to facilitate understanding of the outflow and inflow paths of the hydraulic oil, the outflow and inflow directions of the hydraulic oil are shown for only one opening of a port having a plurality of openings.

[0117] First, the structure of the mother valve 81 is described in detail. Figure 8 As shown, the mother valve 81 is provided with a primary port 811 to which a discharge pressure Pa is applied on one end face side of a hollow cylindrical frame 815, and a secondary port 812 connected to the hollow cylinder and the above-mentioned mother valve pilot port 813 are opened at the side. In addition, a plug 816 is embedded on the other end face side of the frame 815. Here, if the direction of the cylinder axis 110 of the cylindrical frame 815 in the mother valve 81 is set as the up-down direction, and the primary port 811 is set at the lower end side to define the up-down directions, a cylindrical valve column 817 that slides in the up-down direction and a spring 818 that preloads the valve column 817 downward at a relatively weak pressure (e.g., equivalent to 5 Bar) are built in the frame 815.

[0118] A flange-shaped head 817a is formed at the upper end of the valve column 817, and a seat 815a that supports the lower surface 817b of the head 817a is formed in the frame 815 to limit the downward movement of the valve column 817. In addition, the lower end side of the valve column 817 is a cylindrical shape with an outer diameter that is closely attached to the inner surface of the frame 815, and the diameter is reduced halfway from the lower end to the upper side, and the reduced diameter shape is maintained to reach the head 817a. Therefore, in the valve column 817, there is a gap between the side of the cylindrical part directly below the head 817a and the inner surface of the frame 815. A recessed portion (hereinafter, sometimes referred to as "lower recessed portion 817c") with an opening at the lower end is formed below the valve column 817, and the opening of the lower recessed portion 817c becomes the primary port 811. In addition, the inner surface of the lower recessed portion 817c is formed in a shape that connects a cone above the cylinder. On the other hand, a concave portion having a cylindrical inner surface with an open upper end (hereinafter sometimes referred to as "upper concave portion 817d") is formed above the valve stem 817. In addition, a concave portion 816a is formed on the lower end side of the plug 816, which is open downward and has a top surface at the top, and the spring 818 is interposed between the bottom surface of the upper concave portion 817d of the valve stem 817 and the top surface of the concave portion 816a of the plug 816.

[0119] The top of the cone in the lower recess 817c is connected to the lower surface of the upper recess 817d via the throttle valve 814 formed by a thin tubular flow path (throttle hole). In addition, a flow path (hereinafter sometimes referred to as "upper flow path 817e") that communicates with the inner side of the upper recess 817d is formed in the cylindrical area with a reduced diameter just below the head 817a of the valve column 817. In addition, on the side of the valve column 817, in the area on the lower end side that is in close contact with the inner surface of the frame 815, a flow path (hereinafter sometimes referred to as "lower flow path 817f") that communicates with the inner side of the lower recess 817c is formed. In addition, the spring 818 is sandwiched between the lower surface of the plug 816 and the lower surface of the upper recess 817d of the valve column 817.

[0120] Next, the structure of the sub-valve 82 will be described. Fig. 9 As shown, in the sub-valve 82, a hollow cylindrical sleeve 830 is inserted into one end side of a hollow cylindrical frame 824, and a cylindrical valve column 825 that slides along the direction of the cylinder axis 111 is inserted into the sleeve 830. In addition, a ball valve 826 that opens and closes with the sliding of the valve column 825, and a ball seat 828 that holds the ball valve 826 and pre-tightens the ball valve 826 in a direction that attempts to return to a closed state by using a spring 827 are accommodated in the frame 824. In addition, the side surface of the valve column 825 is in close contact with the inner surface of the sleeve 830, and the outer side surface of the sleeve 830 is in close contact with the inner surface of the frame 824. On the other hand, there is a gap between the side surface of the ball seat 828 and the inner surface of the frame 824.

[0121] Here, if the direction of the cylinder axis 111 of the hollow cylindrical frame 824 in the sub-valve 82 is set as the up-down direction, and the sleeve 830 is inserted into the lower end side of the frame 824 to define the up-down directions in the sub-valve 82, the sleeve 830 has openings at both ends, and the opening at the upper end side is reduced in diameter relative to the opening at the lower end side. Moreover, the edge of the opening of the sleeve after the reduction in diameter becomes the valve seat portion 826a as the seat of the ball valve 826. In addition, the primary port 821 of the sub-valve 82 is continuous with the space 829 formed below the valve seat portion 826a of the ball valve 826 in the sleeve 830 from the frame 824. The valve stem 825 is a secondary cylindrical shape with the upper end side reduced in diameter relative to the lower end side, and the upper cylindrical portion after the reduction in diameter protrudes into the space 829 and contacts the ball valve 826. As a result, in the above-mentioned space 829, a filling space for the working oil is formed around the upper cylindrical portion of the valve stem 825. That is, an opening of the valve seat portion 826a is formed above the space 829 in the sleeve 830, and an opening of a hollow portion through which the valve column 825 is inserted is formed below.

[0122] In addition, as in Fig. 9 As indicated by the dotted ellipse, the opening area S2 of the valve seat portion 826a of the sub-valve 82 in contact with the ball valve 826 in the above-mentioned space 829 is smaller than the area S1 of the hydraulic pressure acting on the valve stem 825 in the space 829, that is, the opening area of ​​the lower end side of the sleeve 830 (for example, S2 / S1=0.7). Therefore, the force of the hydraulic pressure of the working oil flowing into the primary port 821 to push the ball valve 826 and the force of the valve stem 825 pressing downward are not equal, and the direction of pushing the ball valve 826 is dominant. In addition, in the hydraulic circuit according to the modified example, the unloading relief valve 80 is constituted by the main valve 81 and the sub-valve 82 of the above-mentioned structure and the flow path connected to these valves (81, 82). In addition, the pilot pressure adjustment mechanism 70 is constituted by the unloading relief valve 80 and the throttle mechanism 83 interposed in the middle of the flow path from the secondary port 822 of the sub-valve 82 to the reservoir 4.

[0123] Next, the operation of the hydraulic circuit of the second modified example will be described. Fig.10 2 is a time chart showing changes in the discharge pressure Pa and the cylinder pressure Pb accompanying the operation of the thruster 1 . Fig.10 The horizontal axis in the figure is the timing (T0 to T3) when the thruster 1 enters a predetermined operating state, and the vertical axis is the hydraulic pressure of the discharge pressure Pa and cylinder pressure Pb at the predetermined timing. Fig.10 In the diagram shown, at T0, the motor 3 is powered on to operate the pump 7, and at T3, the motor 3 is powered off to stop the pump 7. Figure 8 to Figure 10 ,right Figure 7 The operation of the hydraulic circuit shown will be described.

[0124] like Figure 7 As shown in the hydraulic circuit, in the pressurizing flow path 201, the flow path from the pump 7 to the check valve 26, that is, the pilot flow path 301, is connected to the primary port 811 of the mother valve 81. In addition, the mother valve pilot port 813 and the sub-valve primary port 821 are connected. Therefore, the hydraulic pressure of the working oil flowing into the primary port 811 of the mother valve 81 becomes the discharge pressure Pa of the pump 7. In addition, the cylinder pressure Pb is applied to the sub-valve pilot port 823 of the sub-valve 82. In addition, for convenience, the hydraulic pressure applied to the primary port 821 of the sub-valve 82 is called the sub-valve control pressure Pc.

[0125] First, when the pump 7 is stopped, in the mother valve 81, the discharge pressure Pa is not applied to the primary port 811, so the valve rod 817 is pressed down by the preload force of the spring 818, and the lower surface 817b of the head 817a is in contact with the upper surface of the seat 815a formed on the inner side of the frame 815. In this state, the upper flow path 827e and the mother valve pilot port 813, and the lower flow path 817f and the secondary port 812 are all in a closed state. On the other hand, the sub-valve 82 does not apply the cylinder pressure Pb to the sub-valve pilot port 823, so the ball valve 826 is maintained in a state of contact with the valve seat portion 826a by the preload force of the spring 827, and the primary port 821 and the secondary port 822 are in a closed state.

[0126] If the pump 7 is working, then Fig.10 As shown by the solid line in FIG. , the discharge pressure Pa of the pump 7 increases. Fig.10 As shown by the dotted line in FIG. 2 , the cylinder pressure Pb rises slightly later than the discharge pressure Pa due to the time difference from the time point T0 when the pump 7 starts to discharge the working oil to the time when the pressure is increased to the hydraulic pressure (for example, 5 bar) required to pass through the one-way valve 26 of the pressurizing flow path 201. In addition, if the pump 7 is working, the hydraulic pressure to maintain the load state in the unloading valve 61 is lower than the hydraulic pressure required to pass through the one-way valve 26. That is, the unloading valve 61 maintains the load 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.

[0127] More specifically, if the pump 7 is operating, then in the mother valve 81, as in Figure 8 As shown by the dotted arrow in FIG. 8 , the working oil flows into the upper concave portion 817d via the throttle valve 814, and is discharged from the main valve pilot port 813 via the opening on the upper end side of the upper concave portion 817d. Furthermore, the working oil discharged from the main valve pilot port 813 flows into the primary port of the sub-valve 82. In addition, the throttle valve 814 built into the main valve 81 reduces the discharge pressure Pa to be substantially the same as the cylinder pressure Pb. That is, the cylinder pressure Pb≈sub-valve control pressure Pc.

[0128] On the other hand, in the sub-valve 82, the force of the spring 827 to preload the ball valve 826 downward is dominant over the hydraulic pressure of the working oil flowing into the primary port 821, so the ball valve 826 remains closed. Therefore, the discharge pressure Pa continues to rise. In addition, during the rising process of the discharge pressure Pa and the cylinder pressure Pb, if the time point (T1) when the piston 53 starts to rise is reached, the rising tendency becomes slow for a while due to the resistance of the spring 50. Thereafter, if the cylinder pressure Pb overcomes the preload force of the spring 50, the piston 53 at the bottom dead center starts to move to the top dead center, and the discharge pressure Pa and the cylinder pressure Pb continue to rise further.

[0129] The discharge pressure Pa and the cylinder pressure Pb also rise after the piston 53 reaches the top dead center (for example, Pa=87Bar, Pb=82Bar), and at a certain time point (T2), they reach the maximum value (for example, Pa=90Bar, Pb=85bar). Thereafter, the discharge pressure Pa begins to decrease sharply, and the cylinder pressure Pb moves in a manner that almost maintains its maximum value. Moreover, at the time point (T2) when the discharge pressure Pa and the cylinder pressure Pb are at their maximum, the sub-valve control pressure Pc≈85Bar resists the preload force of the spring 818, and pushes the ball valve 826 upward, as shown in FIG. Fig. 9 As shown by the dotted arrow, the internal flow path between the primary port 821 and the secondary port 822 is in an open state, i.e., an unloaded state, via the gap between the ball seat 828 and the inner surface of the frame 824. When the sub-valve 82 is in the unloaded state, the sub-valve control pressure Pc decreases.

[0130] Here, if it is assumed that the cylinder pressure Pb is not applied to the sub-valve pilot port 823, there is a time difference between the increase and decrease trend of the sub-valve control pressure Pc and the increase and decrease trend of the discharge pressure Pa due to the throttle valve 814 of the main valve 81, so at the moment when the sub-valve 82 becomes unloaded and the sub-valve control pressure Pc decreases, a large pressure difference is generated between the high-pressure discharge pressure Pa and the sub-valve control pressure Pc. The sub-valve control pressure Pc is still a force trying to press the valve stem 817 down in the main valve 81, so if the sub-valve 82 becomes unloaded, the valve stem 817 of the main valve 81 is pushed due to the above-mentioned pressure difference, the primary port 811 and the secondary port 812 of the main valve 81 are opened, and the main valve 81 also becomes unloaded. However, at the next moment, in the sub-valve 82, the force of the spring 827 pressing the ball valve 826 down relative to the reduced sub-valve control pressure Pc becomes dominant, and the ball valve 826 is quickly closed, and the sub-valve 82 becomes loaded again. As a result, the sub-valve control pressure Pc is increased, the valve stem 817 of the main valve 81 is pressed down, and the main valve 81 is also restored to the loaded state. That is, when the cylinder pressure Pb is not applied to the sub-valve pilot port 823, the unloading relief valve 80 functions as a relief valve composed of the main valve 81 and the sub-valve 82.

[0131] However, the cylinder pressure Pb is applied to the sub-valve pilot port 823, and the cylinder pressure Pb is maintained by the check valve 26 interposed in the pressurized flow path 201 and the unloading valve 61 in the loaded state. Therefore, at the moment when the sub-valve control pressure Pc, which is also the hydraulic pressure in the above-mentioned space 829 in the sub-valve 82, turns to decrease, the maximum cylinder pressure Pb is applied to the sub-valve pilot port 823. And, in the sleeve 830 of the sub-valve 82, in the above-mentioned space 829 where the working oil contacts the ball valve 826 and the valve rod 825, as described above, the sub-valve control pressure Pc acts as a force that pushes the ball valve 826, according to the size relationship between the area S1 of the valve rod 825 and the opening area S2 of the valve seat portion 826a (S1>S2). Therefore, at the moment when the sub-valve 82 becomes unloaded and the sub-valve control pressure Pc is lower than the cylinder pressure Pb, due to the pressure difference between the high-pressure cylinder pressure Pb applied to the sub-valve pilot port 823 and the reduced-pressure sub-valve control pressure Pc, the valve column 825 is preloaded upward and slides, and the front end of the valve column 825 abuts against the ball valve 826. Moreover, the force accompanying the upward sliding of the valve column 817 acts as a force to further preload the ball valve 826 upward. Thus, the unloaded state of the sub-valve 82 is maintained. If the sub-valve 82 becomes unloaded, the main valve 81 also becomes unloaded as described above. In addition, of course, the cylinder pressure Pb when the sub-valve 82 is maintained in the unloaded state is set to be greater than the cylinder pressure Pb when the piston 53 reaches the top dead center and the thruster 1 becomes the second action state (for example, Pb = 82Bar). Furthermore, if the sub-valve control pressure Pc when the sub-valve 82 is switched to the unload state is set to the cut-off pressure Pco (≈maximum value of Pb) of the unload relief valve 80, the cylinder pressure Pb that cannot maintain the unload state becomes the closed-circuit pressure Pci.

[0132] As described above, in the hydraulic circuit according to the second modified example, when the sub-valve 82 is placed in the unloaded state by the sub-valve control pressure Pc, if the cylinder pressure Pb is greater than the above-mentioned closed circuit pressure Pci, both the main valve 81 and the sub-valve 82 maintain the unloaded state. Furthermore, in the hydraulic circuit according to the second modified example, when both the main valve 81 and the sub-valve 82 are placed in the unloaded state, a hydraulic pressure (for example, 5 Bar) equivalent to the force of the spring 818 attempting to press the valve column 817 downward is applied to the primary port 811 side of the main valve 81 in the unloaded state. In addition, since the throttle mechanism 83 is interposed in the flow path from the secondary port 822 of the sub-valve 82 to the reservoir 4, a hydraulic pressure (for example, 5 Bar) caused by the passage resistance of the throttle mechanism 83 is generated, and this hydraulic pressure acts as the sub-valve control pressure Pc as a force that presses the valve column 817 of the main valve 81 downward. Therefore, in the hydraulic circuit according to the second modified example, even if both the main valve 81 and the sub-valve 82 continue to maintain the unloaded state, the working oil on the primary port 811 side of the main valve 81 is Fig.10As shown, the hydraulic pressure (for example, 10 Bar) is maintained by adding the hydraulic pressure equivalent to the flow resistance between the primary port 811 and the secondary port 812 in the main valve 81 to the hydraulic pressure equivalent to the flow resistance of the throttle mechanism 83 connected to the secondary port 822 side of the sub-valve 82. Moreover, the working oil from the secondary port 822 of the sub-valve 82 via the throttle mechanism 83 and the working oil discharged from the secondary port 812 of the main valve are discharged from the reservoir 4 again from the pump 7. That is, if the unloading relief valve 80 is in the unloading state, the discharge pressure Pa of the pump 7 is only used to maintain the pilot pressure, and the pump 7 is driven at a low load. On the other hand, the discharge flow path 300 for the working oil in the hydraulic cylinder 5 to reach the reservoir 4 via the unloading valve 61 is in a closed state, and the working oil in the pressurization flow path 201 from the pump 7 to the hydraulic cylinder 5 is prohibited from flowing back to the pump 7 side by the check valve 26. Therefore, the cylinder pressure Pb maintains the hydraulic pressure required to continue the second action state.

[0133] Next, if the power supply of the motor 3 is cut off and the pump 7 is stopped (T3), the discharge pressure Pa of the pump 7 disappears, and the pilot pressure also disappears. As a result, the internal flow path of the unloading valve 61 is opened, and the working oil in the hydraulic cylinder 5 returns to the reservoir 4 via the discharge flow path 300, and the pressure Pb decreases sharply. Moreover, in the sub-valve 82, along with the decrease in the cylinder pressure Pb, the hydraulic pressure applied to the sub-valve pilot port 823 also decreases, and the force that attempts to push the valve column 825 against the downward preload force of the spring 827 weakens. Furthermore, if the pressure Pb decreases to the closed circuit pressure (for example, 56 Bar) (T4), the valve column 825 is pressed downward by the spring 827 via the ball seat 828 and the ball valve 826. The ball valve 826 abuts against the valve seat portion 826a, and the internal flow path between the primary port 821 and the secondary port 822 becomes closed.

[0134] In addition, the hydraulic oil in the flow path and the pilot flow path 301 of the pump 7 is connected to the hydraulic oil in the primary port 821 of the sub-valve 82 via the primary port 813 of the main valve and the primary port 811 of the main valve 81. Figure 6 The hydraulic circuit according to the first modification shown above returns to the reservoir 4 via the throttle mechanism 205 disposed in the middle of the flow path 204 connecting the pump 7 and the discharge flow path. This causes the discharge pressure Pa to disappear more quickly. The above is the operation of the hydraulic circuit in the second modification.

[0135] In addition, in the actual hydraulic circuit, it is impossible to completely prevent the leakage of the working oil, so the cylinder pressure Pb will gradually decrease over time. However, in the usual use of the thruster 1, the time for which the second action state is maintained is shorter than the time from when the thruster 1 enters the second action state to when the second action state cannot be maintained due to the decrease in the cylinder pressure Pb over time. Therefore, there is substantially no problem that the cylinder pressure Pb cannot be maintained over time. Of course, the duration of the second action state can also be prolonged by increasing the sealing strength of various parts of the hydraulic circuit or increasing the sealing parts. Therefore, according to the duration of the second action state required in the conceivable use method of the thruster 1, the sealing strength of various parts, the number of sealing parts, etc. can be appropriately determined in the design stage of the hydraulic circuit. By further improving the manufacturing accuracy of the sub-valve 82, the closed-circuit pressure Pci of the sub-valve 82 can also be set to be greater than the pressure when the piston 53 of the hydraulic cylinder 5 reaches the top dead center (for example, 82 bar) and less than the cut-off pressure Pco (for example, 85 bar). Thus, the second operating state can be maintained regardless of the presence or absence of leakage of the hydraulic oil.

[0136] As mentioned above, in Figure 7 The hydraulic circuit shown has a pilot pressure generating mechanism 180, which includes an unloading relief valve 80 composed of a mother valve 81 and a sub-valve 82 and a throttling mechanism 83. Therefore, if the thruster 1 is switched to the second action state, the discharge pressure Pa of the pump 7 is automatically adjusted to a lower hydraulic pressure that maintains the pilot pressure of the unloading valve 61. As a result, even when the preload force of the spring 50 is strong and the cylinder pressure Pb in the second action state needs to be increased, the load of the motor 3 driving the pump 7 is reduced, and the deterioration of the working oil caused by the heat of the motor 3 can be suppressed. In addition, the time for the motor 3 to operate at a high load can be shortened, and the power consumption of the motor 3 can also be reduced. Moreover, in the existing thruster using an electromagnetic valve, since there is power consumption accompanying the connection and disconnection of the electromagnetic valve, Figure 7 The thruster 1 having the hydraulic circuit shown above has a higher effect of reducing power consumption than a conventional thruster when the power supply to the motor 3 is intermittently and frequently turned on and off.

[0137] <Main valve and sub valve cassette structure>

[0138] In the hydraulic circuit of the second modified example, there is an unloading relief valve 80, which is formed by connecting two independent valve mechanisms, a main valve 81 and a sub-valve 82, by a flow path. The flow path connecting the main valve 81 and the sub-valve 82 can also be formed by piping, but if Figure 8 and Fig. 9As shown, the main valve 81 and the sub-valve 82 are plug-type valves having hollow cylindrical frames (815, 824) and Figure 5A and Figure 5B The unloading valve 61 shown is similar to the manifold block 6, the connection block 2, etc., and is configured as a cartridge structure in a manner that can be replaced by inserting and removing from a metal block having a flow path formed therein. Therefore, the unloading relief valve 80 may also be configured as a unit formed by assembling the main valve 81 and the sub-valve 82 into a cartridge structure and assembling the main valve 81 and the sub-valve 82 to a metal block having a flow path formed therein.

[0139] exist Fig.11 FIG. 9 shows a unit 90 in which the mother valve 81 and the sub-valve 82 are configured as a cassette-type unloading relief valve 80. Fig.11 In the unit 90 shown, in addition to the main valve 81 and the sub-valve 82, a pluggable unloading valve 61 and a throttle mechanism 83 (not shown) constituting the pilot mechanism 180 are also assembled. Figure 2 The check valve 26 of the thruster 1 shown, which is assembled to the connection block 2 , is similarly embedded in the flow path in the metal block 91 .

[0140] like Fig.11 As shown, each valve (61, 81, 82) is embedded in the metal block 91 at the lower end thereof so that the ports (611 to 613, 811 to 813, 821 to 823) thereof are arranged in the metal block 91. Fig.11 In order to facilitate understanding of the buried state of each valve (61, 81, 82), each valve (61, 81, 82) is shown in cross section, but the actual buried position of each valve (61, 81, 82) in the front-rear direction of the drawing is sometimes different from each other in the front-rear direction of the drawing. In addition, a flow path is formed in the metal block 91 to connect the pilot flow path 301, the mother valve 81, the sub-valve 82, and the specified ports in the unloading valve 61. In addition, the throttling mechanism 83 is inserted in the middle of the flow path connected to the secondary port 822 of the sub-valve 82. Of course, the metal block 91 constituting the unit 90 may also be the manifold block 6 or the connection block 2.

[0141] In the hydraulic circuit involved in the second variant, in order to realize the function of the unloading relief valve 80, two valves, namely the mother valve 81 and the sub-valve 82, which are linked to each other, are used. Moreover, when any one of the mother valve 81 and the sub-valve 82 is maintained (inspected, replaced, repaired, adjusted, etc.), these valves (81, 82) with a cassette structure can be independently and easily loaded and unloaded relative to the metal block 91. On the other hand, when performing maintenance on the comprehensive function of the unloading relief valve 80, the unit 90 can be removed from the thruster 1. Therefore, the mother valve 81 and the sub-valve 82 are set as a cassette structure, and the unloading relief valve 80 is constructed as a unit 90 in which the mother valve 81 and the sub-valve 82 with a cassette structure are pluggable and installed on the metal block, so that any maintenance can be flexibly handled and the cost required for maintenance can be reduced.

[0142] ===Other Embodiments===

[0143] As an example, the electric hydraulic cylinder (thruster 1) is cited above to illustrate the electric hydraulic actuator according to the present invention, but the present invention is not limited to the above example, and various changes can be made without departing from the scope of the main purpose. Moreover, the above example is described in detail to explain the present invention in an easy-to-understand manner, and is not necessarily limited to all the structures described. In addition, for a part of the structure of the above embodiment, other structures can be added, deleted, or replaced.

[0144] For example, in Figure 4 In the hydraulic circuit shown, discharge ports (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 can also be merged in the manifold block 6 and discharged to the reservoir 4 from one discharge port.

[0145] In the pilot pressure generating mechanism 180 of the hydraulic circuit according to the second modified example, the unloading relief valve 80 is composed of an independent main valve 81 and a sub-valve 82, but the main valve 81 and the sub-valve 82 constituting the unloading relief valve 80 may be integrally formed. Fig.12 8 shows a pilot pressure generating mechanism 180 which is formed by integrating a main valve 81, a sub-valve 82 and a throttle mechanism 83. Fig.12 In, with Figure 7 to Figure 9 The same reference numerals are used to indicate the corresponding structures of the parts and components shown. Fig.12 In FIG. 8 , different hatching lines are used to indicate the parts corresponding to the main valve 81 and the sub-valve 82. Fig.12 The valve body 826 of the sub-valve 82 shown is not a sphere but a cone. In any case, as long as the function and action of the unloading relief valve 80 are the same, its form is not limited.

[0146] A part or all of the flow path constituting the hydraulic circuit may not be formed in a metal block such as the connection block 2 or the manifold block 6, but may be formed using piping. In addition, the unloading valve 61 and the relief valve 62 may not be installed in the manifold block 6, for example, they may be installed in the connection block 2 or inserted in the middle of the piping. Figure 4 The flow paths (201 to 203) corresponding to the hydraulic circuit shown in the figure may be used. In addition, the pump 7 is not limited to an external gear pump, and may be an internal gear pump, an impeller pump, or the like.

[0147] In the above embodiment, the throttling mechanism (27, 83, 205) is not limited to the above throttling hole as a fixed throttling, but can also be a throttling valve as a variable throttling. The throttling valve can fine-tune the opening of the valve body to variably adjust the flow rate. For example, in Figure 4 , Figure 6 In the hydraulic circuit shown, when the pilot pressure set to the unloading valve 61 is not constant depending on the application and specification of the thruster 1, the pilot pressure can be variably set to a desired pilot pressure. On the other hand, throttle valves have individual differences in the relationship between the adjustment amount of the opening and the actual opening of the valve body.

[0148] On the other hand, the individual differences of the throttle holes used as fixed throttling are small. If the thrusters 1 are of the same model, as long as the throttling opening is specified, multiple throttle holes with specified openings can be pre-manufactured, thereby eliminating the need to adjust the openings of multiple thrusters 1 of the same model. As described above, the thruster 1 using the throttle hole as the throttling mechanism can reduce the cost for adjusting the throttling opening. In addition, since the throttle hole has no movable part, it has high reliability and is cheaper than the throttle valve, so the component cost of the thruster 1 can also be reduced. In any case, it is sufficient to adopt an appropriate throttling mechanism (27, 83, 205) according to the specifications of the thruster 1 and the performance required of the thruster 1.

[0149] In the thruster 1 of the above embodiment, the piston 53 is always preloaded downward by a preload mechanism 50 such as an external mechanism connected to the head 12 at the front end of the piston rod 52 of the hydraulic cylinder 5. However, a spring for always preloading the piston 53 downward may be assembled in the cylinder 51. Fig.12 1 shows an example of a hydraulic cylinder 105 with a spring 150 assembled in a cylinder tube 51. Here, the axial direction of the piston rod 52 is set as the up-down direction, and the piston 53 is pushed upward when the pump 7 is operated to define the up-down directions. Fig.12 The piston 53 of the hydraulic cylinder 105 shown is not cylindrical, but is a disk having an upwardly erected edge 151 around it. A spring 150 having a spiral axis in the axial direction of the piston rod 52 is arranged between the upper end inner surface 152 of the cylinder tube 51 and the upper surface 153 of the piston.

[0150] The hydraulic cylinder 5 in the thruster 1 of the above embodiment is configured so that the piston 53 reciprocates in the up-and-down direction, but the hydraulic cylinder 5 may also be configured to reciprocate in a direction intersecting the motor shaft 31 (eg, an orthogonal direction).

[0151] exist Figure 4 , Figure 6 In the hydraulic circuit shown, 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 pass a small hydraulic pressure in the forward direction from the pump 7 to the cylinder 51, while the working oil in the reverse direction from the cylinder 51 to the pump 7 does not flow back due to the function of the check valve 26. Therefore, the check valve 26 is used to pass the working oil in the forward direction when a hydraulic pressure greater than the pilot pressure is applied in the forward direction. As a result, the pilot pressure generating mechanism 20 can be composed of only the check valve 26.

[0152] In addition, when the pilot pressure generating mechanism 20 is composed of only the one-way valve 26, the number of components of the thruster 1 is reduced, and it can be expected that the thruster 1 can be provided at a lower price. On the other hand, since the pilot pressure used to cause the unloading valve 61 to perform an action is a relatively large hydraulic pressure, the one-way valve 26 that prevents the working oil from passing in the forward direction when the hydraulic pressure is lower than this hydraulic pressure naturally becomes a large structure. Therefore, it is difficult to miniaturize the thruster 1. In any case, the structure of the pilot pressure generating mechanism 20 can be appropriately determined according to the manufacturing cost or specifications required by the thruster 1. In any case, the structure of the pilot pressure generating mechanism 20 can be appropriately determined according to the manufacturing cost and specifications required by the thruster 1.

[0153] The thruster 1 shown as an embodiment has a hydraulic cylinder 5 as a hydraulic actuator, but the hydraulic actuator may not be a direct-acting hydraulic actuator in which a movable part such as a piston 53 reciprocates in a linear direction like the hydraulic cylinder 5. For example, the hydraulic actuator may be a hydraulic actuator having a rotor that rotates at a predetermined angle by hydraulic pressure as a movable part in a sealed stator, and may have a structure having a movable part that rotates. Moreover, the electric hydraulic actuator having such a hydraulic actuator in which the movable part rotates may be configured to reciprocate between a first operating state and a second operating state, wherein the first operating state corresponds to the rotation angle position of the rotor when the stator is not pressurized by the working oil, and the second operating state corresponds to the rotation angle position when the stator is filled with fully pressurized working oil and the rotor rotates by a predetermined angle from the first operating state. In addition, as a preload mechanism in the electric hydraulic actuator having a movable part that rotates by hydraulic pressure, for example, a coil spring that always preloads the rotor at the rotation position that becomes the first operating state may be considered.

[0154] Of course, the working fluid in the electric hydraulic actuator is not limited to hydraulic oil, and water, air, steam, etc. may be used as long as it can generate hydraulic pressure for causing the hydraulic actuator to operate.

[0155] Description of the label

[0156] 1 thruster (electrohydraulic actuator, electrohydraulic cylinder),

[0157] 2 connection block, 3 motor, 4 reservoir, 5, 105 hydraulic cylinder,

[0158] 6 manifold block, 7 pumps, 11 hooks, 12 heads,

[0159] 20, 180 pilot pressure generating mechanism, 21 communicating hole, 23 connecting member, 24 inlet,

[0160] 25 outflow port, 26 one-way valve, 27, 73, 205 throttling mechanism,

[0161] 31 motor shaft, 50 preload mechanism, 51 cylinder barrel,

[0162] 52 piston rod, 53 piston, 54 (hydraulic cylinder 5) port,

[0163] 61 unloading valve, 62 overflow valve, 68a, 68b discharge port,

[0164] 80 unloads the relief valve, 81 unloads the mother valve of the relief valve,

[0165] 82 unloading relief valve sub-valve, 150 spring (preload mechanism),

[0166] 90 a unit including an unloading relief valve, 91 a metal block,

[0167] 201 is a pressurizing flow path, 201a and 201b constitute a flow path of the pressurizing flow path,

[0168] 202 is a pressure regulating flow path, 202a to 202c constitute a flow path for the pressure regulating flow path,

[0169] 203 pressure reducing flow path,

[0170] 203a to 203f and 301 constitute a pilot flow path for the pressure reducing flow path.

[0171] 300 constitutes a discharge flow path for the pressure reducing flow path, 811 is a primary port of the mother valve,

[0172] 812 secondary port of the mother valve, 813 pilot port of the mother valve, 814 throttle valve,

[0173] 815 mother valve frame, 817 mother valve stem, 818 mother valve spring,

[0174] The pilot port of the 823 sub-valve, the primary port of the 821 sub-valve,

[0175] 822 secondary port of sub-valve, 824 frame of sub-valve, 825 valve column of sub-valve,

[0176] 826 ball valve, 827 sub valve spring

Claims

1. An electro-hydraulic actuator comprising: a motor, which outputs rotational power; a pump that is actuated by the rotational power of the motor; a hydraulic actuator that performs an action using a working fluid pressurized by the pump; a fluid reservoir storing the working fluid; and a fluid circuit for controlling the action of the hydraulic actuator by hydraulic pressure, The hydraulic actuator reciprocates between a first operating state and a second operating state according to the hydraulic pressure of the supplied working fluid, and is always biased in a direction to return to the first operating state. The fluid circuit comprises: a pressurizing flow path for supplying the working fluid pressurized by the pump to a hydraulic actuator; a pressure reducing flow path which connects the hydraulic actuator and the accumulator via an unloading valve so as to be openable and closable; a pilot flow passage for supplying hydraulic oil pressurized to a pilot pressure to the unloading valve in order to close the pressure reducing flow passage; a pilot pressure generating mechanism, which is used to generate the pilot pressure; and a check valve disposed in the middle of the pressurizing flow path and configured to allow the working fluid to pass only in a forward direction from the pump toward the hydraulic actuator; The pilot pressure generating mechanism generates the pilot pressure during the operation of the pump. 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 the operation of the pump to enter the second operation state. When the pump is stopped, the pilot pressure disappears and the pressure reducing flow path is opened to return to the first operation state.

2. The electro-hydraulic actuator according to claim 1, wherein: A throttle mechanism and the check valve constituting the pilot pressure generating mechanism are sequentially arranged in the middle of the pressurizing flow path from the pump to the hydraulic actuator.

3. The electro-hydraulic actuator according to claim 2, wherein: The throttling mechanism is a throttling hole.

4. The electro-hydraulic actuator according to claim 1, wherein: The check valve also serves as the pilot pressure generating mechanism. The check valve sends the working fluid toward the hydraulic actuator when the working fluid supplied from the pump reaches a predetermined pilot pressure or higher.

5. The electro-hydraulic actuator according to claim 1, wherein: The pilot pressure generating mechanism is composed of an unloading relief valve and a throttling mechanism, and the unloading relief valve is composed of a main valve and a sub-valve. The mother valve has a built-in throttle valve, a mother valve primary port connected to the pilot flow path, a mother valve secondary port connected to the flow path connected to the reservoir, and a mother valve pilot port connected to the mother valve primary port via the throttle valve, and the specified direction is set as the up and down direction, and has a mother valve column preloaded upward by the hydraulic pressure at the mother valve primary port and a mother valve spring preloaded downward. The sub-valve has a sub-valve primary port connected to the mother valve pilot port, a sub-valve secondary port connected to the flow path connected to the reservoir via the throttling mechanism, and a sub-valve pilot port connected to the flow path from the check valve to the hydraulic actuator, and the specified direction is set as the up and down direction, and has a valve body preloaded upward by the hydraulic pressure at the sub-valve primary port, a sub-valve valve column preloaded upward by the hydraulic pressure at the sub-valve pilot port, and a sub-valve spring preloading the valve body downward. The sub-valve is set to P2>P3, so that the hydraulic pressure P1 at the primary port of the sub-valve is dispersed into the hydraulic pressure P2 that presses the valve body upward and the hydraulic pressure P3 that presses the sub-valve valve column downward, and if the hydraulic pressure P1 reaches the specified circuit-breaking pressure, the valve body is pressed in one direction, so that the primary port of the sub-valve and the secondary port of the sub-valve are opened and become an unloading state, The mother valve utilizes the pressure difference between the hydraulic pressure P1 on the mother valve pilot port side and the hydraulic pressure P5 on the mother valve primary port side which is reduced in pressure accompanying the unloading state of the sub-valve to press the mother valve column upward so that the connection between the mother valve primary port and the mother valve secondary port is opened to become an unloading state. If the sub-valve is in the unloaded state, the unloaded state is maintained by the hydraulic pressure P4 at the sub-valve pilot port. If both the mother valve and the sub-valve are in the unloaded state, the hydraulic pressure P5 is maintained as the pilot pressure by utilizing the hydraulic pressure P1 generated by the resistance of the throttling mechanism and the hydraulic pressure generated by the mother valve spring pre-tightening the mother valve valve column downward, and the hydraulic pressure P4 is utilized to maintain the hydraulic actuator in the second action state.

6. The electro-hydraulic actuator according to claim 5, wherein: The unloading relief valve is an integrated unit formed by installing the main valve and the sub-valve on a metal block forming a flow path of the working fluid. The main valve and the sub-valve are box-type structures that are detachably mounted on the metal block.

7. The electro-hydraulic actuator according to claim 6, wherein: The throttle mechanism is interposed in the middle of a flow path formed in the metal block, and the unit constitutes the pilot pressure generating mechanism.

8. The electro-hydraulic actuator according to claim 1, wherein: The fluid circuit has a flow path that branches from the pilot flow path and reaches the reservoir via a throttle mechanism. The throttling mechanism has a flow resistance higher than the flow resistance of the pilot pressure generating mechanism when the pump is in operation, and eliminates the residual pressure of the working fluid remaining in the flow path from the pump to the pilot pressure generating mechanism and the pilot flow path in the pressurizing flow path when the pump stops.

9. The electro-hydraulic actuator according to any one of claims 1 to 8, wherein: The hydraulic actuator is a direct-acting hydraulic actuator. When the piston of the direct-acting hydraulic actuator is at the bottom dead center, the first operating state is achieved. When the piston is at the top dead center, the second operating state is achieved. The piston is biased in a direction to reach a bottom dead center by an external mechanism connected to the front end of the piston rod.

10. The electro-hydraulic actuator according to any one of claims 1 to 8, wherein: The hydraulic actuator is a direct-acting hydraulic actuator. When the piston of the direct-acting hydraulic actuator is at the bottom dead center, the first operating state is achieved. When the piston is at the top dead center, the second operating state is achieved. A spring mechanism is provided for always pre-tensioning the piston toward the bottom dead center.

11. A brake device comprising the electro-hydraulic actuator according to claim 9, The brake device has a brake mechanism for pressing or isolating brake friction linings on both sides of a disc-shaped brake disc. The braking mechanism is always preloaded in the direction of the braking state. The electro-hydraulic actuator releases the braking state of the brake disc when in the second operating state, and puts the brake disc into the braking state when in the first operating state.

12. A brake device comprising the electro-hydraulic actuator according to claim 10, The brake device has a brake mechanism for pressing or isolating brake friction linings on both sides of a disc-shaped brake disc. The brake mechanism releases the braking state of the brake disc when in the second operating state, and puts the brake disc into the braking state when in the first operating state.

Images