Hydraulic actuator with overpressure compensation

Abstract

The present invention relates to a hydraulic actuator comprising a variable displacement pump (12) and a member (20) capable of continuously varying the delivery of the pump (12), the member (20) being driven by a ram (40) supplied by a first directional control valve (48) commanded on the basis of a movement command of the actuator (10). According to the present invention, the actuator (10) comprises a second directional control valve (60) commanded based on the output pressure (P) of the pump (12), the second directional control valve (60) having two positions, one of which (60a) is known as the rest position and is obtained as long as the output pressure (P) of the pump (12) is below a predetermined pressure, and transmits the output from the first directional control valve (48) to the double-acting ram (40), and the other (60b) is called the operating position and transmits the output pressure (P) of the pump (12) to the ram (40) without going through the first directional control valve (48) so as to reduce the output pressure (P) of the pump (12).

Description

[Technical Field]

[0001] The present invention relates to hydraulic actuators. This type of actuator is widely used to move moving elements. The use of hydraulic energy offers advantages over electrical energy due to its very good ratio between the power supply and the mass of the actuator. Another advantage resides in the very good ratio between the power supply and the volume of the actuator. [Background technology]

[0002] Furthermore, actuators employing electric motors are only well suited for high speeds and low torques. In certain applications, particularly robotics, the opposite situation, i.e., low speed and high torque, is often encountered. Therefore, the use of electric motors for low speeds requires large reduction ratios that are complicated to achieve with fixed and limited reduction ratios.

[0003] Furthermore, in the use of any actuator, whether hydraulic or electric, it is often necessary to provide for limiting the load or speed exerted by the actuator. The limiting may be achieved by an actuator control loop comprising a sensor measuring the load or speed, the sensor being associated with a controller making it possible to adjust the command of the actuator according to the output signal from the sensor and a load or speed set point that must not be exceeded.

[0004] This type of limit is often linked to the operational safety of the actuator, in particular to undesirable events, in order to protect the surroundings of the actuator, and also makes it possible to protect the actuator from external attacks.

[0005] This type of limit can be built into the actuation control loop. For example, when the actuation of an actuator requires feedback control over the angular position of the actuator's rotor, it is possible to benefit from the presence of an actuation feedback control loop that incorporates a safety limit therein, for example to limit the force provided by the actuator. However, often the actuation parameters and the safety parameters are different, due to different requirements regarding response time, stability, etc., in which case it is necessary to provide two sensors (one for each of the parameters).

[0006] Furthermore, in the case of open loop operation, it may be necessary to provide a control loop alone to control the safety parameters. Summary of the Invention [Problem to be solved by the invention]

[0007] In general, actuation and / or safety control loops have a number of drawbacks. First, the sequence connecting the measured quantity and the actuator command is long, which tends to increase the response time. This can be problematic in responding to unexpected momentary loads, such as shocks. Furthermore, the multiple components required to create the control loop often lead to reduced actuator reliability. Furthermore, for safety loops designed to protect against shocks, it is necessary to position the shock sensor as close as possible to the area susceptible to shock. This area is often far from the actuator, which increases the length of the path that information must take between the sensor and the actuator. This length reduces the actuator's response in the event of a shock. Furthermore, the length of the path tends to reduce the reliability of the safety loop. [Means for solving the problem]

[0008] The present invention seeks to solve all or part of the above-mentioned problems by proposing a hydraulic actuator that makes it possible to dispense with the control loop in order to prevent the effects of overpressures that arise, which overpressures are generally associated with too high forces, e.g. impacts.

[0009] The present invention allows for the actuator's response time to be reduced in the event of abnormal actuation without compromising its reliability.

[0010] To this end, the subject of the present invention is a hydraulic actuator comprising a variable displacement pump, a first directional control valve commanded on the basis of an actuator movement command, and a ram supplied by the first directional control valve, the pump comprising a movable member whose movement allows the pump delivery to be continuously varied, the member being movable with the ram, the first directional control valve being capable of applying a continuous function relating the movement command to the pump delivery via the position of the member as it moves. According to the invention, the actuator comprises a second directional control valve commanded on the basis of the pump output pressure, the second directional control valve having two positions, one of which is known as the rest position and is obtained as long as the pump output pressure is below a predetermined pressure, and transmits the output from the first directional control valve directly to the double-acting ram, thereby allowing the pump to follow the continuous function, and the other, called the working position, is obtained when the pump output pressure is equal to or greater than the predetermined pressure and transmits the pump output pressure to the ram without going through the first directional control valve and without following the continuous function, so as to reduce the pump output pressure.

[0011] Advantageously, the predetermined pressure is adjustable.

[0012] The member may be configured to allow the pump to reverse its direction of delivery.

[0013] Advantageously, the ram comprises two chambers, in which case the actuator comprises a third directional control valve configured to transmit the output pressure of the pump to one or the other of the two chambers depending on the direction of delivery of the pump.

[0014] The hydraulic actuator advantageously further comprises a valve set configured to command the second directional control valve with the maximum output pressure of the pump.

[0015] The ram advantageously comprises a movable rod connected to the body of the first directional control valve.

[0016] The movable rod may be connected to the body of the first directional control valve by a telescopic connection.

[0017] The pump may be a piston pump with an axial piston, the member allowing the variation of the delivery being a swash plate with variable inclination against which the piston presses, the stroke of the piston being variable by varying the inclination of the swash plate, the inclination of the swash plate being adjusted by a ram driven by a microactuator which defines an actuator command through a first directional control valve, as long as the output pressure of the pump is lower than a predetermined pressure.

[0018] The hydraulic actuator advantageously comprises a casing in which are located a pump, a motor enabling the pump to be operated, a member enabling the pump's delivery to be continuously varied, a ram for operating the member, a first directional control valve supplying the ram, and microactuators for operating the first and second directional control valves. The actuator further comprises at least one electrical connector passing through the casing and enabling the actuator to receive electrical energy for operating the motor and electrical signals for driving the microactuators, and a hydraulic connector passing through the casing and enabling the actuator to deliver hydraulic energy.

[0019] Alternatively, the hydraulic actuator advantageously comprises a casing in which are located a pump, a motor enabling the pump to be operated, a member enabling the pump delivery to be continuously varied, a ram for operating the member, a first directional control valve supplying the ram, and microactuators for operating the first and second directional control valves, the actuator further comprising at least one electrical connector passing through the casing and enabling the actuator to receive electrical energy for operating the motor and electrical signals for driving the microactuators, and a mechanical output passing through the casing and enabling the actuator to deliver mechanical energy.

[0020] The electrical connector advantageously enables the actuator to receive a second electrical signal to drive a regulator at a predetermined pressure.

[0021] The first directional control valve may have a neutral position in which the member is stationary and does not change the pump delivery, and two operating positions in which the member moves and changes the pump delivery. The directional control valve is advantageously configured so that the transition between the neutral position and one of the operating positions occurs continuously.

[0022] The invention will be better understood and further advantages will become apparent from reading the detailed description of one embodiment thereof, given by way of example only, and illustrated in the accompanying drawings, in which: [Brief explanation of the drawings]

[0023] [Figure 1] 1 shows an example of an actuator according to the present invention in the form of a hydraulic diagram. [Figure 2] The actuator of FIG. 1 is shown so that details of the directional control valve can be seen. [Figure 3] 1 shows a schematic representation of the main elements of the actuator. DETAILED DESCRIPTION OF THE INVENTION

[0024] For clarity, identical elements are labeled with the same reference numbers in the various figures.

[0025] There are various types of variable displacement pumps that can be employed in actuators according to the present invention.

[0026] The first type of pump, called a radial piston pump, has a shaft driven to rotate around its axis, a hub with a cylindrical bore, and pistons that move in radial cylinders in the shaft. The pistons slide along the inner surface of the bore. The eccentricity between the axis of the shaft and the axis of the bore allows the pistons to move within their cylinders. In this type of pump, it is the movement of the pistons within their cylinders that drives the fluid. The pump's delivery can be modified by adjusting the eccentricity.

[0027] A second type of pump, called a vane pump, similarly employs an eccentric shaft that rotates in a bore in a hub. The piston is replaced by a sliding vane that slides on the inside surface of the bore. The eccentricity of the shaft and bore increases or decreases the volume located between the two vanes, allowing fluid to flow in or out. Again, pump delivery can be modified by adjusting the eccentricity.

[0028] A third type of pump, called an axial piston pump, can also vary fluid delivery continuously. This type of pump also has a shaft driven to rotate about its axis. Cylinders parallel to the axis are created within the shaft. Pistons move within the cylinders. The pump also has a swashplate that is inclined relative to a plane perpendicular to the axis of rotation of the shaft. The pistons press against the swashplate. The inclination of the swashplate allows the pistons to move within their cylinders. Pump delivery can be modified by adjusting the inclination of the swashplate.

[0029] Generally, the movement of a moving part of a pump modifies its delivery. In the case of a radial piston pump or vane pump, the moving part is fixed to the shaft, and the movement of the part is a translational movement perpendicular to the axis of the bore, so as to correct the eccentricity of the pump. In the case of an axial piston pump, a swash plate forms the moving part, and the movement of the part is an angular movement of the swash plate relative to a plane perpendicular to the axis of rotation of the shaft. In various variable displacement pumps, the pump delivery depends on the position of the part, and the movement of the part provides a continuous modification of the pump delivery. Therefore, it is possible to define a continuous function that relates the actuator movement command or set point to the pump delivery via the position of the part as it moves. This continuous function may be linear, i.e., defined by a proportionality coefficient. Alternatively, the function may follow a nonlinear curve, provided that it remains continuous, i.e., does not contain step changes.

[0030] 1 shows in hydraulic diagram form an example of an actuator 10 comprising an axial piston pump. As noted above, the present invention can be practiced with any type of variable displacement pump.

[0031] The actuator 10 includes an axial piston pump 12 with a shaft 14 that is driven to rotate about an axis 16 by a motor (not shown in FIG. 1). Several cylinders 18 extending parallel to the axis 16 are formed within the shaft 14. The pump 12 includes a swash plate 20 that can be tilted relative to a plane 22 perpendicular to the axis 16. The inclination α of the swash plate 20 is defined about an axis 23 perpendicular to the axis 16. The swash plate 20 is capable of rotational movement about the axis 23 so that the inclination α can be varied. The zero inclination α of the swash plate 20 is defined as when the swash plate is perpendicular to the axis 16, i.e., when the swash plate 20 extends within the plane 22. Pistons 24 may move within each cylinder 18. The pistons 24 press against the swash plate 20. The swash plate 20 forms a member that allows the delivery of the pump 12 to be continuously varied by changing the inclination α of the swash plate 20 relative to the plane 22. The swash plate 20 does not rotate with the shaft 14. When the swashplate 20 is perpendicular to the axis 16, the pistons 24 do not move within their cylinders 18 and the delivery of the pump 12 is zero. In contrast, when the tilt α of the swashplate 20 is non-zero, the pistons move within their cylinders 18 and perform a substantially sinusoidal reciprocating cycle over one revolution of the shaft 14. This cycle of movement enables the pump 12 to move fluid.

[0032] The pump 12 includes a fixed end plate 26 against which the shaft 14 abuts. The end plate includes two orifices 28 and 30, each generally half-moon shaped, penetrating the end plate 26 on opposite sides of the cylinder 18. As the shaft 14 rotates, the piston 24 facing one of the orifices moves away from the end plate 26, forming an inlet orifice. In contrast, as the shaft 14 rotates, the piston 24 facing the other orifice moves closer to the end plate 26, forming a discharge orifice. Changing the sign of the slope α switches the delivery and inlet of the pump 12. Alternatively, it is possible to maintain the same sign of the slope α but reverse the rotation of the shaft 14 about the axis 16 to reverse the flow through the orifices 28 and 30.

[0033] The actuator 10 includes a ram 32 that forms the mechanical output of the actuator 10. More specifically, the actuator receives energy, e.g., in the form of electricity, and transmits the mechanical energy through the ram 32, rotating the shaft 14, e.g., via an electric motor. In FIG. 1, the ram 32 is a linear ram. Of course, a rotary ram could be used instead. The ram 32 includes two chambers 34 and 36, each connected to one of the orifices, which are connected to the orifices 28 and 30, respectively. The pressure difference between the two orifices 28 and 30, achieved by a non-zero slope α, causes the rod 38 of the ram 32 to move in one direction. Changing the sign of the slope α reverses the movement of the rod 38. When the slope α becomes zero, the pressures between the two orifices 28 and 30 become equal, and the rod 38 is stationary.

[0034] In the example shown, the ram 32 is a double-acting ram. A single-acting ram could also be employed. In that case, it would be possible to implement a pump 12 in which the slope α changes sign by connecting one of the pump 12 orifices to the tank. As mentioned above, it would also be possible to reverse the direction of rotation of the shaft 14.

[0035] Ram 32 may be a symmetrical ram, in which hydraulic fluid in each of chambers 34 and 36 acts on the same surface area of ​​the piston. A ram 32 is symmetrical when its rod 38 exits the two chambers and maintains the same cross-section, as shown in Figure 1. Alternatively, an asymmetrical ram can be employed, for example, when rod 38 exits ram 32 on only one side of the piston.

[0036] The swash plate 20 is moved by a ram 40, which in the example shown is a double-acting ram. Alternatively, a single-acting ram with a return spring may be employed. A rotating ram may also be used. The ram 40 comprises two chambers 42 and 44, each of which is supplied with fluid. The ram 40 is connected to the swash plate 20 so that the difference in fluid pressure between the two chambers 42 and 44 modifies the swash plate inclination α. of The rod 46 can be moved.

[0037] Rams similar to the ram 40, which allow the eccentricity of the pump to be varied, are found in radial piston or vane pumps.

[0038] The ram 40 is fed by a directional control valve 48, which is commanded based on the movement command of the actuator 10. More specifically, the directional control valve 48 is connected to two fluid pressure sources: a high-pressure source P and a low-pressure source T. The directional control valve 48 may have three positions. In a neutral position 48a, the directional control valve 48 closes access to chambers 42 and 44, and the swashplate 20 remains stationary. Its orientation α remains unchanged. In one position 48b, the high-pressure source P is connected to chamber 44 and the low-pressure source T is connected to chamber 42. With the swashplate 20 positioned as shown in FIG. 1, position 48b tends to decrease the value of orientation α. ​​Conversely, in one position 48c, the high-pressure source P is connected to chamber 42 and the low-pressure source T is connected to chamber 44; with the swashplate 20 positioned as shown in FIG. 1, position 48c tends to increase the value of orientation α.

[0039] The high pressure source P and the low pressure source T may be generated independently of the pump 12. However, this increases the complexity of the actuator 40, which must be supplied from an external pressure source. To avoid these external sources, it is advantageous to use the pump 12 to create the two pressure sources P and T. By selecting a pump 12 whose slope α always maintains the same sign, the orifices 28 and 30 always maintain a pressure difference in the same direction. Therefore, it is possible to generate the high pressure source P and the low pressure source T directly from the orifices 28 and 30, respectively. To maintain a minimum pressure in the high pressure source P, a check valve can be provided between the discharge orifice and a micro-reservoir forming an accumulator for the high pressure source P. The check valve is rated according to the pressure desired for the high pressure source P. Thus, the accumulator is supplied with fluid only when the pressure at the discharge orifice is sufficient. This pressure is coupled to the minimum slope α.

[0040] In contrast, when the slope α is prone to positive and negative values, the pressure difference between the two orifices 28, 30 may be positive or negative. Nevertheless, it is desirable to generate pressure sources P and T from the two orifices 28, 30. To that end, the actuator 10 includes a valve set 52 configured to supply the high-pressure source P from the orifice 28 or 30 where the higher pressure prevails, and to supply the low-pressure source T from the orifice 28 or 30 where the lower pressure prevails. To that end, the valve set includes four valves: one valve 52a is positioned between the orifice 28 and the source P, one valve 52b is positioned between the orifice 30 and the source P, one valve 52c is positioned between the orifice 28 and the source T, and one valve 52d is positioned between the orifice 30 and the source T. The orientation of the four valves may be best understood by analogy with an electrical circuit in which the set of valves form a full rectifier bridge, with an AC voltage formed between orifices 28 and 30 and a DC voltage formed between sources P and T. The orientation of valves 52a-52d is analogous to the orientation of the diodes in the rectifier bridge.

[0041] The actuator 10 includes a means for limiting the effects of overpressure at the outlet of the pump 12. Such overpressure may be due to an internal malfunction of the actuator or an external event, such as an impact on the rod 38 of the ram 32. Naturally, other sources of overpressure may produce adverse effects that must be limited. To this end, the actuator 10 includes a second directional control valve 60 commanded based on the outlet pressure of the pump 12. The directional control valve 60 has two positions: one, called the rest position 60a, is obtained as long as the outlet pressure of the pump 12 is below a predetermined pressure; the other, called the operating position 60b, is obtained when the outlet pressure of the pump 12 is equal to or greater than a predetermined pressure. This predetermined pressure creates a lower pressure limit than the actuator 10 would normally operate at. In the rest position 60a, the directional control valve 60 transmits the outlet pressure directly from the directional control valve 48 to the chamber of the ram 40. When the outlet pressure of the pump 12 reaches or tends to exceed a predetermined pressure, in the operating position 60b, the directional control valve 60 transmits the high outlet pressure of the pump 12 to one of the chambers 42 or 44 of the ram 40 so as to decrease the inclination α of the swashplate 20 to reduce the outlet pressure of the pump 12. In practice, it is the high pressure source P that is connected to one of the two chambers without passing through the directional control valve 48. The other chamber may be connected to a low pressure source T or sump 61, as shown in FIG. 1. The sump 61 is at atmospheric pressure. In practice, the low pressure T is approximately equal to atmospheric pressure.

[0042] When the output pressure of pump 12 drops below a predetermined pressure value, directional control valve 60 returns to rest position 60a and directional control valve 48 once again directly commands ram 40. The transition of directional control valve 60 between its two positions 60a and 60b is dictated by the output pressure of pump 12.

[0043] In the event of an overpressure, the directional control valve 60 bypasses the directional control valve 48. In other words, the high pressure P is connected to the ram 40 to reduce the high pressure P when the output pressure P of the pump 12 is equal to or greater than a predetermined pressure. A continuous function relating the actuator 10 movement command to the pump's delivery through the directional control valve 48 is disabled. This continuous function represents the nominal operation of the actuator 10. The function override occurs in the event of an overpressure, which is associated with abnormal operation of the actuator 10. By implementing the present invention, the override of the continuous function by bypassing the directional control valve 48 eliminates the need to install a pressure sensor measuring the output pressure of the pump 12 to detect overpressure. Such a pressure sensor could affect the command of the directional control valve 48. By bypassing the directional control valve 48, the present invention allows the pump 12 to react much more quickly.

[0044] It is advantageous to use a pressure source P that directly commands the directional control valve 60. Without the use of a pressure sensor, the response of the actuator 10 to an overpressure is rapid. The only vehicle for this response is the change in position of the directional control valve 60.

[0045] The value of the predetermined pressure at which the directional control valve 60 changes position can be fixed and determined during the design of the actuator 10. To that end, the directional control valve 60 comprises a movable slide pressed by a spring 62. As long as the pressure P is lower than the predetermined pressure, the spring 62 is rated to press the slide so as to maintain the directional control valve 60 in the rest position 60a. When the pressure P reaches or exceeds the predetermined pressure, the command of the directional control valve 60, which is executed through the pressure P, can compress the spring 62, tending to move the slide to reach the operating position 60b. The constant of the spring 62 may be set during the design of the actuator 10.

[0046] It is possible to adjust the predetermined pressure by providing the possibility to modify the constant of the spring 62. The spring constant may be adjusted manually, for example, by means of a screw that allows the length of the spring 62 to be modified. The screw is advantageously accessible from the outside of the actuator 10 so that the operator can make the adjustment. It is also possible to motorize the adjustment so that a command, for example an electrical command, is used to adjust the predetermined pressure. To this end, a stepper motor 64 that turns the screw can be provided. A linear motor may also act directly on the spring 62. In addition to the spring 62, other mechanical components, in particular dampers, can be added to introduce a time constant into the response of the directional control valve 60 when an overpressure occurs. It is therefore possible to ignore certain overpressures that are determined to be too short.

[0047] For example, in the position of swashplate 20 shown in FIG. 1, where the inclination α is considered positive, if an overpressure occurs, directional control valve 60 can supply chamber 44 from source P to decrease inclination α, moving swashplate 20 closer to plane 22. In other words, rod 46 of ram 40 moves to the left in the illustration of FIG. 1. Conversely, if an overpressure occurs when inclination α is negative, it is necessary to supply chamber 42 from source P to move rod 46 to the right. More generally, if an overpressure occurs, it is necessary to decrease the stroke of piston 24. In other words, if an overpressure occurs, it is necessary to decrease the absolute value of inclination α. ​​The selection of whether to supply chamber 42 or 44 to move swashplate 20 in one direction or the other may be obtained automatically using a third directional control valve 68 commanded by inclination α. The directional control valve 68 allows either supplying chamber 44 from the high-pressure source P and connecting chamber 42 to the sump 61, or reversing the supply of the two chambers according to the sign of the tilt α. The directional control valve 68 has at least two positions, 68a without reversal and 68b with reversal. The directional control valve 68 may also have an intermediate third position 68c in which the supply circuits for both chambers 42 and 44 are open. This position corresponds to a zero value of the tilt α. The directional control valve 68 is commanded by the value of the tilt α. To that end, the command of the directional control valve 68 may be performed using a linkage 70 connecting the swashplate 20 and a movable slide of the directional control valve 68.

[0048] 2 shows the three directional control valves 48, 60, and 68 in more detail. The various positions that define the connections that each of the three directional control valves can make are achieved by a movable slide within the body. Movement of the slide opens or closes a particular hydraulic circuit as needed.

[0049] The directional control valve 48 comprises a body 80 and a slide 82 movable within the body 80 under the action of a microactuator 83. The microactuator 83 allows the slide 82 to move relative to a casing 84 of the actuator 10. In FIG. 2, the slide 82 is shown in a central position relative to the body 80. This position forms the neutral position 48a of the directional control valve 48, in which the slide 82 blocks the hydraulic outlet ducts of the directional control valve 48 that supply chambers 42 and 44 of the ram 40. In other words, in normal operation, i.e., as long as the high pressure P does not reach the pressure limit, the inclination α of the swashplate 20 remains unchanged. When the slide 82 is pushed to the right, the directional control valve 48 reaches a position 48b in which the high pressure P is supplied to chamber 44. Conversely, when the slide 82 is pushed to the left, the directional control valve 48 reaches a position 48c in which the high pressure P is supplied to chamber 42. The positions of the slide valve 82 may be discrete. Advantageously, however, the slide 82 moves continuously between its three positions. More specifically, the microactuator 83 allows the slide 82 to be positioned at any intermediate position between the neutral position 48a and one of the positions 48b or 48c. In positions 48b or 48c, the directional control valve 48 fully opens the hydraulic circuit supplying the chambers 42 and 44. Thus, in the intermediate positions, the directional control valve only partially opens the hydraulic circuit, forming a restriction on the supply of the chambers 42 and 44. Therefore, the rate at which the tilt α of the swashplate 20 changes can be controlled.

[0050] Furthermore, the ram 40 comprises a body 86 in which a piston 88 moves, which separates the two chambers 42 and 44. The rod 46 is fixed to the piston 88. The body 86 is fixed to the casing 84.

[0051] The body 80 of the directional control valve 48 may be fixed to a casing 84. In normal use, to move the swashplate 20 between two values ​​of tilt α, as long as the output pressure of the pump 12 remains below a predetermined pressure limit, it is necessary to provide two steps in command of the microactuator 83: a first step from position 48a to, for example, position 48b, and a second step back to position 48a.

[0052] To limit the energy consumption of the microactuator 83, it is desirable to avoid a second step in commanding the microactuator 83 by connecting the body 80 of the directional control valve 48 to the rod 46 of the ram 40. Thus, for example, when the slide 82 is placed in position 48b, the two chambers 42 and 44 are supplied and the piston 88 moves. The movement of the piston 88 sequentially moves the body of the directional control valve 48 via the rod 46 until the directional control valve 48 returns to its position 48a, thereby blocking the supply to the two chambers 42 and 44. In this case, the continuous movement of the slide 82 between its three positions is particularly advantageous. In particular, starting from the neutral position 48a, after actuation of the microactuator 83, which is capable of moving the slide 82, one of the chambers 42 and 44 is supplied with high pressure P and the other with low pressure T. The orientation α of the swashplate 20 changes, and the rod 46 moves the body 80 until the slide 82 returns to the neutral position 48a. This return to the neutral position 48a occurs continuously and gradually comes to a halt.

[0053] The connection between the rod 46 of the ram 40 and the body 80 of the directional control valve 48 may be a telescopic connection. It is also possible to insert one or more elements between the rod 46 and the body 80 making it possible to temporarily modify the transmission of movement from the piston 88 to the body 80. It is thus possible to insert a spring and / or a damper between the rod 46 and the body 80.

[0054] The connection between the rod 46 of the ram 40 and the body 80 of the directional control valve 48 may be performed independently of the mounting of the directional control valve 60 .

[0055] The directional control valve 60 comprises a body 90 and a slide 92 that can move within the body 90 under the action of pressure P. Movement of the slide 92 allows hydraulic ducts within the directional control valve 60 to be placed in communication or blocked, allowing transition of the directional control valve 60 between two positions 60a and 60b. As long as the pressure P is below a predetermined pressure, the slide 92 is held in position 60a by the spring 62. Conversely, when the pressure P reaches or exceeds the predetermined pressure, the spring 62 is compressed, and the slide 92 moves within the body 90 to reach position 60b. The body 90 is fixed to the casing 84. A motor 64 can be used to adjust the compression of the spring 62 relative to the body 90.

[0056] Figure 3 shows the main elements of the actuator 10. It again shows the pump 12, the swashplate 20 and the elements for commanding its tilt α: the ram 40, the directional control valve 48 and its microactuator 83. It again shows the overpressure limiting device comprising the directional control valve 60 and the spring 62, as well as the device for regulating the value of the overpressure comprising the motor 64. The motor, which can be used to turn the shaft 14 of the pump 12, is now designated by the reference number 100. Finally, Figure 3 again shows the hydraulic power part of the actuator 10, which is formed by hydraulic ducts 102 and 104 coming respectively from one of the outlet orifices 28 and 30 of the pump 12.

[0057] The actuator 10 may receive electrical energy and transmit hydraulic energy. To this end, the casing 84 contains at least the motor 100, the pump 12, the swash plate 20, the ram 40, the directional control valve 48, the microactuator 83, and the directional control valve 60. At least one electrical connector 106 passing through the casing 84 allows the transmission of electrical energy required to rotate the pump 12 and a command signal for driving the tilt α of the swash plate 20 to the actuator 10. When a predetermined position adjustment is planned, the electrical connector 106 allows the actuator 10 to receive a command signal for adjusting a predetermined pressure. In practice, the connector 106 may be a single connector or may be divided into two connectors, one for power and the other for command signals. The actuator 10 may transmit energy in hydraulic form, more precisely, in the form of a fluid delivery. To this end, a hydraulic connector 108 arranged to pass through the casing 84 allows the transmission of hydraulic energy to the outside of the actuator 10.

[0058] Alternatively, the actuator 10 receives electrical energy through the connector 106 and transmits mechanical energy through the ram 32 positioned inside the casing 84. In other words, the actuator 10 has a mechanical output 110 that passes through the casing 84 and enables the actuator 10 to transmit mechanical energy. The mechanical output may take various forms, such as the rod of the ram 32 in the case of a linear ram or the end of the rotating shaft in the case of a rotary ram. Hydraulic ducts 102 and 104 supply the ram 32. The hydraulic connector 108 can be omitted. The ducts 102 and 104 do not lead to the outside of the actuator 10. Thus, the actuator 10 has an electrical input and a mechanical output. The hydraulic fluid remains confined to the interior of the casing 84. Therefore, it is possible to replace an actuator based on an electric motor with an actuator according to the present invention, with savings in terms of volume and mass.

Claims

1. A hydraulic actuator (10), comprising: a variable displacement pump (12); a first directional control valve (48) controlled based on a movement command to the hydraulic actuator (10); a double-acting ram (40) hydraulically supplied by the first directional control valve (48); Equipped with the pump (12) comprises a movable member (20); Movement of the movable member (20) allows for continuous variation of the delivery of the pump (12); The movable member (20) can be moved by the double-acting ram (40); The hydraulic actuator (10) is configured such that the first directional control valve (48) realizes a continuous function between the delivery of the pump (12) and the movement command via the position of the movable member (20) when the movable member (20) moves, The hydraulic actuator (10) includes a second directional control valve (60) controlled based on the output pressure (P) of the pump (12); the second directional control valve (60) has two positions; one position (60a) of the two positions is a rest position, and when the output pressure (P) of the pump (12) is lower than a predetermined pressure, the second directional control valve (60) is held in the one position (60a) to transmit the output from the first directional control valve (48) directly to the double-acting ram (40), thereby allowing the pump (12) to follow the continuous function; the other position (60b) of the two positions is an operating position, and when the output pressure (P) of the pump (12) is equal to or greater than the predetermined pressure, the second directional control valve (60) reaches the other position and transmits the output pressure (P) of the pump (12) to the double-acting ram (40) so as to reduce the output pressure (P) of the pump (12) without passing through the first directional control valve (48) and without following the continuous function; the movable member (20) is configured to allow the pump (12) to reverse its direction of delivery; The double-acting ram (40) comprises two chambers (42, 44); the hydraulic actuator (10) comprises a third directional control valve (68) configured to transmit the output pressure (P) of the pump (12) to one or the other of the two chambers (42, 44) according to the direction of delivery of the pump (12) so as to reduce the absolute value of the displacement of the movable member (20); The third directional control valve (68) is controlled by the movement of the movable member (20). characterized in that Hydraulic actuator.

2. The predetermined pressure is adjustable characterized in that The hydraulic actuator of claim 1 .

3. The hydraulic actuator (10) a valve set (52) configured such that the second directional control valve (60) is controlled by the maximum output pressure of the pump (12); Further equipped characterized in that The hydraulic actuator of claim 1 .

4. The double-acting ram (40) includes a movable rod (46) connected to the body (80) of the first directional control valve (48). characterized in that The hydraulic actuator according to any one of claims 1 to 3.

5. The movable rod (46) is connected to the body (80) of the first directional control valve (48) by a screw-on connection. characterized in that 5. The hydraulic actuator of claim 4.

6. The pump (12) is a piston pump with an axial piston (24), The movable member (20) is a swash plate (20) having a variable inclination (α) against which the axial piston (24) presses, By changing the inclination (α) of the swash plate (20), the stroke of the axial piston (24) can be changed. The tilt (α) of the swash plate (20) is adjusted by the double-acting ram (40) driven by a microactuator (83) that defines the movement command to the hydraulic actuator (10) through the first directional control valve (48) when the output pressure (P) of the pump (12) is lower than a predetermined pressure. characterized in that The hydraulic actuator according to any one of claims 1 to 5.

7. The hydraulic actuator (10) The pump (12); a motor (100) enabling the operation of said pump (12); the movable member (20) allowing the delivery of the pump (12) to be continuously varied; the double-acting ram (40) for actuating the movable member (20); the first directional control valve (48) supplying hydraulic pressure to the double-acting ram (40); a microactuator (83) for moving the first directional control valve (48); The second directional control valve (60); a casing (84) in which the The hydraulic actuator (10) at least one electrical connector (106) passing through the casing (84) and enabling the hydraulic actuator (10) to receive electrical energy to power the motor (100) and electrical signals to drive the microactuator (83); a hydraulic connector (108) passing through the casing (84) and enabling the hydraulic actuator (10) to transmit hydraulic energy; Further provide characterized by: A hydraulic actuator according to any one of claims 1 to 6.

8. The hydraulic actuator (10) The pump (12); a motor (100) enabling the operation of said pump (12); the movable member (20) allowing the delivery of the pump (12) to be continuously varied; the double-acting ram (40) for actuating the movable member (20); the first directional control valve (48) supplying hydraulic pressure to the double-acting ram (40); a microactuator (83) for moving the first directional control valve (48); the second directional control valve (60); a casing (84) in which the The hydraulic actuator (10) at least one electrical connector (106) passing through the casing (84) and enabling the hydraulic actuator (10) to receive electrical energy to power the motor (100) and electrical signals to drive the microactuator (83); a mechanical output (110) passing through the casing (84) and enabling the hydraulic actuator (10) to deliver mechanical energy; Further provide characterized by: A hydraulic actuator according to any one of claims 1 to 6.

9. The at least one electrical connector (106) enables the hydraulic actuator (10) to receive a second electrical signal to drive a regulator of the predetermined pressure. characterized in that A hydraulic actuator according to claim 7 or 8 when dependent on claim 2.

10. The first directional control valve (48) a neutral position (48a) in which the movable member (20) is stationary and does not change the delivery of the pump (12); two operating positions (48b, 48c) into which the movable member (20) moves to vary the delivery of the pump (12); and The first directional control valve (48) is configured so that the transition between the neutral position (48a) and one of the operating positions (48b, 48c) occurs continuously. characterized by: A hydraulic actuator according to any one of claims 1 to 9.

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