EP3336363B1

EP3336363B1 - Electro-hydraulic actuator

Info

Publication number: EP3336363B1
Application number: EP17205499.1A
Authority: EP
Inventors: Danilo Manfredi
Original assignee: Elt Fluid Srl
Current assignee: Elt Fluid Srl
Priority date: 2016-12-14
Filing date: 2017-12-05
Publication date: 2021-10-27
Anticipated expiration: 2037-12-05
Also published as: EP3336363A1; IT201600126329A1

Description

TECHNICAL FIELD

The present invention concerns an electro-hydraulic actuator and, more specifically, an electro-hydraulic actuator with mechanical feedback.

PRIOR ART

Electro-hydraulic actuators with mechanical feedback are usually used to actuate hydraulic components like for example directional valves. An example of such an electro-hydraulic actuator is disclosed in DE10330738 A1 .
An electro-hydraulic actuator with mechanical feedback generally comprises a hydraulic cylinder inside which a piston is slidably received that divides the internal volume of the cylinder into a first and a second operative chamber.
The piston is equipped with a stem that extends at least partially in the first and in the second operative chamber and that comes out from an end of the cylinder to be connected to the directional valve.
Each operative chamber is associated with a hydraulic control valve, which generally comprises a slider able to be actuated between a first position, wherein the operative chamber is placed in communication with a tank at atmospheric pressure, and a second position, wherein the operative chamber is connected with a pump adapted to feed a pressurised work fluid inside it. Between the first and the second position, the slider also passes through an intermediate position in which the operative chamber is isolated both from the tank and from the pump of the work fluid.
The movement of the slider from the first position to the second position is generally actuated by a solenoid whereas the contrary feedback movement is actuated by a cam associated with the portion of the stem of the piston that extends in the operative chamber.
In particular, a tappet equipped with a rounded end and a spring adapted to press said tappet against the cam are normally arranged between the cam and the slider.
In order to translate the stem of the actuator by a certain amount, the solenoid of the hydraulic valve is activated so as to push the slider from the first position towards the second position, thus allowing the pressurised fluid to enter into the respective operative chamber of the cylinder and therefore to set the piston in translation.
The translation of the piston also pulls the cam with it, which is configured so as to cause a proportional translation of the tappet towards the slider.
The translation of the tappet towards the slider causes a progressive increase of the preload of the spring arranged between the two, which progressively counteracts and subsequently overcomes the thrust exerted by the solenoid, until the slider is brought into the intermediate position and the translation of the stem is thus locked in the position reached.
If the thrust generated by the solenoid is decreased or completely zeroed, the spring arranged between the tappet and the slider pushes the slider back into the first position, allowing the work fluid contained in the chamber of the cylinder to flow into the tank and thus allowing the piston of the actuator to pull back towards the initial position.
As can be worked out, the relative movement between the cam and the tappet causes a significant wearing of the components, mainly of the cam, which over time causes an alteration of the law of motion of the tappet, with loss of functionality of the electro-hydraulic actuator and consequent need to proceed to maintenance and/or replacement of the device.
A purpose of the present invention is to overcome this drawback of the prior art, in a simple, rational and low-cost solution.
Such purposes are accomplished by the characteristics of the invention given in the independent claim. The dependent claims outline preferred and/or particularly advantageous aspects of the invention.

SUMMARY OF THE INVENTION

The invention provides an electro-hydraulic actuator comprising:

a hydraulic cylinder equipped with a cylinder, a piston slidably received in the cylinder and adapted to divide the internal volume of the cylinder into a first chamber and a second chamber, a stem connected to the piston and passing outside of the cylinder, and a cam associated with a portion of the stem contained in the first chamber of the cylinder, and
a hydraulic valve equipped with a valve body coupled with the cylinder, a first access mouth formed in the valve body and placed in communication with the first chamber through a connection duct formed in the cylinder, a second access mouth formed in the valve body and adapted to be placed in communication with a pump, a third access mouth formed in the valve body and adapted to be placed in communication with a tank, a slider received in the valve body and slidable from a first position, wherein the slider closes the second access mouth leaving the third access mouth in communication with the first access mouth, towards a second position, wherein the slider closes the third access mouth leaving the second access mouth in communication with the first access mouth, passing from an intermediate position between the first and the second position, wherein the slider closes the second and the third access mouth, and a solenoid configured to generate a thrust adapted to actuate the slider,
wherein this electro-hydraulic actuator also comprises a ball that can be at least partially inserted in the connection duct and a spring, which is arranged between the slider and the ball to counteract the thrust generated by the solenoid and keep said ball pressed on the cam.

In this way, thanks to the lower wear of the cam due to the rolling friction between the cam and the ball, it is possible to lengthen the useful life of the cam with respect to the devices of the prior art, thus reducing the maintenance costs of the electro-hydraulic actuator.
According to one aspect of the invention, the connection duct can have a polygonal cross section.
Thanks to such a solution, the fluid that goes to the first chamber of the hydraulic cylinder, or that comes from it, can pass freely at the sides of the ball without encountering obstructions.
According to another aspect of the invention, the electro-hydraulic actuator can comprise an abutment element arranged between the spring and the ball, which is equipped with a cavity in which the ball is partially received.
In this way, it is possible to improve the stability of the ball and of the spring preventing possible misalignments.
According to a further aspect of the invention, the cavity can be configured like a frusto-conical recess, for example said cavity can have a maximum depth comprised between 0.2 and 0.5 times the radius of the ball and a maximum width comprised between 0.7 and 0.9 times the diameter of the ball.
In this way, the cavity promotes a natural centring of the ball and is easy to make.
According to another aspect of the invention, the slider can be equipped with an axial channel placed in communication with the first access mouth and with at least one first radial hole adapted to place the axial channel in communication with the third access mouth, when the slider is in the first position. Thanks to such a solution, the slider, and therefore the valve, is particularly compact.
According to a further aspect of the invention, the slider can comprise at least one second radial opening adapted to place the axial channel in communication with the second access mouth, when the slider is in the second position. In this way, a dedicated opening is provided that increases the passage area available to the fluid that goes from the pump to the chamber, thus decreasing the load losses.
Advantageously, said axial channel can be configured as a blind axial hole open at one end of said slider.
According to another aspect of the invention, the thrust generated by the solenoid can be directed in the direction to actuate the slider to slide from the first position to the second position passing through the intermediate position. In this way, when pressurised fluid is present in the first chamber and there is a drawback like for example the breaking of the spring comprised between the ball and the slider, the thrust that the pressurised fluid exerts on the slider tends to spontaneously take it back into the first position, wherein it connects the chamber of the discharge cylinder with the tank, thus preventing the stem of the actuator going to the end of stroke in an uncontrolled manner. According to a further aspect of the invention, the valve body can comprise a cavity placed constantly in communication with the third access mouth and in which a portion of the slider opposite the first access mouth is slidably received.
Thanks to such a solution, the portion of slider opposite the ball is in an environment at the pressure of the tank, therefore, in the case of a drawback like for example the breaking of the spring comprised between the ball and the slider, on such a portion the fluid does not generate any force that obstructs the passage of the slider from the second position to the first position, i.e. the closure of the second access mouth.
According to another aspect of the invention, the hydraulic valve can comprise a spring contained inside said cavity and adapted to counteract the thrust of the solenoid.
In this way, when the solenoid is not activated, such a spring helps to take the slider back into the first position even in the case of drawbacks, like for example the breaking of the spring comprised between the ball and the slider.
Advantageously, the slider is associated with a magnetic body, which is entirely contained in the cavity and is electro-mechanically coupled with the solenoid.
According to another aspect of the invention, said magnetic body can be equipped with an axial through channel.
In this way, when the slider translates under the effect of the solenoid, the fluid that surrounds the magnetic body can pass freely from one part to the other thereof, without obstructing the movement of the slider.
According to a further aspect of the invention, the electro-hydraulic actuator can comprise: a further hydraulic valve, a further connection duct adapted to connect the first access mouth of the further hydraulic valve to the second chamber of the cylinder, a further cam associated with a portion of the stem contained in the second chamber, a further ball at least partially inserted in the further connection duct, and a further spring arranged between the slider of the further hydraulic valve and the further ball to counteract the thrust generated by the solenoid and keep said further ball pressed on the further cam. Thanks to such a solution an electro-hydraulic actuator is provided that is capable of actuating the stem precisely in both directions of axial translation and that has a stable position, thanks to the springs contained in the chambers of the hydraulic cylinder, even when the solenoids are not excited.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the invention will become clear from reading the following description provided as an example and not for limiting purposes, with the help of the figures illustrated in the attached tables.

Figure 1 is a section view of a first embodiment of an electro-hydraulic actuator according to the invention.
Figure 2 is a section view of a valve body of the electro-hydraulic actuator of figure 1.
Figure 3 is an enlarged section of the electro-hydraulic actuator in a first operative position.
Figure 4 is an enlarged section of the electro-hydraulic actuator in a second operative position.
Figure 5 is an enlarged section of the electro-hydraulic actuator in a third operative position.
Figure 6 is a section view of a second embodiment of the electro-hydraulic actuator according to the invention.
Figure 7 is a section view of two different embodiments of a connection duct of the electro-hydraulic actuator.
Figure 8 is a section view of a further embodiment of the connection duct of the electro-hydraulic actuator.

DETAILED DESCRIPTION

With particular reference to such figures, reference numeral 10 globally indicates an electro-hydraulic actuator with baric and mechanical feedback for the actuation of hydraulic components U, for example for the actuation of a directional valve.
The electro-hydraulic actuator 10 comprises a hydraulic cylinder 15, equipped with a cylinder 20 that has a longitudinal axis X.
The hydraulic cylinder 15 comprises a piston 25 slidably received in the cylinder 20 and that divides the internal volume of the cylinder 20 into a first chamber 30 and a second chamber 35.
The piston 25 is connected to a through stem 40 that extends in both of the chambers 30 and 35 and that has at least one first end 50 that projects outside of the cylinder 20.
The first end 50 can for example be connected to a spool of the directional valve to control the movement thereof.
The cylinder 20 can be made inside an oil-hydraulic block 55 like a blind cavity, the axial opening of which is closed by a cap, through which the stem 40 is free to slide.
In a first embodiment illustrated in figure 1, the hydraulic cylinder 15 comprises a cam 60, for example of the linear type, fixed (for example screwed) to a second end 65 of the stem 40, which is contained in the first chamber 30. The cam 60 comprises for example a frusto-conical side surface 70.
The frusto-conical surface 70 has central axis coaxial to the longitudinal axis X and is oriented so that the imaginary vertex of the frustum of cone that defines said frusto-conical surface 70 faces towards the piston 25.
In this first embodiment, the hydraulic cylinder 15 also comprises a spring 75, for example a helical compression spring, which is received in the second chamber 35 and is configured to push on the piston 25 in the direction of the decrease in volume of the first chamber 30.
Again in this first embodiment, the electro-hydraulic actuator 10 comprises a hydraulic valve 80 connected to the hydraulic cylinder 15.
The hydraulic valve 80 can be partially inserted in a suitable cavity formed in the oil-hydraulic block 55 in which the cylinder 20 is also formed.
With particular reference to figure 2, the hydraulic valve 80 comprises a valve body 85 that is equipped with a cartridge 90 and with a cover 95 fixed to an end of said cartridge 90.
The cartridge 90 internally defines a first cavity 100, which has longitudinal axis perpendicular to the longitudinal axis X of the cylinder 20 and ends with a first access mouth 115 formed at the opposite end with respect to the cover 95.
The cover 95 internally defines a second cavity 105 communicating with the first cavity 100 and having longitudinal axis parallel to, for example coinciding with, the longitudinal axis of the first cavity 100 itself.
The first access mouth 115 of the cartridge 90 is in communication with the first chamber 30 of the cylinder 20 through a connection duct 120 formed in the cylinder 20 itself (see fig.1).
The connection duct 120 has an axis substantially perpendicular to the sliding direction of the piston 25 and can be formed in the oil-hydraulic block 55 in which the cylinder 20 is formed.
The connection duct 120 has polygonal cross section, for example triangular or square (see figure 7).
However, this does not rule out the possibility that the connection duct 120 can have complex cross sections, for example defined by a circular central core from the circumference of which at least one projection (preferably a plurality of projections) projects in the radial direction, oriented in the opposite direction to the centre of the connection duct 120 (as can be seen in figure 8).
The cartridge 90 also comprises a second access mouth 125 and a third access mouth 130, which both open into the first cavity 100 and are adapted to be placed in communication respectively with a pump P and with a tank T, for example with a tank T at atmospheric pressure (see fig.1).
The second access mouth 125 and the third access mouth 130 define the axial extension of a portion 110 of the first cavity 100 (see fig.2), i.e. the second access mouth 125 and the third access mouth 130 define the axial ends of said portion 110.
As illustrated in figure 3, the hydraulic valve 80 is equipped with a slider 135 slidably inserted in the valve body 85, for example slidably inserted to fit at least in the portion 110 of the first cavity 100.
In the illustrated embodiment, the slider 135 extends in particular from the first cavity 100 to the second cavity 105.
Said slider 135 is adapted to slide from a first position (illustrated in figure 3), wherein the slider 135 closes the second access mouth 125 leaving the third access mouth 130 in communication with the first access mouth 115, towards a second position (illustrated in figure 4), wherein the slider 135 closes the third access mouth 130 leaving the second access mouth 125 in communication with the first access mouth 115.
Between the first and the second position, the slider 135 also passes from an intermediate position (illustrated in figure 5), in which the slider 135 closes both the second access mouth 125 and the third access mouth 130.
The slider 135 comprises an elongated cylindrical body and a disc-shaped body having outer radius greater than the radius of the elongated cylindrical body and placed at the end of the slider 135 opposite the first access mouth 115.
The slider 135 also comprises a blind axial channel 140, for example formed in the elongated cylindrical body of the slider itself, which is equipped with an axial opening 145 placed at the end of the slider 135 facing towards the first access mouth 115 and in constant communication with the latter.
The slider 135 also comprises a first radial opening 150 adapted to place the blind axial channel 140 in communication with the third access mouth 130, when the slider 135 is in the first position.
The first radial opening 150 extends between an inner surface of the blind axial channel 140 and an outer surface of the slider 135, for example close to a bottom wall of the blind axial channel 140.
For example, the first radial opening 150 can be globally defined by a pair of through holes having central axis substantially perpendicular to a longitudinal axis of the slider 135 and symmetrically arranged with respect to a middle plane of the slider itself.
The slider 135 finally comprises a second radial opening 155 adapted to place the blind axial channel 140 in communication with the second access mouth 125, when the slider 135 is in the second position.
The second radial opening 155 extends between an inner surface of the blind axial channel 140 and an outer surface of the slider 135, for example distal from the bottom wall of the blind axial channel 140.
Also in this case, the second radial opening 155 can be globally defined by a pair of through holes having central axis substantially perpendicular to a longitudinal axis of the slider 135 and symmetrically arranged with respect to a middle plane of the slider itself.
The distance, in the direction of the longitudinal axis of the slider 135, between the first radial opening 150 and the second radial opening 155 is less than the distance, in the direction of the same axis, between the second access mouth 125 and the third access mouth 130.
In this way, it is possible to make the aforementioned intermediate position of the slider, wherein the channel is not in communication either with the second access mouth 125 or with the third access mouth 130.
In the illustrated embodiment, the slider 135 also comprises an annular recess 160, outside of and coaxial to the blind axial channel 140 with which it communicates through the first radial opening 150 and the second radial opening 155.
The annular recess 160 has an axial extension that is shorter than the distance, in the direction of the longitudinal axis of the slider 135, between the second access mouth 125 and the third access mouth 130.
A magnetic body 165, for example ferromagnetic, is entirely contained and slidably received in the second cavity 105.
The magnetic body 165 is equipped with a cylindrical body, with a rod, which is fixedly connected to the cylindrical body and is adapted to contact the disc-shaped body of the slider 135, and with an axial through channel 170 adapted to place in communication the volumes of the second cavity 105 arranged at the opposite axial ends of the magnetic body itself.
A solenoid 180 is electro-mechanically coupled with the magnetic body 165 and is configured to generate a thrust adapted to actuate the slider 135 from the first position to the second position.
In practice, the solenoid 180 is adapted to generate a thrust on the magnetic body 165 that, translating along the second cavity 105 due to said thrust, transmits the thrust generated from the solenoid 180 to the slider 135.
The solenoid 180 can for example be housed in a portion of the cover 95 of the hydraulic valve 80 that surrounds the magnetic body 165.
The hydraulic valve 80 finally comprises a spring 185 housed between the first 100 and the second cavity 105 and adapted to act on the slider 135 to counteract the thrust of the solenoid 180.
In particular, the spring 185, which can for example be a helical compression spring, has one end housed in a suitable seat formed in the cartridge 90 and an opposite end in contact with the disc-shaped body of the slider 135.
The electro-hydraulic actuator 10 comprises a ball 190 at least partially inserted, for example with reduced clearance, in the connection duct 120 and a spring 195 arranged between the slider 135 and the ball itself to counteract the thrust generated by the solenoid 180 and keep said ball 190 pressed against the cam 60.
The ball 190 can be made of X65Cr14 steel or X105CrMo17 steel or 100Cr6 steel or 100CrMo7 steel.
The ball 190 can for example be a ball made of steel for rolling bearings. The spring 195 has a first end 200 associated with an end of the slider 135 facing towards the connection duct 120 and a second end 205 associated with the ball 190.
For example, the first end 200 of the spring 195 rests on an annular surface of the slider 135 that delimits the axial opening 145 of the blind axial channel 140.
The spring 195 can for example be a helical compression spring.
The electro-hydraulic actuator 10 finally comprises an abutment element 210, which is arranged between the spring 195 and the ball 190 and is equipped with a cavity 215, in which the ball 190 is partially received.
The cavity 215 has a maximum depth comprised between 0.2 and 0.5 times the radius of the ball 190 and a maximum width comprised between 0.7 and 0.9 times the diameter of the ball 190.
The cavity 215 is, for example, configured like a frusto-conical recess.
The abutment element 210 is also equipped with a housing seat 220 for the second end 205 of the spring 195, which is configured like a blind cylindrical hole having central axis coinciding with the longitudinal axis of the slider 135 and equipped with a flat bottom wall.
The abutment element 210 is preferably made of an anti-friction material, for example brass, bronze or teflon.
In a second embodiment illustrated in figure 6, the hydraulic cylinder 15 comprises a first cam 60a associated with a portion of the stem 40 contained in the first chamber 30 and a second cam 60b fixed to a portion of the stem contained in the second chamber 35.
The first cam 60a and the second cam 60b are configured like the cam 60 of the first embodiment.
The hydraulic cylinder 15 also comprises a first spring 75a housed in the first chamber 30 and a second spring 75b housed in the second chamber 35. The first spring 75a and the second spring 75b are configured like the spring 75 of the first embodiment and adapted to keep the stem in a stable position when the electro-hydraulic actuator 10 is not activated.
In this second embodiment, the electro-hydraulic actuator 10 comprises a first hydraulic valve 80a connected to the first chamber 30 of the hydraulic cylinder 15 through a first connection duct 120a and a second hydraulic valve 80b connected to the second chamber 35 of the hydraulic cylinder 15 through a second connection duct 120b.
In this way, unlike the first embodiment, it is possible to precisely control the movement of the stem 40 in both directions of axial translation.
The first hydraulic valve 80a, the second hydraulic valve 80b, the first connection duct 120a and the second connection duct 120b are respectively configured like the hydraulic valve 80 and the connection duct 120 of the first embodiment.
Again in this second embodiment, the electro-hydraulic actuator 10 comprises a first ball 190a partially inserted in the first connection duct 120a and a first spring 195a arranged between the slider 135 of the first hydraulic valve 80a and the first ball 190a.
The electro-hydraulic actuator 10 comprises a second ball 190b partially inserted in the second connection duct 120b and a second spring 195b arranged between the slider 135 of the second hydraulic valve 80b and the second ball 190b.
First ball 190a, second ball 190b, first spring 195a and second spring 195b are configured, respectively, like the ball 190 and the spring 195 of the first embodiment.
A first abutment element 210a is arranged between the first spring 195a and the first ball 190a and a second abutment element 210b is arranged between the second spring 195b and the second ball 190b, said abutment elements being configured like the abutment element 210 of the first embodiment.
A further embodiment not represented in the drawings, substantially unchanged in components and in operation with respect to the first embodiment, foresees that the connection duct 120 is in communication with the second chamber 35 and that the spring 75 is housed in the first chamber 30. In this way, when the slider 135 is placed in the second operative position, the pressurised fluid enters into the second chamber 35 and the first end 50 of the stem 40 is pulled towards the cylinder 20.
The operation of the electro-hydraulic actuator 10 according to the invention, in particular of the first embodiment, is as follows.
When the electro-hydraulic actuator 10 does not have to act on the hydraulic component U, the solenoid 180 is not excited, so that the spring 185 of the hydraulic valve 80 and the spring 195 keep the slider 135 in the first position allowing the communication between the first chamber 30 of the hydraulic cylinder 15 and the tank T.
In this condition, the pressure in the first chamber 30 is equal to that of the tank T and the spring 75 housed in the second chamber 35 takes (or keeps) the piston 25 in the position in which the volume of the first chamber 30 is the minimum.
In order to change the position of the first end 50 of the stem 40 by a certain amount, the solenoid 180 is excited with energy proportional to the movement that it is wished to obtain: the solenoid 180 thus generates a thrust on the slider 135 proportional to the energy received and translates the slider 135 from the first position to the second position.
When the slider 135 reaches the second position, the pressurised fluid coming from the pump P enters into the first chamber 30 flowing into the portion of cross section of the connection duct 120 not occupied by the ball 190. The pressurised fluid, overcoming the force of the spring 75 housed in the second chamber 35, pushes the piston 25 and therefore the stem 40.
In its translation the stem 40 pulls the cam 60 with it, which forces the ball 195 to move towards the slider 135 translating along the connection duct 120.
During such movement, the ball 190 is free to roll on the frusto-conical surface 70 of the cam 60, thus reducing friction and consequently the wearing of the components.
At the same time, the movement of the ball 190 towards the slider 135 causes the compression of the spring 195 arranged between the two, up to the point in which the force generated by the compression of the spring 195 progressively exceeds, and subsequently equals, the thrust generated by the solenoid 180, taking the slider 135 into the intermediate position.
At that point the first chamber 30 is isolated from the rest of the hydraulic circuit and the first end 50 of the stem 40 remains in the position reached thanks to the spring 75 that prevents further translations of the stem 40 and keeps the first chamber 30 pressurised.
Thereafter, it is possible to further change the position of the first end 50 of the stem 40, increasing the energy supplied to the solenoid 180 or decreasing it, depending on whether it is wished to advance or withdraw the first end 50.
In both cases the ball 190, rolling on the cam 60, compresses or extends the spring 195 so that the force generated by said spring again equals the thrust generated by the solenoid 180, taking the slider 135 into the intermediate position and isolating the first chamber 30 from the rest of the hydraulic circuit.
If during the translation of the stem 40 the springs 185 and 195 break, the thrust that the pressurised fluid exerts on the slider 135 takes the slider, after the solenoid 180 has been switched off, back into the first position, thus placing the first chamber 30 in discharge.
In the second embodiment, the operation is substantially the same, but it is necessary to add to the above explanation that when the slider 135, for example of the first hydraulic valve 80a, is brought into the second position allowing the entry of the pressurised fluid into the first chamber 30, the second hydraulic valve 80b is in the first position, allowing a quick outflow of the liquid contained in the second chamber 35 towards the tank T.
The invention thus conceived can undergo numerous modifications and variants all of which are covered by the scope of the invention as defined by the claims.
In practice, the materials used, as well as the contingent shapes and sizes, can be whatever according to the requirements, without for this reason departing from the scope of protection of the following claims.

Claims

Electro-hydraulic actuator (10) comprising:
- a hydraulic cylinder (15) equipped with:
• a cylinder (20),

• a piston (25) slidably received in the cylinder (20) and adapted to divide the internal volume of the cylinder (20) into a first chamber (30) and a second chamber (35),

• a stem (40) connected to the piston (25) and passing outside of the cylinder (20), and

• a cam (60, 60a) associated with a portion of the stem (40) contained in the first chamber (30) of the cylinder (20),

- a hydraulic valve (80, 80a) equipped with:
• a valve body (85) coupled with the cylinder (20),

• a first access mouth (115) formed in the valve body (85) and placed in communication with the first chamber (30) through a connection duct (120, 120a) formed in the hydraulic cylinder (15),

• a second access mouth (125) formed in the valve body (85) and adapted to be placed in communication with a pump (P),

• a third access mouth (130) formed in the valve body (85) and adapted to be placed in communication with a tank (T),

• a slider (135) received in the valve body (85) and able to slide from a first position, in which the slider (135) closes the second access mouth (125) leaving the third access mouth (130) in communication with the first access mouth (115), towards a second position, in which the slider (135) closes the third access mouth (130) leaving the second access mouth (125) in communication with the first access mouth (115), passing from an intermediate position, in which the slider (135) closes the second access mouth (125) and the third access mouth (130), and

• a solenoid (180) configured to generate a thrust adapted to actuate the slider (135) to slide from the first position to the second position passing through the intermediate position, and

• a ball (190, 190a) and a spring (195, 195a), which is arranged between the slider (135) and the ball (190, 190a) to counteract the thrust generated by the solenoid (180) and keep said ball (190, 190a) pressed on the cam (60, 60a).
Electro-hydraulic actuator (10) according to claim 1, wherein the connection duct (120, 120a) has a polygonal cross section.
Electro-hydraulic actuator (10) according to any one of the previous claims, characterised in that it comprises an abutment element (210, 210a) arranged between the spring (195, 195a) and the ball (190, 190a), which is equipped with a cavity (215) in which the ball is partially received.
Electro-hydraulic actuator (10) according to any one of the previous claims, wherein the slider (135) is equipped with an axial channel (140) placed in communication with the first access mouth (115) and with at least one first radial opening (150) adapted to place the axial channel (140) in communication with the third access mouth (130), when the slider (135) is in the first position.
Electro-hydraulic actuator (10) according to claim 4, characterised in that said slider (135) comprises at least one second radial opening (155) adapted to place the axial channel (140) in communication with the second access mouth (125), when the slider (135) is in the second position.
Electro-hydraulic actuator (10) according to claim 4 or 5, wherein said axial channel (140) is configured like a blind axial hole open at one end of said slider (135).
Electro-hydraulic actuator (10) according to any one of the previous claims, wherein the valve body (85) comprises a cavity (105) placed constantly in communication with the third access mouth (130) and in which a portion of the slider (135) opposite to the first access mouth (115) is slidably received.
Electro-hydraulic actuator (10) according to claim 7, wherein the hydraulic valve comprises a spring (185) contained inside said cavity (105) and adapted to counteract the thrust of the solenoid (180).
Electro-hydraulic actuator (10) according to claim 7 or 8, wherein the slider (135) is associated with a magnetic body (165), which is entirely contained in the cavity (105) and is electro-mechanically coupled with the solenoid (180).
Electro-hydraulic actuator (10) according to any one of the previous claims, characterised in that the cam (60, 60a) comprises a frusto-conical surface (70) coaxial with a longitudinal axis (X) of the cylinder (20) and vertex facing towards the piston (25).
Electro-hydraulic actuator (10) according to any one of the previous claims, characterised in that the ball (190) is at least partially inserted in the connection duct (120).
Electro-hydraulic actuator (10) according to any one of the previous claims, characterised in that it comprises:
- a further hydraulic valve (80b),

- a further connection duct (120b) adapted to connect the first access mouth (115) of the further hydraulic valve (80b) to the second chamber of the cylinder (35),

- a further cam (60b) associated with a portion of the stem (40) contained in the second chamber (35),

- a further ball (190b) at least partially inserted in the further connection duct (120b), and

- a further spring (195b) arranged between the slider (135) of the further hydraulic valve (80b) and the further ball (190b) to counteract the thrust generated by the solenoid (180) and keep said further ball (190b) pressed on the further cam (60b).