EP3149344B1

EP3149344B1 - End-of-stroke signalling device for a hydraulic actuator

Info

Publication number: EP3149344B1
Application number: EP14757982.5A
Authority: EP
Inventors: Alessio PIERGIOVANNI; Bruno BIAGI; Massimo Coppola; Teodoro Andrea Dragani
Original assignee: MBDA Italia SpA
Current assignee: MBDA Italia SpA
Priority date: 2014-05-27
Filing date: 2014-05-27
Publication date: 2020-01-08
Anticipated expiration: 2034-05-27
Also published as: EP3149344A1; ES2782874T3; WO2015181839A1

Description

The present description relates to the technical field of hydraulic actuators, such as for example hydraulic stabilizers, oil-pressure actuators, etc., and more in particular it relates to an end-of-stroke signalling device for a hydraulic actuator as defined in the preamble of claim 1.
The provision of a hydraulic actuator of an end-of-stroke signalling device adapted to signal when the main piston of the hydraulic actuator takes a predetermined end-of-stroke position is well known. In particular, end-of-stroke signalling devices are known which are associated with a cylinder end cap of the hydraulic actuator which comprise a detecting piston slidingly mounted to a cylinder end cap and a position sensor, where the position sensor is adapted to cooperate with the detecting piston to signal the achievement of the above-mentioned end-of-stroke position by the main piston of the hydraulic actuator.
With reference, for example, and without thereby introducing any limitation, to the military field, it is known for example to associate end-of-stroke signalling devices of the above-described type with the stabilizers (i.e. to the hydraulic actuators) with which a stabilisation system used to stabilise a surface launcher is provided. As it is known, a surface launcher is a military vehicle provided with a launching frame adapted to accommodate and launch one or more missiles.
A disadvantage of the end-of-stroke signalling devices of the prior art discussed hereinabove is represented by the fact that the signalling of the end-of-stroke position of the main piston of the stabiliser may be influenced by pressure variations of the hydraulic fluid that take place inside the chambers of the stabiliser cylinder. Such pressure variations may be due for example to the external load and/or to thermal expansions caused by variations of the external ambient temperature. Because of this disadvantage, it may occur that the position sensor of the end-of-stroke signalling device is inadvertently activated in an undesired manner. For example it may occur that two end-of-stroke signalling devices, associated with a same stabiliser and intended for respectively signalling two opposite end-of-stroke positions of the main piston of the stabiliser, are activated simultaneously. In such case, the above-mentioned pair of end-of-stroke signalling devices would incorrectly signal that the main piston of the stabiliser is at the same time at two opposite end-of-stroke positions.
An end-of-stroke signalling device of this type is already known from the document US 20040182235 .
A general object of the present description is to provide an end-of-stroke signalling device for a hydraulic actuator which is capable of solving or obviating at least in part the drawbacks mentioned above with reference to the prior art.
These and other objects are achieved by an end-of-stroke signalling device as defined in claim 1 in the most general form thereof and in the dependent claims in some particular embodiments.
Also an object of the present invention are a hydraulic actuator as defined in claim 11 and a surface launcher as defined in claim 15.
The invention shall be better understood from the following detailed description of embodiments thereof, made by way of an example and therefore in no way limiting with reference to the annexed drawings, wherein:

Fig. 1 is an axonometric view of a surface launcher provided with a stabilisation system comprising a pair of stabilisers;
Fig. 2 is a perspective view of a hydraulic actuator according to a currently preferred embodiment, wherein the hydraulic actuator is shown in a first operating configuration;
Fig. 3 is a top plan view of the hydraulic actuator of Fig. 2;
Fig. 4 is a sectional plan view of the hydraulic actuator of Fig. 2 along line C-C of Fig. 3, the hydraulic actuator being shown in a second operating configuration;
Fig. 5 is a sectional plan view of the hydraulic actuator of Fig. 2 along line A-A of Fig. 3, the hydraulic actuator being shown in the configuration of Fig. 4;
Fig. 6 is an enlarged cutaway view of Fig. 5;
Fig. 7 is a sectional plan view of the hydraulic actuator of Fig. 2 along line A-A of Fig. 3, the hydraulic actuator being shown in the configuration of Fig. 2;
Fig. 8 is an enlarged cutaway view of Fig. 7;
Fig. 9 is a partial plan view of the hydraulic actuator of Fig. 2 along line B-B of Fig. 3, the hydraulic actuator being shown in the configuration of Fig. 4;
Fig. 10 is a partial plan view of the hydraulic actuator of Fig. 2 along line B-B of Fig. 3, the hydraulic actuator being shown in the configuration of Fig. 2;

In the annexed figures, elements which are the same or similar will be indicated by the same reference numerals. It should be further noted that in the description that follows, the terms "upper", "lower", "top", "bottom", "clockwise", "counterclockwise" used to describe the parts and/or operation of a hydraulic actuator, are employed with reference to the annexed figures and are only used for a better clarity and brevity of description. Therefore, such terms shall not be intended as limiting of the scope of protection.
It should be noted that the terms "external" and "internal" shall be intended as referred to the centre of the hydraulic actuator.
Fig. 1 shows a military vehicle, in particular a surface launcher, which has been globally indicated with the reference numeral 1. The surface launcher 1 is equipped with a launch frame 2. As it is known, the launch frame 2 is an apparatus intended for accommodating and launching one or more missiles.
The surface launcher 1 is provided with a stabilisation preferably comprising a pair of stabilisers 3 located at two opposite sides of the surface launcher 1. Such stabilisation system has the function of making the surface launcher 1 stable during the movement of the launch frame 2, in order to avoid for example potential rollovers of the surface launcher during the launching steps of the missiles.
Fig. 2 shows a hydraulic actuator in accordance with a preferred embodiment, which has been globally indicated with the reference numeral 10. As it is known a hydraulic actuator is an actuator adapted to operate with a hydraulic fluid, such as for example and not limitingly oil. In accordance with a preferred embodiment, the hydraulic actuator 10 is a pressurised hydraulic actuator.
The hydraulic actuator 10 is adapted to be used as stabiliser in the stabilisation system of the surface launcher 1. In the example the two stabilisers 3 of the surface launcher 1 are made by employing two hydraulic actuators 10.
The actuator 10 comprises an actuator cylinder 11, 12, 13 and a main piston 14 accommodated in the actuator cylinder 11-13. The actuator cylinder 11-13 preferably comprises a sleeve portion 11 or cylinder barrel 11, a first cylinder end portion 12 or first cylinder end cap 12 and a second cylinder end portion 13 or second cylinder end cap 13. With reference to Fig. 6, the cylinder end cap 12 comprises a respective external side 12A, or external face 12A, and an opposite internal side 12B, or internal face 12B, which are intended for respectively facing the outside and the inside of the actuator cylinder.
Returning to Fig. 2, in accordance with a preferred embodiment the cylinder end caps 12, 13 are fastened to two opposite ends of the cylinder barrel 11, and more preferably are screwed to such opposite ends. From now on, for a greater clarity of description, the first and second cylinder end cap 12, 13 will be indicated in the present description respectively as upper end cap 12 and lower end cap 13.
The main piston 14 preferably comprises a main piston shaft 15 and a main piston head 16 (the head 16 is shown for example in Fig. 4) connected to the shaft 15.
The piston 14 is slidingly mounted to the actuator cylinder 11-13.
The hydraulic actuator 10 comprises an end-of-stroke signalling device in accordance with a currently preferred embodiment, which has been globally indicated with the reference numeral 20. The signalling device 20 is adapted to signal an end-of-stroke position of the main piston 14.
In accordance with a preferred embodiment, the signalling device 20 comprises the upper end cap 12, a detecting piston 21, or feeler piston 21, a balancing piston 22, a transmission element 23 operatively interposed between the detecting and balancing pistons 21, 22 and a position sensor 24. Fig. 3 is a top plan view of the hydraulic actuator of Fig. 2, wherein the signalling device 20 is shown. In accordance with a preferred embodiment the position sensor 24 is mounted to the upper end cap 12, preferably by means of a sensor bracket thereof which is secured to the upper end cap 12 for example by means of the fixing screws thereof. The position sensor 24 may be for example a switch adapted to open and/or close an electrical circuit when activated. In accordance with a preferred embodiment, the position sensor 24 comprises a control element 24A (Fig. 9 and Fig. 10), such as for example a control roller 24A, which is provided to activate the sensor 24 cooperating with the detecting piston 21.
Fig. 6 is a partial sectional view along the line A-A of Fig. 3 of the hydraulic actuator 10. In such figure the signalling device 10 takes a first device configuration. Such first device configuration corresponds to an end-of-stroke signalling configuration wherein the detecting piston 21 is adapted to cooperate with the position sensor 24 to signal the achievement of a first end-of-stroke position, or upper end-of-stroke position, by the main piston 14. The detecting piston 21 and the balancing piston 22 are mounted slidingly to the upper end cap 12 so as to be capable of sliding through such end cap 12. The pistons 21, 22 are mounted so as to be capable of translating along two respective sliding directions which are parallel to each other and orthogonal to the end cap 12. In accordance with a convenient embodiment, the detecting piston 21 has a relatively smaller cross section and the balancing piston 22 has a relatively larger cross section as compared to the above-mentioned smaller cross section of the detecting piston 21. In other words, the detecting piston 21 has a cross section having a relatively smaller area and the balancing piston 22 has a cross section having a relatively larger area as compared to the area of the above-mentioned section of the detecting piston 21 having a smaller area. Cross section means in particular a section of the detecting and balancing pistons orthogonal to the sliding direction of each piston 21, 22. In accordance with a preferred embodiment, the detecting piston 21 and the balancing piston 22 each comprise an intermediate piston portion 21A, 22A which has a constant cross section. Preferably, each portion 21A, 22A has a longitudinal prevailing extension. Preferably, the above-mentioned cross sections having smaller and larger area belong to said intermediate piston portions 21A, 22A. In other words, in the illustrated example, wherein both the intermediate portion 21A of the detecting piston and the intermediate portion 22A of the balancing piston are cylindrical portions, the above-mentioned cross section having a relatively smaller area is a circular section having a relatively smaller diameter and the above-mentioned cross section having a relatively larger area is a circular section having a relatively larger diameter as compared to the diameter of the above-mentioned circular section having a smaller diameter.
Again with reference to Fig. 6, in accordance with a preferred embodiment the balancing piston is shorter than the detecting piston. In accordance with a preferred embodiment, the detecting piston 21 and the balancing piston 22 each have a piston head 25, 26 and an opposite piston end portion 27, 28 which is provided to cooperate with the hydraulic fluid. In accordance with a preferred embodiment, the head 25 of the detecting piston is substantially a cam 25 adapted to cooperate with the sensor 24. In accordance with a preferred embodiment, the detecting piston 21 has a projecting flange 29 of the detecting piston which is preferably located at the end portion 27 of the detecting piston. In accordance with a preferred embodiment, the balancing piston 22 has a projecting flange 30 of the balancing piston which is preferably located at the end portion 28 of the balancing piston.
In accordance with a preferred embodiment, the balancing and detecting pistons are removably mounted to the upper end cap 12. Most preferably, the detecting piston and the balancing piston each comprise a main piston body 21A, 27, 29 and 22A, 28, 30, and the above-mentioned piston head 25 and 26. In accordance with a preferred embodiment, each piston head 25, 26 is removably coupled, more preferably screwed, to the respective main piston body 21A, 27, 29 and 22A, 28, 30. Each of such main piston bodies comprises the intermediate piston portion 21A, 22A, the cylinder end portion 27, 28 and preferably the piston projecting flange 29, 30.
In accordance with a preferred embodiment, the transmission element 23 comprises an oscillating transmission member 23, such as for example an oscillating transmission arm 23. The oscillating transmission member 23 is preferably mounted to the upper end cap 12 by means of a transmission element bracket 31, 32 (Fig. 2 and Fig. 3). The bracket 31, 32 is preferably fastened to the upper end cap 12 by means of fixing screws. Preferably, the bracket 31, 32 comprises a pair of brackets 31, 32, such as for example a pair of L-shaped brackets, between which there is interposed the oscillating transmission member 23. The oscillating transmission member 23 comprises an intermediate portion 33 of the transmission member which is pivoted at the bracket 31, 32 and two opposite end portions 34, 35 of the transmission member which are adapted to respectively engage the detecting piston and the balancing piston. More in particular, the end portions 34 and 35 of the transmission member are adapted to respectively engage the head 25 of the detecting piston and the head 26 of the balancing piston. In accordance with a preferred embodiment, the oscillating transmission member 23 is pivoted at the bracket 31, 32 so that it has two identical lever arms 23A, 24A (Fig. 6).
In accordance with an advantageous embodiment the signalling device 20 comprise an elastic element 36 operatively interposed between the head 26 of the balancing piston and the upper end cap 12. In accordance with a convenient embodiment, as will be better described hereinafter, the elastic element 36 is preloaded at a predetermined preload value. In accordance with a preferred embodiment, the elastic element 36 comprises a helical spring 36 fitted onto the balancing piston 22 and having first and second opposite spring ends which are respectively coupled to a projecting resting portion 37 and a balancing piston washer 38. The projecting resting portion 37 is provided on the balancing piston 22 and more preferably is provided on the head 26 of such piston. The balancing piston washer 38 is passed through by the balancing piston. Such washer 38 preferably is a grooved washer 38 which is configured for receiving the second end of the helical spring 36 and for guiding the movement of such spring during the respective compression and elongation steps.
In accordance with a preferred embodiment, a detecting piston washer 39 is passed through by a detecting piston. The washer 39 preferably is interposed between the head 25 of the detecting piston and the upper end cap 12.
It should be noted that, in accordance with a preferred embodiment, each of the detecting and balancing pistons is coupled with the upper end cap 12 by means of a respective bush 40, 41, which is fastened to the upper end cap 12 and more preferably screwed to such bottom.
It should be further noted that, in accordance with a preferred embodiment, each of the detecting and balancing pistons is associated with one or more sealing elements 42, 44 and 43, 45 provided to guarantee the seal of the hydraulic fluid present in the actuator cylinder and the protection from dust. Such sealing elements are preferably accommodated in suitable housing seats provided in the upper end cap 12. In accordance with a preferred embodiment, the sealing elements 42, 44 and 43, 45 comprise, for each of the detecting and balancing pistons, a sealing gasket 42, 43 for the hydraulic fluid, such as for example an O- ring 42, 43 and a gasket 44, 45 having a dust-removal function.
With reference now to Fig. 4, in accordance with a preferred embodiment, the hydraulic actuator 10 comprises in a per se known way a first actuator chamber 50, or upper chamber 50, and a second actuator chamber 51, or lower chamber 51. The chambers 50, 51 are chambers having a variable volume which are adapted for receiving a hydraulic fluid, such as for example and non-limitingly oil, which is needed for the operation of the actuator 10. Preferably the upper chamber 50 is delimited by the cylinder barrel 11, by the main piston 14 and by the upper end cap 12. Preferably the lower chamber 51 is delimited by the cylinder barrel 11, by the main piston 14 and by the lower end cap 13. The upper chamber and the lower chamber respectively communicate with a first conduit 52, or upper conduit 52, and a second conduit 53, or lower conduit 53. Through the upper and lower conduits 52, 53 the hydraulic fluid enters and exits the chambers 50, 51. In the exemplary embodiment, the detecting piston 21 and the balancing piston 22 are partially extended in the upper chamber 50 and are adapted to cooperate with the hydraulic fluid present in such chamber 50. In particular, as it may be observed in Fig. 6, in the end-of-stroke signalling configuration, the intermediate portions 21A, 22A of the detecting and balancing pistons are at least partially extended in the upper chamber 50.
Having described the structure of the hydraulic actuator 10 and of the signalling device 20, there is now described an exemplary operating mode of the signalling device 20 with reference to the embodiment illustrated in the annexed figures.
According to the operating principle, per se known, of a hydraulic actuator, when the hydraulic fluid is input, preferably by means of a pump, in the lower chamber 51 through the lower conduit 53, the main piston 14 moves in a first direction, in particular towards the upper end cap 12, and the hydraulic fluid contained inside the upper chamber 50 exits through the upper conduit 52. Vice versa, when the hydraulic fluid is input or pumped inside the upper chamber 50 through the upper conduit 52, the main piston 14 moves in a second direction opposite the above-mentioned first direction, in particular, towards the lower end cap 13, and the hydraulic fluid contained in the lower chamber 51 exits through the lower conduit 53.
With reference to Fig. 7, in such figure the main piston 14 takes a second end-of-stroke position, or lower end-of-stroke position, which is opposite as compared to the first end-of-stroke position, or upper end-of-stroke position, which is shown in Fig. 5 and Fig. 6. Further, in Fig. 7 the signalling device 20 takes a second device configuration which is preferably associated with the lower end-of-stroke position of the main piston 14. In the upper end-of-stroke position the main piston 14 is completely retracted. In other words, the shaft 15 of the main piston is received almost completely in the actuator cylinder. In the lower end-of-stroke position the main piston 14 is completely extracted. In other words, the shaft 15 of the main piston projects almost completely on the outside of the actuator cylinder.
It is now assumed that the actuator 10 is initially in the configuration of Fig. 7, that is, with the main piston in the lower end-of-stroke position and the signalling device in the second device configuration. Starting from the configuration of Fig. 7, when the hydraulic fluid is pumped in the lower conduit 53, the piston 14 translates towards the upper end cap 12. Before taking the upper end-of-stroke position, the head 16 of the main piston contacts the detecting piston 21 and starts to push it upwards until the main piston takes the upper end-of-stroke position. During the upward translation of the detecting piston, the head 25 or cam 25 of such piston cooperates with the control roller 24A of the position sensor 24. When the main piston achieves the upper end-of-stroke position, the head 25 or cam 25 of the detecting piston is in the configuration of Fig. 9, wherein it activates the position sensor 24 which signals the achievement of the upper end-of-stroke position by the main piston.
In the upward translation movement the head 25 or cam 25 causes the oscillating transmission member 23 to rotate in a first direction of rotation. With reference to the annexed figures, such first direction of rotation is in particular a counterclockwise rotation direction. It should be noted that the transmission member 23 is preferably pivoted at the above-mentioned bracket 31, 32 by means of a pin 61 and is preferably keyed on a plain bearing to reduce friction with such pin 61. In its movement of counterclockwise rotation, the transmission member 23 pushes the head 26 of the balancing piston 22. In particular, the movement of counterclockwise rotation of the transmission member 23 causes the downward translation of the balancing piston 22. During the downward translation of the balancing piston 22, the elastic element 36 or helical spring 36 is compressed. In other words, when the end-of-stroke signalling device 20 takes the end-of-stroke signalling configuration (Fig. 4, Fig. 5, Fig. 6 and Fig. 9) the oscillating transmission member 23 acts on the balancing piston so as to elastically load the elastic element 36 or helical spring 36.
It should be noted that in the end-of-stroke signalling configuration, the detecting piston 21 projects more from the internal side 12B of the upper end cap 12 with respect to the balancing piston 22. More in particular, it should be noted that, in the end-of-stroke signalling configuration, the detecting piston 21 contacts the main piston 14 while the balancing piston 22 does not contact the main piston 14. In other words, in such configuration, the end portion 28 of the balancing piston is located at a predetermined distance from the head 16 of the main piston while the end portion 29 of the detecting piston contacts the main piston.
It should be further noted that in the end-of-stroke signalling configuration, the pressure of the hydraulic fluid present in the upper chamber 50 of the actuator 10 is substantially negligible, or in any case significantly lower, as compared to the pressure of the hydraulic fluid present in the lower chamber 51. In fact, in such configuration the thrust chamber is the lower chamber 51.
Assuming now of starting from the end-of-stroke signalling configuration (Fig. 6), when the hydraulic fluid is pumped in the upper chamber 50 by means of the upper conduit 52, the main piston 14, pushed by the pressure exerted by the hydraulic fluid, translates downwards. As the main piston departs from the upper end cap 12, the detecting piston 21 loses contact with the main piston 14. Furthermore, as the main piston departs from the upper end cap 12, the elastic element 36 or helical spring 36 extends leading the upward translation of the balancing piston 22. The transmission member 23, pushed by the head 26 of the balancing piston, rotates in a second direction of rotation, that is in clockwise direction with reference to the annexed figures, and pushes the detecting piston 21 downwards, until the projecting flange 30 of the balancing piston abuts on the upper end cap 12 or more preferably on the bush 41 of the balancing piston. In the practice, the detecting piston 21, the balancing piston 22 and the transmission element 23 are configured so that starting from the end-of-stroke signalling configuration and upon increase of the pressure of the hydraulic fluid in the upper chamber 50, the balancing piston 22 translates towards the upper end cap 12 (that is, upwards) and determines, by means of the transmission element 23, a translation of the detecting piston 21 in an opposite direction (that is, downwards) as compared to the translation towards the upper end cap 12 of the balancing piston 22.
During the downward translation of the detecting piston 21, the head 25 or cam 25 of such piston deactivates the position sensor 24 which stops signalling the achievement of the upper end-of-stroke position by the main piston. It should be noted, in particular, that when the signalling device 20 takes the second device configuration shown in Fig. 7, Fig. 8 and Fig. 10, the position sensor 24 is deactivated and therefore does not signal the achievement of the upper end-of-stroke position by the main piston.
With reference to Fig. 8, it should be noted that when the signalling device 20 takes the second device configuration, advantageously there is a space between the head 25 or cam 25 of the detecting piston and the detecting piston washer 39. This advantageously allows not overloading the oscillating transmission member 23 and the pin 61 thereof.
It should be noted that when the main piston moves from the upper end-of-stroke position towards the lower end-of-stroke position, such piston has to overcome a certain resisting force that is essentially determined by the external load acting and by the friction of the sealing elements (per se known) associated with the main piston and adapted to ensure the seal between the main piston and the chambers 50, 51 of the actuator cylinder. This implies that the external load induces a pressure in the hydraulic fluid present in the upper chamber 50. If there were not provided the transmission element 23 and the balancing piston 22, the increase in pressure of the hydraulic fluid present in the upper chamber 50 would also lead to the upward translation of the detecting piston 21 and would have as a side and unwanted effect the activation of the position sensor 24, which would incorrectly signal that the main piston is in the upper end-of-stroke position.
This incorrect behaviour is prevented by providing in the signalling device 20 the balancing piston 22 and the transmission element 23. In fact, the pressure induced in the upper chamber 50 acts at the same time on the detecting piston 21 and on the balancing piston 22. Since, as mentioned hereinabove, the balancing piston 22 has a larger cross section than a cross section of the detecting piston 21, the force exerted upwards by the balancing piston on the oscillating transmission member is greater than the force exerted upwards by the detecting piston 21 on the oscillating transmission member 23. The resulting effect is that the balancing piston 22 through the transmission member 23 prevents the detecting piston from translating upwards. The result is that the control roller 24A is not activated by the cam 25 and the position sensor 24 is not activated inadvertently.
It should be further noted that as the pressure in the upper chamber 50 increases, the thrust difference between the balancing piston 22 and the detecting piston 21 increases and thus there is no risk that the position sensor 24 is activated incorrectly, even if in the upper chamber 50 there are high pressures induced by the load or by the thermal expansion of the hydraulic fluid present therein.
It should be further noted that the above-mentioned preload value of the elastic element 36 is design conveniently so as to match the force needed to initiate the movement of the detecting piston, the oscillating transmission member and the detecting piston starting from the end-of-stroke signalling configuration and when the sliding of the detecting piston is not obstructed by the main piston. In other words, the preload value of the elastic element 36 is designed to substantially overcome the mechanical and oil-pressure frictions only which should be overcome to allow the initial movement of the balancing piston, the detecting piston and the oscillating transmission member, starting from the end-of-stroke signalling configuration. Optionally, the preload value of the elastic element 36 may also account for at least one part of the weight of the balancing piston, the detecting piston and the oscillating transmission member. With reference to hydraulic stabilisers, the above-mentioned preload value may for example vary in a range comprised between about 100 N and about 300 N. In the present example, the above-mentioned preload value of the elastic element 36 is in particular of about 120 N. The above-mentioned preload value advantageously implies that in the end-of-stoke signalling configuration (Fig. 6), the elastic element 36 or the compressed spring 36 exerts through the oscillating transmission member 23 and the detecting piston 21 a negligible force on the main piston 14 and thus there is the advantage of not having inadvertent movements of the main piston 14 induced by the signalling device 20 when the hydraulic actuator 10 is not hydraulically supplied.
Based on the foregoing description, it is thus possible to understand how the end-of-stroke signalling device according to the present invention allows achieving the above-cited objects with reference to the prior art.
The fact of providing a balancing piston and a transmission element operatively interposed between the detecting piston and the balancing piston in fact prevents an inadvertent and incorrect activation of the end-of-stroke signal from occurring when the main piston is in a position different from the end-of-stroke position which has to be signalled by the end-of-stroke signalling device. Even when the hydraulic fluid contained in the chambers of the actuator cylinder is subjected to even high pressure variations, caused by external factors, such as for example and not limitingly the external load and/or variations in ambient temperature.
It is clear that numerous modifications and/or variations may be made to an end-of-stroke signalling device according to the present description.
For example it should be noted that in general it is not strictly necessary for the balancing piston to have a larger cross section than a cross section of the detecting piston. For example in accordance with an alternative embodiment, the oscillating transmission member 23 may be pivoted so that it has two lever arms having different length instead of having two identical lever arms, as shown in the annexed figures. In such case, by suitably sizing the above-mentioned lever arms, the detecting and balancing pistons may also be manufactured for example in such a way that the cross sections of the respective intermediate portions 21A, 22A are identical. However, the fact of manufacturing the detecting and balancing pistons with different cross sections as described hereinabove advantageously allows providing a more compact end-of-stroke signalling device.
It should be further noted that in accordance to an alternative embodiment the transmission between the detecting and balancing pistons may be achieved for example by means of a hydraulic transmission associated to the heads of the balancing and detecting pistons, instead of using the above-mentioned oscillating transmission member 23 pivoted to a bracket. However, the fact of providing the oscillating transmission member 23 allows obtaining a more compact and simpler end-of-stroke signalling device than a solution employing a hydraulic transmission between detecting and balancing pistons.
It should be further noted, where needed, that a pair of end-of-stroke signalling devices according to the present description may be applied to both the opposite end portions of a hydraulic actuator so as to signal both the end-of-stroke positions of the main piston.
It should be further noted that an end-of-stroke signalling device according to the present description may also be applied to hydraulic actuators, per se known, provided with a main piston of the telescopic type.
It should be further noted that the teachings of the present description are not limited to stabilisation systems for applications in the military field. In fact the teachings of the present description are generally applicable to any apparatus or system, also to applications in the civil field, wherein there is a need for signalling an end-of-stroke position of the main piston of a hydraulic actuator.
It should be further noted that an end-of-stroke signalling device according to the present description may be easily integrated into hydraulic actuators of the known type by means of simple re-processing of an end cap of the cylinder of the actuator.
The principle of the invention being understood, the manufacturing details and the embodiments may widely vary compared to what described and illustrated by way of a non-limiting example only, without departing from the scope of the invention as defined in the annexed claims.

Claims

An end-of-stroke signalling device (20) for a hydraulic actuator (10), said hydraulic actuator (10) comprising an actuator cylinder (11, 12, 13) and a main piston (14) accommodated in the actuator cylinder (11, 12, 13), said signalling device (20) being adapted to signal an end-of-stroke position of said main piston (14) and comprising:
- a cylinder end portion (12) of said actuator cylinder (11, 12, 13);

- a detecting piston (21) slidingly mounted to the cylinder end portion (12) so as to be capable of sliding through the cylinder end portion (12);

- a position sensor (24) mounted to the cylinder end portion (12);
said signalling device (20) being adapted to take an end-of-stroke signalling configuration wherein the detecting piston (21) is adapted to cooperate with the position sensor (24) to signal the achievement of said end-of-stroke position by the main piston (14);
characterised in that:
- it comprises a balancing piston (22) slidingly mounted to said cylinder end portion (12) so as to be capable of sliding through the cylinder end portion (12), said detecting piston (21) and said balancing piston (22) being mounted so as to be capable of translating along two respective sliding directions which are parallel to each other and orthogonal to the cylinder end portion (12); and

- it comprises a transmission element (23) operatively interposed between said detecting and balancing pistons (21, 22).
An end-of-stroke signalling device (20) according to claim 1, wherein the detecting piston (21) has a relatively smaller cross section and the balancing piston (22) has a relatively larger cross section as compared to said smaller cross section.
An end-of-stroke signalling device (20) according to claim 2, wherein the detecting piston (21) and the balancing piston (22) each comprise an intermediate piston portion (21A, 22A) which has a constant cross section, and wherein said smaller and larger cross sections belong to said intermediate piston portions (21A, 22A).
An end-of-stroke signalling device (20) according to any one of the preceding claims, wherein the cylinder end portion (12) comprises an external side (12A) and an opposite internal side (12B) which are intended for respectively facing the outside and the inside of said cylinder (11, 12, 13), wherein in the end-of-stroke signalling configuration the detecting piston (21) projects more from said internal side (12B) with respect to the balancing piston (22).
An end-of-stroke signalling device (20) according to any one of the preceding claims, wherein the detecting and balancing pistons (21, 22) are removably mounted to the cylinder end portion (12).
An end-of-stroke signalling device (20) according to any one of the preceding claims, comprising a transmission element bracket (31, 32) fastened to the cylinder end portion (12), wherein said transmission element (23) comprises an oscillating transmission member (23) having an intermediate transmission member portion (33) which is pivoted at said bracket (31, 32) and two opposite transmission member end portions (34, 35) which are adapted to respectively engage the detecting piston (21) and the balancing piston (22), the detecting piston (21) and the balancing piston (22) each having a piston head (25, 26) adapted to engage the oscillating transmission member (23) and an opposite piston end portion (27, 28) provided to cooperate with a hydraulic fluid.
An end-of-stroke signalling device (20) according to claim 6, comprising an elastic element (36) operatively interposed between the piston head (26) of the balancing piston (22) and the cylinder end portion (12).
An end-of-stroke signalling device (20) according to claim 7, wherein said elastic element (34) is preloaded at a predetermined preload value.
An end-of-stroke signalling device (20) according to claim 7 or 8, comprising a balancing piston washer (38) passed through by the balancing piston (22), wherein the balancing piston (22) comprises a projecting resting portion (37), wherein said elastic element (36) comprises a helical spring (36) fitted on the balancing piston (22) and having opposite first and second spring ends which are respectively coupled to the projecting resting portion (37) and to the balancing piston washer (38), wherein the balancing piston washer (38) is a grooved washer which is configured for receiving the second spring end and to guide the movement of such spring during the respective compression and elongation steps.
An end-of-stroke signalling device (20) according to any of claims 6 to 9, comprising a detecting piston washer (39) passed through by the detecting piston (21), wherein said signalling device (20) is adapted to take a second device configuration associated with a second end-of-stroke position of the main piston (14), in said second configuration being present a space between the head (25) of the detecting piston and the detecting piston washer (39).
A hydraulic actuator (10) comprising an end-of-stroke signalling device (20) as defined in any one of the preceding claims.
A hydraulic actuator (10) according to claim 11, wherein in the end-of-stroke signalling configuration the detecting piston (21) contacts the main piston (14) while the balancing piston (22) does not contact the main piston (14).
A hydraulic actuator (10) according to claim 11 or 12, wherein said actuator (10) comprises a first and a second actuator chamber (50, 51), said first and second chambers (50, 51) being variable-volume chambers which are adapted to receiving a hydraulic fluid for the operation of the hydraulic actuator, the detecting piston (21) and the balancing piston (22) being partially extended in the first actuator chamber (50) and being adapted to cooperate with the hydraulic fluid present in said first chamber (50), wherein the detecting piston (21), the balancing piston (22) and the transmission element (23) are configured so that starting from the end-of-stroke signalling configuration and upon increase of the pressure of the hydraulic fluid in the first actuator chamber (50), the balancing piston (22) moves towards the cylinder end portion (12) and determines, by means of the transmission element (23), a translation of the detecting piston (21) in a direction opposite to said translation of the balancing piston (22) towards the cylinder end portion (12).
An hydraulic actuator (10) according to claim 13 in that it depends on claim 11 and claim 8, wherein in said end-of-stroke signalling configuration the oscillating transmission member (23) acts on the balancing piston (22) so as to elastically load said elastic element (36) and wherein said preload value of the elastic element is designed so as to correspond to the force needed to initiate the movement of the detecting piston, the oscillating transmission member and the detecting piston starting from the end-of-stroke signalling configuration and when the sliding of the detecting piston is not obstructed by the main piston.
A surface launcher comprising a stabilisation system including a hydraulic actuator as defined in any of claims 12 to 14.