Patent Description:
Helical rotary actuators are hydraulic actuators configured to convert the linear displacement of a piston into rotary movement, by means of helical gears. They are compact, simple and efficient. They produce a high instant torque in both directions of rotation.

These helical actuators are generally used for the movement of parts in the sector of agricultural and earth moving machines, in the maritime sector, in lifting systems, for controlling valves and, more generally, for applications requiring rotation of members along a limited and predefined arc of rotation. In fact, since the angle of rotation is determined by the length of the actuator, in general said actuators can provide in output a rotation of <NUM>°, <NUM>° or, in some cases, up to <NUM>°.

Examples of helical rotary actuators manufactured according to a particularly widespread production method are described in <CIT> and <CIT>.

Said actuators generally comprise an outer cylindrical-shaped casing, a shaft and a piston integral with a cylindrical sleeve. The piston is mounted sliding in the cylindrical casing while the shaft is mounted rotatably with respect to the casing and is housed passing through the piston and the cylindrical sleeve.

On the outer surface of a section of the shaft, a helical toothing is obtained which engages a first corresponding helical toothing obtained on the inner surface of the piston sleeve. The outer surface of the piston sleeve carries a second helical toothing that engages a crown wheel integral with the housing.

The piston sleeve is hydraulically sealed between the housing and the shaft. When a hydraulic pressure is applied to an inlet in the casing, the piston sleeve is axially displaced and rotates in a first direction of rotation since the toothing on its outer diameter and the crown wheel of the housing force said piston sleeve to rotate.

At the same time, the toothing on the inner diameter of the piston sleeve, in turn, forces rotation of the shaft in the above-mentioned first direction of rotation.

The application of hydraulic pressure to another inlet of the casing causes the piston to retract, and the sleeve and therefore the shaft to rotate in a second direction of rotation opposite to the first direction.

The helical rotary actuators conceived as above, although efficient, nevertheless have some limitations.

Of these, the main limitation is their complicated construction and the consequent cost of producing said devices. In fact, the helical toothings provided on the piston sleeve, on the shaft and on the outer casing require particularly accurate and complex machining operations. The presence of a double pair of toothings (shaft/sleeve and sleeve/casing) on the one hand is necessary in order to transmit the rotation to the shaft, but on the other it makes these elements fairly costly to produce.

Hydraulic rotary actuators having the same technical features mentioned in the pre-characterizing portion of the appended claim <NUM> are already known from patent documents, <CIT>, <CIT> and <CIT> for examples.

In this context, the object of the present invention is to propose a hydraulic rotary actuator that overcomes the drawbacks of the known art cited above.

In particular, an object of the present invention is to provide a hydraulic rotary actuator which is simpler to produce in construction terms, and is therefore also cheaper than the known ones.

A further object of the present invention is to provide a more compact and more lightweight hydraulic rotary actuator than those of the known art.

The above-mentioned objects are achieved by a hydraulic rotary actuator in accordance with the attached claim <NUM>.

In detail, according to the present invention the actuator comprises a body that defines at least one cylindrical inner cavity with an axis Xc.

The cylindrical cavity houses in a sliding manner a piston which defines and separates, inside said cavity, a first chamber and a second chamber that can be supplied with a pressurized hydraulic fluid, through respective passages obtained in the body, to cause displacement of the piston in the cylindrical cavity.

The piston comprises in general a substantially cylindrical body. The length of the piston is less than the length of the cylindrical cavity; the difference between the two lengths is therefore equal to the maximum stroke that can be performed by the piston in the cavity.

On the outer surface of the piston at least one seat is obtained adapted to house a seal that co-acts with the inner surface of the cavity of the body to provide the seal between the first chamber and the second chamber.

The piston is also provided with a through seat which extends between a first end and a second end.

In the above-mentioned seat a shaft is inserted which is rotatably mounted in the body around an axis of rotation Xa. Said shaft carries at least at one of its ends a connection flange, obtained in the same piece as the shaft or made integral with it by means of screws or other fastening means, which allows connection of the actuator to a part of the device/apparatus in which it is used.

According to the invention, a section of the outer surface of the shaft is provided with a first threading or toothing adapted to engage a corresponding second threading or toothing obtained on the surface of the piston seat.

According to the invention, the axis of rotation Xa of the shaft, which coincides with the axis of the seat obtained in the piston, is arranged eccentric with respect to the axis Xc of the cylindrical cavity, which coincides with the axis of the piston body.

Said characteristic, together with the presence of the two reciprocally engaged threadings/toothings, allows the translation movement of the piston in the cylindrical cavity to be converted into a rotation movement of the shaft.

In fact, if the above-mentioned axes of the shaft and of the cavity coincided, by applying a hydraulic pressure in one of the two chambers of the cylindrical cavity, the piston would move forward in one direction and simultaneously, due to the threading-toothing pair, it would rotate around the shaft which would remain substantially stationary. For this reason, in the actuators of the known art, a double pair of helical toothings are provided, where the outermost pair allows the outer casing to work as a reaction element and therefore rotate the shaft.

In the actuator according to the present invention, due to the eccentric positioning of the shaft with respect to the cavity and the piston, the latter is not able to rotate in the cylindrical cavity. By applying a hydraulic pressure in one of the two chambers, the piston moves in the cylindrical cavity, rotating the shaft due to the coupling of the two toothings/threadings obtained respectively on the shaft and on the surface of the piston seat.

In practice, the eccentric arrangement of the shaft means that the body can be made to work as a reaction element which, preventing the piston from rotating, allows transmission of the rotary movement to the shaft.

The configuration of the actuator described above has various advantages compared to that of the actuators of the known art described above.

Firstly, as is evident, the structure of the actuator is simpler due to the presence of one single threading/toothing pair, compared to the two helical toothing pairs of the actuators of the known art.

Furthermore, in the variation in which threadings are used, it is possible to produce the two parts, shaft and piston, with traditional and not particularly sophisticated machine tools.

Another advantage is that the actuator body can be lighter. In the known actuators, in fact, the body is generally made of steel since it has to carry on the inner surface, or in any case on a collar welded to the inner surface, the helical toothing that co-acts with the toothing of the piston sleeve.

In the actuator according to the invention, since no toothings or threads are provided on the inner surface of the cavity, it is possible to produce the body with materials having a lower mechanical resistance and also a lower specific weight, like aluminium or other light alloys.

Although the actuator according to the present invention can be produced using a pair of helical toothings on the piston and on the shaft, in the description below reference will be made to a preferred embodiment in which a pair of threadings is used.

According to an aspect of the invention, the ratio Ec/Dp between the eccentricity Ec1 and the diameter of the piston Dp is between <NUM>/<NUM> and <NUM>/<NUM>.

These eccentricity values allow for limitation/reduction of the friction losses between the shaft and the piston and, on the other hand, limitation of the actuator radial dimensions.

According to another aspect of the invention, the threading obtained on the shaft and the threading obtained on the piston have a helix angle (φ) preferably equal to or greater than <NUM>°, more preferably between <NUM>° and <NUM>°.

The choice of the helix angle depends essentially on the desired characteristics of the actuator in terms of reactivity, maximum arc of rotation and dimensions of the body (length).

The number of leads of the shaft and piston threadings varies according to the diameter of the piston and the helix angle.

According to another aspect of the invention, on the outer surface of the piston at least two seats are obtained adapted to each house an annular guide element adapted to co-act with the surface of the cylindrical cavity.

In further detail, said guide elements are interposed between the piston body and the surface of the cylindrical cavity and slide in contact with the latter, preventing direct contact with the piston body.

In fact, since the eccentric coupling between shaft and piston causes a radial thrust on the latter, the sliding in contact on the cylindrical surface would cause significant friction with dissipation of power and considerable wear of the parts.

Said annular guide elements preferably have a substantially rectangular flattened section. According to an aspect of the invention, said guide elements are preferably made of reinforced composite materials such as, for example, Bearite™ or other equivalent polymer materials, with a similar or higher pressure resistance value.

According to the invention, the actuator body comprises a central part, with an annular wall that defines the inner cylindrical cavity, and two closing elements, adapted to close respective open ends of the annular wall.

The central part is typically a machined monolithic element. The closing elements are connected to said central part by means of screws or similar.

The ends of the shaft are rotatably housed in the respective closing elements. Preferably, the shaft is supported in said closing elements by bearings, for example ball or roller bearings, or similar.

According to the invention, each of the two chambers can be connected to a pressurised hydraulic fluid source by means of specific hydraulic passages. Each hydraulic passage comprises a first section, produced in the annular wall of the central part, and a second section, produced in the corresponding closing element, where said second section emerges on an inner face of said corresponding closing element facing the corresponding chamber.

This configuration allows the maximum piston stroke to be obtained (which in turn is proportional to the available arc of rotation) with the same length of the actuator body and without arranging fittings, couplings and the like on said closing elements.

According to another aspect of the invention, the actuator body is provided with fastening means for connecting the actuator to a support structure of the device or of the apparatus in which it is used.

According to a variation, said fastening means comprise holes, if necessary threaded, obtained in one or both the closing elements or, if necessary, also on the central part of the body.

The above-mentioned objects of the present invention are further achieved by an actuator assembly comprising two actuators according to one or more of the variations described above. In detail, the actuator assembly comprises one single common body for the two actuators, the two cylindrical cavities of which are arranged with the respective axes Xc, Yc perpendicular to each other.

According to a preferred variation, said axes Xc, Yc of the first cavity and the second cavity are respectively arranged on parallel planes and are offset from each other.

This variation is designed for applications comprising an articulation that requires a double rotation on two axes perpendicular to each other. Said articulation is applied, for example, in lifting equipment, in particular in systems for the movement of baskets, aerial platforms or equivalent equipment, where a rotation around a first horizontal axis is required to regulate the "pitch" of the basket/platform and a second rotation around a vertical axis to orient said basket/platform in the horizontal plane.

The structure of the two actuators is substantially identical in terms of operating concept.

In further detail, the second cylindrical cavity houses a second piston of the second actuator with a through seat which houses a second shaft, the rotation axis Ya of which is perpendicular to the axis Xa of the first shaft of the first actuator. The surfaces of the shaft and of the seat are provided with respective reciprocally engaged threads.

Also in this case, the axis of rotation Ya of the second shaft is arranged eccentrically, with an eccentricity Ec2, with respect to the axes Yc of the cylindrical cavity and Yp of the piston.

The characteristic dimensions of the two actuators (diameter of the piston, length of the threads on shaft and seat of the piston, helix angle, eccentricity, maximum angle of rotation, etc.) can be the same or different according to requirements.

According to a preferred embodiment, the body of the two actuators (more precisely the respective central parts that define the cylindrical cavities) is made in one single piece.

Alternatively, said body can be formed of two separate elements made integral by means of screws, or similar, and if necessary interlocking and/or centring means.

Further characteristics and advantages of the present invention will become clearer from the description of an example of a preferred, but not exclusive, embodiment of a hydraulic rotary actuator, as illustrated in the attached figures in which:.

With reference to the attached figures from <NUM> to <NUM>, the number <NUM> indicates overall a hydraulic rotary actuator according to the present invention.

The actuator comprises a body <NUM>, a shaft <NUM> and a piston <NUM>.

The body <NUM> comprises in turn a central part <NUM> and two closing elements <NUM>, <NUM>.

The central part <NUM> of the body <NUM> comprises an annular wall that defines within it a cylindrical cavity <NUM> with axis Xc. Said cavity <NUM> is delimited at the ends by the closing elements <NUM>, <NUM>. Said closing elements <NUM>, <NUM> are fixed to the central part <NUM> by means of screws <NUM>.

Preferably, an annular gasket <NUM> is interposed between each closing element <NUM>, <NUM> and an end face 11a of the central part <NUM>, which acts as an abutment for said closing elements.

Preferably, the central part <NUM> and the closing elements <NUM>, <NUM> of the body <NUM> are made of aluminium or other light alloys.

The piston <NUM> and the shaft <NUM> are typically made of steel.

The piston <NUM> comprises a cylindrical body with axis Xp slidingly housed in the cylindrical cavity <NUM> of the body <NUM>. Said piston <NUM> defines and separates two chambers <NUM>, <NUM> in said cylindrical cavity <NUM>. Each of the two chambers <NUM>, <NUM> can be connected to a pressurised hydraulic fluid source by means of specific hydraulic passages obtained in the annular wall or, as in the example illustrated, also in the closing elements.

In detail, according to the embodiment illustrated in <FIG>, a first section <NUM> of the hydraulic passage is obtained in the annular wall of the central part <NUM> and a second section <NUM> of the hydraulic passage is obtained in the closing elements. In further detail, the first section <NUM> extends between the outer surface 11b of the annular wall <NUM> and the end faces 11a of said central part <NUM>.

The second section <NUM> extends between an abutment area 12b,13b of the closing elements <NUM>, <NUM> and the inner face 12a, 13a of said closing elements, facing the cavity <NUM> and the chambers <NUM>, <NUM> respectively.

The first section <NUM> and the second section <NUM> of the hydraulic passage are obtained in the central part <NUM> and in the closing elements <NUM>, <NUM> so that when said parts are assembled, the end of the first section <NUM> that emerges on the abutment face 11a of the central part <NUM> is aligned with the end of the second section <NUM> that emerges on the abutment area 12b, 13b of the closing elements <NUM>, <NUM>.

Said configuration allows for optimisation of the actuator dimension in the longitudinal direction (parallel to the axis Xc of the cavity <NUM>). In fact, unlike the known actuators in which the hydraulic fluid inlets into the chambers are obtained in the wall of the cylindrical cavity, with this configuration it is possible to bring said inlets to the head areas (in the closing elements <NUM>, <NUM>), so that the piston <NUM> can exploit the whole length of the cylindrical cavity <NUM> for its stroke. This is possible without having to connect in the area of the closing elements <NUM>, <NUM> couplings or pipes which, in some cases, can interfere with the connection of the actuator to the relative device/apparatus.

Preferably, according to the invention, the body of the piston <NUM> has a diameter slightly smaller than that of the cylindrical cavity. In general the difference between said diameters is a few tenths of a millimetre.

To guide the sliding of the piston <NUM> in the cavity <NUM>, guide elements <NUM> are provided housed in respective seats <NUM> obtained on the outer surface of the piston.

Said guide elements <NUM> comprise flat annular bands made of Bearite™ or equivalent materials.

The thickness of the guide elements <NUM> is calibrated so that their outer surface protrudes beyond the outer surface of the piston <NUM>, thus the sliding by contact occurs only between said guide elements <NUM> and the surface 14a of the cylindrical cavity <NUM>.

According to the invention, at least one pair of guide elements <NUM> is provided, each of which is arranged in the area of an end of the piston <NUM>. According to the length of the piston <NUM>, there can be four of said guide elements, as in the example of the figures from <NUM> to <NUM>, or more.

To guarantee the hydraulic seal between the two chambers <NUM>, <NUM>, on the outer surface of the piston <NUM> a seat <NUM> is obtained adapted to house an annular gasket <NUM> which slides in contact with the surface 14a of the cavity <NUM>. Said gasket <NUM> is arranged roughly in the area of the centre line of the piston <NUM>, between the guide elements <NUM>.

In the body of the piston, a seat <NUM> is obtained in which the shaft <NUM> is rotatably housed. Said seat <NUM> comprises a cylindrical hole, the axis of which coincides with the axis Xa of the shaft <NUM> and is parallel to the axis Xc of the cylindrical cavity <NUM>. The hole extends throughout the length of the piston <NUM>.

The shaft <NUM> is rotatably supported by the closing elements <NUM>, <NUM>. In detail, each closing element <NUM>, <NUM> is provided with a seat <NUM> in which an end of the shaft <NUM> is housed, preferably by means of bearings <NUM>, for example oblique ball bearings or tapered roller bearings.

To guarantee the hydraulic seal between the two chambers <NUM>, <NUM>, on a cylindrical section <NUM> of the seat <NUM> at least one seat <NUM> is obtained which houses an annular gasket <NUM> adapted to co-act with a corresponding cylindrical section <NUM> of the shaft <NUM>. Preferably, in the seat <NUM>, two seats <NUM> and two respective gaskets <NUM> are obtained.

A section <NUM> of the shaft <NUM> has a thread <NUM> adapted to engage a corresponding threading <NUM> (nut screw) obtained on a section of the seat <NUM>. The threadings <NUM>, <NUM> have square or, if necessary, trapezium-shaped helix profile. The helix angle φ of the threadings <NUM>, <NUM> is typically approximately <NUM>°-<NUM>°.

As mentioned above, said value of the helix angle can be lower or higher according to the operating parameters of the actuator; these can include, for example, the available arc of rotation, the longitudinal dimension (length) of the actuator and the reactivity, namely the rotation speed given the same fluid pressure supplied and torque required.

According to the invention, the axis of rotation Xa of the shaft <NUM> is eccentric with respect to the axes Xc of the cylindrical cavity <NUM> and Xp of the piston <NUM>.

As explained above, by applying a pressure to the hydraulic fluid in one of the two chambers <NUM>, <NUM>, the piston <NUM> is pushed in a direction along the axis Xp. The coupling between the threads <NUM>, <NUM> of the shaft and the piston, followed by displacement of the piston <NUM>, causes rotation of the shaft <NUM>. Thanks to the eccentricity Ec between the shaft <NUM> and the piston <NUM>, the piston cannot rotate on itself, discharging the reaction of the central part <NUM> of the body <NUM> onto the shaft <NUM>.

The value of the eccentricity Ec is parameterized according to the diameter of the piston.

An optimal eccentricity value Ec that limits the diameter of the piston and at the same time minimizes the friction losses between the threads and does not produce an excessive radial stress on the guide elements <NUM> of the piston <NUM>, is approximately one tenth of the diameter Dp of said piston <NUM>.

In the embodiment illustrated in <FIG>, the shaft <NUM> is provided at its ends with two flanges <NUM>, <NUM> which allow connection of the actuator to one of the parts (fixed or mobile) of the device/apparatus. In practice, said flanges <NUM>, <NUM> protrude beyond the seats <NUM> of the closing elements <NUM>, <NUM>.

In detail, a flange <NUM> is made in one piece with the shaft <NUM> while a second flange <NUM> is fixed to the opposite end of the shaft <NUM> by means of screws 47a and if necessary drive pins.

According to this variation, also the closing elements <NUM>, <NUM> are provided with connection means, holes <NUM> in the example illustrated, which allow the body <NUM> of the actuator to be fixed to the other part of the device/apparatus.

<FIG>, <FIG> and <FIG> illustrate an actuator <NUM> according to another embodiment of the present invention. The operation and particular characteristics are the same as those described for the variation of <FIG>.

Unlike the previous one, in this variation the shaft <NUM> has only one connection flange <NUM>, preferably integral with it. The opposite end of the shaft <NUM> is covered with a cover <NUM> fixed to the closing element <NUM> in the area of the seat <NUM>.

According to this variation, furthermore, both the closing elements <NUM>, <NUM> and the central part <NUM> of the body are provided with connection means, for example in the form of holes <NUM>, <NUM>, for connecting the actuator to a part of the device/apparatus.

According to a preferred variation, said holes <NUM>, <NUM> are provided in the area of seats <NUM>, obtained on said central part <NUM> and said closing elements <NUM>, <NUM>, for the positioning and centring of a bracket <NUM> or equivalent fastening means, as illustrated in <FIG>.

<FIG> illustrate an actuator assembly <NUM> that comprises a first actuator <NUM> and a second actuator <NUM> produced according to the inventive concepts described for the previous variations.

According to this particular embodiment, the actuator assembly <NUM> comprises a single monolithic body <NUM> in which both the cavities <NUM>, <NUM> that house the respective pistons <NUM>, <NUM> are obtained. In practice, said body <NUM> comprises two central parts <NUM>, <NUM> of the respective first and second actuators.

According to this variation, the axes Xc, Yc of the first cavity <NUM> and second cavity <NUM> respectively are perpendicular to each other; likewise, the axes Xa, Ya of the respective shafts <NUM>, <NUM> of the first actuator <NUM> and second actuator <NUM> are perpendicular.

In the example of the figures, both the shaft <NUM> of the first actuator <NUM> and the shaft <NUM> of the second actuator <NUM> are provided with two connection flanges <NUM>, <NUM>, <NUM>, <NUM>.

This embodiment is applied particularly effectively for the movement of baskets or aerial platforms connected to a lifting arm.

The first actuator <NUM>, generally having larger dimensions and therefore providing a higher torque, has the task of controlling the pitch movement (rotation around a horizontal axis Xa) of the basket or platform to keep the support surface parallel to the ground during deployment of the lifting arm.

The second actuator <NUM> has the task of controlling rotation of the basket or platform around a vertical axis Ya to orient them in the horizontal plane.

Said actuator assembly allows considerable simplification of the movement system used in lifting systems of the known art, where in general the pitch movement is governed by a linear hydraulic piston and the rotation movement is governed by a helical rotary actuator of the known art like those described above.

Claim 1:
A hydraulic rotary actuator (<NUM>) comprising:
- a body (<NUM>) comprising a central part (<NUM>) with an annular wall that defines at least one cylindrical cavity (<NUM>) with an axis (Xc) and two closing elements (<NUM>, <NUM>), adapted to close respective open ends of said annular wall;
- a piston (<NUM>), housed moving in the cylindrical cavity (<NUM>) and adapted to separate, in said cavity (<NUM>), a first chamber (<NUM>) and a second chamber (<NUM>) which can be supplied with a pressurized hydraulic fluid, said piston (<NUM>) having a through seat (<NUM>) between a first end and a second end; and
- a shaft (<NUM>), housed in the trough seat (<NUM>) of the piston (<NUM>) and mounted rotatable in the body (<NUM>) about an axis of rotation (Xa), said shaft (<NUM>) carrying at the end at least one connection flange (<NUM>);
wherein the ends of the shaft (<NUM>) are rotatably housed in seats (<NUM>) produced in the closing elements (<NUM>, <NUM>),
wherein a section (<NUM>) of the shaft (<NUM>) is provided on the outer surface with a first thread (<NUM>) adapted to engage a corresponding second thread (<NUM>) produced on the surface of the seat (<NUM>) of the piston (<NUM>),
wherein the axis of rotation (Xa) of the shaft is arranged eccentric with an eccentricity (Ec) with respect to the axis (Xc) of the cylindrical cavity (<NUM>);
wherein each of the two chambers (<NUM>, <NUM>) is connectable to a source of a pressurized hydraulic fluid by means of specific hydraulic passages (<NUM>, <NUM>), the actuator (<NUM>) being characterized in that each hydraulic passage comprises a first section (<NUM>) produced in the annular wall of the central part (<NUM>) and a second section (<NUM>) produced in the corresponding closing element (<NUM>, <NUM>), said second section emerging on an inner face of said corresponding of closing element (<NUM>, <NUM>) facing the corresponding chamber (<NUM>, <NUM>).