The present invention relates to a rotary hydraulic machine having radial pistons.

Hydraulic machines are devices which transform kinetic energy from a shaft into pressurising energy of a liquid, and vice versa.

In the first case the hydraulic machine functions as a pump, while in the second case the hydraulic machine functions as a motor. In both cases, the operating liquid is oil.

Rotary hydraulic machines are those in which the element transmitting the kinetic energy to the outside (in the case of motors) or which introduces the kinetic energy to the inside (in the case of pumps) is a shaft provided with continuous rotary motion.

For the sake of simple presentation, from here on explicit reference will be made to the case of motors, as motors are differentiated from pumps only in regard to the direction of energy flow and not in regard to constructional mechanisms.

Rotary hydraulic motors with pistons are constituted by one or more chambers in which a volume is continually varied by the motion of a piston internally of a cylindrical seating.

The chambers are placed periodically in fluid communication with the supply environment and with the discharging environment by means of holes which are freed by the relative motion between the piston and the cylinder.

In rotary hydraulic motors having radial pistons, to which the present invention relates, the pistons translate along axes which are arranged perpendicularly to the rotation axis of the drive shaft. Rotary hydraulic motors with radial pistons are known which have a static cylinder block internally of which a plurality of housing seatings for the cylinders are afforded. These seatings are arranged radially equidistanced (in a star fashion) with respect to the axis of the drive shaft.

The cylinders are constrained to the cylinder block by means of pins which enable the cylinders to oscillate in "pendulum fashion" about axes that are parallel to the drive shaft.

Respective pistons are arranged internally of the cylinders, which pistons can slide along directions that are perpendicular to the drive shaft.

The pistons are active on a crank of the drive shaft, which crank rotates eccentrically with respect to the drive shaft.

An annular crown is keyed rotatably on the crank and is associated to the pistons.

When the chamber defined between the piston and the head of the respective cylinder is placed under pressure, the piston translates distancingly from the cylinder head and transmits a force to the annular crown.

The crown transmits a force to the crank of the drive shaft directed perpendicularly to the rotation axis thereof.

This force is clearly offset with respect to the rotation axis of the drive shaft, and thus generates a torque which sets the drive shaft in rotation. The combined action of the various cylinders guarantees a continuous rotary drive of the rotating shaft.

These types of motors and, equally, pumps, exhibit an important drawback. The pistons perform translations along directions which intersect in the centre of the annular crown, the centre of which crown does not coincide (but as mentioned, it is eccentric) with the rotation axis of the drive shaft. On the contrary, the cylinders are arranged in a star-fashion concentrically to the rotation axis of the drive shaft.

Therefore, the translation of the pistons generates a torque on the cylinders which induce the cylinders to oscillate in a "pendulum fashion" during functioning of the motor.

The pressure transmitted by the pistons to the cylinders (responsible for the torque mentioned above) is identical (net of friction) to the force transmitted by the piston to the annular crown (a force which sets the drive shaft in rotation).

Thus the pressure transmitted by the pistons to the cylinders is of considerable entity (directly proportional to the power of the motor).

This pressure is unloaded on the cylinder body only via the two pins which constrain each cylinder to the cylinder body.

Therefore great attention must be paid during the design stage with regard to the dimensioning and mechanical properties of the cited pins.

Further, the inevitable wear on these pins (or the relative seatings) creates play in the coupling between the cylinder and the cylinder body which play requires the rectification of the motor.

What is more, the maximum power of these motors has physical limitations in the possibility of realising pins and relative seatings which are able to guarantee an adequate working life of the motor.

In this context, the technical objective underpinning the present invention is to provide a rotary hydraulic machine having radial pistons which obviates the drawbacks in the prior art as cited herein above.

In particular, an aim of the present invention is to provide a rotary hydraulic machine having radial pistons which requires only small reconditioning operations. A further aim of the present invention is to provide a rotary hydraulic machine with radial pistons which is dimensionable for any power.

The set technical objective and the set aims are substantially attained by a rotary hydraulic machine having radial pistons, comprising the technical characteristics set out in one or more of the appended claims.

Further characteristics and advantages of the present invention will more clearly emerge from the following non-limiting description of a preferred but not exclusive embodiment of a rotary hydraulic machine having radial pistons, as illustrated in the accompanying drawings, in which:

- figure 1 is a section view of a rotary hydraulic machine having radial pistons of the present invention, with some parts removed better to evidence others;

- figure 2 is a view of the machine of figure 1 in a different operating configuration;

- figure 3 is a view of the machine of figure 1 in a further different operating configuration;

- figure 4 is a section according to plane IV-IV of the machine of figure 1 ; and

- figure 5 is an enlarged view of a detail of the machine of figure 1.

With reference to the figures of the drawings, 1 denotes in its entirety a rotary hydraulic machine having radial pistons of the present invention. The machine 1 comprises a rotating shaft 2 which, in the case of a motor, is a drive shaft and in the case of a pump is the shaft introducing energy into the pump.

The rotating shaft 2 rotates with a continuous motion about a rotation axis R (illustrated in figure 4).

The machine 1 further comprises a fixed cylinder body 3 exhibiting a plurality of housing seatings 4. The housing seatings 4 are arranged radially equidistanced to the axis R of rotation of the rotating shaft 2, such as to realise a star-configuration.

In the preferred embodiment of the invention the housing seatings are five in number (see figures 1 , 2 and 3).

A relative cylinder 5 is provided internally of each housing seating 4, which cylinder 5 is able to rotate internally of the housing seating 4 about an axis C which is parallel to the rotation axis R of the rotating shaft 2. A relative piston 6 is provided internally of each cylinder 5. Each piston 6 is slidably coupled to the respective cylinder 5 along a sliding axis P (in the accompanying figures, and in particular in figures 1, 2 and 3 a cylinder 5 and the respective piston 6 have been removed so that the housing seating 4 can be more clearly illustrated).

The sliding axes P are perpendicular to the rotation axis R of the rotating axis 2 and perpendicular to the rotation axes C of the cylinder 5 internally of the respective housing seatings 4.

Each piston 6 is further coupled to a crank 7 of the rotating shaft 2. The crank 7 is eccentric with respect to the rotation axis R of the rotating shaft 2 (see figure 4).

By crank, in the context of the present invention, reference is made to a portion of the rotating shaft 2 which develops in a "goose-neck" shape with respect to the rotating shaft, i.e. which forms a hook shape with respect to the straight development of the rotating shaft.

An annular crown 8 is keyed on the crank 7, which crown 8 is rotatable with respect to the crank about an axis that is parallel to the rotation axis R of the rotating shaft 2.

Each piston 6 is constrained to the annular crown 8 along a direction coinciding with the sliding axis P, while it is free to slide with respect to the annular crown 8 along a perpendicular direction to the sliding axis P. In other words, each piston 6 cannot distance from the annular crown 8 but the crown 8 can rotate with respect to the piston 6.

For this purpose, the annular crown 8 comprises retaining organs 9 which retain the base of the piston 6 on the external surface 8 a of the annular crown 8 (as illustrated in figure 4).

Note that the retaining organs 9 guarantee however that the base of the piston 6 can slide along the external surface of the annular crown 8.

The retaining organs 9 are, for example, constituted by a pair of skids acting between the base of the piston 6 and the external surface 8a of the annular crown 8.

Rollers 10 (figure 4) are interposed between the annular crown 8 and the crank 7, which rollers 10 enable the annular crown 8 to rotate on the crank 7.

In this way, when a force is applied on the external surface of the annular crown 8 directed towards the centre thereof, this force generates a torque with respect to the rotation axis R of the rotating shaft 2 which causes rotation thereof.

To this end, note that the sliding axes P of the pistons 6 converge at a point coinciding with the centre of the annular crown 8 (and therefore eccentric with respect to the rotation axis R of the rotating shaft 2).

When the pressure increases in the expansion chamber 11 (the variable- volume chamber which is created between the piston head 6 and the cylinder 5), the piston 6 transmits a force to the annular crown 8 which sets the rotating shaft 2 in rotation (according to the mechanism as described above).

In this regard one or more conduits 12 are enslaved to each cylinder 5, which conduits 12 are delivery conduits of pressurised oil, and one or more discharge conduits 13 of the oil (see figure 4). In particular, when a piston 6 transmits the above-cited force to the annular crown 8, the crown 8 sets the crank 7 in motion and the piston 6 translates internally of the cylinder 5.

Since, as mentioned, the sliding axis P of the pistons 6 passes through the centre of the annular crown 8 while the cylinders 5 are free to rotate internally of the seatings 4 arranged equidistanced from the rotation axis R of the rotating shaft 2, the sliding of the piston 6 internally of the cylinder 5 causes a rotation of the cylinder 5.

In other words, the pistons 6 near and distance from the rotation axis R of the rotating shaft 2, while the cylinders 5 are always at the same distance from the rotation axis R.

Therefore, in order to have a sliding motion of the piston 6 internally of the cylinder 5, the cylinder must be able to rotate internally of the seating 4. By comparing figures 1 , 2 and 3 with one another, the entity of the rotation can be noted, as a function of the piston 5 run and thus of the translation of the crank 7.

In particular, between figure 1 and 2 the crank 7 is translated, bringing it into a distanced position by 120° in a clockwise direction with respect to the original position thereof. The same type of motion differentiates figure 2 from figure 3 and figure 3 from figure 1.

As can be observed, the cylinders 5 perform a pendular oscillation during a complete revolution of the rotating shaft 2.

The rotation of the cylinders 5 is guaranteed by the coupling between the cylinder 5 and the respective housing seating 4.

In particular, the cylinders 5 and the housing seatings 4 have a cylindrical- sector conformation (see figures 1, 2 and 3). In detail, each cylinder 5 comprises an external wall 14 having a cylindrical-sector development and each housing seating 4 comprises a surface 15 having a cylindrical-sector development.

The external wall 14 of the cylinder 5 is slidably in contact with the surface 15 of the housing seating 4, i.e. it slides along the surface 15.

Note that there are no pins present active between the cylinder 5 and the respective housing seating 4 for to guaranteeing relative rotation between the two elements.

The surface 15 of the housing seating 4 and the external wall 14 of the cylinder 5 have a greater development than the development of a semi- cylinder (as illustrated in figures from 1 to 3).

In this way, the cylinder 5 is retained in the housing seating 4 by mechanical interference between the cylinder 5 and the seating 4.

The machine 1 advantageously comprises a compensating chamber 16, afforded between each cylinder 5 and the respective housing seating 4, set in fluid communication with a source of pressurised fluid (see in particular figure 5).

The compensating chamber 16 creates a thrust on the cylinder 5 which is able to compensate, at least in part, the thrust that is exerted on the cylinder during the travel run of the piston.

Note that the pressure internally of the expansion chamber 11 generates a thrust on the piston 6 that is directed towards the centre of the annular crown 8 (as mentioned above) and, contemporaneously, generates a reaction force which is equal and opposite on the cylinder 5.

This force is the main one responsible for the friction forces which oppose the rotation of the cylinder 5 in the housing seating 4. As mentioned herein above, the compensating chamber 16 enables a force to be generated on the cylinder 5 which is opposite the above-mentioned reaction force.

The compensating chamber 16 is preferably in fluid communication with the expansion chamber 11 such as to receive pressurised fluid directly from the expansion chamber 11.

This enables the same source of pressurised oil to be used for supplying both the expansion chamber 11 and the compensating chamber 16.

Further, as the pressure internally of the expansion chamber 11 varies during the functioning of the machine, the pressure internally of the compensating chamber 16 also varies in the same way.

In order to guarantee fluid communication between the expansion chamber

11 and the compensating chamber 16, the cylinder 5 comprises a conduit

17 which, by crossing the whole breadth of the chamber 5, connects the expansion chamber 11 and the compensating chamber 16.

In order to guarantee maximum efficiency of the compensating chamber

16, the chamber 16 is set in a position such that the sliding axis P of the piston 6 crosses the compensating chamber 16 (see figure 5).

The compensating chamber 16 preferably exhibits a maximum dimension at the sliding axis P of the piston 6.

In particular, the compensating chamber 16 is symmetrical with respect to the sliding axis P.

In this way, the efficiency of the compensating chamber 16 is maximised since the force transmitted to the cylinder 5 by the compensating chamber 16 is perfectly aligned with and in an opposite direction to the reaction force (see above) transmitted to the cylinder 5.

In the preferred embodiment of the invention, the compensating chamber 16 is defined by a rectified portion of the external wall 14 of the cylinder 5 - lo

in combination with the surface 15 of the housing seating 4 (as shown in figure 5).

In other words, the external wall 14 of the cylinder 5 exhibits a straight portion which, in combination with the curvature of the surface 15 of the housing seating 4, creates a space which defines the compensating chamber 16.

Note that the position of the compensating chamber 16 is fixed with respect to the cylinder 5 and varies with respect to the housing seating 4 as a function of the relative position of the cylinder internally of the seating 4 (compare figures 1, 2 and 3).

The machine 1 also comprises a further compensating chamber 18 active between the piston 6 and the external surface 8a of the annular crown 8. The further compensating chamber 18 performs the same function as the above-described compensating chamber 16, though it is active between the base of the piston 6 and the annular crown 8.

In other words, the further compensating chamber 18 reduces the friction between the piston 6 and the annular crown 8.

The further compensating chamber 18 too is crossed by the sliding axis P of the piston 6 and exhibits a maximum dimension at the sliding axis P. The further compensating chamber 18 is in fluid communication with the expansion chamber 11 via a conduit 19.

The invention thus attains the set aims.

The compensating chamber 16, in combination with the cylindrical-sector development of the housing seatings 4 and the cylinders 5 rotating therein, guarantee avoiding a concentration of forces at a few points (for example the pins in the prior art) and thus reduce wear on the machine and as a consequence limit the need for reconditioning operations. The force transmitted to the cylinder by the piston 6 is in fact well distributed over a wide surface and is compensated (at least partially) by the compensating chamber 16.

Further, the compensating chamber 16, the housing seatings 4, the cylinders 5 and the pistons 6 can be dimensioned as required without incurring any drawbacks, so that the machine 1 can be dimensioned for any power rating.