System comprising a mixer-wagon, for the mixing and distributing fodder, and a mechanical power transmission unit for actuating the mixer-wagon

Abstract

A system includes a mixer-wagon and a mechanical power transmission unit (100) to actuate the rotating members of the mixer-wagon; the transmission unit includes a box (20), a first shaft (1) accessible from the outside of the box (20) and a second shaft (4) accessible from the outside of the box (20). The first shaft (1) and the second shaft (4) are coupled by an epicyclical gear train (19).

Claims

1. A mechanical power transmission unit adapted to be arranged along a shaft line, the mechanical power transmission unit comprising: a housing; a power input shaft accessible from outside the housing; a power output shaft accessible from outside the housing, the power output shaft being co-axial with the power input shaft; an epicyclical gear train between the power input shaft and the power output shaft, the epicyclic gear train comprising a ring gear mounted on the power input shaft for co-rotation with the power input shaft, the epicyclic gear train further comprising a planet-carrier mounted on the power output shaft for co-rotation with the power output shaft and the planet-carrier idly supporting at least one planet gear meshing with the ring gear and with a sun gear, the sun gear being co-axial with the power output shaft and idly supported on the power output shaft, the sun gear being co-axial to a variable speed gear and drivingly coupled to the gear variable speed gear for co-rotation with the gear variable speed gear around the power output shaft, the variable speed gear being drivingly coupled to a variable speed motion source, wherein a speed variation of the variable speed gear controlled by the variable speed motion source causes a variation of a transmission ratio of the epicyclic gear train.

2. The power transmission unit of claim 1, further comprising a supplemental gear mounted for co-rotation with the power input shaft and drivingly coupled to a hydraulic pump of the variable speed motion source, the hydraulic pump being hydraulically coupled to a hydraulic motor of the variable speed motion source, at least one of the hydraulic motor and the hydraulic pump having a variable displacement, the hydraulic pump and the hydraulic motor being mounted on the housing coaxial with one another, the variable speed motion source being configured to modify the speed ratio of the epicyclic gear train by varying the displacement of said at least one of said hydraulic motor or hydraulic pump.

3. The power transmission unit of claim 2, wherein the hydraulic pump and the hydraulic motor are arranged collinear to one another on the housing.

4. The power transmission unit of claim 3, wherein the hydraulic pump is drivingly coupled to the power input shaft through the supplemental gear and a further pump driving gear coaxial to the pump, the hydraulic motor being drivingly coupled to the variable speed gear through a motion exit gear, co-axial to the hydraulic motor.

5. The power transmission unit of claim 1, wherein the variable speed motion source comprises a variable displacement hydraulic motor, configured to be hydraulically coupled to an external pump, wherein the variation of the transmission ratio of the epicyclic gear train is controlled by varying displacement of the hydraulic motor.

6. A system comprising: a mixer-wagon; a shaft line for transmitting power to rotating members of the mixer-wagon; and a mechanical power transmission unit configured to be arranged along said shaft line, the mechanical power transmission unit comprising: a housing; a power input shaft accessible from outside the housing; a power output shaft accessible from outside the housing and co-axial to the power input shaft; an epicyclical gear train between the power input shaft and the power output shaft, wherein the epicyclic gear train comprises a ring gear mounted on the power input shaft for co-rotation with the power input shaft, the epicyclical gear train further comprising a planet-carrier mounted on the power output shaft for co-rotation with the power output shaft and idly supporting at least one planet gear meshing with the ring gear and with a sun gear, the sun gear being co-axial to the power output shaft and idly mounted on the power output shaft, the sun gear being co-axial to a variable speed gear and drivingly coupled to the gear variable speed gear for co-rotation with the gear variable speed gear around the power output shaft, the variable speed gear being drivingly coupled to a variable speed motion source, wherein a speed variation of the variable speed gear controlled by the variable speed motion source causes a variation of a transmission ratio of the epicyclic gear train.

7. The system according to claim 6, further comprising an electronic central control unit configured and arranged to control the variable speed motion source and the transmission ratio between the power input shaft and the power output shaft of the mechanical power transmission unit.

8. A mechanical power transmission unit adapted to be arranged along a shaft line, the mechanical power transmission unit comprising: a housing; a power input shaft, at least a portion of the power input shaft being located outside of the housing; a power output shaft, at least a portion of the power output shaft being located outside of the housing, the power output shaft and the power input shaft being rotatable about a rotation axis; an epicyclical gear train arranged between the power input shaft and the power output shaft, the epicyclic gear train comprising a ring gear mounted on the power input shaft and a sun gear, wherein the ring gear is rotatable based on rotation of the power input shaft about the rotation axis, the epicyclic gear train further comprising a planet-carrier mounted on the power output shaft, the planet-carrier being rotatable with the power output shaft, the planet-carrier supporting at least one planet gear, the at least one planet gear being in contact with the ring gear and with the sun gear, the sun gear being rotatable about the rotation axis and the sun gear being supported by the power output shaft, the sun gear being co-axially arranged with a variable speed gear and the sun gear being coupled to the gear variable speed gear for rotation with the gear variable speed gear about the power output shaft, the variable speed gear being coupled to a variable speed motion source, wherein a speed variation of the variable speed gear controlled by the variable speed motion source causes a variation of a transmission ratio of the epicyclic gear train.

9. The power transmission unit of claim 8, further comprising a supplemental gear mounted for co-rotation with the power input shaft and drivingly coupled to a hydraulic pump of the variable speed motion source, the hydraulic pump being hydraulically coupled to a hydraulic motor of the variable speed motion source, at least one of the hydraulic motor and the hydraulic pump having a variable displacement, the hydraulic pump and the hydraulic motor being mounted on the housing coaxial with one another, the variable speed motion source being configured to modify the speed ratio of the epicyclic gear train by varying the displacement of said at least one of said hydraulic motor or hydraulic pump.

10. The power transmission unit of claim 9, wherein the hydraulic pump and the hydraulic motor are arranged collinear to one another on the housing.

11. The power transmission unit of claim 10, wherein the hydraulic pump is drivingly coupled to the power input shaft through the supplemental gear and a further pump driving gear coaxial to the pump, the hydraulic motor being drivingly coupled to the variable speed gear through a motion exit gear, co-axial to the hydraulic motor.

12. The power transmission unit of claim 8, wherein the variable speed motion source comprises a variable displacement hydraulic motor, configured to be hydraulically coupled to an external pump, wherein the variation of the transmission ratio of the epicyclic gear train is controlled by varying displacement of the hydraulic motor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the drawings:

(2) FIG. 1 is a cross-sectional view of a possible embodiment of a mechanical power transmission unit, according to a plane containing the support shafts for the gears contained therein;

(3) FIG. 2 is a simplified view, according to line II-II of FIG. 1, of the gears of the epicyclical gear train;

(4) FIG. 3 is a cross-sectional view similar to the cross-section of FIG. 1 of a different embodiment of the mechanical power transmission unit of the invention;

(5) FIG. 4 is a cross-sectional view similar to the cross-section of FIG. 1 of a different embodiment of the mechanical power transmission unit of the invention;

(6) FIG. 5 is a view of a regulation scheme of the mechanical power transmission unit comprising a hydrostatic transmission to adjust the transmission ratio;

(7) FIG. 6 is a cross-sectional view according to line VI-VI of FIG. 7 of a system comprising a mixer-wagon combined with a mechanical power transmission unit as illustrated in FIGS. 1-5; and

(8) FIG. 7 is a plan view according to line VII-VII of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(9) The following detailed description of the exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. Additionally, the drawings are not necessarily drawn to scale. Also, the following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims.

(10) Reference throughout the specification to one embodiment or an embodiment or some embodiments means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase in one embodiment or in an embodiment or in some embodiments in various places throughout the specification is not necessarily referring to the same embodiment(s). Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

(11) With initial reference to FIGS. 1 and 2, a first configuration is described below of one embodiment of a mechanical power transmission unit, indicated as a whole with number 100, which is part of a system comprising a mixer-wagon for preparing and distributing fodder and the related mechanical transmission.

(12) The mechanical power transmission unit 100 comprises a box or housing 20, inside which gears are arranged for transmitting motion and reducing or multiplying the number of revolutions between a first shaft 1 and a second shaft 4. In the illustrated embodiment, splined portions of the shafts 1 and 4 project from the box 20, for mechanically coupling to outer mechanical members. It is also possible that one of the shafts 1 and 4, or both, are integrally housed in the box 20 and accessible from the outside, for example through openings provided in the box 20. In this case, the shafts 1 and 4 may have axial holes with inner spline for coupling to outer shafts of mechanical members coupable to the mechanical power transmission unit 100.

(13) The first shaft 1 and the second shaft 4 are coaxial. A-A indicates the common axis of the two shafts 1 and 4.

(14) As it will be clearly apparent from the description below of various configurations of the mechanical power transmission unit 100, the shaft 1 may act as a drive shaft and the shaft 4 may act as a driven shaft or vice versa, based on whether the mechanical power transmission unit 100 is used as a reduction gear or as a multiplier of the number of revolutions.

(15) In the configuration of the mechanical power transmission unit 100 illustrated in FIG. 1, the first shaft 1 acts as drive shaft, or input shaft, of the mechanical power transmission unit 100, while the second shaft 4 acts as driven shaft, or output shaft.

(16) The mechanical coupling between the first shaft 1 and the second shaft 4 occurs by means of the following mechanical members. A ring gear 2, with inner toothing, of an epicyclical gear train 19 is torsionally coupled to the first shaft 1. The ring gear 2 integrally rotates with the first shaft 1. The epicyclical gear train further comprises a planet-carrier 3 torsionally coupled to the second shaft 4, so as to rotate integrally with it.

(17) In some embodiments, the planet-carrier 3 is torsionally constrained to the second shaft 4 by means of a coupling 24 with male and female splined profiles.

(18) The epicyclical gear train 19 further comprises a sun gear 5, meshing with one or more planet gears 6. In the illustrated embodiment, as shown in particular in the schematic view of FIG. 2, the epicyclical gear train 19 comprises three sun gears 6. Each sun gear 6 also meshes, in addition to the sun gear 5, with the ring gear 2. In FIG. 2, the planet-carrier 3 has been omitted for the sake of clarity of representation; only the gears of the epicyclical gear train 19 are shown in this figure.

(19) As clearly apparent from what described above, assuming for example that the shaft 1 is used as drive shaft, or input shaft, the power is transmitted from the first shaft 1 to the second shaft 4 by means of the epicyclical gear train 19, through the ring gear 2, the planet gears 6 and the planet-carrier 3. The opposite occurs if the second shaft 4 is used as drive shaft, or input shaft, and the first shaft 1 is used as output shaft, or driven shaft.

(20) The transmission ratio between the first shaft 1 and the second shaft 4 may be changed by acting on the rotation speed of the sun gear 5. In order to rotate the sun gear 5 in a controlled manner, or to keep it still, according to the value of the required transmission ratio obtainable through the mechanical power transmission unit 100, the members described below are also provided.

(21) In the configuration of FIG. 1, a gear 7 is torsionally coupled to the first shaft 1, so as to rotate integrally therewith at the same angular speed of the first shaft 1 and of the ring gear 2. The gear 7 meshes with a second gear 8 of smaller diameter. The rotation of the first shaft 1 is transmitted to a pump 9 through the pair of gears 7, 8. The pump may be a variable-displacement pump, known per se and being part of a hydrostatic transmission, the other components whereof are described below.

(22) The pump 9 is connected to a hydraulic motor 10 through a (closed or open) hydraulic circuit not shown in FIG. 1. The motion transmitted to the pump 9 by means of the pair of gears 7, 8 causes working fluid, for example oil, to circulate from the pump 9 to the hydraulic motor 10, and from this latter to the pump again. The rotation speed of the pump 9 is proportional to the speed of the first shaft 1, wherein the speed ratio is given by the transmission ratio between the gears 7 and 8. Vice versa, the speed of the hydraulic motor 10 is variable with respect to the rotation speed of the first shaft 1, and can be controlled by acting on the displacement of the pump 9 and, thus, on the flow rate of the working fluid. The variable-displacement pump 9 may be also controlled so as to reverse the flow in the circuit connecting the hydraulic motor 10 to the pump 9, i.e. so as to reverse the rotation speed of the hydraulic motor 10, which can consequently rotate clockwise or counterclockwise.

(23) Instead of a variable-displacement pump 9, a variable-displacement hydraulic motor 10 may be provided with the same function. It is also possible to use a variable-displacement pump 9 and a variable-displacement hydraulic motor 10 in combination.

(24) Generally speaking, the hydrostatic transmission, comprising the pump 9 and the hydraulic motor 10, is so configured that the rotation speed of the hydraulic motor 10 can vary independently of the rotation speed of the pump 9.

(25) The hydraulic motor 10 transmits motion to an exit gear 11 meshing with a gear 12 idly supported on the second shaft 4 and torsionally coupled to the sun gear 5.

(26) Therefore, the hydrostatic transmission comprising the pump 9, the hydraulic motor 10, the hydraulic circuit connecting the pump 9 and the hydraulic motor 10, as well as the pairs of gears 7, 8 and 11, 12 allows to rotate the sun gear 5 at controlled speed.

(27) By acting on the displacement of the pump 9 (or of the hydraulic motor 10), and thus on the flow rate of the working liquid, it is possible to vary the rotation speed and direction of the sun gear 5. If the hydrostatic transmission is controlled so that the hydraulic motor 10 remains still, the sun gear 5 remains blocked with respect to the box 20 and the transmission ratio between the first shaft 1 and the second shaft 4 is defined by the number of teeth of the gears forming the epicyclical gear train 19. In order to modify the transmission ratio, it is necessary to act on the flow rate of working liquid circulating in the hydrostatic transmission, driving into rotation the sun gear 5 in the desired direction and at the required angular speed. Numeric examples of various operating modes of the mechanical power transmission unit 100 will be provided below.

(28) The pump 9 may be configured so as to make the hydraulic motor 10 rotate selectively in clockwise or in counterclockwise direction, and therefore so as to make the sun gear 5 rotate with respect to the box 20 in the same direction or in opposite direction with respect to the ring gear 2 and to the shafts 1 and 4. This can be achieved by acting on the mechanical members regulating the displacement of the pump 9. When the rotation direction of the sun gear 5 is the same as the rotation direction of the ring gear 2, the rotation speed of the planet-carrier 3 increases, and therefore the speed of the second shaft 4 with respect to the conditions when the sun gear 5 is still. Vice versa, if the sun gear 5 rotates in a direction opposite to the rotation direction of the ring gear 2, the rotation speed of the planet-carrier 3, and therefore of the second shaft 4, decreases with respect to the speed when the sun gear 5 is stationary.

(29) In any case, the rotation direction of the two coaxial shafts 1 and 4 remains the same: both the first shaft 1 and the second shaft 4 rotate in clockwise direction, or in counterclockwise direction.

(30) More construction details of the mechanical power transmission unit 100 briefly described above will be described below in greater detail, with reference to FIGS. 1 and 2 again.

(31) The first shaft 1 may be supported by means of one or more bearings 14, for example a pair of roller bearings mounted in an X-like manner to support both radial and axial loads. The bearings 14 may be housed in a seat 16 provided in the box 20.

(32) The second shaft 4 may be supported by means of one or more bearings 18, for example rolling bearings. In the illustrated embodiment, a single ball bearing 18 is provided, housed in a respective seat 22 provided in the box 20.

(33) In advantageous embodiments, the second shaft 4 extends towards the first shaft 1, beyond the grooved profile 24 coupling the planet-carrier 3 and the second shaft 4. Number 25 indicates an end shank of the second shaft 4 engaging an axial seat 29 of the first shaft 1 by means of a bearing 27. In this way, the inner end of the second shaft 4 is supported by the first shaft 1. The planet-carrier 3 is housed inside the ring gear 2, so that the axial dimension of the set formed by the ring gear 2, the planets 6 and the planet-carrier 3 is equal to the axial dimension of the ring gear 2.

(34) In the illustrated embodiment, the sun gear 5 is torsionally coupled to the gear 12 through a splined coupling 26, while the gear 12 may be supported through bearings 33 on the second shaft 4, so that the second shaft 4 and the sun gear 5 can freely rotate with respect to one another around the common axis A-A. In less advantageous embodiments, the sun gear 5 may be integral with the gear 12.

(35) The gear 11 is torsionally coupled, for instance keyed, on an auxiliary drive shaft 39. In other embodiments, the gear 11 may be integral with the auxiliary drive shaft 39, which receives motion from the hydraulic motor 10. In the configuration of FIG. 1, the auxiliary drive shaft 39 is mounted rotatable on the box 20 by means of two bearings 41, 43 spaced from one another, the gear 11 being arranged between the two bearings. The bearing 41 is mounted in a seat 45 provided in the outer wall of the box 20, while the bearing 43 is mounted in a seat 47 provided in an annular element 49 inside the box 20 and integral therewith, for example molded with a main body of the box 20.

(36) The diameter of the gear 12 is greater than the diameter of the gear 11, so that the rotation speed of the auxiliary drive shaft 39 is transmitted to the sun gear 5 with such a reduction ratio that the sun gear 5 rotates at an angular speed substantially lower than the angular speed of the auxiliary drive shaft 39.

(37) B-B indicates the axis of the auxiliary drive shaft 39. In the illustrated embodiment, the axis B-B is parallel to the axis A-A of the first shaft 1 and the second shaft 4. The hydraulic motor 10 may also have a different orientation, for example with an output shaft orthogonal to the axis A-A. In this case, the gears 11, 12 may be conical. The orientation of the auxiliary drive shaft 39 with respect to the axis A-A of the first shaft 1 and of the second shaft 4 may be chosen according to construction and economical needs, for example in order to reduce the dimensions of the mechanical power transmission unit 100.

(38) In the illustrated embodiment, the gear 8 transmitting motion to the pump 9 is keyed on an actuating shaft 53 of the pump 9, or formed integrally therewith. The actuating shaft 53 may be oriented parallel to the axis A-A of the first shaft 1 and the second shaft 4, and may be coaxial with the auxiliary drive shaft 39, as illustrated in the embodiment shown in the attached drawing. This is however not necessary. The orientation with respect to the other members of the mechanical power transmission unit 100 may be different than that illustrated, if necessary by using conical gears 7 and 8, so that the actuating shaft 53 of the pump 9 has an orientation orthogonal to the axis A-A.

(39) In possible embodiments, the actuating shaft 53 of the pump 9 may be supported in the box 20 by means of a pair of bearings 57, 59. The first bearing 57 may be mounted in a seat 61 provided inside the box 20, for example in the annular element 49. The bearing 59 may be mounted in a seat 63 provided in the outer wall of the box 20.

(40) In the embodiment illustrated in FIG. 1, the gear 7 is integral with a hollow cylindrical body 7A forming internally a torsional coupling with the first shaft 1, for instance by means of a key. Externally, the hollow cylindrical body 7A forms a torsional coupling with the ring gear 2, for example through splined profiles. In this way, the gear 7, the ring gear 2 and the first shaft 1 rotate integrally at the same angular speed around the axis A-A.

(41) Through an electronic control system for controlling the hydrostatic transmission comprising the pump 9, the hydraulic motor 10 and the hydraulic circuit connecting the pump 9 to the hydraulic motor 10, it is possible to fully control the mechanical power transmission unit 100. In particular, it is possible to continuously vary the output rate of the mechanical power transmission unit 100 without varying the input rate. This allows, for example, to use an endothermic engine, such as a diesel engine, to actuate a driven machine through the mechanical power transmission unit 100, operating the endothermic engine at its optimal speed, thus reducing the fuel consumption, while the speed of the driven machine may vary within a range according to the features of the hydrostatic transmission comprising the pump 9 and the hydraulic motor 10.

(42) FIG. 5 schematically shows a system comprising the mechanical power transmission unit 100 provided with hydrostatic transmission and the main components of a possible control system. The mechanical power transmission unit 100 comprises the pump 9 and the hydraulic motor 10 that form, together with a hydraulic circuit schematically indicated with 70, the hydrostatic transmission indicated as a whole with number 71. The system may further comprise a sensor 73 for detecting the rotation speed of the pump 9, a sensor 75 for detecting the rotation speed of the hydraulic motor 10, one or more pressure sensors 77 for detecting the pressure in the circuit 70. The sensors 73, 75, 77 are connected to an electronic central control unit 79. This latter is also connected to the pump 9, that comprises an actuator (not shown) for varying the displacement of the pump 9. Through the electronic central control unit 79 it is therefore possible to modify the displacement of the pump 9, and therefore the transmission ratio of the mechanical power transmission unit 100.

(43) Through the speed of the pump 9 and of the hydraulic motor 10 it is possible to calculate the rotation speed of the output shaft (for instance the shaft 4) by knowing the rotation speed of the input shaft (for example the shaft 1). Through the pressure value in the closed circuit 70 it is possible to estimate or to calculate the output torque of the mechanical power transmission unit 100. By knowing the value of the transmitted torque it is possible to control the work load of the driven machine connected to the second shaft 4, and to manage it avoiding excessive loads.

(44) Maximum-pressure valves 82 in the closed circuit 70 may act, if adequately controlled, as torque limiter for the mechanical power transmission unit 100 and for the driven machine connected to it.

(45) As can be clearly understood from FIG. 1, the power is transmitted from the input to the output directly through the epicyclical gear train 19, whose rotation axis A-A (i.e. the axis of the ring gear 2, of the planet-carrier 3 and of the sun gear 5) coincides with the axis A-A of the first shaft 1 and of the second shaft 4.

(46) While in the configuration of the above described FIG. 1 the mechanical power transmission unit is configured to act as a reduction gear, with the first shaft 1 acting as drive shaft and the second shaft 4 acting as output shaft, in other configurations the mechanical power transmission unit 100 may be used as multiplier. FIG. 3 illustrates a configuration of the mechanical power transmission unit 100 in this operation mode. The same numbers indicate identical or equivalent parts to those illustrated in FIG. 1. These parts will not be described again.

(47) In the configuration of FIG. 3, the input shaft, or drive shaft, is the second shaft 4, while the first shaft 1 is the driven shaft, or output shaft. To take motion for the pump 9 from the drive shaft 4, it is possible in this case to reverse the positions of the pump 9 and of the hydraulic motor 10 and to use a longer auxiliary drive shaft 39 than the auxiliary drive shaft 39 of the configuration of FIG. 1. In this case, the auxiliary drive shaft 39 is supported by means of bearings 57 and 59 mounted in the seat 47 provided in the annular element 49 and in the seat 63 provided in the wall of the box 20. The gear 11 is mounted in a cantilevered manner on the auxiliary drive shaft 39.

(48) The actuating shaft 53 of the pump 9 is supported by means of bearings 41 and 43 mounted in the seat 47 provided in the wall of the box 20 and the gear 8 is mounted in a cantilevered manner on the actuating shaft 53.

(49) The gears 11 and 8 mesh again with respective gears 12 and 7 coaxial with the axis A-A of the shafts 1 and 4. However, differently from the configuration of FIG. 1, both gears 12 and 7 are arranged between the planet-carrier 3 and the bearing 18, i.e. at the same side of the epicyclical gear train 19. More in particular, while the gear 12, integral with the sun gear 5, is in the same position as in FIG. 1, the gear 7 is arranged between the gear 12 and the side wall of the box 20.

(50) The operation of the mechanical power transmission unit 100 in the configuration of FIG. 3 is equal to that of the configuration of FIG. 1, with the difference that the input power is applied to the second shaft 4, acting as the drive shaft, while the output power is on the first shaft 1, acting as the output shaft, and the transmission ratio is such that the speed of the output shaft 1 is greater than the speed of the drive shaft 4.

(51) Analogously to what described above, the transmission ratio may be modified by acting on the pump 9 and the hydraulic motor 10 of the hydrostatic transmission, so as to rotate the sun gear 5 in one direction or in the opposite direction and at controlled and adjustable speed through the hydraulic motor 10.

(52) In the embodiments described above, the mechanical power transmission unit 100 comprises both a hydraulic motor 10 and a pump 9. However, this is not strictly necessary.

(53) In alternative embodiments, the pump 9 may be external with respect to the mechanical power transmission unit 100. For example, a pump may be used available on a tractor or other machine, with which the mechanical power transmission unit 100 may interface. FIG. 4 schematically shows a configuration of this type, wherein the pump 9 is separated with respect to the mechanical power transmission unit 100 and is hydraulically coupled to the motor 10 through the hydraulic circuit schematically indicated with 70. A lid 81 closes the opening of the box 20, in correspondence of which the pump 9 is usually flanged, when this latter is part of the mechanical power transmission unit 100 and is carried by the box 20.

(54) The gears 8 and 7, as well as the actuating shaft 53 of the pump 9 and the respective support bearings are not necessary and they are therefore not provided in the arrangement of FIG. 4. The remaining parts of the mechanical power transmission unit 100 are equal to those illustrated in FIG. 1, are indicated with the same reference numbers and will be not described again. In the configuration of FIG. 5, the mechanical power transmission unit 100 may act as multiplier or reduction gear, according to whether the drive shaft is the second shaft 4 or the first shaft 1 respectively.

(55) The following tables show examples of two different configurations of the mechanical power transmission unit 100 according to what described above.

(56) By assuming to combine a hydrostatic transmission (hydraulic motor 10 and pump 9) allowing the following features: speed of the hydraulic motor=3000+3000 rpm transmission ratio between motor 10 and sun gear=3
the following operation modes are possible:

(57) Operation as Reduction Gear (FIG. 1)

(58) TABLE-US-00001 Component of the unit Speed [rpm] drive shaft (1) 1000 1000 1000 hydraulic motor (10) 3000 0 3000 ring gear (2) 1000 1000 1000 sun gear (5) 1000 0 1000 planet-carrier (3) 334 667 1000 output shaft (4) 334 667 1000 transmission ratio (input/output) 3 1.5 1

(59) Operation as Multiplier (FIG. 3)

(60) TABLE-US-00002 Component of the unit Speed [rpm] drive shaft (4) 1000 1000 1000 hydraulic motor (10) 3000 0 3000 planet-carrier (3) 1000 1000 1000 sun gear (5) 1000 0 1000 ring gear (2) 1000 1500 2000 output shaft (1) 1000 1500 2000 transmission ratio (input/output) 1 0.667 0.5

(61) The mechanical power transmission unit 100 described above may have many applications in different mechanical sectors. Particularly, a system, is described, and forms a specific aspect of the present invention, which comprises a combination of a mixer-wagon for preparing and distributing fodder to animals, and a mechanical power transmission unit 100 in one of the embodiments described above. As mentioned in the introductory part of the present description, the operation of the mixer-wagon is subdivided into three main steps: the step of loading and mixing fodder; the step of moving, necessary to achieve the cowshed; the step of distributing fodder to animals.

(62) These steps require different work speeds. The loading and mixing step requires medium speeds, variable according to the type and quantity of fodder to be mixed. The moving step occurs once the right mixing has been obtained, and requires very low speeds, to avoid the conglomeration of the material. The distributing step requires high speeds, increasing as the mixer-wagon empties.

(63) The problems described above with regard to the actuating of a mixer-wagon are solved by using a mechanical power transmission unit 100 of the type described herein, interposed between the drive shaft of a tractor or other power source and the output shaft of the mixer-wagon.

(64) FIGS. 6 and 7 schematically illustrate a system 200 comprising a mechanical power transmission unit 100 according to anyone of the embodiments described above and a mixer-wagon 202. In the present description and in the attached claims, mixer-wagon means any wagon suitable to receive fodder for animals, to mix it, if necessary to chop it or to process it in any other way, to transport it to the cowshed and to distribute it to animals. Therefore, the term mixer-wagon also comprises, for example, a silage cutter, a total mixed ration wagon, or any other machine suitable to receive one or more components for preparing food for animals and for distributing it. The mixer-wagon may have one or more augers, with vertical or horizontal axes, with or without silo-unloader means.

(65) In the embodiment illustrated in FIGS. 6 and 7 just by way of example, the mixer-wagon 202 has two augers with vertical axes. In the illustrated example the mixer-wagon 202 comprises a tank 201, inside which two augers 203, 205 are arranged rotating around a vertical axis A-A and B-B respectively. The mixer-wagon further comprises a door 207, which can be opened to unload the fodder. To the door 207 a conveyor 209 is associated, transporting the fodder ejected from the tank 201 through the door 207 open towards the manger in the distribution step.

(66) The mixer-wagon 202 comprises a frame 211 with coupling means 213 for coupling to a tractor, not shown.

(67) 215 indicates as a whole a shaft line from an input 215A, configured to be mechanically coupled to the power take off of the tractor, towards the augers 203 and 205. The shaft line 215 comprises the mechanical power transmission unit 100 and a series of universal transmissions, i.e. of shaft portions with universal joints. More in particular, a first universal transmission or shaft portion 217 couples the input 215A of the shaft line 215 to the input of the mechanical power transmission unit 100. A second universal transmission or shaft portion 219 connects the output of the mechanical power transmission unit 100 to an actuating box 223 of the mixing auger 203, and a third universal transmission or shaft portion 221 connects the actuating box 223 of the first mixing auger 203 to a second actuating box 225 of the second auger 205.

(68) By suitably selecting the ratios of the epicyclical gear train 19 of the mechanical power transmission unit 100, for instance according to what described above, it is possible to obtain a transmission allowing:

(69) to have slow start-up speed and therefore limited torque peaks;

(70) to vary the work speed of the mixer-wagon 202 in a continuous and not-discrete manner, without interrupting the rotation of the augers 203 and 205;

(71) to select the most suitable chopping speed for each type of material and condition, thus allowing a more homogeneous product;

(72) to vary the chopping speed of the augers 203 and 205 independently of the rotation speed of the endothermic engine of the tractor, thus optimizing and reducing the fuel consumption;

(73) to have low speed during the moving step, allowing a limited fuel consumption and avoiding to restart the mixer-wagon when it is full;

(74) to have high distribution speeds variable according to the quantity of material in the tank 201 of the mixer-wagon 202, so that it is not necessary to modify the speed of the tractor to have a uniform distribution of fodder in the manger;

(75) to eliminate the dead times due to gear changing, stops and restarts of the machine;

(76) to eliminate the dead times due to the intervention of the torque limiters at full-load restarts.

(77) Through suitable electronic management (for instance by means of the central control unit 79) of the pump 9 mounted on the mechanical power transmission unit 100 it is possible to optimize the operation of the system 200 to obtain:

(78) a better quality of the mixed product;

(79) a reduction in fuel consumption;

(80) a reduction in work times;

(81) a general improvement of the work comfort as the system can gradually adapt to the sudden power changes that can be generated during the work steps, in particular during the loading step and the start.

(82) The embodiments described above use a hydraulic motor 10 actuated by a variable-displacement pump 9 to modify the transmission ratio of the epicyclical gear train. This solution is particularly advantageous, as it uses only mechanical power available for example from a power take off of a tractor or other machine.

(83) However, in other embodiments it is also possible to use a different system to modify the transmission ratio of the mechanical power transmission unit 100, for example a system using a different power source to drive the sun gear 5 into rotation. To this end, in some embodiments an electric motor, with electronic control of the rotation speed, may be used.

(84) It is also possible to use a hydrostatic transmission, wherein the pump 9 is actuated by means of an electric motor. In this case, the rotation speed of the sun gear 5 may be controlled by acting on the speed of the electric motor. Therefore, the electronic management of the transmission ratio occurs through electronic control of the electric motor driving the pump 9 into rotation.

(85) In the description above reference has been made to a hydrostatic transmission system with a hydraulic motor 10 and a variable-displacement pump 9. It is also possible to use a variable-displacement hydraulic motor 10 to adjust the rotation speed of the sun gear 5. The variable-displacement hydraulic motor may be used in combination with a fixed-displacement pump or with a variable-displacement pump. In this case, the central control unit 79 may act on the variable-displacement motor, or on both the variable-displacement motor and the variable-displacement pump.

(86) While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.