The present invention relates to a transmission for vehicles with hydrostatic propulsion systems, in particular agricultural or industrial vehicles, of the type comprising a movement combination device of the type comprising an epicyclic mechanism.

In the context of the technical field of agricultural and industrial vehicles, there are widely used transmissions of the hydrostatic type which use a hydraulic group for propelling the vehicle.

Some known hydrostatic transmissions allow a combination of the movement provided by the internal combustion engine with the movement of the hydrostatic group so as to obtain different behaviours of the vehicle, particularly in terms of cruising speed, in accordance with requirements. One possible solution for a hydrostatic transmission is described in the patent application US 2011/0015022.

This patent describes a transmission for vehicles which provides an epicyclic system which is capable of combining the movement in accordance with three operating modes.

However, one of the problems associated with this solution involves the fact that the sun gear of the epicyclic system does not vary its speed continuously during the movement between one mode and another, particularly between the ones indicated as mode 2 and mode 3, but instead is subject to discontinuity . It is evident that this discontinuity is an undesirable characteristic because it requires action on the clutches which are present in the transmission in order to carry out a reversal in the position of the disk of the pump. However, this procedure causes a reduction of the pulling torque or can, in some situations, bring about a gap in the transmission thereof.

Another hydrostatic transmission is described in the German patent application DE 102016 209 943.

In this case, however, there are also found discontinuities during the movement between one mode and the other of the transmission. In fact, by analyzing the behaviour of the sun gear in accordance with the speed of the vehicle, it is possible to observe that at 20 km/h the sun gear has to invert its direction of rotation, changing from a rotation speed of 3500 rpm to a speed of -800 rpm. In order to compensate for this jump, therefore, it is necessary to provide a complex system of clutches.

Therefore, the technical problem which forms the basis of the present invention is to provide a transmission for vehicles which allows one or more of the disadvantages mentioned above with reference to the prior art to be at least partially overcome .

In the context of this problem, a main object of the present invention is to provide a hydrostatic transmission which is capable of being able to switch continuously from one operating mode to another. This problem is solved by the transmission for vehicles with hybrid propulsion systems according to claim 1.

As a result of the solution provided by the present invention, it is possible to obtain a transmission for vehicles with hydrostatic propulsion which is capable of providing different operating modes without being subjected to operational discontinuities. The solution used is further found to be particularly simple from the construction point of view. Therefore, this solution provides for the use of a structure which is capable of having a mainly longitudinal extent, thereby being adapted to conventional vehicles in a suitable manner.

Therefore, the dimensions are particularly small or in any case optimized for the needs of an industrial vehicle with respect to the known solutions. Preferred features of the invention are further defined in the dependent claims.

According to preferred aspects, the blocking element of the transmission comprises a brake. In some embodiments, the brake has at least one disk which is preferably coaxial with the high-speed shaft.

In some embodiments, the low-speed shaft is connected to the movement combination device by means of a transmission shaft.

In some embodiments, the low-speed shaft and/or the high speed shaft is/are connected to the movement combination mechanism, for example, at the planet gear carrier of an epicyclic mechanism and the sun wheel or the planet gear carrier of the second epicyclic mechanism by means of respective transmission mechanisms with gears with fixed rotation axes which are constructed, for example, by means of gears.

Preferably, the output shaft is connected to the planet gear carrier of the second epicyclic mechanism of the movement combination device.

According to another aspect, the low-speed shaft is connected to the planet gear carrier of the first epicyclic mechanism. Preferably, the high-speed shaft of the transmission is connected to the ring gear of the second epicyclic mechanism, According to a preferred embodiment, the ring gear of the first epicyclic mechanism is directly connected to the planet gear carrier of the second epicyclic mechanism.

According to yet another aspect of the invention, the high- speed shaft of the transmission is connected to the ring gear of the first epicyclic mechanism. Preferably, the low-speed shaft is connected to the ring gear of the second epicyclic mechanism. According to a preferred embodiment, the planet gear carrier of the first epicyclic mechanism of the movement combination device is directly connected to the planet gear carrier of the second epicyclic mechanism.

Other advantages, features and the methods for use of the present invention will become evident from the following detailed description of a number of embodiments which are set out by way of non-limiting example. Reference will be made to the Figures of the appended drawings, in which: - Figure 1 is a schematic illustration of a transmission according to the present invention;

- Figures 2A to 2C are schematic illustrations which depict the movement chain in three different operating conditions of the transmission; and

- Figure 3 is a graph which illustrates the progression of the rotation speed of the sun gear as a function of the speed of the vehicle according to the transmission of the present invention.

Initially with reference to Figure 1, a transmission according to the present invention is generally designated 100. The transmission according to the present invention is of the type intended to be used in vehicles of the agricultural and industrial type with hydrostatic propulsion systems.

In other words, the vehicle propulsion system in which the transmission according to the present invention is used comprises an internal combustion engine 1 and a hydraulic motor 2.

The hydraulic motor 2 may be part of the transmission 100 as a whole. In any case, it is evident that the transmission may be formed as a separate structure with respect to the hydraulic motor and the other components of the propulsion system and can be connected thereto during the assembly step of the vehicle.

In preferred embodiments, the internal combustion engine 1 is connected to an input shaft 7 of the transmission. The input shaft 7 further acts on a pump 21, preferably of the variable displacement type, which supplies the pressurized operating fluid to the hydraulic motor 2 in order to rotate an output shaft 23.

In preferred embodiments, the pump 21 can receive the movement from the input shaft 2 indirectly by means of a transmission which is not illustrated in the Figures. In any case, the input shaft 7 may be used for directly actuating a power take-off which is connected to the transmission .

As illustrated in Figure 1, the input shaft 7 is connected to a low-speed shaft 11 and a high-speed shaft 12 which allow the transmission of the movement to the wheels, with methods which will be described in greater detail below in accordance with two different transmission ratios. According to an additional aspect of the invention, the input shaft 7 transmits the movement to the low-speed shaft 11 and the high-speed shaft 12 by means of respective pairs of gears 71A, 71B, 72A, 72B which are keyed to the shaft 7 itself. This advantageously allows the provision of the low-speed shaft 11 and the high-speed shaft 12 parallel with the input shaft, thereby generating two different branches, via which the movement can develop, and therefore the transmission. According to an aspect of the invention, the low-speed shaft 11 and the high-speed shaft 12 can be selectively coupled by using respective clutches 9, 10. In this manner, one of the two shafts can be selected in accordance with the desired operating conditions.

Preferably, the clutches 9 and/or 10 are arranged along the respective shafts in an intermediate position between the gears which receive the movement from the input shaft 7 and additional gears 73, 74 which in turn transmit the movement to a movement combination device 5 which is illustrated in detail below.

In some embodiments, the low-speed shaft 11 and the high speed shaft 12 comprise a respective first portion 11A, 12A and second portion 11B, 12B which are coaxial with each other and which can be coupled to each other by means of the respective clutches 9, 10.

As can be observed in Figures 2B and 2C, when the first clutch 9 is closed the movement reaches the low-speed shaft via the pairs of gears 71A, 71B and therefore via a transmission shaft 14 the movement combination device 5 while, when the second clutch 10 is closed, the movement of the input shaft 7 is transmitted to the high-speed shaft 10 and from there directly to the movement combination device 5. As will be better described below, these configurations correspond to two different operating modes of the transmission which are also indicated as the second and third operating modes. Still with reference to Figure 1, the movement combination device 5 to which the shafts 11 and 12 are connected comprises a first epicyclic mechanism 5A and a second epicyclic mechanism 5B which are connected to each other, in a preferred embodiment, by means of connection between the ring gear 53A of the first mechanism 5A and the planet gear carrier 52B of the second mechanism. In other words, the movement combination device 5 comprises a connection element 50 which joins, by making them rotationally secure, the ring gear 53A of the first mechanism 5A and the planet gear carrier 52B of the second mechanism.

The low-speed shaft 11 and the high-speed shaft 12 are connected to the movement combination device 5 which combines the movement thereof according to methods which will be described below.

In some embodiments, the low-speed shaft 11 is connected to the planet gear carrier 52A of the first epicyclic mechanism 5A.

The low-speed shaft 11 can be connected directly to the low- speed shaft 11 or indirectly, as in the example of Figure 1, by means of the transmission shaft 14. In this last case, a gear 14A of the transmission shaft 14 can engage with the gear 74 and a second gear 14B of the shaft 14 engages with a toothed portion of the planet gear carrier 52A. It will be noted that, in the context of the present invention, one element of the transmission is considered to be connected to another when there is a synchronous transmission of the movement between the two elements, except for any occurrences of play between the movement transmission components. This is generally the case if there is a direct connection if there are used movement transmission elements with fixed rotation axes, unlike systems with movable axes as, for example, in an epicyclic mechanism. According to a preferred embodiment, the high-speed shaft 12 is connected to the ring gear 53B of the second epicyclic mechanism 5B, preferably by means of the gear 73 which engages directly with the ring gear 53B.

On the basis of what is set out above, therefore, it will be appreciated that, according to an aspect of the invention, the low-speed shaft 11 and the high-speed shaft 12 are connected to the planet gear carrier and the sun gear of one or other epicyclic mechanism by means of respective transmission mechanisms with gears with fixed rotation axes.

Furthermore, the movement combination device 5 receives movement from the hydraulic motor 2 which is preferably connected both to the sun gear 51A of the first mechanism 5A and to the sun gear 51B of the second mechanism 5B. In some embodiments, as can be observed in the diagram of Figure 1, the sun wheels 51A and 51B are keyed to the same rotation axis 20 of the hydraulic motor 2.

Therefore, it is evident that, as a result of the above- mentioned configuration, in accordance with the methods with which the low-speed shaft 11, the high-speed shaft 12 and the hydraulic motor are caused to rotate, the movement combination device will be capable of obtaining specific output conditions by means of an output shaft 8 of the movement combination mechanism 5 which is typically connected to the wheels of the vehicle in which the transmission is used. Preferably, the output shaft 8 transmits the movement by means of additional gears to a gearbox and therefore to the wheels. According to another aspect of the invention, the output shaft 8 is connected to the planet gear carrier 52B of the second epicyclic mechanism 5B. It will also be noted that the above-described configuration allows positioning of the movement combination device 5 in the region of an end of the transmission opposite the one connected to the internal combustion engine. The transmission according to the present invention further comprises a blocking element 13 which is configured to block the low-speed shaft 11 or the high-speed shaft 12, that is to say, more generally, the input of the movement combination device 5.

In preferred embodiments, the blocking element 13 comprises a brake which has at least one disk 131 and preferably a disk assembly. Preferably, the brake is keyed to the high-speed shaft 12.

Still in order to obtain a solution which can also be adapted to the greatest possible extent to different configurations of the vehicle, the blocking element 13 is preferably interposed between the relative clutch and the gear of the shaft, on which the brake which transmits the movement to the movement combination device 5 is mounted.

The blocking element 13 allows an additional operating mode of the transmission to be obtained.

In fact, when the blocking element 13 is engaged, by blocking the ring gear 53B of the second epicyclic mechanism 5B, as illustrated in Figure 2A, where the kinematic flow is described using a portion of greater thickness, the energy for moving the vehicle is supplied by the hydraulic motor 2.

By unblocking the blocking element 13, it is possible to obtain the other two operating modes which have already been briefly described above.

In the second mode, illustrated in Figure 2B, still using a portion with a greater thickness, the clutch 9 of the low- speed shaft 11 is engaged while the other clutch and the blocking element 13 are not engaged.

The energy supplied by the internal combustion engine is partially used for actuating the pump 21 and partially flows into the movement combination device 5 in which it is added to the energy supplied by the hydraulic motor 2.

The third operating mode is instead described in Figure 2C. In this case, the clutch 10 of the high-speed shaft is instead engaged while the other clutch 9 and the blocking element 13 are not engaged. The energy supplied by the internal combustion engine 1 flows into the epicyclic mechanism in which it can be added to the energy supplied by the hydrostatic motor.

In this case, therefore, the transmission shaft and the relevant gear transmission not being present, a transmission ratio different from the preceding case is obtained.

Therefore, it is evident that the transmission described solves the problems identified with reference to the present invention, allowing the following advantages in particular to be afforded: a) the torque does not have any discontinuity; b) the clutches during the movement from one operating mode to the following/preceding one close without any speed difference between disks and counter-disks; c) in the first operating mode, the blocking element is blocked: in this manner, there is a change from forward to reverse with continuity (moving continuously through zero), therefore on a slope it can travel forwards and backwards extremely smoothly with continuous power transmission.