The present invention relates to a planetary gear system and an assembly method for assembling a planetary gear system.

Planetary gear system refers to a transmission system comprising a plurality of gear wheels known as satellites, mounted on a guide member called gear train (or planetary gear). The above-mentioned gear wheels mesh with a central pinion (or sun pinion) to provide a kinematic coupling. In this way, the rotation of the gear wheels with respect to the central pinion induces relative rotational motion between the central pinion and the gear train.

The gear wheels also mesh with an internally toothed ring gear, thereby providing a kinematic coupling between the outer ring gear and the central pinion.

In other words, a planetary gear system substantially consists of a central pinion, a gear train and an internally toothed ring gear, which are coaxially arranged and kinematically connected to provide drive torque transmission.

Generally, the central pinion feeds the drive torque to the transmission system. The drive torque is transferred to the gear train, which is rotated with respect to the central pinion with an angular speed which varies according to the diameter and number of teeth of the central pinion and the gear wheels. In this configuration, the ring gear is kept fixed so that the gear wheels, by rotating relative thereto, can transfer the drive torque introduced by the central pinion to the planetary gear.

According to different applications, the planetary gear or the central pinion can be prevented from rotating to obtain different technical effects.

Planetary gear systems are typically used in speed reducers in order to obtain a predetermined gear ratio. Particular applications involve the use of more than one planetary gear system, which are operatively connected to achieve two or more reduction ratios.

Planetary gear systems are specially sized according to the drive torque value that must be transmitted during the different operating configurations.

For example, heavy vehicles such as buses, trucks, earthmoving machines and agricultural vehicles are equipped with particularly robust planetary gear systems in order to withstand the high stresses induced by the high maximum torque values to be transmitted.

However, within the same range of vehicles previously mentioned and equipped with the same type of transmission, the applied loads can vary considerably, resulting in highly variable stresses to which the transmission system is subjected.

Disadvantageously, the use of undersized systems leads to misalignment of the pins on which the gear wheels are mounted.

In fact, the high torque values induce stresses concentrated on the transmission pins, i.e. the pins on which the gear wheels are arranged, causing misalignment.

This misalignment causes a change in the kinematic coupling between the gear wheels and the central pinion, reducing the transmission effectiveness thereof.

Disadvantageously, once the kinematic coupling between the gear wheels and the central pinion is damaged, flexional-torsional moments tend to occur on the pins of the gear train due to the inertia of the bodies, which may cause yielding.

Moreover, this misalignment induces abnormal wear of the teeth of the gears, causing reduced operational life and premature failure.

Similarly, the use of oversized systems leads to reduction in efficiency as it involves an unjustified increase of the rotating mass; often such oversizing is impossible due to the available space dictated by the size of the tires, brakes, steering systems.

Moreover, similar problems may also be encountered in other industrial sectors in which planetary gear systems are commonly used; consider, for example, load handling, robotics, or the production of power tools.

In all applications known to date, it is necessary to redesign the transmission components according to the different transmittable drive torques, which entails a considerable expenditure of resources in terms of production and storage.

The object of the present invention is therefore to provide a planetary gear system, which allows the above-mentioned drawbacks of the prior art to be overcome.

In particular, it is an object of the present invention to provide a highly versatile transmission system which can be adapted to the different operating conditions.

A further object of the present invention is to provide a transmission system and a method for assembling the same, which is highly efficient and able to reduce storage costs.

The specified technical task and object are substantially achieved by means of a planetary gear system comprising the features set out in one or more of claims 1 to 12, as well as an assembly method according to claims 13 or 14.

Preferably, the planetary gear system comprises a cup-shaped body defining an inner base portion and a side portion. Preferably, the cup shaped body has a plurality of integrated pins arranged on the inner base portion. Preferably, the integrated pins are suitably sized to withstand the stresses generated by a first maximum transmittable torque. Preferably, the planetary gear system further comprises a plurality of gear wheels rotatably mounted on said integrated pins to define an operating condition of said planetary gear system. Preferably, the planetary gear system comprises axial locking means mounted on a top portion of at least one of said integrated pins. According to one aspect of the present invention, the present planetary gear system comprises at least one (first or second) reinforcing body rigidly connected to said cup-shaped body and shaped to bind together said top portions of said integrated pins.

In other words, the presence of a (first or second) reinforcing body reversibly connected to the pins allows the cup-shaped body to be used both in a minimum load configuration, in which the reinforcing body is absent, and in a greater load configuration, in which the body is present. Advantageously, this feature avoids the requirement of the redesign process when the load or the maximum transmittable torque vary and significantly reduces storage costs, since it is the reinforcing body alone that differentiates the minimum load-version storage from the greater load one.

Preferably, the cup-shaped body has a plurality of first coupling areas, each formed at the top portion of the respective pin, and a plurality of second coupling areas formed at the inner base portion; according to a further aspect of the present invention, the reinforcing body alternatively comprises a plate-like portion rigidly connected to said first coupling areas; or a plate-like portion provided with a plurality of radially retaining elements, each fitted on a respective pin, and at least one coupling portion rigidly connected to said second coupling areas.

In other words, the reinforcing body can be provided in a first version, in which it only connects together the top portions of the pins, or in a second version, in which, in addition to connecting the top portions to each other, it binds to the cup-shaped body to increase the rigidity.

Advantageously, in this way, the load that can be supported by the same cup-shaped body is further increased, allowing the producer to broaden the range of products with no engineering costs.

A further object of the present invention is an assembly method for assembling a planetary gear system comprising the steps of: - providing a cup-shaped body having a plurality of integrated support pins suitably sized to withstand the stresses generated by a first maximum transmittable torque;

- providing axial locking means that can be mounted on a top portion of each of said integrated pins;

- providing at least a first and a second reinforcing body, which are sized in order to increase the strength of the integrated pins so as to adapt it to the stresses respectively generated by a second and a third maximum transmittable torque, both greater than said first maximum transmittable torque; said third maximum transmittable torque being greater than said second maximum transmittable torque;

- fitting a gear wheel on a respective integrated support pin;

- selecting among said axial locking means said first reinforcing body and said second reinforcing body according to the desired maximum transmittable torque;

- binding the axial locking means alone to the integrated pins if the desired maximum transmittable torque approximates the first maximum transmittable torque;

- binding the first reinforcing body to the integrated pins if the desired maximum transmittable torque approximates the second maximum transmittable torque;

- binding the second reinforcing body to the integrated pins if the desired maximum transmittable torque approximates the third maximum transmittable torque.

Advantageously, the method is easy to apply because the individual steps are mostly independent of the transmittable torque with the sole exception of the possible selection and assembly of the reinforcing body.

Further features and advantages of the present invention will become more apparent from the indicative, and therefore non-limiting description of a preferred, hence non-exclusive embodiment of a planetary gear system and a method of assembling the same. This description will be set forth hereinafter with reference to the accompanying drawings, which are provided for illustration purposes only, therefore not for limiting purposes, in which:

- Figure 1 is a schematic view of a planetary gear system in accordance with a possible embodiment of the present invention;

- Figure 2 is a schematic view of a planetary gear system in accordance with a possible embodiment of the present invention;

- Figure 3 is a schematic view of a planetary gear system in accordance with a possible further embodiment of the present invention;

- Figure 4 is a sectional view of the planetary gear system in Figure 2;

- Figure 5 is a sectional view of the planetary gear system in Figure 3;

- Figure 6 is a schematic view of a detail of the planetary gear system in Figure 3.

In the attached figures, the reference numeral 1 generally designates a planetary gear system, hereinafter referred to as the planetary system 1.

It should be noted that hereinafter reference will be explicitly made to a planetary gear to be applied to vehicles; however, this specification is provided for dissemination purposes, as the application of the example described is an automotive/industrial application, but in no way intended to represent a limitation to the applicability of the present invention, which should be construed as suitable for any type of planetary gear.

The planetary gear system 1 comprises a cup-shaped body 2 defining a containment volume "V".

The cup-shaped body 2 comprises an inner base portion 3 and a side portion 4. Preferably, the inner base portion 3 has a substantially circular conformation extending around a central axis "X".

Preferably, the side portion 4 is integrally formed in one piece with the base portion 3.

In accordance with a possible embodiment and as shown in the attached figures, the cup-shaped body 2 comprises an anchoring portion 5, which extends radially with respect to an edge of the aforementioned side portion 4, preferably substantially parallel to the aforementioned inner base portion 3.

In particular, the anchoring portion 5 has a plurality of coupling holes 6 suitable to allow the cup-shaped body 2 to be coupled to an external support, for example a casing 2a suitable to at least partially enclose the containment volume "V" defined by the cup-shaped body 2.

Advantageously, the cup-shaped body 2 is made of a high-strength metallic material, for example steel, spheroidal cast iron. Alternatively, lighter materials could also be used for other applications.

The cup-shaped body 2 has a plurality of integrated pins 7 arranged on the inner base portion 3. In particular, the integrated pins 7 extend along a direction substantially perpendicular to the base portion 3, parallel to the aforementioned central axis "X".

In particular, the integrated pins 7 are formed integrally in one piece with the cup-shaped body 2.

Preferably, the integrated pins 7 are equally angularly spaced and radially equidistant from the central axis "X".

Advantageously, the integrated pins 7 are suitably sized to withstand the stresses generated by a first predetermined maximum transmittable torque.

In other words, the integrated pins 7 have diameters and lengths suitable to withstand the loads induced by a predetermined drive torque shifted through the planetary system 1.

The planetary system 1 further comprises a plurality of gear wheels 8 rotatably mounted on the integrated pins 7 to define an operating condition of the planetary system 1.

In particular, the integrated pins 7 are configured to support the gear wheels 8.

Advantageously, the planetary system 1 may comprise rotatable coupling means 9 interposed between the integrated pins 7 and a respective gear wheel 8 to facilitate the rotation thereof. Preferably, the rotatable coupling means 9 comprise at least one bearing.

In accordance with the embodiment shown in the attached figures, the planetary system 1 comprises four integrated pins 7 and four respective gear wheels 8.

In particular, the gear wheels 8 are suitable to mesh with an internally toothed ring gear 10 that can be housed inside the cup-shaped body 2 so that it is arranged along the perimeter of the inner side portion 4 of the cup-shaped body 2.

The planetary system 1 further comprises axial locking means 11 mounted on a top portion 7a of at least one of the integrated pins 7.

Advantageously, the axial locking means 11 support the gear wheels 8 during rotation on the integrated pins 7, preventing them from slipping out of place.

In accordance with a possible embodiment of the present invention, the axial locking means 1 1 can be bound to the integrated pins 7 by means of a screw-and-nut type coupling.

In accordance with the embodiments shown in figures 2 and 3, the planetary system 1 comprises a reinforcing body 12', 12" rigidly connected to the cup-shaped body 2 and shaped to bind together the aforementioned top portions 7a of the integrated pins 7.

Preferably, the reinforcing body 12', 12" comprises the axial locking means 1 1 .

In particular, the axial locking means 1 1 can be formed integrally in one piece with the reinforcing body 12', 12".

Advantageously, the reinforcing body 12', 12" gives rigidity and robustness to the planetary system 1 , helping to support the actions resulting from the predetermined maximum transmittable torque.

In particular, the geometrical conformation and the mechanical properties of the reinforcing body 12', 12" are defined as a function of the drive torque transmitted during an operating condition of the planetary system 1. In this regard, the reinforcing body can be a first reinforcing body 12' (Figure 2) or a second reinforcing body 12" (Figure 3).

In particular, the first reinforcing body 12' is sized in order to adjust the strength of the integrated pins 7 to the stresses generated by a second maximum transmittable torque.

The second reinforcing body 12” is sized in order to adjust the strength of the integrated pins 7 to the stresses generated by a third maximum transmittable torque.

Both the second and the third maximum transmittable torque are greater than the first.

In addition, the third maximum transmittable torque is greater than the second.

Preferably, said maximum transmittable torques are sufficiently spaced apart, in value, to allow categorization of the applied loads. In other words, the first transmissible torque will be representative of “light” applications {light duty), the second transmittable torque will be representative of “medium” applications ( medium duty), and the third transmittable torque will be representative of“heavy” applications {heavy duty).

In other words, the sizing of the pins and the reinforcing bodies is such that the integrated pins, by themselves, are able to meet applications that generate maximum torque around the first transmittable torque, or anyway a lower torque.

The integrated pins reinforced with the first reinforcing body 12' are able to meet applications that generate maximum torque around the second transmittable torque, or anyway between the first and the second maximum transmittable torque.

The integrated pins reinforced with the second reinforcing body 12” are able to meet applications that generate maximum torque around the third transmittable torque, or anyway between the second and the third maximum transmittable torque. As shown in the attached figures, both the first reinforcing body 12' and the second reinforcing body 12" preferably comprise a respective plate-like portion 13', 13” defining a lying plane "P".

In particular, the plate-like portion 13', 13" is configured to be connected to the top portion 7a of the integrated pins 7 so as to limit the relative movement thereof.

Advantageously, the plate-like portion 13', 13" gives rigidity to the planetary system by counteracting the flexional-torsional moment induced on the integrated pins 7 by the movement of the gear wheels 8.

In particular, the plate-like portion 13', 13" can be rigidly connected to a plurality of first coupling areas 14, each formed at the top portion 7a of a respective integrated pin 7.

In accordance with a possible embodiment shown for example in figures 3 and 6, the second reinforcing body 12” comprises a plate-like portion 13 provided with a plurality of radially retaining elements 15, each fitted on a respective integrated pin 7.

Advantageously, the radially retaining elements 15 may be defined by at least one unilateral shoulder.

The second reinforcing body 12" further comprises at least one coupling portion 16 rigidly connected to a plurality of second coupling areas 17 formed at the inner base portion 3.

In particular, each of the plurality of second coupling areas 17 is angularly interposed between two successive integrated pins 7.

“Angularly interposed” means that the integrated pins 7 are arranged alternately with the second coupling areas 17 according to a circumferential direction with respect to the central axis "X".

Advantageously, this alternate arrangement causes a reduction in the inertial forces induced on the cup-shaped body 2 during the operating conditions.

In accordance with this embodiment, the coupling portion 16 comprises a plurality of connecting arms 18 extending out of the above-mentioned lying plane between a first end bound to the plate-like portion 13” and a second end rigidly connected to a respective second coupling area 17.

Preferably, the coupling portion 14 is integrally formed in one piece with the plate-like portion 13”.

As shown in the attached figures, the plate-like portion 13', 13" of the first 12' or the second reinforcing body 12" has an opening 19 suitable to allow insertion of a transmission gear, preferably a central pinion 20, intended to form a kinematic coupling with the gear wheels 8.

Preferably, the planetary system 1 comprises a pinion assembly 20a, with a respective central pinion 20, and a ring gear assembly 10a, with a respective internally toothed ring gear 10, operatively connected to the cup-shaped body 2 for transmitting a drive torque.

According to a typical operating configuration, the central pinion 20 is rotated and transmits a drive torque to the gear wheels 8. These gear wheels 8 are in mesh with the internally toothed ring gear 10, and thanks to this coupling transfer the drive torque to the cup-shaped body 2, which rotates accordingly with an angular speed defined by the predetermined gear ratio.

In particular, this rotation is allowed thanks to the presence of a plurality of bearings 21 interposed between the cup-shaped body 2 and the pinion assembly 20a and/or the ring gear assembly 10a.

According to a further inventive aspect, the present invention refers to an assembly method for assembling a planetary gear system.

This method is preferably, but not exclusively, implemented for assembling the planetary gear system 1 as described heretofore. For this reason, the features already extensively described in relation to the planetary gear system, if in common with the method described below, shall also apply mutatis mutandis to the subsequent description of the method object of the invention. This method comprises providing a cup-shaped body having a plurality of integrated support pins suitably sized to withstand the stresses generated by a first maximum transmittable torque.

Also provided are a plurality of gear wheels 8 and a corresponding plurality of axial locking means 1 1 mountable on a top portion 7a of each one of said integrated pins 7.

The gear wheels 8 are each fitted on a respective integrated pin 7.

At least a first 12' and a second reinforcing body 12” are provided (preferably in stock), which are sized in order to increase the strength of the integrated pins 7.

In particular, the first reinforcing body 12' is sized in order to adjust the strength of the integrated pins 7 to the stresses generated by a second maximum transmittable torque.

The second reinforcing body 12” is sized in order to adjust the strength of the integrated pins 7 to the stresses generated by a third maximum transmittable torque.

Both the second and the third maximum transmittable torque are greater than the first.

In addition, the third maximum transmittable torque is greater than the second.

According to one aspect of the invention, there is provided a step of selecting among the axial locking means 1 1 , the first reinforcing body 12' and the second reinforcing body 12" according to the desired maximum transmittable torque.

In other words, the strength to be given to the system 1 , i.e. which, if any, reinforcing bodies are required, is selected according to the desired (or design) maximum transmittable torque.

Following this selection, the method comprises either:

- binding the axial locking means 1 1 alone to the integrated pins 7 if the desired maximum transmittable torque approximates (or is smaller than) the first maximum transmittable torque; - binding the first reinforcing body 12’ to the integrated pins 7 if the desired maximum transmittable torque approximates the second maximum transmittable torque (or is comprised between the first and the second);

- binding the second reinforcing body 12” to the integrated pins 7 if the desired maximum transmittable torque approximates the third maximum transmittable torque (or is comprised between the second and the third). Advantageously, with a simple selection step (carried out for example by means of a management system) it is possible to identify the ideal configuration for the desired application and provide an assembly capable of conferring the desired strength to the system without the need for any component redesign and without the risk of unnecessary oversizing or undersizing.

Preferably, the cup-shaped body 2 has a plurality of first coupling areas 14, each formed at the top portion 7a of a respective pin 7, and a plurality of second coupling areas 17 formed at an inner base portion 3.

The method further comprises, in case the transmittable torque approximates the second one, a step of binding the first reinforcing body 12' to the first coupling areas 14.

Alternatively, if the transmittable torque approximates the third one, the method comprises binding the second reinforcing body 12" to the second coupling areas 17 so as to assist the integrated pins 7 in supporting the loads induced by the drive torque transmitted during an operating condition.

The present invention achieves the intended objects, overcoming the drawbacks of the prior art.

In fact, the planetary gear system according to the present invention allows increased versatility of the transmission systems so that they can adapt more effectively to the different operating conditions in which they can be used thanks to the presence of a reinforcing body suitable to assist the transmission pins in supporting the loads induced by the drive torques transmitted during the operational life of the transmission system. Advantageously, the planetary gear system and the related assembly method allow the efficiency of the production cycle to be increased and the storage costs to be reduced thanks to the possibility of increasing the maximum torque transmittable by the transmission system simply by replacing the reinforcing body.