GEAR SYSTEM"

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from Italian patent application no. 102020000003485 filed on 20/02/2020, the entire disclosure of which is incorporated herein by reference .

TECHNICAL FIELD

The invention relates to an axle for a vehicle, in particular an axle of a heavy vehicle comprising a reducing gear system integrated in the axle.

KNOWN STATE OF THE ART

As it is known, in a wheel vehicle provided with at least one internal combustion engine, reducing the torque coming from the driveshaft relative to the axles of the vehicle is essential .

As it is further known, vehicles are normally provided with a differential gear assembly, which is configured to differentiate the torque coming from the driveshaft between a pair of axle shafts of the axle, due to known reasons of dynamics while driving the vehicle.

The aforementioned torque reduction is normally carried out by means of known gearbox devices arranged between the driveshaft and the aforesaid differential gear assembly. However, in case of heavy vehicles, these reduction ratios are insufficient, in terms of number, to be able to provide a suitable reduction ratio between the torque of the driveshaft and the torque delivered to the wheels of the axle in the different load conditions.

Indeed, it is clear that a heavy vehicle, such as a truck, has to bear a significant weight difference between the unloaded condition and the maximum load condition and, hence, the highest gears are not necessarily the most suited ones for the unloaded condition of the vehicle.

A known solution to this problem is described in document IT1427916, which discloses a torque reducing system integrated in a wheel hub of a heavy vehicle. Thanks to this reducing system, a further torque reduction can be provided downstream of the differential gear of the vehicle, thus doubling the number of reduction ratios available compared to normal.

However, the system described in the aforementioned document has particularly large dimensions and cannot be used for different types of brakes or platforms that can be applied to the wheel of the vehicle.

Furthermore, it is particularly hard to be mounted as well as complicated to be subjected to maintenance.

Therefore, there is a strong need for a reducing gear system for an axle of a vehicle, which can solve the problems discussed above.

The object of the invention is to fulfil the aforementioned needs in an optimized and economic fashion.

SUMMARY OF THE INVENTION The aforesaid object is reached by an axle provided with a reducing gear system and by a vehicle according to the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be best understood upon perusal of the following detailed description of a preferred embodiment, which is provided by way of non-limiting example, with reference to the accompanying drawings, wherein:

• figure 1 is a schematic, longitudinal section view of an axle comprising a reducing gear system according to the invention in a first operative condition;

• figure 2 is a schematic, longitudinal section view of the axle of figure 1 in a first operative condition; and

• figures 3 and 4 are enlarged views of portions of figures 1 and 2, respectively. DETAILED DESCRIPTION OF THE INVENTION

In figures 1 and 2, number 1 indicates, as a whole, an axle of a vehicle, preferably a heavy vehicle, such as truck, basically comprising a casing 2 defining a space 3 and a pair of axle shafts 4, 5 at least partially housed in the space 3. The casing 2 defines a shape extending along a longitudinal axis A and basically comprises a central portion 2a and a pair of side portions 2b extending in a continuous manner from the central portion 2a along the axis A. Advantageously, the central portion 2a has an extension in a transverse direction relative to the axis A which is greater than the extension of the side portions 2b in the same direction.

According to the embodiment described herein, the side portions 2b are open at the ends thanks to respective openings 2c obtained at the respective ends of the side portions 2b so as to allow the space 3 to communicate with the outside ad so as to allow respective outer end portions

4a, 4b of the axle shafts 4, 5 to project out of the casing 2.

Furthermore, the axle 1 comprises a pair of wheel hubs 6, which are advantageously carried by the casing 2 so as to be free to rotate and are each configured to cooperate with a respective end portion of the axle shafts 4, 5, as described more in detail below.

The central portion 2a of the casing 2 also defines a further opening 2d, which is configured to allow for the passage of a driveshaft 7, which is operatively connected to a torque source, such as an internal combustion engine (not shown). The driveshaft 7 is operatively connected to the axle shafts 4, 5 by means of a torque splitting assembly 8, which is configured to divide the torque coming from the driveshaft 7 between the axle shafts 4, 5. In the example described herein, the driveshaft 7 is perpendicular to the longitudinal axis and the torque splitting assembly 8 comprises a known differential gear 9, which is operatively interposed between the driveshaft 7 and the axle shafts 4, 5.

The differential gear 9 basically comprises a gear train carrier 10, which is carried, so that it can freely rotate, between the casing 2 and each one of the axle shafts 4, 5 by means of rolling members 11, for example ball bearings. Therefore, according to the embodiment described herein, the gear train carrier 10 comprises a cylindrical portion 10a, which is interposed, in a coaxial manner relative to the axis A, between respective inner end portions 4b, 5b of the axle shafts 4, 5 and supporting flanges 12 extending into the space 3 from the central portion 2a of the casing 2 perpendicularly to the longitudinal axis A and advantageously manufactured as one single piece together with the casing itself.

The gear train carrier 10 further comprises a flanged portion 10b perpendicularly extending from the cylindrical portion 10a into the space 3 towards the casing 2 and defining, at the end, a toothing 13, which is configured to mesh with a toothing 14 carried by the driveshaft 7. The gear train carrier 10 also carries a plurality of planet gears 15, for example four planet gears, which are angularly equally spaced apart from one another by 90° and are supported by a cross-shaped support 16, which is rigidly carried by the central portion 10a of the gear train carrier 10 and around whose arms the planet gears 15 can rotate. In particular, the planet gears rotate on the support 16 around axes contained in a plane B, which is perpendicular to the axis A.

The planet gears 14 cooperate with a respective driven gear respectively comprising a left bevel gear 17a and a right bevel gear 17b, each respectively carried by one of the axle shafts 4, 5.

According to the invention, the left and right bevel gears 17a, 17b are carried by the respective axle shaft 4, 5 in a movable manner along the longitudinal axis A, however always operatively connected to the respective axle shaft.

In particular, the connection between the left and right bevel gears 17a, 17b and the respective axle shaft 4, 5 is obtained by means of respective grooved couplings 18', 18'' obtained between the inner end portions 4b, 4b of the axle shafts 4, 5 and an inner spline surface of the left and right bevel gears 17a, 17b. Said grooved couplings 18', 18'' allow the axles shafts 4, 5 to slide along the longitudinal axis

A relative to the left and right bevel gears 17a, 17b, though allowing them to be continuously coupled to one another in a rotary manner.

Advantageously, the axle 1 comprises elastic means 20, which are operatively interposed between each inner end portion 4a, 5b of the axle shafts 4, 5 and the gear train carrier 10 and are configured to impart a force along the longitudinal axis A to the axle shafts 4, 5 so as to keep them in an operative position in which the left and right bevel gears 17a, 17b mesh with the inner end portions 4b, 5b.

In particular, in the embodiment described herein, the elastic means 20 comprise a coil spring 21, which is axially interposed, along the axis A, between each inner end portion 4a, 5b of the axle shafts 4, 5 and the cross-shaped support 16.

More in detail, a first end of each coil spring 21 cooperates in contact with a striker surface obtained in a seat 22 of the respective inner end portion 4a, 5b of the axle shafts 4, 5 and a second end of each coil spring 21 cooperates in contact with a striker surface obtained on a supporting element 23 carried by the cross-shaped support 16 in an integral manner.

Furthermore, both seats 22 are coaxial to the longitudinal axis A and each seat 22 partially surrounds a plurality of coils of the coil spring 21 even in the greatest extension condition (Figures 1, 3). Moreover, the support 23 defines, on both sides of the cross shaped support 16, respective lowered central portions 23a, which are coaxial to one another and, furthermore, are coaxial to the longitudinal axis A and, hence, to each seat 22. In this way, the central portion 23 of the support 23 defines a housing seat for the portion of the end of the respective coil spring 21.

Back to the wheel hubs 6, for the sake of simplicity reference will be made to only one of them, for example the left wheel hub, which is enlarged in figures 2 and 3. Obviously, the information given below also applies, in the same way, to the right wheel hub, as the structure described below is mirror-like relative to the plane B f the planet gears 15.

The wheel hub 6, as mentioned above, is supported in such a way that it can freely rotate relative to the casing 2, in particular it is hollow and is supported on the outside of the side portion 2b of the casing 2, coaxially to the longitudinal axis A. In the example described herein, the wheel hub 6 is supported by means of supporting means 25, such as a pair of conical bearings, and by means of sealing means 26, such as an O-ring.

In particular, the hub 6 comprises a main portion 6a with a substantially cylindrical shape defining, around the side portion 2b of the casing 2, a chamber 27, which is radially delimited between the outer surface of the side portion 2b and the inner surface of the main portion 6a of the wheel hub 6. Longitudinally, namely along the axis A, the chamber 27 is delimited by the sealing means 26, in a position close to the central portion 2a of the casing 2, and by a slidable element 28, which is arranged on the opposite side relative to the sealing means 26 with respect to the central portion 2a of the casing 2 and is described more in detail below.

In particular, the chamber 27 is divided into several portions, which are not numbered for greater clarity but can clearly be identified in the accompanying figures, fluidcally connected to one another by means of a plurality of ducts 29 so that there is a fluid-leading continuity between the sealing means 26 and the slidable element 28, namely among all portions of the chambers 27.

The axle 1 further comprises valve means 31, which are configured to be fluidically connected to a pressurised air circuit (no shown) of the vehicle in order to allow compressed air to be injected into the chamber 27 so as to pressurise it or in order to allow air to be released from the chamber into a circuit of the vehicle or into the atmosphere. Advantageously, said valve means 31 comprise an injector 32, which is configured to allow for the aforementioned flows between the chamber 27 and the compressed air circuit and/or the atmosphere. The compressed air injected by the injector 32 into the chamber 27 is configured to exert a pressure F upon the slidable element so as to cause it to move between a first operative condition (figures 2, 4), in which the volume of the chamber 27 reaches a greater and maximum value compared to a second operative condition (figures 1, 3), with a low or absent pressure in the chamber 27, for example released by means of the injection means 31, in which the volume of the chamber 27 is smaller, minimum. According to the embodiment described herein, the slidable element 28 is housed, in a sliding and fluid-tight manner, in a portion 27a of the chamber 27, which is radially delimited by an inner portion 6b of the wheel hub 26 and is longitudinally delimited, along the axis A, on one side, by the inner portion 6b itself fluidically connected to the rest of the chamber 27 by a channel 29 and, on the other side, is open towards the opening 2c of the casing 2 so as to allow the outer end portion 4a of the axle shaft 4 to be housed. In particular, the inner portion 6b of the wheel hub 6 extends inside the chamber 27 so as to surround the axle 4 and is substantially arranged at the opposite end relative to the sealing means 26 of the wheel hub 6. The inner portion 6b is connected to the cylindrical portion 6a by means of an intermediate portion 6c. Hence, based on the configuration described above by way of example, the slidable element 28 is configured to move along the longitudinal axis A in order to define the aforesaid first and second operative conditions, wherein, in the first condition, it is substantially in contact with the inner portion 6a of the wheel hub 6 and, in the second condition, it is spaced apart from the latter.

Advantageously, the slidable element 28 is carried by the outer end portion 4a of the axle shaft 4 and, preferably, it is manufactured as one single piece together with the latter. Consequently, the axle shaft 4 is caused to move along the axis A thanks to the force exerted by the pressure F upon the slidable element 28.

According to the invention, the axle shaft 4 comprises at least one toothing 33, in the case described herein one single toothing, which extends from the outer surface of the axle shaft 4 perpendicularly to the longitudinal axis A and is configured to selectively engage toothings 34, 35 carried by the wheel hub 6, respectively, so as to define different transmission ratios.

Advantageously, the toothing 33 is configured to mesh with one of the toothings 34, 35 in order to define a transmission ratio equal to 1, whereas the same toothing 33 is configured to mesh with the other one of the toothings 34, 35 in order to define a transmission ratio other than one and preferably ranging from 1.5 to 2.5.

Advantageously, said toothing 33 can slide relative to the toothings 34, 35 and the axle 1 comprises a transmission 36, which is interposed between the toothing 35 defining a transmission ratio other than 1 and the wheel hub 6.

According to the embodiment described herein, the first toothing 34 is integral to the wheel hub 6, in particular along the an inner surface of the inner portion 6b and, therefore, the torque of the axle 4 is directly transmitted to the wheel hub 6 according to the transmission ratio between the toothings 33 and 34.

On the other hand, advantageously, the transmission 36 comprises an epicyclic gear 37, which is advantageously interposed, inside the chamber 27 and along the axis A, between the inner portion 6b of the wheel hub 6 and the supporting elements 25. According to the embodiment described herein, the epicyclic gear comprises a sun gear 38 defining the second gearing 35; advantageously, the sun gear 38 is coaxial to the longitudinal axis A and is supported, in a rotary and sliding manner, by the inner portion 6a, for example by means of friction rings 39 or bearings axially interposed, along the longitudinal axis A, between the sun gear 38 and the inner portion 6a.

The epicyclic gear 37 further comprises a plurality of planet gears 41, which are carried by the wheel hub 6, hence serving as gear train carrier, and are configured to mesh with a toothing 42 obtained on a portion of the sun gear 38 and with a second toothing 43 obtained on the side portion 2b of the casing 2, advantageously close to the relative opening 2c Consequently, since the planet gears 41 are rigidly carried by the wheel hub 6 and since the sun gear 38 cooperating with the planet gears 41 is caused to rotate by the axle shaft 4, they cause the wheel hub 6 to rotate around the axis A with a transmission ratio with a predetermined value, for example within the aforementioned range.

In particular, the planet gears 41 are bevel gears and, hence, the toothings 42, 43 are configured to cooperate in order to form a bevel gearing with the planet gears 41. Furthermore, the planet gear 41 are preferably supported by the wheel hub 6 in such a way that they can freely rotate relative to the respective rotation axis, for example by means of respective supporting elements 45, such as bushings, interposed between a hub 41a of the planet gears 41 and respective seats 46 obtained in the intermediate portion 6c. Advantageously, the axis of the planet gears 41 is inclined both relative to the plane B of the planet gears 15 of the differential gear 8 and relative to the longitudinal axis A of the axle 1.

According to the enlarged views of figures 3, 4, which contain more constructive elements of the axle 1, the wheel hubs 6 and the casing 2 advantageously consist of a plurality of elements connected to one another to define the shapes described above, merely in order to allow the different elements described above to be mounted. Therefore, since figures 1, 2 and also figures 3 and 4 are substantially schematic views, the axle 1 can clearly comprise further elements, such as threaded elements, lateral and axial containing rings, friction rings, bushings and bearings, which are not shown herein, for they are known elements, and are designed to allow the axle 1 described above to be mounted and to correctly operate.

The different toothings mentioned in the description above advantageously have straight teeth, but they can be of any type. The axle 1 according to the invention described above works as follows.

In any operating condition, the torque coming from the driveshaft 27 is imparted to the gear train carrier 10 of the differential gear 8 thanks to the meshing between the toothings 13 and 14 and, as it is known, is divided between the axle shafts 4, 5 depending on known dynamic conditions of the vehicle.

Hereinafter, for the sake of brevity and simplicity, reference will be made to the sole left wheel hub 6, since the operation of the right hub is identical. In a first operating condition, which is shown in figures 1 and 3, the chamber 27 has a low pressure/atmospheric pressure and, hence, the slidable element 28 is consequently placed in contact with the inner portion 6c of the wheel hub. Consequently, the axle shaft 4 is placed in such a way that the toothing 33 meshes with the first toothing 34 thanks to the thrust exerted by the spring 21, which acts so as to impart a force in the direction of the axis A, which is configured to hold the slidable element 28 in contact with the inner portion 6b. In this condition, as described above, the torque coming from the axle shaft 4 is directly transmitted to the wheel hub, without any reduction, since the toothing 34 is integral to the inner portion 6b of the wheel hub 6 and, hence, to the latter.

In a second operating condition, which is shown in figures 2 and 4, the chamber 27 is pressurised thanks to the compressed air injected by the valve means 31. Thanks to the channels 29, the compressed air comes into contact with an outer surface of the slidable element 28, thus exerting a force against it. The force exerted by the air pressure is such as to exceed the force imparted by the spring 21, which tends to become compact due to the thrust of the axle shaft 4, which tends to move until the spring 21 reaches a packed condition and, preferably, the inner end portion 4b of the axle shaft 4 comes into contact with the supporting element 23 housed inside the differential gear 9. In this position, the torque, from the axle shaft 4, is transmitted from the meshing of the toothings 33 and 35 to the sun gear 38 and, from here, to the planet gears 41, which mesh between the sun gear 38 and the casing 2. Since the latter is fixed and the planet gears 41 are supported by the wheel hub 6 with the sole freedom of rotation around their axis, the wheel hub 6 is caused to rotate by the planet gears 41 around the axis A. This transmission, through the elements of the epicyclic gear 37, allows the torque reduction value obtained to be within the range described above.

In order to shift from the second to the first operating conditions, the chamber 27 needs to be released, for example by means of valve means 31, so that the force exerted by the spring 21 pushes again the axle shaft 4 and, hence, the slidable element 28, causing it to strike against the inner portion 6b of the wheel hub 6, thus going back to the configuration described above, which enables the first operating condition of figures 1 and 3. Owing to the above, the advantages of an axle comprising an integrated reducing gear system according to the invention are evident.

Thanks to this system, a reducing gear system is provided, which is integrated in an axle, is versatile, compact and economic as well as easy to be mounted and subjected to maintenance compared to known systems.

Thanks to the additional reducing gear system and to the reduction range that can be optimized depending on the type and size of the vehicle, fuel consumptions as well as pollutant emissions can be reduced.

Furthermore, compared to the solution described in IT1427916, fewer elements are present, for example the housing of the spring by means of a sleeve is absent in this invention, where the spring is directly housed between the differential gear and the axle shaft.

In this way, besides simplifying assembly and reducing costs, it is easier for the lubricant to flow along the axle shaft, thus improving the lubrication of all components of the gear 37. Indeed, the sleeve of the prior solution acted as lubricant collecting element, thus preventing it from being correctly spread to the adjacent gears.

Furthermore, by eliminating the sleeve of the spring from the wheel hub, a compact wheel hub can be provided, which, hence, can adjust to different types of wheels and brakes. Furthermore, the elimination of the sleeve and the integration of the spring housing between the axle shaft and the differential gear, which are connected to one another by a spline, allows for a more sturdy and safe solution than the previous one. Finally, the axle comprising an integrated reducing gear system according to the invention can be subjected to changes and variants, which, though, do not go beyond the scope of protection set forth in the appended claims.

Obviously, as mentioned above, the casing 2 and the wheel hub 6 can have different shapes and consist of more and different pieces.

In addition, the gears described above could change and there could be elements that are not described herein, but are known when dealing with the assembly of an axle according to the invention.

Clearly, the description above relates to an air actuation, which is deemed to be the most effective and economic one, however the use of equivalent actuator means should not be excluded, said equivalent actuator means being, for example, electromagnetic, mechanical or fluid actuator means, which are configured to move the slidable element 28 instead of the air pressing force described herein.