Patent Description:
The ecological transition increasingly requires the use of electric motors to aid or replace internal combustion engines for vehicle transport.

To this end, it is known to provide traction assemblies configured to provide torque to the wheels of a vehicle, while comprising a power take-off configured to connect to an output shaft of an internal combustion engine and one or more electric motors configured to cooperate or replace said internal combustion engine.

These traction assemblies are required to be compact and versatile, in other words, not to increase the vehicle's overall dimensions and weight excessively, but to provide various functional configurations. This requirement is all the more so in commercial vehicles where it is necessary to be able to supply torque to the wheels according to the different operational requirements of the vehicle.

Examples of known systems are known in publications <CIT>, <CIT> or <CIT>.

There is therefore a need to provide traction assemblies that can be versatile and compact.

The object of the present invention is to meet the above requirements in a cost-effective and optimized manner.

Said object is achieved by means of a traction assembly and a vehicle as claimed in the appended claims.

For a better understanding of the present invention, a preferred embodiment is described below by way of non-limiting example and with reference to the accompanying drawings, wherein:.

The reference number <NUM> in the attached figures indicates a traction assembly according to the invention, configured to transmit torque to respective axle shafts <NUM>, <NUM>, a left and a right axle shaft, respectively.

Each axle shaft <NUM>, <NUM> is configured to drive a wheel hub 2a, 3a, attached to an outer end <NUM>', <NUM>' of the respective axle shaft <NUM>, <NUM>, which is configured to be integral with a wheel assembly <NUM>, e.g., in the case shown, a twin wheel assembly.

In particular, the traction assembly <NUM> is configured to supply torque to the axle shafts <NUM>, <NUM> via at least one electric machine 5a, 5b, optionally even only configured as an electric motor, configured to supply torque using electrical energy, for example provided by a vehicle battery assembly (not shown), or to absorb torque to generate electrical energy to be supplied to said battery assembly.

In the example shown, the traction assembly <NUM> comprises a pair of electric machines 5a, 5b whose respective operating shaft 5a', 5b' is parallel to a longitudinal axis A of the axle shafts <NUM>, <NUM> which are coaxial with each other.

The traction assembly <NUM> comprises a transmission <NUM> operatively interposed between the left and right axle shafts <NUM>, <NUM> and the pair of electric machines 5a, 5b and configured to allow torque transmission in a first configuration, in which a single electric machine 5b supplies torque to both axle shafts, and in a second configuration, in which each electric machine 5a, 5b supplies torque to the axle shafts independently of each other.

Advantageously, the traction assembly <NUM> comprises a casing <NUM> configured to delimit a space <NUM> isolated from the outside; the space <NUM> is configured to house the transmission <NUM> as described below. Preferably, the casing <NUM> comprises a central portion 7a and a pair of lateral portions 7b located at the axle shafts <NUM>, <NUM>.

As shown, the transmission <NUM> comprises, between each electric machine 5a, 5b and the respective axle shaft <NUM>, <NUM>, a reduction stage 9a, 9b configured to vary the speed/torque transmitted between the operating shaft 5a', 5b' and the respective axle shaft <NUM>, <NUM>.

It is noted that, advantageously, the electric machines 5a, 5b are located opposite the longitudinal axis A and that the reduction stages 9a, 9b are arranged symmetrically in relation to a transverse centreline axis (not shown) perpendicular to the axis A.

In particular, each reduction stage 9a, 9b comprises a first toothed wheel 11a, 11b driven by the operating shaft 5a', 5b' and configured to mesh with a second toothed wheel 12a, 12b carried integrally by a support shaft 13a, 13b carried in a rotationally free way by the casing <NUM> parallel to the axis A. The support shaft 13a, 13b rigidly carries a third toothed wheel 14a, 14b configured to mesh with a toothing 15a, 15b described in greater detail below.

One of the toothings 15a, 15b is advantageously made on a carrier <NUM> of a differential <NUM>. In particular, the differential <NUM> is operatively connected between one of the axle shafts <NUM>, <NUM> and a support hub <NUM>. In the case described in <FIG>, the differential <NUM> connects an inner end <NUM>" of the left axle shaft <NUM> to the support hub <NUM>, which is interposed, on the opposite side along the longitudinal axis A, with an inner end <NUM>'' of the right axle shaft <NUM>.

As shown, the differential <NUM> may be of a known type, i.e., comprising the carrier <NUM> which carries a plurality of planet wheels <NUM>, e.g., four planet wheels angularly equally spaced at <NUM>° from each other and supported by a cross-shaped support <NUM> rigidly carried by the carrier <NUM> and around whose arms the planet wheels <NUM> can rotate. In particular, the planet wheels rotate on the support <NUM> around axes contained in a plane perpendicular to the axis A.

The planet wheels <NUM> cooperate with a respective sun gear respectively comprising a left bevel toothed wheel <NUM>" and a right toothed wheel <NUM>" rigidly carried by the left axle shaft <NUM> and the support hub <NUM>, respectively.

The other one of the toothings 15a, 15b is integral with the right axle shaft <NUM>, in particular with a portion rigidly connected thereto and defining the inner end <NUM>".

According to the embodiment in <FIG>, the transmission <NUM> comprises first selector means <NUM> configured to selectively make the support hub <NUM> integral with the inner end <NUM>' of the right axle shaft <NUM>, and second selector means <NUM> configured to selectively make two portions of the operating shaft 5a' of the first electric machine 5a integral with each other.

Both the first and second selector means <NUM> comprise a sleeve <NUM> which is integral with the rotation but free to translate on the axis A on the respective support.

In particular, the sleeve <NUM> of the first selector means defines a first and a second toothing <NUM>, <NUM>, which are configured to cooperate with respective toothings <NUM>, <NUM> integral with the support hub <NUM> and the end <NUM>" of the right axle shaft, respectively. Advantageously, these toothings <NUM>, <NUM>, <NUM> and <NUM> are toothings axial in relation to the axis A.

On the other hand, the sleeve <NUM> of the second selector means <NUM> defines an inner radial toothing <NUM>' configured to selectively cooperate with a pair of outer radial toothings <NUM>', <NUM>' formed on the two portions of the operating shaft 5a' or only on one of them.

In particular, the selector means <NUM> comprise actuator means <NUM> configured to move the sleeve <NUM> along the longitudinal axis A on the support hub <NUM>. Advantageously, said actuator means <NUM> are pneumatic actuator means.

Preferably, according to the described embodiment, said actuator means <NUM> comprise a rod <NUM> configured to carry a piston <NUM> which is free to move in a chamber <NUM> designed to selectively house a pressurized fluid, e.g., compressed air.

The actuator means <NUM> may also include elastic means <NUM>, such as a helical spring <NUM>, operatively interposed between the rod <NUM> and the casing <NUM> in order to keep the sleeve <NUM> in a predefined position.

In particular, in the embodiment shown, the elastic means <NUM> are configured to keep the sleeve <NUM> of the first selector means <NUM> so that the toothing <NUM> does not cooperate with the toothing <NUM> and to keep the sleeve <NUM> of the second selector means <NUM> so that the toothing <NUM>' meshes with both the toothings <NUM>', <NUM>'.

The embodiment in <FIG> differs from the embodiment in <FIG> in that the operating shaft 5a' of the first electric machine 5a is directly connected to the toothed wheel 11a and the toothed wheel 15a is integral with a hub <NUM> rotatably carried by the casing <NUM>.

In particular, the hub <NUM> is also housed in a rotationally free way on the inner end <NUM>" of the right axle shaft <NUM>.

The first selector means <NUM> of the embodiment in <FIG> are operatively interposed between the inner end <NUM>'' of the right axle shaft <NUM> and the support hub <NUM>, similar to the embodiment in <FIG>, whereas the second selector means <NUM> are operatively interposed between the hub <NUM> and the right axle shaft <NUM> and are configured to selectively connect the latter.

In particular, therefore, in this embodiment, the selector means <NUM> comprise an inner radial toothing <NUM>" configured to cooperate with a corresponding outer radial toothing <NUM>" made on the right axle shaft and a toothing <NUM>" configured to cooperate with a toothing <NUM>'' made on the hub <NUM>. In particular, the toothings <NUM>" and <NUM>" are axial toothings.

The toothed wheels shown herein all have straight teeth, although it is clear that they can be made using different toothing types.

Clearly, additional mechanical elements such as rolling and sliding supports, gaskets, and fasteners, although illustrated, have not been described for the sake of brevity and because they are related to construction details that may vary according to different assembly and manufacturing settings.

The operation of the traction assembly <NUM> according to the first embodiment described above (<FIG>) is as follows.

In a first operating condition, shown in <FIG>, where the broken lines indicate the torque path, both the electric machines 5a, 5b supply torque to the respective wheel hubs 3a, 3b. In this configuration, the first selector means <NUM> are controlled by the actuator means <NUM> so that only the toothing <NUM> cooperates with the toothing <NUM>, and the second selector means <NUM> are controlled by the actuator means <NUM> so that the toothing <NUM>' meshes with both the toothings <NUM>', <NUM>', thus making the toothed wheel 11a integral with the operating shaft 5a. In this operating condition, the differential <NUM> allows the entire torque to be passed to the left axle shaft <NUM>, whereas the torque supplied by the first electric machine 5a flows to the right axle shaft alone, which is disconnected from the support hub <NUM> and thus independent of the differential <NUM>. The control of the torque/speed compensation at the two axle shafts can therefore be adjusted electronically via an electronic unit (not shown) connected to the two electric motors 5a, 5b.

In a second operating condition, shown in <FIG>, where the broken lines indicate the torque path, the second electric machine 5b alone supplies torque to both the wheel hubs 3a, 3b. In this configuration, the first selector means <NUM> are controlled by the actuator means <NUM> so that only the toothing <NUM> cooperates with the toothing <NUM> and so that the toothing <NUM> cooperates with the toothing <NUM>, whereas the second selector means <NUM> are controlled by the actuator means <NUM> so that the toothing <NUM>' meshes with the toothing <NUM>' alone, thus making the toothed wheel 11a idle with respect to the first portion of the operating shaft 5a, i.e., not drivable or driving the electric machine. In this operating condition, the differential <NUM>, as is known, splits the torque from the second electric machine 5b to both the axle shafts <NUM>, <NUM>.

A further operating configuration, not shown, is possible, where the selector means connect the first electric machine 5a to the toothed wheel 11a in the second operating configuration. This alternative configuration can be useful in some system mode conditions in which the electric machines 5a, 5b operate as a generator and are driven by the axle shafts <NUM>, <NUM>, for example in neutral mode of the vehicle or downhill/in motion without positive acceleration by the driver.

The operation of the traction assembly <NUM> according to the second embodiment described above (<FIG>) is as follows.

In a first operating condition, shown in <FIG>, where the broken lines indicate the torque path, both the electric machines 5a, 5b supply torque to the respective wheel hubs 3a, 3b. In this configuration, the first selector means <NUM> are controlled by the actuator means <NUM> so that only the toothing <NUM> cooperates with the toothing <NUM>, and the second selector means <NUM> are controlled by the actuator means <NUM> so that the toothing <NUM>'' meshes with the toothing <NUM>", thus making the hub <NUM> integral with the right axle shaft <NUM>. In this operating condition, the differential <NUM> allows the entire torque to be passed to the left axle shaft <NUM>, whereas the torque supplied by the first electric machine 5a flows to the right axle shaft <NUM> alone, which is disconnected from the support hub <NUM> and thus independent of the differential <NUM>. The control of the torque/speed compensation at the two axle shafts can therefore be adjusted electronically via an electronic unit (not shown) connected to the two electric motors 5a, 5b.

In a second operating condition, shown in <FIG>, where the broken lines indicate the torque path, the second electric machine 5b alone supplies torque to both the wheel hubs 3a, 3b. In this configuration, the first selector means <NUM> are controlled by the actuator means <NUM> so that only the toothing <NUM> cooperates with the toothing <NUM> and so that the toothing <NUM> cooperates with the toothing <NUM>, whereas the second selector means <NUM> are controlled by the actuator means <NUM> so that the toothings <NUM>" and <NUM>'' do not mesh with each other, thus making the hub <NUM> idle with respect to the right axle shaft <NUM>. In this operating condition, the differential <NUM>, as is known, splits the torque from the second electric machine 5b to both the axle shafts <NUM>, <NUM>.

Similar to the first embodiment, a further operating configuration, not shown, is possible, where the selector means connect the hub <NUM> to the right axle shaft <NUM> in the second operating configuration. This alternative configuration can be useful in some system mode conditions in which the electric machines 5a, 5b operate as a generator and are driven by the axle shafts <NUM>, <NUM>, for example in neutral mode of the vehicle or downhill/in motion without positive acceleration by the driver.

The advantages of a traction assembly and a vehicle according to the invention are clear from the foregoing.

The traction system allows purely electric traction to be provided up to a tonnage of <NUM> tons, in particular even just using one of the electric machines.

In detail, both electric machines can be used at start or in some overload conditions, unclogging the differential and controlling the torque split electronically. Thus, when not needed, it is possible to consume less electrical energy since only one of the electric motors is activated.

The traction system is also particularly compact and uses very few mechanical elements, therefore the manufacturing costs are reduced. Moreover, the layout of the electric machines and reduction stages is optimized to reduce the tilting stress.

Furthermore, since all the rotating mechanical elements are inside the transmission housing casing, which is lubricated, the service life of the traction system is increased, and maintenance costs are reduced.

Lastly, it is clear that modifications and variations may be made to the traction assembly and the vehicle according to the present invention, without however departing from the scope of protection defined by the claims.

For example, it is clear that the described toothed wheels, the differential, and other types of mechanical connections can be replaced by equivalent devices.

Claim 1:
A traction assembly (<NUM>) for a vehicle, said traction assembly (<NUM>) comprising a left and a right axle shaft (<NUM>, <NUM>) extending along a longitudinal axis (A) and defining an outer end configured to be connected to a wheel hub (2a, 3a) of said vehicle,
said traction assembly (<NUM>) comprising at least a first and a second electric machine (5a, 5b),
said traction assembly (<NUM>) comprising a casing (<NUM>) defining a housing (<NUM>) and a transmission (<NUM>) housed in said housing (<NUM>) and comprising a differential (<NUM>) and selector means (<NUM>),
wherein the second electric machine (5b) is operatively connected to one of said axle shafts (<NUM>, <NUM>) and the first electric machine (5a) is operatively connectable to one of said axle shafts (<NUM>, <NUM>) by means of first selector means of said selector means (<NUM>),
characterized in that said differential (<NUM>) is operatively connectable between said axle shafts (<NUM>, <NUM>) by means of second selector means of said selector means (<NUM>),
said selector means (<NUM>) being controlled so that said transmission (<NUM>) allows at least two operating conditions:
- in one of said operating conditions only the second electric machine (5b) provides torque to said axle shafts (<NUM>, <NUM>), said differential (<NUM>) being operatively connected to said axle shafts (<NUM>, <NUM>);
- in another of said operating conditions, the first and second electric machines (5a, 5b) provide torque to a respective axle shaft (<NUM>, <NUM>), said differential (<NUM>) being operatively disconnected between said axle shafts (<NUM>, <NUM>).