AXLE AND MOTOR VEHICLE COMPRISING SAID AXLE

An electric axle for a motor vehicle, comprising: a first wheel, which can rotate around a first axis; a second wheel, which can rotate around a second axis; and an electric motor, which is operatively connected to said first and second wheel; the electric motor comprises, in turn, an output shaft, which can rotate around a third axis orthogonal to said first and second axis.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from Italian patent application no. 102023000007071 filed on Apr. 13, 2023, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The invention relates to an axle, in particular a motor-driven electric axle.

The invention also relates to a motor vehicle comprising said axle.

BACKGROUND

Electric motor vehicles comprise, in a known manner:a front axle comprising a pair of front wheels;a rear axle comprising a pair of rear wheels; anda drive assembly comprising at least one electric machine operating as electric motor and operatively connected to the front and/or rear wheels so as to transmit a drive torque to the front and/or rear wheels.

Said motor vehicles further comprise one or more electric batteries designed to power the electric machine with the necessary quantity of electric power in the batteries.

The range of electric motor vehicles is determined by the quantity of electrical energy than can stored per volume unit.

In the state of the art, said value approximately is one tenth of the quantity of energy that can be stored per volume unit through the use of a fossil fuel.

This sets limits to the performances of electric motor vehicles, especially when they are used on tracks or for professional races.

Indeed, as it is known, when driving along a bend, motor vehicles counter centrifugal force through the friction of the tyres against the ground in a radial direction relative to the arc described by the bend.

As a consequence, for a given radius of the bend, the square of the maximum travelling speed of a motor vehicle in conditions of grip is proportional to the vertical load acting upon the tyres.

In order to increase said load up to values exceeding the weight of the motor vehicle, motor vehicles are provided with downforce aerodynamic surfaces, namely shaped so as to generate an additional vertical downward thrust. Said vertical downward thrust, known as “downforce”, is proportional to the square of the driving speed of the motor vehicle and to a downforce coefficient associated with the shape of the aerodynamic surface.

The increase in said downforce inevitably leads to an increase in the aerodynamic resistance of the motor vehicle.

This is due to the fact that the downforce coefficient of the aerodynamic surface is proportional to the resistance coefficient.

Because of this increase in aerodynamic resistance, electric motors must deliver a greater electric power in order to maintain desired speed values on straight stretches of road.

Said electric power increase further jeopardizes the range of the motor vehicle.

Therefore, in order to increase the range of the motor vehicle, thus enabling an acceptable sports use, the aerodynamic resistance of the motor vehicle should be reduced as much as possible, without jeopardizing the overall weight acting upon the wheels.

In other words, the overall resistance coefficient of the motor vehicle should be reduced, though without affecting the downforce coefficient of the aerodynamic surfaces.

As it is known, said resistance coefficient is determined, to a significant extent, by the layout of the rear portion of the motor vehicle, namely by the dimensions of the motor vehicle along a transverse dimension, which is orthogonal to a normal forward driving direction of the motor vehicle.

Axles are known, for example from EP-A-3597464, which comprise a pair of electric machines operatively connected to respective wheels and comprising respective output shafts arranged parallel to the transverse direction of the motor vehicle.

The dimensions of said electric machines determine a lower limit for the maximum front section of the motor vehicle in the rear portion and, hence, a lower limit for the overall resistance coefficient and for the resulting energy consumptions of the motor vehicle.

In the automotive industry, an electric axle for a motor vehicle is needed, which reduces energy consumptions, though preserving a high aerodynamic load, so as to significantly increase the range of the motor vehicle, especially in racing mode.

Furthermore, the overall inertia of the motor vehicle needs to be reduced, with a consequent improvement in the dynamic performances of the motor vehicle.

US-A-2011/259657 discloses an axle according to the preamble of claim1or7.

SUMMARY

The object of the invention is to provide an axle, which is capable of fulfilling at least one of the needs discussed above.

The aforesaid object is reached by the invention, as it relates to an axle for a motor vehicle as defined in claim1or7.

DESCRIPTION OF EMBODIMENTS

With reference toFIG.1, number1indicates a motor vehicle comprising a body2defining a passenger compartment3.

The motor vehicle1is a top-of-the-range motor vehicle designed both for a conventional urban/suburban use and for a racing track use.

Furthermore, the motor vehicle1is a hybrid or electric vehicle and is provided with electric batteries (not shown).

Hereinafter, expressions such as “above”, “under”, “in front of”, “behind” and others similar to them are used with reference to normal driving conditions of the motor vehicle1.

Furthermore, it is possible to define:a longitudinal axis X integral to the body2, which, in use, is horizontal and parallel to a normal driving direction of the motor vehicle1indicated inFIGS.1to4;a transverse axis X integral to the body2, which, in use, is horizontal and orthogonal to the axis X; andan axis Z integral to the body2, which, in use, is vertical and orthogonal to the axes X, Y.

The axes X, Y define a horizontal plane P integral to the body2and arranged, in use, substantially horizontal.

The axes X, Z define a vertical plane Q integral to the body2and arranged, in use, substantially vertical.

For the purposes of the following disclosure, the plane Q is a longitudinal middle plane of the motor vehicle1.

The body2defines a front6and a rear7, with reference to a normal forward driving direction parallel to the axis X.

The axle10comprises, in turn:a pair of front wheels11,12, which can rotate around respective axes A, B; anda pair of axle shafts20,21connected to the respective front wheels11,12.

The axle15comprises, in turn:a pair of rear wheels16,17, which can rotate around respective axes C, D; anda pair of axle shafts22,23connected to the respective rear wheels16,17.

Hence, the motor vehicle1comprises:an unsprung mass45(FIG.2) comprising, in turn, the body2;a sprung mass46comprising, in turn, the axles10,15;a pair of front suspensions (not shown) of the known kind and configured to elastically suspend the front wheels11,12of the unsprung mass45to the body2of the sprung mass46; anda pair of rear suspensions24,25of the known kind and configured to elastically suspend the rear wheels16,17of the unsprung mass45to the body2of the sprung mass46.

Each front and rear suspension24,25comprises, extremely in short, an elastic element28and a damping element29interposed between the respective front wheels11,12(rear wheels16,17) and the body2.

Each front suspension and rear suspension24,25allows the front wheels11,12(rear wheels16,17) to move, in a known manner, relative to the body2, following the irregularities of the ground according to an approximately vertical trajectory, hence parallel to the axis Z.

Consequently, the axes A, B (C, D) of the front wheels11,12(rear wheels16,17) always remain approximately parallel to the axis Y of the body2.

The axle15further comprises:an electric motor30comprising an output shaft31operatively connected to the rear wheel16; andan electric motor35comprising an output shaft36operatively connected to the rear wheel17.

The motor vehicle1further comprises:an assembly37consisting of the electric motor30and of a transmission assembly40interposed between the output shaft31and the axle shaft22; andan assembly38consisting of the electric motor31and of a transmission assembly41interposed between the output shaft32and the axle shaft23.

In particular, the transmission assemblies40,41comprise respective output power take-offs42,43opposite the respective output shafts30,31and connected to respective axle shafts22,23.

The output shafts31,32can advantageously rotate around respective axes X1, X2, which are orthogonal relative to the axes C, D.

More in detail, the axes X1, X2are parallel to one another and to a common axis K.

The axis K lies on the plane Q of the motor vehicle1.

The axis K defines, with the axis X, an angle α (FIG.3) oriented towards the front6and ranging from 0 to 90 degrees, more preferably between three and seven degrees.

The angle α is, in the specific case shown herein, five degrees.

In particular, each assembly37,38has a length L1parallel to the axis K, which is greater than a width L2parallel to the axis Y.

The motor vehicle1further comprises a casing50accommodating both motors30,35and the relative transmission assemblies40.

In particular, the casing50serves as stator for the electric motors30,35.

The casing50has a length L3parallel to the axes X1, X2and a width L4parallel to the axes X1, X2. The length L3is greater than the length LA (FIG.4).

Each casing50consists of a pair of half-shells51,52shown inFIG.4.

The motors30,35extend from the side of the front6, with reference to the axes C, D.

The motors30,35can be operated independently of one another, so as to exert respective drive torques, which can be adjusted independently of one another, upon the rear wheels16,17.

The motor vehicle1further comprises a braking system (not shown) configured to exert a plurality of braking torques upon the respective front wheels11,12and rear wheels16,17.

The aforesaid braking system could be of the traditional kind, namely acting through “friction”, or of the regenerative kind capable of transforming the kinetic energy of the braked front wheels11,12and the rear wheels16,17into electric energy to be stored in the batteries or of the combined heat-regenerative kind.

In use, the electric motors30,35are operated independently of one another so as to generate respective drive torques acting upon the rear wheels16,17by means of the corresponding transmission assemblies40,41, so as to cause the motor vehicle1to move forward.

The disclosure above reveals evident advantages that can be reached with the invention.

In particular, the output shafts31,32of the electric motors35of the axle15can rotate around respective axes X1, X2orthogonal to the axes C, D of the corresponding rear wheels16,17.

In this way, the electric motors30,35are side by side and are parallel to the axis K of the motor vehicle1.

This reduces the overall dimensions of the motor vehicle1parallel to the axis Y in the region of the axle15, namely at the rear7of the body2.

This reduction of dimensions allows the body2—in particular the rear7—to be shaped according to a more aerodynamic layout compared to known solutions discussed in the introduction to the description.

By so doing, the overall resistance coefficient of the motor vehicle1can be reduced, though without affecting the downforce coefficient of the motor vehicle1.

Therefore, consumptions are reduced and, hence, the range of the motor vehicle1increases, preserving at the same time the ability of the motor vehicle1to travel along curved trajectories at high speeds.

In short, the motor vehicle1ensures particularly high performances and can be used for races.

The assemblies37,38have a longitudinal length L1parallel to the axis K, which is greater than transverse length L2parallel to the axis Y.

Besides the advantages indicated above, this further reduces the overall inertia of the motor vehicle1, with a consequent improvement in the dynamic performances of the motor vehicle1.

Finally, the axle15and the motor vehicle1according to the invention can be subjected to changes and variations, which, though, do not go beyond the scope of protection set forth in the appended claims.

In particular, the motor vehicle1could comprise one single electric motor30,35connected to one or both of the rear wheels16,17or front wheels11,12.

The electric motors30,35could be part of the front axle10, instead of being part of the rear axle15, thus obtaining a front-wheel drive motor vehicle1.

The front axle10could comprise electric motors similar to the electric motors30,35available on the axle15, thus obtaining an all-wheel drive motor vehicle1.