Patent Description:
Work vehicles like wheel loaders are known to operate in extremely variable speed conditions.

For example, this aspect particularly holds during operations that involve the moving of loose materials, such as demolition debris or raw minerals, aside of a working site and the loading of such material into or onto a conveying machine, e.g. a truck or a conveyor belt.

Indeed, the wheel loader is in this case supposed to move repeatedly back and forth between the working site and the conveying machine, which are in addition often placed quite near to each other.

Therefore, during the above operations, the wheel loader undergoes continuous accelerations and decelerations along a reduced movement space.

Furthermore, when the wheel loader uses its loading tool or bucket to shovel the materials, very low speeds and large traction torques are required, in comparison with common requirements for traction of passenger cars.

For the above reasons, wheel loaders usually mount a torque converter between the engine and the gearbox; a torque converter is a known hydraulic device for coupling the engine to the gearbox.

The torque converter is known to have the property of automatically decoupling the engine from the gearbox when the latter is subject to high torques, e.g. at lower speeds of the wheel loader, such that the latter can remain stationary while the engine is still operating.

As well, for lower torques on the gearbox that does not imply the decoupling, the torque converter has the property of multiplying the output torque.

When the torque converter operates as a torque multiplier, a significant portion of the input power is wasted in the form of heat generation, which provides for the need of a specific cooling means for avoiding the overheating of the torque converter.

In other words, although commonly implemented for their known useful decoupling properties, torque converters are less efficient and more complex than other hydraulic or mechanic transmissions that, although implying less energy dissipation, are not suitable for carrying out the functions of torque converters.

Therefore, a need is felt to provide improved solutions, e.g. in the form of new devices carrying out at least the same functions of the torque converters with increased efficiency.

<CIT> and <CIT> disclose examples of hybrid electric architectures.

further examples of hybrid electric architectures.

An aim of the invention is to satisfy the above-mentioned need, preferably in a simple and cost effective manner.

Such an aim is reached by a hybrid electric architecture for a vehicle as set forth in independent claim <NUM>.

Dependent claims define particular embodiments of the invention.

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

In <FIG>, reference symbol <NUM> indicates a vehicle, in particular a work vehicle like a wheel loader. Vehicle <NUM> includes a hybrid electric architecture <NUM> and an axle <NUM> (only partially shown), in particular a rear axle, comprising the input shaft <NUM> of an automotive differential (not shown).

The architecture <NUM> is coupled to the axle <NUM> and configured to supply power thereto, during the operation of vehicle <NUM>.

The architecture <NUM> comprises a plurality of machines, including an internal combustion engine <NUM> and two electric machines <NUM>, <NUM>. The electric machine <NUM> can operate as a generator and the electric machine <NUM> can operate as a motor. More precisely, both the electric machines <NUM>, <NUM> comprise motor-generators for operating both as motors and as generators, e.g. depending on the actual operating conditions of vehicle <NUM>.

The architecture <NUM> further comprises a planetary gear <NUM> that couples the engine <NUM> and the electric machines <NUM>, <NUM>. Moreover, the architecture <NUM> comprises a transmission <NUM> with an input shaft <NUM>, which is connected to the planetary gear <NUM> to be driven thereby, and an output shaft <NUM>, which is connected to the axle <NUM>, such that the latter is driven by the transmission <NUM>.

The planetary gear <NUM> includes a sun gear <NUM> and a ring gear <NUM>, being in particular coaxial cylindrical gears around an axis A, as well as a planet carrier <NUM> arranged to rotate around axis A and carrying a plurality of planet gears <NUM> that meshes both with the sun gear <NUM> and the ring gear <NUM>.

Here, planet gears <NUM> are cylindrical gears with respective axes parallel to axis A.

Specifically, the sun gear <NUM>, the ring gear <NUM>, and the planet carrier <NUM> are respectively connected to the electric machine <NUM>, the input shaft <NUM>, and the engine <NUM>. However, the configuration of the three members of the planetary gear <NUM>, i.e. the sun gear <NUM>, the ring gear <NUM>, and the planet carrier <NUM> may also be different, with respect to the other members of the architecture <NUM>, i.e. the electric machine <NUM>, the input shaft <NUM>, and the engine <NUM>.

With greater detail, the engine <NUM> has an output shaft <NUM> extending parallel to axis A, in particular along therewith; the output shaft <NUM> passes through the sun gear <NUM>, although being rotationally free with respect to the latter, and couples to the planet carrier <NUM>. In particular, the planet carrier <NUM> is keyed to the output shaft <NUM>.

The electric machine <NUM> is arranged around axis A between the sun gear <NUM> and the engine <NUM>, and so around the output shaft <NUM>. The output shaft <NUM> passes through the electric machine <NUM>, without being rotationally coupled thereto.

The electric machine <NUM> has a rotor shaft <NUM> that extends parallel to axis A, in particular along therewith, toward the sun gear <NUM>, which is coupled to the same rotor shaft <NUM>, for instance by means of a key or a spline coupling.

Furthermore, the planetary gear <NUM> has a hollow casing <NUM> that is fixedly coupled to the ring gear <NUM> and to the input shaft <NUM>. Specifically, the casing <NUM> is realized in a single piece with the ring gear <NUM> and with the input shaft <NUM>.

The hollow casing <NUM> houses the planet carrier <NUM>. In particular, the hollow casing <NUM> has an axial symmetry with respect to axis A and, more in particular, is bell-shaped around axis A.

Preferably, the architecture <NUM> comprises a lock-up clutch <NUM> that is configured to interlock the engine <NUM> and the input shaft <NUM> or the planet carrier <NUM> and the ring gear <NUM>, which means that the planet carrier <NUM> and the ring gear <NUM> are constrained to rigidly rotate together or to integrally rotate with each other. In other words, the lock-up clutch <NUM> has an engaged configuration, in which the transmission ratio between the engine <NUM> and the input shaft <NUM> is constant, precisely equal to one in the embodiment shown, and a disengaged configuration, in which the same transmission ratio is based on the operation of the electric machine <NUM> and, more in general, of vehicle <NUM>.

The lock-up clutch <NUM> is housed within the casing <NUM> and arranged between the planet carrier <NUM> and the input shaft <NUM>.

Specifically, the lock-up clutch <NUM> is a disk type friction clutch, in particular with a plurality of disks; essentially, in the embodiment shown, the lock-up clutch <NUM> includes a fixed portion 19a fastened to the planet carrier <NUM> and a movable portion 19b that is rotationally fixed and axially movable with respect to the casing <NUM>, in particular in a sliding manner. Preferably, the movable portion 19b is coupled to the casing <NUM> through a spline coupling.

Both the fixed portion 19a and the movable portion 19b are arranged around axis A and thus they are coaxial.

The lock-up clutch <NUM> further includes a known-kind driving device 19c, for example electric or pneumatic, for driving the movable portion 19b between the engaged and the disengaged configuration of the lock-up clutch <NUM>.

According to the invention, the electric machine <NUM> is arranged to be coupled to the transmission <NUM>, in such a manner that an output torque of the electric machine <NUM> is transmitted or supplied to the transmission <NUM> in parallel to torques passing through the planetary gear <NUM>.

In other words, the torque supplied by the electric machine <NUM> is transmitted to the transmission <NUM> bypassing the torque-splitting portion of the planetary gear <NUM>, i.e. the planet carrier <NUM> and the planet gears <NUM>.

The torque transmitted to the ring gear <NUM>, which is the result of a mechanical balance between the torque at the planet carrier <NUM> and electric machine <NUM>, i.e. at the output and rotor shafts <NUM>, <NUM>, sums up to the torque supplied by the electric machine <NUM>. The sum of the torques is then transferred to the axle <NUM> via the transmission <NUM>.

Hence, electric machine <NUM> is configured to supply torque to the ring gear <NUM>. This torque is summed to a portion of the torque supplied by engine <NUM>, which is the portion of torque transmitted from the planet carrier <NUM> to the ring gear <NUM> via the planet gears <NUM>.

The electric machine <NUM> is coupled to the input shaft <NUM> of the transmission <NUM> by means of mechanical transmission elements. In particular, the architecture <NUM> comprises an ordinary gear train <NUM> to couple the electric machine <NUM> to the input shaft <NUM>.

As shown in <FIG>, the gear train <NUM> includes a first couple of meshing gears <NUM>, <NUM>, and a second couple of meshing gears <NUM>, <NUM> arranged in series to the first couple, so as to form two successive reduction stages. Specifically, gear <NUM> is coupled (e.g. keyed) to a rotor shaft of the electric machine <NUM>; gears <NUM>, <NUM> are coupled (e.g. keyed) to an intermediate shaft; and gear <NUM> is coupled to (e.g. realized in a single piece with) the input shaft <NUM>.

As further shown in <FIG>, transmission <NUM> comprises a geared transmission or a gearbox that is adapted to establish multiple gear ratios between the input shaft <NUM> and the output shaft <NUM>.

More precisely, transmission <NUM> comprises three gears <NUM>, <NUM>, <NUM>, which are carried in a fixed manner by the input shaft <NUM>. In particular, gears <NUM>, <NUM>, <NUM> are cylindrical gears. Conveniently, gears <NUM>, <NUM>, <NUM> are realized in a single body with the input shaft <NUM>. Gears <NUM>, <NUM>, <NUM> have different diameters; in particular, gears <NUM> and <NUM> are respectively the greatest and the smallest ones. Gear <NUM> is arranged between the other two gears <NUM>, <NUM> with respect to axis A.

Furthermore, transmission <NUM> further comprises other three gears <NUM>, <NUM>, <NUM>, which are carried in a fixed manner by the output shaft <NUM>. In particular, gears <NUM>, <NUM>, <NUM> are cylindrical gears. Conveniently, gears <NUM>, <NUM>, <NUM> are realized in a single body with the output shaft <NUM>. Gears <NUM>, <NUM>, <NUM> are arranged to mesh respectively with gears <NUM>, <NUM>, <NUM>, such that three different gear ratios are defined.

The output shaft <NUM> extends along an axis B parallel to axis A.

In order to select one of the gear ratios, the transmission <NUM> further comprise a shifting device <NUM> configured to engage each one of the gear ratios. Specifically, the shifting device <NUM> includes dog clutches <NUM> and driving devices <NUM> to drive the dog clutches <NUM> and accordingly allow the shifting from one gear ratio to another one as known in the art.

The architecture <NUM> comprises a further electric machine <NUM> that can operate at least as a motor. More precisely, the electric machine <NUM> comprises a motor-generator for operating both as a motor and as a generator, e.g. depending on the actual operating conditions of vehicle <NUM>.

The electric machine <NUM> is arranged to be coupled to the transmission <NUM>, in such a manner that an output torque of the electric machine <NUM> is supplied to the output shaft <NUM>.

The electric machine <NUM> is coupled to the output shaft <NUM> of the transmission <NUM> by means of mechanical transmission elements. In particular, the architecture comprises an ordinary gear train <NUM> to couple the electric machine <NUM> to the output shaft <NUM>, more in particular between the gears <NUM>, <NUM>, <NUM> and axle <NUM>.

As shown in <FIG>, the gear train <NUM> includes just a couple of meshing gears <NUM>, <NUM> that form a single reduction stage. Specifically, gear <NUM> is coupled (keyed) to a rotor shaft of the electric machine <NUM>, and gear <NUM> is coupled (keyed) to the output shaft <NUM>.

Electric machines <NUM>, <NUM>, <NUM> comprise respective power converters <NUM>, <NUM>, <NUM>, that are connected to an electric network N of the architecture <NUM>. Such an electric network N includes a storage device, such as a battery <NUM>, for storing the electrical energy generated by the electric machine <NUM>, for example, as well as for supplying the stored energy to the electric machines <NUM>, <NUM>, for example.

The architecture <NUM> further comprises a control unit ECU, which is configured to control the engine <NUM> and the electric machines <NUM>, <NUM>. Control unit ECU is further configured to control the electric machine <NUM>. Furthermore, control unit ECU is configured to control the lock-up clutch <NUM>, in particular the driving device 19c. Moreover, control unit ECU is configured to control the shifting device <NUM>, in particular the driving devices <NUM>.

More precisely, control unit ECU controls the power converters <NUM>, <NUM>, <NUM>.

Control unit ECU is electrically connected to each of the components controlled by the same control unit ECU.

The architecture <NUM> further comprises a plenty of transducers or sensors (not shown) coupled to control unit ECU for detecting quantities that are known to be indicative of operative parameters of the architecture <NUM>, such as the actual output speeds of the electric machines <NUM>, <NUM>, <NUM>, the actual output speed of the engine <NUM>, the actual output torques of the electric machine <NUM>, <NUM>, <NUM>, the actual output torque of the engine <NUM>, and the required speed and torque at the output shaft <NUM>. Unambiguously, each element of the above exemplary list of operative parameters shall be considered as singularly disclosed in an independent manner from the other elements, without any loss of generality. The term "actual" may be construed with the meaning of "current".

The transducers or sensors of the architecture <NUM> provide the control unit ECU with the necessary and sufficient information to feedback control the engine <NUM> and the electric machines <NUM>, <NUM>.

More precisely, the transducers or sensors include:.

Preferably, the transducers or sensors further include one to three additional speed sensors to measure correspondingly the speeds of one to all the three members of the planetary gear <NUM>, i.e. the sun gear <NUM>, the ring gear <NUM>, and the planet carrier <NUM>.

Control unit ECU is configured to extract information from the transducers or sensors about the detected or measured quantities and to evaluate, estimate, or predict in a known manner the operative parameters, for example by direct acquisition of the parameters, determination by means of physical formula or experimental models, estimation by means of observers, and the like, without any loss of generality.

In particular, control unit ECU determines or stores at least:.

More precisely, with load torque, it is intended the torque required by the electric machine <NUM> to generate electric energy. For example, this load torque can be actively controlled through electronic control devices, such as inverters.

Furthermore, control unit ECU stores information about the constructional features or mechanical properties of the planetary gear <NUM>. It is known that planetary gears are characterized by a fundamental speed ratio, in particular entering the so called "Willis formula" and here indicated as τ<NUM>, where τ<NUM> represents a speed ratio between the ring gear and the sun gear, assuming the planet carrier as fixed or locked up.

Other speed ratios, in particular three speed ratios can be identified between two members of the sun gear, the ring gear, and the planet carrier, assuming the other member as fixed or locked up. Those speed ratios are derivable from τ<NUM>, since being equal to τ<NUM> itself when the planet carrier is fixed, (τ<NUM> - <NUM>)/τ<NUM> when the sun gear is fixed, and <NUM> - τ<NUM> when the ring gear is fixed, as known.

Specifically, the above mechanical properties of the planetary gear <NUM> comprise the fundamental speed ratio thereof and, conveniently, the other speed ratios.

Control unit ECU is programmed or configured to execute a control method of the architecture <NUM> when the electric machines <NUM>, <NUM> respectively operate as a generator and as a motor. In other words, control unit ECU stores computer programs comprising instructions for causing the architecture <NUM> to carry out the method of the invention.

As a first step <NUM> of the method, control unit ECU determines a desired output speed of the engine <NUM>.

Preferably, the desired output speed of the engine <NUM> is determined based on a request of a driver of the vehicle <NUM>, for example by means of a control device of vehicle <NUM>, such as an accelerator pedal, button, or lever. More precisely, the desired output speed is determined as a function of the position or configuration of the control device.

With greater detail, control unit ECU controls the output speed of engine <NUM> setting the desired output speed as a target speed for the engine <NUM>.

More precisely, the output speed of engine <NUM> is feedback controlled; in particular, control unit ECU applies a control law, for example a PID control law.

Furthermore, control unit ECU is configured to set the desired output speed, possibly multiplied to a gain representing a speed variation, e.g. due to a transmission, as an input in a stored model of a conventional torque converter.

Actually, control unit ECU is provided with information that is sufficient for determining an output torque and an output speed of the torque converter from an input speed of the torque converter.

Thanks to the stored model of the torque converter, control unit ECU is configured to determine an expected output of the torque converter in terms of output speed and torque, whose values can be used as references or targets for the input shaft <NUM>. In other words, control unit ECU is configured to determine the speed and the torque with which the input shaft would have been driven if the modelled torque converter had replaced the planetary gear <NUM>, provided that the input speed is the same and specifically equal or proportional to the determined desired output speed of the engine <NUM>.

Precisely, the stored model is a mathematical model or a parametric model, i.e. a model defined by model parameters.

Preferably, the stored model or the information provided to control unit ECU is also sufficient for determining the input torque of the torque converter from the input speed thereof.

For example, the stored model may comprise a first table linking values of the input speed of the torque converter to values of the torque converter speed ratio nue. Moreover, the stored model may comprise a second table linking values of the speed ratio nue for a given reference input speed to values of the torque converter torque ratio mue, the efficiency of the torque converter, and the input torque of the torque converter.

The tables may be provided on an experimental basis, for instance.

According to the stored model, the input torque of the torque converter for different input speeds than the reference one is obtainable as a product of the value of the input torque from the second table, according to the relevant value of the speed ratio nue, and a corrective coefficient, which is given by a ratio between the squared actual input speed and the squared reference input speed. The usage of this corrective coefficient for modelling the torque converter is well known in the art; therefore, no further details will be provided in this regards for reasons of conciseness.

On the other hand, the torque ratio mue and the efficiency are only functions of the speed ratio nue.

Therefore, the values of the ratios nue, mue allows the determination of the input torque, the output torque, and the output speed of the torque converter.

Hence, as a second step <NUM> of the method, control unit ECU determines the output torque and the output speed of the torque converter based on the stored information assuming the input speed of the torque converter as a given function of the desired speed of the engine <NUM>, for example equal or proportional thereto. Preferably, control unit ECU determines also the input torque of the torque converter based on said information.

Then, as a third step <NUM> of the method, control unit ECU controls the electric machines <NUM>, <NUM> based on respective reference parameters to drive the input shaft <NUM> according to the determined output speed and torque of the torque converter as target parameters.

The reference parameters are determined from the target parameters by using the knowledge of the mechanical properties of the planetary gear <NUM>.

<FIG> shows with greater detail a plurality of steps of step <NUM>.

In step <NUM>, control ECU computes two ratios based on the mechanical properties of the planetary gear; the ratios represent respective fractions of the total power delivered by the engine <NUM>, such that the sum of the two ratios is equal to one. More precisely, the second ratio represents the fraction of power delivered to the electric machine <NUM>; therefore, the first ratio represents the fraction of power transmitted to the input shaft <NUM> through the planetary gear <NUM>. In particular, the latter fraction of power will sum up to the amount of power delivered by electric machine <NUM> for supplying the axle <NUM>.

The ratios are computed from the determined output of the torque converter, assuming the efficiency of the architecture <NUM> as ideal, i.e. equal to one.

For example, the first ratio is computed through the following formula: <MAT> where Xt is the first ratio, ωR is specifically the speed of the ring gear <NUM>, and ωC is specifically the speed of the planet carrier <NUM>. ωR is computed by control unit ECU as equal to the determined output speed of the torque converter. Control unit ECU can compute ωC from the desired output speed of the engine <NUM>, since the planet carrier <NUM> is coupled to the engine <NUM>. Indeed, control unit ECU stores in any case any necessary information about the mechanical properties of the coupling between the engine <NUM> and the planet carrier <NUM>. Possibly, in case the input shaft <NUM> should be coupled to the ring gear <NUM> via a transmission, control unit ECU would store information about the mechanical properties of the transmission in order to compute ωR from the output speed of the torque converter accordingly.

More in general, as derivable from the specific example above, the first ratio Xt is computed as a ratio between speed ratios of the planetary gear <NUM>. Both the two speed ratios involved in the computation are between the member of the planetary gear <NUM> that is coupled to the input shaft <NUM> (here, the ring gear <NUM>) and the member of the same planetary gear <NUM> that is coupled to the engine <NUM> (here, the planet carrier <NUM>). The speed ratio in the denominator is to be evaluated assuming the other member of the planetary gear <NUM> (here, the sun gear <NUM>) as fixed. On the other hand, the speed ratio in the numerator is the actual speed ratio with all three members that rotate.

Actually, the ratio of the two speed ratios computed as above well indicates the percentage of the power delivered by the engine <NUM> that is supplied to the input shaft <NUM> via the planetary gear <NUM>. Indeed, when the other member is fixed, all the power is transmitted through the members of the speed ratios.

Evidently, the second ratio (here indicated as Xvt) is computed as one minus the first ratio Xt.

In step <NUM>, control unit ECU computes two powers Pmt and Pvt, that are the product of a power Pout and respectively the ratios Xt, Xvt, where Pout is the product of the output speed and torque of the torque converter, i.e. the target power for the input shaft <NUM>.

Pvt is the power delivered to the electric machine <NUM>, whereas Pmt is the power that from the engine <NUM> is transmitted to the input shaft <NUM> via the planetary gear <NUM>.

Control unit ECU controls the electric machine <NUM> with the aim of delivering therefrom an amount of power equal to Pvt, i.e. the same power delivered to the electric machine <NUM>.

In step <NUM>, control unit ECU computes torques Tmt, Tvt by respectively dividing Pmt, Pvt by ωR. Conveniently, Tvt is set as a target output torque for the electric machine <NUM>.

In the light of the mechanical properties of the planetary gear set <NUM>, once a torque on one of the three members is retrieved, all the other torques can be derived accordingly as known in the art.

Here, in step <NUM>, control unit ECU determines the load torque of the electric machine <NUM> from Tmt, based on the mechanical properties of the planetary gear <NUM>.

Conveniently, the determined load torque is set as a target load torque for the electric machine <NUM>.

In an alternative example, the same steps can be conceptually merged together or changed to obtain the same result, i.e. the determination of the target torques for the electric machines <NUM>, <NUM>.

Advantageously, the electric machines <NUM>, <NUM>, are feedback controlled; in particular, control unit ECU applies a control law, for example a PID control law.

Therefore, the aforementioned reference parameters are a target output torque and a target load torque for the electric machines <NUM>, <NUM>, respectively.

Alternatively, the electric machines <NUM>, <NUM> might be differently controlled, e.g. in open loop or according to a speed closed loop. In the latter case, the target speeds need to be determined from the output speed and torque of the torque converter, based on the mechanical properties of the planetary gear <NUM>.

The electric machine <NUM> is adapted to generate electric energy for any possible speed of the rotor shaft <NUM> as a function of the speeds of engine <NUM> and input shaft <NUM>.

Control unit ECU may control the electric machines <NUM>, <NUM> to operate both as motors, for example, when a peak in the required torque at the output shaft <NUM> occurs.

Control unit ECU may control the driving device 19c to bring the lock-up clutch <NUM> in the engaged configuration when the desired speed of the engine <NUM> is almost stationary, e.g. when an increment or a derivative thereof is below a threshold, or equivalent conditions occur.

In addition, preferably, control unit ECU controls the electric machine <NUM> to operate as a motor and to supply entirely the required power at the output shaft <NUM>, while the same control unit ECU controls the shifting device <NUM>, in particular the driving devices <NUM>, to carry out a shift of the currently engaged gear ratio.

In other words, the power for driving the axle <NUM> is held for a very short time by the electric machine <NUM> operating as a motor. In this way, the shifting device <NUM> can be operated freely since it is not subject to loads or torques, and the electric machine <NUM> is generating the appropriate traction power.

This way of operating the architecture <NUM> will be called E-shift.

In view of the foregoing, the advantages of the architecture <NUM> according to the invention are apparent.

In particular, the planetary gear <NUM> and the electric machines <NUM>, <NUM> replace the torque converter of the prior art without losing any functionality but with an apparent gain in efficiency due to the replacement of a fluid coupling with electric components. Even more, the electric machine <NUM> generates electric energy that can be used for the traction via the electric machine <NUM>. On the contrary, the torque converter of the prior art only dissipates energy to decouple the axle and the engine.

Furthermore, the planetary gear <NUM> and the electric machines <NUM>, <NUM> can be cooled through cooling devices that are simpler and more economic than that used for cooling a torque converter. Indeed, the torque converter is a dissipative element and so requires a dedicated cooling device with high capacity of heat rejection. Similarly, the requirements for lubrication are different for a torque converter. Actually, a torque converter requires a specific dedicated assembly for providing a correct lubrication.

As a result of the above, the architecture <NUM> is simplified with respect to solutions employing the torque converter.

The presence of the electric machine <NUM>, other than the electric machine <NUM> is particularly advantageous, since the electric machine <NUM> can freely provide torque to the input shaft <NUM> without affecting the dynamic equilibrium imposed by the constructional features of the planetary gear <NUM> to the electric machine <NUM> and to engine <NUM>.

For example, without the electric machine <NUM>, the electric machine <NUM> would be required to support the engine <NUM> in case of necessity; however, in that case, an increment in the torque supplied by the electric machine <NUM> should require a corresponding increment of torque supplied by the engine <NUM> due to the torque distribution caused by the planetary gear <NUM>. Apparently, there may be conditions for which such an increase of torque by the engine <NUM> is not possible due to physical limits of the same engine <NUM>. Those conditions, on the other hand, can be easily satisfied by employing the electric machine <NUM>, which offers its output torque in parallel to that offered by engine <NUM>.

Even more advantageously, electric machines <NUM>, <NUM> can both work as motors to supply a significant amount of torque together with engine <NUM>.

Moreover, since the electric machine <NUM> may operate as a generator even when a torque peak is exerted on axle <NUM>, there is no actual need of a great electric energy storage and the battery <NUM> can have a reduced size accordingly.

Eventually, it is clear that modifications can be made to the described architecture <NUM> of the invention, which do not extend beyond the scope of protection defined by the claims.

Claim 1:
A hybrid electric architecture (<NUM>) for a vehicle (<NUM>), in particular a work vehicle, the architecture comprising an internal combustion engine (<NUM>), a first electric machine (<NUM>) suitable for operating at least as a generator, a planetary gear (<NUM>), and a transmission (<NUM>) having an input shaft (<NUM>) and an output shaft (<NUM>), the output shaft being adapted to be coupled to an axle (<NUM>) of the vehicle (<NUM>),
wherein the planetary gear (<NUM>) includes a first member, a second member, and a third member that are each comprising a corresponding one of a sun gear (<NUM>), a ring gear (<NUM>), and a planet carrier (<NUM>),
the architecture (<NUM>) further comprising:
- first means (<NUM>, <NUM>, <NUM>) to mechanically connect the first member, the second member, and the third member respectively to said engine (<NUM>), the first electric machine (<NUM>), and the input shaft (<NUM>);
- a second electric machine (<NUM>) distinct from the first electric machine (<NUM>) and suitable for operating at least as a motor;
- second means (<NUM>) to mechanically connect the second electric machine (<NUM>) to the transmission (<NUM>), such that a first drive torque from the third member and a second drive torque from the second electric machine (<NUM>) are supplied in parallel to the transmission (<NUM>); and
- a control unit (ECU) configured to control the engine (<NUM>), the first electric machine (<NUM>), and the second electric machine (<NUM>);
wherein the transmission (<NUM>) includes:
- a gearbox for establishing a plurality of gear ratios between the input shaft (<NUM>) and the output shaft (<NUM>); and
- shifting means (<NUM>) for engaging each of the gear ratios;
the control unit (ECU) being further configured to control said shifting means (<NUM>);
wherein said second means (<NUM>) are configured to mechanically connect the second electric machine (<NUM>) to the input shaft (<NUM>);
characterized in that
the hybrid electric architecture further comprises a third electric machine (<NUM>) suitable for operating at least as a motor and third means (<NUM>) to mechanically connect the third electric machine (<NUM>) to the output shaft (<NUM>), the control unit (ECU) being further configured to control the third electric machine (<NUM>), which is distinct from the second electric machine (<NUM>).