Method of management of an electric propulsion system and electric propulsion system implementing the method

1. An electric propulsion system comprising a first and a second propulsion line, operatively connectable individually to a common driving axle, each propulsion line comprising

an electric motor,

a gearbox including at least two gear ratios,

a clutch to connect/disconnect the related propulsion line from the driving axle,

the system comprising processing means configured to distribute a requested torque between the first and second propulsion lines and to select, for each propulsion line, a relating transmission ratio and wherein when it is requested to vary the transmission ratio of both the first and second propulsion lines, the processing means are configured for commanding:

interruption of the supply of driving torque and consequent variation of the transmission ratio, first in a first propulsion line which has a lower maximum deliverable torque between the two propulsion lines and, at the end of the variation of the transmission ratio, reactivation of the torque delivery of a first transmission line, interruption of torque delivery and consequent variation of the transmission ratio, in the other propulsion line and, at the end of the variation of the transmission ratio, and

reactivation of the torque delivery of the other transmission line.

2. The electric propulsion system according to claim 1 , wherein the processing means are configured so that when they control the interruption of the torque delivery of one of the two propulsion lines, they simultaneously control the other propulsion line to deliver the entire requested driving torque, limited to a maximum torque value that can be delivered by a single propulsion line.

3. The electric propulsion system according to claim 1 , wherein when it is requested to vary the transmission ratio of both the first and second propulsion lines and both the first and second propulsion lines deliver equal driving torque, then, as propulsion line delivering lower driving torque, one of the two propulsion lines according to a predetermined criterion is selected.

4. The electric propulsion system according to claim 3 , wherein the criterion is random or balanced.

5. The electric propulsion system according to claim 2 , comprising the following steps in succession:

selection of the propulsion line that has the highest deliverable driving torque, when the propulsion lines have a different maximum deliverable torque, or of one of the two propulsion lines according to a predetermined selection criterion, when the propulsion lines have an equal maximum deliverable drive torque;

delivery of the entire requested driving torque by the selected propulsion line and variation of the transmission ratio by the other propulsion line; and

delivery of the entire driving torque by the unselected propulsion line and variation of the transmission ratio by the selected propulsion line.

6. The electric propulsion system according to claim 1 , wherein the processing means are configured to differentiate a torque delivered between the first and second propulsion lines to minimize a sum of the mechanical and electrical losses of the propulsion system.

7. The electric propulsion system according to claim 6 , wherein the processing means comprise storage means in which one or more tables are stored which are arranged for returning a distribution ratio of the requested torque between the first and second propulsion lines and a relating transmission ratio as a function of the requested torque and a speed of rotation of the driving axle.

8. The electric propulsion system according to claim 6 , wherein the storage means comprise a first table in which, as a function of the torque requested to the propulsion system and a rotation speed of the driving axle, it returns a value of distribution of the requested torque between the first and second lines and in which the table is arranged so that,

a first zone contiguous with an axis of the requested torque, the torque requested to the propulsion system is equally divided between the first and second propulsion lines;

a second zone contiguous with an axis of the rotation speed of the driving axle, the torque requested by the propulsion system is supplied only by one of the two propulsion lines, while the other propulsion line is deactivated and disconnected from the driving axle;

a third zone contiguous with the second zone, the torque requested by the propulsion system is equally divided between the first and second propulsion lines; and

a fourth zone delimited by two approximately linear curves that originate in the origin of the axles, the torque requested to the propulsion system is delivered differently between the two propulsion lines in order to minimize the electrical and mechanical losses of the propulsion system.

9. The electric propulsion system according to claim 1 , wherein a residual available torque is a function of electro-mechanical characteristics of the electric motor of the transmission line and of the current temperature of the electric motor.

10. A method of generating a torque distribution and gear ratio selection scheme for each of the first and second propulsion lines of the propulsion system according to claim 6 , wherein,

for each requested torque value,

for each value of rotation speed of the towing axle,

identification of a predetermined number of distribution ratios of the requested torque between the two propulsion lines, considering all possible permutations due to the transmission ratios of the two propulsion lines,

calculation of mechanical and electrical losses, and

memorization of the permutation which allows to minimize the sum of mechanical and electrical losses.

11. A method for controlling of an electric propulsion system comprising a first and a second propulsion line, operably connectable to a driving axle, each propulsion line comprising:

an electric motor,

a gearbox including at least two gear ratios

a clutch to connect/disconnect the relating propulsion line from the driving axle,

the method comprising a strategy of distributing a requested torque between the first and second propulsion lines and for selecting, for each propulsion line, a relating transmission ratio wherein when it is requested to vary the transmission ratio of both first and second propulsion lines, the method includes the following steps:

interruption of the supply of driving torque and consequent variation of the transmission ratio, first in a first propulsion line which has a lower maximum deliverable torque between the two propulsion lines and, at the end of the variation of the transmission ratio,

reactivation of the torque delivery from the first transmission line, interruption of torque delivery and consequent variation of the transmission ratio on the other propulsion line and, at the end of the variation of the transmission ratio,

reactivation of the torque delivery of the other transmission line.

12. The electric propulsion system according to claim 2 , wherein when it is requested to vary the transmission ratio of both the first and second propulsion lines and both the first and second propulsion lines deliver equal driving torque, then, as propulsion line delivering lower driving torque, one of the two propulsion lines according to a predetermined criterion is selected.

13. The electric propulsion system according to claim 3 , comprising the following steps in succession:

selection of the propulsion line that has the highest deliverable driving torque, when the propulsion lines have a different maximum deliverable torque, or of one of the two propulsion lines according to a predetermined selection criterion, when the propulsion lines have an equal maximum deliverable drive torque;

delivery of the entire requested driving torque by the selected propulsion line and variation of the transmission ratio by the other propulsion line;

delivery of the entire driving torque by the unselected propulsion line and variation of the transmission ratio by the selected propulsion line.

14. The electric propulsion system according to claim 2 , wherein the processing means are configured to differentiate a torque delivered between the first and second propulsion lines to minimize a sum of the mechanical and electrical losses of the propulsion system.

15. The electric propulsion system according to claim 3 , wherein the processing means are configured to differentiate a torque delivered between the first and second propulsion lines to minimize a sum of the mechanical and electrical losses of the propulsion system.

16. The electric propulsion system according to claim 4 , wherein the processing means are configured to differentiate a torque delivered between the first and second propulsion lines to minimize a sum of the mechanical and electrical losses of the propulsion system.

17. The electric propulsion system according to claim 5 , wherein the processing means are configured to differentiate a torque delivered between the first and second propulsion lines to minimize a sum of the mechanical and electrical losses of the propulsion system.

18. The electric propulsion system according to claim 7 , wherein the storage means comprise a first table in which, as a function of the torque requested to the propulsion system and a rotation speed of the driving axle, it returns a value of distribution of the requested torque between the first and second lines and in which the table is arranged so that,

a first zone contiguous with an axis of the requested torque, the torque requested to the propulsion system is equally divided between the first and second propulsion lines;

a second zone contiguous with an axis of the rotation speed of the driving axle, the torque requested by the propulsion system is supplied only by one of the two propulsion lines, while the other propulsion line is deactivated and disconnected from the driving axle;

a third zone contiguous with the second zone, the torque requested by the propulsion system is equally divided between the first and second propulsion lines; and

a fourth zone delimited by two approximately linear curves that originate in the origin of the axles, the torque requested to the propulsion system is delivered differently between the two propulsion lines in order to minimize the electrical and mechanical losses of the propulsion system.

19. The electric propulsion system according to claim 2 , wherein a residual available torque is a function of electro-mechanical characteristics of the electric motor of the transmission line and of the current temperature of the electric motor.

20. The electric propulsion system according to claim 3 , wherein a residual available torque is a function of electro-mechanical characteristics of the electric motor of the transmission line and of the current temperature of the electric motor.