Drive system for a hybrid or electric vehicle

A drive system for a hybrid or electric vehicle, comprising:

• an electrical energy source;
• an electric machine equipped with a rotor rotating around a rotation axis and a stator containing a plurality of phases extending between respective terminals;
• a switching device linked to the electric machine and selectively switchable between a first configuration, wherein the phases are in a first electrical configuration, and a second configuration, wherein the phases are in a second electrical configuration;
• an adjusting device linked to the electric machine and configured to vary operating parameters of the electric vehicle;
• a control unit linked to said switching device and to said adjusting device and configured to drive said switching device and said adjusting device according to the operating conditions of said electric vehicle;
• wherein, in said first configuration, the electric machine includes a first number of conductors in series by phase, configured to supply a first driving torque and having a first knee speed and a pre-set first no-load operation speed;
• wherein, in said second configuration, the electric machine includes a second number of conductors in series by phase, configured to supply a second driving torque, lower than the first driving torque, and having a second knee speed higher than the first knee speed;
• wherein a ratio between said first no-load operation speed;
• and said second knee speed (ωcp2) ranges between 0.7 and 1.3;
• wherein said control unit is configured to drive the adjusting device to control the electric machine in a flux weakening mode when a rotation speed of said rotor is higher than said first knee speed;
• wherein said control unit is configured to bring the switching device from the first configuration to the second configuration to reach a switching speed higher than said first knee speed;
• and lower than said first no-load operation speed,
• wherein:
• said first configuration has a first characteristic curve extending on a torque-speed plane with a constant torque equal to said first driving torque for speed values lower than or equal to said first knee speed and with constant power equal to a first maximum deliverable power for speeds higher than said first knee speed;
• said second configuration has a second characteristic curve extending on a torque-speed plane with constant torque equal to said second driving torque for speed values lower than or equal to said second knee speed (ωcp2) and with constant power equal to a second maximum deliverable power for speeds higher than said second knee speed (ωcp2), wherein said first characteristic curve intersects said second characteristic curve at an intersection speed;
• a ratio between the intersection speed;
• and the second knee speed ranges between 0.7 and 1;
• said first no-load operation speed, is equal to at least 1.5 times the first knee speed;
• a ratio between said first and said second number of conductors in series by phase ranges between 1 and 5;
• wherein a value of said second knee speed (ωcp2) results from the following relationship:
• ω
• cp
• ⁢
• 2
• =
• 1
• (
• ξ
• *
• L
• d
• *
• i
• s
• *
• sin
• ⁡
• (
• γ
• )
• n
• t
• 2
• )
• 2
• +
• (
• L
• d
• n
• t
• 2
• *
• i
• s
• *
• cos
• ⁡
• (
• γ
• )
• +
• λ
• m
• n
• t
• )
• 2
• wherein:
• ξ is the machine anisotropy;
• Ld is the direct reluctance on a d-axis;
• nt is the ratio between said first and said second number of conductors in series by phase;
• γ is a current angle along a maximum torque per an Ampére curve;
• λm is the magnetic flux;
• is is a peak current of a line.