Squirrel-cage rotor for asynchronous motors

A squirrel-cage rotor for asynchronous motors, comprising:

• a lamination stack made of magnetic material defining a plurality of slots;
• a cage comprising:
• a) a plurality of bars having intermediate portions that engage said slots, and opposing end portions that protrude with respect to said lamination stack;
• b) two shorting rings fixed to said end portions;
• a plurality of spaces defined, axially, by said lamination stack and said shorting rings, and tangentially by said end portions;
• wherein some of said spaces are engaged by stiffening blocks, each stiffening block being in contact with the end portions of both the adjacent bars;
• the number, the positions and the dimensions of said stiffening blocks being defined so as to increase at least the first torsional eigenfrequency of the rotor to a value higher than the first harmonic frequency of the torque oscillations.