Motor protector

Apparatus for preventing damage to an electric motor during dynamic braking comprising:

• sensing means for electrical detecting dynamic brake current of the electric motor;
• means responsive to said detected dynamic brake current for generating an output whenever said current exceeds a predetermined level;
• and
• means responsive to the output of said current responsive means for interrupting dynamic braking and substituting mechanical braking therefor whereby damage to the motor by excessive dynamic braking currents may be prevented.

Apparatus for preventing wheel locking in an electrically powered vehicle having dynamic and mechanical brake assemblies, comprising:

• first electrical detector means adapted to be coupled with the vehicle electric motor for providing a first output in response to motor dynamic brake current exceeding a preset level;
• second detector means adapted to be coupled to the mechanical brake assembly for providing a second output in response to brake pressure exceeding a preset level;
• and
• means connected to said first and second detectors for causing the interruption of dynamic braking when said first and second outputs coexist for greater than a predetermined length of time.

Apparatus for preventing overcurrent and overvoltage damage to a traction motor and for preventing wheel lockout in an electrically powered rapid transit system having a brake relay and a mechanical brake assembly, comprising:

• means adapted to be connected to the brake relay for controlling energization thereof;
• first sensing means for electrically detecting dynamic brake voltage of the traction motor and generating an output whenever said dynamic brake voltage exceeds a predetermined voltage value;
• first means coupled to said brake relay control means and operatively communicating with said first sensing means for interrupting energization of the brake relay in response to the output of said first sensing means;
• second sensing means for electrically detecting dynamic brake current of the traction motor and generating an output whenever said dynamic brake current exceeds a first predetermined current level;
• second means coupled to said brake relay control means and operatively communicating with said second sensing means for interrupting energization of the brake relay in response to the output of said second sensing means;
• third sensing means for electrically detecting dynamic brake current of the traction motor and generating an output whenever said dynamic brake current exceeds a second predetermined current level;
• means adapted to be coupled with the mechanical brake assembly and responsive to mechanical brake pressure exceeding a predetermined value for assuming a particular operative state;
• and
• third means coupled to said brake relay control means and said brake pressure responsive means and operatively communicating with said third sensing means for interrupting energization of the brake relay in response to the output of said third sensing means only when said brake pressure responsive means is in said particular operative state;
• said first, second and third sensing means being electrically isolated from said first, second and third interrupting means.

Apparatus for preventing overvoltage and overcurrent damage to a traction motor and for preventing wheel locking in a rapid transit system having a brake relay and a mechanical brake assembly, comprising:

• first means for electrically detecting dynamic brake voltage of the traction motor and generating a first output whenever said voltage exceeds a predetermined value;
• second means for electrically detecting dynamic brake current of the traction motor and generating a second output whenever said current exceeds a first predetermined level;
• third means for electrically detecting dynamic brake current of the traction motor and generating a third output whenever said current exceeds a second predetermined level;
• means adapted to be coupled to the mechanical brake assembly and responsive to mechanical brake pressure exceeding a predetermined value for assuming a particular operative state;
• and
• circuit means coupled to said first, second and third detecting means and said brake pressure responsive means and adapted to be coupled to the brake relay for interrupting energization of the brake relay and for maintaining the brake relay deenergized for the duration of each braking cycle in response to said first output, said second output or the coincidence of said third output and said brake pressure responsive means assuming said particular operative state;
• said circuit means being electrically isolated from said first, second and third detecting means.