Motor-driven compressor provided with torque control device

A motor-driven compressor comprising:

• an electric motor having a rotor and a stator;
• a rotary compressor having a casing and a rotor connected to said electric motor through a main shaft connected to the rotor of said electric motor;
• a revolution velocity control means for supplying said electric motor with a current to rotate the rotor of said electric motor and for desiredly changing the revolutional frequency of the rotor of said electric motor;
• a current detection means for detecting a current supplied to said electric motor and for producing a signal indicative of a current value thereof;
• a detecting means including a gear-like disk fixed to said main shaft and provided with a plurality of regularly arranged protrusions and a contactless switch disposed in opposition to said protrusions of said disk for producing an AC signal corresponding to repetition of successive approaching to said protrusions, for detecting time required for said main shaft to rotate said plurality of protrusions of said disk one by one successively;
• operation circuit means for obtaining a difference between the required time detected by said detecting means and a reference required time, and for producing a command current value necessary for generating an output torque agreeing with a load torque for performing compression in accordance with the obtained difference;
• and
• a torque control means for comparing said command current value and said detected current value and for producing a signal for controlling output torque of said electric motor in accordance with an obtained difference so as to make the output torque of said electric motor agree with load torque required for performing compression, said torque control means transmitting said produced signal to said revolution velocity control means.

A motor-driven compressor provided with an electric motor having a rotor and a stator, a compressor driven by said electric motor through a main shaft connected to the rotor of said electric motor, a closed casing containing said electric motor and said compressor, and a revolution velocity control means for supplying said electric motor with a current to rotate the rotor of said electric motor and for desiredly changing the revolutional frequency of the rotor of said electric motor;

• the imporvement comprises:
• current detecting means for detecting a current supplied to said electric motor and for producing a signal indicative of a current value thereof;
• angular velocity detecting means for detecting a velocity of said main shaft per unit revolution angle including a disk fixed to said main shaft and provided with a plurality of regularly arranged protrusions, and switching means disposed in opposition to said protrusions for producing an AC signal corresponding to repetition of successive approaching to said protrusions;
• operation circuit means for obtaining a difference between the angular velocity of said main shaft detected by said angular velocity detecting means and a reference angular velocity for providing a command current value necessary for generating an output torque agreeing with load torque required for performing compression in accordance with the obtained difference;
• and
• a torque control means for comparing said command current value with said detected current value and for producing a signal for controlling output torque of said electric motor so as to make substantially zero a difference between load torque required for compression of said compressor and output torque of said electric motor in any revolution angular position of said main shaft, said torque control means transmitting said produced signal to said revolution velocity control means.

A motor-driven compressor comprising:

• an electric motor having a rotor and a stator;
• a compressor driven by said electric motor through a main shaft connected to said rotor;
• a revolution velocity control means for supplying said electric motor with a current to rotate said rotor an for desiredly changing the revolutional frequency of said rotor;
• a current detection means for detecting a current supplied to said electric motor and for producing a signal indicative of a current value thereof;
• an angular velocity detecting means for detecting a velocity of said main shaft per unit revolution angle, said angular velocity detecting means including a disk fixed to said main shaft and provided with a plurality of regularly arranged protrusions, and a switching element disposed in opposition to said protrusions of said disk for producing an AC signal corresponding to repetition of successive approaching to said protrusions;
• an operation circuit for obtaining a difference between the angular velocity of said main shaft detected by said angular velocity detecting means and a reference angular velocity and for providing a command current value necessary for generating an output torque agreeing with a load torque for performing compression in accordance with the obtained difference;
• and
• a torque control means for comparing said command current value provided by said operation circuit with the current value detected by said current detection means and for forming a signal for changing said current value so that a difference between said command current value and said current value becomes zero and for transmitting the signal to said revolution velocity control means so as to make the output torque of said electric motor substantially agree with the load torque.