US 5,630,009 A · Method and apparatus for controlling a DC electric motor

Abstract

A direct current (DC) electric motor is shifted between higher and lower operating speeds in response to motor operating conditions to prevent motor stalling, overheating and burnout. Switches are performed between two or among more than two operating curves defined for the DC motor with switches preferably taking place approximately at points of intersection of the operating curves. The high or higher speed curve typically results from inducing inefficiency into the motor such that continued operation along the high or higher speed curve can lead to motor stalling and even burnout. At or near the intersection points of motor operating curves, operation is switched from the high or higher speed operating curve to a lower speed, higher efficiency operating curve such that motor current is immediately reduced for the same motor speed and torque. If the motor is able to once again operate along the high or higher speed curve, a switch-back is made at or near the point of intersection. If more than two operating curves are provided for a DC motor, switches can be made from one curve to an adjacent curve. For more than two operating curves, switching is from the least efficient, to the next least efficient, etc. until operation of the motor is along the most efficient operating curve for the motor. Switch-backs are also effected as the energy dissipated in the motor is reduced, the load is reduced, etc. Preferably, some level of hysteresis is provided to prevent oscillation or hunting between two operating curves.

Claims15

Dependent claims

A control circuit for operating a two speed direct current (DC) motor comprising:

switch means for selecting among a zero speed or motor off, a low speed and a high speed for operation of said two speed DC motor, said switch means connecting power to a first terminal for selection of said low speed and a second terminal for selection of said high speed;
and
control means connected between said first and second terminals and low speed and high speed inputs for said motor for preventing stalling of said motor in said high speed by switching between said high speed input and said low speed input dependent upon motor operating conditions when said high speed is selected by said switch means.

A method of controlling a direct current (DC) motor operable along one of two or more operating curves having different operating efficiencies and intersecting one another within the operating range of said DC motor, the method comprising the steps of:

selecting an operating curve which is less efficient than at least one other operating curve such that said DC motor is operated in accordance with desirable operating characteristics corresponding to said selected operating curve;
monitoring at least one operating characteristic of said DC motor;
comparing said at least one monitored operating characteristic to a value of said at least one monitored operating characteristic which corresponds approximately to intersection of said selected operating curve and said at least one other operating curve;
and
switching between the selected operating curve and said at least one other operating curve in response to the preceding comparing step.

2 more elements

Dependencies are inferred from the claim text.

Method and apparatus for controlling a DC electric motor

Life of this patent

Method and apparatus for controlling a DC electric motor

Life of this patent

Abstract

Claims15