Electricity: motive power systems – Motor load – armature current or force control during...
Reexamination Certificate
1997-02-24
2001-11-27
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Motor load, armature current or force control during...
C318S434000, C318S461000, C388S903000, C388S921000
Reexamination Certificate
active
06323611
ABSTRACT:
BACKGROUND OF THE INVENTION
Related Art
The invention is based on a circuit for operating an electric motor, of the type having an arrangement that produces a signal serving as a measure for the rpm of electric motor and having a monitoring arrangement for detecting an increased load state of the electric motor. DE-PS 30 34 118 discloses a generic circuit that has a sensor which produces a signal serving as a measure for the rpm of the electric motor. The known circuit includes a monitoring arrangement for ascertaining an increased load state of the electric motor; the arrangement monitors rpm, comparing the actual rpm determined from the sensor signal to a predetermined limit value. The limit value is derived from an initial actual rpm value established after a predetermined time following startup of the known circuit. The known circuit for operating an electric motor is used in electronic monitoring of an opening and closing process of electrically-operated motor vehicle parts. The limit value is tailored to the task of detecting jammed objects or body parts. The known circuit is not provided with an increased load state of the electric motor, or of a provided end stage, that can lead to a thermal overload of these parts.
SUMMARY OF THE INVENTION
It is the object of the invention to provide a circuit for operating a motor that in particular assures the protection of an end or drive stage and/or the electric motor against thermal overload.
The object is accomplished by a circuit of the above mentioned type which is characterized in that the monitoring arrangement compares an rpm difference, between a predetermined nominal rpm value and the actual rpm determined from the actual rpm signal, to a predetermined limit value, and emits an overload signal if the limit value is exceeded.
A monitoring arrangement provided in accordance with the invention compares the difference between a provided nominal rpm value and an actual rpm value determined from a sensor signal. If the limit value is exceeded, the monitoring arrangement emits an overload signal.
The concept underlying the circuit of the invention is that, in the steady operating state, the difference between the predetermined nominal rpm value and the detected actual rpm value either lies within specific limits as a function of a predetermined rpm regulator or is zero. Sluggishness of the electric motor or of a part driven by the motor, as well as complete blockage, cause the limit value to be exceeded, and thus lead to triggering of the overload signal.
An advantage of the circuit of the invention for operating an electric motor is that an increased load state or complete blockage can be recognized with electrical signals that can be detected with simple means. No further sensors, such as a temperature sensor, are necessary.
The circuit of the invention for operating an electric motor is particularly suited for use in a fan, in which instance the fan is used to cool an electric motor and/or the drive stage simultaneously.
In comparison to establishing a limit value based on a predetermined rpm value, the circuit of the invention for operating an electric motor has the advantage that both the electric motor and the drive stage only need to be designed for low thermal stress.
A particularly advantageous modification of the circuit of the invention provides that the limit value for the rpm difference, which is provided in the monitoring arrangement, is determined as a function of the predetermined nominal rpm value. With this measure, the limit value can be adapted to different operating relationships.
An advantageous embodiment provides that the predetermined nominal rpm value is reduced when the overload signal is emitted. With another advantageous measure, when the overload signal occurs, a control variable of a controlled voltage source is reduced, which source is instrumental in the actuation of the drive stage. Implementing one of these measures ensures that, despite an increased load state, the electric motor can continue to be operated reliably without the threat of thermal destruction.
In a particularly advantageous modification, the monitoring arrangement does not emit the overload signal until a predeterminable period of time has passed. The predeterminable time is a delay time that takes into account the run-up of the electric motor, for example starting from the off state. The unsteady state that occurs during run-up and could lead to erroneous generation of the overload signal can be kept in check with this measure.
Another advantageous modification provides that the overload signal is suppressed following a predetermined time. If the electric motor is further overloaded, the overload signal is emitted again. In this operation, periodic attempts are made to turn on the electric motor. The times during which the overload signal occurs or is suppressed are advantageously measured such that, despite an overload or complete blockage of the electric motor, the average power is limited to a value that does not represent a danger of thermal overload of the electric motor and/or the drive stage.
Further advantageous embodiments and advantageous modifications discussed in the description below.
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patent: 2228715 (1972-12-01), None
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Ro Bentsu
Robert & Bosch GmbH
Spencer George H.
Venable
Wood Allen
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