Electricity: electrical systems and devices – Safety and protection of systems and devices – Motor protective condition responsive circuits
Reexamination Certificate
1999-05-17
2001-10-09
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Motor protective condition responsive circuits
C361S103000, C361S115000
Reexamination Certificate
active
06301090
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an electric motor drive, having an electric motor that is triggerable via an end stage.
2. Prior Art
Electric motor drives of this generic type are known. They are used for instance in motor vehicles, as control motors. They are then operated at a supply voltage furnished by a motor vehicle battery. The electric motors embodied as direct current motors can be used in thermally critical areas of the motor vehicle, such as in the immediate vicinity of an internal combustion engine, among other areas. It is also known to provide electric motor drives with an overload protection that is intended to protect the electric motors against irreparable thermal damage, for instance if sluggishness suddenly occurs.
To protect electric motors against thermal overload, it is known to detect a housing temperature and/or an armature winding temperature of the direct current motor via a temperature sensor or a bimetallic element. The electric motor is rendered currentless if a permissible temperature is exceeded.
It is also known for electric consumers, such as motor end stages for direct current motors in motor vehicles, to be triggered with a pulse-width modulation signal. The electric consumer is connected to a voltage source or disconnected from the voltage source in accordance with a duty factor of the pulse-width modulation signal.
From International Patent Disclosure WO 94/27349, an electric motor drive is known in which a motor end stage is connected to a trigger circuit, and the trigger circuit generates an overload signal as a function of a temperature of the electric motor. A temperature of the electric motor can be calculated here from a power loss, or a variable proportional to it, on the basis of measured motor data during the duty cycle of the electric motor and integrated; for forwarding the overload signal, the integration value is compared with a predeterminable threshold value. A disadvantage here is that the requisite measurement of motor data during the duty cycle of the electric motor dictates effort and expense for measurement that moreover involves error, so that an exact overload signal cannot be ascertained.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved electric motor drive, which is simpler and less complex than those of the prior art.
According to the invention the electric motor drive comprises an electric motor; an end stage comprising means for triggering the electric motor; a trigger circuit associated with the end stage, the trigger circuit having a microprocessor and comprising means for pulse-width-modulated triggering of the end stage, the trigger circuit including an overload stage, the overload stage comprising means for detecting an overload on the electrical motor according to a temperature of the electric motor and means for obtaining the temperature from a pulse-width-modulation signal generated by the trigger circuit without means for directly measuring operating parameters of the electric motor, the means for directly measuring operating parameters including current measuring means or temperature measuring means.
The electric motor drive of the invention has the advantage over the prior art that in a simple way, an exact overload signal for turning off the electric motor drive can be furnished. Because the temperature of the electric motor is obtained from a pulse-width modulation signal of the trigger circuit, measurement of motor data during electric motor operation can be dispensed with. The complexity of the circuitry is thus simplified considerably. Sources of error associated with measuring motor data during operation are also circumvented, so that the signal can be generated with high accuracy. Ascertaining the motor temperature is done solely on the basis of already existing signals, namely the pulse-width modulation signal for triggering the electric motor. No other additional direct measurements of operating parameters of the motor, such as a current or a temperature, are necessary.
Other preferred features of the invention will become apparent from the other characteristics recited in the dependent claims.
REFERENCES:
patent: 4977507 (1990-12-01), Matsuoka et al.
patent: WO 94/27349 (1994-11-01), None
Jackson Stephen W.
Robert & Bosch GmbH
Striker Michael J.
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