Electricity: motive power systems – Limitation of motor load – current – torque or force
Patent
1996-02-15
1998-01-27
Masih, Karen
Electricity: motive power systems
Limitation of motor load, current, torque or force
318257, 318599, 363 58, 361 24, H02K 1732
Patent
active
057125503
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to an arrangement for controlling a power control element of a drive unit of a motor vehicle.
BACKGROUND OF THE INVENTION
Such an arrangement is known form U.S. Pat. No. 4,951,188. There, a full-bridge circuit is provided for controlling a power control element, especially a throttle flap in the context of an electronic accelerator pedal system. The full-bridge circuit comprises four actuable circuit elements which can be driven by at least one pulse-shaped drive signal. The consumer, the electric motor, is arranged in the bridge diagonal and is connected to the power control element. Two diagonally opposite lying switch elements are closed for actuating the motor in a first direction of rotation in the sense of opening the power control element. The two other diagonally opposite lying switch elements are actuated when actuating in the second direction. The so-called free-running phase is in contrast to these current flow phases in which the drive signal exhibits an active level. In the free-running phase, the drive signal exhibits an inactive level and none of the switch elements is driven. A mean current is generated by the consumer because of the clocked driving of the power control element and the clocked control comprises the current flow phase and the free-running phase. The mean current holds the consumer against a return force in the position pregiven by the electronic accelerator pedal system.
In order to protect the output stage against short circuits, a measuring resistor in the region of the ground connection of the full bridge detects the total current flowing through the entire bridge and through the consumer. This current is compared to a pregiven maximum value and, when this maximum value is exceeded, the control is reduced to a pulse-duty factor of 1% and is resumed when there is a drop below the pregiven maximum value. A current value is fixed as the maximum current value and this current value is that current which would flow through the bridge when there is a short circuit in the consumer. The known output stage is protected against short circuits because of the reduction of the drive when the threshold value is exceeded. By reducing the drive to a pulse-duty factor of 1%, intense current fluctuations occur in the case of a short circuit when the threshold is exceeded or there is a drop below the threshold which would cause an unsatisfactory performance of the control system.
The mechanics of the control element and the control apparatus electronics must be matched to each other when driving a power control element, especially a throttle flap, with a direct-current motor. In this context, opposing requirements occur. Pregiven maximum displacement times for the power control element are to be maintained and an excess of torque of the drive is to be made available in the case of binding or icing of the control element. The direct-current motor should be held in a pregiven position with the lowest possible current; the smallest peak loads in the vehicle electrical system are to be generated and, finally, the driving output stage should be configured so as to be protected against short circuits and be integratable in a simple manner; that is, the maximum current required by the output stage should be as low as possible.
Not all of these requirements are satisfied in the known output stage which is secure against short circuits. A maximum current up to the short-circuit current is permitted for the known output stage in order to obtain a displacement time which is as short as possible. This also leads to a high excess torque. However, the direct-current motor utilized generates high currents or current peaks when changing the drive control especially during displacement operation during its acceleration and braking. In this way, the electrical system of the motor vehicle is greatly loaded so that large collapses in voltage and drops can be the consequence. Furthermore, a very power intensive output stage, which can only be integrated with diff
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Boll Leonhard
Muller Klaus
Zeller Thomas
Masih Karen
Ottesen Walter
Robert & Bosch GmbH
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