Electricity: motive power systems – Motor-reversing – Automatic and/or with time-delay means
Patent
1996-08-15
1999-01-19
Shoop, Jr., William M.
Electricity: motive power systems
Motor-reversing
Automatic and/or with time-delay means
318443, 318444, H02P 100
Patent
active
058617230
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention is based on a windscreen wiper device of the type having at least one wiper arm that is driven by an electric motor whose rotary direction is variable at least in the extreme positions, with the electric power made available to the electric motor being reduced upon the change of rotary direction. From German Patent 29 44 224, a windscreen wiper device of this generic type is known that includes an electric motor whose direction of rotation can be varied in the extreme positions of a wiper arm. A pendulum gear, which produces a reciprocating motion from a rotary motion, can be dispensed with. The known device includes a drive stage that performs a reversal of the polarization of the electric motor operating voltage in the extreme positions. Imposing the full operating voltage on the electric motor that has come to a stop in the extreme positions leads to the occurrence of a starting current in the electric motor that is multiple times above the normal operating current. If the reversal of polarization of the electric motor takes place after the extreme position has been reached without any deceleration process, which is accomplished for instance by short-circuiting the electric motor, then the starting current can rise to twice the value, since the electromotive contrary force of the electric motor is added to the voltage of the energy source.
SUMMARY OF THE INVENTION
The object of the invention is to provide a windscreen wiper device that has a reduced load on the electric motor and on the end stage.
This object is attained by providing a windscreen (or windshield) wiper device which is characterized in that a timer is provided, which is started by an extreme-position signal, and in that the rated power is not made available to the electric motor until after a period of time specified by the timer has elapsed.
The windscreen wiper device of the invention has the advantage that the thermal load on the electric motor and that of the drive stage are reduced during the change of rotary direction of the electric motor in the region of the extreme positions of the wiper arm. According to the invention, it is provided that the electric power made available to the electric motor is reduced upon the change of rotary direction. With this provision, the occurrence of a high starting current, which in combination with ohmic resistances leads to a thermal load on the end stage and the motor, is lessened.
In a first advantageous embodiment it is provided that the rated power is not made available to the electric motor until after a specified position has been reached. Another provision provides that the rated power is not made available to the electric motor until after a specified position of the wiper arm has been reached. The specified position is located within the sweep range in the vicinity of the associated extreme position. What is necessary is one additional position sensor, which can be in the form of a wiper contact, for instance, and cooperates with a wiper disk.
One suitable provision for reducing the power made available to the electric motor compared to the rated power is attainable by reducing the furnished operating voltage. Another advantageous option for reducing the electrical power made available to the electric motor compared with the rated power contemplates reducing the current flowing through the electric motor. Reducing the current, in particular, can be accomplished by especially simple means in the context of a clocked mode of operation. The clocked mode provides that the electric motor is either connected to the full available operating voltage, or disconnected from it entirely. The clock signal may have a variable frequency and/or a variable duty cycle. Both the frequency and the duty cycle can be chosen for instance taking the motor specifications into account. As a further criterion, the undesired emission of electromagnetic interference radiation can also be taken into account.
Another advantageous feature of the device of the invention provi
REFERENCES:
patent: 4614903 (1986-09-01), Betsch et al.
Lockett Kim
Robert & Bosch GmbH
Shoop Jr. William M.
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