Electricity: motive power systems – Motor structure adjustment or control – Brush or other current-collector control
Patent
1990-05-02
1991-06-11
Ro, Bentsu
Electricity: motive power systems
Motor structure adjustment or control
Brush or other current-collector control
318DIG2, 310148, H02K 2320, H02P 700
Patent
active
050235320
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a drive mechanism for windshield wiper systems on motor vehicles and includes a two-speed d.c. motor having a collector and a plurality of carbon brushes.
The windshield wiper systems of modern motor vehicles typically are driven by permanent-magnet d.c. motors, which may be driven in two different speeds of operation. In order to switch on the two different speeds of operation a total of three carbon brushes are provided, of which two rest against the collector substantially diametrically. One of these carbon brushes is connected with the ground terminal of a voltage source. The other of these two carbon brushes is connected to the positive terminal of the voltage source, when the d.c. motor is to be driven at low speed in the first speed of operation. The third carbon brush rests against the collector between the first and the second carbon brush. It is thereby set off at a particular angle relative to the carbon brush which, in the first speed of operation, may be connected with the positive terminal, which angle is in general not larger than 90.degree.. In order to driven the d.c. motor in the second speed of operation at a higher speed the third carbon brush is connected with the positive terminal of a voltage source instead of the second carbon brush.
A wiper system also is known in which the d.c. motor may be driven with three different speeds of operation. In this known system two further carbon brushes are arranged on one side of the neutral zone defined by the connecting line of the two carbon brushes connected with the voltage source in the low speed of operation, so that a total of three carbon brushes may be selectively connected with the positive terminal of the voltage source.
In a comparison with other solutions, in which different speeds are adjusted by variable series resistors or by a variable armature voltage, these known systems include considerable cost advantages. It is however true that the starting torque is smallest for the higher no-load speed selected speed of operation.
In order to circumvent this disadvantage it is known to insert a diode between the carbon brush of the lowest speed of operation and a carbon brush with a higher speed of operation, which diode provides a current flow from the lead to the carbon brush for the higher speed of operation to the carbon brush for the lowest speed of operation. However, this solution is rather expensive. Moreover it is difficult to dissipate the heat generated at the diode.
The present invention is based on the problem of developing a drive mechanism of the type described above in such a way that in the high speed of operation a starting torque of the d.c. motor is achieved which is at least substantially as great or greater than the starting torque in the low speed of operation.
SUMMARY OF THE INVENTION
This problem is solved according to the invention in that a drive mechanism of the type described is additionally equipped with a collector and a plurality of brakes and which are selectively coupled to the voltage source. Basically four carbon brushes preferably are provided. It has turned out that in a drive mechanism according to the present invention the starting torque in the higher speed of operation is much higher than in customary drives. It can even be higher than in the low speed of operation.
Advantageously, the third and fourth carbon brushes are to a different extent set off relative to the second carbon brush. In this manner a better symmetry of the sliding surface relative to the second carbon brush can be obtained. The sliding surfaces are thereby are disposed on the front faces of the third and fourth carbon brushes facing the collector between the former and the collector. The displacement will suitable by made no greater than that the after-running edge of the third carbon brush is to the same extent set off relative to the second carbon brush as the after-running edge of the fourth carbon brush.
In particular in drives in which the d.c. motor may be controll
REFERENCES:
patent: 1523839 (1925-01-01), Rudenberg
patent: 1857202 (1932-05-01), Lee
patent: 2151678 (1939-03-01), Blankenbuehler et al.
patent: 3310722 (1967-03-01), Diello
patent: 3335305 (1967-08-01), Pasculle et al.
patent: 4500819 (1985-02-01), Trusock et al.
patent: 4704552 (1987-11-01), Masterman
patent: 4843286 (1989-06-01), Suriano et al.
Lewis J. Gordon
Ro Bentsu
Seitter Robert P.
SWF Auto-Electric GmbH
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