Electricity: motive power systems – Field or secondary circuit control – Plural – diverse or diversely connected or controlled field...
Patent
1998-06-10
1999-11-30
Nappi, Robert E.
Electricity: motive power systems
Field or secondary circuit control
Plural, diverse or diversely connected or controlled field...
318244, 318245, 318246, 318375, H02P 100
Patent
active
059948604
DESCRIPTION:
BRIEF SUMMARY
SCOPE OF APPLICATION
The present invention relates to the field of electromotors. It regards a series-wound motor with electric brake, comprising an armature provided with an armature winding and at least two exciter coils disposed on pole shoes as well as switchgear means which, in the operating phase of the motor, connect the exciter coils in series with the armature winding and connect the series connection with terminal clamps for the operating voltage and which, in the braking phase, interrupt and short-circuit the armature winding by the parallel connection of a winding.
STATE OF THE ART
A series-wound motor is known e.g. from the DE-A1-35 31 685 (or U.S. Pat. No. 4,630,862) or from the DE-C2-30 35 185.
In motor-driven electric power tools such as per example chain saws, hedge clippers or lawn mowers, it is desirable on account of safety requirements, to brake the motor after the switching-off as speedily and safely as possible so as to limit risks of injury by the over-travel or after-running of the power tool or to avoid such risks altogether. Such a braking or deceleration can be effected either mechanically or else electrically. In this case the electric braking possesses the advantage that it involves virtually no wear, calls for only a minor additional expenditure and can be integrated in a space-saving fashion into the driving system.
The electric braking can be realized in a particularly simple fashion if the electric power tool is driven by a series-wound motor, in which the field winding and the armature winding, in the course of normal operation, is serially connected to the supply voltage. In the DE-c2-30 35 185 mentioned in the beginning, a resistance braking has been proposed for the braking of such a series-wound motor, in which the voltage supply is interrupted and the armature or the armature winding is short-circuited via the field winding connected in the inverse direction and a serially disposed NTC resistor. What is problematic in this solution is that an additional NTC resistor is required and that the NTC resistor has to be highly accurately dimensioned in order to make an effective, wear-resistant braking possible. If, on the other hand, the NTC resistor is bridged across, extremely high electric currents arise at the beginning of the braking operation, which cause a flashing over on the collector.
In the DE-A1-35 30 685, according to FIG. 1, it is proposed for the electric braking as a series-wound motor 10, in a field winding comprised of two exciter coils 13, 14, for the braking operation, to interrupt the connection to the terminal clamps 16 and to merely change the polarity of one exciter coil 14 of the field winding and to connect the armature winding 17 in parallel. The motor or the electric contacts in the motor and in the switch are, according to the publication, hardly subjected to a load in the process since, in the short-circuiting with only one exciter coil, relatively low short circuits do occur. However, it is disadvantageous in this solution that it is not possible to adjust to optimize the driving and braking behavior independently from one another. When the exciter coils are modified in order to change the driving behavior in the number of windings or in the geometry or the like, this modification also has an unintentional effect on the braking behavior because the same coil is used for both driving and braking. An independent adjustment would at most be conceivable if the coil employed for the braking would, in the form of a separate coil, be accommodated in the stator in addition to the exciter coil. However, in order to do this, the bundle of laminations in an existing motor would have to be modified, which calls for a considerable additional expenditure.
TECHNICAL PROBLEM, SOLUTION, ADVANTAGES
That is why it is the technical problem of the invention to provide a series-wound motor with electric braking which, with regard to the electric braking, can be flexibly adapted at low cost to the various cases of application.
In this case provision is made
REFERENCES:
patent: 3596161 (1971-07-01), Swanke et al.
patent: 3673481 (1972-06-01), Hardin
patent: 3678357 (1972-07-01), Swanke et al.
patent: 4250436 (1981-02-01), Weissman
patent: 4751414 (1988-06-01), Davis et al.
patent: 5063319 (1991-11-01), Mason et al.
patent: 5294874 (1994-03-01), Hessenberger et al.
patent: 5648706 (1997-07-01), Polk et al.
Krahn Klemens
Krueger Andreas
Dolmar GmbH
Leykin Rita
Nappi Robert E.
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