Electricity: electrical systems and devices – Control circuits for electromagnetic devices – Systems for magnetizing – demagnetizing – or controlling the...
Patent
1988-01-19
1989-09-05
Hix, L. T.
Electricity: electrical systems and devices
Control circuits for electromagnetic devices
Systems for magnetizing, demagnetizing, or controlling the...
361187, H01H 4728
Patent
active
048644579
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and device for controlling an electromagnet whose energization, by means of a AC current, causes engagement of two parts.
It applies more particularly to the control of electromagnets used in electric contactors whose closure is caused following energization of the coil of the electromagnet by an AC current, such energization causing the application of the mobile contacts of the contactor on the fixed contacts. However, the invention is not limited to this type of application. It may, in fact, be suitable for numerous other devices actuated by an electromagnet such, for example, as electromagnetic valves.
In devices of this kind, the mechanical energy communicated to the mobile part of the electromagnet for causing closure is variable depending on the closure angle of the switch which controls the energization of the coil of the electromagnet, that is to say depending on the time marking the beginning of the energization, considered in the corresponding period of the AC current.
This is why, at the present time, electromagnets are dimensioned so as to make them operational in all cases, including for the most unfavorable closure angles.
However, besides the increase in cost and size which this dimensioning involves, these measures have a certain number of drawbacks due mainly to the excess of energy developed particularly when the closure angle is favorable.
It has been been discovered in fact that, because of this extra energy, there often occurs in the contactors a brutal impact of the mobile contacts on the fixed contacts which is accompanied by bouncing causing premature wear. Furthermore, the mobile contact assembly and/or the armature of the electromagnet strike the fixed part of the electromagnet at high speed, which causes bouncing of the magnetic circuit (crunching), hammering, even rupture of the magnetic circuit, as well as considerable noise.
Similar problems also arise in other electromagnetic devices such as electromagnetic valves which are then the seat of premature wear of the seals and of more pronouned bouncing phenomena due, in particular, to the resilience of said seals.
The purpose of the invention is therefore to overcome these drawbacks. For this, it is based on the discovery that an electromagnet of said type has at least one privileged closure angle leading to optimum actuation of the mobile assembly associated with the electromagnet. Consequently, by imposing this privileged closure angle, it becomes possible to overcome the above mentioned drawbacks.
To reach this result, the invention provides a method for controlling an electromagnet including a coil to which may be applied an AC current following the emission of a control order, to causing the engagement of two parts, this method being more particularly characterized in that it includes the following steps:
previous determination of a period of time which corresponds to a privileged energization control angle of the electromagnet;
detection, from the moment when said control order has been emitted, of a zero cross-over of the AC current;
the application, of the AC current to the coil, when said period of time following after said zero cross-over has elapsed.
This method may be used by associating, with a controllable switch device in series with the coil of the electromagnet, a relatively simple electronic circuit comprising:
a member for determining the voltage zero of the AC current;
a delay element connected to the output of the zero determination member, this delay element being adjusted so as to obtain a delay time which corresponds to the privileged control angle of the electromagnet;
a switch-over device controlled by said delay element for delivering to the switch device, following a control order, a signal for controlling energization of the coil delayed by said delay time.
The control thus obtained of the speed communicated to the mobile contact assembly and/or to the mobile armature avoids the above mentioned drawbacks.
Tests carried out on such devices have shown that it is
REFERENCES:
patent: 3557381 (1971-01-01), Henry
patent: 4461990 (1984-07-01), Bloomes
Christian Bataille
Elie Belbel
Gast Jean-Noel
Michel Lauraire
Drucker William A.
Gray David M.
Hix L. T,.
La Telemecanique Electrique
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