Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Polarity-responsive
Reexamination Certificate
2000-08-22
2001-06-12
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Polarity-responsive
C335S129000, C335S133000
Reexamination Certificate
active
06246306
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to electromagnetic relays, more particularly, to a miniature power switching relay specifically designed for mounting on printed circuit boards. The present invention utilizes a pressure spring inserted into the relay housing for pressuring a center contact spring into position and providing for normally contact pressure without pre bending the center contact spring. The present invention further utilizes ultrasonic welding of the copper terminals and the center contact springs as well as the copper terminals and the normally open and normally closed contact springs creating higher conductivity properties and greater contact area.
2. Description of the Prior Art
Electromagnetic switching devices, commonly referred to as relays, have been used for many years and there is a continuing need for such a device which is small in size. Yet, moreover, there is a need for such a device capable of reliably handling relatively high current switching jobs. This requirement for miniaturization together with higher contact rating reliability has become particularly important in recent years because of the increasingly common practice of mounting relays on printed circuit boards.
In the design of an electromagnetic relay and other such electromagnetic devices an important consideration is the design of the “magnetic circuit.” The design of an effective magnetic circuit determines to a great extent the current switching capability of the relay and the power needed to operate it. The magnetic circuit of a relay generally includes the core inside the relay coil, the relay frame and the armature that moves an actuator, and then the actuator moves the relay contacts. In addition, air gaps exist between the armature and the core of the relay coil at an exposed end.
In relay operation electrical current is sent throughout the relay coil. The current running throughout the relay coil sets up a magnetic field in this magnetic circuit and it is the strength of the magnetic field generated in the air gap between the armature and the core inside the relay coil at an exposed end that is the force that causes the armature to move into contact with the core inside the relay coil at an exposed end providing the motion to operate the switching of the relay contacts. In the relay, the core inside the relay coil, the frame and armature are made of materials that can be easily magnetized and has low residual magnetism. The air gaps, however, resist the establishment of a magnetic field, and the air gap between the armature and the core inside the relay coil has by far the most significant resistance to a magnetic field in the magnetic circuit. In obtaining switching capability for the relay, it is desirable to design effective contact travel distances and rapid movement of the contacts by the armature. It is also desirable to provide the strongest possible magnetic field at this armature gap for the available coil current. This provides for positive and rapid contact movement. A strong return (pressure) spring allows for return movement of the armature when the relay current is removed causing positive and rapid contact movement.
Therefore, the mechanical arrangement of the magnetic core, relay armature, resulting air gap and the design of their interfaces significantly affect the ability of the relay to perform its function as an electrical switching device. It is desirable to maintain a minimum air gap between the core and the armature. This air gap must be tailored to the design of the relays function achieving the intended movement needed to move the center contact spring(s) with the center contact rivets to the required distance for proper contact switching.
Conventional relays presently on the market use a center contact spring with single headed contact buttons for normally closed and normally open contact arrangement or with double headed contact buttons for change over contact arrangement. The center contact spring is pre bent to achieve the necessary contact pressure and to hold the actuator in place of the relay where the pre bent center contact spring holds down above the actuator to contact the rivet of the normally closed contact spring. The overtravel is the distance between where a rivet of the center contact spring starts to contact a rivet of either the normally closed spring or normally open spring and where the contacting rivets reach stable position. This overtravel causes contact wiping between the contact areas of a rivet of the center contact spring and corresponding contact areas of rivets of either the normally closed spring or normally open spring.
Overtravel and contact wiping are essential in a relay for better reliability and longer life of the relay. The overtravel is necessary to make sure that burned off or evaporated material, which occurs at every switching operation, is eliminated. The overtravel further causes contact wiping which cleans the contact surfaces. At every switching operation, a micro weld is formed which needs to be broken when the contact is supposed to open. To break these micro welds, a shearing force is provided by the contact wiping. To achieve the overtravel, a minimum contact force is required. This required contact force is generated by the deflection of the pre bending of the center contact spring in conventional relays.
Pre bending of the center contact spring, though, contains limitations. The pre bending results in limits of the flexibility and deflection of the center contact spring. In order to achieve the required contact pressure for the overtravel and to hold the actuator down in the un-energized state, a minimum deflection is required. Based on the material characteristics of the center contact spring, a maximum deflection of the center contact spring is allowed before the center contact spring loses its spring property partially, which means that the center contact spring will no longer be able to return to its original position. Thus, the center contact spring may be stressed beyond its limits resulting in loss of contact pressure and causing the failure of the relay. In order to remedy this situation, conventional relays reduce the thickness of the center contact spring which results in reduced contact pressure, reduced overtravel, reduced center contact spring cross section and reduced contact rating.
The present invention fulfills the need for a device, which is small in size, yet capable of reliably handling high current switching jobs relative to known designs. The present invention solves the high current problem in a small size by using a combination contact assembly with a pressure spring.
Further, in conventional relays, it is known that bi-metal contact assemblies are used in electromagnetic relays. These known electromagnetic relays use bronze and brass materials for the springs and terminals. In addition, the springs and terminals are spot welded together.
A problem with the known brass and bronze materials is that these materials have low current conductivity properties. In addition, spot welding produces a limited contact area for the electrical current to flow through between the springs and the terminals resulting in lower current handling potential. During assembly, it is difficult to join the springs as single entities with almost no electrical resistance between the connections. Low electrical resistance is required if high electrical current is carried over these contact spring assemblies. The difficulty in assemblies lies in the high electrical conductivity of the individual springs and terminals, which do not allow for spot welding. Even if spot welding were possible, the springs are only connected during spot welding by small areas, which would then become bottle necks for the current flow.
U.S. Pat. No. 5,160,910 issued to Tsuji discloses an electromagnetic relay comprising a relay motor, an armature interacting with the relay motor, an actuator, first and second terminals, contact springs, and a center contact spring assembl
Donovan Lincoln
Meroni & Meroni P.C.
Meroni, Jr. Charles F.
Nguyen Tuyen T.
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