Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – With magneto-mechanical motive device
Patent
1981-08-21
1983-01-18
Broome, Harold
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
With magneto-mechanical motive device
335259, 335265, H01F 708
Patent
active
043694195
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to electrically operated solenoids, and more particularly to a solenoid having a plunger which includes a spring biased lost motion link adapted to be connected to a load.
2. Background Art
Various types of electromagnetically operated solenoids are well known in the art. Many of such solenoids are of the type having a linearly shiftable plunger member disposed within an electrically energizable coil. The plunger is coupled with a load which is normally operated by a mechanical connection that causes the plunger to shift away from the coil. Energization of the coil using a D.C. electrical source creates a magnetic field around the plunger which urges the plunger to shift linearly back toward the coil, thereby displacing the load.
Some types of prior art solenoids employ dual coils; one coil is of a low resistance type and is particularly designed to produce magnetic fields which develop a high initial pulling force on the plunger. The other coil is of a high resistance type which generates a relatively low level of pulling force and merely functions to hold the plunger in its actuated position after the plunger has displaced the load.
Solenoids of the type described above are typically employed for operating engine throttles, chokes, valves, clutches and any other device requiring a linear stroke. Some of these applications involve loads which present a relatively high initial resistance to the solenoid, due to starting friction and the like. Due to their inherent design, these solenoids develop a minimum level of pulling force when the plunger is fully extended, since in the fully extended position, the magnetic field produced by the coil exerts the least amount of influence on the magnetically attracted plunger.
As a consequence of the above, it has been necessary in the past to resort to dual coil type or oversized solenoids in order to develop sufficient pulling force on the initial part of the retraction stroke thereby to "break loose" the load. Obviously, dual coil and oversized single coil solenoids are more costly to manufacture due to their complexity and size compared to a simple, single coil solenoid which is matched to meet the minimum pull force requirement for a particular application.
DISCLOSURE OF THE INVENTION
The present invention overcomes the disadvantages of prior art solenoids through the provision of a plunger having a spring biased, lost motion link connection to the load which has the net effect of increasing the initial pulling force imparted to the load, thereby allowing a coil of minimum capacity to be employed in a given application.
More specifically, the solenoid comprises a casing, a single electrically energizable coil within the casing, and an elongate plunger assembly slidably mounted in an opening in the coil. The plunger assembly includes an elongate body and a lost motion link adapted to be coupled with the load and mounted on one end of the body for sliding movement relative to the body. A spring trapped between the link and the plunger body normally biases the body in a direction toward the link thereby to normally maintain the link and the plunger body in retracted operating relationship relative to each other. In the absence of abnormally high starting resistance presented by the load, the plunger body and link remain in retracted relationship relative to each other throughout the entire pulling and return strokes of the plunger assembly, i.e., the plunger body does not shift relative to the link or the load. The link is defined by a piston-like member slidably confined in a cavity within one end of the plunger body. In the event that the load presents an abnormally high level of starting resistance to the solenoid, the link allows the plunger body to shift away from the link (and therefore from the load) a predefined distance into the coil without displacing the load. This partial displacement of the plunger body into the coil increases the magnetic influence imparted thereto by the coil, consequently, the
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Broome Harold
Caterpillar Tractor Co.
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