Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – With magneto-mechanical motive device
Reexamination Certificate
2000-02-22
2001-10-16
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
With magneto-mechanical motive device
C335S258000, C251S129010
Reexamination Certificate
active
06304161
ABSTRACT:
BACKGROUND OF THE INVENTION
German Offenlegungsschrift (application published without examination) No. 33 07 070 discloses an electromagnetic actuator for operating a component, particularly a cylinder valve of an internal-combustion engine. The actuator has an armature which may be reciprocated back and forth between the pole faces of two electromagnets by magnetic forces against oppositely oriented resetting springs. The actuator system is designed in such a manner that in case the electromagnets are in a de-energized state, the armature, urged by the oppositely acting resetting springs, assumes a position between the two pole faces. In such a known system it is assumed that the two resetting springs are identical in their geometry, especially as concerns their length in a relaxed state and their spring curve. The purpose of such an identical arrangement is to ensure that essentially identical magnetic forces are needed for attracting and holding the armature at the respective pole faces and that essentially identical spring forces are present first, for accelerating the armature when its leaves the respective pole face and second, for braking the armature when it approaches the respective opposite pole face. Such springs are conventionally compression coil springs. In a mass manufacture of such coil springs, however, it is not feasible to make identical springs in sufficient quantities at an acceptable cost.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved actuator of the above-outlined type which permits greater tolerances for the geometry and characteristics of the resetting springs.
This object and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the electromagnetic actuator for operating a driven component includes first and second electromagnets having respective first and second pole faces oriented toward one another and defining a space therebetween; an armature disposed between the electromagnets and movable back and forth between the first and second pole faces in a direction of motion; a driving component attached to the armature for moving therewith as a unitary structure; and a resetting spring unit attached solely to the driving component or to the driven component and exerting forces opposing movements of the armature caused by electromagnetic forces generated by the electromagnets. The resetting spring unit is in a relaxed state when the armature is in a mid position between the first and second pole faces and is in an armed (stressed) state upon movement of the armature from the mid position in either direction. A mechanism connects the driving component with the driven component for effecting a transmission of moving forces from the driving component to the driven component to cause displacements of the driven component as a function of displacements of the armature and the driving component.
An actuator according to the invention as summarized above has the advantage that the resetting spring arrangement may be composed of a single spring, whereby a reduction of the structural height is feasible. The spring arrangement is so designed that when the armature moves out of its mid position between the two pole faces in either direction, the spring arrangement is armed to exert a resetting force on the armature against the magnetic force. The coupling device provides for the required form-fit between the driving component (such as a guide bar affixed to the armature) and the driven component (such as an engine valve of an internal combustion engine). In this manner the armature and the driven component are reciprocated as a unit. Further, by the slack adjusting means incorporated in the coupling device a reliable end position of the armature and the driven component are ensured.
Thus, if the electromagnetic actuator is used for operating an engine valve, in the de-energized state of the electromagnets the engine valve is maintained by the resetting spring arrangement in a halfway open stroke so that upon energization of one of the electromagnets, the engine valve is moved into the closed position and upon energizing the other electromagnet, the engine valve is moved into the fully open position. To counteract external interferences which disturb the operation of the engine valves, such as fluctuating temperatures which result in alternating lengths of the driving and the driven components, and also to compensate for component wear which may likewise lead to length changes, the coupling element provides for an automatic length compensation. In particular, in case the actuator is used for driving an engine valve, it is of importance that in the closed position of the engine valve the valve head lies tightly against the valve seat and at the same time the armature engages the pole face of the closing magnet. Only these simultaneous occurrences ensure that the closed position of the valve may be maintained with a minimum holding current and thus with a small energy input. Upon an increase of the operating temperature, a lengthening of the driving component (that is, the guide bar affixed to the armature) and the driven component (that is, the valve stem of the engine valve) occurs. Consequently, in case of a rigid coupling between the two components the valve head would no longer engage its valve seat when the armature lies against the pole face of the closing magnet. Likewise, upon a shortening of the overall length due to a cold engine condition, the armature would not engage the respective pole face when the valve is already seated. Therefore, the coupling device has to be designed such that an overall length change of the two components (lengthening or contracting) is compensated for. Thus, in the cold condition when the total length of the components is reduced, the armature may arrive into contact with the pole face of the closing magnet when the valve head has reached the valve seat, and likewise, in case of a lengthening due to a heat-up of the valve seat, the valve head may be firmly seated when the armature has reached the pole face of the closing magnet. In this manner an automatic compensation is achieved so that in the closed position the valve head as well as the armature reliably assume at all times their contacting position with the valve seat and the pole face of the closing magnet, respectively.
In accordance with an advantageous feature of the invention, the spring assembly is connected with the driving component by an adjusting mechanism for adjusting the mid position of the armature between the two pole faces of the electromagnet. Such a mechanism permits the mass manufacture of the springs which have essentially the same spring curve but which, because of manufacturing tolerances, may have different lengths. With the aid of the adjusting mechanism it is thus possible to compensate for various lengths so that the mid position of the armature between the two pole faces of the electromagnets is ensured when the springs are in a relaxed state and the electromagnets are in their de-energized condition.
According to a further advantageous feature of the actuator of the invention, the spring assembly is formed by at least one wound spring. Such wound springs may be mass manufactured in a great variety of configurations.
In accordance with a further advantageous embodiment of the invention, the spring is wound as a coil spring and may be loaded by either tensioning or compressing forces. In such a system the spring may be connected in the housing of the actuator with the valve in a “classical” manner, that is, the coil spring surrounds the valve stem and is affixed at one end to the cylinder head and at the other end to a spring seat disk secured to the valve stem. The spring is dimensioned in its length such that in the relaxed state the valve is maintained in a half-open state. A construction in which the valve stem is connected with the driving component of the actuator via the coupling device, may likewise be moved in the desired manne
Goebel Hans Willi
Hartmann Ernst-Siegfried
Lange Holger
Schebitz Michael
Wahnschaffe Jurgen
Donovan Lincoln
FEV Motorentechnik GmbH
Kelemen Gabor J.
Nguyen Tuyen
Venable
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