Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – With magneto-mechanical motive device
Reexamination Certificate
1997-12-10
2001-03-06
Donovan, Lincoln (Department: 2832)
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
With magneto-mechanical motive device
C251S129100
Reexamination Certificate
active
06198370
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application claims the priority of German Application No. 196 51 846.6 filed Dec. 13, 1996, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 4,455,543 describes an electromagnetic actuator for operating a cylinder valve in an internal-combustion engine. The actuator essentially is formed of two spaced electromagnets wherein the pole faces of one electromagnet are oriented towards the pole faces of the other electromagnet. In the space defined between the pole faces of the two electromagnets an armature is disposed which is coupled with the cylinder valve and which, dependent upon the alternating energization of the electromagnets, moves back and forth against the force of resetting springs. In the respective terminal position of the cylinder valve (open or closed position) the armature is in engagement with the pole face of the respective holding magnet and is maintained there as long as the holding electromagnet is in an energized state. In the position of rest the armature is in a mid position between the pole faces of the two electromagnets, determined by the force equilibrium of the two oppositely working resetting springs.
If, during operation, the armature is to be displaced from one of its end positions into the other, the holding electromagnet is de-energized so that the armature, together with the cylinder valve, is moved by the force of the associated return spring in the direction of the mid position (position of rest). Upon subsequent energization of the opposite, capturing electromagnet, the armature will be in the effective range of the magnetic field of the capturing electromagnet and is moved by means of the magnetic force against the force of the other return spring into the other end position. As the armature impacts on the pole face of the capturing electromagnet, noise is generated whose intensity is dependent from the magnitude of the impact velocity. At the same time, risks are high that the armature rebounds which, for example, upon closing the cylinder valve, may lead to a brief reopening of the valve after the latter has already been seated. By a suitable control of the energization of the momentarily capturing electromagnet it is feasible to reduce the impact velocity; yet, the impact velocity has to be at all times sufficiently high to ensure that the armature is securely captured, that is, it securely arrives into engagement with the pole face.
To minimize the unavoidable impact noises, an impact velocity of approximately 0.02 m/s is required for the armature in electromagnetic valve drives of the above-outlined type. Such low impact velocities have to be ensured in all real operating conditions while taking into consideration all related stochastic fluctuations; this, however, requires a substantial circuitry outlay. In vehicle engines irregularities in the road surface or other effects in the terminal approaching phase of the armature are sufficient to cause a sudden drop of the armature in case the magnetic force is oriented precisely in the direction of force requirement which is necessary for such a minimum impact velocity. A residual noise, however, cannot be avoided.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved method and apparatus for operating an electromagnetic valve actuator from which the discussed disadvantages are eliminated.
These objects and others to become apparent as the specification progresses, are accomplished by the invention, according to which, briefly stated, the current supply to at least one of the two electromagnets of the electromagnetic valve actuator is so controlled and the generated electromagnetic field is so oriented that in an end position of the cylinder valve the reciprocatable armature which operates the valve is held at the electromagnet against a resetting spring force and out of contact with the pole faces of the electromagnet.
According to the invention as outlined above, the armature does not impact on the pole face but is “softly” caught by an appropriately oriented magnetic field. By a suitable control of the energization of the electromagnet it is feasible to achieve a close-to-zero velocity as the armature reaches its end position. In case such an attempt is unsuccessful, the armature nevertheless may move without impacting the pole face, because the holding force and the positioning of the armature are effected exclusively by the magnetic field and the counterforce of the return spring. By virtue of an appropriate control of the energization (current supply) the magnetic field may have an excessive force which prevents an unintended “drop” of the armature in response to external force effects. Thus, even in case of a “creeping” of the armature into the end position, external impact forces cannot lead to a drop of the armature.
According to an advantageous feature of the invention, the magnetic field provided for a contactless holding of the armature is oriented substantially perpendicularly to the direction of armature motion, relatively to the end position of the armature. This is effected, for example, by providing that the respective electromagnet has two spaced pole faces which are essentially oriented towards one another. Upon release from the holding electromagnet the armature receives sufficient kinetic energy to move beyond the position of equilibrium determined by the resetting springs and it approaches the capturing electromagnet to such an extent that it arrives in the force range of the magnetic field of the capturing electromagnet and is thus continued to be moved in the direction of motion against the force of the effective return spring. As soon as the armature is situated between the two pole faces of the capturing electromagnet, the maximum magnetic force is exerted thereon so that the armature is maintained in the end position determined by those pole faces. The force of the magnetic field has to be designed such that it corresponds to the force of the compressed resetting spring.
According to a further advantageous feature of the method of the invention, upon energization of the electromagnet which holds the armature in a contactless manner, the current is reduced before the armature reaches its end position. In this manner it is possible to reduce the approaching velocity of the armature to avoid “overshooting”. The energization may be controlled such that as the armature reaches its end position, the current is again increased to such an extent that the necessary holding force is exerted securely on the armature and thus an undesired armature motion triggered by outer force effects is avoided.
According to a further advantageous feature of the invention, the armature which is held in its end position in a contactless manner by the electromagnet, is additionally exposed to the force of at least one permanent magnet. The permanent magnet force is oriented in the same direction as the electromagnetic field and is of such a magnitude that it affects the armature less than the force of the associated return spring. By providing such a permanent magnetic field, the current required for holding the armature may be advantageously reduced particularly in the open position of the engine valve, because one part of the magnetic force is applied by the permanent magnet. To release the armature, the surplus force of the return spring is sufficient to overcome the force of the permanent magnet field after de-energization of the electromagnet.
REFERENCES:
patent: 4455543 (1984-06-01), Pischinger et al.
patent: 5636601 (1997-06-01), Moriya et al.
patent: 5734309 (1998-03-01), Schmitz
Donovan Lincoln
FEV Motorentechnik GmbH & Co. KG
Kelemen Gabor J.
Venable
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