Internal-combustion engines – Poppet valve operating mechanism – Electrical system
Reexamination Certificate
2000-02-09
2001-08-28
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Electrical system
C123S090650, C251S129010, C251S129160, C335S257000, C335S277000
Reexamination Certificate
active
06279524
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application claims the priority of German Application No. 199 05 176.3 filed Feb. 9, 1999, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
In an electromagnetic actuator for operating a driven member at least one electromagnet is provided which has a yoke body and with which a back-and-forth movable armature plate is associated. When the electromagnet is energized, the armature plate is moved against the force of a resetting spring from a first switching position into a second switching position in which the armature plate engages the pole face of the yoke body. If the electromagnet is de-energized, the armature plate is returned to its first switching position under the effect of the resetting force of the resetting spring.
For certain applications, for example, for operating an engine valve of a piston-type internal-combustion engine where the engine valve constitutes the driven member, two spaced electromagnets are provided whose pole faces are oriented towards one another and between which the armature plate, attached to a guide bar, is movable back and forth against the force of resetting springs. When the electromagnets are de-energized, the armature plate assumes a mid position between the two electromagnets. If the electromagnets are alternatingly energized, the armature plate moves from a first switching position which is defined by its engagement with the pole face of one electromagnet, into its second switching position after de-energization of the last-named, momentarily holding electromagnet and energization of the other, momentarily capturing electromagnet. The second switching position of the armature plate is defined by its engagement with the pole face of the other, capturing electromagnet. By means of a suitable control of current supply in an alternating manner, the armature plate and thus the driven member may again be moved into the first switching position.
In the earlier-noted mode of application for operating an engine valve in a piston engine not only a high switching frequency is obtained but, based on the relatively large stroke of the engine valve, the armature has an oscillating path (stroke) of significant length. Despite the resetting force of the resetting spring arranged at the capturing electromagnet and acting on the armature plate during its approach to the pole face of the capturing electromagnet, the net attracting force on the armature plate increases exponentially, since, as the distance between the armature plate and the pole face of the capturing electromagnet decreases, the electromagnetic force increases exponentially, while the opposing spring force increases only linearly. As a result, the armature plate is increasingly accelerated until it impacts on the pole face of the capturing electromagnet. The resulting high impact velocity leads to a significant noise generation and may also lead to disadvantageous rebounding phenomena.
Conventional pneumatic dampening arrangements for braking the armature, such as disclosed, for example, in published European Patent Application 0 870 906, not only require a significant structural height; also, they are not capable of delivering the required dampening force with acceptable frictional values.
By means of controlling the current supply of the momentary capturing electromagnet, it is feasible to change the magnetic force during the approaching phase of the armature plate in such a manner that the armature plate arrives into contact with the pole face with a reduced speed. It is, to be sure, in principle possible to change, by controlling the current supply of the capturing electromagnet, the magnetic force in such a manner that the armature plate arrives with a “zero” impact velocity in contact with the pole face of the capturing electromagnet. Because of stochastic oscillations in the system, however, a reliable, secure capturing and holding of the armature plate is not feasible. Thus, for reasons of operational reliability the current supply of the capturing electromagnet must be set in such a manner that the armature plate arrives in contact with the pole face with a reduced, but significant residual speed. While rebound phenomena are in this manner prevented, noise generation nevertheless persists. By means of the above-described reduction of the impact velocity, however, significantly reduced dampening forces are required.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved electromagnetic actuator which has a pneumatic dampening element of compact construction.
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 member includes an electromagnet having a yoke provided with a pole face and a coil supported by the yoke and adapted to be supplied with electric current to produce an electromagnetic force; and an armature connectable to the driven member and movable in a path of motion into a first position and a second position spaced from the first position. The armature is moved by the electromagnetic forces into the second position in contact with the pole face. A resetting spring is coupled to the armature and exerts a spring force thereon for urging the armature away from the second position toward the first position. The actuator further includes a dampening assembly which has a piston affixed to the armature and a dampening cylinder provided in the yoke and having an open end oriented toward the armature and being in an axial alignment with the piston. In the first position of the armature the piston is axially spaced from the dampening cylinder. The piston enters the dampening cylinder solely during a terminal portion of the path of motion of the armature during displacement thereof toward the second position.
Since in case of a suitable control of the current supply of the capturing electromagnet the impact velocity is reduced, a very compact dampening element may be provided which may be integrated directly into the electromagnetic actuator without adversely affecting the course of the magnetic field lines of the electromagnet. It is a further advantage of the invention that such a dampening element may be utilized in armature plates with different circumferential contour without changing the construction; that is, the same dampening element may be used for an armature plate whether its contour is, for example, circular or polygonal.
According to an advantageous feature of the invention, the armature plate is coupled with a guide bar which, in turn, is guided in a bore of the yoke body and further, the dampening cylinder is arranged in the region of the bore and surrounds the guide bar. Such an arrangement has the advantage that the dampening element is situated in the region of the pole face of the yoke body in which the course of the field lines is, in any event, distorted by the preferably non-magnetic guide bar so that an arrangement of the dampening cylinder in the pole face, on the one hand, and the associated dampening piston on the face of the armature plate, on the other hand, does not lead to additionally disturbing the magnetic flux. The piston body is formed by an annular collar surrounding the guide bar in the zone of the plane of the armature plate. Expediently, the terminal peripheral edge of the dampening piston oriented towards the dampening cylinder is rounded. As a result, the dampening force exerted by the air in the annular chamber of the dampening cylinder on the dampening piston does not increase abruptly as the dampening piston enters the dampening cylinder; rather, by virtue of the rounded piston edge the pressure increases progressively because of the progressively narrowing air gap.
According to a further advantageous feature of the invention, the dampening cylinder is arranged in a cavity of the yoke body. Such a cavity may be, for example, an enlargement of the guide bore for the guide bar. The enlargement is dimens
FEV Motorentechnik GmbH
Kelemen Gabor J.
Lo Weilun
Venable
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