Internal-combustion engines – Poppet valve operating mechanism – Electrical system
Reexamination Certificate
2000-04-27
2001-10-30
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Electrical system
C251S129100, C251S129160
Reexamination Certificate
active
06308667
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
BACKGROUND OF THE INVENTION
The present invention relates to actuators for moving the intake and exhaust valves of internal combustion engines, and specifically to an electronically actuable engine valve providing improved force characteristics and a signal indicating the valve position.
Electrically actuable valves, in contrast to valves actuated mechanically by cams and the like, allow a computer-based engine controller to easily vary the timing of the valve opening and closing during different phases of engine operation.
One type of actuator for such a valve provides a flat plate armature which moves back and forth between two electromagnets. The armature is attached to a valve stem of a valve.
When the electromagnets are unpowered, the armature is held in equipoise between the two electromagnets by two opposing springs. Prior to operation, the armature is drawn against one of the electromagnets by an “initialization” current in the retaining electromagnet. The spring between the armature and the retaining electromagnet is compressed while the opposing spring is stretched. Once the armature is drawn fully toward the receiving electromagnet, the initialization current is reduced to a “holding” level sufficient to hold the armature against the electromagnet until the next transition is initiated.
A change of valve state from open to closed or vice versa, is effected by interrupting the holding current. When this occurs, the energy stored in the opposed compressed and stretched springs accelerates the armature off of the releasing electromagnet toward the new receiving electromagnet. When the armature reaches the receiving electromagnet, that electromagnet is energized with the “holding” current to retain the armature in position against its surface.
In a frictionless system, the armature reaches a maximum velocity at the midpoint between the two electromagnets (assuming equal spring forces) and just reaches the receiving electromagnet with zero velocity. In a physically realizable system in which friction causes some of the stored energy of the springs to be lost as heat, the armature will not reach the receiving electromagnet unless the energy lost to friction is replaced. This is accomplished by creating a “capture” current in the receiving electromagnet prior to the armature contacting that electromagnet.
The capture current must be of sufficient magnitude to overcome the opposing forces resisting movement of the armature, however, it is equally important that the capture current be limited to prevent damage to the armature, electromagnet, or valve and to limit impact noise. If the capture current is turned on too soon (or is too great in magnitude), the armature may be accelerated into the electromagnet (and the valve into its seat) at excessive velocity. Conversely, the armature may not be captured by the receiving electromagnet and the valve may not close if the capture current is turned on too late or is too low in magnitude.
Accurate control of the capture current is facilitated if the position and velocity of the armature as it approaches the receiving electromagnet can be measured. Because the force between the electromagnet and armature varies rapidly with distance, sensors for measuring armature distance must be very accurate. Small measurement errors in distance can produce large errors in the calculated force applied to the armature, upsetting correct armature control.
Unfortunately, position sensors that are sufficiently accurate for this purpose and yet robust enough to survive in the environment of an internal combustion engine are expensive and therefore impractical.
BRIEF SUMMARY OF THE INVENTION
The present invention provides inter-engaging teeth and sockets on opposing armature and electromagnet core faces to reduce the variation in the force of attraction between the armature and a core. As the force profile of the actuator becomes more linear, the demands on the position sensor are reduced and peak initialization and capture currents are reduced. In addition, the teeth and socket structure creates a mutual inductance between opposed electromagnets that may be measured to derive armature position.
Specifically, then, the present invention provides an electrically actuable engine valve having a first and second coil wound about a common actuation axis and spaced apart by an actuation distance. A first and second core, incorporating the first and second electromagnets, respectively, present opposed core faces across the actuation distance. A valve having a valve head sized to cover a valve seat of an internal combustion engine is attached to a valve stem, the latter supported by valve stem supports holding the valve stem aligned with the actuation axis for movement along the actuation axis. An armature plate extends in a plane perpendicular to the axis and attaches to the valve stem for movement therewith along the actuation axis. At least one spring is attached to the armature plate to bias the armature plate to a neutral position between the core faces. The armature plate and at least one given core have a mating tooth and socket extending parallel to the actuation axis, the tooth and socket sized to provide a more linear relationship in the attractive force between the given core and the armature as a function of separation distance between the given core and the armature for a constant coil current.
Thus it is one object of the invention to provide a more linear attractive force between the armature and the core as a function of distance thereby providing better initialization of the armature position and improved control of armature position and speed.
The tooth may be on the armature plate and the socket on the core or the socket may be on the armature plate and the tooth on the core.
Thus it is an advantage of the invention that it provides flexibility in design as may be necessary to minimize armature weight or maximize armature flux path.
The tooth and the socket may be on only one side of the armature and a corresponding surface of the core.
Thus it is another object of the invention to provide different force profiles for the two sets of coils, which will be suitable for the actuation of an exhaust valve since the exhaust gases provide additional resisting force on the opening of the valve.
The armature plate may include a plurality of slots extending along the actuation axis.
Thus it is another object of the invention to reduce induced eddy currents in the armature plate such as cause resistive losses.
The foregoing and other objects and advantages of the invention will appear from the following description. In this description, reference is made to the accompanying drawings, which form a part hereof, and in which there is shown by way of illustration, a preferred embodiment of the invention. Such embodiment does not necessarily represent the full scope of the invention, however, and reference must be made therefore to the claims for interpreting the scope of the invention.
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patent: 5941201 (1999-08-01), Shimizu et al.
patent: 6125803 (2000-10-01), Hattori et al.
Tsai Hong
Xiang Youqing
Lo Weilun
Quarles & Brady LLP
Visteon Global Technologies Inc.
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