Information
-
Patent Grant
-
6308667
-
Patent Number
6,308,667
-
Date Filed
Thursday, April 27, 200024 years ago
-
Date Issued
Tuesday, October 30, 200122 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
-
CPC
-
US Classifications
Field of Search
US
- 123 9011
- 251 12901
- 251 1291
- 251 12915
- 251 12916
-
International Classifications
-
Abstract
An electrically actuated engine valve provides an armature having one or more teeth extending outward from the armature along the actuation axis to be received by corresponding sockets in the cores of opposed electromagnets. The teeth do not restrain the movement of the armature but in approaching the cores provides a magnetic flux path that produces a more constant force of attraction during actuation of the valve. This enables the valves to overcome initial opposing forces such as caused by pressure on the valve heads to which the armature is attached and provides a path of inductive coupling between the opposed coils that can reveal armature position providing a method of accurately controlling armature seating speed.
Description
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.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a phantom, fragmentary perspective view of a cylinder head and its valve assembly showing location of the electromagnet actuator of the present invention;
FIG. 2
is a cross-section of the electromechanical actuator of
FIG. 1
taken along lines
2
—
2
showing an armature attached to a valve stem and positioned between two coils;
FIG. 3
is a graph depicting force of attraction between an actuated coil and the armature of the present invention for a prior art planar armature and for the tooth and socket armature of the present invention showing the greater linearity of force as a function of distance for the latter;
FIGS. 4
a
and
4
b
are fragmentary cross-sections similar to
FIG. 2
showing alternative embodiments of the tooth and socket design of the present invention;
FIG. 5
is a fragmentary cross section similar to that of
FIG. 2
showing an asymmetric armature plate useful for exhaust valves;
FIG. 6
a
is a fragmentary perspective view of a rectangular version of the armature plate of
FIG. 2
showing parallel surface slots to reduce eddy current flow;
FIG. 6
b
is a fragmentary perspective view of a circular version of the armature plate of
FIG. 2
showing radial surface slots to reduce eddy current flow;
FIG. 7
is a block diagram of a controller useful for use with the actuator of
FIG. 1
for alternately driving one coil and reading induced voltage in the second opposed coil for armature control; and
FIG. 8
is a simplified graph of voltage versus armature distance from the unpowered coil showing the decreasing amplitude of coupled voltage to the unpowered coil as the armature moves toward the driven coil when the coil that is driven is driven with an alternating current such as produced by a hysteretic controller.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to
FIG. 1
, an electromagnetically actuated valve
10
suitable for use with the present invention provides a coil assembly
12
fitting around a valve stem
14
, the latter which may move freely along its axis. The valve stem
14
extends downward from the coil assembly
12
into a piston cylinder
16
where it terminates at a valve head
18
. Generally, power applied via leads
20
of the coil assembly
12
will move the valve head
18
toward or away from a valve seat
22
within the cylinder so as to provide for the intake of air and fuel or recirculated exhaust gas, or exhaust of exhaust gas depending on the engine and valve type.
Referring now to
FIG. 2
, the coil assembly
12
provides two toroidal coils
24
and
26
of helically wound electrical wire. The coils
24
and
26
are spaced apart coaxially along the valve stem
14
and fit within cores
28
and
30
, respectively, which provide for the concentration of magnetic flux at opposed open faces
32
when the coils
24
and
26
are energized.
Between the open faces
32
of the cores
28
and
30
is a disk-shaped armature plate
34
attached to the valve stem
14
. The armature plate
34
may be a solid soft iron plate for easy manufacturing and high magnetic attraction. The surface of the armature plate
34
extends perpendicularly to the axis of the valve stem
14
. The space between the open faces
32
is sufficient so that the valve stem
14
may move by its normal range along actuation axis
36
before the armature plate
34
is stopped against either the open faces
32
of core
28
or core
30
.
Helical compression springs
38
extend outward from the cores
28
and
30
away from the armature plate
34
about the valve stem
14
to be constrained by collars
39
on the valve stem
14
. Absent the application of current to either of coils
24
and
26
, the springs
38
bias the armature plate
34
to a point approximately midway between the cores
28
and
30
.
Referring now to
FIG. 3
for prior art valves similar to that of
FIG. 2
but having a planar armature plate
34
, the function
40
, relating force of attraction between the armature plate
34
and an energized one of the cores
28
or
30
to distance between the armature plate
34
and that cores
28
or
30
for a constant current through the cores
28
or
30
, varies abruptly as a function of distance, the force decreasing rapidly in the first few millimeters of separation. This rapid fall-off in force with distance makes it extremely hard to produce sufficient force to initially attract the armature plate
34
to one of the cores
28
and
30
. Further the non-linearity makes control of the velocity of the armature plate difficult.
The present invention, in contrast, provides a more nearly linear function
42
relating force to distance between the armature plate
34
and the cores
28
or
30
of an energized one of coils
24
or
26
. This function
42
is much more constant providing greater forces at greater distances between the armature plate
34
and cores
28
or
30
and less variation in force for a given current as may provide greater precision to control the armature velocity.
Referring again to
FIG. 2
, the greater linearity of force provided by the present invention results from the use of one or more teeth
44
extending along the actuation axis
36
out from the broad surfaces of the armature plate
34
toward corresponding open faces
32
of the cores
28
and
30
. The cores
28
and
30
have sockets
46
corresponding to the teeth
44
to interfit with the teeth
44
as the armature plate
34
moves toward either of the respective open faces
32
. Importantly, the sockets
46
are in the cores
28
and
30
and the coils
24
and
26
are not affected and remained encased in cores
28
and
30
.
Referring now to
FIGS. 2 and 6
a
, teeth
44
extending outward along the actuation axis from a base
50
of the armature plate
34
, the base
50
being generally a portion of the armature plate
34
aligned with the coils
24
or
26
. The teeth are generally trapezoidal in cross section, having sloped walls
53
terminating at a plateau tip
52
.
The height of the teeth
44
from base
50
to tip
52
substantially equals the separation between the base
50
and the opposing portion of the core
28
or
30
when the armature plate
34
is in a neutral position biased by the springs
38
with no energizing either of the coils
24
and
26
. Thus the tips
52
of the teeth
44
nearly engage their corresponding sockets
46
prior to powering of either coil
24
or
26
. Other heights may also be selected among those that render the force function
40
more linear. Generally however, the height of the teeth
44
will be considerable and at least half the distance between the base
50
and the portion of the open faces
32
, which it abuts. Precise shaping of the teeth
44
and sockets
46
may be determined with commercially available finite elements magnetic device modeling programs.
Referring still to
FIG. 6
a
, the broad surfaces of the armature plate
34
may be scored with a plurality of longitudinal slots
54
extending into the surface of the armature plate
34
along the actuation axis
36
to break the path of eddy current flows which may tend to run cyclically around the surface of the armature plate
34
dissipating energy as resistive heating. These slots
54
may be filled with an electrically insulating material or left open and may run at a variety of orientations around the surface generally across to the expected path of such eddy currents. Reduction of eddy current losses is particularly important because of the high electromagnetic transience necessary for the operation of a valve of this kind. Winding structure and wire geometry with reduced proximity loss and eddy current loss may also be used.
Referring now to
FIG. 6
b
, in an alternative embodiment the armature plate
34
is disk shaped and has multiple annular teeth
44
which correspond with multiple sockets
46
on the cores
28
and
30
(not shown). In this case the slots
54
extend radially.
Referring now to
FIGS. 4
a
and
4
b
, alternative versions of the teeth
44
and sockets
46
may be provided. In
FIG. 4
a
, teeth
44
a
may be positioned symmetrically about the valve stem
14
centered on the windings of a coil (e.g.
24
). The plateau tips
52
a
of the teeth
44
a
are as wide as the windings of the coil
24
and the sloped walls
53
a
cover the remainder of the open face
32
a
leaving minimal base
50
close to the valve stem
14
. Sockets
46
a
are formed in the open face
32
of the core
28
and hold each of the windings of the coil
24
at their deepest portions and are shaped corresponding to the teeth
44
a.
Referring to
FIG. 4
b
, in an alternative embodiment, the teeth
44
b
have hemicircular cross-sections (similar to the teeth of
FIG. 6
b
) as opposed to the trapezoidal cross sections. As in the embodiment of
FIG. 2
, the teeth
44
b
flank the windings of the coil
24
so that the windings are positioned in between sockets
46
b
. In each of the embodiments of
FIGS. 4
a
and
4
b
, no change in the basic dimensions of the windings of coils
24
and
26
is required and they remain encased in the cores
28
and
30
.
Referring now to
FIG. 5
, the armature plate
34
may be asymmetric across a bisecting plane perpendicular to the valve stem
14
with the teeth
44
extending on only one side of the armature plate
34
toward sockets
46
on only one core
30
and wherein the opposite side of the armature plate
34
and its opposing core
28
is planar. In this way, armature mass is reduced and fabrication simplified while improved actuation force is provided toward core
30
which may preferably be the lower core of cores
28
and
30
allowing improved opening, for example, of an exhaust valve where exhaust back pressures resist that opening and greater initial forces are required.
Referring now to
FIG. 7
, the operation of the teeth
44
and sockets
46
such as provide an interdigitation of the armature plate
34
and the cores
28
and
30
promotes a mutual inductance between an activated one of the coils
24
and the other inactivated coil
26
or visa versa. This mutual inductance is dependent on the position of the armature plate
34
with respect to those coils
24
and
26
and the armature plate
34
, which serves as a magnetic pathway between these two coils
24
and
26
. Accordingly, a measure of the mutual inductance may be used to determine the position of the armature plate
34
.
During activation of one coil (
24
for example) by means of a switching amplifier
60
producing a fluctuating magnetic field, an induced current will be detectable in the other coil
26
dependent on the proximity of the armature plate
34
to that coil
26
. The switching amplifier
60
may be a hysteretic amplifier switching current to the coil
24
on and off in a varying duty cycle to control the average current to a predetermined amount dictated by a s control signal
62
indicating that the valve should be opened or closed.
Both of the coils
24
and
26
are connected to a mutual inductance calculator
68
receiving a measure of drive current through the coil
24
and induced voltage across the coil
26
to deduce a measure of mutual inductance. This measure may be provided to a look-up table
70
to be related to an armature position according to empirically derived table entries. The armature position is provided to a controller (not shown) which uses it to allow sophisticated control of the valve operation.
Generally, as shown in
FIG. 8
, the mutual inductance calculator
68
will see a voltage curve
70
following a decreasing envelope
72
as the armature plate
34
moves toward the activated coil
24
. This envelope
72
may be compared by the mutual inductance calculator
68
to the current output to the coil
24
by the switching amplifier
60
(which is also varying according to the signal
62
received by the switching amplifier
60
to control armature plate velocity) and the relationship between current and voltage is used to deduce the mutual inductance and hence the position of the armature plate
34
. This position is used by a valve controller (not shown) to control armature plate velocity. Depending on that velocity, the drive current to coil
24
may be increased or decreased to provide for a soft seating of the valve.
Generally the position signal will be used to decrease the current drive as the armature plate
34
approaches the respective coil so that the armature plate and electromagnet will contact at zero velocity. Subsequent to that time, a holding current less than the capture current used to draw the armature plate
34
in is used to hold the armature plate
34
in position making use of the far greater forces that exist when the electromagnet armature plate contacts. Other more complex control strategies may be enabled by this system.
Upon seating of the valve and a contacting of the armature plate
34
against the core
28
, a holding current is maintained as is understood in the art until the time when the valve state is to be changed and switching amplifier
60
output to coil
24
is turned off. The valve controller (not shown) will then provide a signal to the switching amplifier
60
to connect to coil
26
via an internal commutator formed of solid state switches as is understood in the art. Now the process is reversed with coil
24
serving to provide a position measurement of the armature plate
34
as it is drawn to coil
26
.
The teeth
44
and sockets
46
provide improved inductive coupling between the two coils
24
and
26
thus rendering this technique practical and provide increased linearity of the forces exerted on the armature plate
34
by the respective coils
24
and
26
rendering improved control of the armature motion possible.
The above description has been that of a preferred embodiment of the present invention, it will occur to those that practice the art that many modifications may be made without departing from the spirit and scope of the invention. For example, it will be understood that an auxiliary coil may also be used for the purpose of measuring mutual inductance or other magnetic sensing means. In order to apprise the public of the various embodiments that may fall within the scope of the invention, the following claims are made.
Claims
- 1. An actuator for use with an engine valve, the valve having a valve stem and a valve head, the valve head sized to cover a valve seat of an internal combustion engine, the actuator comprising:a first and second coil receiving a coil current and opposed along a common actuation axis and spaced apart by an actuation distance; a first and second core incorporating the first and second coils, respectively, and presenting opposed core faces across the actuation distance; valve stem supports holding the valve stem aligned with the actuation axis for movement along the actuation axis; an armature plate extending in a plane perpendicular to the actuation axis and attached to the valve stem for movement therewith along the actuation axis; at least one spring attached to the armature plate to bias the armature plate to a neutral position between the core faces; and wherein the armature plate and a core face of at least one core have a mating tooth and socket extending parallel to the actuation axis, the tooth and socket sized to provide a more constant relationship in the attractive force between the core and the armature as a function of separation distance between the core face and the armature for a constant coil current.
- 2. The actuator of claim 1 wherein the tooth is on the armature plate and the socket is on the core.
- 3. The actuator of claim 2 wherein the socket is centered about the coil of the core.
- 4. The actuator of claim 1 wherein the tooth is on the core and the socket is on the armature plate.
- 5. The actuator of claim 4 wherein the tooth surrounds the coil of the core.
- 6. The actuator of claim 1 including multiple teeth and sockets radially displaced with respect to the valve stem on mating portions of the core face and armature inside and outside the radial position of the coil.
- 7. The actuator of claim 1 wherein the valve is attached to the armature to move away from the valve seat when the armature plate moves toward a lower core and wherein the tooth and socket are on facing portions of the armature plate and lower core only.
- 8. The actuator of claim 1 wherein the armature plate is symmetric about a plane perpendicular to the actuation axis.
- 9. The actuator of claim 1 wherein the armature plate further includes a plurality of slots extending into the armature plate across a direction of eddy current flow as induced by a magnetic field produced by the coil current.
- 10. The actuator of claim 1 including further:a switching amplifier receiving a valve control signal to produce the coil current for a first of the coils; a mutual inductance calculator communicating with a second of the coils to sense a decrease in mutual inductance from a coupling between the second coil and the first coil as a function of armature position to provide a position output indicating armature position.
- 11. The actuator of claim 10 wherein the switching amplifier further includes an input related to the position output to modify the coil current thereby to control armature velocity.
- 12. The actuator of claim 10 wherein the mutual inductance calculator corrects the position output to compensate for modifications of the coil current made by the switching amplifier.
- 13. The actuator of claim 10 wherein the switching amplifier produces a switched coil current.
- 14. The actuator of claim 10 wherein the switching amplifier includes further a commutator switching the drive current to different coils according to the valve control signal received by the switching amplifier.
US Referenced Citations (10)