Internal-combustion engines – Poppet valve operating mechanism – Electrical system
Reexamination Certificate
2001-03-16
2002-12-31
Corrigan, Jaimie (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Electrical system
C251S129150, C251S129160
Reexamination Certificate
active
06499447
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
This application claims the priority of German Application No. 100 12 988.8, filed Mar. 16, 2000, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a process for operating an electromagnetic actuator and, more particularly, to a process for actuating a gas exchange lift valve of an internal combustion engine, with an armature, which is moved oscillatingly between two electromagnetic coils against the force of at least one return spring via an alternating supply of current to the electromagnetic coils.
A preferred application for an electromagnetic actuator of the type described above is for electromagnetically actuating a valve drive mechanism of an internal combustion engine. That is, the gas exchange lift valves of an internal combustion piston engine are actuated by such actuators in the desired manner, so as to be opened and closed in an oscillating manner. In such an electromechanical valve drive mechanism, the lift valves are moved individually (or also in groups) by means of electromechanical actuating elements - the so-called actuators - whereby the time for opening and closing each lift valve can be selected in essence arbitrarily. Thus, the valve timing of the internal combustion engine can be adjusted optimally to the current operating state (which is defined by the speed and the load) and to the respective requirements with respect to consumption, torque, emission, comfort and response characteristics of a motor vehicle, driven by the internal combustion engine.
The essential components of a known actuator for actuating the lift valves of an internal combustion engine are an armature and two electromagnets for holding the armature in the position “lift valve open” or “lift valve closed” with the related electromagnetic coils. Furthermore, return springs are provided for the movement of the armature between the position “lift valve open” and “lift valve closed”. In this respect reference is also made to the attached
FIG. 1
, which depicts such an actuator with a related lift valve in the two possible end positions of the lift valve and the actuator-armature. Between the two illustrated states or positions of the actuator lift valve unit, diagrams illustrate the curve of the armature lift z or the armature path between the two electromagnetic coils and, furthermore, the current flow I in the two electromagnetic coils over time t in accordance with the known state of the art (which is simpler than the mechanism described in German Patent document DE 195 30 121 Al, discussed in the introductory part of the specification).
FIG. 1
depicts the closing operation of an internal combustion engine lift valve, which is marked with the reference numeral
1
. As usual, a valve closing spring
2
a
acts on the lift valve
1
. Furthermore, the actuator, which is generally designated by reference numeral
4
in its entirety, acts on the shaft of the lift valve
1
- here with intercalation of a hydraulic valve play compensating element
3
(which is not absolutely necessary). The actuator
4
comprises not only two electromagnetic coils
4
a,
4
b,
but also a push rod
4
c,
which acts on the shaft of the lift valve
1
and which bears an armature
4
d.
The armature
4
d
can be slid longitudinally and oscillatingly between the electromagnetic coils
4
a,
4
b.
Furthermore, a valve opening spring
2
b
acts on the end of the push rod
4
c,
facing away from the shaft of the lift valve
1
.
Thus,
FIG. 1
depicts an oscillatory system, for which the valve closing spring
2
a
and the valve opening spring
2
b
form a first and a second return spring, for which consequently the reference numerals
2
a,
2
b
are also used.
The first end position of this oscillatory system is shown on the left hand side of
FIG. 1
, where the lift valve
1
is completely open and the armature
4
d
rests against the bottom electromagnetic coil
4
b.
This coil
4
b
is also called hereinafter the opener coil
4
b,
since it holds the lift valve
1
in its opened position.
The second end position of the oscillatory system is shown on the right hand side of
FIG. 1
, where the lift valve
1
is completely closed and the armature
4
d
rests against the upper electromagnetic coil
4
a.
This coil
4
a
is also called hereinafter the closer coil
4
a,
since it holds the lift valve
1
in its closed position.
At this point, the closing operation of the lift valve
1
will now be described, that is, in
FIG. 1
the transition from the open state, illustrated on the left hand side, into the closed state, illustrated on the right hand side. Between the two sides the corresponding curves of the electrical currents I, flowing into the coils
4
a,
4
b,
and the lift curve or the path coordinate z of the armature
4
d
are plotted, respectively, over time t.
Starting from the left-hand side position “lift valve open”, the supply of current is guided first to the opener coil
4
b
so that the armature
4
d
pushes in this position against the stressed valve closing spring
2
a
(=bottom first return spring
2
a
), whereby the current I in this coil
4
b
is shown with a dashed line in the I-t diagram. If at this stage the current I of the opener coil
4
b
is turned off for a desired transition to “lift valve closed”, the armature
4
d
detaches from this coil
4
b
and the lift valve
1
is accelerated by means of the stressed valve closing spring
2
a
into approximately its central position (in the direction toward the top of the page), but then continues to move owing to its mass inertia so as to thereby stress the valve opening spring
2
b,
so that the lift valve
1
(and the armature
4
d
) are decelerated. Then, at an appropriate time, the supply of current is guided to the closer coil
4
a
(the current I for the coil
4
a
is shown with a solid line in the I-t diagram). Thus, this coil
4
a
“catches” the armature
4
d
(this operation is the so-called “catch” process), and holds it finally in the position “lift valve closed”, illustrated on the right hand side of FIG.
1
. After the armature
4
d
has been securely caught by the coil
4
a,
the current in this coil is switched over, moreover, to a lower holding current level (see I-t diagram).
Starting from the position, illustrated on the right hand side in
FIG. 1
, the reverse transition from “lift valve closed” to “lift valve open” takes place analogously. The current I in the closer coil
4
a
is turned off and the current for the opener coil
4
b
is turned on with a time delay. Generally, for the supply of current to be guided to the coils
4
a,
4
b,
sufficient electric voltage is applied to said coils, whereas the turning off of the electric current I is triggered by lowering the electric voltage to the value “zero”. The necessary electric energy for operating each actuator
4
is taken either from the electrical system of the vehicle, driven by the related internal combustion engine, or provided by means of a separate energy supply, adjusted to the valve drive mechanism of the internal combustion engine. In this respect the electric voltage is held constant by the energy supply; and the coil current I of the actuators
4
, assigned to the internal combustion engine lift valves
1
, is controlled in such a manner by a controller that the necessary forces for the opening, closing and holding of the lift valve(s)
1
in the desired position are generated.
In the state of the art, described above, the aforementioned controller or a control unit adjusts through timing the coil current I during the so-called catch process (wherein one of the two coils
4
a,
4
b
endeavors to catch the armature
4
d
) to a value that is large enough to catch reliably the armature
4
d
under all conditions. Now the force of the catching electromagnetic coil
4
a
or
4
b
on the armature
4
d
is approximately proportional to the current I and inversely proportional to the distance between the coil and the armature. If at this stage—as in the known state of the art
Cosfeld Ralf
Reif Konrad
Bayerische Motoren Werke Aktiengesellschaft
Corrigan Jaimie
Crowell & Moring LLP
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