Note: Descriptions are shown in the official language in which they were submitted.
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The invention relates generally to the energization of
an electromagnet and, more particularly, to the energization
of an electromagnet of the kind useful in driving and
retaining a gas exchange valve of an internal combustion
engine in its terminal positions.
It is well known that an electromagnet requires
significantly higher current le~els for attracting the
armature into engagement with its stator or pole piece than
it requires for subsequently maintaining the engagement. It
would, therefore, be possible to reduce the energy
consumption of an electromagnet during each operating cycle
~y initially driving it at the high current level required
for attracting the armature into engagement with the stator
and by thereafter reducing the current to a level sufficient
15 to maintain the engagement.
The invention is directed, inter_alia, to an
electromagnetic operation in which an ~lectromagnet
cyclically repeats its operation of attracting and
maintaining its armature in engagement with its stator, each
operating cycle consisting of a high current level phase
followed by a phase of reduced current level.
Electromagnetically controlling the driving of gas
exchange valves of internal combustion engines moved between
their open and closed positions by spring bias is one
possible field of advantageous application of the
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pre~ent lnvention. Such a system has been generally dis-
closed in west German Patent Specification DE-OS 30 2~ 109.
One of the problems encountered in operating a
gas exchange valve in the manner referred to resides in
the fact that the instant at which energization of the
electromagnet has -to commence must be chosen in such a
manner that even at slowly increasing current the armature
is a~tracted into engagement with the stator at a
predetermined time. This, however, is affected by such
variables as changes in temperature and supply voltage,
current distribution, or changes occurring generally
during the course o~ engine operation. '~hese variables
cannot be neglected since on the one hand the voltage
supply of an automotive vehicle i5 subject to considerable
variations and, on the other hand, the temperature o~ an
internal combustion engine during its initial start~up
operation is markedly different from its normal operating
temperature. One way of operating electromagnetically
controlled gas exchan~e valves in a manner assuring proper
engine performance would be to drive its electromagnets at
high but energy consuming currents levels.
Circuits accommodating the attraction and reten-
tion phases during energiæation cycles of electromagnets
are generally known and have been found to be useful in
reducing the energy that would otherwise be required or
properly drivin~ such electromagnets. Such a reduction in
energy requirements is oE particular advantage in automo-
tive vehicles where solenoids have of late found applica-
tion for controlling the movement of gas exchange valves.
A driver circuit for energizing an electroma~net
of this kind is generally disclosed in west German Patent
D~-A 35 07 103. The circuit purports to provide for reli-
able switchin~ between an attracting or energizing phase
and a subse~uent retention or holding phase during an
operating cycle o~ an electromagnet. Assured attraction of
the armature o~ the electromagnet against its stator is
said to be attainable by monitoring the current in the
coil of the solenoid, for instance by measuring the maximum
current level. During the energization or at-traction phase the
current is measured by a comparator. A similar arrangement of
current level monitoring of means of a comparator is the general
sub~ect of west German Patent Specification DE-A 29 32 859.
s The devices of the prior art may function satisfactorily under
certain static operating conditions. They fail, however, to take
into consideration the dynamics of autumotive engine operation.
For instance, variations in the rate of current level increases
as a result of temperature-induced changes ln the inductance of
the solenoid coil, would prevent, or at least mitigate against,
an assured attraction of the solenoid armature against the
stator.
It is, of course, well-known that proper operation of an internal
combustion engine requires flawless operation of its gas exchange
valves. That is to say, fuel intake and exhaust valves must move
between their open and closed positions in phase with the
movement of the piston. Movement of the valves out of phase with
the piston, or no movement at all, would result in faulty or no
running of the engine, and may ha~e a serlously adverse effect on
fuel consumption.
The present invention provides for circuitry which permits proper
operation of an electromagnet for driving a gas exchange valve.
The invention also provides circuitry for eneryizing an
electromagnet in a manner which comp~nsates for changes in its
inductance.
The invention further provides circuitry which determines the
instant at which energization of an electromagnet must commence
to move the armature into engagement with the stator at a
predeterm~ned time.
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The invention again provides an energization circuit for an
electromagnetic gas exchange valve actuator whlch determines the
instant at which energization must commence to assure proper
valve functioning changes in the inductance of the electromagnet
notwithstanding.
The invention also provides circuitry for commencing energization
of an electromagnet at an instant depending on the rate of
current increase during the previous operating cycle of the
electromagnet.
The invention further provides for circuitry responsive to the
operational pàrameters of an internal combustion engine for
determining the rate of energization of an electromagnet used for
driving a gas exchange valve.
The invention also provides an ene~gization circuit for an
electromagnet used for driving a gas exchange valve which is
responsive to changes in vol-tage levels or operating temperature
for determining the instant at which energization commences.
The invention again provides a method of energizing an
electromagnet used for controlling the movement of a gas exchange
valve in a manner compensating for changes in operating
conditions and current levels.
Thus according to the present invention there is provided
apparatus for periodically energizing an electromagnet, each
period lncluding a phase for driving the armature of the
electromagnet to engage the stator at a predetermined time and a
phase for maintaining said engagement, comprising: means actuable
at a predetermined instant during each period for selectively
connecting said electromagnet to a source of energizing current;
means ior measuring changes in the energizing current ~lowing in
said elec-tromagnet during at least a portion of said period;
means for deriving ~rom said change in current a value
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representative oE said instant for a subse~lent period and means
responsive to said deriving means for actuating said connecting
means. Suitably said measuring means comprises current level
detection means having an input connected to resistance means
between said electromagnet and said source of current. Desirably
said measuring means further comprises an output member connected
to switch means between said electromagnet and said source of
current. Preferably said switch means comprises a transistor
hav~ng its base connected to said output member of said measuring
lo circuit.
In one embodiment of the present invention said measuring means
comprises first timing means for defining the length of sald
portion of said period. Suitably said measuring means comprises
storage means for storing a value representative of the current
level in the electroma~net at the end of said portion. Desirably
said apparatus further comprises second timing means connected to
said storage means for generating a signal derived from said
stored current level value for actuating said connecting means.
Preferably said second timlng means is connected to logic circuit
means, said logic circuit means controlling the actuatlon of said
connecting means. Desirably said logic circult means is
connected to said measuri~g means for controlling said output
member thereof. Preferably said logic circuit is connected to
said first timing means for controlling the actuation thereof~
The present invention also provides a method of periodically
energizing an electromagnet~ each period comprising a phase for
driving the armature of said electromagnet to engage said stator
at a predetermined time and a phase for maintaining said
engageme~t, comprising the steps of: connecting said
electromagnet to a source of energizing current at least during a
predetermined portion of said period; measuring the change ln
current at least during a part of said portion; and deriving from
sald change a value representatiYe of the instant at which said
electromagnet is to be connected to said source of energlzlng
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current in a subsequent period to cause engagement of the
armature with the stator at said predetermined tlme. Suitably
said measuring step commences at the beginning of said portion.
Preferably said measuring commences with said driving phase.
Desirably said measuring step is undertaken for a predetermined
period to measure the level of current extant in said
electromagnet at the end of said period. Suitably a value
representative of said extant current level i~ stored in storage
means. Deslrably said value determines the instant at which said
electromagnet is connected to said source of energizing current
in a subsequent period.
In one embodiment of the invention said measuring step is
undertaken for a period sufficient for the current to decay to a
predetermined level. Suitably a~value representative of said
level is storsd in storage means for determining the instant at
which said electromagnet is connected to said source of
energizing current in a subsequent period.
The invention accordingly comprises a mechanism and system
possessing the construction, com~ination of ~lements and
arrangements of parts whlch are exemplified in the detailed
disclosure.
The invention provides novel circuitry for periodically
energizing an electromagnet in cycles including an energization
phase and a subseguent holding phase, comprising means for
monitoring current levels in the electromagnat at least during a
portion of the e~ergization phase and means responsive to a
predetermined current level for adjusting the instant at which
energization of the electromagnet must commence in a subsequent
- energization cycle. Means may be provided for monitoring the
rate of change in the current level during a predetermined
interval during the energization phase. In accordance with the
invention the monitoring interval may commence simultaneously
with the flow of energizing current. In accordance with the
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invention means may also be provided for monltoring the rate of
current increase up to a predetermined threshold level.
Advantageously, the circuit in accordance with the invention
comprises logic circuit means ~or controlling the flow of current
S through the electromagnet in response to external control
signals, level detecting means for monitoring the level of
current flowing in the electromagnet, a first variable timing
member for providing an input signal to the logic circuit means
for defining the instant at which the flow of energizing current
commences, and a second timing member operatively connected with
the level detecting means for monitoring the rate of change of
the current level. In accordance with the invention the second
timing member defines a predetermined interval at the end of
which the level detecting means is actuated to transfer a current
value stored therein to a storage means. Alternatlvely, the
second timing member may comprise means for monitoring the time
required for reaching the threshold value and for transferring
this value to a storage means. Furthermore, means may be
provided for adjusting the interval generated by the first timing
member in response to the value stored within the storage means.
The present invention will be further illustrated by way of an
illustrative embodiment when read in connection with the
accompanying drawings, in which:
FIG. l is a diagram of a circuit in accordance wlth the
invention for energ1zing an electromagnet;
:
FIG. 2 is a graphical representation of
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electrical signals generated by the clrcuit of FIG. 1;
FIG. 8 i~ a diagram of a circui.t o.f an alternate
embodime~t of the invention; and
FIG. 4 is a ~raphical representation of
electrical signals yenerated by the circuit of FIG. 3.
DESCRIPTION OF THE ~ D~D '~y~DI-MENTS
FIG. 1 shows an electromagnet or solenoid 10 with
a freewheeling or feedback circuit 24 connected in paral-
lel thereto. A diode 12 is connected in the freewheeling
circuit 24 to control the direction o~ current ~low there-
in. ~ne side of the solenoid 10 is connected to the posi-
tive terminal 14 of a voltage supply . The other side o~
the ~olenoid 10 is connected, by way of a line 22, to
ground 16. A bias resistor 20 and a switch, shown as a
transistor 18, are connected in series between the sole-
noid 10 and ground 16. The purpose of the resistor 20 is
to provide a signal representative o~ a predetermined
level of current in the solenoid 10. This signal is
applied to a first input terminal of a measuring circuit
or level detector A by way of a line 26 connected to the
junction o~ the transistor 18 and the resistor 20. The
level detector A may be of a kind well known in the art
and i~ deemed not to require further description. A first
output 28 o~ the level detector A is connected to the base
of the transistor 18. A second input 30 of the level
detector A i5 connected to the output of a logic circuit B
which at times applies to the level detector A a pulse
controlling the instant at which energization of the
solenoid 10 must commence to assure engagement of the
ar~nature with the stator o~ the electromagnet at the
proper time.
The logic circuit B in turn is connected by a
line 40 to a first timing circuit ~ which clocks an
interval at the expiration of which the transistor 18 must
be rendered conductive by the pulse applied to its base by
the level detector A. To start its timing function the
timing circuit E responds to a pulse S1 supplied from an
external source (not shown) along line 42.
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A second o~tp~t of the level d~tector A is
connected to a storage register C along line 32. The
register C ~urnishes signals representative of its
contents to the first timing circuit ~ by way of a line
34, as well as to a se~ond timing circuit D along li.ne 36.
The second timing circuit D i~ also connected to the logic
circuit B by a line 38.
The instant at which energization of the elec-
tromagnet 10 must commence is determined as follows:
The pulse S1 is fed to the timing circuit E. The
pulse S1 i9 shown at 2c in FIG. 2. The timing member E
responds to the leading edge of the pulse 2c to start its
timing function and furnishes a pulse shown in FIG. 2 at
2g. The trailing edge of the pulse 2g determines the time
t1 at which logic circuit B applies a pulse to the level
detector A to render the transistor 18 conductive. Once
the transistor 18 conducts, energizing current begins to
flow through the solenoid 10 as shown by curve 2a. The
energizing current i~creases until time to at which
inst~nt the armature strikes the stator to be retained by
it. The energi2ation phase is thus safely termi~ated.
Striking of the stator by the armature is usually accom-
panied by a current drop of short duration as shown by the
slight break in curve 2a, owing to the change in the
inductance o~ the solenoid coil,.
In accordance with the invention, the flow of
current in the solenoid is monitored during the energi-
zation phase, and any drop in voltage is detected by the
level detector A. At the same time as the energization
phase commences the second timing member D is aotuated as
shown by curve 2e of FIG. 2. At the instant of the
trailing edge of pulse 2e a signal of the current level
--W1 in FIG 1-- then present in the level detector A is
~ed to, and stored in, the register C.
Thereafter, at time to, a signal 2d i5 applied to
an input gate of the lo~ic circuit B. Signals S1 and S2
are present during the holding phase of the cycle. Short-
ly be~-ore termination of the holding phase, the signal S
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is turned off, and the logic circuit ~ swltches from a
phase of prov.iding the electromagnet with cyclical holding
current pulses ~lowiny in the freewheeling or feedback
circuit 2~ to a phase oP con~tant current which at the
termination of signal S2 drops to O to deenergize the
electromagnet for the release of the armature.
In accordance with the invention the timing
circuit E reads the current value stored in register C
before a new energization cycle is commenced, for the
interval 2g set by the timing circuit E is derived from
the current value stored in register C.
If, ~or instance because o~ higher operating
temperatures or a lower supply voltage, the inc~ease in
current is slower as shown for instance by curve 2b than
that shown by curve 2a, the voltage is monitored during an
interval 2f starting at tim~ t2 and set by the second
timing circuit D. In the example shown it will have
reached value W2 --which is lower than W1-~ at the end of
the interval set by the second timing circuit D.
OThe interval set by the first timing circuit E for the
succeeding energization cycle is a function f W2. The
pulse will be shorter since the energization commences
earlier.
For this reason and as shown at 2h in FIG. 2, the
first timing circuit E releases its W2 derived pulse upon
receipt of pulse S1 depicted by curve 2c. The pulse ?h is
markedly shorter than pulse 2g of the previous energi-
zation cycle. Hence, the energization current of the new
cycle begins to flow at the earlier instant tz.
As previously mentioned, the present invention
may advanta~eously be applied to the control of gas
exchange valves of internal combustion engines.
Therefore, each second of operation entails several
energization cycles. However, the paramet~rs affecting
the slope or profile of the energizing current flow change
comparatively slowly. Thus, i~ may not always be
necessary to make adjustments in response to abrupt
changes in engine operation. The invention does, however,
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provide simple means responding to significant changes in
operating conditions for making appropriate adjustments,
and ~or assuring flawless opening and closing o the
valves at a very low energy consumption level.
FIG. 3 depicts an alternative embodiment of the
invention. The circuit of this embodiment differs from
the one of Fig. 1 in that the bias resistor 20' is
connected in the ~reewheeling circuit 24' rather than
hetween the transistor 18 and ground 16. In all other
respects the circuit arrangement is substantially the same
as that o~ FIG. 1. Therefore, the reference characters
are those o~ FIG. 1, but they have been primed.
Curve ~a in FIG. ~ depict~ a curr~nt profile
comprising an energising phase and a holding phase
substantially identical to that of curve 2a, except that
in this case evaluation or monitoring of the profile
commences when the energizin~ current is turned of f .
Instead o~ monitoring th~ rise in current during
a predetermined interval as in the previous embodime~t,
the circuit of FIG. 3 measures the interval required for
the current in the feedback circuit 24' to decay from the
peak energi~ation level W1' to a lower level W2'. The
interval is represented as pulse ge. The length oE the
pulse 4e is in this case detected by the second timing
circuit D' and is stored in the register C'. It will
subse~uently determine the timing interval ~f the first
~iming circuit E' shown as curve 4g'. To be ahle to
measure the current in the freewheeling circuit 24' the
bias resistor 20' must, of course, be connected in the
~eedback circuit 24'.
Energization o~ the electromagnet 10' commences
with a pulse S1 shown by curve 4c. The pulse S1 also
starts the timing circuit E'. Curve 4g depicts the
interval set by the timing circuit E' under conditions of
a relatively teep current increase.
However, where the current increases at a
relatively slow rate as shown by curve 4b, the drop in
current from W1' ~o W2' re~uires a commensurately longer
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interval. Thus, a value is stored in the register C' which
corresponds to the pulse shown at 4f. Thi.s value controls
the subsequent energization cycle by causing the timing
circuit to yenerate a signal as shown at 4h. Hence, the
instant at which the transistor 18' begins to conduct occurs
earlier than in the previous energization cycle.
Those skilled in the art will appreciate that the
measuring of current as described in connection with the
embodiment of FIG. 1 may al50 take place at the trailing
flank of the energizing current curve, and that the measurin~
of current described in connection with the embodiment of
FIG. 4 could also be done in the leading flank of the
energizing current curve.
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