U.S. patent application number 10/042084 was filed with the patent office on 2002-07-18 for method and device for charging a capacitive actuator.
Invention is credited to Hoffmann, Christian, Lingl, Wolfgang, Pirkl, Richard.
Application Number | 20020093313 10/042084 |
Document ID | / |
Family ID | 7913870 |
Filed Date | 2002-07-18 |
United States Patent
Application |
20020093313 |
Kind Code |
A1 |
Hoffmann, Christian ; et
al. |
July 18, 2002 |
METHOD AND DEVICE FOR CHARGING A CAPACITIVE ACTUATOR
Abstract
A method and a device for charging a capacitive actuator are
described. The capacitive actuator, in particular for a fuel
injection valve of an internal combustion engine, is charged or
discharged with different charging and discharging times. In order
to shorten the charging time, the capacitance of the recharging
capacitor which is dimensioned for a maximum charging time is
reduced at a predefined time during the charging process. Two
exemplary embodiments of a device for carrying out the method are
explained in more detail.
Inventors: |
Hoffmann, Christian;
(Regensburg, DE) ; Lingl, Wolfgang; (Regensburg,
DE) ; Pirkl, Richard; (Regensburg, DE) |
Correspondence
Address: |
LERNER AND GREENBERG, P.A.
Post Office Box 2480
Hollywood
FL
33022-2480
US
|
Family ID: |
7913870 |
Appl. No.: |
10/042084 |
Filed: |
January 7, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10042084 |
Jan 7, 2002 |
|
|
|
PCT/DE00/02216 |
Jul 6, 2000 |
|
|
|
Current U.S.
Class: |
320/166 |
Current CPC
Class: |
F02D 41/2096 20130101;
F02D 2041/201 20130101; F02D 2041/2006 20130101; F02D 2041/2017
20130101; H02N 2/067 20130101 |
Class at
Publication: |
320/166 |
International
Class: |
H02J 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 7, 1999 |
DE |
199 31 235.4 |
Claims
We claim:
1. A method for charging a capacitive actuator from a charge source
through a series circuit formed of a recharging capacitor and a
recharging coil, and for discharging the actuator into the
recharging capacitor having a much smaller capacitance than the
charge source, which comprises the steps of: dimensioning the
recharging capacitor to have a maximum capacitance for a predefined
maximum charging time; and reducing the capacitance of the
recharging capacitor to a predefined value at a specific point in
time after a start of a charging process for achieving a shorter
charging time.
2. The method according to claim 1, which comprises: reaching the
maximum capacitance of the recharging capacitor using a parallel
connection of at least two recharging capacitors; and disconnecting
at least one of the two recharging capacitors from the charge
source at the specific point in time after the start of the
charging process.
3. The method according to claim 1, which comprises using the
actuator in a fuel injection valve of an internal combustion
engine.
4. A device for charging a capacitive actuator, comprising: a
charge source to be connected to a power source; a first series
circuit disposed between said charge source and the capacitive
actuator, said first series circuit having a first charge switch, a
first blocking diode connected to said first charge switch, a first
recharging capacitor connected to said first blocking diode, and a
recharging coil connected to said first recharging capacitor; a
reference potential terminal; a discharge switch connecting a
connecting point of said first blocking diode and said first
recharging capacitor to said reference potential terminal; at least
one second series circuit containing a second charge switch, a
second blocking diode connected to said second charge switch, and a
second recharging capacitor connected to said second blocking
diode, said second series circuit connected in parallel with a
third series circuit composed of said first charge switch, said
first blocking diode and said first recharging capacitor; a control
circuit connected to and controlling said discharge switch, said
first charge switch and said second charge switch, said control
circuit switching on simultaneously said first charge switch and
said second charge switch for charging the capacitive actuator, and
one of said first charge switch and said second charge switch being
switched off at a specific point in time for removing a capacitive
effect of one of said first recharging capacitor and said second
recharging capacitor; a third diode for conducting current in a
direction of said discharge switch and connected between said first
and second recharging capacitors; and a fourth diode for conducting
the current and disposed between said first recharging capacitor
and said discharge switch.
5. The device according to claim 4, wherein if said discharge
switch is conductive, the capacitive actuator is discharged through
said first recharging capacitor and through said second recharging
capacitor.
6. The device according to claim 4, wherein said first charge
switch, said second charge switch and said discharge switch are
MOSFET switches.
7. A device for charging a capacitive actuator, comprising: a
charge source to be connected to a power source; a first series
circuit disposed between said charge source and the capacitive
actuator, said first series circuit having a first charge switch, a
first blocking diode connected to said first charge switch and
conducting way from said first charge switch, a first recharging
capacitor connected to said first blocking diode, and a recharging
coil connected to said first recharging capacitor; a reference
potential terminal; a second blocking diode connected to a
connection point of said first blocking diode and said first
recharging capacitor and conducting current toward said reference
potential terminal; a third blocking diode connected in series with
said second blocking diode and having a current conducting
direction equivalent to that of said second blocking diode; a
discharge switch connected to said third blocking diode and
coupling said connecting point of said first blocking diode and of
said first recharging capacitor to said reference potential
terminal through said second blocking diode and said third blocking
diode; a second series circuit formed of a second recharging
capacitor, a second charge switch connected to said second
recharging capacitor, and a fourth blocking diode connected to said
second charge switch, said second series circuit connected between
said reference potential terminal and a connecting point of said
first recharging capacitor and said recharging coil, said fourth
blocking diode conducting current in a direction from said
reference potential terminal to said second recharging capacitor,
said fourth blocking diode having a cathode connected to said
connecting point of said second and third blocking diodes; and a
control circuit connected to and controlling said discharge switch,
said first charge switch and said second charge switch, said
control circuit switching on simultaneously said first charge
switch and said second charge switch for charging the capacitive
actuator, and one of said first charge switch and said second
charge switch being switched off at a specific point in time for
removing a capacitive effect of one of said first recharging
capacitor and said second recharging capacitor.
8. The device according to claim 7, wherein if said discharge
switch is conductive, the capacitive actuator is discharged through
said first recharging capacitor, and through said second recharging
capacitor and said second charge switch or said fourth blocking
diode.
9. The device according to claim 7, wherein said second charge
switch is operated inversely with respect to said charge switch,
that is to say said second charge switch is switched on when said
discharge switch is switched off, and vice versa.
10. The device according to claim 8, wherein said first charge
switch, said second charge switch and said discharge switch are
MOSFET switches.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of copending
International Application PCT/DE00/02216, filed Jul. 6, 2000, which
designated the United States.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to a method for charging a capacitive
actuator, in particular for a fuel injection valve of an internal
combustion engine. The invention also relates to a device for
carrying out the method.
[0004] One of the advantages when actuating fuel injection valves
of an internal combustion engine by piezo actuators instead of
solenoids is the short switching time of the actuators, which leads
to steep needle edges and low degrees of variation of the injected
quantities of fuel. From the point of view of combustion
technology, charging times that are as short as possible are to be
aimed at.
[0005] In order to achieve a more gentle combustion profile, the
quantity of fuel is divided into a pre-injection quantity and main
injection quantity, which permits slower combustion and thus makes
it possible to reduce the combustion noise. The actuators have
previously been actuated with a constant charging and discharging
time (a duration of the transfer of charge from a power source to
the actuator, or vice versa), which must be very short (for example
100 .mu.s ) so that a predefined pre-injection fuel quantity can
still be injected even in the highest load range or rotational
speed range of the internal combustion engine.
[0006] The charging process takes place, for example, as a ringing
process which includes the charging from one charge source (of a
series connection of a charging capacitor and of a recharging
capacitor) via a recharging coil to the actuator. An inductance of
the recharging coil determining, together with capacitances of the
recharging capacitors and of the actuator, the time constant for
the charging and discharging processes (the charging and
discharging time). Such a device is known from German Patent DE 196
52 801.
[0007] German Patent DE 195 29 667 C2 discloses a configuration for
the actuation of two piezoelectric actuators in which the frequency
of the oscillating circuits in which the piezoelectric actuators
are disposed can be changed in order to compensate for temperature
effects and aging effects.
[0008] Published, Non-Prosecuted German Patent Application DE 197
14 607 A1 describes a method for incrementally charging and
discharging a piezoelectric element. The recharging process is
switched over to a specific point in time after the start of
charging from a charging path with a resistor and a capacitor to a
charging path with a coil and a further capacitor. The discharging
process takes place in reverse order.
[0009] However, the short charging times lead to high noise
emissions in frequency ranges which are unpleasant for human ears.
This is felt to be very troublesome, for example in a motor
vehicle, if the combustion noises are low when the internal
combustion engine is idling.
SUMMARY OF THE INVENTION
[0010] It is accordingly an object of the invention to provide a
method and a device for charging a capacitive actuator which
overcome the above-mentioned disadvantages of the prior art devices
and methods of this general type, which makes possible a
significant reduction in the noise emissions of the actuator.
[0011] With the foregoing and other objects in view there is
provided, in accordance with the invention, a method for charging a
capacitive actuator from a charge source through a series circuit
formed of a recharging capacitor and a recharging coil, and for
discharging the actuator into the recharging capacitor having a
much smaller capacitance than the charge source. The method
includes the steps of dimensioning the recharging capacitor to have
a maximum capacitance for a predefined maximum charging time; and
reducing the capacitance of the recharging capacitor to a
predefined value at a specific point in time after a start of a
charging process for achieving a shorter charging time.
[0012] The charging times and the discharging times of the actuator
can be varied, in particular in a low-load and idling range of the
internal combustion engine, by various measures during the charging
process, for example in a range between 100 .mu.s and 200
.mu.s.
[0013] The method according to the invention consists in the fact
that the overall capacitance of the recharging capacitors via which
the actuator is charged, that is to say in this case the
capacitance of at least two recharging capacitors which are
connected in parallel and which make possible, for example, a
maximum charging time of 200 .mu.s, is reduced at a specific point
in time during a charging process by switching off at least one of
the parallel recharging capacitors, as a result of which the
charging time is shortened.
[0014] The following applies to the selection of optimum charging
times. The duration of the charging time limits the minimum period
of fuel injection. This is critical in particular at high injection
pressures because the injected quantity of fuel rises with the fuel
pressure that is proportional to the load, given an identical
period of injection. In order to achieve a specific injection
quantity, in particular a low pre-injection quantity, ever shorter
injection periods are therefore necessary as the fuel pressure
increases.
[0015] On the other hand, in the case of a main injection, the
injection quantities are load-dependent and/or pressure-dependent.
Given a low load, small injection quantities are required, but
given a high load large injection quantities with a high fuel
pressure are required. The correlation between the fuel quantity
and fuel pressure permits the use of relatively long charging times
for the main injection, even in the high load range.
[0016] Within certain limits, for example between 100 .mu.s and 200
.mu.s, different charging times of a capacitive actuator have no
influence on the injection profile which is relevant for a
combustion process, with the exception of delay effects (delays of
the start and end of injection) which can be compensated by
shifting the timing of the actuation signals.
[0017] In accordance with an added mode of the invention, there are
the steps of reaching the maximum capacitance of the recharging
capacitor using a parallel connection of at least two recharging
capacitors; and disconnecting at least one of the two recharging
capacitors from the charge source at the specific point in time
after the start of the charging process.
[0018] In accordance with an additional mode of the invention,
there is the step of using the actuator in a fuel injection valve
of an internal combustion engine.
[0019] With the foregoing and other objects in view there is
provided, in accordance with the invention, a device for charging a
capacitive actuator. The device contains a charge source to be
connected to a power source, and a first series circuit disposed
between the charge source and the capacitive actuator. The first
series circuit has a first charge switch, a first blocking diode
connected to the first charge switch, a first recharging capacitor
connected to the first blocking diode, and a recharging coil
connected to the first recharging capacitor. A reference potential
terminal is provided. A discharge switch connects a connecting
point of the first blocking diode and the first recharging
capacitor to the reference potential terminal. At least one second
series circuit is provided and contains a second charge switch, a
second blocking diode connected to the second charge switch, and a
second recharging capacitor connected to the second blocking diode.
The second series circuit is connected in parallel with a third
series circuit composed of the first charge switch, the first
blocking diode and the first recharging capacitor. A control
circuit is connected to and controls the discharge switch, the
first charge switch and the second charge switch. A third diode is
provided for conducting current in a direction of the discharge
switch and is connected between the first and second recharging
capacitors. A fourth diode is provided for conducting the current
and is disposed between the first recharging capacitor and the
discharge switch. The first charge switch and the second charge
switch are switched on simultaneously, by the control circuit, to
charge the capacitive actuator, and one of the first charge switch
and the second charge switch is switched off at a specific point in
time for removing the capacitive effect of one of the first and
second recharging capacitors.
[0020] In accordance with an additional feature of the invention,
if the discharge switch is conductive, the capacitive actuator is
discharged through the first recharging capacitor and through the
second recharging capacitor.
[0021] In accordance with a further feature of the invention, the
first charge switch, the second charge switch and the discharge
switch are MOSFET switches.
[0022] With the foregoing and other objects in view there is
provided, in accordance with the invention, a device for charging a
capacitive actuator. The device includes a charge source to be
connected to a power source, and a first series circuit disposed
between the charge source and the capacitive actuator. The first
series circuit has a first charge switch, a first blocking diode
connected to the first charging switch and conducts way from the
first charge switch, a first recharging capacitor connected to the
first blocking diode, and a recharging coil connected to the first
recharging capacitor. A reference potential terminal is provided. A
second blocking diode is connected to a connection point of the
first blocking diode and the first recharging capacitor and
conducts current toward the reference potential terminal. A third
blocking diode is connected in series with the second blocking
diode and has a current conducting direction equivalent to that of
the second blocking diode. A discharge switch is connected to the
third blocking diode and couples the connecting point of the first
blocking diode and of the first recharging capacitor to the
reference potential terminal through the second blocking diode and
the third blocking diode. A second series circuit is provided and
is formed of a second recharging capacitor, a second charge switch
connected to the second recharging capacitor, and a fourth blocking
diode connected to the second charge switch. The second series
circuit is connected between the reference potential terminal and a
connecting point of the first recharging capacitor and the
recharging coil. The fourth blocking diode conducts current in a
direction from the reference potential terminal to the second
recharging capacitor. The fourth blocking diode has a cathode
connected to the connecting point of the second and third blocking
diodes. A control circuit is connected to and controls the
discharge switch, the first charge switch and the second charge
switch. The first charge switch and the second charge switch are
switched on simultaneously, by the control circuit, to charge the
capacitive actuator, and one of the first charge switch and the
second charge switch is switched off at a specific point in time
for removing the capacitive effect of one of the first and second
recharging capacitors.
[0023] In accordance with another feature of the invention, if the
discharge switch is conductive, the capacitive actuator is
discharged through the first recharging capacitor, and through the
second recharging capacitor and the second charge switch or the
fourth blocking diode.
[0024] In accordance with a concomitant feature of the invention,
the second charge switch is operated inversely with respect to the
charge switch, that is to say the second charge switch is switched
on when the discharge switch is switched off, and vice versa.
[0025] Other features which are considered as characteristic for
the invention are set forth in the appended claims.
[0026] Although the invention is illustrated and described herein
as embodied in a method and a device for charging a capacitive
actuator, it is nevertheless not intended to be limited to the
details shown, since various modifications and structural changes
may be made therein without departing from the spirit of the
invention and within the scope and range of equivalents of the
claims.
[0027] The construction and method of operation of the invention,
however, together with additional objects and advantages thereof
will be best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a block circuit diagram of a device according to
the prior art;
[0029] FIG. 2 is a block circuit diagram of a first exemplary
embodiment of the device according to the invention;
[0030] FIG. 3 is a graph of charging and discharging times of the
exemplary embodiment shown in FIG. 2;
[0031] FIG. 4 is a block circuit diagram of a second exemplary
embodiment of the device according to the invention; and
[0032] FIG. 5 is a graph of the charging and discharging times of
the exemplary embodiment shown in FIG. 4.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0033] Referring now to the figures of the drawing in detail and
first, particularly, to FIG. 1 thereof, there is shown a basic
circuit of a known device for charging and discharging a capacitive
actuator P. The basic circuit is composed of a series circuit that
is connected to a ground reference potential at both ends and is
composed of a charge source which can be charged from a power
source V, a charging capacitor C1, a charge switch T1, a blocking
diode D1, a recharging capacitor C2, a recharging coil L and one or
more actuators P, P' which are connected in parallel, and a
selection switch S, S' connected in series with each of the
actuators P, P'. A terminal of the recharging capacitor C2 which
leads to the charge switch T1 can be connected to the ground
reference potential via a discharge switch T2 which is in series
with a further blocking diode D2. The two switches T1 and T2 are
controlled by a control circuit or switch ST. The capacitance of
the charge capacitor C1 is significantly higher than that of the
recharging capacitor C2: C1>>C2.
[0034] When the terms charging, discharging or selection switches
are used, switches are preferably to be understood which are
switched on or off, for example thyristors, or MOSFETs (with a
diode in a series connection) which automatically become
non-conductive again if the current flowing them drops to zero.
[0035] The charging of the actuator P takes place by closing
(switched on) the charge switch T1. Here, the charge moves backward
and forward with a current I in the form of a half sinusoidal
oscillation of the charge source (the charging capacitor C1) via
the recharging capacitor C2 and the recharging coil L to the
actuator P. During the charging time, the actuator voltage U rises
to a specific value, and the actuator P opens the fuel injection
valve. If the current I drops to zero, the charge switch T1 is
opened again (switched off), and the actuator voltage U is
maintained until the discharge process starts when the discharge
switch T2 is closed (switched on). The charge then moves backward
and forward from the actuator P into the recharging capacitor C2
via the recharging coil L. The actuator voltage U drops to zero
again, the current I drops to zero and the fuel injection valve is
closed by the actuator P. The discharge switch T2 must be opened
again (switched off) before the next charging process. An injection
process is thus terminated. Recharging into the charging capacitor
C1 is prevented by the blocking diode D1.
[0036] FIG. 2 shows a circuit of a first exemplary embodiment
according to the invention, which differs from the known circuit
according to FIG. 1 in that connected in parallel with a first
series circuit composed of a charge switch T1a, a blocking diode
Dia and a recharging capacitor C2a is a second series circuit of
the same type. The second series circuit is composed of a further
charge switch T1b, a further blocking diode D1b and a further
recharging capacitor C1b. The terminals of the two recharging
capacitors C2a and C2b which face the charging switches T1a and T1b
are connected to one another by a diode D2b which conducts current
from the recharging capacitor C2b to the recharging capacitor C2a.
Further series circuits of this type that are connected in parallel
can be provided, which is indicated by dotted arrows.
[0037] The mode of operation of the circuit is explained below with
reference to the diagram in FIG. 3 showing a current profile I in
the actuator P and the switched settings of the charge switches T1a
and T1b as well as the discharge switch T2. The two recharging
capacitors C2a and C2b are dimensioned in such a way that the
actuator P, (or P') is charged from a parallel connection of the
two capacitors C2a and C2b with a desired, maximum charging time
of, for example, 200 .mu.s.
[0038] For this purpose, at a point in time T0 (FIG. 3), both
charge switches T1a and T1b are switched on simultaneously, as a
result of which the actuator P is charged from the capacitors C1,
C2a and C2b via the recharging coil L, and a sinusoidal current I
begins to flow through the actuator P, which has been selected by
the selection switch S. A voltage at both of the recharging
capacitors C2a and C2b drops uniformly. If both charge switches T1a
and T1b (shown by dashed lines) remain switched on until the
current I (dashed curve) drops to zero at the point in time t3, the
charging time is t3-t0=200 .mu.s.
[0039] According to the invention, in order to achieve a shorter
charging time, the charge switch T1a, for example, is prematurely
opened at the point in time t1, i.e. switched off. As a result, the
current continues to flow only from the series circuit of the two
capacitors C1 and C2b, as a result of which the current I (unbroken
curve) already drops to zero at the point in time t2, at which
point in time the second charge switch is also switched off. As a
result of this measure, the charging time only then has the
duration t2-t0. The end of the charging time which starts at the
point in time t0 can be varied in this way between <t1 and t3,
as a result of which charging times of <100 .mu.s up to the
selected maximum, here 200 .mu.s can be selected. At the end of the
charging process (t2), there is still a voltage of, for example,
+80 V at the first recharging capacitor C2a, which has not been
entirely discharged, while the voltage at the second recharging
capacitor C2b can be -50 V, for example.
[0040] During the discharging of the actuator P, starting for
example at the point in time t4, both charge switches T2a and T2b
are already switched off, the discharge switch T2 is switched on.
As a result, the actuator P is discharged via the recharging coil L
into both recharging capacitors C2a and C2b which are now connected
in parallel by the diodes D2a and D2b. The second recharging
capacitor C2b is charged until it reaches the voltage (+80 V) of
the first recharging capacitor C2a.
[0041] Both recharging capacitors are then uniformly charged
further until the actuator P is discharged. In this way, each
discharging time corresponds to the respective preceding charging
time. In the selected example, the discharging time (charging time
to to t2) therefore already ends at the point in time t5 (unbroken
curve), instead of at the point in time t6 (dashed curve).
[0042] The respective selection switch, S or S', must be switched
on, at least from the start (to) of the charging time up to the end
of the discharging time (t5 or t6).
[0043] FIG. 4 shows the circuit of a second exemplary embodiment
according to the invention, which differs from the known circuit
according to FIG. 1 in that connected in series with the second
blocking diode D2 is a third blocking diode D3 with the same
current conducting direction, in that a series circuit composed of
a second recharging capacitor C2b, a further charge switch T3 and a
fourth blocking diode D4 is connected to reference potential from
the connecting point of the recharging capacitor C2a and the
recharging coil L. The anode of the fourth blocking diode D4
conducting current in the direction from the reference potential to
the second recharging capacitor C2b, and in that the cathode of the
fourth blocking diode D4 is connected to the connecting point of
the second and third blocking diodes D2, D3. C1>>C2a, C2b
also applies here. The two recharging capacitors C2a and C2b are
also dimensioned in the exemplary embodiment in such a way that the
charging of the actuator P (or P') takes place from a parallel
connection of the two capacitors C2a and C2b with a desired,
maximum charging time of, for example, 200 .mu.s.
[0044] For this purpose, at the point in time t0 (FIG. 5), both
charge switches T1 and T3 are switched on simultaneously, as a
result of which the actuator P is charged from the capacitors C1,
C2a and C2b via the recharging coil L, and a sinusoidal current I
begins to flow through the actuator P, which has been selected by
the selection switch S.
[0045] The voltage at both recharging capacitors C2a and C2b drops
uniformly. If both charge switches T1 and T3 remain switched on
until the current I (dashed curve) drops to zero at the point in
time t3, the charging time is thus t3-t0=200 .mu.s.
[0046] In order to achieve a shorter charging time, the charge
switch T1 is prematurely opened at the point in time t1, i.e.
switched off. As a result, the current continues to flow only from
the recharging capacitor C2b via the recharging coil L to the
actuator P, and from the actuator P via the selection switch, the
blocking diode D4 and the further charge switch T3 back into the
recharging capacitor C2b, as it were as a "freewheeling current" in
order to discharge C2b and L, until the current drops to zero at
the point in time t2 (unbroken curve from t1 to t2 in FIG. 5).
During this time the further charge switch T3 must be switched
on.
[0047] As a result, in the exemplary embodiment also, the charging
time continues to have only the duration t2-t0. The end of the
charging time which starts at the point in time t0 can in this way
be varied between <t1 and t3, as a result of which charging
times of <100 .mu.s up to the selected maximum, here 200 .mu.s,
can be selected.
[0048] At the end of the charging process (t2), there is still, as
in the first exemplary embodiment, a voltage of, for example, +80 V
at the first recharging capacitor C2a which was not entirely
discharged, while the voltage at the second recharging capacitor
C2b can be, for example, -50 V.
[0049] During the discharging of the actuator P, starting at the
point in time t4 (charge switch T1 is switched off), the discharge
switch T2 is switched on. If the further charge switch T3 is still
switched on at this point in time, the actuator P is discharged, as
already described in the first exemplary embodiment, via the
recharging coil L into both recharging capacitors C2a and C2b which
are now connected in parallel by the diode D2, the second
recharging capacitor C2b being charged until it reaches the voltage
(+80 V) of the first recharging capacitor C2a. Both recharging
capacitors are then uniformly charged further until the actuator P
is discharged. In this way, any discharging time corresponds again
to the respectively preceding charging time. In the selected
example (charging time to to t2), the discharging time therefore
already ends at the point in time t5 (unbroken curve), instead of
at the point in time t6 (dashed curve).
[0050] During the discharging of the actuator P, starting at the
point in time t4 (FIG. 5), in which the charge switch T1 is
switched off, the discharge switch T2 is switched on. Here, the
charge switch T3 is either still actively conducting or, if it is
embodied as a MOSFET, conducts current in the direction of the
discharge switch T2 (illustrated by dashed lines in FIG. 5) through
the arbitrarily inverse diode.
[0051] As a result, the actuator P is discharged via the recharging
coil L into both recharging capacitors C2a and C2b which are
connected in parallel, the second recharging capacitor C2b being
charged again until it reaches the voltage (+80 V) of the first
recharging capacitor C2a. Both recharging capacitors are then
uniformly charged further until the actuator P is discharged. In
this way, any discharging time corresponds to the respectively
preceding charging time. In the selected example (charging time t0
to t2), the discharging time therefore already ends at the point in
time t5 (unbroken curve), instead of at the point in time t6
(charging time to to t3, shown by the dashed curve).
[0052] The respective selection switch S or S' must be switched on
at least from the start (to) of the charging time up to the end of
the discharging time (t5 or t6).
[0053] In the second exemplary embodiment with a shortened charging
time (charge switch T1 is switched off before the further charge
switch T3), the fuel injection quantity can be minimized by
operating the further charge switch T3 and the discharge switch T2
inversely. T3 is switched on when T2 is switched off, and vice
versa, as a result of which the discharging time follows the
charging time immediately. In the event of T1 and T3 being
synchronously switched on at the point in time t0 and switched off
at the point in time T3, an inverse operation of T2 and T3 is to be
avoided. If, in fact, T1 and T3 are switched off simultaneously and
T2 is switched on, T1 and T2 are switched on owing to brief
overlaps and the charging capacitor C1 and the power source V are
thus short-circuited.
* * * * *