WO2009153130A1 - Circuit arrangement and method for charging a capacitive load - Google Patents

Abstract

A circuit arrangement for charging a capacitive load, in particular a piezo actuator for a fuel injection valve on an internal combustion engine is disclosed. The circuit arrangement comprises a circuit node and a current regulator arranged in series with the load to energise the load on charging. The charging current flows through the circuit node. A measuring circuit is provided for measuring the current through the current regulator. A controller is provided for controlling the current regulator device such that the current through the current regulator device is regulated using a measuring circvuit.A voltage regulation circuit is provided for changing the voltage at The circuit node during charging of the capacitive load.

Description

description

Circuit arrangement and method for charging a capacitive load

The present invention relates to a circuit arrangement and a method charging a capacitive load, in particular a piezoelectric actuator for a fuel injection valve of an internal combustion engine.

Such circuit arrangements and methods are known, for example, from DE 199 44 733 A1, DE 198 14 594 A1 and DE 199 52 950 A1.

In particular, the now lately strict emissions standards for engines ^¬ have been drawn in the automotive industry, the development of fuel injectors with fast and free verzoge- approximately responsive actuators and actuators. In the practical implementation of such actuators, in particular piezoelectric elements (in short: piezoactuators) have proved to be advantageous. Piezoelectric elements of this type are usually composed as a stack of piezoceramic disks which are operated via an electrical parallel circuit in order to be able to achieve the electric field strengths necessary for a sufficient lift.

When driving a capacitive load such as a piezoelectric actuator, which is used to actuate an injection valve, ie when charging and discharging the capacitive load by means of an electrical load current, considerable ^{Anforderun ¬} conditions are made to the control electronics. An injection valve actuated by means of a piezoactuator is used in internal combustion engines for injecting fuel (eg gasoline, diesel, etc.) into a combustion chamber. Here are very high Requirements for ern exact and reproducible opening and closing of the valve and thus also provided to the control electronics. Thus, voltages in the range of up to several 100 V and short-time load currents for charging and discharging of more than 10 A must be provided. The Ansteu ^¬ tion is usually in fractions of milliseconds. At the same time during this charging and discharging of the precedent current and voltage should be supplied as possible kontrol ^¬ lines to the actuator.

A common feature of the known circuit arrangements and methods mentioned above is that by means of geschal ^¬ Teter Speicheπnduktivitaten the energy is transported in portions. Thus, good efficiencies can be achieved, albeit with a very large component expenditure. There are also significantly higher short-term currents than the average of the current flowing in the piezoelectric actuator current. This requires correspondingly high-load components, such as semiconductor switching elements, capacitors and inductances th.

This requires comparatively large assemblies and also makes considerable demands on the component and production technologies Pro ^¬ In addition, due to the switched operation of the driving stages usually a lot of effort for filtering / suppression of the resulting high-frequency interference (EMC problem).

It is an object of the present invention to provide a way of charging and discharging a capacitive load, by means of which a good efficiency with simultaneously ge ^¬ ringem circuit complexity is possible. This object is achieved by the subject matter of the independent claims to ^¬. Advantageous embodiments will be apparent from the respective dependent claims.

A circuit arrangement is provided for charging a capacitive load, in particular a piezoactuator for a fuel injection valve of an internal combustion engine. The circuit arrangement has a switching node and, disposed in Rei ^¬ henschaltung with the load Stromeinstelleinπch- tung for energizing the load during charging, on. The charging current flows through the switching node. A measuring circuit is provided for measuring the current through the current setting means. A control device is used to control the current setting device, such that the current is regulated by the current controller device with the aid of a measuring circuit. A voltage setting circuit is provided for changing the voltage at the switching node during the charging of the capacitive load.

Em charging current can affect both a charging current and a discharge current. The charging current increases the voltage across the piezo actuator, while a discharge current decreases the voltage, the reference point for the voltage being the ground.

In the scheme, the instantaneous load current can be measured and adjusted during charging or discharging. As a result, the voltage applied to the piezoelectric actuator can be set accurately despite low component costs. The change in the voltage at the switching node ensures that the power loss in the current setting device does not become too large. As an equivalent circuit for the Stromeinstelleinrichtung a resistor can be used. If the voltage dropping above this resistance is too great, the power loss is also great. The temperature or the heat output of the piezo control must not be too great to prevent failures of the piezo control or adjacent control systems. Therefore, the voltage drop across the current ^{setting device} is ^limited by the change in the voltage at the switching ^node .

In one embodiment, the current setting device is designed as a controlled resistor, through the load ^¬ stretch of the charging current flows. Em controlled resistor can be linearly einge- very accurately over a wide resistance range is such that the entire charging or discharging can be the charging characteristic is ^¬ provides while.

Alternatively, the current setting device contains a transistor, through the load path of which the charging current flows. The

Using a transistor has the advantage that it can react quickly and thus changes in the load or in the supply can be compensated quickly.

Preferably, the current during charging is controlled so that the transistor operates in the linear operating range. The characteristic of a transistor is divided into a linear region and a saturation region. In the linear working range, the resistance of the load path can be set continuously, which allows precise control of the current.

Preferably, a reference value generator is provided for presetting a reference value for the charging current through the current setting device. Based on a comparison of the setpoint with the current current flowing into the load during the Aufla ^¬ tion or discharge, a simple actual value / setpoint comparison allows whether the Stromeinsteinrichtung should be further controlled or closed. The reference value may be varied over time to achieve certain charging and discharging waveforms, for example, to underpress the piezo resonances.

An inventive circuit arrangement according to a first embodiment comprises:

a voltage source for providing a supply voltage related to an electrical ground,

a capacitor arranged between a first circuit node and a second circuit node, the first circuit node being connected to the voltage source via a diode, and the second circuit node being connectable to the voltage source via a first switch,

a first current path leading from the first circuit node to one of the load terminals and a second current path leading from the second circuit node to the other of the load terminals,

- which is arranged in series with the load Stromein- stellemπchtung over which the load during charging and Ent ^¬ load is supplied with current, and comprising a first current path and / or arranged in the second current path current source,

a second switch via which the first current path can be connected to the second circuit node, and

a control device for controlling the switches and the current setting device such that a) during a first charging phase both switches are open and the load is partially charged from the supply voltage, b) closed during a second charging phase, the first switch ge ^¬ and the second switch is open and the load from the resulting series connection of the voltage source and the capacitor continues to be charged, c) during a first discharging phase, both switches are opened and the load in the Capacitor is partially discharged, and d) during a second discharge phase of the first switch ge ^¬ opens and the second switch is closed and the load is further discharged into the electrical ground.

A basic idea of this first embodiment is that the positive properties of a "linear power amplifier", ie, a current supply to the capacitive load in an adjustable current source, with the high efficiency of a "switched output stage" (z. B. use of an inductor as Energiespei ^¬ cher in During a Umschwmgfunktion in which energy portions are transported) to connect.

As is apparent from the exemplary embodiment described below in detail yet, the use of a memory ^¬ or Umschwingmduktivitat is dispensable. Nevertheless, a high degree of efficiency can be achieved, in particular because a load current flowing during the "first discharge phase" is used to feed back electrical energy into the capacitor. In addition, components such as the capacitor and semiconductor switching elements can be designed with lower load capacity. This is because a necessary maximum charging voltage for the piezoelectric actuator is achieved by voltage conversion (essentially voltage doubling) by means of the capacitor.

In the realization of erfmdungsgemaßen basic idea is important in this embodiment that each charging process such as Also, each discharge takes place in two temporally successive phases, namely a first and second charging phase and a first and second discharge phase. During the second loading phase, the load of a series connection is processing the voltage source and the capacitor to the desired final voltage ge ^¬ charged. During the first discharging, the load is discharged into the capacitor part, wherein advantageously, energy is stored in this jerk Kon ^¬ capacitor.

In particular, in the case of an application in the field of automotive electronics (for example, for controlling a piezo-fueled fuel injection valve), the voltage source which provides the supply voltage, for. B. be formed by a DC / DC voltage converter. For example, an on-board voltage (eg 12 V or 24 V) can thus be converted into the supply voltage of the circuit arrangement.

In a preferred embodiment, the supply voltage, for example greater than 50 V. The maximum charging voltage is can tor produced with the circuit arrangement for the ^¬ Piezoak- for example, greater than 150% of its supply voltage, and for example, amount to more than 100V. According to a preferred embodiment, the Stromeinstellein- πchtung on a first power source for charging the load and separately from a second power source for discharging the load. A separation of the current sources for charging and discharging has proven to be advantageous, in particular with regard to the circuitry realization or adjustability of the current sources. In addition, so that in the

Area of the current setting resulting power loss can be advantageously divided into at least two branches. A power source in the context of the present invention can be very simple z. B. as a transistor (field effect transistor or bipolar transistor) may be formed, the control terminal (gate or base) is acted upon by a drive signal for determining the current flowing through the transistor current. However, it is also conceivable to use a bidirectionally operable current source, which is used in one direction for charging and in the other direction for discharging in the adjustment of the load current. A bidirectional power source can be very simple z. B. be realized using two transistors arranged parallel to each other.

According to a preferred embodiment, a power source provided for charging the load is arranged in the first current path and / or a current source provided for discharging the load is arranged in the second current path.

Preferably, at least one of the switches, in particular all of the switches, each formed as a transistor. Preferably, the switches (eg, transistors) are driven by a control device, which also controls the current setting device for determining the supplied current (for example, by outputting control voltages for the transistors in question).

If at least one of the switches is designed as a transistor, then it is possible to use this transistor not only for switching, but also as a component of the current setting device. In other words, the transistor then forms an on and off switchable current source in the sense of the present invention, thus uniting the function of current setting and switching in itself. As a transistor which may be formed as a switching transistor or as a switching / Stromeinstell transistor, z. B. a FET, in particular MOS-FET be provided.

According to a preferred embodiment of the invention, the charging and / or the discharge of the load is regulated. For example, the instantaneous load current and / or the current voltage applied to the load (load voltage) during charging or discharging can be measured and compared with a setpoint, based on an actual value / setpoint comparison, the control signals for the switch and the Stromguelle (n) are generated.

Due to the first charging phase, the load is preferably charged essentially to the supply voltage. By the second charging phase, the load is preferably charged to substantially twice the supply voltage. By the first discharge phase, the load is preferably discharged substantially to the supply voltage. Through the second discharge phase, the load is preferably discharged substantially completely (to "zero" or electrical ground). In one embodiment it is provided that in the first current path, a diode is arranged, via which the load current flows during the first discharge phase. Parallel to this discharging diode, a current source for charging the load (in the reverse current flow direction) may be provided.

Further diodes can advantageously be arranged in series with the first switch and / or with the second switch.

Advantageously, the invention can be realized by using a single voltage source (eg a DC / DC converter) whose supplied supply voltage is advantageous. is wartseltelt to reach about twice as large load voltage when charging the load can. For this purpose, an "auxiliary voltage source" for the purpose of voltage excitation is effectively created with the capacitor, which is switched on in the second charging phase of the actual supply voltage.

A DC / DC converter used to generate the supply voltage can operate at about "half voltage" (compared to the desired maximum voltage at the load), which reduces the demands on the circuit components and in particular allows the use of lower maximum voltage components. For lower voltages, a larger and thus more cost-effective component offer can be used.

According to a preferred embodiment of the invention, the capacitor can also be used as a so-called "bootstrap" voltage source for drive units for driving the first switch and / or the second switch. Because of the (compared to the maximum load voltage) relatively low supply voltage such control parts for driving the two switches can be supplied with simple means (linear stabilization).

In summary, a circuit-technically simple, compact and low-loss realization of the charging and discharging of a capacitive load can be provided with the present invention. Essential is the use of two different voltages, one of which is provided as a supply voltage and the other is provided by a capacitor and acts as a kind of auxiliary voltage in each case running in two phases charging operations or discharging. A use of "linear current swelling "advantageously allows almost any charging ^¬ or Entladekurvenformen.

The inventive circuit arrangement according to a second embodiment comprises:

a first voltage source for providing a first voltage related to an electrical ground,

a second voltage source for providing a second voltage related to the electrical ground, which is smaller than the first voltage,

a circuit node which can be connected to the first voltage via a first switch, to the second voltage via a second switch and to the electrical potential via a third switch, a current-setting device arranged in series with the load, via which the load is charged during charging and discharging, and

- a control device for controlling the switch and the current adjustment, such that a) during a first charging phase of the second switch ge ^¬ closed to charge the load from the second voltage part, b) during ge ^¬ joined to a second charging phase, the first switch to further charge the load from the first voltage, c) during a first discharge phase, the second switch is closed to partially discharge the load to the second voltage, and d) during a second discharge phase, the third switch is closed, to further discharge the load into the electrical ground.

A basic idea of the second embodiment is the positive characteristics of a "linear amplifier", ie a Energizing the capacitive load from an adjustable current source to connect with the high efficiency of a "switched output stage" (eg use of an inductance as an energy storage in the course of a Umschwmgfunktion in which energy pores are transported).

As is apparent from the approximate examples detailed below Ausfuh- still, in the invention the USAGE ^¬ dung a memory or Umschwinginduktivitat is dispensable. Nevertheless, a high degree of efficiency can be achieved, in particular because a load current flowing during the "first discharge phase" is used for the feedback of electrical energy into the "second voltage source" and because the losses in the current setting direction are reduced by the switching between the two different voltages , Thus, components such as capacitors and semicon ^¬ ter switching elements can be designed with lower load capacity.

In the realization of the basic idea according to the invention, it is essential that each charging process as well as each discharging process does not take place from or into a single power supply in a continuous process, but rather in two successive phases. Charging and subsequent unloading, as z. B. for controlling a piezobetatigten fuel injection valve of an internal combustion engine for effecting an injection process is he ^¬ required, is divided according to the invention in a first charging phase, a second charging phase, a first discharge and a second discharge phase. According to one in the

In practice, most advantageous execution is provided that the transition between the first and second charging phase and / or discharge takes place gradually, ie that the switches concerned are not turned on or off abruptly. In order to can z. B. a resulting power loss during switching can be better distributed.

Particularly in the case of an application in the field of automotive electronics (for example for the control of a piezo-actuated

Fuel injection valve), the two voltage sources, which provide the first voltage and the second voltage, for. B. be formed by DC / DC voltage converter. For example, an on-board voltage (eg 12 V or 24 V) can be converted into one or two higher voltages. For example, in a preferred embodiment, the first voltage is greater than 100 V and / or the second voltage is greater than 50 V. The second voltage may, for example, be less than 70%, in particular less than 60%, of the first voltage.

According to a preferred embodiment it is provided that the Stromeinstellemrichtung comprises at least one separately formed from the switches power source. A power source in the context of the present invention may, for. B. as a transistor (field effect transistor or bipolar transistor) may be formed, the control terminal (gate or base) is acted upon by a drive signal for determining the flow through the transistor ^¬ the current. It can, for. For example, such a separate power source for charging during the first and second charging phase and a further separate power source for discharging at least during the first and possibly also second discharge phase be provided.

Alternatively, a bidirectionally operable current source may be provided which is used in one direction for charging and in the other direction for discharging in the adjustment of the load current. A bidirectional power source can be very simple z. Using two pairs of be realized parallel to each other arranged transistors.

When the current adjustment device comprises at least one separately formed from the switches power source, so it is provided according to a further development, is that the circuit node u- about this current source to the load (or an intended for connection to the load output terminal of the circuit ^{arrangement),} respectively. Alternatively, the load (or an output terminal of the circuit arrangement) can be connected to the electrical ground via the current source.

In a preferred embodiment, at least one of the switches, in particular all the switches, each formed as a transistor. Preferably, the switches (eg, transistors) are driven by a control device, which also controls the current setting device for determining the supplied current (for example, by outputting control voltages for the transistors in question).

If at least one of the switches is designed as a transistor, then it is possible to use this transistor not only for switching, but also as a component of the current setting device. In other words, the transistor then forms an on and off switchable current source in the sense of the present invention, thus uniting the function of current setting and switching in itself. As a transistor which may be formed as a switching transistor or as a switching / current setting transistor, z. B. a FET, in particular MOS-FET be provided.

According to a preferred embodiment of the invention, the charging and / or the discharge of the load is regulated. For example, the instantaneous load current and / or the current tan applied to the load voltage (load voltage) during charging or discharging and compared with a setpoint, based on an actual value / setpoint comparison, the drive signals for the switch and the power source (s) are generated.

By the first charging phase, the load is preferably charged to substantially the second voltage. Through the second charging phase, the load is preferably charged substantially to the first voltage. By the first discharge phase, the load is preferably discharged substantially to the second voltage. By the second discharge phase, the load is preferably discharged substantially completely (to "zero" or electrical ground).

In a preferred embodiment of the invention, the second voltage source is formed by a capacitor which can provide, for example, the second voltage at one of its terminals, wherein preferably the other terminal is connected to the first voltage.

In this development, it can be provided that the voltage at the capacitor adjusts itself automatically to a balance between discharged and jerk-fed energy (whereby this equilibrium can be almost in the energetic optimum).

Advantageously, this eliminates the need for a more complex design of the second voltage source (eg, by means of a DC / DC converter). Thus, on the one hand, the cost of circuit implementation can be further reduced and, on the other hand, the possibility of integration of essential parts of the circuit or power amplifier in a load Having component (eg Piezoinj ector) simplified ^¬ who.

In summary, a simple circuit design, compact and low-loss realization of charge and discharge ei ^¬ ner capacitive load can be provided. What is essential is the use of two different voltages, of which a "second voltage" effectively acts as an auxiliary voltage for charging processes or discharging processes which take place in each case in two phases. A use of "linear current sources" advantageously permits virtually any charging ^¬ or Entladekurvenformen.

According to a third embodiment, the circuit arrangement has a n variety, n> 2, of switches. Each of these switches is provided for connecting the switch node to one of a plurality of voltages. It has been found that in some constellations the power dissipation across the current setting means can be further reduced if the switching node is charged to a plurality of intermediate voltages during charging.

In one embodiment, the plurality of n voltages are provided by a circuit having a plurality of capacitors connected in series. The series connection of capacitors makes it possible to generate the n voltages outside the charging process and then to store the energy in the capacitors. During the charging process, the individual voltages can be connected to the switching node. The charging of the capacitors can thus be done relatively slowly, which further reduces the number or the size of the necessary components. In one embodiment, the n voltages are each supplied by a wound over a magnetizable core of a transformer coil. Transformers with magnetizable cores enable energy transfer with low power loss, whereby energy is transferred from a power source to the capacitors with relatively little heat development.

According to a fourth embodiment, the circuit arrangement includes a voltage converter for generating a linear

Increasing the voltage at the switching node when charging the load. For the increase of the voltage at the piezoelectric actuator as linear as possible is sought. If the voltage at the switching node also increases linearly, the voltage drop across the current setting device can be kept constant over long periods of time. Thus, the power loss over the charging process does not vary so much and can be reduced overall.

The power dissipation during discharge can also be reduced by providing a voltage converter for generating a linear drop in the voltage at the switching node when discharging the load.

If a voltage measuring circuit is provided for checking whether the voltage across the current setting device exceeds a predetermined threshold value, the power loss caused by the current setting device can be estimated at any time and the voltage at the switching node can be adjusted again when the threshold value is exceeded.

According to a fifth embodiment, a measuring resistor is in the path of the series connection of load and current setting device for measuring the current through the current setting device intended. The voltage drop across this measuring resistor can be used directly as a control parameter for the regulation of the current through the load.

In an expanded fifth embodiment, the circuit arrangement also serves for switching at least one further capacitive load, in particular a piezoelectric actuator. The circuit arrangement has a further current setting device, which is arranged in series with the further load and via which the further load is supplied with current during charging, the charging current flowing through the switching node.

The measuring resistor is arranged so that charging currents for the load and for the additional load flow through the measuring resistor. Thus, the current for the measuring resistor can be used both as a feedback quantity when charging the load and at the La ^¬ the other load. This has the advantage over an arrangement with two measuring resistors that it is not necessary to calibrate two measuring resistors. In addition, this also helps to further reduce the number of components.

The invention also relates to a method for charging a ka ^¬ pazitiven load, in particular a piezoelectric actuator for a fuel-injection valve of an internal combustion engine. First, a first voltage is provided at a switching node. Em charging current into the load is controlled by means of a Stromeinstellem- πchtung as an actuator. In this case, the current setting device is connected in series with the load and the charging current flows through the switching node.

During the charging of the load, the voltage at the switching node is changed so that the amount of current over the current Emstelleemrichtung falling voltage during the charging process does not exceed a predetermined threshold.

By limiting the voltage drop across the current setting device, it is ensured that the power loss of the current setting device remains limited.

If the voltage at the switching node is changed in stages, the change in the voltage can be effected by means of a relatively inexpensive circuit, which successively connects different voltages to the switching node.

If, in contrast, the voltage at the switching node is changed continuously, the power loss over the entire charging time can be kept constant and thus further reduced.

Preferably, both the charging current and the discharging current flows through the switching node, so that both charging processes can be improved equally with regard to lower power loss.

The invention also relates to a method for charging and discharging a capacitive load, in particular a piezo actuator for a fuel injection valve of an internal combustion engine, comprising

- Providing a reference to an electrical ground supply voltage by means of a voltage source, and

- Setting a load current that flows through the load during charging and discharging, in at least one of two to

Load carrying current paths, wherein the charging and discharging takes place in such a way that a) during a first charging phase (a) a recharging ei ^¬ nes capacitor and a partial charging of the load takes place in each case from the supply voltage, b) during a second charging phase (b) fertil a further loading of the load (P) from a series circuit of Voltage source and the capacitor (Ch) takes place, wherein in the capacitor (Ch) stored energy is partially transferred to the load (P), c) during a first discharge phase (c) a partial discharge of the load (P) in the condenser (Ch ), so that

Energy from the load (P) in the capacitor (Ch) is fed back, and d) during a second discharge phase (d), a further discharge of the load takes place in the electrical mass.

The invention is also realized in a method for charging and discharging a capacitive load, in particular a piezoactuator for a fuel injection valve of an internal combustion engine, comprising - providing a first voltage related to an electrical ground,

Providing a second voltage related to the electrical ground, which is smaller than the first voltage,

- Setting a current that flows through the load during charging and discharging, and

- Control of switches and the current setting such that a) during a first charging phase, the load from the second voltage is partially charged, b) during a second charging phase, the load from the first voltage is further charged, c) during a first discharge phase, the load partially discharged into the second voltage, and d) continues to be discharged, the load in the elekt ^¬ generic mass during a second discharging phase.

The advantage of the method lies in the realization without large and expensive passive power components such as inductors and capacitors, as they are necessary in conventional, based on switching converter concepts, control stages for capacitive loads. At the same time still a vergleichba ^¬ rer efficiency can but achieved and the disadvantages of switching converter with EMC and controllability (energy packets of finite size) can be avoided.

The invention is illustrated in more detail in the drawings with reference to several exemplary embodiments. Show

1 shows a first embodiment of a circuit arrangement for controlling a piezoelectric actuator,

2 shows the time course of some large in the operation of the circuit arrangement of Fig. 1,

3 shows an output stage for driving a plurality of piezoelectric actuators using the circuit arrangement of FIG. 1, FIG.

4 shows a second embodiment of circuit arrangement for controlling a piezoelectric actuator,

5 shows the time course of some large in the operation of the circuit arrangement of Fig. 4,

6 shows a circuit arrangement according to a third exemplary embodiment, 7 shows the time course of some large in the operation of the circuit arrangement of Fig. 3,

8 shows a fourth embodiment of a circuit arrangement for controlling a piezoelectric actuator,

FIG. 9 the time profile of the voltages during charging of the piezoactuator,

FIG. 10 shows the time profile of the voltages during discharging of the piezoactuator,

11 shows a fifth embodiment of a circuit arrangement for controlling a piezoelectric actuator,

FIG. 12 the time profile of the voltages during charging of the piezoactuator in the fifth embodiment,

FIG. 13 shows the generation of the voltage in the fifth embodiment;

FIG. 14 shows a sixth embodiment of a circuit arrangement for controlling a piezoelectric actuator,

Figure 15 is a schematic diagram of a circuit arrangement for controlling a piezoelectric actuator.

Fig. 1 shows a circuit arrangement 10 for controlling a piezoelectric actuator P of a fuel injection valve of an internal combustion engine of a motor vehicle. The control is carried out by charging and discharging of a capacitive load performing piezoelectric actuator P. The circuit arrangement 10 comprises a voltage source for providing a supply voltage Ub related to an electrical ground GND. In the illustrated embodiment, Ub z. B. about 100 V.

A capacitor Ch is arranged between a first circuit node K1 and a second circuit node K2, the first circuit node K1 being connected to the voltage source via a diode D1 and the second circuit node K2 being connectable to the voltage source via a first switch S1. In this case, the diode D1 is polarized such that a current can flow from the voltage source to the circuit node K1.

In the illustrated embodiment, a diode D3 is also arranged in series with the first switch Sl.

To output terminals Al and A2 of the circuit 10, which are connected to the two load terminals of the piezoelectric actuator P, starting from the circuit node Kl, a first current path or starting from the circuit node K2, a second current path.

The first current path is formed by a first current source CS1 and the second current path by a second current source CS2. Parallel to the first current source CS1, by means of which a current flow from the circuit node K1 to the output terminal A1 can be set, a diode D2 is arranged with oppositely set flux polarity. With the second power source

CS2, a current flow can be set from the circuit node K2 to the output terminal A2, which is connected to the electrical ground GND. The two current sources CS1 and CS2 form a series circuit with the piezoelectric actuator P angeord- Neten Stromemstellemrichtung, via which the piezoelectric actuator is energized during charging and discharging. In the illustrated exemplary embodiment, this current setting device comprises the first power source CS1 in the first current path and the second current source CS2 in the second current path.

Furthermore, the circuit arrangement 10 comprises a second switch S2 (with a diode D4 connected in series therewith), via which the first current path (between the first current source CS1 and the output terminal A1) with the second

Circuit node K2 is connectable. The switching operation during operation of the circuit arrangement 10 will be described in detail below and are effected by a control device SE, which generates and outputs control signals sl (for the switch Sl) and s2 (for the switch S2) for this purpose.

Although this is not shown for convenience in the figure, the switches Sl and S2 in this exemplary embodiment, by switching transistors (z. B. FETs) are formed overall, whose control Connections (z. B. Gates) with the Ansteu ^¬ ersignal sl or s2 are supplied.

The current sources CSI and CS2 are also trained in the illustrated det Ausfuh ^¬ approximately example each as a transistor whose control terminal is supplied with a drive signal SIPL or sip2 applied, which is also generated by the control unit SE. Unlike the drive signals s1 and s2, no switching on and off of the respective transistors is effected with the drive signals sipl and sip2, but in each case a specific load current Ip1 or Ip2 is set during charging and discharging in the first or second current path. The activation of the piezoelectric actuator P by means of the circuit arrangement 10 will be described below with reference also to FIG.

2 shows the example of a drive cycle (a charge and a subsequent discharge), the course of different magnitudes in the operation of the circuit 10 as a function of the time t.

In the upper part of FIG. 2, the course of a first node voltage Uboost (between K1 and GND), a second node voltage Uh (between K2 and GND) and the load or peak voltage Up are indicated. In the lower part of Fig. 2, the course of the load current Ip is shown, which is formed during charging of the piezoelectric actuator P from the current IpI and the discharge of the piezoelectric actuator P from the current Ip2. The charging of the Pie ^¬ zoaktors P takes place during a period of time which is composed of a first charging phase "a" and an immediately subsequent second loading phase "b".

The discharge of the piezoelectric actuator P takes place during a period of time which is composed of a first discharge phase "c" and a second discharge phase "d". The phases Slon the drawn and S2on in Fig. 2 except ^¬ denote diejeni- gen time periods in which the switching elements are turned on or Sl S2.

In the illustrated exemplary embodiment, the illustrated, overall trapezoidal profile of the piezo voltage Up is to be accomplished. The individual phases can be described as follows: During the first charging phase "a" both switches S1, S2 are open and the piezoelectric actuator P is partially charged from the supply voltage Ub. The piezo voltage Up rises continuously. The concrete course is by appropriate control of the current source CSl adjustable ^¬ bar. At the end of this phase, the piezo voltage Up has increased to the supply voltage Ub less a minimum voltage (ΔUip) necessary for the function of the current source CS1.

During the second charging phase "b", the first switch Sl is closed and the second switch S2 is opened and the piezo actuator P is further charged from the resulting series connection of the voltage source and the capacitor Ch.

Closing Sl namely raises the voltage level at the input of the current source CSl by means of the charged to the supply voltage Ub ^¬ clamping capacitor Ch to about twice the supply voltage Ub. The specific course of the further rising piezo voltage Up or of the load current flowing into the piezoelectric actuator is set again by the corresponding control of the current source CS1.

During the first discharging phase "c" are both switches Sl, S2 opened and the piezoelectric actuator P is partially discharged into the Kon ^¬ capacitor Ch. This partial discharge takes place via the diode D2 in the first current path and via the second current source CS2 in the second current path. In this case, energy from the piezoelectric actuator P in the condenser Ch is returned. The specific course of the piezo voltage Up or the load current Ip2 is determined by the corresponding control of the current source CS2. This partial discharge can be fortge ^¬ sets until the node voltage is decreased Uh to the necessary for the function of current source CS2 minimum voltage (AUIP) or the piezo voltage Up has fallen to the level of supply voltage Ub.

During the second discharge phase "d", the first switch S1 is opened and the second switch S2 is closed and becomes the piezoelectric actuator P in the electrical ground GND further entla ^¬ . In this phase, the piezoelectric actuator P via the diode D4, the switch S2 and the power source CS2 is connected to electrical ground GND. This allows a complete discharge of the piezoelectric actuator P. At the end (time Tn) of this second

Discharging is also the previously incurred in the condenser Ch "charge deficit" (charging / discharging efficiency in practice not equal to 1) replenished, whereby (with unchanged current Ip2), the slope of the piezoelectric discharge current is flattened. If this flattening effect is not desired, this can be compensated by a corresponding increase in the discharge current in this final phase.

By erfmdungsgemaß provided at the transition from the first charging phase to the second charging phase switching of lying at the current source CSl voltage (Ub to Ub plus the capacitor voltage) results in the charging of the advantage of a significantly reduced power dissipation in the current source CSl. A corresponding improvement in efficiency also results for the unloading process. Thus, an overall efficiency can be achieved, which is comparable to the efficiency of known final stage concepts.

An even more significant advantage of the circuit arrangement described or of the control method implemented thereby lies in the cost range. In fact, significant savings can be achieved with expensive inductors, capacitors and power semiconductors. In particular, due to the voltage excess realized by means of the circuit arrangement, a DC / DC converter which provides the supply voltage Ub can operate at approximately "half voltage" (in comparison to the desired maximum voltage at the piezoactuator), which makes the use of less expensive scarf - components (including those of the DC / DC converter).

Many components of the circuit arrangement only have to be designed for something more than the supply voltage Ub and not for the full maximum piezo voltage Up. In addition, the circuit arrangement less space requirements and has a high durability, which is particularly ^so-¬-called "suburban electronics" (z. B. in the engine compartment of a motor vehicle) of great importance.

An arrangement for a plurality of capacitive loads, for example, several piezobetatigte fuel-injection valves in a motor vehicle, can be in a simple manner z. B. by mas- ssseige "selection switch" realize. Such a circuit arrangement or output stage for controlling a plurality of piezo actuators is shown in FIG.

Fig. 3 shows a power amplifier 100 comprising a Schaltungsan- order 10 ', which may be formed for example identical to the above ^¬ be written circuitry 10 and (tig versorgungssei-) has correspondingly two output Connections Al and A2 (ground side).

As can be seen from the figure, the output terminal Al is connected to one of the two load terminals of all the piezo actuators P1, P2, whereas the other load terminal of these piezo actuators is connected to the output terminal A2 via a respectively assigned selector switch (transistors T1, T2,) is. In this connection path

(Between A2 and the selection switches) is also still a current measuring resistor Rs arranged by means of which the instantaneous load current of the selected piezoelectric actuator can be measured. In known manner, this is the Voltage drop across the measuring resistor Rs measured, for which the circuit arrangement 10 'is provided with an input terminal El, via which the measured voltage drop of the corresponding control device within the circuit arrangement 10' for evaluation or consideration in the control is supplied. The voltage drop to be measured is called Uirs.

The circuit arrangement 10 'can thus be used advantageously also for charging and discharging a plurality of piezoelectric actuators. Activation signals for switching the selector switches Tl, T2 can also be generated and output by the relevant control device (not shown).

It is noteworthy that in the case of the output stage 100, the selection switches T1, T2,... Can advantageously also assume the function of a current setting, as is realized, for example, in FIG. 1 by the current source CS1. This can z. B. a current source CSl corresponding common current source of the circuit part 10 'to be replaced or occurring at such a current adjustment power dissipation be better distributed.

4 shows a circuit arrangement (output stage) 10 for controlling a piezoactuator P of a fuel ejection valve of an internal combustion engine of a motor vehicle. The control is carried out by charging and Entla ^¬ the capacitive load representing a piezoelectric actuator P.

The circuit arrangement 10 comprises a first voltage source for providing an electrical ground GND bezo ^¬ antigenic first voltage Ub and a second voltage source for providing related to the electrical ground GND second voltage Uh, which is smaller than the first voltage Ub is. In the illustrated embodiment, Ub z. B. about 200 V and Uh about 100 V.

Em circuit node K is connected via a first switch Sl with the voltage Ub, via a second switch S3, S4 with the voltage Uh and a third switch S2 to the ground GND.

The switching operations during operation of the circuit arrangement 10 will be described in detail below and are effected by a control device SE, which for this control signals sl (for the switch Sl), s2 (for the switch S2), s3 and s4 (for the switch S3, S4) generates and outputs. Although this is not shown in the figure for the sake of simplicity, the switches in this exemplary embodiment are formed by switching transistors (eg FETs).

The switches S1 and S2 are each formed by a transistor whose control terminal (gate or base) is supplied with the on control signal s1 or s2. The switch S3, S4 is shown in the figure as a series connection of two individual switches S3 and S4. This is because this switch is actually formed of a series connection of two FETs in order to switch a current in both opposite directions. When S3 is turned on, current may flow through S3 and the "intrinsic source-drain diode" of S4 in one direction (from right to left in FIG. 4). The reverse current flow (in Fig. 4 from left to right) can be released accordingly by turning on S4. The control signals required for switching the individual switches S3 and S4 and supplied by the control device SE are designated s3 and s4, respectively. The piezoelectric actuator P is connected to the output terminals Al and A2 to the circuit 10. Connected in series with the piezoelectric actuator P is a current setting device in the form of a current source CS, via which the piezoelectric actuator P is energized during charging and discharging.

The current source CS is also formed in the illustrated embodiment as a transistor, the control terminal is acted upon by a drive signal sip, which is also generated by the control device SE. Unlike the drive signals sl to s4, no turning on and off of the relevant transistor is effected with the drive signal sip, but a specific load current Ip is set during charging and discharging. Deviating from the illustrated "supply-side" arrangement of the current source CS between the circuit node K and the output terminal Al is in practice often a variant of particular advantage in which the current source CS "ground side", ie between the electrical ground GND and the output terminal A2 is arranged.

Subsequently, the driving of the piezoelectric actuator P by means of the circuit 10 will be described with reference also to FIG.

5 shows the example of a drive cycle (a charge and a subsequent discharge), the course of different magnitudes in the operation of the circuit 10 as a function of time t.

In the upper part of Fig. 5, the course of a node voltage Us (between the circuit node K and the electrical ground GND), and the load or piezo voltage Up are located. The lower part of FIG. 5 shows the course of the load current. with Ip is shown. The charging of the piezoelectric actuator P er ^¬ follows during a period of time, which is composed of a first charging phase "a" and a directly subsequent thereto second charging phase "b". The discharge of the piezoelectric actuator P takes place during a period of time which is composed of a first discharge phase "c" and a second discharge phase "d".

The phases Slon, S2on, S3on and S4on, which are also shown in FIG. 5, denote those time periods in which the switching elements S1, S2, S3 and S4 are switched on. In the illustrated control example, the shown, ins ^¬ total trapezoidal course of the piezoelectric voltage to be accomplished. The individual phases can be described as follows:

During the first charging phase "a", the second switch S3, S4 (strictly speaking: S4) is closed in order to partially charge the piezoactuator P from the voltage Uh. The piezo voltage Up rises continuously. The specific course can be set by appropriate control of the current source CS. At the end of this phase, the piezo voltage Up to the "Auxiliary voltage" Uh less costs necessary for the functioning of the current source CS ^¬ minimum voltage (ΔUip) has risen.

During the second charging phase "b", alternatively or additionally, the first switch S1 is closed in order to continue charging the piezoelectric actuator P from the (higher) voltage Ub. In this case, the piezo voltage Up continues to increase, for example, up to twice the supply voltage Ub. The concrete course is determined again by the corresponding control of the current source CS. During the first discharge phase "c", the second switch S3, S4 (strictly speaking: S3) is closed in order to partially discharge the piezoactuator P into the voltage Uh. Energy from the piezoelectric actuator P is fed back into the power supply. The concrete course of the piezo voltage Up or the

Load current Ip is set again by the corresponding control of the current source CS. At the end of this phase, the piezo voltage Up reaches the level of the voltage Uh zuzüg ^¬ lich necessary for the function of the current source CS minimum voltage (ΔUip).

During the second discharging phase "d" is closed alternatively or ^¬ satzlich the third switch S2, to discharge the piezo actuator P in the electric ground GND on. The concrete discharge curve is again defined by the control of the current source CS. The discharge may be complete (except for Up = 0). The switching of the voltage present at the current source CS (from Ub to Uh or vice versa) provided by the invention results in the advantage of a significantly reduced power loss in the current source. Thus, an efficiency can be achieved, which is comparable to the efficiency of known power amplifier concepts.

An even more significant advantage of the circuit arrangement described or of the control method implemented therewith lies in the cost range. In fact, significant savings can be achieved with expensive inductors, capacitors and power semiconductors. In addition, the circuit arrangement has low space requirements and has a high degree of robustness, which is of great importance, in particular in so-called "on-the-spot electronics" (eg in the engine compartment of a motor vehicle). In the exemplary embodiment described above, the two required voltages Ub and Uh can be provided in particular as output voltages of two DC / DC voltage converters of an automotive electronics. Hereinafter, a modified exemplary embodiment will be described with reference to FIGS. 6 and 7, which enables the saving of a DC / DC voltage converter.

FIG. 6 shows a circuit arrangement 100 which substantially corresponds in construction and function to the circuit arrangement 10 described above. Corresponding circuit components are designated by the same reference numerals.

The modification of the circuit arrangement 100 is that the second voltage or "auxiliary voltage" Uh is generated in a very simple manner within the circuit arrangement 100 (ultimately from the supplied first voltage Ub). A capacitor Ch is provided which, as shown in FIG. 6, is connected on the one hand to the voltage Ub and, on the other hand, is connected to the switch S3, S4. The capacitor terminal connected to S3, S4 effectively forms the source of the "second voltage" Uh.

During operation of the circuit arrangement 100, which takes place in the same way as described above for the circuit arrangement 10, the capacitor Ch automatically adjusts itself to a balance between discharged and jerk-fed energy, which advantageously eliminates the need for generating its own voltage at this point. Notwithstanding the illustrated embodiment, the capacitor Ch could instead of the first voltage Ub with a different fixed voltage, in particular z. B. the e- lektπschen mass GND be connected. FIG. 7 is a timing diagram similar to FIG. 5, but for operation of the circuitry 100 shown in FIG. 6.

Fig. 8 shows a circuit arrangement according to a fourth embodiment. As in the previous circuit arrangements, the circuit arrangement has a switching node K, a current setting device CS1 and the load P. However, the voltage setting circuit 30 for changing the voltage Uk at the switching node K is different from the embodiments described above.

The voltage adjusting circuit 30 includes a battery B, a primary switch SP1, a transformer 20, a series circuit of capacitors C1, C2, C3, C4 and C5, and selector switches S1O, Sil, S12, S13 and S14.

The battery B is connected to the ground with its negative pole, while its positive pole is connected to a first terminal of the primary switch SP1. The transformer 20 ent ^¬ holding a Pπmarspule 21, a magnetizable core 23 and secondary coils 220, 221, 222, 223 and 224, wherein the Pπmarspule 21 and the secondary coils 220, 221, 222, 223 and 224 wound around the core 23 ,

The parking coil 21 is provided between the second terminal of the primary switch SP1 and the ground. The secondary ^coils 220, 221, 222, 223 and 224 are connected in series, one end point of this series circuit of secondary coils being connected to one of the end points of the series connection of capacitors and simultaneously to ground. The second end ^¬ point of the series circuit of the secondary coil is coupled to the second end point of the series circuit of the capacitors through the diode D14, the anode of this diode D14 with second end point of the series connection of the secondary coils and the cathode is connected to the second end point of the series connection of the capacitors.

The connection points between the secondary coils 220, 221, 222, 223 and 224 are each coupled via one of the diodes D10, D11, D12, D13 to a connection point between the capacitors C1 to C5 such that the anode of the respective diode D10 to D13 is connected to the Terminals of the secondary coils 220,221,222,223,224 and the cathode to the terminals of the capacitors Cl, C2, C3, C4, C5 is connected.

By periodically opening and closing the primary switch SP1, current is generated in the parking coil 21, which changes the magnetic field of the core 23 and thus induces a voltage in the secondary coils 220, 221, 222, 223, 224. As a result, a current is generated in each case, which flows through the diodes D10 to D14 and increases the charges stored in the capacitors C1 to C5. This also increases the voltages provided by the capacitors. Depending on the charging state of the piezo is selectively via the switches SLO Sil, S12, S13, S14 provided by the one of the series connection of capacitors voltages on the switching node K ge ^¬ on.

An idea of this embodiment is based on instead of a constant voltage to increase the supply voltage of the current source CSl in several stages, corresponding to the increase of the voltage at the piezo P. Instead of a current source CS1, a controlled resistance can also be used, this is only a question of the control characteristic.

The mean differential voltage ΔUb thus drops significantly and thus also the power loss in the current source CS1. ever the higher the number of stages, the smaller the difference voltage ΔUb dropping at the current source and thus the power loss can be kept.

The reasonable number of steps resulting from the vertretba ^¬ ren circuitry and the achievable reduction in power dissipation. In practice, the number of intermediate stages will be between 2 and about 5, with an intermediate designating a voltage between the lowest voltage ground and the maximum voltage. As the intermediates were further increased, no significant improvement was found.

FIG. 8 shows a voltage multiplication. The desired voltage Uk can also be achieved by switching to several constant supply voltages.

FIG. 9 shows the voltage curve of the voltage Uk at the switching node K over the time during charging. The voltage applied to the capacitor plates with the respective higher potential is referred to for the capacitors Cl, C2, C3 and C4 as UhI, Uh2, Uh3 and Ub.

The voltage Uk initially has the value UhI, in this phase the secondary switch S10 is closed and the remaining switches S2, S11, S12, S13, S14 and S15 are closed. In the following phase, the secondary switch SlO is opened and the secondary switch Sil closed. As a result, the voltage Uk rises to the value Uh2. Subsequently, the secondary switch Sil is opened again and the secondary switch S12 is closed, whereupon the voltage Uk rises to Uh3. At the end of the charging process, the secondary switch S12 is closed and the secondary switch S13 is closed. rises to the end voltage Ub through the voltage Uk at the switching node.

The diagram also shows the voltage Up applied across the load. Due to the Re ^¬ gelung of the charging current, this voltage has a continuous course. The voltage Uk must always be greater than Up, since the load from the switching node K is charged. The differential voltage AUb = Uk-Up is set so that a specific threshold value is not exceeded in order to limit the power loss of the current setting device CS1. According to FIG. 8, a voltage measuring circuit 40 is provided which measures the voltage ΔUb during the charging and discharging operations.

Figure 10 shows the corresponding method for the discharge of the piezo. In this case, the reference voltage Uk for the discharge current source must always be lower than the voltage Up at the piezo in this case. The energy is fed back into the supply. The switches S12, SIO SIO and S2 are opened sequentially one at a time, so that the clamping ^¬ shown extending voltage, with voltage levels Uh3, Uh2, Uhl, OV is obtained.

Fig. 11 shows a circuit arrangement according to a fourth Ausfuh ^¬ approximate shape. The load P, the switching node K and the current source CSl correspond in arrangement and function to the previous figures. The voltage-generating circuit 30 includes a battery B, a coil L, a first switch Sl, a first diode D1, a second diode D2, a second switch S2, and a capacitor C.

The battery B is connected to its negative pole to the ground ver ^¬ prevented, while its positive pole is connected to a first terminal of the coil L, the second terminal is connected to the intermediate node ZK. The first diode is connected to Cathode connected to the intermediate node ZK and its anode to the ground. The first switch S1 is designed as an NMOS field-effect transistor, which is connected with its drain to the intermediate node ZK and its source to the ground.

The second diode D2 is verbun ^¬ with its anode to the intermediate node ZK and with its cathode to the switching node K verbun ^¬ . The capacitor C with its connections to the switching node K and ground connected. The second switch S2 is connected to the switching node K at one of its source and drain terminals and to the intermediate node ZK at the other of the source and drain terminals.

Alternatively, e.g. the charge on the DC link capacitor C are generated by means of LC resonant circuit. It is only important that this supply voltage always provides a sufficient, but not too large difference ΔUb to the voltage at the piezo available.

FIG. 12 shows the voltage curve of the voltage Uk applied to the switching node K over time. The Emspeisung takes place with a time-invariant, continuously än ^{¬-promoting,} but the desired variation of the voltage at the piezo not reproducing voltage.

FIG. 13 illustrates, on the basis of four diagrams, how the rise or fall of the voltage Uk is realized. The upper two diagrams show the charging of the capacitor C. The first switch S1 is closed while the second switch S2 remains open. The current IL through the coil L increases linearly from 0, thereby establishing a voltage across the coil and storing energy in the magnetic field of the coil. If the first shell ter Sl is opened again, the voltage at the intermediate node ZK increases, so that the current flows through the diode D2. The current IL flows through the second diode to the switching node K, where the capacitor C is charged.

The second diagram shows the course of the voltage Uk. During the first phase, in which the first switch S1 is closed, the voltage remains constant, whereas in the second phase, when the switch is open, it rises in the form of a sine wave quarter wave. The voltage Uk is opened or closed again in one cycle.

In the two lower diagrams, the curves of the current IL through the coil L and the voltage Uk during discharge of the capacitor C are shown. When unloading the switch Sl always remains open. During the first phase, the switch S2 is closed and the current flows back through the switch S2 and the coil L into the battery. In the second phase, the switch S2 is opened. The negative voltage arising at the intermediate node ZK is dissipated by a current flow through the coil L and the first diode D1. During the first phase, the voltage UK on the capacitor C is reduced.

Fig. 14 illustrates a circuit arrangement for driving a plurality of loads. The circuit arrangement has a first switch S1, a second switch S2, a measuring resistor Rs, a discharge control 15, a charge control 14, a load P, a further load P2, a first selection switch T1, a second selection switch T2, a first reference value transmitter 16 and a second setpoint generator 17. The first switch Sl and the second switch S2 are connected in series between the supply voltage Ub and ground, wherein the connection node between the two switches Sl and S2 of the switching node K is. The load P and the further load P2 are each connected to a connection to the switching node K, while their second terminals are connected to a first terminal of the selector switch T1 or T2. The second An ^{¬ connections of} the two selection switches Tl and T2 are connected in common with a first terminal of the measuring resistor Rs, whose second terminal is connected to the ground. The first terminal of a selection switch Tl or T2 and the second terminal of the same selection switch form the load path, wherein the height of the current flowing through the load path are determined by the control input of the selection switches Tl and T2. The selection switches Tl and T2 are formed as MOSFET transistors. It is also possible to use IGBTs with a parallel diode.

The charging control unit 14 and the discharge controller 15 respectively receive the voltage drop across the measuring resistor Rs voltage to the currents through the second switch S2 and the selection switches Tl and T2 to control by their control inputs are driven ent ^¬ speaking. The charge controller 14 and the discharge controllers 15 each receive a setpoint value for the charge current from the setpoint generator 16 or 17.

The already existing ground-side semiconductor switches Tl and T2 for selecting the active injector P and P2 are used simultaneously for controlling the current during charging of the respective injector. At this time, the common current sense resistor Rs in the ground line can be used both for controlling the charging and discharging. The current control loops must therefore not be switched on the input side. For charging only one current control loop is necessary, which is switched within the control unit to the respective active transistor. All inactive can be switched firmly to ground via their control input. In addition to the displacement of the charging current source into the easy-to-control ground path, the distribution of the charging losses to a plurality of power semiconductors, which are in any case necessary anyway, is achieved in particular. Because of the charging / discharging efficiency of the piezo, the charging losses are significantly higher than the power loss in the discharge current source.

The discharge can also be done using the same current sense resistor to ground reference, which allows the realization in a common ASIC. There remains only the likelihood of a switch Sl, which disconnects the supply voltage of the output stage during the discharge.

FIG. 15 shows an overview of the inventive circuit arrangement.

A current source CSl is connected in series with the load P. The series circuit is connected between the ground and a voltage setting circuit 30, which provides a voltage which, depending on U _P , minimizes the power loss across the voltage source CS1.

Claims

claims 1. Circuit arrangement for charging a capacitive load (P), in particular a piezoelectric actuator for a fuel injection valve of an internal combustion engine, comprising: a switching node (K, Kl), a current setting device (CS1, CS, T1) arranged in series with the load (P) for energizing the load (P) during charging, the charging current flowing through the switching node (K, Kl), a measuring circuit (14, 15) for measuring the current through the current setting device (CS1, CS, T1), a control device (SE) for controlling the current setting device (CS1, CS) such that the current is regulated by the current regulator device (CS) by means of a measuring circuit, - And a Spannungsemstellschaltung (Sl, S2, Ch) for changing the voltage (Uboost, Us) at the switching node (K) during the charging of the capacitive load. 2. Circuit arrangement according to claim 1, characterized in that the power control device is a controlled resistor, flows through the load path of the charging current. 3. Circuit arrangement according to claim 1, characterized in that the Stromeinstelleinrichtung contains a transistor (Tl), flows through the load path of the charging current. 4. Circuit arrangement according to claim 3, characterized in that the transistor (Tl) is controlled during charging so that the transistor (Tl) operates in the linear characteristic region. 5. Circuit arrangement according to one of claims 3 to 4, characterized in that a diode (D2) is connected in parallel to the load path of the transistor. 6. Circuit arrangement according to one of claims 3 to 5, characterized in that a setpoint generator (16,17) is provided for setting a reference value for the charging current through the current setting. 7. Circuit arrangement according to one of claims 1 to 6, characterized by - a voltage source for providing a reference to an electrical ground (GND) supply voltage (Ub), a capacitor (Ch) arranged between a first circuit node (K1) and a second circuit node (K2), the first circuit node (K1) being connected to the voltage source via a diode (D1) and the second circuit node (K2) being connected via a first one Switch (Sl) is connectable to the voltage source, a first current path leading from the first circuit node (Kl) to one of the load terminals and a second current path leading from the second circuit node (K2) to the other of the load terminals, a current setting device (CS1, CS2) arranged in series with the load (P), through which the load is energized during charging and discharging, and which comprises a current source arranged in the first current path and / or a current path arranged in the second current path, a second switch (S2) via which the first current path is connected to the second circuit node (K2) is connectable, and - A control device (SE) for controlling the switches (Sl, S2) and the Stromeinstelleinrichtung (CSl, CS2), such that a) during a first charging phase (a) both switches (Sl, S2) are open and the load from the Supply voltage (Ub) is partially charged, b) during a second charging phase (b), the first switch (Sl) is closed and the second switch (S2) is open and the load (P) from the resulting C) during a first discharge phase (c) both switches (Sl, S2) are open and the load (P) is partially discharged into the capacitor (Ch), and d) during a second discharge phase (d) the first switch (S1) is opened and the second switch (S2) is closed and the load (P) is further discharged into the electrical ground (GND). 8. Circuit arrangement according to claim 7, wherein the Stromeinstellemrichtung (CSl, CS2) has a first current source (CSl) for charging the load (P) and separately a second current source (CS2) for discharging the load (P). 9. Circuit arrangement according to one of claims 7 to 8, wherein a for charging the load (P) provided power source (CSl) is arranged in the first current path. 10. Circuit arrangement according to one of claims 7 to 9, wherein a for discharging the load (P) provided in the current source (CS2) is arranged in the second current path. 11. Circuit arrangement according to one of claims 7 to 10, wherein in the first current path, a diode (D2) is arranged, via which the load current (Ip) during the first discharge phase (c) flows. 12. Circuit arrangement according to one of claims 1 to 6, characterized in that the Spannungsseinstellschaltung - A first voltage source for providing a reference to an electrical ground (GND) first voltage (Ub), and - A second voltage source for providing a reference to the electrical ground (GND) second voltage (Uh), which is smaller than the first voltage (Ub), wherein the circuit node (K) via a first switch (Sl) with the first Voltage (Ub), via a second switch (S3, S4) with the second voltage (Uh) and via a third switch (S2) with the electrical ground (GND) is connectable, and a control device (SE) for controlling the Switch (Sl to S4) and the Stromeinstelleinrichtung (CS), such that a) during a first charging phase (a), the second switch (S3, S4) is closed to the load (P) from the second voltage (Uh) partially b) during a second charging phase (b) the first switch (Sl) is closed in order to continue charging the load (P) from the first voltage (Ub), c) during a first discharge phase (c) the second switch (S3 , S4) is closed to partially Entla the load (P) in the second voltage (Uh) and, d) during a second discharge phase (d) the third switch (S2) is closed to further discharge the load (P) into the electrical ground (GND). 13. Circuit arrangement according to claim 12, characterized in that claims, wherein the second voltage source is formed by a capacitor (Ch). 14. Circuit arrangement according to one of claims 12 and 13, characterized in that wherein the second voltage (Uh) is provided at a terminal of the condenser ^¬ sators (Ch) whose other connection to the first voltage (Ub) or with electrical ground ( GND) is connected. 15. Circuit arrangement according to one of claims 1 to 6, characterized in that a n variety, n> 2, is provided by switches, wherein each of the n switch for connecting the switching node (K) is provided with one of n n variety of voltages , A circuit arrangement according to claim 15, characterized in that said plurality of n voltages are provided by a circuit (20) having a plurality of series connected capacitors (Cl, C2, C3, C4, C5). 17. Circuit arrangement according to claim 16, characterized in that the n voltages in each case by a magnetisierba- via a core (23) of a transformer (20) wound coil (220,221,222,223,224) are generated. 18. Circuit arrangement according to one of claims 15 to 17, characterized in that for n: 2 <n <7. 19. Circuit arrangement according to one of claims 1 to 6, characterized by a voltage converter for generating a linear increase of the voltage at the switching node (K) during charging of the load (P). 20. Circuit arrangement according to claim 19, characterized in that a voltage converter for generating a linear drop in the voltage at the switching node (K) during discharge of the load (P). 21. Switching arrangement according to one of claims 19 and 20, characterized in that a voltage measuring circuit (40) is provided for checking whether the voltage across the current setting means exceeds a predetermined threshold value (ΔUb). 22. Circuit arrangement according to one of claims 1 to 21, characterized in that a measuring resistor (Rs) in the path of the series connection of load (P) and power control device (Tl) for measuring the current through the Stromeinstelleinrichtung (Tl) is provided. 23. Circuit arrangement according to claim 22, characterized in that the circuit arrangement also serves for switching at least one further capacitive load (P2), in particular a piezoelectric actuator, and a further current setting device (T2) arranged in series with the further load (P2) via which the further load (P2) is energized during charging, the charging current flowing through the switching node (K), - Wherein the measuring resistor (Rs) is arranged so that charging currents for the load (P) and for the further load (P2) in each case through the measuring resistor (Rs) flow. 24. A method for charging a capacitive load (P), in particular a piezoelectric actuator for a fuel injection valve of an internal combustion engine, comprising the steps a) providing a first voltage (Uboost, Uk) at a switching node (K), b) regulating the charging current in the load (P) by means of a Stromeinstelleinπchtung (CS) as an actuator, the Stromeinstelleinrichtung (CS) m series with the load (P) is switched, and wherein the charging current flows through the switching node (K), c) during the Charging the load (P), changing the voltage at the switching node (K) such that the amount of above the current setting device (CS) decreasing voltage (.DELTA.U8) does not exceed a predetermined threshold during the charging process. 25. The method according to claim 24, characterized in that in step c) the voltage (U _K ) at the switching node (K) is changed in stages. 26. The method according to claim 24, characterized in that in step c), the voltage (U _κ ) at the switching node (K) is changed continuously. 27. The method according to any one of claims 24 to 26, characterized in that both the charging current and the discharge current flows through the switching node (K). 28. A method for charging and discharging a capacitive load (P), in particular a piezoelectric actuator for a Fuel injection valve of an internal combustion engine, comprising - Providing a reference to an electrical ground (GND) supply voltage (Ub) by means of a voltage source, and Adjusting a load current (Ip) flowing through the load (P) during charging and discharging in at least one of two current paths leading to the load, said charging and discharging being such that a) during a first charging phase (a) Recharging a capacitor (Ch) and a partial charge of the load (P) in each case from the supply voltage (Ub), b) during a second charging phase (b) further charging the load (P) from a series circuit of Voltage source and the capacitor (Ch) takes place, wherein in the capacitor (Ch) stored energy is partially transferred to the load (P), c) during a first discharge phase (c) is a partial discharge of the load (P) in the condenser (Ch) such that energy from the load (P) is fed back into the capacitor (Ch), and d) during a second discharge phase (d) further discharge of the load (P) into the electrical ground (GND). 29. A method for charging and discharging a capacitive load (P), in particular a piezoelectric actuator for a fuel injection valve of an internal combustion engine, comprising Providing a first voltage (Ub) related to an electrical ground (GND), Providing a second voltage (Uh) related to the electrical ground (GND) which is less than first voltage (Ub) is, Setting a current (Ip) flowing through the load (P) during charging and discharging, and - Control of switches (Sl to S4) and the current setting (CS), such that a) during a first charging phase (a) the load (P) from the second voltage (Uh) is partially charged, b) during a second charging phase (b) the load (P) is further charged from the first voltage (Uh), c) during a first discharge phase (c), the load (P) is partially discharged to the second voltage (Uh), and d) during a second one Discharge phase (d) the load (P) in the electrical ground (GND) is further discharged.