DE10303779A1 - Device for charging and discharging piezoelectric elements e.g. for motor vehicle common rail diesel fuel injectors, has two parallel circuits connected together at their output sides and to choke terminal - Google Patents

Abstract

A device for charging and discharging piezoelectric elements, has a DC/DC converter (1) with charge- or switching-converter (2) and first- and second power switches (S1,S2). A stop switch (3) is connected to the piezoelectric element (P). In the charge/switching converter first- and second capacitors (C1,C2) is connected in parallel to each of the power switches and to the diodes (D1,D2). The parallel circuit of the first power switch (S1), first diode (D1) and first capacitor (C1) is connected to a first output terminal of the DC/DC converter device, and a parallel circuits of the second power switch (S2), second diode (D2) and second capacitor (C2) are connected to a second output terminal of the DC/DC converter device. The two parallel circuits are connected to one another at their output and to one terminal of a choke (L), the latter being connected at its other terminal to a first output terminal of the switching converter (2).

Description

The invention relates to a device for charging and discharging piezoelectric elements, in particular of piezoactuators in injectors for fuel injection in Motor vehicles.

From "Piezo actuators replace solenoid valve technology", Electronics Automotive, April 2002, it is known piezo actuators in common-rail diesel fuel injection systems Instead of using solenoid valves, because of the faster Switching from piezo injectors a better temporal and spatial distribution the injected fuel is possible. The amount of fuel can be distributed to several single injections, i. several Pre-injections of very small amounts of fuel follow the main injection and, if necessary, several injections again.

For example, is from the DE 199 27 087 A1 a device for charging and discharging a plurality of piezoelectric elements known, said piezoelectric elements may be used among other things as actuators piezoelectric elements, such as those used in fuel injection nozzles for internal combustion engines. A known from this document for loading and unloading a piezoelectric element is in 6 shown. How out 6 can be seen, a first terminal of the piezoelectric element P is permanently connected to ground, that is connected to a first pole of a voltage source, where against a second terminal of the piezoelectric element P via a throttle L and a parallel circuit of a charging switch S11 and a diode D1 with a second pole of the voltage source and via the inductor L and a parallel circuit of a discharge switch S22 and a diode D2 is connected to the first pole of the voltage source. The inductor L, the charging switch S11, the diode D1, the discharging switch S22, and the diode D2 constitute a charging / switching converter 2 , Furthermore, the device comprises a DC / DC converter device 1 with the voltage source B, a DC / DC converter 10 and a storage capacitor C _SP .

The voltage source is formed by a capacitive element comprising, in the example considered, a storage capacitor C _SP . The storage capacitor C _SP is powered by a battery B, for example, a motor vehicle battery and one of these downstream DC voltage. DC / DC converter 10 loaded. The DC / DC converter 10 sets the battery voltage (for example 12V) in a substantially any other DC voltage and charges the storage capacitor CS _P to this voltage.

The charging and discharging of the piezoelectric element P takes place by carrying out a charge transport from an element having capacitive properties, namely the storage capacitor C _SP via an element having inductive properties, for example the inductor L, to the piezoelectric element P or vice versa.

The charging and discharging of the piezoelectric Elements P is clocked, i. the charging switch S11 and the discharging switch S22 will be during of the charging or discharging repeatedly closed and opened.

It is still from this document known, with several to be charged and discharged piezoelectric Elements each piezo element over a connect the first resistor to ground and parallel to it Arrangement a series connection of a second resistor and to provide a parallel circuit of a stop switch and a diode.

The second resistor, the stop switch and the diode serve to completely close the piezoelectric elements unload if they are not completely discharged by the "normal" unloading were. The stop switch is preferably after the "normal" unloading, i. the clocked unloading over closed the discharge switch S22. He concludes the piezoelectric Element over the resistances short and ensures so the removal of any remaining in the piezoelectric element Residual charge.

The first resistor is for measurement the currents flowing during charging and discharging of the piezoelectric elements.

The knowledge of these currents allows a regulated Charging and discharging the piezoelectric elements P; in particular can by a depending on the size of the streams Conclude and open the charging switch S11 and the discharging switch S22 are reached, that the charging current and the discharge current to predetermined average values are set and / or predetermined maximum values and / or minimum values do not exceed or fall below.

The parallel with the stop switch switched diode prevents the occurrence of negative voltages at the piezoelectric elements, as these may be destroyed by this can.

Problematic in such devices for Charging and discharging piezoelectric elements, however, is a very high power loss. The heat generated in the devices is possibly by a simple air cooling no longer dischargeable, so an extra water cooling is required, which increases the space and increases the cost.

It is therefore an object of the present invention an apparatus for loading and unloading pie To provide zoelektrischer elements having a reduced power loss, so that an additional water cooling is no longer required.

According to the invention this object is achieved by a Device for charging and discharging piezoelectric elements, in particular of piezoactuators in injectors for fuel injection in Motor vehicles solved with the features of claim 1. advantageous Further developments of the invention are specified in the subclaims.

By the inventive device for Charging and discharging piezoelectric elements can be low Component overhead using two circuit breakers, from which only one energized is and has low forward losses, the power loss be significantly reduced. Shutdown losses are due to the training of Capacitors over the two circuit breakers and zero voltage switching almost completely avoided. An additional water cooling is no longer necessary.

These and other tasks, features and advantages of the present invention will become apparent from the following Description of a preferred embodiment in conjunction with the drawing obvious.

Show it:

1 a basic structure of a device for charging and discharging piezoelectric elements,

2 a schematic representation of the course of the piezoelectric voltage and the average value of the charging and discharging of the piezoelectric element,

3 the principle of a device according to the invention for charging and discharging piezoelectric elements,

4 a principal current and voltage curve in a device for charging and discharging piezoelectric elements according to 3 suppressing the turn-off losses in S1 through C1 and C2,

5 Current and voltage curves in the inventive device for charging and discharging piezoelectric elements during charging and

6 a conventional device for charging and discharging piezoelectric elements.

For new diesel engines with common-rail injection or petrol engines with spray-guided Direct injection, injectors with piezoactuators are used, to the high dynamic requirements of multiple injections fulfill. Piezoactuators behave electrically like non-linear lossy ones Capacities. During operation of the actuator, the non-linear capacitor is opened and closed unloaded, i. it has to be charged or taken down and taken down become. The charge curve is hysteresis.

The present invention relates Therefore, a device for loading and unloading piezoelectric Elements for the aforementioned Purpose is usable and a significantly reduced power dissipation which means no additional water cooling is required. However, there is no limitation to such use piezoelectric elements; The piezoelectric elements can basically in any devices for be used for any purpose.

In 1 a basic structure of a device for charging and discharging piezoelectric elements is shown. The device according to the invention comprises a DC / DC converter device 1 and a charging or switching converter 2 , An input of the DC / DC converter device 1 an energy E _{D is} supplied and an operating voltage U _B is applied thereto. This energy E _D is supplied from the DC / DC converter device 1 with an efficiency η _{D to} a storage capacitor C _SP , across which a voltage U _SP drops. E _{V D} denotes the loss energy of the DC / DC converter device 1 , The switching converter 2 takes the storage capacitor C _SP in the DC / DC converter device 1 Energy E _HS for an extension of the piezoelectric element and leads them to the memory C _SP minus the losses in the piezoelectric element and the switching converter 2 in the compression of the piezoelectric element as energy E _{R S} again. E _VHS and E _VRS represent the energy losses in the transmission of the energy back and forth from / to the DC / DC converter device 1 while E _VS the energy loss in the switching converter 2 designated. The energy transport in both directions is associated with losses. From the switching converter 2 is at an extension of the piezoelectric element of the piezoelectric capacitance C _P , via which a piezoelectric voltage U _P drops, an energy E _HP supplied, or at a compression of the piezoelectric element, an energy E _{RP is received} by the piezoelectric capacitor. An energy E _{C P is} stored in the piezo capacity and a current I _P flows during a charging or discharging process.

• – Maximale Piezospannung U_P = 200V
• – Piezokapazität bei 200V C_P = 6μF
• – Lade- bzw. Entladezeit t = 200μs

For example, the efficiency of the switching converter 2 in the charging of the piezoelectric element η _{H S} = E _{H P} / E _HS , where E _HP that of the switching converter 2 output energy and E _HS from the memory C _SP in the DC / DC converter device 1 taken energy is. For example, the piezo injector uses a servo-assisted injector with the following characteristics:

• - Maximum piezo voltage U _P = 200V
• - Piezocapacity at 200V C _P = 6μF
• - Charging or discharging time t = 200μs

In 2 is the course of the piezo voltage U _P and the average value of the charging and discharging current I _P shown schematically. It can be seen that the current through the piezoelectric capacitance I _P during charging is a positive rectangular pulse, while it is a negative rectangular pulse during the discharge process and equal to zero during the periods in between.

• – Der mittlere Ladestrom für das piezoelektrische Element muss I_P = 6A sein.
• – Für den eingangsseitigen mittleren Lade- bzw. Schaltwandlerstrom von 6A wird eine eingangsseitige Speicherspannung von U_SP > 200V benötigt.
• – Es ist ein Gleichspannungs/Gleichspannungs(DC/DC)-Wandler zur Wandlung der Betriebsspannung U_B = 14V auf U_SP > 200V erforderlich.
• – Wegen der kurzzeitigen hohen Leistungsaufnahme von 200·6VA ist ein Speicher erforderlich, damit der DC/DC-Wandler für eine wesentlich geringere Spitzenleistung ausgelegt werden kann.

The specifications by the piezoelectric properties lead in the preferred embodiment to the following consequences:

• - The average charging current for the piezoelectric element must be I _P = 6A.
• - For the input-side average charging or switching converter current of 6A, an input-side storage voltage of U _SP > 200V is required.
• - It is a DC / DC converter (DC / DC) to convert the operating voltage U _B = 14V to U _SP > 200V required.
• - Due to the short-term high power consumption of 200 · 6VA, a memory is required, so that the DC / DC converter can be designed for a much lower peak power.

The storage capacitor C _SP , for example, has a capacity of about 50μF.

A device for charging and discharging piezoelectric Elements generates waste heat during operation. The effort for the derivation the heat loss and thus the amount of heat loss should therefore be as low as possible his. In conventional devices for charging and discharging piezoelectric elements is the heat however high.

The main part of the power loss the device for charging and discharging piezoelectric elements arises conventionally in the charging or switching converter in the components with ohmic Wi resistance, which carry a high charging current. These are semiconductor switches and a choke in the switching converter. The losses in the semiconductor switches consist of switch-off losses and transmission losses together. The turn-off losses could be due to faster switching transistors are reduced. Shorter switching times, however, would higher quality transistors require the effort for increase the driver circuit, a low-inductance Require driver construction and therefore increase the cost.

These above-mentioned disadvantages from in conventional Devices for charging and discharging piezoelectric elements, in particular by the charge or switching converter used there should now by the inventive device for loading and Discharge piezoelectric elements are eliminated.

An inventive device for charging and discharging piezoelectric elements is in 3 shown. The device according to the invention for charging and discharging piezoelectric elements has a DC / DC converter device 1 , A switching converter according to the invention 2 for the charging and discharging of the piezoelectric capacitor P only two power switches S1, S2 and one arranged in parallel to each circuit breaker diodes D1, D2 and a stop switch 3 on, which can safely bring the piezo voltage U _P to the value zero.

In the DC / DC converter device 1 is a DC / DC-converted operating voltage U _B connected in parallel with a storage capacitor C _{S P} , so that the voltage drop across the storage capacitor C _SP voltage applied to the output terminals.

The switching converter 2 has two power transistors designed as first and second power switches S1, S2. To each of these power switches S1, S2 is respectively a first and second diode D1 and D2 and a first and second Kon capacitor C1 and C2 connected in parallel. The parallel connection of the first power switch S1, the first diode D1 and the first capacitor C1 is connected to the first output terminal of the DC / DC converter device 1 while the parallel connection of the second power switch S2, the second diode D2 and the second capacitor C2 to the second output terminal of the DC / DC converter device 1 which is at a mass level. The voltage dropping across the parallel connection of the first power switch S1, the first diode D1 and the first capacitor C1 is designated U3, while the voltage across the parallel circuit comprising the second power switch S2, the second diode D2 and the second capacitor C2 is designated U2 referred to as. The two parallel circuits are connected at their output to each other and to a terminal of a choke L. A current flowing through the reactor L is indicated by IL. The throttle L is at its other terminal to a first output terminal of the switching converter 2 connected. The input of the parallel circuit of the second power switch S2, the second diode D2 and the second capacitor C2 is connected to ground.

The stop switch 3 is in turn connected to the first and second output terminals of the switching converter 2 When the piezoelectric element is fully discharged, it is completely discharged by the "normal" discharge, and a parallel circuit of a power switch S3 and a diode is arranged between its two input and output terminals, preventing the diode from experiencing negative voltages on the piezoelectric element.

The output terminals of the stop switch 3 are finally connected to a piezoelectric capacitance P, which is connected on the one hand via a first measuring resistor R _mess1 to ground and to which furthermore a series connection of two further measuring resistors R _mess , R _mess2 is connected in parallel. The Messwi resistances R _mess , R _mess1 , R _mess2 serve to measure the current flowing during charging and discharging of the piezoelectric element currents and the voltage lying on the piezoelectric element.

The following is the function of the Switching converter in the inventive device for loading and Discharge piezoelectric elements explained in more detail.

During the charging process of the piezo capacity P are in the switching converter 2 a first power switch S1 or a second diode D2 and during discharge of the piezoelectric capacitance, a second power switch S2 or a diode D1 energized.

In order to avoid turn-off losses of the power semiconductors are in the inventive device for charging and discharging piezoelectric elements in the switching converter 2 the capacitors C1 and C2 are formed in parallel with the power switches S1 and S2 and the diodes D1 and D2.

In 4 For example, in the case of charging of the piezoelectric capacitance P, the principal current and voltage characteristic in suppressing the turn-off losses in the first power switch S1 is shown by the first and second capacitors C1 and C2. In this case, U3 is a voltage drop across the first power switch S1 and U2 is a voltage drop across the second power switch S2. If the first power switch S1, which is like the second power switch S2, preferably a MOSFET, turns off, the voltage U3 changes only slowly because of the first and second capacitors C1 and C2. The shutdown of S1 is in the 4 shown. The current IS1 through the first power switch S1 is reduced to zero as long as the voltage U3 is still small. Thus, the losses during the switching times of the first circuit breaker S1 are virtually negligible.

Before the first power switch S1 can be switched on again, the voltage U3 must again be brought to the value zero or U2 to U1, as in FIG 5 illustrated. Otherwise, the charge current for the first and second capacitors C1 and C2 would flow across the power switch S1 causing switching losses. The transhipment happens with a negative current IL through the choke L. This is in 5 illustrated.

The second power switch S2 remains as long as closed, until one is enough high current or sufficient energy stored in the inductor L. is. After opening of the second power switch S2 become the first and second Capacitors C1 and C2 are recharged with the negative current.

Analogous operations apply to switching off the second circuit breaker S2 when discharging the piezo capacity.

The energy for the reloading process must be taken from the piezo capacity P beforehand. A negative current is associated with a slight decrease in the piezo voltage U _P. In the preferred embodiment, the current varies between 18A and -6A. With this current, the piezo capacity of 6μF in 200μs is charged from 0V to 200V. The frequency is about 50 kHz.

Thus, in the device according to the invention for charging and discharging piezoelectric elements with few components and low switched current and in each case only one current-carrying Circuit breaker at a given time switch losses be significantly reduced. By using MOSFETs for the circuit breakers instead of IGBTs the forward losses are further reduced. In this way can with the switching converter according to the invention a significantly reduced power loss can be achieved. Thereby it is in the device according to the invention possible to charge and discharge piezoelectric elements an additional cooling to renounce.

Of course, it is also possible to have only one DC / DC converter device 1 in parallel with a number of switching converters 2 and these downstream stop switches 3 and piezocapacities P to connect, for example, to realize a control of piezo actuators in different cylinders.

In summary, the present invention discloses a device for charging and discharging piezoelectric elements, with a significantly reduced power loss and thus a significant reduction in heating can be achieved, so that no costly cooling is required. In the device for charging and discharging piezoelectric elements is a DC / DC converter device 1 with at least one switching converter 2 connected via a stop switch 3 , which can bring the piezo voltage safely to the value zero, is connected to a piezo capacitance P. With each input terminal of a switching converter contained this device 2 in each case a parallel circuit of a power switch S1, S2, a diode D1, D2 and a capacitor C1, C2 is connected. The output of the two parallel circuits is via a throttle L with a first output terminal of the switching converter 2 connected while a second output terminal directly to a second input terminal of the switching converter 2 connected is. By the parallel connection of the capacitors C1, C2 to the circuit breakers S1, S2 and the diodes D1, D2 shutdown losses of the power switches S1, S2 can be suppressed.

Claims (7)

Apparatus for charging and discharging piezoelectric elements, comprising a DC / DC converter device ( 1 ), a switching converter ( 2 ) for the charging and discharging process of at least one piezoelectric element (P) having a first and a second circuit breaker (S1, S2), to each of which a diode (D1, D2) is connected in parallel, and a stop switch ( 3 ), which is connected to the at least one piezoelectric element (P) and can bring the piezoelectric voltage (U _P ) safely to the value zero, characterized in the switching converter ( 2 ) to each of the first and second power switches (S1, S2) in each case in addition to the first and second diode (D1, D2), a first and second capacitor (C1, C2) is connected in parallel, the parallel circuit of the first power switch (S1) , the first diode (D1) and the first capacitor (C1) having a first output terminal of the DC / DC converter device ( 1 ), while the parallel connection of the second power switch (S2), the second diode (D2) and the second capacitor (C2) to a second output terminal of the DC / DC converter device ( 1 ), which are connected to ground level, the two parallel circuits are connected to one another at their output and to one terminal of a choke (L), and the choke (L) is connected at its other terminal to a first output terminal of the switching converter ( 2 ) connected is. Device according to Claim 1, characterized in that the first and second power switches (S1, S2) in the switching converter ( 2 ) Are power transistors. Device according to claim 1 or 2, characterized in that in the DC / DC converter device ( 1 ) a DC / DC-converted operating voltage (U _B ) is connected in parallel with a storage capacitor (C _SP ), so that the voltage across the storage capacitor (C _SP ) voltage applied to the output terminals. Device according to one of claims 1 to 3, characterized in that the stop switch ( 3 ) with the first and second output terminal of the switching converter ( 2 ) and is used to completely discharge the piezoelectric element when it has not been completely discharged by the "normal" discharge. Apparatus according to claim 4, characterized in that between both input and output terminals of the stop switch ( 3 ) is arranged a parallel circuit of a power switch (S3) and a diode. Device according to one of claims 1 to 5, characterized in that the first and second power switches (S1, S2) are MOSFETs. Device according to one of claims 1 to 6, characterized in that the DC / DC converter device ( 1 ) with several switching converters ( 2 ), each connected to a stop switch ( 3 ) and a piezoelectric element (P) are connected.