DE10245135A1 - Piezo actuator drive circuit for internal combustion engine, has diode connected between inductor and capacitor to pass flywheel current of inductor to piezo stacks - Google Patents

Abstract

The capacitors (CA,CB) and piezostacks (P1-P4) are connected through a switch (SA) and an inductor (L). The capacitor (CB) is serially connected to capacitor (CA) which is charged by a direct current (DC) power source (21). A diode (DB) is connected between the inductor and capacitor (CB) to pass flywheel current of the inductor to the piezo stacks. The switch (SA) is repeatedly switched to charge the piezo stacks.

Description

The invention relates to a piezo actuator Drive circuit and more precisely a piezo actuator Drive circuit for a vehicle Fuel injection system.

A piezo actuator uses the piezoelectric Effect of a piezoelectric material such as PZT, in which a piezo stack as a capacitive element by charge or Discharge can expand (expand) or itself can contract (contract), causing a piston can be moved linearly. For example, is a Fuel injection device for an internal combustion engine, the a piezo actuator for switching an on / off Valve of an injector for one Fuel injection known. With this device a driving force applied to a valve body Switching an on / off valve acts, and a stroke size the valve body using a charge size of a piezo stack.

JP-A-10-308542 proposes a device for charging one Piezo stack over an inductor before to a current from one charged by a DC converter Restrict capacitor. This device is with a first conduit through which the flow of a charging current in the piezo stack over the coil from the capacitor is made possible, as well as with a second line path through which the flow of a charging current in the Piezo stack with energy stored in the coil is enabled when the capacitor from the coil through Turning off a switching element is separated, the Piezo stack a charge in the capacitor in small Sizes by repeatedly switching the Switching element can be supplied (first example from the state of the art).

Furthermore, JP-T-2000-506950 discloses an apparatus which is arranged such that a piezo stack over a Inductance from capacitors in one fell swoop a resonance effect of inductance and Capacitors can be charged. In this device is a switch to start charging between the capacitor and the inductor is provided a thyristor with a forward direction that the same as the direction from the capacitor to that Is inductance. After transferring a load in the Piezo stack in one fell swoop due to the resonance effect, the thyristor works to avoid a backward flowing current, causing the charging process can be stopped automatically.

The capacitors have two capacitors in series connected. The charging capacitor on the ground side will charged by a switched power supply. The Blocking capacitor on the inductance side is pre- loaded. One between a port of the Blocking capacitor on the charging capacitor side and the Mass is related to a contraction order from the Piezo stack turned on, and then electrical Charge from the piezo stack through the blocking capacitor withdrawn (second example from the prior art).

The first prior art example requires a higher voltage between terminals of the Capacitor as a target voltage of the piezo stack. However, if there is a voltage between the terminals is above the target voltage, plenty of time to charge required, which is why inadequate charging efficiency provided. Incidentally, there is a DC converter required, which is high Can output tension.

The second example from the prior art is required a device that is capable of supplying sufficient electricity Loading of the piezo stack flow in one go leave, which is why the shape of the inductor is enlarged.

In addition, when trying to load the Piezo stack to end halfway, one Line path thereof are forcibly switched off, whereby the current flows through the inductor. Therefore, that can Device essentially doesn't charge to one stop desired timing and it has a insufficient flexibility in charge control of the Piezo stack and does not necessarily have one sufficient accuracy to control a charge size on.

The invention has been made in relation to the above facts described, and you are the Task based on a piezo actuator To create drive circuit that is good Charging efficiency can be achieved even if one Output voltage of a DC voltage converter over the target voltage of the piezo stack, and a to achieve precise charge controllability.

This task is performed by a piezo actuator. Drive circuit according to claim 1 and alternatively by a piezo actuator Drive circuit solved according to claim 7.

Advantageous refinements are the subject of Dependent claims.

According to a first embodiment of the invention Piezo actuator drive circuit created with a DC voltage supply, a first one Capacitor that is in parallel with the DC voltage supply is switched and by the DC power supply is charged, Piezo actuators, piezo stacks, each in the piezo actuators are included, one Conduction path that the first capacitor and the Piezo stack connects one control unit to one Inductance at an intermediate point in the Route is provided, a first switching unit, provided at an intermediate point in the pipeline is, wherein the first switching unit is the first capacitor and the inductance under the control of the Control unit separates from each other and with each other connects, a second capacitor which is provided and in series with the first capacitor between the first switching unit and the inductance is switched, and a diode used to connect a connection of the second capacitor on the inductor side and the mass is provided, the diode being a Pass direction that is the same as one Direction is in which a charging current from the inductor flows into the piezo stack via the diode, and the Control unit for repeated switching on and off the first switching unit in response to one Piezo stack expansion command is set up to the Piezo stack to load.

According to the invention, the inductance is not enlarged because of the piezo stack in the capacitor stored energy can be supplied in small sizes can, in which the switching unit is switched on and off becomes. In addition, an output voltage of DC power supply can be limited while a to the connection of the inductor on the side of the second capacitor voltage to be applied by a Magnitude of a voltage between the connections of the second Capacitor can be secured.

In addition, it is possible to add an amount of energy depending on the number of times the switching unit is switched on and off freely to control, as a controllable minimum energy unit through the Piezostile supplied energy is defined in which the Switch unit switched on and off at a time becomes.

For a second advantageous embodiment of the invention is considered to continue in a case where the capacitor at the time of Piezo stack contraction absorbs discharged energy high voltage between the terminals of the capacitor can lead to inadequate removal efficiency, which accordingly leads to heat generation. Therefore, it is necessary to use parts of such Drive circuit considering the thermal resistance and Select and interpret temperature characteristics.

According to this second embodiment of the invention hence a piezo actuator drive circuit be created that the above described Can solve the problem of the invention and additional energy efficiently from the piezo stack into the capacitor take.

According to this second embodiment of the invention hence the piezo actuator drive circuit continue on: a route that bypasses the first capacitor and the first switching unit and Connection of a connection of the second capacitor the side of the first switching unit with the mass is provided a second switching unit that is parallel connected to the diode, and a third Switch unit for opening and closing the Line path is provided, the control unit as a control unit for controlling the second Switching unit and the third switching unit as well first switching unit is used, and the Control unit is set up on a Piezo stack contraction command and to switch off the to respond to the first switching unit, the third Switch on switching unit and the second switching unit repeatedly turn on and off, causing will that the piezo stack towards the second capacitor be discharged.

For a period during which the second switching unit is in an on state, becomes a gradually increasing current from the piezo stack to Mass over the inductance and the second switching unit made to flow, and the energy in the piezo stack is partly in magnetic energy of inductance converted. For a period during which the second Switch unit itself in an off state a freewheeling current flows into the second Capacitor from the inductance. Hence the energy of the piezo stack by the second capacitor.

When energy is withdrawn, a connection is made to the second capacitor on the side of the first Capacitor grounded so that a potential at the Connection of the second capacitor on the side of the Inductance lower than that in the charge control in response to a piezo stack expansion command, being efficient in extracting energy is improved instead of the energy of the Piezo stack is removed when the second capacitor is connected in series with the first capacitor.

For a third embodiment of the invention also takes into account that a tension between the Connections of the capacitor to control one Charge size of the piezo stack and to carry out a Charge control based on the detected voltage is detected, as in the case of the first example the state of the art. In a case where the Capacitor or the piezo stack a large capacity has, however, a voltage change is smaller, even with the same size of an energy transfer what leads to insufficient detection accuracy.

Therefore, according to the third embodiment of the invention created a piezo confirmation drive circuit be to solve the problem described above can and continue to have good accuracy for detection an amount of energy change in the capacitor or Piezo stack has.

Therefore, according to this third embodiment in the Piezo actuator drive circuit Control unit set up on a Piezo stack expansion command to respond and the first Switch unit in an off state to note if there is a potential at the connection of the second capacitor on the inductor side predetermined value reached.

As a connection potential of the second capacitor the side of the inductor becomes low when the first Capacitor and the second capacitor a high amount of Energy is supplied to the piezo stack and becomes high when the first capacitor and the second capacitor a small one Feeding the amount of energy to the piezo stack can do that Connection potential of the second capacitor on the side of inductance used as a measure of energy that have been fed to the piezo stack. there changes, the smaller the capacity of the second Capacitor, the sharper a voltage between the connections of the second capacitor depending from the energy quantity supplied to the piezo stack, which is why the size of the energy is regulated more precisely can be.

In the piezo actuator drive circuit, the Control unit as a control unit for Control of the DC voltage supply used, and the control unit is set up, an amount of charge of the first capacitor through the DC voltage supply is charged to increase in this way and decrease that change in voltage between the terminals of the second capacitor before and after discharging the piezo stack in response to a piezo stack contraction command a predetermined one Reference value is.

Because one from the piezo stack through the second capacitor withdrawn amount of charge is regulated so that it is at a reference value, the Piezo stack a correct amount of energy of the second Capacitor received when the piezo stack is charged is why an amount of energy of the piezo stack with can be controlled with high accuracy.

For a fourth advantageous embodiment of the invention is taken into account that in the case of the first Example from the prior art, in which energy in small sizes is given by inductance flowing current is not controlled at a time can be when the piezo stack is its target charge size has reached, with energy corresponding to the size of the Current in the piezo stack is transmitted, causing a Error in the charge size is generated.

According to a fourth embodiment of the invention hence a piezo actuator drive circuit be created that the above described Can solve the object of the invention, and continue to be a good one Has controllability for energy.

According to this fourth embodiment, the Piezo actuator drive circuit still on: Disconnect switching units that are used to disconnect the Piezo stacks are provided by the conduction path, and one Diode used to connect a connector of the first Capacitor on the side of the switching unit, which for Disconnect and connect the first capacitor and the Inductance is provided with a connection of Inductance provided on the side of the piezo stack the diode has such a direction, that a voltage between both terminals of the first Capacitor becomes a reverse voltage, the Control unit as a control unit for Control of the disconnect switch unit is used, and the control unit is set up, the Switch off switching unit and the piezo stack from that Disconnect line route when charging the Piezo stack is complete.

By switching off the switching unit and switching off the Disconnect switch unit for separating the piezo stack from the conduction path comes through the inductance current flowing through a Extraction diode and is through the first capacitor taken, whereby the loss can be reduced. It it is also possible to load the piezo stack due to a freewheeling current caused by the inductance after switching off the switching unit, to avoid which is why a charge size of the piezo stack is correctly below Can be controlled using a time period during which the switching unit is in one switched off state.

For a fifth advantageous embodiment of the invention is taken into account that in the case of the second Example from the prior art of the blocking capacitor connected in series with the charging capacitor to the DC-DC converter to be loaded what the Circuit complicated. For example, one is Switching only required for charging separately.

Therefore, according to the fifth embodiment, a Piezo actuator drive circuit created be the task of Can solve invention and in addition a simple Setup without such a problem when loading the Has blocking capacitor.

According to the fifth embodiment of the invention, the Piezo actuator drive circuit still on: a route that bypasses the first Capacitor and the first switching unit and Connection of a connection of the second capacitor the side of the first switching unit with the mass is provided a second switching unit that is parallel connected to the diode, and a third Switch unit for opening and closing the Line path is provided, the control unit as a control unit for controlling the second Switching unit and the third switching unit as well first switching unit is used, and the Control device is set up to carry out: a first step of an activation control including switching on the first switching unit, the second switching unit and the third Switching unit are in a switched-off state a time of activation of a device for charging the piezo stack, a second step of the Activation control, the first step of Activation control follows, including Switch off the first switching unit and switch on the third switching unit to discharge the second Effect capacitor and a third step of Activation control, the second step of Activation control follows, including Switch on the third switching unit and repeat Switch the second switching unit on and off in order to Discharge the piezo stack towards the second capacitor to effect.

The DC power supply can be used to charge the second Capacitor and the first capacitor used be what a simplified structure without the need to include an additional energy source allows to charge the second capacitor is needed.

For a sixth embodiment of the invention takes into account that one in the capacitor or in the Piezo stack remaining charge when the device is not in normal operating conditions, one Can cause errors in cargo size, and also additional processing such as that it must first be confirmed whether there is cargo is or not, and a corresponding discharge include when performing maintenance, for example can.

Therefore, according to the sixth embodiment of the invention a piezo actuator drive circuit are provided which are the object of the invention can solve and continue to avoid a residual charge.

According to the sixth embodiment of the invention, the Piezo actuator drive circuit according to the Invention on: a DC power supply, one first capacitor, which is in parallel with the DC voltage supply is switched and by the DC power supply is charged, Piezo actuators, piezo stack, each in the Piezo actuators are included, one Conduction path that the first capacitor and the Piezo stack connects an inductor connected to one An intermediate point is provided in the route Switching unit located at an intermediate point in the Line path is provided, the switching unit first capacitor and the inductance from each other separates and connects, and a resistance, which is connected in parallel to the piezo stack.

The piezo stack discharges accordingly Time constants that differ from a resistance value of the Resistance and a capacitance of the piezo stack depends. It is possible due to residual charges and charge build-up to avoid temperature changes in the piezo stack, that would generate a mistake in energy since one Discharge path for the piezo stack is secured. In addition, operations to remove the residual charge in the piezo stack, for example during maintenance omitted. During the discharge of the piezo stack itself then takes place when the piezo actuator is in an expansion state, a charge size of the piezo stack and a resistance value of the resistor be set with regard to a time during which the piezo actuator its necessary Expansion state and the like must maintain.

The piezo actuator drive circuit has continue on: a second capacitor that is provided is in series with the first capacitor between the first switching unit and the inductance is switched, a diode used to connect a connection of the second capacitor on the inductor side and the mass is provided, the diode being a Pass direction that is the same as one Is in the direction of loading the piezo stack used charging current from the inductance in the Piezo stack flows over the diode, a conduction path that for connecting a connection of the second capacitor provided on the side of the switching unit with the mass is a second switching unit that is parallel to the diode is switched, and another switching unit, which for Opening and closing the line path is provided, and a control unit that is set up repeats the switching units in opposite phases on and off.

When the switching unit is in an on Condition, a current flows through one Line path from the second capacitor through the Inductance to the resistor. Hence Capacitor energy through the resistance in part consumed, and charges become the second Transfer capacitor. If another switching unit is in an on state, becomes a closed circuit bypassing the first capacitor are formed and charges in the second capacitor unload to the crowd. The ones described above States are repeated, whereby charge amounts of the first capacitor and the second capacitor to zero can be brought.

The invention is described below with reference to Embodiments with reference to the enclosed drawing described in more detail. Show it:

Fig. 1 is a diagram of a Piezobetätigungsglied- drive circuit according to a first embodiment,

Fig. 2 is a block diagram of a fuel injection apparatus according to the first embodiment,

Fig. 3 is a cross sectional view of an injector of a fuel injection apparatus according to the first embodiment,

Fig. 4 is a time chart illustrating an operation state of a piezo actuator driving circuit according to the first embodiment,

Fig. 5 is a time chart illustrating an operation state of the piezoelectric actuator drive circuit according to the first embodiment,

Fig. 6 is a circuit diagram of a Piezobetätigungsglied- drive circuit according to a second embodiment,

Fig. 7 is a time chart illustrating an operation state of the piezoelectric actuator drive circuit according to the second embodiment, and

Fig. 8 is a time chart illustrating an operation state of the piezoelectric actuator drive circuit according to the second embodiment.

Below is a first embodiment described.

In Fig. 1, a structure of a Piezobetätigungsglied- shown driving circuit. Fig. 2 shows the construction of a common rail fuel injection apparatus of a diesel internal combustion engine. Fig. 3 shows the structure of an injection device. Before describing the piezo actuator drive circuit, the fuel injector is described. As shown in Fig. 2, as many injectors 1 are provided corresponding to the individual cylinders as there are cylinders in the diesel engine. Only one of these injection devices 1 is illustrated in this drawing. The injector 1 is arranged to be supplied with fuel via a supply line 45 from a common rail 44 , and to inject fuel into a combustion chamber of each cylinder at an injection pressure that is approximately equal to a fuel pressure is within the common rail 44 , hereinafter referred to as common rail pressure. The fuel in a fuel tank 41 is pressurized and introduced into the common rail 44 by a high pressure supply pump 43 and stored therein at high pressure.

The fuel supplied to the injector 1 from the common rail 44 is used for hydraulic pressure control for the injector 1 as well as for injection into the combustion chamber as described above, and then the fuel flows back to the fuel tank 41 from the injector 1 via a drain line 46 at a low pressure.

A CPU (central processing unit) 31 calculates the injection timing and the injection amount of the fuel based on detected signals such as a crank angle, and outputs an injection signal INJ and a cylinder signal for identifying a cylinder to be injected to a piezo actuator drive circuit 2 in accordance with Calculation results. The piezo actuator drive circuit 2 drives piezo actuators installed in the individual injectors 1 to effect fuel injection by the injectors 1 during a given period.

The common rail 44 is provided with a pressure sensor 32 which detects a common rail pressure. The CPU 31 controls a regulator valve 42 based on the detected common rail pressure to regulate an amount of fuel that is pressurized and introduced into the common rail 44 .

As shown in FIG. 3, the injector 1 is in the form of a rod and is attached such that its leading end, which is shown on the lower side as shown in FIG. 3, protrudes into the combustion chamber. The injection device 1 is arranged such that it has a nozzle section 1 A, a back pressure control section 1 B and a piezo actuator 1 C in the order from bottom to top.

Within a sleeve-shaped body (nozzle body) 104 of the nozzle section 1 a, a needle 121 is slidably held in its rear end section. The needle 121 is set on an annular seat 1041 or is lifted off the annular seat 1041 formed in a leading end portion of the nozzle body 104 . In a surrounding free space 104 in the leading end portion of the needle 121 , high-pressure fuel is introduced from the common rail 44 through a high-pressure passage 101 and the introduced fuel is injected through an injection port 103 when the needle 121 is lifted off. The needle 121 has an annular stepped surface 1211 , on which a fuel pressure from the high-pressure passage 101 acts in the lifting direction, ie upwards.

Behind the needle 121 , a back pressure chamber 106 is formed for generating a back pressure on the needle 121 , into which fuel as control oil is introduced from the high pressure passage 101 via an inlet port 107 . This back pressure acts on the rear end surface 1212 of the needle 121 in the seat direction, ie downward, together with a spring 122 which is arranged in the back pressure chamber 106 .

The back pressure is increased by the back pressure control section 1 B and decreased. The back pressure control section 1 B is controlled by the piezo actuator 1 C with the piezo stack 127 .

The back pressure chamber 106 always communicates with a valve chamber 110 of the back pressure control section 1 B via an outlet mouth 109 . The valve chamber 110 is shaped in a conical shape with a ceiling plane 1101 with an upward slope. In the top of the ceiling level 1101 , a low pressure connection 110 A is opened, which communicates with a low pressure chamber 111 . The low pressure chamber 111 communicates with a low pressure passage 102 that leads to the drain line 46 . In the lower surface of the valve chamber 110 , a high pressure port 110 B is opened, which communicates with the high passage 101 via a high pressure control passage 108 .

A ball 123 is arranged in the valve chamber 110 , the lower section of which is cut away horizontally. The ball 123 is a valve body that can be moved up and down. When the ball moves 123 downward, it continues with the above-described cut-off surface to the bottom surface 1102, the valve chamber (designated the hereinafter referred to as high-pressure side seat) as a valve seat is used, and closes the high-pressure port 110 B from, whereby the valve chamber 110 is cut off from the high pressure control passage 108 . When the ball 123 moves upward, it settles on the above-described ceiling plane 1101 , which is used as the valve seat (hereinafter referred to as the low pressure side seat), and closes off the low pressure port 110 A, thereby cutting off the valve chamber 110 from the low pressure chamber 111 becomes. Thus, when the ball 123 is in the lower position, the back pressure chamber 106 communicates with the low pressure chamber 111 via the outlet port 109 and the valve chamber 110 , so that back pressure in the needle 121 is reduced and the needle 121 is lifted. In contrast, when the ball 123 is in the up position, the back pressure chamber 106 is cut off from the low pressure chamber 111 and only communicates with the high pressure passage 101 , so that back pressure in the needle 121 increases and the needle 121 is set.

Ball 123 is pushed and driven by piezo actuator 1 C. Piezo actuator 1 C has an elongated opening 112 formed in the vertical direction above low pressure chamber 111 , two pistons 124 and 125 with different diameters located in elongated opening 112 are held displaceably, and a piezo stack 127 , the expansion and contraction directions of which coincide with the up and down direction and which is arranged above the upper piston 125 with a large diameter.

The large diameter piston 125 is held in contact with the piezo stack 127 by a spring 126 held below the large diameter piston and is arranged to be up and down by the same size as that when expanded and Contraction of the piezo stack 127 is offset.

An offset enlargement chamber 113 is formed and filled with fuel in a space delimited from the lower small diameter piston 124 in the opposite direction from the ball 123 , the large diameter piston 125 and the elongated opening 112 . When the large diameter piston 125 is displaced downward by the expansion of the piezo stack 127 , the fuel in the displacement enlargement chamber 113 is compressed, whereby the compressive force is transmitted to the small diameter piston 124 via the fuel in the displacement enlargement chamber 113 . Because the small diameter piston 124 has a smaller diameter than the large diameter piston 125 , an expansion size of the piezo stack 127 is increased and converted into an offset of the small diameter piston 124 . When fuel is injected, the piezo stack 127 is first loaded to expand, whereby the small diameter piston 124 moves downward to push the ball 123 down. As a result, the ball 123 is lifted from the low pressure side seat 1101 and placed on the high pressure side seat 1102 to establish communication between the back pressure chamber 106 and the low pressure passage 102 , thereby reducing the fuel pressure in the back pressure chamber 106 . As a result, the force acting on the needle 121 in the lift direction dominates the force acting on the seat direction, and therefore the needle 121 is lifted to start the fuel injection.

To stop fuel injection, unloading the piezo stack 127 causes the piezo stack 127 to contract (contract) again, thereby releasing the actuation force acting on the ball 123 . At this time, since the inside of the valve chamber 110 is at a low pressure and the lower surface of the ball 123 receives a high fuel pressure from the high pressure control passage 108 , an overall upward fuel pressure acts on the ball 123 . Then, the ball 123 is removed from the high pressure side seat 1102 by releasing the operating force acting on the ball 123 , and the ball 123 is placed on the low pressure side seat 1101 again. As a result, the needle 121 is set by increasing the fuel pressure in the valve chamber 110 so that the injection is stopped.

Referring to FIG. 1, the piezo actuator drive circuit 2 for charging and discharging the piezo stack 127 is described. To simplify the description, the piezostack 127 is shown as a piezostack P1, a piezostack P2, a piezostack P3 and a piezostack P4 corresponding to four cylinders. The piezo actuator drive circuit 2 has a charge and discharge circuit section 20 , a DC-DC converter 21 , which is a DC voltage supply, and a control device 22 , which is a control unit. The charge and discharge circuit section 20 has first and second capacitors CA and CB for applying voltages to the piezo stacks P1 to P4, the capacitors being arranged such that they form a functional main and subsystem relationship (master and slave). The first capacitor CA is connected to an output of the DC / DC converter 21 . The DC-DC converter 21 is a step-up chopper circuit for boosting a voltage applied from a battery B attached to a vehicle to apply the voltage to the first capacitor CA.

The first capacitor CA has an adequately large capacitance. The capacitance of the second capacitor CB is sufficiently smaller than that of the first capacitor CA, and the second capacitor CB is connected in series with both the first capacitor CA and the DC-DC converter 21 . The second capacitor CB and the first capacitor CA are connected to one another via a first switching element SA, which is a first circuit unit.

The first switching element SA consists of a MOSFET, the parasitic diode DA (which is suitably referred to as the first parasitic diode hereinafter) is connected to the first capacitor CA such that a voltage between both terminals of the first capacitor CA charged by the DC-DC converter 21 is used as reverse voltage (inverted bias).

In addition, the second capacitor CB with the Piezo stacks P1-P4 connected via an inductance L, which is why a first power path W1 is formed in such a way that the piezo stacks P1-P4 are fed.

Furthermore, the inductance L forms a second one Route W2. This route W2 is with a provided second switching element SB, the second Switching unit is at one end of the inductance L on the Side of the second capacitor CB to ground connect. The route W2 forms a closed one Circle including the inductance L, the piezo stack P1-P4 and the second switching element SB. The second Switching element SB is also made of a MOSFET built up. The second switching element SB is like this interconnected that a forward direction of its Parasitic Diode DB (the following in an appropriate manner is referred to as the second parasitic diode) the same as is the direction in which a charging current through the parasitic diode DB and then by the inductance L in the piezo stack P1-P4 flows.

The routes W1 and W2 are shared by the single piezo stack P1-P4 used. The ones to be controlled or the piezo stack P1-P4 to be driven can be like selected below. The Piezo stack P1-P4 are with switching elements SP1, SP2, SP3 and SP4 (suitably referred to below as Selection switching elements are called) each in series connected. From the selection switching elements SP1-SP4 at the time of injection, only the one with the Piezo stack P1-P4 connected switching element accordingly the injecting cylinder turned on.

Each of the individual selection switching elements SP1-SP4 is off a MOSFET and connected in such a way that the Directions of their parasitic diodes DP1, DP2, DP3 and DP4 (which are appropriately referred to below as parasitic Selection diodes are labeled) opposite to the Directions are in which the charging current from the Inductance L flows to the piezo stacks P1-P4 each.

A line path W3 is for connecting a connection of the second capacitor CB on the first side Switching element SA provided with the mass, and in the Line path W3 are a third switching element SC and one Diode DE connected in series. The switching element SC is made up of a MOSFET. The parasitic diode DC of the Switching element SC and the diode DE are of this type interconnected that they are opposite to each other Have directions, and in addition the diode DE set such that their forward direction is the same what is the direction in which a stream is coming from the side of the second capacitor CB flows to ground.

In addition, the diode DE is in the line path W3 such a direction that a tension between both connections of the second capacitor CB becomes a reverse voltage (inverted bias).

Furthermore, the piezo stack is between the connections P1-P4 on the side of inductance L and ground one Diode DG provided in such a direction that a voltage between the terminals of each piezo stack P1-P4 a reverse voltage at the time of expansion becomes.

The switching elements SA, SB, SC and SP1-SP4 each receive control signals SWSA, SWSB, SWSC, SWS1, SWS2, SWS3 and SWS4 from the control device 22 at their gates (control connections). The control device 22 switches on and off for the individual switching elements SA-SP4 in a suitable manner.

The control device 22 receives a potential VCBL at the connection of the second capacitor CB on the inductor L side and a voltage VCBD between the connections of the second capacitor CB. A detection circuit 23 detects the potential VCBL and the voltage VCBD.

For example, an injection signal INJ supplied to the control device 22 is a binary signal with logic L and H levels (low and high levels). The leading edge of the signal is used as a piezo stack expansion command, and its trailing edge is used as a piezo stack contraction command. The control device 22 outputs a switching signal DCSW for the DC / DC converter 21 .

In Figs. 4 and 5 time curves are shown which represent the operating states of individual parts of the piezoelectric actuator drive circuit 2. The function of the control device 22 and the operation of the piezo actuator drive circuit 2 are described below.

In the time profiles described below, the signals observed in the individual sections of the drive circuit 2 are designated by the following reference symbols. SA, SB, SC, SP1, SP2, SP3 and SP4 each show switched-on and switched-off states of the individual switching elements, the high level indicating a switched-on state. VCAS is a potential at the connection of the first capacitor CA on the side of the switching element SA. VCBL is a voltage at the connection of the second capacitor CB on the inductor L side. VCBS is a potential at the connection of the second capacitor CB on the switching element SA side. VCBD is a voltage between the terminals of the second capacitor CB. VP1L is a potential at the connection of the piezo stack P1 on the side of the inductance L. IL is a current which flows through the inductance L. IDF is a current flowing through the diode DF according to the second embodiment.

VCAD is a voltage between the terminals of the first capacitor CA.

The starting procedure is described below.

As shown in the left half section in Fig. 4, the first capacitor CA and the second capacitor CB are charged at the time of activation of the device before charging the piezo stack P1-P4. Thus, charging the first capacitor CA and the second capacitor CB brings the connection of the first capacitor CA on the switching element SA side to a higher potential with respect to the ground side. At the same time, this brings the connection of the second capacitor CB on the inductor L side to a higher potential with respect to the connection on the switching element SA side. When the switching element SA is turned on, a voltage is applied to the terminal of the inductor L on the side of the second capacitor CB, which voltage is generated by adding a voltage between the terminals of the first capacitor CA and a voltage between the terminals of the second capacitor CB , A voltage between the connections of the first capacitor CA is set in such a way that it is somewhat higher than the target charge voltages of the piezo stack P1-P4.

The activation of the device is described below.

The control device 22 is set to output control signals to the first, second and third switching elements SA, SB and SC as well as the selection switching elements SP1-SP4, for example in response to an actuation for switching on the ignition switch (key switch) of the internal combustion engine when the device is activated, such as it is shown in the first half of the time profiles according to FIG. 4. This process causes the first capacitor CA and the second capacitor CB to be charged initially.

This activation control is made up of three Steps of control put together. First, in the first step of activation control all Selection switching elements SP1-SP4 and the first switching element SA switched on. This process causes the first capacitor CA and the second capacitor CB as well the piezo stacks P1-P4 are loaded. The second Capacitor CB is the connector on the side of the switching element SA at a higher potential than that Connection on the side of the inductance L during the Period of this first step of activation control, in contrast when loading the piezo stack P1-P4 controlled according to a piezo stack expansion command becomes.

According to this exemplary embodiment, the potential at the connection on the side of the switching element SA does not exceed a voltage between the connections of the first capacitor CA, since the second capacitor CB is connected in series with the piezo stacks P1-P4. In addition, since the capacitances of the second capacitor CB and the piezo stack P1-P4 define voltages between the connections of the piezo stack P1-P4, the capacitance of the second capacitor CB can assume such a value that charge voltages of the piezo stack P1-P4 do not lead to a compressive force can, which is required to lift the ball 123 . The capacity of the second capacitor CB is reduced to limit the charge voltages of the piezo stack P1-P4. The range of values that the capacitance of the second capacitor CB can assume is spread by connecting the piezo stacks P1-P4 in parallel to reduce a combined capacitance of all the piezo stacks P1-P4.

The second step is then the Activation control for the third switching element SC a predetermined period of time in an on Status. This forms a closed circle that itself from the second capacitor CB via the diodes DE and DB extends, and then the second capacitor CB discharged to a voltage between its terminals to bring it to zero. The time until a tension between the connections of the second capacitor CB zero can be reached in advance on the basis of a Time constants of the closed described above Circle can be calculated. It is therefore advantageous to Time during which this third switching element SC is in in an on state longer than that set calculated time.

In the third step of the activation control, the second switching element SB and the third switching element SC are subsequently switched on and off in the opposite phase. As a result, the piezo stacks P1-P4 are discharged toward the second capacitor CB, as in the case of controlling the discharges of the piezo stacks P1-P4 in response to a piezo stack contraction command. This brings the connection of the second capacitor CB on the inductor L side to a positive potential and increases a voltage between the connections of the second capacitor CB. Thus, a state of charge can be achieved that enables charge control in response to a piezo stack expansion command, and a voltage exceeding the supply capacity of the DC-DC converter 21 can be applied to the terminal of the inductor L on the side of the second capacitor CB in response to a piezo stack expansion command.

As for the number, how often the second and third Switching element SB and SC in this third step Activation control can be switched on and off a predetermined fixed number due to the effect of Diode DG sufficient enough as in the above described case of controlling the discharges in Response to a piezo stack contraction command.

Therefore, it is possible to charge the selected piezostacks P1-P4 with sufficient voltages in response to a piezostack expansion command without the need to enlarge the DC-DC converter 21 .

Furthermore, a state of charge is achieved in which the second Capacitor CB has a positive potential at its Has connection on the side of the inductance L, by once the second capacitor CB and the Piezo stack P1-P4 loaded and later the second one Capacitor CB is discharged, and subsequently in the Piezo stacks P1-P4 stored charges to the second Capacitor CB are transferred as needed an additional circuit for charging the second Capacitor CB eliminated. Therefore, the structure of the Device can be very simple.

The charging process is described below.

The control device 22 is set up in such a way that control signals are output to the first switching element SA and the selection switching elements SP1-SP4, as are shown in the latter half of the time profiles according to FIG. 4 at the time of starting the injection, ie when a piezo stack expansion command is received, the selected piezo stack can be loaded.

For example, in response to an expansion command for the piezo stack P1, the selection switching element SP1 is switched on in accordance with the piezo stack P1 and the first switching element SA is switched on and off repeatedly. The right half section in FIG. 4 shows a state of charge of the piezo stack P1. For a period of time during which the first switching element SA is in an on state, a gradually increasing charging current is used in the selected piezo stack P1 from the first capacitor CA and the second capacitor CB, which are connected in series with the switching element SA of the first route W1 made to flow. For the subsequent period, during which the switching element SA is in an off state, a gradually falling current is made to flow into the piezo stack P1 in the conduction path W2 by the parasitic diode DB, which bypasses the first and second capacitors CA and CB while the energy stored by the inductor L is consumed according to the magnitude of a current which has flowed through the inductor L at the end of the one-period of the switching element SA.

The point in time at which the switching element SA is switched off is before the point in time at which a current IL flowing through the inductance L reaches saturation. The switching element SA can be switched off at the time when a detected current of IL reaches a predetermined upper limit of its current value. In addition, with respect to the time when the off period is switched to the on period, the switching element SA is turned on at a time when a detected current of IL reaches a lower limit of its current value, which is set to approximately zero. For this purpose, a unit 24 is provided for detecting a current IL flowing through the inductance L. For example, resistors with small resistance values can be provided at some middle points in the line paths W1 and W2 to obtain information regarding a current IL based on the voltages between the terminals of the resistors.

The charge of the piezo stack P1 passes through Repetition of switching the switching element on and off SA advance as shown, creating a potential on the VP1L Connection of the piezo stack P1 on the side of the Inductance L gradually increases. In contrast to the voltages between the terminals of the Capacitors CA and CB on below an initial Voltage value decreased, which is why the potential VCBL reduced.

According to this embodiment, the capacity of the first capacitor CA is large and is the capacitance of the second capacitor CB small, so the potential VCBL changes greatly while the potential of the first Capacitor CA shows no major changes. If a charge size of the second capacitor CB is such that a voltage between the terminals of the second Capacitor CB did not turn negative at the time changes if any of the piezostacks P1-P4 with Charge sizes according to its target voltages is therefore possible, a potential above the target voltages of the piezo stack P1-P4 on the Connection of the inductance L on the side of the Switching element SA when charging the piezo stack P1-P4 guarantee.

When the potential VCBL reaches a given value, the switching element SA is switched off State, and then it becomes Selection switching element SP1 turned off, which the Charge is completed. It will Selection switching element SP1 switched off at the time when a current flowing through the inductor L (the hereinafter appropriately referred to as L-current is) reached a lower limit current thereof, and after that the current is considered to be zero would have become. This is because the simultaneous Switching off the switching element SP1 and the switching element SA causes an inductor L flowing electricity go everywhere at this time can.

This loading of the piezo stack P1 expands the piezo stack P1, thereby pushing and lifting the ball 123 through the displacement enlargement chamber 113 . Thus, the needle 121 is raised, whereby the injection is started.

The unloading process is described below.

The control device 22 outputs control signals for the second switching element SB and the third switching element SC, as shown in the first, left half of the time profiles according to FIG. 5, in order to discharge the piezo stack P1 at the time of stopping the injection, ie at To effect receipt of a piezo stack contraction command.

Regarding the piezo stack contraction command, that will be second switching element SB and the third switching element SC repeatedly in and in the opposite phase switched off.

For a period of time during which the second switching element SB is in an on state a gradually increasing discharge current from the Piezo stack P1 to ground via inductance L and that Switching element SB using the second Line route W2 made to flow. During this Period is the diode DE in the line path W3 in one such a direction inserted that a tension between both connections of the second capacitor CB becomes a reverse voltage, so the second capacitor CB is not discharged when the switching element SB is in is in an on state since the diode does not conduct backwards.

For the subsequent period during which the third switching element SC in an on state is a gradually decreasing freewheeling current from the piezo stack P1 through the inductance L in the second capacitor CB, namely to ground, below Using the first route W1 for flow brought.

According to this embodiment, as in the case of charging the on period of the second Switching element SB on the on period of the third Switching element SC switched when a detected current of IL reaches the upper limit while the Switch-on period of the switch-on element SC to the Duty cycle of the second switching element SB is switched when the detected current of the IL lower limit reached.

The on / off operations of the second switching element SB and the third switching element SC become one Time ends when the discharge of the piezo stack P1 is completed. The passage of time can affect the potential VCBL based in the case of loading, or can for example by detecting a voltage between the connections of the piezo stack P1 can be determined.

The DG diode is between the connection of the Piezo stack P1 on the side of the inductance L and the Mass provided in such a direction that a Voltage between the connections of the piezo stack P1 to becomes a reverse voltage at the time of expansion, and the diode DG prevents the connection of the Piezo stack P1 on the side of the inductance L. has lower potential than on the side of the Selector switch element SP1 so that it is not required is, the course of time with high accuracy determine. Therefore, to simplify the number, how often the second switching element SB and the third Switching element SC until the discharge of the Piezo stack P1 on and in an extraction state be turned off, appreciated, so that second switching element SB and the third switching element SC at the time in an off state each be recorded if the number of entries / Switching off these switching elements such a number achieved that the discharge is considered complete can be.

The discharge of the piezo stack P1 causes the contraction of the piezo stack P1, which releases a compression force that acts on the ball 123 due to the fuel pressure of the displacement enlargement chamber 113 , so that the ball 123 is set. As a result, the needle 121 is set to stop injection.

Thereafter, in response to injection signals INJ from the CPU 31, the piezo stacks P1, P2, P3 and P4 corresponding to the injection cylinders are sequentially subjected to the charge and discharge control as described above. For example, the right half of FIG. 5 shows the charge of the piezo stack P2.

In addition, a voltage between the terminals of the second capacitor CB can be detected to perform switching control of the DC-DC converter 21 such that a change in the detected voltage between the terminals before and after the piezo stack P1-P4 is discharged in response to the piezo stack contraction commands Reference value is, and to perform a feedback control such that a charge size of the first capacitor CA is increased and decreased by the DC-DC converter 21 . Since the voltage between the connections of the capacitor CB is obtained in this case under a condition in which the switching element SA is grounded (is at ground potential), such a detected voltage between the connections precisely represents charge quantities that result from the piezo stack P1-P4 be withdrawn by the second capacitor CB. Therefore, the selected piezo stack P1-P4 can be controlled in the energy quantity with high accuracy by controlling the DC-DC converter 21 in such a way that this detected voltage is used as a reference value.

Below is a second embodiment described.

In Fig. 6 is a Piezobetätigungsglied- drive circuit is described according to the second embodiment. This piezo actuator drive circuit 2 A has the same basic structure as according to the first embodiment, but differs from the piezo actuator drive circuit according to the first embodiment in that it has a diode DF and a resistor R and the setting of a control device 22 A differs , While the piezo actuator drive circuit is described here in terms of the differences between the first and second embodiments, like parts that perform substantially the same functions as those of the first embodiment are denoted by the same reference numerals as those of the first embodiment.

The diode DF is between one connection Inductance L on the side of the piezo stack P1-P4 and a connection of a first capacitor CA on the Side of a first switching element SA switched. The Diode DF has a cathode on the side of the first Capacitor DA on and uses a voltage between the terminals of the first capacitor CA as their Blocking voltage.

The resistance R is between the terminals of the Piezo stack P1-P4 on the side of the inductance L and the mass switched.

Also according to this embodiment receives the control device 22 A voltages VP1D, VP2D, VP3D and VP4D between the terminals of the piezo stack P1-P4 and determined on the basis of the received voltages between the terminals if the piezo stack each have reached the target charge sizes. These voltages between the terminals are detected by detection circuits 25 , 26 , 27 and 28 .

FIGS. 7 and 8 are diagrams illustrating operating states of individual parts of the piezoelectric actuator drive circuit 2 A. The operation of this piezoelectric actuator drive circuit 2 A and the setting of the control device 22 A will be described below with reference to FIGS. 7 and 8.

The control device 22 A performs essentially the same control as the control device according to the first embodiment, but differs from the control device according to the first embodiment in a different setting of the charge control in response to a piezo stack expansion command and by the addition of a new discharge control when the device has stopped.

The charging process is described below.

Fig. 7 shows timings in the case of charging the piezo stack P1 in response to a piezo stack expansion command. In this illustration, a dotted line shows a waveform in a case where the diode DF is not used. If the first switching element SA is repeatedly turned on and off while holding a selection switching element SP in an on state in the same manner as in the first embodiment, a potential at the terminal of the first capacitor CA on the inductor L and on side decreases Potential at the terminal of the second capacitor CB on the inductance L side gradually, while a voltage between the terminals of the piezo stack P1 gradually increases. In addition, a voltage between the connections of the first capacitor CA is set such that it is equal to or greater than a target voltage between the connections of the piezo stack P1, so that a current from the second capacitor CB cannot flow back through the diode DF.

If there is a voltage between the terminals of the Piezo stack P1 a target voltage Vtg at a time T1 reached, the switching element SA and that Selection switching element SP1 switched off.

At this time, if a current flows through the Inductance L flows (the inductance L stores namely magnetic energy), a freewheeling current IDF through the diode DF in the first capacitor CA, while the magnetic energy stored by inductance L. is consumed in a closed circle that is through the inductance L, the diode DF, the first Capacitor CA and a parasitic diode DB extends.

In contrast, it is in a case where the Drive circuit SA has no diode DF, it does not suitable, the selection switching element SP1 during a Turn off period in which a current through the Inductance L flows even if the first one Switching element SA is switched off at the time if there is a voltage between the terminals of the Piezo stack P1 reaches the target voltage as per the first embodiment is described. consequently a current flows through the inductance L. the piezo stack P1, creating a voltage between the Connections of the piezo stack P1 in relation to the Target voltage becomes excessively large. Because this is excessive Voltage magnitude depending on one Temperature condition of the device and the like itself changes, this can be done by an offset correction or the like cannot be completely eliminated.

In contrast, this piezo actuator drive circuit 2 A, even if the first switching element SA and the selection switching element SP1 are kept in a switched-off state, in order to avoid overloading the piezo stack P1 at a time when a voltage between the connections of the piezo stack P1 is the target voltage reached, a current flowing through the inductance L through the diode DF is taken out through the first capacitor CA, so that it is possible to carry out a charge control with greater accuracy and improvement in its energy efficiency.

Below is a shut down operation described.

FIG. 8 shows timings that illustrate operations in a case where the operation of the device is shut down, for example, when the engine is shut down. First, the first switching element SA is switched on. This causes a current to flow through a current path that extends through the first capacitor CA, the first switching element SA, the second capacitor CB, the inductor L, and the resistor R. Heat generated by the resistor R (Joule heat) reduces the energy stored in the first capacitor CA and the second capacitor CB. A large voltage drop occurs in the second capacitor CB with low capacitance, and the connection on the inductor L side becomes electrically negative with respect to the connection on the switching element SA side.

At a time t1 when the potential VCBL becomes zero, the first switching element SA is switched off and is the third switching element SC turned on. This causes the second capacitor CB to discharge.

Subsequently, the third switching element SC is switched off at a time t2 and the first switching element SA is switched on. Then, the resistor R generates heat (Joule heat) and a voltage between the terminals of the first capacitor CA is further reduced, whereby the charges are transferred to the second capacitor CB. Thus, repeatedly turning the first switching element SA and the third switching element SC on and off in opposite phase reduces voltages between the terminals of the first capacitor CA and the second capacitor CB, respectively, and both become zero as in the example shown in FIG. 8.

It is therefore possible to switch off the device without in the capacitors CA and CB as well as the piezo stack P1-P4 charge remains even when the first capacitor CA and the second capacitor CB connected in series are of a different charge size. Consequently, additional work can be done to discharge the Capacitors CA and CB, for example during maintenance omitted.

Furthermore, the piezo stack P1-P4 are charged in such a way that their connections on the side of the inductor L. higher potential in terms of connections on the Side of the selector switch elements SP1-SP4, so that even if charge remains in it, the remaining charge through the resistor R out to the Mass can flow because the tensions between the Connections of the piezo stack P1-P4 forward Biases related to the parasitic selection diodes Can become DP1-DP4. This enables the charges can escape in the piezo stacks P1-P4, for example even in a case when charges spontaneously due to fluctuations in temperature in the Piezo stacks P1-P4 have been generated.

It is also possible for loads to remain in the Avoid piezo stacks P1-P4, which is why an error in charge control due to remaining charge can be restricted.

The discharge effect of the resistor R occurs also during fuel injection. Therefore, a resistance value of the resistance R becomes such selected that the selected piezo stack P1-P4 one Expansion state during the longest injection period can maintain. Will continue while charges due to temperature changes and the like in the Piezo stacks P1-P4 occur these charges over the Discharge resistor R. Because the ambient temperature is slow fluctuates, can take a long enough time Discharge of the piezo stack P1-P4 compared to the time be taken to keep their expansion states is required. Therefore, a time constant becomes one closed circle that extends through the piezo stack P1-P4, the resistor R and the selection switching element SP1-SP4 extends, set such that the piezo stack P1-P4 can maintain its state of expansion without problems and no charge due to temperature fluctuations and the like remains.

Although according to this embodiment, charges in the Capacitors CA and CB by repeated input and Turn off the first switching element SA and the third Switching element SC are discharged is the invention not so limited, and such charges can be discharged while the current values with the Resistor R can be limited.

Although according to those described above Embodiments the application in one Fuel injector has been described, the Invention on a piezo actuator Drive circuit for driving a Piezo actuator can be applied to others Applications is used.

Although the invention is related to their preferred embodiments with reference to the accompanying drawing has been described noticed that various changes and modifications are clear to the expert. Such changes and Modifications are considered to be within the scope of the attached claims defined invention as included to understand.

In the foregoing, a piezo actuator drive circuit has been provided which includes a first capacitor (CA) which is charged by a DC power supply ( 21 ) prior to charging piezo stacks (P1-P4), a second capacitor (CB) which is in series with the first capacitor (CA) is connected, and has a diode (DB), which is connected between a connection of the second capacitor (CB) on the side of an inductor (L) and the ground, so that a freewheeling current of the inductor is caused to flow to the piezo stack becomes. In the piezo actuator drive circuit, a switch (SA) is repeatedly turned on and off to gradually charge the piezo stack from the two capacitors (CA, CB), thereby improving the controllability of the energy. According to the invention, the time required for charging can be reduced without increasing the DC voltage supply.

Claims (8)

1. Piezo actuator drive circuit with
a DC voltage supply (B, 21 ),
a first capacitor (CA), which is connected in parallel with the DC voltage supply and is charged by the DC voltage supply,
Piezo actuators,
Piezo stacks (P1, P2, P3, P4), which are each contained in the piezo actuators,
a line path that connects the first capacitor (CA) and the piezo stack,
a control unit ( 22 ),
an inductance (L) provided at an intermediate point in the conduction path,
a first switching unit (SA), which is provided at an intermediate point in the line path, the first switching unit (SA) separating and connecting the first capacitor (CA) and the inductance (L) under the control of the control unit ( 22 ),
a second capacitor (CB) which is provided and is connected in series with the first capacitor (CA) between the first switching unit (SA) and the inductance (L), and
a diode (DB), which is provided for connecting a connection of the second capacitor (CB) on the side of the inductance (L) and the ground,
wherein the diode (DB) has a forward direction that is the same as a direction in which a charging current flows from the inductance (L) into the piezo stack via the diode, and
the control unit ( 22 ) is set up to repeatedly switch the first switching unit (SA) on and off in response to a piezo stack expansion command in order to load the piezo stack. 2. Piezo actuator drive circuit according to claim 1, further comprising
a line path (W3) which is provided to bypass the first capacitor and the first switching unit (SA) and to connect a connection of the second capacitor on the side of the first switching unit to the ground,
a second switching unit (SB) which is connected in parallel to the diode, and
a third switching unit (SC), which is provided for opening and closing the line path (W3),
wherein the control unit ( 22 ) is used as a control unit for controlling the second switching unit and the third switching unit as well as the first switching unit, and
the control unit ( 22 ) is set up to respond to a piezo stack contraction command and to switch off the first switching unit, to switch on the third switching unit and to switch the second switching unit on and off repeatedly, thereby causing the piezo stack to be discharged towards the second capacitor. 3. Piezo actuator drive circuit according to claim 1 or 2, wherein the control unit ( 22 ) is configured to respond to a piezo stack expansion command and to hold the first switching unit (SA) in an off state when a potential at the connection of the second capacitor on the side the inductance reaches a predetermined value. 4. Piezo actuator drive circuit according to claim 3, wherein the control unit ( 22 ) as a control unit for controlling the
DC voltage supply (B, 21 ) is used, and
the control unit ( 22 ) is set up to increase and decrease a charge amount of the first capacitor which is charged by the DC voltage supply such that a change in a voltage between the terminals of the second
Capacitor before and after discharging the piezo stack in response to a piezo stack contraction command becomes a predetermined reference value. 5. Piezo actuator drive circuit according to claim 1, further comprising
Disconnect switching units (SP1, SP2, SP3, SP4) which are provided for separating the piezo stack from the line path, and
a diode (DF), which is provided for connecting a connection of the first capacitor on the side of the switching unit, which is provided for separating and connecting the first capacitor and the inductor, to a connection of the inductance on the side of the piezo stack, the diode has a direction such that a voltage between the two connections of the first capacitor becomes a reverse voltage,
wherein the control unit ( 22 ) is used as a control unit for controlling the disconnection switching unit, and
the control unit ( 22 ) is set up to switch off the disconnection switching unit and to disconnect the piezo stack from the line path when the charging of the piezo stack has been completed. 6. Piezo actuator drive circuit according to claim 1, further comprising
a line path (W3) which is provided to bypass the first capacitor and the first switching unit (SA) and to connect a connection of the second capacitor on the side of the first switching unit to the ground,
a second switching unit (SB) which is connected in parallel to the diode, and
a third switching unit (SC), which is provided for opening and closing the line path (W3),
wherein the control unit ( 22 ) is used as a control unit for controlling the second switching unit and the third switching unit as well as the first switching unit, and
the control device ( 22 ) is set up to carry out:
a first step of an activation control including switching on the first switching unit, the second switching unit and the third switching unit being in a switched-off state at the time of activation of a device for charging the piezo stack,
a second step of activation control that follows the first step of activation control, including turning off the first switching unit and turning on the third switching unit to cause the second capacitor to discharge, and
a third step of the activation control that follows the second step of the activation control, including switching on the third switching unit and repeatedly switching the second switching unit on and off in order to cause the piezo stack to be discharged towards the second capacitor. 7. Piezo actuator drive circuit with
a DC voltage supply (B, 21 ),
a first capacitor (CA), which is connected in parallel with the DC voltage supply and is charged by the DC voltage supply,
Piezo actuators,
Piezo stacks (P1, P2, P3, P4), which are each contained in the piezo actuators,
a line path that connects the first capacitor (CA) and the piezo stack,
an inductance (L) provided at an intermediate point in the conduction path,
a switching unit (SA) at an intermediate point
is provided in the line path, the switching unit (SA) separating and connecting the first capacitor (CA) and the inductance (L), and
a resistor (R), which is connected in parallel to the piezo stack. 8. Piezo actuator drive circuit according to claim 7, further comprising
a second capacitor (CB) which is provided and is connected in series with the first capacitor (CA) between the first switching unit (SA) and the inductor (L),
a diode (DB) which is provided for connecting a connection of the second capacitor (CB) on the inductor (L) and the ground side, the diode (DB) having a forward direction which is the same as a direction in which a charging current used to charge the piezo stack flows from the inductance (L) into the piezo stack via the diode,
a line path (W3) which is provided for connecting a connection of the second capacitor on the side of the switching unit (SA) to the ground,
a second switching unit (SB) which is connected in parallel to the diode, and
a switching unit (SC), which is provided for opening and closing the line path, and
A control unit ( 22 ) which is set up to repeatedly switch the switching units on and off in the opposite phase to one another.