METHOD AND CIRCUIT ARRANGEMENT FOR CHARGING AND DISCHARGING A LOAD WITH A CAPACITIVE COMPONENT

Abstract: A method and a circuit arrangement (1) for charging and discharging a load (4) with a capacitive component is proposed, having an energy source (3) which provides a direct voltage between a positive (+) and a negative (-) or earth terminal, a charging circuit and a discharging circuit, each of which has a coil (6, 9), and switching means (7, 8, 12, 13) controlled by a controlling system (2). The charging and discharging of the load (4) is intended to be controlled in an improved manner with a method and a circuit arrangement of that kind. For that purpose the controlling system (2) compares a report-back signal (C, H, K, L) from the circuit arrangement, or a signal derived therefrom, with an external desired value signal (Vin), and actuates the switching means (7, 13, 8, 12) as a function of a difference in the two signals. The charge is supplied to or down from the load in the form of quanta, the magnitude of the quanta being variable.

Description: Method and circuit arrangement for charging and discharging a load with a capacitive component. The invention relates to a method and a circuit arrangement for charging and discharging a load with a capacitive component, in particular a piezoelectric element, having an energy source, which provides a direct voltage between a positive and a negative or earth terminal, a charging circuit and a discharging circuit, each of which has a coil, and switching means controlled by a controlling system. In a known circuit arrangement of that kind (EP 460 660 A2) , a piezoelectric element, that is to say, a load that is distinguished essentially by its capacitive behaviour, is discharged by way of a first and a second discharging circuit, the first discharging circuit comprising a coil, a diode and a switch, and being connected to the negative terminal of the energy source, while the second discharging circuit comprises the same coil, but an additional switch and an additional diode and is connected to the positive terminal of the energy source. It should accordingly be possible to return a part of the charge stored in the piezo element to the energy source. The coil is of sufficiently large dimensions for the piezo element to be discharged to a negative value. Charging is then effected by way of the charging circuit, a charging coil being provided so that the piezo element can be charged to about twice the value of the supply voltage. The piezo element serves to control a fuel injection valve, which can only open or close. US 5 095 256 discloses a drive circuit for a piezoelectric actuating element in which the same coil is used to charge and to discharge the piezo element. Here, however, the piezo element can be charged only to the voltage value that the energy source makes available. On discharge, a part of the energy is returned to the energy source. In both cases charging and discharging is effected following a tripping signal, which leads, for example, to actuation of a switch, only as a function of system parameters. Discharging can be influenced by choosing the opening time of a switch within certain limits. If, for example, a piezoelectric element is being used as a load, only the movement of the piezoelectric element can be initiated and ended, the course of movement of this element cannot, however, be influenced. The invention is based on the problem of providing a method and a circuit arrangement with which control of the charging and discharging of the load can be improved. This problem is solved with a method for charging and discharging a load with a capacitive component, in particular a piezoelectric element, in which electrical charge in the form of quanta are supplied to the load and discharged from the load, the size of the quanta being controlled in dependence on an input signal. Charge quanta can be measured relatively easily, for example by integrating a current over time. By dividing the charge into individual quanta or packets, the control of the charging and discharging process is quite considerably simplified. The currents required for charging and discharging can be controlled in a much easier manner. Since the magnitude of the charge quanta is controlled, this magnitude can also easily be adapted to conditions dictated by the equipment or the circuit. The circuit complexity can therefore be kept within reasonable bounds. The use of charge quanta also enables the voltage at the load to be raised above the supply voltage. Each supply of charge to the capacitive load causes an increase in the voltage at the load, regardless of the level of the existing voltage. That produces the advantageous side effect that virtually no, or only very little, energy is lost on the electrical path. Normal conduction losses are, of course, inevitable. By controlling the magnitude of the quanta it is possible to monitor very accurately the amount of charge that has been supplied to the load and the amount of charge that has been released from the load. The prevailing charge state of the load can accordingly be monitored better than previously. Preferably, currents are measured to ascertain the magnitude of the charge quanta, the magnitude of the quanta also being limited by a maximum current magnitude. If, therefore, a load is to be charged or discharged as rapidly as possible, in succession one or more charge quanta of identical magnitude are supplied or released, this magnitude being limited by the maximum current flow. If the actual charge state approaches a predetermined desired value, these charge quanta can be reduced in dependence on the difference between the actual value and the desired value. Although there is occasionally a time delay caused by limiting the charge quanta to a maximum magnitude, the circuit arrangement used to implement the method is burdened to a lesser extent, which is an advantage in particular from thermal considerations. Saturation phenomena, such as those that may occur in some inductors even at relatively high currents, can also be very reliably suppressed. The moved charge quanta for storing energy in kinetic form preferably generate a magnetic field, and at least for the major part of a charging or discharging process the magnetic field does not fall below a predetermined minimum value. During charging and discharging, the incoming and outgoing current respectively produces, preferably in an inductor, a magnetic field, in which the electrical energy that was present in the energy source or in the load as potential energy, is now stored temporarily in kinetic form. The speed of the charge transfer is dependent inter alia on the magnitude of the flowing current. If the magnetic field can be guaranteed not to fall below a predetermined value, in the same way the current generating the magnetic field can also automatically be guaranteed always to have a predetermined minimum value. But at the same time a certain minimum amount of charge per unit of time is transferred, that is to say, is supplied to or removed from the load. The magnitude of the magnetic field will, of course, fall short at the start and the end of the charging or discharging process. Measured against the total duration of the charging and discharging process, however, this can be regarded as negligibly small. In a further preferred embodiment, provision is made for the load to be divided into several part-loads, and for the magnetic field generated in an inductor during discharge of a part-load to be used when charging another part-load for driving the charge quanta. That is especially advantageous when the two part-loads, in dependence on their charge state, operate in phase opposition. As a result of the charge change-about, relatively rapid processes can take place, and at the same time a mutual dependence can be adhered to without greater circuit complexity. In a circuit arrangement of the kind mentioned in the introduction, the problem is solved in that the controlling system compares a report-back signal from the circuit arrangement, or a signal derived therefrom, with an external desired value signal, and actuates the switching means as a function of a difference in the two signals. In this manner it is possible to cause the charging and the discharging to follow a predetermined sequence. When using a piezoelectric element, the expansion or the contraction of the piezoelectric element can accordingly be influenced to that purpose. Since only as much charge is introduced into the load as is necessary to achieve consistency between the desired signal and the report-back signal, there is a saving of energy. In a preferred embodiment, the charging circuit comprises a first charging current circuit, in which a charging coil and the energy source, but not the load, are connected together in a loop, and a second charging current circuit, in which the charging coil is connected to the load arid the loop is interrupted, wherein the controlling system switches over in dependence on the difference from the first to the second circuit and vice versa. With a construction of that kind, it is possible to charge the load to high voltage values even when the supply voltage of the energy source is relatively low. In that case, the charging coil is used as a temporary energy store. The energy source must merely be capable of delivering a current of sufficient magnitude. If the voltage is applied to the coil in the loop, a continuously growing current forms in the first charging current circuit. If the current flow is interrupted and the second charging current circuit is switched, the current flowing through the coil flows on further and transfers charge into the load. The voltage at the load increases as a result. By repeated switching between the first and the second circuit it is therefore possible to generate in the load a voltage that exceeds the voltage of the energy source by a multiple. This feature not only allows the energy source to be of relatively inexpensive construction; it also enables energy to be saved in a simple manner in that the charge fed to the load is returned to the energy source again. At least for as long as the voltage at the load exceeds the voltage of the energy source, during discharging the charge is able to flow without difficulty from the load back to the energy source again. For that purpose, the energy source can contain, for example, a capacitor for power output. In order to recover as large a part as possible of the remaining energy from the load, in a further preferred embodiment provision is made for the discharging circuit to comprise a first discharging current circuit, which contains a discharging coil and the load connected to a first coil connection, and a second discharging current circuit, in which the discharging coil is not connected to the load, switching means being provided which interrupt a connection of the other coil connection to the earth terminal and the negative terminal of the energy source respectively and this other coil connection is connected by way of a diode to the positive terminal of the energy source. During discharging, a first circuit can now be connected in which the load drives a current through the discharging coil. As soon as the current has reached a certain magnitude, the connection to the load can be interrupted. The current flowing into the coil, which stores energy in kinematic form, is then fed back to the energy source, the kinetic energy being converted into potential energy. In this manner it is not only possible to recover to a large extent the energy stored in the load, it is also possible to reverse the load to a negative value which in combination with piezoelectric elements can be an advantage. The control arrangement preferably switches within a cycle from the first, to the second circuit and back, all cycles being the same length. The control is simplified by this feature. The controlling system can for that purpose be clocked, for example. On the other hand, oscillations which could be caused by switching of the switching means remain within a predetermined frequency range. Since it is virtually impossible to construct a circuit arrangement based on leads without inductive elements, and together with the capacitive component of the load oscillating circuits are therefore inevitably created, by suitable selection of the cycle lengths a frequency range far enough removed from the natural frequency of the oscillating circuits can be set. This can be yet further improved in that the time within a cycle for which the first circuit is active is limited to a predetermined maximum value. In that case, frequencies which can be created by switching within a cycle can also be excluded. Preferably, the controlling system measures the current through the coils at least in a part of the cycle and switches from the first to the second circuit when the current reaches a predetermined maximum value. That avoids not only overloading of the coils, for example, thermal overloading, but also prevents the coils being saturated by too great a current. This feature also produces a saving on energy. The efficiency of the switching arrangement is thereby increased. It is also preferable for the controlling syste to ascertain the charge which has flowed into the load. In the case of a piezoelectric element, this charge is approximately proportional to the expansion of the element. The expansion of the piezoelectric element can therefore be controlled by the charge supplied. For that purpose, the controlling system ascertains preferably the voltage across the load. The voltage is a measure of the charge that has flowed into the load, and non-linearities and hysteresis effects may have to be taken into account. In addition, or as an alternative, the controlling system can measure the current flowing into and out of the load or a corresponding current, and integrate it over time. Measuring the current can be effected, for example, by way of a measuring resistor with the assistance of a measuring amplifier. The measuring resistor is for that purpose connected in series with the coil. Since the current corresponds to a charge flow, that is, a charge per time, the time integral of the current must correspond to the charge that has flowed into the load. By means of the integration, which can be carried out using known and simple circuit elements, it is relatively easy to obtain information about the charge that has flowed into the load. If the measuring resistor connected in series with the coil is small enough, it has a virtually negligible effect on the energy credit and debit balance of the circuit arrangement. It is here especially preferred for the controlling system to measure the current flowing in the first circuit through the coil in question. This is admittedly not the current that flows directly into the load, but it is the current that is stored temporarily in the coil as kinetic energy. Since this kinetic energy is released into the load, it is immaterial whether the current that serves to build up the field in the coil is measured or the current that reduces it. In a preferred embodiment, the discharging coil has switching means at both coil connections, the first coil connection being connected to the cathode of a first discharge diode, the anode of which is connected to earth or to the negative terminal of the energy source, and the second coil connection is connected to the anode of a second discharging coil, the cathode of which is connected to the positive terminal of the energy source. With a construction of this kind. first of all a field which is fed by a current from the load can be built up in the discharging coil. After interrupting the current path from the load to the discharging coil and interrupting the path on the other side of the coil, a current path is then formed that leads from the negative terminal of the energy source by way of the discharging coil and the second discharge diode to the positive terminal of the energy source. The kinetic energy stored in the field of the discharging coil is then released to the energy source. In this manner it is possible to recover a large part of the energy stored in the load. Without this measure, the load would be certain to discharge to a voltage that corresponds to the voltage at the energy source. But with this embodiment it is possible by switching backwards and forwards repeatedly between the first and second circuits to discharge the load even further, if desired even to negative values. It is especially preferred for switching means which interrupt the current path through the first discharge diode to be provided, and for the first coil connection to be connected by way of switching means directly to the positive terminal of the energy source, the first discharge diode being connected to earth. In this manner the load can be discharged to negative values even when the energy source itself has no negative terminal but only an earth terminal. Preferably, in the second charging current circuit a charging diode is connected in series with the charging coil, switching means being arranged between the diode and the load. Using these switching means, unintentional charging of the capacitive load can be prevented. This unintentional charging can arise, for example, when the capacitive load has a negative charge. In that case, an uncontrolled current could flow through the charging coil and the charging diode. which would lead to a similarly uncontrolled length change if a piezo element were being used. It is preferable for a voltage-limiting device to be arranged parallel to the series connection comprising charging coil and charging diode. A voltage-limiting device of that kind can be formed, for example, by a Zener diode. Other active or passive components can, of course, also be used. A voltage- limiting device of that kind prevents disruptive voltage peaks, such as those that may occur during operation of the switching means, from reaching the circuit arrangement. Advantageously, the load also has an ohmic and/or inductive component. A capacitive component is present in all cases. This circuit arrangement can be used with particular advantage when, in the presence of such a load, a voltage that is a multiple of the supply voltage of the energy source is desired. Advantageously, the charging coil and the discharging coil are constituted by the same component which is arranged on the diagonal of a bridge circuit, each branch of which contains switching means and across the other diagonal of which the energy source is connected, the load being in series with switching means and connected to a bridge point to which the diagonal containing the component is also connected. The circuit arrangement is accordingly of inexpensive and compact construction. The same coil can be used both for charging and for discharging; here too, charging to a higher voltage than that available through the energy source is possible. With appropriate control, the coil can take the load into the negative range during discharge. The diagonal in series with the component preferably includes a measuring resistor. The current through the coil can therefore be continuously monitored. A current-measuring device is then required with which, for example, the report-back signal can be obtained in order to monitor and adjust the charging and discharging process of the load in accordance with external requirements. The load is preferably divided into several part-loads, two part-loads being connected in series by means of switching means with opposite ends of the diagonal. A charge-reversal of the two part-loads, that is to say, discharging of the one part-load and charging of the other part-load, is then effected by way of the diagonal, and the electrical energy is stored temporarily in kinetic form in the coil, which here functions simultaneously as a discharge and a charging coil. By this means, not only is the charge between the two part-loads equalised, which would ultimately lead to both part-loads containing the same charge, but it is, in fact, possible to achieve a full discharge of one part-load, if desired even a charge reversal to a negative polarity, whilst in the same procedure the other part-load is charged. Several part-loads with associated switching means in series can be connected, parallel to one another, to one of the bridge points to which also the diagonal is connected. Each part-load can be individually charged and discharged by means of the switching means. In that case, the two part-loads connected to a bridge point of the diagonal can be charged or discharged parallel to one another or in succession. If desired, they can also be connected up so that charge equalisation takes place between them. The invention also relates to the use of a circuit arrangement in a hydraulic or pneumatic valve arrangement, in which the part-loads are in the form of piezoelectric elements and are arranged in bridge branches of a hydraulic or pneumatic bridge circuit, in the diagonals of which a main slide member of a hydraulic or pneumatic valve is arranged. The extent of the piezo elements can be controlled by supply or dissipation of charge. The throttle gaps of control valves which contain the piezoelectric elements as actuators and which are arranged in the bridge branches of the hydraulic or pneumatic bridge circuit, may accordingly not only be fully closed or fully opened, but also enlarged or reduced to a desired degree. The pressures acting on the main slider member can therefore be set relatively exactly and above-all, very rapidly. Since the piezoelectric elements respond very quickly, very rapid adjustment of the pressures acting on the main slider member can be effected, and oscillations, for example, which occur in the hydraulic or pneumatic system which contain the valve, can be evened out or compensated. The auxiliary valves actuated by the piezoelectric elements can be arranged in all four bridge branches. In some applications, however, it is sufficient for them to be arranged in just two parallel bridge branches, when fixed throttles are provided in the two other bridge branches lying in series with these first two bridge branches. The invention is described hereinafter with reference to preferred embodiments. In the drawings. Fig. 1 shows a first embodiment of a circuit arrangement. Fig. 2 shows a second embodiment of a circuit arrangement, Fig. 3 shows signal characteristics at different points of the circuit arrangement according to Fig. 1, Fig. 4 shows signal characteristics at the points of the circuit arrangement according to Fig. 1 when the given criteria have been changed. Figs 5 to 7 show alternative configurations of a load. Fig. 8 shows a third embodiment of a circuit arrangement, Fig. 9 shows a construction of the circuit arrangement, Fig. 10 shows a fourth example of a circuit arrangement, Fig. 11 shows a first bridge circuit and Fig. 12 shows a second bridge circuit. Fig. 1 shows a first embodiment of a circuit arrangement 1 with a controlling system 2 and an energy source 3. The energy source 3 has a positive terminal denoted by "+" and a negative terminal denoted by ••-• » . and an earth terminal. The positive terminal of the energy source 3 is connected to a charging coil 6. The charging coil 6 is connected by way of a charging diode 5 and a switch 13 to the load 4 , which in this configuration is illustrated as a capacitor. A line with a switch 7, which is connected by way of a measuring resistor 16 to the negative terminal of the energy source 3, branches off between the charging coil 6 and the charging diode 5. Connected in parallel with the series circuit constituted by the charging coil 6 and the charging diode 5 there is a Zener diode 20 as voltage-limiting means. The load 4 is earthed at one end. The other end, which is connected to the switch 13, is also connected to a switch 8, which in its turn is connected to a discharging coil 9. The cathode of a first discharge diode 11 is connected between the switch 8 and the discharging coil 9. The anode of this first discharge diode 11 is connected to the negative terminal of the energy source 3. The discharging coil 9 is connected by way of a switch 12 and a measuring resistor 15 likewise to the negative terminal of the energy source 3. The anode of a second discharge diode 10, the cathode of which is connected to the positive terminal of the energy source 3, is connected between the discharging coil 9 and the switch 12. The two measuring resistors 15, 16 are very low- resistance resistors. The controlling system 2 has an input terminal 17 via which an external desired voltage Vin is supplied. The controlling system 2 also has measuring inputs C, L, K and H, by means of which it measures the voltage across the measuring resistor 16 and consequently the current through the switch 7, the voltage across the load 4 and the voltage across the measuring resistor 15, and thus the current through the switch 12. Furthermore, the controlling system 2 has outputs B, D, F and G, by means of which it is able to produce signals to actuate the switches 1 , 13, 8 and 12. In an alternative embodiment, not illustrated, the measuring resistors 15, 16 can also be arranged directly in series with the charging coil 6 and the discharging coil 9 respectively. In that case, the controlling system 2 measures the current through the coils 6, 9 not just when the switches 7 and 12 are closed, but permanently. To explain the mode of operation of the circuit arrangement, the signals on the lines and at the points A to K have been plotted in Figs 3 and 4. Curve A represents the desired signal Vin, which in Fig. 3 consists of a step-change signal, while in Fig. 4 it is a continuously changing signal. To charge the load 4, the switch 13 is closed. A switch is closed whenever the associated signal assumes a positive value. The controlling system 2 now makes a periodic closure of the switch 7, creating a loop which effects a flow of current from the energy source 3 through the coil 6, the switch 7 and the measuring resistor 16 back to the energy source 3. As a result, a field builds up in the coil 6. When the field is large enough, the switch 7 is opened. Since the current in the charging coil 6 is unable to jump in value, but must continue to flow, the current flows through the charging diode 5 and the closed switch 13 into the load 4, since the switch 8 is open. Because of the counter-voltage building up in the load 4 or, in later cycles, already present, the field in the discharging coil 6 decays. The switch 7 is now closed and opened, again under the control of the controlling system 2, so that the load 4 is gradually charged up. The controlling system 2 measures the current through the measuring resistor 16, as illustrated in Fig. 3C. This is not the current that flows into the load 4. But as a comparison of Figs 3C and 4C with Figs 3E and 4E respectively shows, the current increase in line C of Figs 3 and 4 corresponds exactly to the current decrease in line E of Figs 3 and 4. This is the current through the charging diode 5. Measurement of the current by the branch containing the switch 7 thus gives an indication of how much current is flowing into the load 4. The signal C can now be used, for example, as a report-back signal. After optional integration, it provides an indication of the charge state of the load 4, which can then be compared with the given criterion of signal A. As clear, for example, from the sixth cycle in Fig. 3, after a certain time the charge state has been brought so nearly up to the given criterion that the switch 7 remains open only for a shorter time than previously in order to effect a correspondingly lower charge increase of the load 4 during this cycle. The closure time of the switch 7 in the following cycle is even more drastically shortened. In addition to the limitation on the closing time of the switch 7 imposed by the difference between the given criterion signal A and the charge state of the load 4, there are two further limitations. Firstly, the time for which the switch 7 is closed may not exceed a predetermined duration within the cycle. This measure serves to keep the switching frequency at an adequate distance from the natural frequency or frequencies which may occur as a result of the oscillating circuits in the switching arrangement formed by the capacitive load and coils. Furthermore, the closure time of the switch 7 is limited by a maximum current through the charging coil 6. If the current exceeds a certain value, the coil becomes saturated, which leads to a drop in efficiency. In addition, thermal damage may occur. As a comparison of Figs 3 and 4 reveals, with a continuously changing given criterion signal A, the closure time of the switch 7 is shorter than with a step-change signal. This is attributable to the fact that the difference between the actual state across the load and the desired signal Vin is smaller than with the step-change signal. The currents flowing through the coil are also correspondingly smaller. If a step- change function is stipulated, it takes a certain time for the charge state of the load to match the stipulation. This time is acceptable, however, because on the other hand the desired charge state of the load 4 is reached exactly with great reliability. Once the desired charge state of the load 4 has been reached, the switch 13 is opened. Since the charge is no longer open to external influence, the charge in the load 4 remains unchanged. For discharge, the switches 8 and 12 are closed. Current now flows from the load 4 by way of the switch 8, through the coil 9, by way of the switch 12 and the measuring resistor 15 to the negative terminal of the energy source 3. The load 4 is consequently discharged. After a pertain time, which is also dependent on the difference between the charge state of the load 4 and the signal Vin, the switches 8 and 12 are opened. Since the current in the discharging coil 9 is unable to jump in value, there is a current flow from the negative terminal of the energy source 3 by way of the first discharge diode 11, the discharging coil 9 and the second discharge diode 10 to the positive terminal of the energy source 3. In this manner, a large part of the energy stored in the load 4 in the form of electrical charge is returned to the energy source 3 again. The current in the discharging coil 9 becomes smaller. As soon as it has dropped to a predetermined minimum value, which should be greater than zero, the switches 8 and 12 are closed again, and a new cycle begins. The current may, of course, also be allowed to drop to zero. The charge transfer is effected more quickly, however, when the currents are larger. Here too, there are, on the one hand, constant cycle lengths; on the other hand, the closure time of the switch 8 is limited by the maximum current flow through the discharging coil 9 and by a maximum closure time. As evident from the lines H and I in Figs 3 and 4 , which represent currents, the increase in current through the coil 9 , which can be detected by means of the measuring resistor 15, corresponds to the decrease in current through the first discharge diode 11, so that measurement of the current by the measuring resistor 15 is sufficient to obtain information about the discharge of the load 4. Discharge of the load 4 can also be controlled by a switching of the switches 8 and 12 to that end. If the load 4 is charged to a very much higher voltage value than is available to it from the energy source 3, discharge can also be effected in that the switch 8 is closed while the switch 12 remains open. In that case, the load 4 discharges at least to a value that corresponds to the voltage of the energy source 3. As soon as the load 4 has discharged to the desired value, which in some cases may even be negative, then the switch 8 is also opened. When the load 4 is isolated from other elements by the switches 8 and 13, no further change in the charge can take place. The control unit 2 can set both the frequency and the mark-to-space behaviour of the switches 7 , 13 , 8 and 12. This adjustment is effected as a function of the difference between the desired signal Vin and the charge state of the load 4, which, for example, can be led back to the control unit 2 by way of the line 14 as a signal K. Measurement of the current during charging has the advantage that the current on the one hand provides information about the field in the coils 6, 9, that is, is independent of the voltage available from the energy source 3, but on the other hand also provides information about how much charge has flowed into or out of the load 4. Both signals C and H as well as signal K can be used as report-back signals. All signals can be evaluated so that they provide information about the charge state of the load 4. They are therefore suitable to serve as a basis for comparison with the desired signal Vin. Fig. 2 shows a similar circuit arrangement, in which identical parts are provided with the same reference numbers. Unlike Fig. 1, the energy source 21 is not provided with an earth terminal. It has only a positive terminal and a negative terminal. The measuring resistors 15, 16 are connected to the negative terminal. In order nevertheless to enable the load 4 to be charged to a negative value, the first discharge diode 11 is connected by way of a switch 19 to the connection point between the switch 8 and the discharging coil 9. This point is connected by way of a further switch 18 to the positive terminal of the energy source 21. Charging is effected in the same way as in the circuit arrangement shown in Fig. 1. The switch 19 is closed and the switches 8 and 18 are opened. When the load 4 is to be discharged to a negative potential, this can be effected in that first of all a field is built up in the coil 9 by opening the switches 8 and 19, while the switches 18 and 12 are closed. This creates a current path from the positive terminal of the energy source 21 by way of the switch 18, the discharging coil 9, the switch 12 and the measuring resistor 15 and back to the energy source 21. The control unit 2 measures the current that causes the voltage drop across the measuring resistor 15. When this current reaches a fixed value, the switches 18, and optionally 12, open, and the switch 8 is closed. The field which has built up in the discharging coil 9 now drives a current from the load 4 through the switch 8, the discharging coil 9 and the second discharge diode 10 to the positive terminal of the energy source 21. The normal discharge of the load 4, a discharge to a positive value down to the value zero, can be effected in that the switch 19 is closed and the switch 18 is opened. The switches 8 and 12 are then actuated as described in conjunction with Fig. 1. Figs 5 to 7 show alternative configurations of the load 4. In Fig. 5, the load consists of a parallel circuit of a capacitor with an ohmic resistor. Fig. 6 shows a parallel circuit consisting of a capacitor and an inductor. Fig. 7 shows a parallel circuit consisting of a capacitor with an ohmic resistance and an inductor. All the loads can be used instead of the load 4 in the circuit arrangements according to Figs 1 and 2. Fig. 8 shows an alternative configuration of a circuit arrangement, in which the charging coil and the discharging coil are combined in a single component. namely, the coil 107. This coil 107 is arranged in series with a measuring resistor 106 in a diagonal branch of a bridge, across the other diagonal of which the voltage of the energy supply is applied. The branches of the bridge contain a respective switch 101, 102, 103 and 104. The bridge point to which the diagonal containing the coil 107 is attached is connected by way of a switch 105 to a piezo element 108, which in its turn is connected to earth. A control unit which controls the five switches and takes current measurements, charge measurements and voltage measurements is provided, but is not illustrated. To charge the load, the switches 102, 104 and 105 are opened. The switches 101 and 103 are closed. A current then flows from the positive terminal 109 of the energy source, not illustrated in detail, through the switch 101, the measuring resistor 106, the coil 107 and the switch 103 to the negative terminal 110 of the energy source. A field consequently builds up in the coil 107. When the controlling system, not illustrated in detail, determines from the voltage across the measuring resistor 106 that a certain and desired field has built up in the coil 107, which is manifested by a current flowing in the coil 107, the switch 103 is opened and the switch 105 is closed. The current now flows from the positive terminal 109 through the switch 101, the measuring resistor 106, the coil 107 and the switch 105 into the load 108. The change between the switches 103 and 105 can be effected repeatedly, in order to charge the load 108 to the desired value. Alternatively, the switch 101 can be opened and the switch 102 closed. The second current circuit then contains only the load 108, the switches 105 and 102 and the diagonal branch 106, 107. For discharge, a route for current from the load 108 through the closed switch 105, the coil 107, the measuring resistor 106 and the switch 101 is set up. Provided that the voltage across the load 108 is higher than the voltage at the positive terminal 109 of the energy source, current now flows back to the energy source. When an adequate field has built up in the coil 107, the switch 105 is opened and the switch 103 is closed. With its field, the coil 107 now drives a current from the negative terminal 110 of the energy source through the switch 103, the coil 107, the measuring resistor 106 and the switch 101 to the positive terminal 109 of the energy source. The current for building up a field in the coil can also be generated by closing the switches 105 and 102. In order to charge up or change-about the charge of the load 108 to a negative potential, a current path from the positive terminal 109 by way of the switch 104, the coil 107, the measuring resistor 106 and the switch 102 to the negative terminal 110 is set up. When the controlling system establishes that the field has built up, the switches 104 and, if desired, 102, are opened and the switch 105 and, if desired, 101 are closed. The field in the coil now drives the current from the load 108 through the switch 105, the coil 107, the measuring resistor 106 and the switch 101 to the positive terminal 1O9 of the energy source. By repeated change-over the load 108 can be discharged to the desired value. In this embodiment, the switches must be able to open and close in both directions. This can be effected, for example, with parallel-connected oppositely-poled semiconductor components, such as transistors or thyristors. Here, protective diodes may need to be used in order to protect the semiconductor components from negative voltage. Fig. 9 is a detailed diagram of a configuration of a circuit arrangement, as illustrated diagrammatically in Fig. 1. A charging circuit 60 and a discharging circuit 70 are drawn in here in dot-dash lines. The desired signal acts on a desired value input 17 of a regulator 25 to which the report-back signal 45 is also supplied. The report-back signal is either obtained directly from a voltage value feed-back of the voltage across the load 4 or by way of a charge value feed-back resulting from connecting a measuring resistor 35 in series with the load 4. The voltage across the measuring resistor is integrated with the aid of an integrator 34, the output voltage of the integrator being the charge in the load 4 which, when using a piezoelectric element as the load 4, corresponds approximately to the expansion of this element. Using a switch 36, it is possible to choose between these two signals. The load 4 can also be replaced by the parallel connection of a capacitor with any impedance, as illustrated in Figs 5 to 7. The load 4 may also, if the charge value feed-back is omitted, be connected directly to earth. The regulator 25 is connected to a divider circuit 26, which has two output signals, namely, UL as the input signal for the charging circuit 60 and UE as the signal for the discharging circuit 70. Both signals denote the difference between the desired value 17 and the actual value returned by way of the line 45. The input signal UL from the divider circuit 26 is supplied to the negative terminal of a comparator 27. The corresponding positive terminal of the comparator 27 is connected to an end of the measuring resistor 16 that is also connected to the switch 7, while the other end of the measuring resistor 16 is connected to* the negative terminal of the energy source 3. The output of the comparator 27 is supplied to the R-input of a flip-flop 29, the S-input of which is supplied with the output signal of an oscillator 28, which delivers a square-wave voltage. The output of the oscillator 28 is also connected to an AND-gate 30, the other input of which is supplied with the output signal Q of the flip- flop 29. The output of the AND-gate 30 is connected by way of an amplifier 31 to a control input of the switch 7, which can be in the form, for example, of a field-effect transistor. A second comparator 32, which receives at its plus input the output signal UL of the divider circuit 26 and the negative terminal of which is earthed, is connected by way of an amplifier 33 to a control connection of the switch 13. The amplifier 33 provides galvanic separation. The switch 13 is moreover in the form of a field-effect transistor. The remaining parts of the charging circuit correspond to those shown in Fig. 1. The comparator 32 decides whether the signal UL is positive or negative. Only when it is positive does the charging circuit 60 become active. The discharging circuit 70 also has a comparator 37, the negative input of which is supplied with the output signal UE of the divider circuit 26. The positive input of the comparator 37 is supplied with the voltage across the measuring resistor 15. The output of the comparator 37 is connected to the R-input of a flip-flop 39, the S-input of which is connected to the output of an oscillator 38, which delivers a square-wave voltage. The output Q of the flip-flop 39 and the output of the oscillator 38 are connected to an AND-gate 40, the output of which is supplied on one side to an amplifier 42 providing galvanic separation and on the other side to an amplifier 41. The amplifier 42 controls the switch 8 while the amplifier 41 controls the switch 12. Fig. 10 shows a fourth embodiment of a circuit arrangement, which corresponds substantially to that shown in Fig. 8. Identical parts are provided with the same reference numbers. The single load 108 present in Fig. 8 has now been divided into four part- loads 111 to 114. Each load is arranged in series with switches 115-118 and with a measuring resistor 119-122, the sequence in which these three elements are connected in series being unimportant. Thus, for example, in the case of the part-load 111, the switch 115 is arranged on one side and the measuring resistor 119 is arranged on the other side, while in the case of the part-load 112, the switch 116 and the measuring resistor 120 follow the part-load. The part-loads are in each case connected in pairs to an end point of the bridge diagonal, which also contains the coil 107 and the measuring resistor 106. Each part-load pair 111, 112 and 113, 114 is formed with parallel part-loads which are individually triggerable by means of their respective switches 115-118. The branch containing the part-load 111 and the branch containing the part-load 112 are arranged parallel to the switch 103, while the branch containing the part-load 113 and the branch containing the part- load 114 are arranged parallel to the switch 102. For the part-loads 113 and 114 the associated switches 117 and 118 are arranged between the part-load and the negative terminal 110. That has the advantage that the switches 117, 118 have to switch only relatively low voltages. The part-loads 111, 112 can at first be charged as described in connection with the load 108 in Fig. 8. The part-loads 113, 114 can also be charged correspondingly. The arrangement of the part-loads at the two ends of the diagonal has the advantage, however, that the coil 107 can be used simultaneously as the discharging coil for the part-loads 111, 112 and as a charging coil for the part-loads 113, 114. If, for example, the part-load 111 is to be discharged, a current flowing in the coil 107 to the right hand side (in Fig. 10) is generated, for example, by closing the switches 102 and 104 while all the other switches are opened. If the switches 104 and 102 are now opened, while the switches 115 and 117 are closed, charge is transferred from the part-load 111 to the part-load 113. On the basis of the kinetic energy stored in the coil 107, this charge transfer effects not only a simple charge equalisation; on the contrary, the charge from the part-load 111 can be transferred completely into the part-load 113. By suitable cycling of the individual switches, in which the individual closure times can be mark-to-space modulated, the charge can be transferred in quanta or packets from one part-load to the other. A number of possibilities are conceivable here. For example, the charge from the part-load 111 can be transferred alternately to the part-loads 113 and 114. The charge transfer can also be effected in that the part-loads 113, 114 are charged simultaneously. On the other hand, the part-loads 111 and 112 can also be simultaneously discharged, while the charge is then taken up only by one part-load, for example 113. The same applies when the part-loads 113, 114 are discharged. Fig. 11 shows a use of such a circuit arrangement for controlling the position of a main slider member 123 in a hydraulic or pneumatic valve 124 which serves to control a fluid flow in a hydraulic or pneumatic circuit, not illustrated in detail. The valve can be in the form, for example, of a proportional valve or a servo valve. The position of the main slider member 123 is decisive for the magnitude of the flow volume and/or the pressure of the fluid on the output side of the valve 124. For that purpose, control inputs 125, 126 of the valve 124 are connected to diagonal points of a bridge 127, the other diagonal points of which are connected to a pump connection P and a tank connection T. Adjustable throttles 128-131 are arranged in the bridge branches. The throttles have variable throttling gaps and the size of the throttling gaps can be varied by expansion or contraction of piezoelectric elements, such as those formed, for example, by the part-loads 111-114. For that purpose, the throttle 128 contains, for example, the part-load 111, the throttle 129 contains the part-load 113, the throttle 130 contains the part-load 114 and the throttle 131 contains the part-load 112. It is therefore always diagonally opposite throttles 128, 131, and 129, 130 which are equally loaded, that is to say, the associated piezoelectric elements are simultaneously discharged or simultaneously charged. Conversely, when the piezoelectric elements of a throttle pair are discharged, the piezoelectric elements of the other throttle pair are charged, producing a counteracting behaviour which permits very rapid regulation. Fig. 12 shows a somewhat simplified embodiment of a hydraulic circuit 127' in which the throttles 128" and 129'' are in the form of fixed throttles. Only the throttles 130 and 131 are constructed as adjustable throttles. The position of the main slider member 123 in the valve 124 can also be changed with such a hydraulic or pneumatic circuit.

Claims: Patent Claims 1. A method for charging and discharging a load with a capacitive component, in particular a piezoelectric element, in which electrical charge in the form of quanta are supplied to the load and discharged from the load, the size of the quanta being controlled in dependence on an input signal. 2. A method according to claim 1, characterized in that currents are measured to ascertain the magnitude of the charge quanta, the magnitude of the quanta also being limited by a maximum current magnitude. 3. A method according to claim 1 or 2, characterized in that the moved charge quanta for storing energy in kinetic form generate a magnetic field, and at least for the major part of a charging or discharging process the magnetic field does not fall below a predetermined minimum value. 4. A method according to one of claims l to 3, characterized in that the load is divided into several part-loads, and the magnetic field generated in an inductor during discharge of one part-load is used when charging another part-load to drive the charge quanta. 5. A circuit arrangement for charging and discharging a load with a capacitive component, in particular a piezoelectric element, having an energy source which provides a direct voltage between a positive and a negative or earth terminal, a charging circuit and a discharging circuit, each of which has a coil, and switching means controlled by a controlling system, characterized in that the controlling system (2) compares at least one report-back signal (C, H, K, L) from the circuit arrangement, or a signal derived therefrom, with an external desired value signal (Vin) , and actuates the switching means (7, 13, 8, 12, 18, 19, 101-113) as a function of a difference in the two signals. 6. A circuit arrangement according to claim 5, characterized in that the charging circuit (60) comprises a first charging current circuit, in which a charging coil (6) and the energy source (3) , but not the load (4) , are connected together in a loop, and a second charging current circuit, in which the charging coil (6) is connected to the load (4) and the loop is interrupted, the controlling system (2) switching over from the first to the second circuit and vice versa in dependence on the difference. 7. A circuit arrangement according to claim 5 or 6, characterized in that the discharging circuit (70) comprises a first discharge current circuit, which contains a discharging coil (9) and the load (4) connected to a first coil connection, and a second discharge current circuit, in which the discharging coil (9) is not connected to the load, switching means (12) being provided which interrupt a connection of the other coil connection to the earth terminal and the negative terminal of the energy source (3, 21) respectively and this other coil connection is connected by way of a diode (10) to the positive terminal of the energy source (3) . 8. A circuit arrangement according to claim 6 or 7, characterized in that the control arrangement (2) switches within a cycle from the first to the second circuit and back, all cycles being of the same length. 9. A circuit arrangement according to claim 5, characterized in that the time within a cycle for which the first circuit is active is limited to a predetermined maximum value. 10. A circuit arrangement according to claim 8 or 9, characterized in that the controlling system (2) measures the current through the coils (6, 9, 107) at least in a part of the cycle and switches from the first to the second circuit when the current reaches a predetermined maximum value. 11. A circuit arrangement according to one of claims 5 to 10, characterized in that the controlling system (2) ascertains the charge which has flowed into the load (4). 12. A circuit arrangement according to claim 11, characterized in that the controlling system (2) ascertains the voltage across the load (4) . 13. A circuit arrangement according to claim 11 or 12, characterized in that the controlling system (2) measures the current flowing into and out of the load (4) or a corresponding current, and integrates it over time. 14. A circuit arrangement according to claim 13, characterized in that the controlling system (2) measures the current flowing in the first circuit through the coil (6, 9) in question. 15. A circuit arrangement according to one of claims 7 to 14, characterized in that the discharging coil (9) has switching means (8, 12) at both coil connections, the first coil connection being connected to the cathode of a first discharge diode (11) , the anode of which it connected to earth or to the negative terminal (3, 21) of the energy source, and the second coil connection is connected to the anode of a second discharging coil (10) , the cathode of which is connected to the positive terminal of the energy source (3, 21). 16. A circuit arrangement according to claim 15, characterized in that switching means (19) which interrupt the current path through the first discharge diode (11) are provided, and the first coil connection is connected by way of switching means (18) directly to the positive terminal of the energy source (21) , the first discharge diode (11) being connected to earth. 17. A circuit arrangement according to one of claims 6 to 16, characterized in that, in the second charging circuit, a charging diode (5) is connected in series with the charging coil (6), switching means (13) being arranged between the charging diode (5) and the load (4). 18. A circuit arrangement according to claim 17, characterized in that a voltage-limiting device (20) is arranged in parallel with the series connection comprising charging coil (6) and charging diode (5) . 19. A circuit arrangement according to one of claims 5 to 18, characterized in that the load (4) also has an ohmic and/or inductive component (Fig. 5-7) . 20. A circuit arrangement according to one of claims 7 to 19, characterized in that the charging coil and the discharging coil are constituted by the same component which is arranged on the diagonal of a bridge circuit, each branch of which contains switching means (101, 102, 103, 104) and across the other diagonal of which the energy source (109, 110) is connected, the load (108) being connected in series with switching means (105) having a bridge point with which the diagonal containing the component (107) is also connected. 21. A circuit arrangement according to claim 20, characterized in that the diagonal in series with the component (107) includes a measuring resistor (106) . 22. A circuit arrangement according to one of claims 20 or 21, characterized in that the load is divided into several part-loads (111-114) , two part-loads (111, 112; 113, 114) being connected in series by means of switching means (115, 116; 117, 118) with opposite ends of the diagonal (106, 107) . 23. A circuit arrangement according to one of claims 20 to 22, characterized in that several part-loads (111, 112; 113, 114) with associated switching means (115, 116; 117, 118) are connected in series, parallel to one another, to one of the bridge points to which also the diagonal (106, 107) is connected. 24. Use of a circuit arrangement according to one of claims 22 or 23 in a hydraulic or pneumatic valve arrangement, in which the part-loads are constructed as piezoelectric elements and are arranged in bridge branches of a hydraulic or pneumatic bridge circuit (127, 127'') in the diagonals of which a main slider member (123) of a hydraulic or pneumatic valve is arranged.

Inventors: WUERTH THEO, WUERTH, THEO
Applicants: DANFOSS AS, WUERTH THEO, DANFOSS A/S, WUERTH, THEO
Application year: 1993
Main classification: H01L41
IPC codes: H01L41, H02N2