DE602004000190T2 - Method for controlling a piezo drive - Google Patents

Method for controlling a piezo drive

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Publication number
DE602004000190T2
DE602004000190T2 DE602004000190T DE602004000190T DE602004000190T2 DE 602004000190 T2 DE602004000190 T2 DE 602004000190T2 DE 602004000190 T DE602004000190 T DE 602004000190T DE 602004000190 T DE602004000190 T DE 602004000190T DE 602004000190 T2 DE602004000190 T2 DE 602004000190T2
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actuator
stack
charge
value
positive
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DE602004000190T
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DE602004000190D1 (en
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Michael P. Gillingham Cooke
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Delphi Technologies Holding SARL
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Delphi Technologies Inc
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Description

  • The The present invention relates to a control method for a piezoelectric Actuator or Actuator (a piezoelectric actuator) and in particular a control method for a piezoelectric actuator of the kind as in a fuel injection valve or injector for delivering fuel to a combustion chamber a compression ignition combustion engine is used.
  • In a known piezoelectrically operable fuel injector, such as in our co-pending European patent application EP 0 995 901 A As shown, a piezoelectric actuator is operably configured to control the position occupied by a control piston for controlling the fuel pressure in a control chamber. A surface of an injector needle is exposed to the fuel pressure in the control chamber so that when the fuel pressure in the control chamber is relatively high, the needle is forced into a closed non-injection condition in which fuel delivery to the engine is prevented. As the fuel pressure in the control chamber decreases, the valve needle is caused to rise to an open injection state to begin fuel injection. Thus, by controlling the fuel pressure within the control chamber by means of the piezoelectric actuator, the injector can be switched between an injection and a non-injection state.
  • The piezoelectric actuator or the piezoelectric actuator comprises a stack of elements made of a piezoelectric material are over which A voltage is applied across the length of the piezoelectric stack to change. The Applying a first voltage over The stack causes the stack to a first activation level being brought, being its length is relatively low. Applying a second voltage across the Stack causes the stack to a second higher activation level is brought, and the length of the piezoelectric stack increases (i.e., the stack is extended). By changing the activation level of the piezoelectric stack can be the movement Therefore, the control piston to be controlled so that a movement the injection valve needle between its injection and its non-injection state is effected. The voltages applied to the stack will be so selected that they cause the stack to expand by an amount that the required extent Movement of the control piston results to the injector needle between switch back and forth between their injection and non-injection states.
  • It it was recognized that the amount of switching between two selected activation levels achieved stack expansion over the lifetime of the actuator varies. Therefore, get started the use of an actuator in switching, e.g. between Voltage levels V1 and V2, a larger stack expansion reached than after several hours of operation of the actuator. It has shown that the biggest change the expansion characteristic of the stack during the first hours of operation occurs, after which the expansion characteristic tends to stabilize.
  • This Problem must be tackled since it is important to ensure that the required maximum expansion of the stack during the entire service life of the injector can be achieved. To overcome This problem is known to "override" the actuator so that the initial Expansion of the actuator greater than the required maximum extension is the required maximum extension however, even after several hours of actuator use always can still be achieved. A disadvantage of this solution, however, is that that the actuator by overdrive damaged can be, so that the life of the actuator and thus shortened the injection valve. About that In addition, the maximum voltage is limited to the actuator can be applied before a dielectric breakdown takes place, as well as due to limitations of the drive circuits or the acceptable tensile stress in inactive parts of the stack or his external electrodes. This limits the maximum extent one that can be achieved with a new actuator.
  • One The aim of the present invention is to alleviate the problems or overcome that with the change the expansion characteristic of an actuator or piezoelectric Actuator (piezoelectric actuator) during its lifetime, and at the same time the deficiencies known techniques to remedy these problems or reduce to avoid.
  • According to a first aspect of the present invention, a method of operating a piezoelectric actuator having a stack of one or more piezoelectric material elements comprises: at a first time (i), varying the charge present on the stack between a first positive charge level or value and a first negative charge level or value to change the stack length by a first amount, (ii) measuring a first charge difference between the first positive charge value and the first negative charge value, and (iii) determining a first operating characteristic of the actuator , and after following, at a later time, changing the charge present on the stack between a second positive charge level and a second negative charge level to change the staple length by a second amount, the second positive and the second negative charge value as a function of the first operating characteristic and is chosen so that the difference between the second positive charge value and the second negative charge value is substantially the same as the first charge difference to ensure that the second amount by which the length of the actuator changes is essentially the same as the first amount.
  • It is understood that the charge itself can be varied directly, about the charge present between the stack and the positive charge level and the negative charge level, or alternatively another control parameter, e.g. the tension, to be changed, about the required change of the charge value.
  • at an embodiment For example, the method may involve applying a current through the actuator, measuring the voltage and the current that on the actuator can be applied, as well as measuring the first and second, positive and negative charge levels or values Integrating an instantaneous value for the current in relation to Include time.
  • The Invention allows it, the actuator length change while the total lifetime of the actuator is substantially constant keep up by changing the actuator expansion characteristic in the course of aging of the actuator be compensated. The method also provides the advantage that in all Operating phases the maximum stroke or the maximum extent of the Actuator can be achieved. An advantage of the invention exists in that while the operation of the actuator only the voltage present in the stack and charge must be measured it is not necessary is to measure the actuator extent, which is a parameter its measurement is difficult and costly.
  • The The method may include determining, at the first time, an operating characteristic which is a voltage-charge characteristic, by measuring the over the voltage applied across the stack as a function of the stack existing charge.
  • The piezoelectric material typically has a polarization reversal voltage value on, in which a polarization reversal takes place. In a preferred embodiment the method comprises selecting of the first negative charge value such that the over the Stack applied voltage at the first negative charge value just bigger than (i.e., less negative than) the polarization reversal voltage value is to thereby avoid polarization reversal of the material.
  • Of the Voltage level or value at which a polarization reversal of the Piezoelectric material may appear over the course of aging of the actuator as well as in dependence of several other factors that include the temperature change. Of the Polarization reversal voltage level for a new actuator can due to test measurements determined in advance and this value stored electronically in software so that the first negative charge level during the Beriebs so chosen is that the polarization reversal voltage is avoided.
  • at a further preferred embodiment The method comprises selecting the first positive charge level or value such that the over the Stack applied voltage at the first positive charge level or value is less than the maximum positive voltage level or value at which a dielectric breakdown of the piezoelectric Material occurs.
  • at a further preferred embodiment According to the invention, the method may further include selecting the second negative Charge value such that a voltage-charge characteristic at the chosen second negative charge value, a gradient (i.e., some Extent of change the voltage with the charge, dV / dQ), which is substantially equal to a gradient of the first voltage-charge characteristic at the first negative charge value.
  • It It should be clear that alternatively the method of selecting the second negative charge value may include such that Charge-voltage characteristic at the chosen second negative charge value a gradient (i.e., a certain amount of change the charge with the voltage, dQ / dV), which substantially equal to a gradient of a first charge-voltage characteristic at the first negative charge value.
  • In an alternative embodiment of the invention, the method may further comprise selecting the second positive charge value such that a voltage-charge characteristic at the selected second positive charge value has a gradient (dV / dQ) substantially equal to a gradient of the first voltage-charge characteristic at the first positive charge value. As before, alternatively, the charge-voltage characteristic may be used as the operating characteristic such that the amount of charge change with voltage (dQ / dV) is used to determine the second positive charge value. Whether dQ / dV or dV / dQ is to be measured is typically selected as a function of the electrical drive circuit of the actuator. If the natural characteristic of the driver circuit is to generate a voltage value, then it is preferable to measure dQ / dV. If the natural characteristic of the driver circuit is to produce a charge value, then it is preferable to measure dV / dQ.
  • Based on the assumption that the gradient is at the maximum negative or positive charge value remains substantially constant, and the assumption that difference between the first and second charge values at respective ends of the stroke substantially at any time is constant, it is possible the absolute size of the change in length Control the actuator so that it throughout its life is essentially the same. The method requires no measurement the actuator length change and allows it, the maximum possible stroke or the maximum possible change in length of the stack. The process also avoids the maximum negative voltage at which a polarization reversal occurs, as well as the maximum positive voltage at which a dielectric Puncture occurs.
  • Of the Step of determining the operating characteristic at the first time may refer to a previously stored operating characteristic of the actuator or measuring the operating characteristic in real time include. The prestored operating characteristic can be a Voltage-charge characteristic (i.e., a data set, the over the Stack applied voltage with the charge present on the stack brings into relationship).
  • The The method may further include measuring an operating parameter for the later Timing and adjusting the chosen second positive and second negative charge level by a relatively small amount, to set the operating parameter to a maximum or minimum and at the same time the difference between the second positive and the second negative charge level on the substantially same To keep value like that of the first charge difference.
  • at an actuator, for example, in which the voltage through a Actuator driver circuit the stack is applied, the method may include measuring an operating parameter in the form of the energy consumed in the driver circuit and the Set or adjust the selected second positive and the chosen one second negative charge value until a minimum of the measured consumed energy is reached. By allowing that the chosen one second positive and second negative charge values each vary slightly while a constant charge difference over is maintained throughout the stack, and by monitoring in the actuator driver circuit consumed energy until the minimum energy point is determined is, is it possible to optimize the efficiency of the actuator or actuator.
  • It should again be clear that the charge itself set directly can be to the across the charge present in the stack for the purpose of carrying out a Minimize routine, or alternatively, another Control parameters changed such as the tension, which results in the stack being present Charge is set.
  • at an alternative embodiment of this aspect of the invention the total energy consumption of the stack measured and the selected second positive and second negative charge levels are set be that the energy consumption measurement is minimized.
  • According to one The second aspect of the invention comprises a method of operation a piezoelectric actuator or actuator with a stack of one or more elements of piezoelectric material: changing the charge across the Stack between a first positive charge value and a first one negative charge value at a first time to order the stack a first amount between a positive stroke end and a negative one Offset stroke end (or to change its length by that amount), and below, at a later date Timing, changing the cargo across the stack between a second positive charge value and a second negative charge value to the stack by a second amount to offset (or by its length to change this amount), wherein the second positive and the second negative charge value so chosen be ensured that a loss of actuator extension at the positive end of the stroke to the later Time due to the increase in actuator expansion at the negative End of stroke to the later Time is essentially compensated.
  • This Aspect of the invention has the advantage that any Hubebbuße on the positive Voltage / load stroke end as the actuator ages compensated by the increase in actuator expansion at the negative voltage / charge stroke end becomes.
  • The piezoelectric material typically has a polarization reversal voltage value on which a polarization reversal occurs, and the method can choose of the first negative charge value such that the corresponding one of Voltage value just greater than (i.e., less negative than) the polarization reversal voltage value is to thereby avoid polarization reversal of the material. The maximum positive charge level is also preferably chosen such that the corresponding voltage level is lower than that at a dielectric breakdown of the piezoelectric material occurs.
  • According to one The third aspect of the invention comprises a method of operation a piezoelectric actuator or actuator with a stack of one or more elements of piezoelectric material: changing the charge across the Stack between a first positive charge value and a first one negative charge value at a first time to order the stack to offset a first amount (or its length around this Change amount), and below, at a later date Time, changing the Load across the stack between a second positive charge value and a second negative charge value to the stack by a second amount to move (or to its length to change this amount), wherein the second positive and the second negative charge value in accordance with a predetermined operating characteristic of the actuator chosen to ensure that the second amount to the the actuator is displaced (or by which its length changes), essentially the same as the first amount.
  • at an embodiment According to this aspect of the invention, the method may include selecting the second positive and second negative charge values in accordance with a predetermined operating characteristic include depends on one or more of the following conditions: Actuator age, actuator frequency of use, temperature of the actuator, average time span over which the positive charge value is applied to the stack, average time span over which the negative charge value is applied to the stack.
  • A Control unit can be used to control a piezoelectric actuator or actuator with a stack of one or more elements be provided of piezoelectric material, wherein the control unit comprising: a control device (i) for changing, at a first time, over the Stack away existing charge between a first positive Charge value and a first negative charge value around the stack to offset a first amount or to its length by this Change amount, (ii) for measuring a first charge difference between the first positive charge value and the first negative charge value, and (iii) for determining a first operating characteristic of the actuator, and (iv) for subsequent modification, at a later time, the over charge applied across the stack between a second positive Charge value and a second negative charge value to the stack to offset a second amount or its length by this amount Change amount, wherein the control unit further comprises means for selecting the second positive and second negative charge value in dependence from the first operating characteristic, so that the difference between the second positive charge value and the second negative Charge value is substantially the same as the first charge difference, to thereby ensure that the second amount to which the actuator is offset or changes its length, in Essentially the same is like the first amount.
  • A Control unit or processor through which a method for Controlling the piezoelectric actuator applied to the actuator be sure that the length change of the actuator during its whole life is kept at a substantially constant value.
  • The Control unit may also be provided with means for performing the preferred and optional Features to be equipped by the in this document defined methods are defined.
  • For the purpose In this description, the term "new actuator" or "new actuator" means an actuator still understand that no significant amount of time has been in operation, so its Displacement characteristic essentially the same as when first operating (i.e. initial Expansion characteristic corresponds). The expression "older actuator" or "old actuator" is to be understood as meaning that an actuator is meant, which is in a phase of his Service life is in which the length change characteristic already across from the initial one Displacement characteristic changed has, but it should not be limited to an actuator, that is at the end of its useful life.
  • The Method is especially for use with an actuator or actuator suitable, which is part of a fuel injection valve forms, which is a valve needle for controlling the fuel injection in an associated Engine, with a change of the charge value between the first positive charge value and the first negative charge value as well as between the second positive charge Charge value and the second negative charge value, a movement the valve needle between an injection and a non-injection state causes. It is understood that the actuator, depending on the type of injection valve, it can be designed so that the injection either towards the positive or negative end of the actuator stroke takes place.
  • The Invention will now be described, by way of example only, with reference to the accompanying drawings Drawings described. It shows / shows:
  • 1 a sectional view of a piezoelectrically actuable fuel injection valve of the type comprising a piezoelectric actuator to which the method according to the invention can be applied;
  • 2 an enlarged view of an upper portion of the piezoelectrically actuable fuel injection valve according to 1 ;
  • 3 an enlarged view of a central portion of the piezoelectrically actuable fuel injection valve according to 1 ;
  • 4 FIG. 4 is a graph illustrating the actuator length change as a function of the applied voltage to show the change in the length change characteristic of a piezoelectric actuator of the type which is a part of the injector according to FIGS 1 to 3 forms;
  • 5 Figure 11 is a graph illustrating the actuator length change as a function of applied voltage to show one embodiment of a method of compensating for the change in length change characteristic as the actuator ages in use;
  • 6 a diagram illustrating the actuator length change as a function of the applied voltage to a to the in 5 the compensation method shown alternative embodiment to illustrate;
  • 7 and 8th Charts showing the actuator length change as a function of the charge to illustrate embodiments that are alternatives to those in FIGS 5 and 6 represent compensation methods shown;
  • 9 a diagram showing the voltage against the charge for a piezoelectric actuator with the in 4 shown length change characteristic to an application of the in 8th to illustrate the compensation method shown;
  • 10 a flow chart illustrating the operating steps of an embodiment of the in the 8th and 9 represents the compensation method shown;
  • 11 a flow chart illustrating the operating steps of a further preferred embodiment of the in the 8th and 9 represents the compensation method shown; and
  • 12 a diagram for comparing the energy consumption of a new actuator with that of a relatively old actuator as a function of the voltage applied to the actuator voltage.
  • Referring to the 1 to 3 For example, a piezoelectrically actuable fuel injector typically includes a valve needle 10 , which can come to rest on a seat to control the fuel delivery to an associated engine cylinder. One of the valve needle 10 associated surface becomes the fuel pressure in a control chamber 12 exposed. The valve needle 10 is movable between a first position in which it is in contact with its seating surface, and a second position in which the valve needle is lifted from its seating surface. When the valve needle 10 is in its first closed position (seated position), there is no fuel injection, and when it is moved from its first position to its second position, fuel injection begins.
  • The fuel injection valve includes a hydraulic booster assembly that includes a control piston 18 includes, which can be actuated to the volume of the control chamber 12 to change. The movement of the control piston 18 is controlled by a piezoelectric actuator assembly comprising a stack 14 comprising one or more elements made of a piezoelectric material. The actuator stack 14 carries at its lower end an anvil element 16 that has a load transfer element 20 with the control piston 18 connected is. By controlling the length of the actuator stack 14 and thus the position of the control piston 18 the movement of the valve needle is controlled between its sitting position and its open or raised position, the change in the extent of the stack 14 is reinforced to the valve needle 10 to move an amount determined by the characteristics of the hydraulic boosting assembly. A feather 22 serves to the valve needle 10 to press against its seat, wherein the biasing force of the spring by a provide a screw threaded rod 24 is determined by the control piston 18 passes.
  • How best in 2 to see is the top end of the actuator stack 14 on an electrical connector 26 attached, that has a first and a second connection 26a . 26b includes, resulting in a radial bore 28 in an actuator housing 30 extend to allow the production of suitable electrical connections for controlling the piezoelectric actuator. If a first, relatively high voltage across the actuator stack 14 is applied, the piezoelectric material is brought to a first higher activation level, wherein the length of the stack is relatively large. In this position, the valve needle takes 10 a position in which it is located on its seat (ie in a non-injection state). If a second, relatively low voltage to the actuator stack 14 is applied, the piezoelectric material is brought to a second, lower activation level, wherein the length of the stack 14 is lower. The actuator is thus changed in its length, which has the consequence that the valve needle 10 is made to stand out from its seat (ie is brought into an injection state). Between the first and the second activation level of the actuator stack 14 have a "staple length change" or an "actuator stroke", that of the length change of the stack 14 between the two activation levels. The voltages and / or other control signals are supplied to the actuator by a computer processor or engine control unit (not shown) in a conventional manner. Further construction or operating details of the injection valve according to 1 to 3 are in our co-pending patent application EP 0 995 901 A1 described and are therefore not detailed here.
  • With fuel injectors of the type generally discussed above, it is important to maximize stacking throughout the life of the injector or injector, although the current position of the stack is less important. 4 shows the actuator length change of a piezoelectric stack 14 as a function of the voltage applied to the stack. Line A (solid line) represents the initial actuator length change characteristic (ie, the length change as a function of applied voltage) of a new actuator, while line B (dashed line) shows the later actuator length change characteristic of an older actuator towards the end of its life. The actuator is connected to the piezoelectric stack by applying a positive voltage, + V1 14 brought to its first activation level and by reducing it to the stack 14 applied voltage to a negative voltage level, -V2, brought to a second, lower activation level. When the actuator is new (line A), decreasing the voltage across the stack from + V1 to -V2 causes a length change of the actuator between positions D1 (voltage level + V1) and D2 (voltage level -V2), reducing its length changed by an amount shown by the arrow Z1. When the actuator is in operation towards the end of its life (line B), a change in the voltage applied to the stack between the voltage level + V1 and the voltage level -V2 will move the actuator from position D3 to position D4, increasing the length of the actuator Actuator is changed by an amount which is shown by the arrow Z2. By comparing the arrow lengths, Z1 and Z2, it can be seen that the actuator length change is smaller in an older actuator to which the same voltage variation is applied. It is therefore not possible to operate the actuator throughout its life between the fixed voltage limits, + V1 and -V2, when it is necessary to always maintain a substantially constant maximum actuator length change.
  • One way to avoid this problem is to operate the actuator between variable voltage levels and to use the increase in length at the negative voltage stroke end to compensate for the length loss at the positive voltage stroke end (the positive or negative voltage stroke end may also be positive or negative charge stroke end, positive) or negative stroke end or as positive or negative length change stroke end). The effect is in 5 showing the actuator length change Z1 at a new actuator (line A) compared to the actuator length change characteristic at an older actuator (line B). When the voltage levels + V3 and -V4 are applied to a new actuator, the actuator displacement is between D5 and D6, resulting in a stroke length indicated by the arrow Z1. In the older actuator, a voltage change between + V3 and -V4 results in an actuator length change between D7 and D8, the magnitude of the change (as shown by arrow Z2) being substantially equal to that of arrow Z1. This is due to the fact that the length change loss occurring in the course of the aging of the actuator at the positive voltage stroke end of the actuator is compensated by the increase in length increase at the negative voltage stroke end of the actuator. Thus, by careful selection of the actuation voltages + V3, -V4, it is possible to keep the dimension of the actuator at a substantially constant value throughout its useful life.
  • However, this scheme is only a solution under some circumstances, as it is not possible for many actuators to choose a negative voltage, -V4, which is large enough to compensate for the loss of length at the positive voltage swing end, without falling within the voltage range. in which the polarization of the piezoelectric material begins to reverse. Polarization reversal of the material occurs near the minimum of the voltage-length change characteristic, at the voltage -V R. Operating the actuator with more negative voltages requires an excess of energy which makes operation in this range inefficient. In addition, operating the actuator at voltage levels that are more negative than the polarization reversal level can damage the piezoelectric material. Another problem is that the polarization reversal voltage of a piezoelectric material is temperature sensitive, so that any choice of the maximum negative operating voltage to avoid polarization reversal must take into account the effects of temperature variations. Consequently, this technique for compensating for changes in the length change throughout the life of the actuator may not be precise enough.
  • 6 shows an alternative technique for compensating for changes in actuator length change over the lifetime of the actuator. Prior to installation in the engine, multiple piezoelectric actuators are tested to determine how the actuator length change characteristic varies over time. As before, the line A represents the actuator length change characteristic in a new actuator (ie, the first time operation) and the line B represents the actuator length change characteristic in the same actuator after being in operation for a long period of time. The measured change in length and the corresponding voltage values are stored in a look-up table or a data card in the processor memory. A control algorithm is executed in operation, wherein different voltage values are selected from the look-up table in dependence on the measured change in length of the actuator. Thus, one way to implement this idea is to measure the actuator length change and continuously adjust the applied voltage in response to the measured extent. In this way, the length change when the actuator is new and operates between the voltages + V1 and -V2 is shown by the arrow Z1. If it is determined that the change in length during operation decreases between these levels, the voltage levels are adjusted until it is determined that the new levels + V3 and -V4 give substantially the same extent (as shown by the arrow Z2). In some circumstances, however, the method of measuring actuator length change and adjusting voltage and charge levels may be difficult to implement in response, as measuring actuator displacement in an operating system is difficult and costly.
  • In There is a possibility in practice to implement this scheme, provided the actuator length change characteristic proved to be predictable, in that actuators among several different operating conditions in advance to test and suitable condition-based lookup data tables for use with to store the control algorithm. The change in length characteristic of a Actuator, which is often and over longer continuous Time periods can be, for example, the one Actuator less frequently and over shorter Periods is used, differentiate. Therefore it may be necessary be to test actuators and the data in dependence from the period in which the actuator was in operation has, and the frequency of Store operation. Theoretically, it allows such a scheme the change in length of the actuator during its entire life on a substantially constant To keep level. Other possible Conditions that influence the actuator length change characteristic impair can, The average time span in the stack is one positive charge is present, the average time span, in which there is a positive charge at the stack, and the average Operating temperatur.
  • It is desired to select the voltage levels so that the negative voltage at which a polarization reversal of the piezoelectric material takes place, in all operating phases of the actuator is avoided. In similar Way, there is a positive voltage at which a dielectric breakdown of the material occurs, and it is desirable that the positive voltage levels so chosen be that the dielectric breakdown in all phases of operation of the actuator is avoided. The control unit can be programmed in this way Be sure that the selected voltage levels are the limits for polarization reversal and dielectric breakdown during all phases Do not exceed the life of the actuator. In practice can be the limit of the positive voltage applied to the actuator can be created, however, by the efficiency be determined the control unit.
  • A possible disadvantage of this method is that it can be used to accurately set the voltage levels for the many different resistors In practice, it is necessary to carry out demanding endurance tests and store large amounts of data in the processor memory.
  • It has been found that a more linear actuator length change characteristic is achieved when the actuator is operated with a "constant charge differential". This is in 7 which represents the actuator length change as a function of load on both a new actuator (line A) and an older actuator (line B). It can be seen from a comparison of the lines Z1 and Z2 that a change in the charge value between + Q1 and -Q2 in the new actuator results in substantially the same actuator length change as in an older actuator.
  • at an embodiment the operating charge values or levels are set to the values + Q1 and -Q2, when the actuator is new, resulting in a length change by the arrow Z1 is shown. The charge level -Q2 is chosen it is ensured that a polarization reversal of the piezoelectric Material is avoided, both when the actuator is new as well as with advanced life. By this procedure can while an almost constant actuator length change throughout the life of the actuator be achieved, even if the maximum stroke to a certain extent the need is impaired is for the maximum negative charge level (-Q2) has a conservative value to ensure that the polarization reversal level while all Operating phases of the actuator is avoided, even then, when the actuator length change characteristic changed Has.
  • Another preferred embodiment is with reference to FIGS 8th and 9 and includes changing the charge levels throughout the life of the actuator so that the negative charge level is always chosen as close as possible to the polarization reversal charge but not exceeding it, while maintaining a substantially constant charge change between the selected negative and negative positive levels. Suitable charge levels + Q1 and -Q2 and their associated voltage values + V1, -V2 are chosen by reference to predetermined length change measurements on a new actuator to provide substantially the largest possible actuator length change while ensuring that the negative charge level, -Q2, has a value that is less negative than the maximum negative charge at which polarization reversal occurs. At the positive voltage stroke end, the voltage is chosen so that it does not exceed the level at which polarization reversal of the material takes place (unless the control unit itself assigns the maximum voltage a lower than the applicable limit value).
  • 8th FIG. 12 shows the length change characteristic for a new actuator (line A) with a stroke length or actuator length change shown by the arrow Z1 when the charge level is switched between + Q1 and -Q2. The length change characteristic for an older actuator (line B) is also shown, it being understood that substantially the same stroke length is achieved in this actuator (as shown by arrow Z2) when the charge level is switched between + Q3 and -Q4. The charge difference between + Q1 and -Q2 and between + Q3 and -Q4 is substantially the same (it is called a constant charge-differential state) and it is said that the actuator is operated with "constant charge". This embodiment of the present invention utilizes this characteristic of the behavior of piezoelectric actuators and avoids having to measure the instantaneous actuator length change characteristic.
  • A possibility for implementing a constant charging operation is first the appropriate charge levels, + Q1 and -Q2, at the beginning of the actuator use based on pre-determined measurements the charge-length change characteristic of a new actuator, and then the actuator charge-length change characteristic to predict for an older actuator, by setting up two hypotheses: (i) the actuator length change is linear during constant charge operation and (ii) the gradient dV / dQ remains at the maximum negative charge level on the the actuator can be operated (before a polarization reversal takes place), essentially during constant actuator life (referred to as "constant gradient state").
  • 8th shows the constant charge difference state as described above, and 9 shows the voltage-charge characteristic of a new actuator (line A) compared to that of an older actuator (line B), from which it can be seen that the gradient (dV / dQ) of the characteristic at the maximum negative charge values -Q2, -Q4 of the new or older actuator is substantially the same.
  • The method steps for carrying out an embodiment of this method will now be described in more detail with reference to the flow chart according to FIG 10 described. If necessary, put it in the pile 14 applied voltage V can do this directly using a suitable Voltage measuring circuit can be performed. If it is necessary to measure the charge Q, this can also be done directly by integrating the current driving the stack in relation to time. In a driver circuit of the type in which charge pulses are transmitted to the actuator, the current track may suffer from too high a noise level to directly measure the charge, in which case the charge is known by knowing the charge transfer characteristic of the driver circuit for each pulse and Multiplying the same can be measured with the number of pulses. Both the voltage and the charge measurement can therefore be carried out relatively easily.
  • Referring to 10 are at time T (step 100 ) is selected from + V1 and -V2 using a pre-stored actuator-voltage-length change characteristic of a new actuator, avoiding the polarization inversion voltage at the negative voltage swing end and the dielectric breakdown voltage at the positive voltage lift end. Corresponding values for + Q1, -Q2 are selected, the charge levels at time T being designated as + Q1 T and -Q2 T.
  • After a predetermined time T + 1 (step 102 ), wherein the voltage present at the stack is switched between the levels + V1, -V2 to cause the length of the actuator to be changed between its first and second states, the corresponding charge -Q2 T + 1 is measured. When in step 104 -Q2 T + 1 is substantially equal to -Q2 T , it is considered that the actuator length change characteristic has not changed significantly, and the voltage and charge levels + V1, -V2, + Q1, -Q2 become the operation for Time T + 1 held at the same values as for the operation at time T.
  • When in step 104 if the charge deviates by a substantial amount, ΔQ, from -Q2 T , the voltage level -V2 is adjusted by an amount ΔV and the corresponding charge is measured again. Provided that the gradient, dV / dQ, of the voltage-charge characteristic of a new actuator at time T at a charge of -Q2 T (ie, rate of charge change with voltage at time T) is substantially equal to the gradient dV / dQ of the actuator at the charge level -Q2 (T + 1) at time T + 1, the process of adjusting the voltage level (and thus the charge level) can be continuously repeated (steps 106 . 108 ) until suitable values for charge and voltage are determined (step 110 ). These values correspond to the charge level -Q4 and the voltage -V4 according to the 8th and 9 , It is understood that in the steps 106 and 108 of in 10 the voltage level -V2 (T + 1) is increased or decreased by an amount ΔV until the voltage and charge (-V4, -Q4) are determined to satisfy the constant gradient state.
  • After suitable values for -V4 and -Q4 have been determined, in step 112 the appropriate positive charge level, + Q3, is determined by assuming that the constant charge differential state exists (ie, the change in length for a charge change of the actuator between + Q1 and -Q2 at time T equals the length change of the actuator at a charge change between + Q3 and -Q4 at time T + 1).
  • The Method can also be done using a charge-voltage characteristic such implied that a gradient dQ / dV is used to to determine the second positive or negative charge level. It is appropriate to use the gradient dQ / dV to determine the second positive or to use negative charge level when a natural one Characteristic of the driver circuit is to provide a voltage level produce. If a natural one Characteristic of the driver circuit is a charge level then it is more appropriate to use the gradient dV / dQ for Determination of the second positive or negative charge level use.
  • The method steps according to 10 may be repeated at regular intervals during operation of the actuator. For example, if processor time permits, the process steps may be repeated continuously so that levels -V3, -Q3 are continuously adjusted to compensate for changes in the actuator length change characteristic as the actuator ages. Alternatively, the process steps may be repeated at regular intervals, such as every 10 minutes. In particular, during the initial operation of the actuator, it may be appropriate to adjust the values or levels frequently because it is this phase during the life of the actuator during which the most significant change in the length change characteristic occurs.
  • When another alternative can the voltage and charge levels only once or just a few Times during lifetime, although at most practical embodiments less desirable is.
  • As an alternative to selecting the initial values of + V1, -V2 at time T on the basis of predetermined data, real time measurements of the charge can be made according to the selected voltage value or real time measurements of the voltage according to the selected charge value.
  • At another, with reference to 10 instead of monitoring the maximum negative charge level, -Q2, the maximum positive charge level, + Q1, may be monitored, and a suitable value for + Q3 is determined based on the assumption that the gradient dV / dQ of the voltage charge Characteristic remains invariable at this maximum charge point. The negative charge level, -Q4, is then determined based on the assumption that the constant state of charge is present, as described above. However, this method may be less desirable because the change in gradient dV / dQ as a function of charge at the positive stroke end is less significant, so the appropriate maximum charge level, + Q3, is not well defined.
  • A Another alternative technique involves measuring the through the stack consumed energy as a function of the applied voltage and the Change the voltage, so that the gradient of the energy-voltage characteristic at the negative or positive voltage stroke end always maintained at a substantially constant value. When Alternative to changing the voltage can change the charge be to the gradient of the energy-charge characteristics at Negative or positive voltage lift end on a substantially constant Value.
  • It It is understood that in practice the control parameter for the actuator or actuator can be either the voltage or the charge, so that to select the required charge level either the existing over the stack away Charge itself changed directly can be or the over the voltage applied across the stack.
  • To increase the efficiency of injector operation, those described above with reference to FIGS 9 and 10 modified techniques are described. As before, appropriate values for + Q1 and -Q2 are initially selected to obtain the required length change for a new actuator. During appropriate actuator life phases, values for + Q3 and -Q4 are determined using the dV / dQ measurements and applying the constant charge differential state. The charge and voltage levels are then adjusted stepwise based on the selected values, with each adjustment performing a measurement of the energy consumed in the actuator drive circuitry. The voltage and charge levels are adjusted continuously or adjusted until the energy consumption measurement is at a minimum.
  • In each phase of the adjustment or adjustment process is allowed, that the voltage and charge levels are slightly different from the selected values deviate, and the energy consumed is measured. If found will be that one energy measurement is less than the previous one the voltage and charge levels are slightly in the same direction (e.g. negative) until the minimum energy point is reached. If it is determined that an energy measurement is greater than the previous one, the voltage and charge levels are slightly lower in the opposite direction (e.g., positive) until the minimum energy point is reached.
  • 11 Figure 9 is a flow chart showing in more detail how the charge and voltage levels + Q1, -V1, + Q2, -V2, and + Q3, + V3, -Q4, -V4 are selected and adjusted until a minimum power measurement is obtained. In all phases, the voltage and charge levels may differ only by small amounts, ΔQ and ΔV, from the selected values, Q3, -Q4, (calculated from the dV / dQ characteristic and the constant charge differential state), and the charge change between the positive and negative charge levels is always kept at a constant value.
  • The energy E that is consumed by the driver circuit can be built up by integrating it to the stack 14 applied instantaneous voltage, multiplied by the current in proportion to the time to be measured. Alternatively, if the current can not be measured directly, an estimate of the energy consumed may be made from the energy-per-drive pulse characteristic of the driver circuit. In another alternative technique, the temperature of the heat sink on the control unit may be monitored to arrive at an estimate of the power consumption in the driver circuit.
  • 12 Figure 12 is a graph showing the energy consumed in the driver circuit as a function of the voltage applied to the stack for a new actuator (line A) and an older actuator (line B). Out 12 It can be seen that the older actuator consumes less energy than a new actuator with the same actuator length change (stroke length). This has been shown to occur as the properties of an older actuator evolve from those of "soft" piezo materials to those of "hard" piezo materials. It has been found that a hard piezoelectric material has lower losses due to Hysteresis effects than softer piezo materials and therefore can work more efficiently.
  • When Alternative for setting the selected charge and voltage levels for the purpose of minimizing the energy consumed in the driver circuit can the charge and voltage levels are adjusted so that the Stack fed Energy is minimized. In a further alternative embodiment can the charge and voltage levels are adjusted so that the Total energy consumption of the actuator is minimized. The vote, which operating parameter is monitored, depends on it which characteristic is considered decisive.
  • It is understood that the application of the control method described here for operating a piezoelectric actuator or actuator or piezoelectric actuator not on an injection valve in the 1 to 3 described is limited, but rather suitable for use in the control of any piezoelectrically actuated injector or injector. The method can be, for example, both on directly actuated injectors, such as in the 1 to 3 shown, as well as on auxiliary or sequence controlled, piezoelectrically actuated injectors apply. The method is equally applicable to piezoelectric actuators used in applications other than fuel injection systems, as long as the current length change position of the stack is not critical and a constant stroke length is of great importance.

Claims (25)

  1. Method for operating a piezoelectric actuator which comprises a stack ( 14 ) comprising one or more piezoelectric material elements, the method comprising: at a first time (i) varying the charge across the stack between a first positive charge value (+ Q1) and a first negative charge value (-Q2) to offset the stack by a first amount (Z1) (or to change the stack length by that amount), (ii) measure a first charge difference between the first positive charge value (+ Q1) and the first negative charge value (-Q2), and (iii) determining a first operating characteristic (dV / dQ; dQ / dV) of the actuator, and subsequently, at a later time, varying the charge across the stack between a second positive charge value (+ Q3) and a second negative charge value (-Q4) to offset the stack by a second amount (Z2) (or to change the staple length by that amount), wherein the second positive and the second te negative charge value depending on the first operating characteristic (dV / dQ, dQ / dV) and is selected such that the difference between the second positive charge value (+ Q3) and the second negative charge value (-Q4) is substantially the same as the First charge difference, to ensure that the second amount (Z2) by which the actuator is offset or by which it changes its length, is substantially the same as the first amount (Z1).
  2. The method of claim 1, wherein the load is across the stack ( 14 ) is changed between the first and second positive and negative charge values by changing one of the two: the voltage or charge applied across the stack.
  3. The method of claim 1 or claim 2, wherein the piezoelectric material has a polarization reversal voltage value at which a polarization reversal occurs, the method comprising selecting the first negative charge value (-Q2) such that the voltage across the stack ( 14 ) at the first positive charge value (+ Q1) is just greater than the polarization inversion voltage value to avoid polarization reversal of the material.
  4. The method of any one of claims 1 to 3, wherein the piezoelectric material has an insulation breakdown voltage value at which a dielectric breakdown of the material occurs, the method comprising selecting the first positive charge value (+ Q1) such that the voltage across the stack ( 14 ) at the first positive charge value is less than the insulation breakdown voltage value during all stages of the life of the actuator.
  5. Method according to one of claims 1 to 4, comprising determining an operating characteristic, which is a first voltage-charge characteristic, by measuring across the stack ( 14 ) applied voltage across the stack, at the first time.
  6. The method of claim 5, comprising selecting the second negative charge value (-Q4) such that a voltage-charge characteristic at the chosen second negative charge value has a gradient (dV / dQ), substantially equal to a gradient of the first voltage-charge characteristic the first negative charge value (-Q2).
  7. The method of claim 5, comprising selecting the second positive charge value (+ Q3) such that a voltage-charge characteristic at the chosen second negative charge value has a gradient (dV / dQ), substantially equal to a gradient of the first voltage-charge characteristic the first positive charge value (+ Q1).
  8. Method according to one of claims 1 to 4, comprising determining an operating characteristic, which is a first voltage-charge characteristic, by measuring across the stack ( 14 ) applied charge as a function of the voltage across the stack, at the first time.
  9. Method according to one of claims 1 to 8, comprising Measuring an operating parameter and adjusting the selected second positive and second negative charge value by a relatively small amount Amount (+/- ΔQ) to the Set operating parameters to maximum, while the difference between the second positive and the second negative charge value (+ Q3, -Q4) held substantially the same value as the first charge difference becomes.
  10. Method according to one of claims 1 to 8, comprising Measuring an operating parameter and adjusting the selected second positive and second negative charge value by a relatively small amount Amount (+/- ΔQ) to the Set operating parameters to minimum, while the difference between the second positive and the second negative charge value (+ Q3, -Q4) held substantially the same value as the first charge difference becomes.
  11. The method of claim 10, comprising measuring the actuator or actuator supplied energy and adjusting the chosen second one positive and second negative charge value (+ Q3, -Q4), that the measurement of said supplied energy is set to minimum becomes.
  12. The method of claim 10, comprising applying the cargo across the stack using a driver circuit, measuring in the Driver circuit consumed energy and adjusting the selected second positive and second negative charge value (+ Q3, -Q4) to minimize the measurement of said consumed energy.
  13. The method of claim 10, comprising measuring the total energy consumption of the stack and adjusting the selected second positive and second negative charge value (+ Q3, -Q4) such that the measurement of said energy consumption is set to minimum becomes.
  14. A method according to any one of claims 1 to 13, wherein the step determining the operating characteristic at the first time Referring to a previously stored operating characteristic of actuator includes.
  15. A method according to any one of claims 1 to 13, wherein the step determining the operating characteristic at the first time Measuring the operating characteristics in real time.
  16. The method of claim 14 or claim 15 wherein the step of determining the operating characteristic to the first Time determining a voltage value and a corresponding charge value includes.
  17. A method according to any one of claims 1 to 16, comprising Applying a current (transverse) through the actuator or actuator, Measuring the voltage applied to the actuator or actuator and the corresponding stream and determining the first and second positive and negative charge values (+ Q3, -Q4) by integrating a Instantaneous value for the current in relation to Time.
  18. Method for operating a piezoelectric actuator which comprises a stack ( 14 ) comprising one or more piezoelectric material elements, the method comprising: varying the charge across the stack between a first positive charge value (+ Q1) and a first negative charge value (-Q2) at a first time to cause the charge to increase Stacking between a positive stroke end and a negative stroke end by a first amount (Z1) (or changing its length by that amount), subsequently, at a later time, changing the charge across the stack between a second one positive charge value (+ Q3) and a second negative charge value (-Q4) to offset the stack by a second amount (Z2) (or to change its length by that amount), wherein the second positive and the second negative charge value (+ Q3, -Q4) are selected so as to ensure that a loss of actuator length change at the positive end of the stroke at a later time is determined by the gain a Actuator length change is compensated at the negative end of the stroke at the later time substantially.
  19. The method of claim 18, wherein the piezoelectric material has a polarization reversal voltage value having a polarization reversal occurs, the method comprising selecting the first and second negative charge values (-Q2, -Q4) such that the voltage across the stack has a less negative value than the polarization inversion voltage value during all states of operation of the actuator.
  20. The method of claim 18 or claim 19, wherein the piezoelectric material has an insulation breakdown voltage value possesses, occurs at the dielectric breakdown of the material, the method selecting the first and the second positive Charge value (+ Q1, + Q3) such that the voltage across the Stack is just less than the insulation breakdown voltage value while of all states the operation of the actuator.
  21. Method for operating a piezoelectric actuator or actuator, comprising a stack ( 14 ) comprising one or more piezoelectric material elements, the method comprising: varying the charge across the stack between a first positive charge value (+ Q1) and a first negative charge value (-Q2) at a first time to cause the charge to increase Stacking to offset (or to change its length by that amount) by a first amount (Z1), subsequently, at a later time, changing the charge across the stack between a second positive charge value (+ Q3) and a second one negative charge value (-Q4) to offset (or change by length) the stack by a second amount (Z2), wherein the second positive and the second negative charge values (+ Q3, -Q4) are in accordance with one certain operating characteristic of the actuator or actuator are selected, thereby ensuring that the second amount (Z2) by which the actuator is offset or its L changes substantially the same as the first amount (Z1).
  22. The method of claim 21, comprising the selection of the second positive and the second negative charge value (+ Q3, -Q4) according to a previously determined operating characteristics of one or more depends on the following operating conditions: Age of the actuator or actuator, frequency of use the actuator, Temperature of the actuator, average period during which the positive charge value is applied to the stack, average Period during which the negative charge value is applied to the stack.
  23. Method according to one of Claims 1 to 22, in which the charge is transported across the stack ( 14 ) is changed during use for the first, at the subsequent and at a plurality of further times.
  24. The method of claim 23, wherein the charge is across the stack ( 14 ) is changed at regular intervals during operation of the actuator.
  25. Method according to one of claims 1 to 24, wherein the actuator or a part of a fuel injection valve with a valve needle ( 10 ) for controlling the injection of fuel into an associated engine, and wherein a change in the charge value between the first positive charge value (+ Q1) and the first negative charge value (-Q2) and between the second positive charge value (+ Q3) and the second negative Charge value (-Q4) movement of the valve needle ( 10 ) between injection and non-injection states.
DE602004000190T 2003-01-17 2004-01-19 Method for controlling a piezo drive Active DE602004000190T2 (en)

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2009112525A1 (en) 2008-03-11 2009-09-17 Epcos Ag Method for operating a piezoelectric element

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2009112525A1 (en) 2008-03-11 2009-09-17 Epcos Ag Method for operating a piezoelectric element
DE102008013590A1 (en) 2008-03-11 2009-09-24 Epcos Ag Method for operating a piezoelectric element

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AT311531T (en) 2005-12-15

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Owner name: DELPHI TECHNOLOGIES HOLDING S.A.R.L., BASCHARA, LU