EP1525596A1

EP1525596A1 - Method for determining the position of a positioning element of an electrically-operated actuator, corresponding circuit arrangement and device

Info

Publication number: EP1525596A1
Application number: EP03766167A
Authority: EP
Inventors: Wenmin Qu; Horst Peter Mannebach; Joachim Morsch
Original assignee: Hydac Electronic GmbH
Current assignee: Hydac Electronic GmbH
Priority date: 2002-07-26
Filing date: 2003-07-15
Publication date: 2005-04-27
Also published as: CN1596451A; US20040016461A1; AU2003250949A1; CN1286128C; US6895997B2; JP2005534189A; WO2004013874A1; DE10235188B3

Abstract

The invention relates to a method for determining the position (x) of a positioning element of an electrically-operated actuator, activated by means of a controlled switch (18) on reaching a lower threshold value (i1) and deactivated on reaching an upper threshold value (i2). A activation duration (tein) and a deactivation duration (taus) result from the lower threshold value (i1), the upper threshold value (i2) and the electrical switching profile of the actuator, dependent on the position (x) of the positioning element and the position (x) of the positioning element is determined from a comparison of the quotients from activation duration (tein) or deactivation duration (taus) and the sum (tein + taus) of activation duration (tein) and deactivation duration (taus) and from a comparison of the sum (tein + taus) of activation duration (tein) and deactivation duration (taus) with stored reference data. The invention further relates to a corresponding circuit arrangement (24) for carrying out said method and a corresponding device (12) in particular a hydraulic valve (42).

Description

Method for determining the position of an actuating element of an electrically drivable actuator, associated circuit arrangement and device

The invention relates to a method for determining the position of an actuating element of an electrically drivable actuator and to an associated circuit arrangement and device, in particular a hydraulic valve.

Typical areas of application for such methods are, for example, electromagnetically operated valves or switches. The inductance of the electromagnet is dependent on the respective position of the armature. Measuring the inductance therefore basically enables the position of the armature to be determined.

DE 43 41 797 A1 discloses a method and a device for controlling an electromagnetic consumer, in particular for use in the field of metering fuel in internal combustion engines. By triggering a solenoid valve, the start of injection, the end of injection and thus the amount of fuel injected is determined. It is necessary that the point in time is known at which the armature of the solenoid valve reaches its end position. This switching time can be obtained by evaluating the time profile of the solenoid valve current. To reduce the Power loss is known from DE 44 20 282 A1 that clocked voltage control takes place during the time window in which the switching time can be determined.

From DE 33 26 605 A1 a method and a circuit arrangement for monitoring the stroke position or position of the armature of a valve magnet is known. The winding is fed with a direct current, which has an alternating current component. The AC component depends on the position of the armature and therefore on the valve position and is tapped at a measuring resistor by means of a high-pass filter.

The known method has the disadvantage that the switching frequency is also dependent on the ohmic resistance of the coil, which in turn is relatively strongly dependent on the temperature, which consequently occurs as a disturbance variable in the output signal relating to the position of the armature. This interference is to be compensated for by circuitry measures based on the measured direct current component.

The invention is based on the problem of providing a method and an associated circuit arrangement and a device which overcome the disadvantages of the prior art. In particular, the position of the actuating element should be able to be determined with great accuracy and in particular with sufficient compensation for the influence of temperature. The method and the associated circuit arrangement and

The device should be inexpensive to manufacture and maintain and, moreover, should ensure reliable operation over the long term. The problem is solved by the method defined in claim 1 and by the circuit arrangement and device determined in the independent claims. Particular embodiments of the invention are defined in the subclaims.

According to the invention, the problem is with a method for determining the position x of an actuating element of an electrically drivable actuator, which is switched on by means of a controlled switch when a lower threshold value is reached and is switched off when an upper threshold value is reached, the upper threshold depending on the lower threshold value threshold value and from the position x of the control element dependent electrical switching behavior of the actuator, a duty cycle t _and an off-time t _off results, achieved in that the position x of the actuating element from a comparison of the ratio of duty cycle t _or off time t _off and the

Sum _ejn t + t _from t duty _and off-time t _off, as well as from a comparison of the sum t _on + t _off of duration t is determined _and OFF time t _from each stored reference data.

The electrically drivable actuator can be, for example, an electromagnetically drivable actuator, a piezoelectrically drivable actuator, or any type of actuator that carries out a mechanical movement on the basis of an electrical control signal and thereby acts, for example, as an actuator or switching element in a control circuit. In a . In a special embodiment of the invention, the actuating element of the actuator is the armature of an electromagnet. The movement of the armature can be translatory and / or rotary. In the case of a translatory movement, the adjustment path of the adjusting element can between a few fractions of a millimeter and a few centimeters or more.

In principle, the quotient of the on-time or off-time and the sum of the on-time and off-time can also be formed by means of an analog computer, but is preferably carried out, for example, for reasons of interference immunity or for reasons of cost, by a digital electronic computing unit. The switch-on and switch-off times can be determined, for example, by counting the pulses of a correspondingly high-frequency and possibly central clock, the switch-on or switch-off signal serving as a switching signal for the high-frequency clock. The comparison with the stored reference data, which is usually obtained empirically, for example on the basis of an actuator typical of the respective design, is likewise preferably carried out by the electronic computing unit.

The quotient of the on time or off time and the sum of the on and off time can be referred to as the pulse width ratio or duty cycle, which depends both on the position x of the actuating element of the actuator and, as a rule, also on the temperature of the arrangement. Typical temperature values during the operation of corresponding devices are between 50 and 100 ° C, and can also be above or below depending on the application and the ambient temperatures.

As a rule, the comparison of a determined quotient with the stored reference data will not guarantee sufficient accuracy with regard to the determination of the position x of the control element. The contribution of temperature contained in this quotient could can be calculated, for example, using a temperature sensor located near the arrangement. However, the temperature influence is preferably compensated for by comparing the sum of the switch-on and switch-off times with corresponding reference data.

For example, of the stored reference data pairs “position x” and “temperature T”, which are suitable on the basis of the quotient determined, the pair of values for which corresponding reference data relating to the determined sum signal is stored is identified as valid on the basis of the sum of the switch-on and switch-off duration also determined are. If necessary, an interpolation can also be carried out to calculate an intermediate value between two determined or two stored values.

As an alternative or in addition, a comparison is possible to the extent that parameterized equations that are representative of the respective design of the actuator are stored, in which the measured quotients and sum values are used as variables. It is essential that both the quotient and the sum are used to determine the position of the actuating element.

In a special embodiment of the invention, the actuating element actuates a valve, for example a hydraulic or pneumatic valve. The valve can be a switching valve or a

Act proportional valve, for example a control valve for the continuous adjustment of a predeterminable flow or pressure. The controlled switch can be a contactless, electronically controlled switch such as a transistor, in particular a MOS transistor. In addition to a first and a second switching electrode, such switches usually have a third control connection, via which by means of a low control! high switching capacities are wear-free and can be switched with low power loss.

In the case of an electromagnet, the coil current of the winding of the electromagnet is regulated. Lower and upper threshold values can be specified for this coil current, which threshold values can in particular be adjustable and / or programmable by memory. These threshold values determine the operating point of the electromagnet. The choice of this operating point and the difference between the threshold values determine the oscillating switching behavior that occurs. In order to monitor the reaching of the threshold values, a voltage signal! evaluated on a resistor through which the coil current flows. In principle, the ohmic resistance of the coil winding could also be considered. Preferably, however, an ohmic resistor electrically connected in series to the actuator and in particular to the coil winding is used, which is further preferably with an electrode at a reference potential of the evaluating control device, in particular at ground potential.

In a special embodiment of the invention, the monitoring of the reaching of the threshold values, and / or the actuation of the switch, and / or the comparison with the reference data is carried out by a microcontroller. In particular, this can involve a few or even a single integrated circuit, through which an analog / digital conversion of the input signals and the electronic circuit can also be carried out Arithmetic unit for calculating the quotient and the sum of the on and off duration and the subsequent comparison with stored reference data. The output signal of the microcontroller can be coded in an analog and / or digital manner, including the output of a frequency-analog signal. In addition, the microcontroller can also generate all self-diagnosis signals and error signals required in accordance with the applicable standards and output them via predefinable interfaces.

In a special embodiment of the invention, the holding current is reduced when the actuator is switched through. This not only results in an energy saving, but also a reduction in the mechanical and thermal load, not only of the respective device, but in particular also of the entire apparatus environment. The holding current can be reduced, for example, by reducing the nominal coil current, by setting a predeterminable pulse width ratio or the like.

In a special embodiment of the invention, the switching current is increased compared to the nominal current when the actuator is switched. In this way, faster switching behavior can be achieved if necessary. The switching current can be increased, for example, by a temporary short circuit of resistors which are connected in series with the coil winding, by connecting an overvoltage or the like.

The present invention also relates to a circuit arrangement for realizing the circuit described above Method and a device, in particular a hydraulic valve, with such a circuit arrangement.

In a special embodiment of the invention, the computing unit is designed as an integrated circuit, the signal processing being carried out predominantly or exclusively digitally. The miniaturization associated with the design as an integrated circuit makes it possible to implement the circuit arrangement in a structural unit with the device. In addition to corresponding interference immunity and processing speed, there is in particular the possibility of structurally arranging the electronics very close to the actuator.

As can be seen from the method described above, not only the position x of the actuating element can be determined, but also the temperature T of the actuator, in particular the coil winding. The

Temperature detection is therefore possible without a separate temperature sensor. In some applications, the temperature of the coil winding will be substantially the same as the temperature of the medium in the device, for example the temperature of the fluid in the hydraulic valve, or in any case a meaningful measure of this. In addition, the temperature determined in this way can be used to implement overtemperature protection for the coil winding of the electromagnet.

Further advantages, features and details of the invention emerge from the subclaims and the following description, in which an exemplary embodiment is described in detail with reference to the drawings. The can in the claims and in the Description mentioned features may be essential to the invention individually or in any combination.

1 shows the profile i (t) of the coil current i of an electromagnet over time t at a first position x, of the armature,

2 shows the curve i (t) at a second position x _{2 of} the armature, FIG. 3 shows an enlarged representation of the current curve i (t) of FIG. 2 in the region of the lower and upper threshold value i, or i ₂ , Fig. 4 shows an embodiment of the circuit arrangement according to the invention, and

Fig. 5 shows a schematic representation of a cross section through a device according to the invention.

Fig. 1 shows the course of the coil current i over time t of the coil winding 10 of an electromagnet of an inventive

Device 12 (Fig. 5). During the switch-on process O <t <t, the nominal voltage U ₀ is applied to the electromagnet, which together with the ohmic resistance R of the coil winding gives the final value of the current i ₀ according to i ₀ = U _Q / R. During the switch-off process t, <t <t ₂ , the nominal voltage U _{0 is} switched off from the connections of the coil winding 10 and an exponentially falling current i (t) results. The associated time constant τ is determined by the quotient of the coil inductance L and the ohmic resistance R of the coil winding. The temperature T of the arrangement is a first value T, for the course of i (t) shown in FIG. 1.

The inductance L is an electromagnet which, according to the exemplary embodiment of the device 12 according to the invention shown in FIG. 5 as a hydraulic proportional valve 42 has an axially movable armature 14, is dependent on the position x of the armature M with respect to the coil winding 10. For the first position x, there is thus a coil inductance L ,, of which the current profile i (t ) is to be assumed in FIG. 1.

With the circuit arrangement shown in FIG. 4, an electrical operating point of the coil winding 0 can be set by evaluating the voltage drop caused by the coil current i across the measuring resistor R, such that when a lower threshold value i- is reached by the control device 16 Switch 18 is turned on. When the upper threshold value i ₂ is reached, the switch 18 is switched off. This results in the time profile of the coil current i (t) shown in FIG. 1. The duty cycle of _a T and the off-time t _off depends on the choice of the lower

Threshold value i _{1 of} the upper threshold value i ₂ and the inductance L of the coil winding and therefore dependent on the position x of the armature 14 and the ohmic resistance R of the coil winding, which in turn is dependent on the temperature T of the coil winding 10.

2 shows the profile i (t) of the same coil winding 10 for a second position x _{2 of} the armature 14, but with the temperature 1] unchanged. In this position x ₂ , the armature 14 has further entered the coil winding 10, so that the inductance L => L ₂ (x ₂ ) is greater than the inductance L ^ x,), which is at a position x = x ^ des Anchor 14 results.

The current waveform i (t) shown in FIG. 2 with the associated quotient _eιn of t and t, _{respectively,} and the sum of t _a + t _(see Fig. 3) can also x in the case of an unchanged position = the Anchor 14, however at a correspondingly increased temperature T ₂ > T. It is therefore not yet possible to conclude unambiguously from the changed current profile i (t) whether this has occurred due to a changed position x of the armature 14 and / or a changed temperature T.

FIG. 3 shows an enlarged representation of the current profile i (t) of FIG. 2 in the region of the lower and the upper threshold values i- and i ₂ . In the illustrated operating point results in a duty _{cycle, a} t and a switched-off t _off. These are detected by an electronic computing unit 20 of the controller 16 (Fig. 4) and then continuously evaluated in that firstly the quotient of the duration t _and the sum t _on + t _off of Eirischaltdauer t _and off time t _off is formed. This quotient is compared with reference data which are stored in an electronic storage means 22 in the control device 16. The stored reference data are determined empirically on one or more specimens typical of the design of the respective device 12. The reference data can be predefined or can be changed in a programmable manner. For example, a read-only memory (ROM) or a programmable read-only memory (PROM, EPROM, EEPROM) can be built into the control device 16 or can be inserted interchangeably.

Further, the sum of the control device 16 (t _on + t _off) is formed and compared with corresponding stored and also in the electronic memory means 22 reference data. From this comparison, which is preferably carried out under program control with automatic processing of a corresponding control program, which can also be stored in the electronic storage means 22, can be determine both the position x of the armature 14 of the device 12 and the temperature T of the coil winding 10.

In the exemplary embodiment of the circuit arrangement 24 according to the invention shown in FIG. 4, the switch 18 is designed as a MOS transistor which, with negligibly small control powers, can also switch high loads with low volume resistance. The series circuit consisting of coil winding 10 and measuring resistor R, a freewheeling diode D is connected in parallel. After a steady state has been reached, for example switched on, the control device 16 can reduce the holding current, for example by means of a predetermined pulse width ratio. For a quick switching operation, the control device 16 can briefly increase the switching current, for example with a short circuit in the measuring resistor R, or by a brief overvoltage. The preferably using or as

In addition to the signal 44 for the position x of the armature 14, the control device 16 implemented by the microcontroller can also output a self-diagnosis and / or fault signal 46 which may meet the existing standards.

FIG. 5 shows a schematic representation of a cross section through a device 12 according to the invention. This exemplary embodiment is a hydraulic proportional valve 42 that can be actuated in an impure manner , which is preferably ferromagnetic or ferromagnetic. When current is applied to the coil winding 10, the armature 14 experiences a force against the action of the force accumulator 28 arranged in the valve 42, which can be formed, for example, by a helical compression spring. The armature 14 has a bore 30 which corresponds to the inlet and outlet channels 32, 34 of the valve 42 and is rectified in the exemplary embodiment. The position x of the armature 14 determines the effective cross section of the bore 30 and thus the flow 36 of a fluid through the valve 42. When the coil winding 10 is in a de-energized state, the armature 14 takes a preferably annular flange 38 through the contact of the end-shaped and preferably annular flange an annular contact surface 40 also forms an end position closing the valve 42.

Claims

1.4

P a t e n t a n s r u c h e

, Method for determining the position (x) of an actuating element. electrically drivable actuator, which is controlled by a

Switch (18) is turned on when a lower threshold (i,) is reached and when an upper threshold is reached

(i ₂₎ is switched off, whereby depending on the lower threshold value (i,), the upper threshold value (i ₂₎ and the function of position (x) of the actuating element electrical switching behavior of the actuator, a duty cycle (t _a) and a Switch-off duration (t _off ) results, and the position (x) of the

Adjusting element from a comparison of the ratio of on-time (t _on) or off-time (t _-US) and the sum (t _a + t _alls) of on-time (t _on) and off-time (t _off), as well as from a comparison of the sum (t _eιn + t _off) of on-time (t _on) and off-time (t _off), each stored reference data is determined.

2. The method according to claim 1, characterized in that the actuating element of the actuator is an armature (14) of an electromagnet.

3. The method according to claim 1 or 2, characterized in that the actuating element actuates a valve (42).

4. The method according to any one of claims 1 to 3, characterized in that the threshold values (ii ₂ ) can be predetermined, in particular adjustable and / or programmable.

5. The method according to any one of claims 1 to 4, characterized in that the monitoring of the reaching of the threshold values (i ,, i ₂ ), the activation of the switch (18) and the comparison with the reference data is carried out by a microcontroller.

6. The method according to any one of claims 1 to 5, characterized in that for monitoring the reaching of the threshold values (i ,, i ₂ ) a voltage signal is evaluated at a resistor R electrically connected in series with the actuator.

7. The method according to any one of claims 1 to 6, characterized in that the holding current is reduced when the actuator is switched through.

8. The method according to any one of claims 1 to 7, characterized in that the switching current is increased compared to a nominal value when switching the actuator.

9. Circuit arrangement (24) for determining the position (x) of a

Control element of an electrically drivable actuator which can be switched on by means of a controlled switch (18) when a lower threshold value (i,) is reached and can be switched off when an upper threshold value (i ₂ ) is reached, with the function of the lower threshold value (i,) the upper threshold value (i ₂₎ and of the position (x) of the control element dependent electrical ^"switching behavior of the actuator, a duty cycle (t _on) and turn-off (t _off) results, and wherein by means of an electronic computing unit (20) the duty cycle ( t _on ) and the switch-off time (t _off ) can be measured and that the position (x) of the actuating element can be determined by means of the electronic computing unit (20) by comparing the quotient of the on time (t _em ) or off time (t _off ) and the sum (t _eln - + - t _off) of on-time (t _on) and off-time (t _off), as well as from a comparison of the sum of (t _a + t _off) of on-time (t _eiπ) and off-time (t _off), each stored reference data can be determined.

10. The device (12), in particular hydraulic valve, with a circuit arrangement (24) according to claim 9 for executing the

Method according to one of claims 1 to 8, characterized in that the computing unit (20) is designed as an integrated circuit and is designed as a unit with the device (12).