DE3713562A1 - Method for determining the position of control elements with inductive position encoders - Google Patents

Abstract

In such methods, the inductive position encoder consists of one or more electrical coils, in which an armature is displaceable as a result of which the position of opening of a valve body can be provided electrically as analog output signal for an evaluating device. Component tolerances can have the result that the relative position between the armature and the coil or coils is different for each encoder produced. The novel method therefore provides: that when the control element is taken into operation, the control element or the position encoder or both is/are aligned in that the control element is brought into a predetermined alignment position (HM) which is different from the final position (h0) and the position encoder is aligned with regard to its measuring distance in such a manner that the alignment measurement value (UAM) obtained during this process assumes a predetermined quantity and during the subsequent operation of the control element, the actual measurement value (UA) is correlated with a particular position (H) of the control element in that the difference between the actual electrical measurement value (UA) and the zero-point electrical measurement value (U0) is divided by the difference between the alignment measurement value (UAM) and the zero-point measurement value (U0). This makes it possible to use only few accurate components and carry out simple alignment.

Description

The invention relates to a method for determining the position pneumatically operated control elements by means of an inductive Weggers with an evaluation device in the

• a) the actuating element is brought into an end position (h ₀) when it is put into operation and the electrical zero point measurement value (U ₀) of the displacement sensor determined by the evaluation device is stored by the evaluation device and
• b) during the subsequent operation of the control element for determining the position of the position sensor, the difference between the actual electrical measured value (UA) and the electrical zero point measured value (U ₀) of the position sensor is determined and a specific position (h) of the control element is assigned.

In such methods, the inductive displacement sensor usually consists of one or more electrical coils in which an armature is axially displaceable and which are surrounded by a magnetic yoke element. These position sensors are used to determine the position of an actuator, e.g. B. for stroke measurement on a pneumatically operated exhaust gas recirculation valve of an internal combustion engine. For this purpose, the axial opening position (h) of the valve body is provided electrically as an analog output signal (UA) at the output of an evaluation device.

The valve body is adjusted by applying a Differential pressure on the pneumatic control element. Hereby becomes a membrane of the actuator axially against a spring force adjusted. The diaphragm adjusts the valve body and moves one in the direction of your movement onto the anchor of the Push rod and / or pull rod acting as a encoder.

The output signal (UA) of the evaluation device changes due to the axial change in position of the armature relative to the one or more coils of the displacement sensor. Each output signal is a certain position, in particular opening position of the actuated element, for. B. the exhaust gas recirculation valve assigned.

Due to component tolerances, it can also happen in an end position (h ₀) of the actuated device, such as the exhaust gas recirculation valve, that the relative positions between the armature and the spool (s) turn out differently for each specimen, as a result of which different zero point measured values (U ₀ ) result. Accordingly, the actual measured values (UA) with the same opening position (h) of the actuated device are different.

This deficiency is eliminated in known displacement transducers and control elements in that when the actuator is started up, it is first moved into an end position (h ₀) of the device to be actuated and the electrical zero point measurement value (U ₀) is determined for the special specimen as the initial value of the measurement curve becomes. This zero point measured value is stored by a control unit of the evaluation device or the like.

During operation, the stored zero point measured value (U ₀) is compared with the respective actual measured value (UA) . The difference between the two is then the measure for the current position (h) of the actuated device or the distance between the position (h) and the end position (h ₀).

An exact assignment between the actual measured value (UA) and the position (h) of the control element or the device actuated by it further requires that the measurement curves of all copies, that is to say all control elements, in particular all displacement sensors, have the same gradients. To solve this problem, it was previously necessary to build the displacement sensors so precisely that the slope tolerance of the measurement curves was as narrow as possible. This could be achieved by using relatively long coils, precise core and coil dimensions, and tightly specified magnetic properties of the armature material. The manufacturing effort was correspondingly high. In particular, the production of coils with thin coils with thin winding wires is difficult.

Proceeding from this, the invention is based on the object To provide methods of the type mentioned, which the use of relatively simple controls and ins special simply built encoder, which is an inherently have a correspondingly large number of specimens to allow; at the same time, the measurement accuracy achieved with this should be similarly good as with the well-known elaborate control elements and inductive Be away.

To solve this problem, a method of ge called kind proposed, which is characterized in that

• c) when the control element is started up, the control element or the displacement sensor or both is / are adjusted by
  • c₁) the actuating element is brought into a predetermined, from the end position (h ₀) different adjustment position (HM) and
  • c₂) the displacement sensor is adjusted with respect to its measuring path in such a way that the adjustment measured value (UAM) obtained thereby assumes a predetermined size and
• d) during the subsequent operation of the control element, the assignment of the actual measured value (UA) to a specific position (h) of the control element takes place in that the difference between the electrical actual measured value (UA) and the electrical zero point measured value (U ₀ ) is divided by the difference between the adjustment measured value (UAM) and the zero point measured value (U ₀). This quotient represents a measure of the position (h) of the control element; it can be multiplied by a freely selectable scale factor, preferably by the path difference between the end position (h ₀) and the adjustment position (HM) , which may also be multiplied by a constant.

By the invention it is u. a. possible, relatively inexpensive and to use relatively little precise components where ins especially the steepness of the measuring curve is in relatively wide To lerances can move.

Appropriate configurations of the subject matter of the invention Ensure easy adjustment in particular included further claims.

Further details, features and advantages of the item the invention result from the following description an embodiment with reference to the drawing; in this shows:

Figure 1 shows a device for determining the position of an exhaust gas recirculation valve in axial section.

FIG. 2a shows a voltage-displacement diagram for different examples of the device according to FIG. 1 - for different zero point measured values before the adjustment process;

FIG. 2b shows a voltage-displacement diagram for different examples of the device according to FIG. 1 - for different measuring curve steepnesses before the adjustment process;

Fig. 2c is a voltage-displacement diagram for different copies of the device Fig. 1 - for different zero point measured values and different curve steepnesses after the adjustment process and

Fig. 3 is a voltage-displacement diagram for explaining a preferred adjustment method.

In Fig. 1, an inductive displacement sensor 20 is provided in the upper third, which consists of an armature 3 , coils 2 and 4 , a return circuit 16 , a compression spring 1 and a needle-shaped push rod 6 for moving the armature 3 .

This displacement sensor is used for displacement measurement or position determination of a pneumatically operated actuating element 30 , with which the valve body 11 of an exhaust gas recirculation valve 40 of an internal combustion engine, not shown in the drawing, is adjusted.

The respective axial opening position (position) h of the valve body 11 is detected by the displacement sensor 20 and provided as an analog output signal UA (actual measured value) at the output of the evaluation circuit.

The exhaust gas recirculation valve 40 is opened by applying a negative pressure to a pressure port 5 of the actuating element 30 . The negative pressure acts on a membrane 10 of the control element 30 , which works against a compression spring 7 and moves the valve body 11 of the exhaust gas recirculation valve 40 (upward) in the opening direction. For this purpose, a housing 13 of the actuating element 30 is rigidly connected to the housing of the exhaust gas recirculation valve 40 . Likewise, a push rod 17 is connected on the one hand to the valve body 11 and on the other hand to the membrane 10 in a pressure-resistant and tensile manner.

A needle-like push and / or pull rod 6 is of the actuating member 30 axially movably disposed between the armature 3 of the displacement sensor 20 and the membrane 10 such that the loaded by the compression spring 1 anchor bran 3 each position adjustment of Mem 10 of the control element 30 is immediately followed by . The push and / or pull rod 6 is permanently under the action of the compression spring 1 against a contact surface 8 of the membrane 10 . The actuating element 30 and the displacement sensor 20 are also rigidly connected to one another.

Axial movement of the valve body 11 causes the armature 3 to move relative to the fixed coils 2 and 4 . As a result of this relative displacement, a signal (actual measured value) UA which is dependent on the opening position h of the valve body 11 is obtained at the output of an evaluation circuit 14 connected downstream of the displacement sensor 20 .

Typical measurement curves of different copies of the same device type are shown in Fig. 2a to 2c. Each measurement curve (characteristic curve) belongs to a special example of the device.

Due to component tolerances, it can happen with the exhaust gas recirculation valve closed (stroke h = 0 corresponding to h ₀) that the axial relative position between the armature 3 and the coils 2 and 4 turns out differently in different examples. This is shown in Fig. 2a by parallel offset curves Darge. For this reason, it is necessary that the zero point measured value U ₀ is determined for each copy of the device before the actuating element 30 is put into operation. For this purpose, the actuating element of the membrane (not shown in detail) 30 through the pressure port 5 due to a corresponding command of a control unit 15 next to both sides applied with ambient pressure Conversely 10th As a result, the compression spring 7 closes the exhaust gas recirculation valve 40 in that the valve body 11 is pressed onto its valve seat 12 . The zero point measured value U ₀ which is consequently set at the output of the evaluation circuit 14 is automatically stored in the control unit 15 and compared with the respective actual measured value UA in the subsequent operation, forming a difference. - This procedure is known per se.

As with the three different specimens of the same type of device characteristics of Fig. 2b shows different slope for one and the same opening position h different output signals UA 1 to UA supply 3, and therefore different opening positions mimic when the slope efficiency of the respective path having encoder 20 relatively wide tolerances. This problem is eliminated by the adjustment procedure described below:

When commissioning the control element 30 , this is first rigidly fixed, for. B. on the curling edge 9 for the membrane 10 BEFE Stigt. Now the valve body 11 is in a defined adjustment position HM = defined stroke, z. B. by lifting from below. The adjustment position HM is preferably in the middle between the maximum opening position H max. and the closed position h ₀ (end position); this ensures the relatively greatest measurement accuracy.

Subsequently, the relative position between the armature 3 and the coils 2 and 4 is adjusted so that a predetermined adjustment measured value UAM is obtained at the output of the displacement sensor 20 . This adjustment measured value is preferably equal to the electrical center value of the displacement sensor, which lies in the middle between the maximum and minimum output signal of the displacement sensor 20 and is preferably located at the turning point of the characteristic curve. This choice of the measured measured value is preferred with a symmetrical structure of the encoder 20 ; the armature 3 extends equally far into both coils 2 and 4 .

The adjustment process is particularly simple if the housing 13 of the actuating element is deformed axially in its cover region E by pressing or pulling, while the actuating element 30 is fixed on its curling edge 9 . In this way, the axial length tolerances of the individual parts are compensated and the adjustment measured value UAM is adjusted to the mechanically defined opening position h = HM (adjustment position).

In Fig. 3 it is shown how the Jus tier measured value UAM is advantageously determined as the electrical average of the displacement sensor for all copies of the same type of device for the adjustment. By swapping the electrical contacts of the position sensor, that is, the contacts A and C , the position sensor characteristic never takes a mirror image - shown in dashed lines in Fig. 3 and designated UA ' -. The intersection of the mirror image with the usual characteristic lies in the elec trical center of the encoder, which in the case of a reference voltage U _Ref for the center signal (adjustment measured value UAM) is 0.5 U _Ref . The adjustment, ie in the case of FIG. 1, the permanent deformation of the housing 13 of the actuating element 30 , is carried out with the exhaust gas recirculation valve 40 (valve body 11 in the fixed position HM) constantly open until the output signal of the evaluation circuit 14 exchanges when the contacts A are exchanged and C no longer changes; then the adjustment measured value UAM is reached, which is identical for all copies of this type of device. This does not require external or absolutely precise voltmeters. In this way, the characteristics of all copies of a device type intersect at the same point UAM, HM .

The invention therefore makes it possible to detect a single measured value, namely the zero-point measured value U ₀, both the zero point and the slope of the characteristic curve of each individual encoder. In comparison to the known methods, no further storage space and also no further absolute measured value acquisition are required when the device is started up.

In an advantageous manner, the zero point measured value U ₀₁ is determined and stored as the initial value of the corresponding encoder sensor copy after its adjustment in the control unit 15 with a start routine. In addition, the difference between the adjustment measured value UAM and the zero point measured value U ₀ 1 can be stored as an instance constant. To determine the position, the control unit 15 calculates the stroke h from the electrical actual measured values UA as follows:

Through the procedure according to the invention, the simplest Means and working methods extremely precise measurement results  achieved, although the individual components are comparatively have large specimen scatter.

Instead of the device explained in the exemplary embodiment, consisting of a linear displacement sensor 20 , a pneumatic control element 30 and exhaust gas recirculation valve 40 , other displacement sensors or valves or, instead of valves, also other components to be set by an adjustment element can be adjusted and operated in the manner according to the invention; it can also be used in other ways as pneumatically operated actuators.

Through the method according to the invention, the specimen is also scatter of the amplification factor of the evaluation circuit with com pens. Otherwise, the evaluation circuit and the inductive displacement transducers can be replaced individually without the Ex scatter of these parts the accuracy of the measurement result it suffers.

Claims (6)

1. Method for determining the position of pneumatically actuated control elements by means of an inductive displacement sensor with an evaluation device in the

• a) the actuating element is brought into an end position (h ₀) when it is put into operation and the electrical zero point measurement value (U ₀) of the displacement sensor determined by the evaluation device is stored by the evaluation device and
• b) during the subsequent operation of the actuating element for determining the position of the displacement sensor, the difference between the actual electrical measured value (UA) and the electrical zero point measured value (U ₀) of the displacement sensor is determined and a specific position (h) of the actuating element is assigned,

characterized in that

• c) when the control element is started up, the control element or the displacement sensor or both is / are adjusted by
  • c₁) the actuating element is brought into a predetermined, from the end position (h ₀) different adjustment position (HM) and
  • c₂) the displacement sensor is adjusted with respect to its measuring path in such a way that the adjustment measured value (UAM) obtained thereby assumes a predetermined size and
• d) during the subsequent operation of the control element, the assignment of the actual measured value (UA) to a specific position (h) of the control element takes place in that the difference between the electrical actual measured value (UA) and the electrical zero point measured value (U ₀ ) is divided by the difference between the adjustment measured value (UAM) and the zero point measured value (U ₀).

2. The method according to claim 1, characterized in that the adjustment measured value (UAM) is equal to the electrical center value of the displacement sensor. 3. The method according to claim 2, characterized in that the electrical center value (UAM) is determined by interchanging the electrical contacts of the encoder. 4. The method according to any one of claims 1 to 3, characterized in that the adjustment position (HM) is located in the middle between end positions of the actuating element. 5. The method according to any one of claims 1 to 4, characterized in that a housing cover of the actuating element is deformed until the adjustment measured value (UAM) is reached.