DE3713562C2 - Method for determining the position of control elements with inductive displacement sensors - Google Patents

Description

The invention relates to a method for determining the position of pneumatically operated Adjusting elements, for example that of DE-A1-31 27 470, by means of an inductive Encoder with an evaluation device, in which

• a) the actuating element is brought into an end position (h₀) when it is started up and the electrical zero point determined by the evaluation device Measured value (U₀) of the displacement sensor is stored by the evaluation device and
• b) in the subsequent operation of the control 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 (U₀) of the encoder determined and one certain position (h) of the actuator is assigned.

In such a method or control element, the inductive displacement sensor consists of a or several electrical coils in which an armature is axially displaceable and are surrounded by a magnetic yoke element. These pathfinders serve determining the position of an actuator, e.g. B. a vacuum converter (DE-A1 31 27 470) or for stroke measurement on a pneumatically operated exhaust gas recirculation system valve of an internal combustion engine. For this purpose, the axial opening position (h) of the Valve body by electrical means as an analog output signal (UA) at the output an evaluation device provided.

The valve body is adjusted by applying a differential pressure the pneumatic actuator. As a result, a membrane of the actuator axially adjusted against a spring force. The diaphragm adjusts the valve body and moves one in the direction of movement onto the anchor of the encoder acting push and / or pull rod.

Due to the axial change in position of the armature relative to the or the coils of the Displacement sensor, the output signal (UA) of the evaluation device changes. Each The output signal is a specific position, in particular the opening position of the actuated element, e.g. B. the exhaust gas recirculation valve assigned.  

Due to component tolerances, it can also be in an end position (h₀) of the actuated actuator direction, such as the exhaust gas recirculation valve, occur that the relative positions between the anchor and the spool (s) for each specimen, which results in different zero point measurements (U₀). They are accordingly Actual measured values (UA) with the same opening position (h) of the actuated device differently.

This deficiency is found in known displacement sensors and actuators, for example the position transmitter described in DE-C2-29 45 895 for hydraulic or pneumatic cylinder eliminated by the fact that when starting the Stell member first in an end position (h₀) of the device to be operated driven and the electrical zero point value (U₀) for the special copy as Initial value of the measurement curve is determined. This zero point measurement value is from a control unit of the evaluation device or the like.

During operation, the stored zero point measurement value (U₀) is compared with the actual Measured value (UA) compared. The difference between the two is then the measure of the current position (h) of the actuated device or the distance between the Position (h) and the end position (h₀).

An exact assignment between the actual measured value (UA) and the position (h) of the Actuating element or the device actuated by it further requires that the Measurement curves of all specimens, i.e. all control elements, especially all displacement sensors, have the same gradients. So far, it has been necessary to solve this problem Lich to build the encoder so precisely that the slope tolerances of the measurement ven were as narrow as possible. This could be done by relatively long coils, precise dimensions core and coil as well as narrowly specified magnetic properties of the Anchor material can be achieved. Correspondingly high  was the manufacturing effort. In particular, the production is la coiled coils with thin winding wires 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 to have a correspondingly large number of specimens; at the same time, the measurement accuracy achieved with this should be similarly good as with the well-known complex control elements and inductive Be away.

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

• c) when commissioning the control element Adjusting element or the displacement sensor or both adjusted will / become by
• c₁) the actuator in a predetermined, from the end position (h₀) different adjustment positions (HM) is brought and
• c₂) the displacement sensor is adjusted in this way with regard to its measuring path is that the adjustment measured value (UAM) obtained is a predetermined size and
• d) the assignment during the subsequent operation of the control element the actual measured value (UA) for a specific position (h) of the control element in that the difference between the electrical actual measured value (UA) and the electrical zero point measurement value (U₀) is divided by the difference between the adjustment measured value (UAM) and the Zero point measured value (U₀). This quotient sets Measure for the position (h) of the control element; he can multiplied by a freely selectable scale factor are preferred, with the path difference between the end point sition (h₀) and the adjustment position (HM) if necessary is multiplied by a constant.

By the invention it is u. a. possible, relatively inexpensive and to use relatively little precise components where ins in particular, the steepness of the measurement 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 demonstrate:

Fig. 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-path diagram for different copies of the device according to FIG. 1, for different zero-point measured values and different measuring 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 Stellelemen tes 30 , which works against a compression spring 7 and the valve body 11 of the exhaust gas recirculation valve 40 (upwards) 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-shaped push and / or pull rod 6 is axially movable Lich between the armature 3 of the displacement sensor 20 and the membrane 10 of the actuating element 30 arranged such that the spring loaded by the compression spring 1 armature 3 each position adjustment of the membrane 10 of the actuating element 30 directly follows. The thrust 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 type of device 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 h₀) 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 U₀ is determined for each copy of the device before the actuating element 30 is put into operation. For this purpose, the actuating element 30 is first applied to the pressure 10 on both sides of the membrane 10 with ambient pressure via the pressure port 5 due to a corresponding command from a control unit 15 (not shown in detail). As a result, the compression spring 7 closes the exhaust gas recirculation valve 40 by the valve body 11 being pressed onto its valve seat 12 . The resultant zero point measured value U₀ 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 differences. 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 supply and UA1 to UA3 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. moved by lifting from below. The adjustment position HM is preferably in the middle between the maximum opening position H max. and the closed position h₀ (end position); this ensures the highest relative measuring 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 maxima len 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 axially deformed in its cover region E by pressing or pulling, while the actuating element 30 is fixed to its curling edge 9 . In this way, the axial length tolerances of the individual parts are compensated for 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 bull measured value UAM is determined as the electrical mean of the encoder for all copies of the same type of device for adjustment be. 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 labeled UA '-. The intersection of the mirror image with the usual characteristic lies in the electrical center of the position sensor, which in the case of a reference voltage U _Ref for the center signal (adjustment measured value UAM) is equal to 0.5 U _Ref . The adjustment, ie in the case of FIG. 1, the permanent deformation of the housing 13 of the control 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. External or absolutely precise voltmeters are not required for this. In this way, the characteristic curves 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 U₀, both the zero point as well as the slope of the characteristic curve each individual path encoder. Compared to the known So there is no further storage space and neither further absolute measured value acquisition when commissioning the pre direction required.

Advantageously, the control device 15 with a start routine of the zero-point measured value U₀₁, as the initial value of the corresponding encoder sensor, is determined and stored after it has been adjusted. In addition, the difference between the calibration measured value UAM and the zero point measured value U₀₁ can be stored as an instance constant. To determine the position, the control unit 15 calculates the stroke h from the actual electrical measured values UA as follows:

The procedure according to the invention makes it easy Most 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 sensors can be replaced individually, without the Ex scatter of these parts the accuracy of the measurement result it suffers.

Claims (5)

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 (h₀) when it is put into operation and the electrical zero point measurement value (U₀) 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 (U₀) 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 (h₀) 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 (U₀) is divided by the difference between the adjustment measured value (UAM) and the zero point measured value (U₀).

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