Abstract:
The invention relates to a method for the contactless detection of the position of a butterfly-valve shaft of a butterfly valve connecting piece, the butterfly-valve shaft being driven by an electric actuator and having a magnet at one end, which is aligned in a contactless manner with a sensor that is located on a cover. An aim of the invention is to reliably guarantee the detection of the position of the butterfly-valve shaft, even over particularly long periods of time using a contactless position detection device. To achieve this, the sensor has a first and a second magnetoresistive sensor element, an approximately sinusoidal signal being generated in the first sensor element and an approximately cosinusodial signal being generated in the second sensor element by means of the magnet, during the rotation of the butterfly-valve shaft. According to the method, an approximately arc tangential signal is generated in the butterfly-valve connecting signal. The control signal is fed to the actuator that is located in the butterfly-valve connecting piece, to adjust the position of the butterfly-valve shaft.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    The present application is a continuation of international application PCT/DE02/02129, filed Jun. 11, 2002, and which designated the United States, and further claims priority to German reference 10133631.4, filed Jul. 11, 2001, the both of which are herein incorporated by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    The invention relates to a method for the contactless detection of the position of a butterfly valve shaft of a butterfly valve connecting piece, the butterfly valve connecting piece having a housing which can be closed off by a lid, and a throttle orifice which is arranged in the housing, for a butterfly valve which is arranged on the butterfly valve shaft, the butterfly valve shaft being capable of being driven by an electric actuator drive and having, at one of its ends, a magnet which is arranged in contactless alignment with a sensor which is arranged on the lid. It also relates to a butterfly valve connecting piece having a housing which can be closed off by a lid, and having a throttle orifice which is arranged in the housing, for a butterfly valve which is arranged on a butterfly valve shaft, the butterfly valve shaft being capable of being driven by an electric actuator drive and having, at one of its ends, a magnet which is arranged in contactless alignment with a sensor which is arranged on the lid.  
           [0003]    Butterfly valve connection pieces are generally used to control the quantity of fresh gas in a motor vehicle. Butterfly valve connecting pieces comprise a housing with a throttle orifice and a throttle element which is arranged in the throttle orifice. The throttle element generally comprises a butterfly valve which is arranged on a butterfly valve shaft and which is arranged so as to be capable of pivoting in the housing of the butterfly valve connecting piece. The butterfly valve assumes a specific position in the throttle orifice to permit a specific quantity of fresh gas to pass through. For this purpose, the butterfly valve shaft can be actuated mechanically or electromechanically.  
           [0004]    When the butterfly valve shaft is actuated electromechanically, the butterfly valve connecting piece normally has a position detection device which can be used to detect the current position of the butterfly valve shaft. Depending on the respective current position of the butterfly valve shaft, a signal, with which the butterfly valve shaft can be actuated using the actuator drive arranged in the butterfly valve connecting piece, is then generated either inside or outside the butterfly valve connecting piece.  
           [0005]    With respect to these position detection devices, a distinction is made between those in which contact with the butterfly valve shaft is at least indirectly necessary in order to detect the respective current position of the butterfly valve shaft, and on the other hand contactless position detection devices. A position detection sensor which is not contactless is a potentiometer in which a sliding contact which is coupled to the rotary movement of the butterfly valve shaft moves back a certain distance along a contact surface when there is a rotary movement of the butterfly valve shaft, the distance by which the sliding contact moves back being a measure of the rotary movement of the butterfly valve shaft. Such potentiometers are subject to a certain degree of wear which is decisively determined by the mechanical abrasion between the sliding contact and the contact path.  
           [0006]    In order to reliably avoid mechanical wear of position detection devices which are not contactless, butterfly valve connecting pieces have been developed in which the detection of the rotary movement of the butterfly valve shaft can be carried out in a contactless fashion. An example of such a contactless sensor is a Hall sensor which is positioned in alignment with a ring magnet which is arranged on the butterfly valve shaft. This Hall sensor supplies a signal which is proportional to the magnetic induction B which is generated by the magnetic field of the ring magnet. The ring magnet generally comprises an outer shielding ring, and, in the interior, two flux permeable parts which are arranged approximately in parallel. The Hall sensor is then located in the gap between the two flux permeable parts. This principle is well protected against magnetic interference fields as they are kept away from the Hall sensor by the outer shielding ring. The linear, usable measuring range is however restricted to approximately two times 75° in the case of this principle. For this reason, the magnetic zero point cannot be positioned in the mechanical idling stop (butterfly valve closes the throttle orifice virtually completely) in order to detect the typical butterfly valve working range, and would therefore be outside the idling position of the butterfly valve. However, as the measuring precision is highest at the magnetic zero point and decreases with increasing distance from the magnetic zero point, the measuring precision in the idling range of the butterfly valve would then be smaller than in a range which is positioned between the idling range and the full load range. This does not correspond to the customary precision requirements made of a contactless position detection device for a butterfly valve shaft of a butterfly valve connecting piece in which the measuring precision is to be highest during idling.  
           [0007]    Alternatively, the Hall sensor can project vertically into a parallel field which is formed between two magnet squares connected by means of a yoke, the magnet squares being permanently connected to the butterfly valve shaft. This principle is known from JP 8 068 606 A. The necessary signal amplification is carried out here in evaluation electronics which are connected to the Hall sensor via a punched grill. The electrical interface with the outside is also produced here by means of a punched grill or else lead frame which is formed into plug contacts at its ends. According to this principle, linearization is dispensed with in an angular range of approximately +/−45° around the zero crossover, which involves concessions in terms of linearity. Given customary working angles of less than 90°, it is theoretically possible to detect the butterfly valve position if the zero crossover is positioned in the center of the measurement range. However, the idling range would then be located in a measurement range in which the linearity error rises excessively because the precision of a Hall sensor is actually highest around the zero crossover of the induction. The maximum errors would occur in the case of maximum actuation in the region of +/−45°, that is to say full load and idling, as temperature drift and aging effects would then be felt. On the other hand, the measurement precision would be highest in the intermediate range. However, a position detection device which is provided for a butterfly valve connecting piece should be particularly high precisely with small angles of aperture of the butterfly valve, and thus particularly small rotary movements of the butterfly valve shaft. For this reason, this application is not particularly well suited for a position detection device of a butterfly valve shaft. In addition, the precision levels which are usually required cannot normally be achieved with this last-mentioned principle, even with particularly long operating times. It also proves disadvantageous that the open sides of the approximately U-shaped yoke are open to magnetic interference fields, and there is thus the risk of the sensor signal being falsified from the outside.  
           [0008]    As an alternative to a Hall sensor it is possible to use a magnetoresistive sensor, referred to below as MR sensor, in a contactless position detection device for detecting a rotary movement of a butterfly valve shaft. The MR sensor requires a field which turns in the plane which is formed by the sensor structure. For this it is necessary for the sensor element to be arranged perpendicularly with respect to the shaft, and thus not in a plane parallel to the axis of rotation of the shaft. As the output characteristic curve of MR sensors is periodic at 180°, the linear usable angular range is restricted to approximately 45°. For this reason, an MR sensor also does not usually have the angular range of approximately 90° which is necessary to detect a rotary movement of the butterfly valve shaft.  
         SUMMARY OF THE INVENTION  
         [0009]    The invention is therefore based on the object of specifying a method of the abovementioned type with which the position of the butterfly valve shaft of the butterfly valve connecting piece can be reliably detected in a detection range of approximately 90° by means of a contactless position detection device even over relatively long time periods. In addition, a device which is suitable for the method is to be specified.  
           [0010]    This object is achieved according to the invention in that the sensor has a first magnetoresistive sensor element and a second magnetoresistive sensor element, an approximately sinusoidal signal being generated in the first magnetoresistive sensor element and an approximately cosinusoidal signal being generated in the second magnetoresistive sensor element by means of the magnet when there is a rotary movement of the butterfly valve shaft, the first approximately sinusoidal signal and the second approximately cosinusoidal signal being fed to evaluation electronics which are arranged in the sensor, an approximately arctan-shaped signal being generated in the evaluation electronics from the approximately sinusoidal signal of the first magnetoresistive sensor element and the approximately cosinusoidal signal of the second magnetoresistive sensor element, the approximately arctan-shaped signal being fed to a control unit arranged outside the housing, a control signal being generated as a function of the approximately arctan-shaped signal in the control unit, and the control signal being fed to the actuator drive, arranged in the butterfly valve connecting piece, in order to adjust the butterfly valve shaft.  
           [0011]    The invention is based here on the idea that a method which particularly reliably ensures detection of a rotary movement of a butterfly valve shaft of approximately 90°, even over particularly long time periods, should detect the respective current position of the butterfly valve shaft in a contactless fashion. This is possible by means of a sensor which comprises a magnetoresistive sensor element. However, this magnetoresistive sensor element does not have the necessary precision when detecting the position of the butterfly valve shaft. The precision of the detection can be increased by virtue of the fact that, instead of a single magnetoresistive sensor element, a second magnetoresistive sensor element is arranged in relation to the first magnetoresistive sensor element. If these two sensor elements then output approximately the same signal but with a phase shift, the current position of the butterfly valve shaft can be detected particularly precisely using the phase shift which can be determined comparatively precisely. For this purpose, a first and a second magnetoresistive sensor element are positioned in relation to a magnet which is arranged on the butterfly valve shaft, an approximately arctan-shaped signal, which characterizes the position of the butterfly valve shaft with sufficient precision, being capable of being generated from the signal of the first magnetoresistive sensor element and from the signal of the second magnetoresistive sensor element. The approximately arctan-shaped signal is independent of temperature here, whereas the amplitudes of the signals of the first magnetoresistive sensor element and of the second magnetoresistive sensor element are temperature-dependent.  
           [0012]    The scaling (amplification, offset) of the sensor by means of an additional pin of the evaluation electronics is advantageously performed using a serial protocol, data for setting the characteristic curve being stored in a nonvolatile memory. This reduces the number of electronic components to a single one, a printed circuit board not being absolutely necessary.  
           [0013]    The signal of the first magnetoresistive sensor element is advantageously subjected to plausibility checking with the signal of the second magnetoresistive sensor element. If a predefined plausibility condition is infringed, a signal is output which is recognizably outside the customary working range. As a result, a redundant embodiment of a first and second sensor, which is otherwise customary for safety reasons, can be dispensed with, making the method particularly easy to handle.  
           [0014]    The object is achieved according to the invention with respect to the butterfly valve connecting piece by virtue of the fact that the magnet is of approximately ring-shaped design, and the sensor has a first magnetoresistive sensor element and a second magnetoresistive sensor element so that an approximately sinusoidal signal is generated in the first magnetoresistive sensor element and an approximately cosinusoidal signal is generated in the second magnetoresistive sensor element by means of the magnet when there is a rotary movement of the butterfly valve shaft, and that the two sensor elements for generating an approximately arctan-shaped signal are connected to evaluation electronics, and that the evaluation electronics are connected to a control unit arranged outside the housing, in order to generate a control signal for the actuator drive.  
           [0015]    The two magnetoresistive sensor elements give rise to a high degree of precision when detecting the position of the butterfly valve shaft. However, if these two sensor elements output approximately the same signal but with a phase shift, the current position of the butterfly valve shaft can be detected particularly precisely using the phase shift which can be determined comparatively precisely. By means of the two magnetoresistive sensor elements it is possible to produce two characteristic curves which, as long as the characteristic curves are phase shifted, can be used according to the method described above to detect the rotary movement of the butterfly valve shaft particularly precisely.  
           [0016]    It is advantageous if the magnet has diametrical magnetization. This results in a more homogenous field, as a result of which relatively large degrees of eccentricity between the sensor head and the magnet axis are acceptable without this leading to an unacceptable linearity error. As a result, the method mentioned above can be carried out particularly reliably even when there are structurally unavoidable imprecisions in the positioning between the magnet and the sensor.  
           [0017]    Alternatively, the magnet comprises a first ring part segment and a second ring part segment, with both the first ring part segment and the second ring part segment being radially magnetized. The radial magnetization results in a less homogenous field in comparison with diametrical magnetization, the field lines of the magnetic field being focused in the center of the magnet. As a result, particularly high fields can be produced by means of radial magnetization of the magnet, which makes the position detection device particularly immune to interference fields.  
           [0018]    In both embodiments, the sensor advantageously projects axially and centrally into the magnet. If the sensor projects axially and centrally into the magnet, the amplitude of the useful field is then particularly large in this position and the shielding effect against external interference fields is also particularly well utilized. As a result, the angular position of the shaft can be determined in a fault-free fashion even in the immediate vicinity of the electromagnetic drive.  
           [0019]    The sensor advantageously comprises a first housing and a second housing, the first magnetoresistive sensor element and the second magnetoresistive sensor element being arranged in the first housing, and evaluation electronics being arranged in the second housing, the first housing being arranged approximately perpendicularly to the butterfly valve shaft, and the second housing being arranged approximately parallel to the butterfly valve shaft. As a result, the installation space which is necessary for the sensor has particularly small dimensions.  
           [0020]    The evaluation electronics for setting the characteristic curve using a serial protocol advantageously comprise a pin. As a result, it is possible to dispense with a multiplicity of electrical components which would otherwise be necessary as an alternative to setting the characteristic curve.  
           [0021]    The sensor is advantageously surrounded virtually completely by a sleeve made of plastic. If it is constructed in this way, the sensor forms a premolding which is encapsulated with plastic by means of injection molding when the lid is manufactured, as a result of which the lid of the housing of the butterfly valve connecting piece is fabricated.  
           [0022]    The lid of the housing is advantageously made of plastic, the sensor being at least partially enclosed by the plastic of the lid. As a result of the integration of the sensor into the lid, the sensor can be integrated into the lid at a strictly predefined location. At the same time, the mounting step during which the sensor has to be arranged in the lid and adjusted in relation to the magnet is dispensed with.  
           [0023]    The advantages which are achieved with the invention comprise, in particular, the fact that the method for detecting the position of the butterfly valve shaft operates in a contactless fashion and at the same time a degree of precision which is sufficient for detecting the position of the butterfly valve shaft is reliably ensured even over particularly long time periods. In this process, the signals of the first sensor element and of the second sensor element are detected simultaneously and also used for a plausibility checking means which transmits a corresponding signal to the control electronics in the case of a fault. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0024]    An exemplary embodiment of the invention will be explained in more detail with reference to a drawing, in which:  
         [0025]    [0025]FIG. 1 is a schematic view of a butterfly valve connecting piece having a gearbox and an actuator drive,  
         [0026]    [0026]FIG. 2 is a schematic view of the lid of the butterfly valve connecting piece according to FIG. 1,  
         [0027]    [0027]FIG. 3 is a schematic view of a butterfly valve connecting piece having a direct drive, and  
         [0028]    [0028]FIG. 4 is a schematic view of the lid of the butterfly valve connecting piece according to FIG. 3.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0029]    Corresponding parts are provided with the same reference symbols in all the figures.  
         [0030]    The butterfly valve connecting piece  10  according to FIG. 1 has the purpose of supplying an air or fuel/air mixture to an actuator (not illustrated), for example an injection device of a motor vehicle (also not illustrated), the quantity of fresh gas which is to be fed to the actuator being capable of being controlled by means of the butterfly valve connecting piece  10 . For this purpose, the butterfly valve connecting piece  10  has a housing  12  which is fabricated from metal  14  which is constructed from aluminum in this exemplary embodiment. Alternatively, the housing  12  can however also be manufactured from plastic using an injection molding method. The housing  12  comprises a continuous throttle orifice  16 . Air or a fuel/air mixture can be fed to the actuator (not illustrated) via the throttle orifice  16 .  
         [0031]    In order to set the volume of fresh gas which is to be fed to the actuator, a butterfly valve  20  is arranged on a butterfly valve shaft  18  with an axis of rotation  19 . The butterfly valve  20  is fabricated from a material  22  which is constructed as metal  24  in this exemplary embodiment. The metal  24  is in turn aluminum. Alternatively, the butterfly valve can however also be fabricated entirely or partially from plastic. A rotation of the butterfly valve shaft  18  simultaneously brings about pivoting of the butterfly valve  20  which is arranged on the butterfly valve shaft  18 , as a result of which the active cross section of the throttle orifice  16  is increased or decreased. The throughflow rate of the air or fuel/air mixture through the throttle orifice  16  of the butterfly valve connecting piece  10  is regulated by increasing or decreasing the active cross section of the throttle orifice  16  through the butterfly valve  20 .  
         [0032]    The butterfly valve shaft  18  can be connected to a pulley (not illustrated in more detail) which is connected in turn via a Bowden cable to a setting device for a power request. The setting device can be embodied here as an accelerator pedal of a motor vehicle so that activation of this setting device by the driver of the motor vehicle the butterfly valve  20  can be moved from a position of minimum opening, in particular a closed position, into a position of maximum opening, in particular an open position, in order in this way to control the power output of the motor vehicle.  
         [0033]    The butterfly valve shaft  18  (shown in FIG. 1) of the butterfly valve connecting piece  10  is in contrast capable of being set either in a subrange by an actuator drive and otherwise by means of the accelerator pedal, or else the butterfly valve  20  can be set by an actuator drive over the entire adjustment range. In these so-called E-gas or drive-by-wire systems, the mechanical power control, for example the depression of an accelerator pedal, is converted into an electrical signal. This signal is in turn fed to a control unit which generates an actuation signal for the actuator drive. In these systems there is no mechanical coupling between the accelerator pedal and the butterfly valve  20  during normal operation.  
         [0034]    In order to adjust the butterfly valve shaft  18 , and thus the butterfly valve  20 , the butterfly valve connecting piece  10  therefore has a drive housing  26 . The drive housing  26  is embodied in one piece with the housing  12  of the butterfly valve connecting piece  10 , but the housing  12  of the butterfly valve connecting piece  10  and the drive housing  26  may also be embodied in two pieces as separate single-piece components.  
         [0035]    An actuator drive  30  which can be actuated via a control unit  28  arranged outside the housing  12  and is embodied as an electric motor is arranged in the drive housing  26 . The actuator drive  30  is suitably electrically connected to the control unit  28 , which connection is not illustrated in more detail in the drawing. The control unit  28  transmits, to the actuator drive  30  which is embodied as an electric motor, a control signal C by means of which the actuator drive  30  which is embodied as an electric motor adjusts the butterfly valve shaft  18  using a gearbox  31 . Here, the actual position of the butterfly valve shaft  18  is detected by means of a position detection device  32 .  
         [0036]    The position detection device  32  comprises a magnet  34  which is arranged at a first end  36  of the butterfly valve shaft  18 . The magnet  34  is diametrically magnetized and embodied in one piece as a ring  38 . A sensor  40  is arranged aligned with the axis of rotation  19  of the butterfly valve shaft  18 , in the center  39  of the ring  38 . The sensor  40  comprises a first housing  42  and a second housing  44 . The two housings  42  and  44  of the sensor  40  are encapsulated with plastic  46  using injection molding. The two housings  42  and  44  which are encapsulated using plastic  46  are in turn integrated into the lid  50 , also fabricated from plastic, of the butterfly valve connecting piece  10  by means of injection molding methods. In the first housing  42  of the sensor  40 , a first sensor element  52  and a second sensor element  54  are arranged. In addition, a temperature sensor  55  is arranged on the housing  42  of the sensor  40 . Evaluation electronics  56  are arranged in the second housing  44  of the sensor  40 . The first housing  42  of the sensor  40  projects in a particularly space-saving way here into the ring  38  of the magnet  34 . The second housing  44  of the sensor  40  which is permanently connected to the first housing  42  of the sensor  40  is arranged in the lid  50  of the housing  12  of the butterfly valve connecting piece  10 , bent through 90° in relation to the first housing  42  of the sensor  40  and at right angles with respect to the axis of rotation  19  of the butterfly valve shaft  18 .  
         [0037]    The butterfly valve shaft  18  is mounted in bearings  60  which are arranged on both sides of the throttle orifice  16  in the housing  12 . A spring system  62  with so-called restoring springs and/or emergency operation springs is accommodated between the one bearing  60  and the position detection device  32 . The restoring springs and/or emergency operation springs of the spring system  62  cause the butterfly valve shaft  18  to be prestressed in the closing direction with the result that the actuator drive  30  which is embodied as an electric motor operates counter to the force of the restoring springs and/or emergency operation springs. A so-called restoring spring and/or emergency operation spring of the spring system  62  has the effect that if the actuator drive  30  which is embodied as an electric motor fails, the butterfly valve  20  is moved into a defined position which is normally above the idling speed.  
         [0038]    Alternatively, or in addition, the butterfly valve shaft  18  can also protrude out of the housing  12  of the butterfly valve connecting piece  10  at the end  64  of the butterfly valve shaft  18  which faces away from the position detection device  32 . It is then possible to mount, for example, a pulley (not illustrated in the drawing) at the end of the butterfly valve shaft  18 , said pulley being connected to an accelerator pedal via a Bowden cable, which provides a mechanical means of predefining set point values. This mechanical coupling of the butterfly valve shaft  18  to the accelerator pedal (not illustrated in the drawing in more detail) can ensure that the butterfly valve connecting piece  10  operates in emergency situations, for example if the actuator drive fails.  
         [0039]    When the butterfly valve connecting piece  10  is operating, the butterfly valve shaft  18  is pivoted by means of the actuator drive  30  which is embodied as an electric motor. As a result, the butterfly valve  20  which is attached to the butterfly valve shaft  18  clears the throttle orifice to a greater or lesser extent, as a result of which the quantity of fresh gas which is to be fed to the internal combustion engine is to be controlled.  
         [0040]    [0040]FIG. 2 is a schematic detailed view of the lid  50  of the housing  12  of the butterfly valve connecting piece  10 . The sensor  40  which is surrounded by the plastic  46  is not represented raised from the inside in this plan view of the lid  50  as it protrudes out of the plane, facing the viewer. Electrical connections run from the sensor  40  to an electrical contact  66  which is arranged in the lid  50 . The sensor  40  can be connected via this contact  66  to the control unit  28  which is arranged outside the butterfly valve connecting piece  10 . At the same time, the sensor  40  can be supplied with electrical energy via the electrical contact  66 . The lid  50  also has centering aids  68  via which the lid can be positioned in relation to the housing  12  of the butterfly valve connecting piece  10 , and the sensor  40  can thus be positioned in relation to the magnet  34  arranged on the butterfly valve shaft  18 .  
         [0041]    The butterfly valve connecting piece  100  according to FIG. 3 can be used in a motor vehicle in the same way as the butterfly valve connecting piece  10  according to FIG. 1. The butterfly valve connecting piece  100  comprises a housing  112  in which a continuous throttle orifice  116  is arranged. The throttle orifice  116  has an approximately cylindrical cross section  117 . A butterfly valve  120  is arranged in the throttle orifice  116  on a butterfly valve shaft  118  which has an axis of rotation  119 .  
         [0042]    The butterfly valve shaft  118  can be directly adjusted by an electric actuator drive  130  which is arranged in a drive housing  126  and can be actuated via a control unit  128  which is arranged outside the housing  112 . As a result, the butterfly valve connecting piece  100  according to FIG. 3 differs from the butterfly valve connecting piece  10  according to FIG. 1 in which the butterfly valve shaft can be driven indirectly by the actuator drive  30  via a gearbox  31 . The actuator drive  130  is embodied here as a commutated electric motor.  
         [0043]    The rotary movement of the butterfly valve shaft  118  of the butterfly valve connecting piece  100  can also be detected by a position detection device  132 . The position detection device  132  comprises a magnet  134  which is arranged at a first end  136  of the butterfly valve shaft  118 . A sensor  140  is arranged in the center  139  of the magnet  134  aligned with the axis of rotation  119  of the butterfly valve shaft  118 . The sensor  140  comprises a first housing  142  and a second housing  144 . The sensor  140  is encased virtually completely by plastic  146 . The first housing  142  of the sensor  40  is arranged at a right angle with respect to the second housing  144  of the sensor  40 . The sensor  140  which is encased with plastic  146  has been integrated as a premolding into the lid  150  of the butterfly valve connecting piece  100  when said lid  150  was manufactured using an injection molding method.  
         [0044]    The sensor  140  comprises, in its first housing  142 , a first magnetoresistive sensor element  152 , a second magnetoresistive sensor element  154  and a temperature sensor  155 . Evaluation electronics  156  are arranged in the second housing  144  of the sensor  140 . The evaluation electronics  156  comprise a pin  158  via which the evaluation electronics  156  can be set in order to set the characteristic curve using a serial protocol. The pin  158  does not end in the electrical contact  166  which is embodied as an equipment plug, but instead contact is made only in the fabrication process, and is sealed off after that.  
         [0045]    The butterfly valve shaft  180  is mounted in bearings  160 . The butterfly valve connecting piece  100  also has a spring system  162  which is arranged at the end  164  of the butterfly valve shaft  118  which is applied to the position detection device  132 . This spring system  162  can be used to position the butterfly valve shaft  118  into an emergency operating position if the actuator drive  130  fails.  
         [0046]    The lid  150  of the butterfly valve connecting piece  100  is illustrated in detail in FIG. 4. The lid  150  which is fabricated from plastic  148  comprises, virtually completely, the both the first housing  142  and the second housing  144  of the sensor  140 . The second housing  144  of the sensor  140  projects out of the plane of the drawing in FIG. 4, which is not illustrated as raised owing to the plan view of the lid. The pins of the evaluation electronics  156  of the second housing  144  of the sensor  140 , with which the evaluation electronics  156  can be connected to a control unit (not illustrated in more detail in the drawing), can be clearly made out.  
         [0047]    The configuration of the magnet  34  of the butterfly valve connecting piece  10  is shown by FIG. 5 in detail. It is possible to clearly see the diametrical field lines of the magnet  34 , embodied as a ring  38 , of the butterfly valve connecting piece  10 . The ring  38  is surrounded here by a shielding ring  74 . The field lines wander here approximately horizontally through the center  39  of the magnet  34  which is embodied as a ring  38 . The center  39  is free of magnetic material. The sensor  40  can be positioned in the region of the center  39 .  
         [0048]    In contrast to this, the magnet  134  of the butterfly valve connecting piece  100  is magnetized radially, which is shown in FIG. 6. For this purpose, the magnet  134  has a first ring part segment  170  and a second ring part segment  172 . The field lines are focused significantly more strongly in the center in the case of the magnet  134  with radial magnetization than in the case of the magnet  34  with diametrical magnetization of the butterfly valve connecting piece  10 . The magnet  134  has a shielding ring  174 , in the same way as the magnet  34 . No magnetic material is again arranged in the center  139  of the magnet  134 . The sensor  140  can be positioned in this region.  
         [0049]    Both the position detection device  32  of the butterfly valve connecting piece  10  and the position detection device  132  of the butterfly valve connecting piece  100  can be operated according to the same method, which is illustrated schematically in FIG. 7.  
         [0050]    In this method, the first sensor element  52  or  152  and the second sensor element  54  or  154  are offset with respect to one another by a quarter period. As a result, when the butterfly valve connecting piece  10  or  100  operates, two signals S 1  and S 2  can be detected. The first signal S 1  is approximately sinusoidal and is supplied by the first sensor element  52  or  152 . The second signal S 2  is approximately cosinusoidal and is supplied by the second sensor element  54  or  154 . In addition, a temperature signal T M  is continuously supplied via the temperature sensor  55  or  155 . The two signals S 1  and S 2  as well as the temperature signal T M  pass via electrical connecting means (not illustrated in more detail) into the second housing  44  or  144  of the sensor  40  or  140 . They are fed to the evaluation electronics  56  or  156  in the housing  44  or  144 .  
         [0051]    The evaluation electronics  56  or  156  digitizes, by means of a digitization device  200 , the first signal S 1 , the second signal S 2  and the temperature signal T M . Here, the digital signal Ds 1 , is produced from the first signal S 1 , the digital signal D s2  is produced from the second signal S 2 , and the digital signal D TM  is produced from the temperature signal T M . The three digital signals D S1 , D S2  and D TM  are then fed to a computing unit  202  which is also arranged in the evaluation electronics  56  or  156 . The computing unit  202  comprises a memory and a comparator unit, neither of which are illustrated in more detail in the drawing.  
         [0052]    In the computing unit  202 , an approximately arctan-shaped signal P is generated as a position signal from the first digital signal D S1  and the second digital signal D S2 . The position signal P is compared in the comparator unit with data from the memory. The data of the memory  206  comprises both correction values (bridge offsets) of the sensor elements  52 ,  152  and  54 ,  154  which are necessary for correctly calculating the angular position of the butterfly valve shaft, as well as characteristic curve parameters for the outward characteristic curve, for example gradient and angle offset. From this comparison between the approximately arctan-shaped signal P and the data of the memory  206  it is possible to determine the current position of the butterfly valve shaft  18  or  118 . The current position of the butterfly valve shaft  18  or  118  can be fed as an output signal A to the control unit  28  or  128 . The control unit  28  or  128  outputs, as a function of the output signal A of the evaluation electronics  56  or  156 , a control signal C which is transmitted to the actuator drive  30  or  130  and by means of which the actuator drive  30  or  130  can be actuated as a function of the currently detected position of the butterfly valve shaft  18  or  118 .  
         [0053]    When the method is carried out, a plausibility check of the signals S 1  and S 2  of the first sensor element  52  or  152  and of the second sensor element  54  or  154  takes place cyclically, that is to say at regular intervals in the evaluation electronics  56 ,  156 , taking into account the measured temperature signal T M . The two signals S 1  and S 2  of the sensor elements  52  or  152  and  54  or  154  follow approximately the functions here:  
           S   1   =S   1max *sin(2*Φ)*[1+α 1 *( T   M1   −T   R )  
         and  
           S   2   =S   2max *cos(2*Φ)*(1+α 2 *( T   M2   −T   R )].                                                        S 1max  and S 2max     are amplitudes of the signals in               the unit M v ,           φ   is the mechanical angle through               which the butterfly valve shaft               18, 118 has rotated,           α 1 , α 2     are temperature coefficients in           1/K,   the unit           T R     Reference temperature                        
         [0054]    The amplitudes temperature response of the signals S 1  and S 2  is taken into account here by the difference between the measured temperature and the reference temperature. The reference temperature is usually room temperature.  
         [0055]    As both sensor elements  52 ,  54  and  152 ,  154  are constructed on the same substrate, a single temperature sensor can be used for the temperature measurement, said sensor supplying the measured temperature T M . Correspondingly, the temperature coefficients can also be equated:  
         T M1 =T M2 =T m ,  
         α 1 =α 2 =α.  
         [0056]    These equations characterize the signals S 1  and S 2 . In the case of fault-free function the following must apply:  
         sin 2 (2Φ)+cos 2 (2Φ)=1.  
         [0057]    This condition is additionally integrated cyclically in the computing unit  202 . When this condition is infringed, a signal F, which lies recognizably outside the normal working range, is output. This signal F can also be fed, in a way which is not illustrated in more detail, to the control unit which is also not illustrated in more detail in the drawing. This safety function makes it possible to dispense with a redundant design, as a result of which the position detection device  32  or  132  has a particularly simple design. In addition, for compatibility reasons and in order to be able to detect errors in the transmission link, two complementary characteristic curves are output. As a result of the temperature information being taken into account, the plausibility check reliably takes place in a temperature range of, for example, −40° to +140° C.  
         [0058]    The method is characterized by the fact that two signals S 1  and S 2  which are phase shifted with respect to one another can be generated by means of a magnetoresistive sensor  40  or  140  which has a first magnetoresistive sensor element  152  or  52  and a second magnetoresistive sensor element  54  or  154 . The current position of the butterfly valve shaft  18  or  118  can be detected with sufficient precision by means of these two signals S 1  and S 2 . At the same time, it is particularly reliably ensured that the device does not have any mechanical wear phenomena even when the method operates for a particularly long time.