Abstract:
A method for determining information regarding a final position of an element of a gear, in particular a drive gear wheel, the information regarding the final position representing a stop position of a throttle valve at a mechanical stop, includes moving the element from a starting position in the direction of the final position, until the element comes to a standstill despite a specified supply of drive energy; determining information regarding the position of the element at standstill despite the supply of drive energy; and determining the information regarding the final position in that information of a correction distance is applied to the information regarding the position of the element, in particular subtracted, counter to the direction of the final position at standstill despite the supply of drive energy.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    The present application claims priority to Application No. DE 10 2011 083 590.3, filed in the Federal Republic of Germany on Sep. 28, 2011, which is expressly incorporated herein in its entirety by reference thereto. 
       FIELD OF INVENTION 
       [0002]    The present invention relates to a method for determining information regarding a final position of an element of a gear, a device for determining information regarding a final position of an element of a gear, and a drive having the device. 
       BACKGROUND INFORMATION 
       [0003]    The freedom of movement of a throttle valve is delimited by mechanical stops. These mechanical stops must be known in order to regulate the position of the throttle valve. 
         [0004]    Usually, the mechanical stops are learned in that the positional control moves the throttle valve against the mechanical stops until the position of the throttle valve is no longer able to comply with the positional setpoint value, and the actuating signal from the control, and thus the drive energy for moving the throttle valve, becomes increasingly greater. If the drive energy exceeds a particular threshold value, the current positional setpoint value is stored as the position of the mechanical stop and utilized to delimit the positional control. 
         [0005]    However, it has become apparent that the position of the throttle valve is set imprecisely using the known stops and that, for example, the throttle valve supplies an incorrect air mass to an internal combustion engine. 
       SUMMARY 
       [0006]    A method for determining information regarding a final position of an element of a gear is provided, as well as a device and a drive. 
         [0007]    According to one exemplary aspect of the present invention, a method for determining information regarding a final position of an element of a gear, especially a drive gear wheel, the information regarding the final position representing a stop position of a throttle valve at a mechanical stop, comprises the following steps:
       moving the element from a starting position in the direction of the final position, until the element comes to a standstill despite a specified supply of drive energy;   determining information regarding the position of the element at standstill despite the supply of drive energy; and   determining the information regarding the final position in that information about a correction distance is applied to, especially subtracted from, the information regarding the position of the element, counter to the direction of the final position, at standstill despite the supply of drive energy.       
 
         [0011]    The method is based on the notion that the gear for driving the throttle valve does not have an ideal rigidity. Furthermore, the present invention recognizes that the position sensors of the throttle valve are frequently situated on an element of the gear, such as the drive gear wheel. Therefore, if the throttle valve is moved in the direction of the mechanical stops, the stopping point for the element of the gear is able to be determined only when the element of the gear is no longer rotating. At this time, however, the throttle valve is already pressing against the mechanical stop with high force and, without the mechanical stop, would be positioned behind the stop, by a particular excursion differential. If this stopping point for the element of the gear thus defined is used as the basis for the positional control of the throttle valve, the throttle valve is always placed next to its actual position, by the distance of the excursion differential, which leads to the aforementioned inaccurate positioning. In the present invention the determined stopping point of the gear is therefore corrected, in that it is moved away again from the mechanical stop by a correction distance. This makes the positional control of the throttle valve more precise. 
         [0012]    According to another exemplary aspect of the present invention, a device for determining information regarding a final position of an element of a gear, especially a drive gear wheel, the information regarding the final position representing a stop position of a throttle valve at a mechanical stop, comprises the following features:
       a drive device for moving the element from a starting position in the direction of the final position, until the element comes to a standstill despite a specified supply of drive energy;   a measuring device for determining information regarding the position of the element during standstill despite the supply of drive energy; and   the measuring device being provided to determine the information regarding the final position, in that information regarding a correction distance is applied to, especially subtracted from, the information regarding the position of the element, counter to the direction of the final position, during standstill despite the supply of drive energy.       
 
         [0016]    The measuring device may be equipped with a comparison unit which is suitable to determine standstill, to ascertain the drive energy, and to output an event indicating standstill when the drive energy has reached a threshold value or exceeds it. The threshold value for the drive energy ensures that the standstill of the gear is measured, but without running the risk that the connection between the element of the gear and the throttle valve will fracture because of an excessive supply of drive energy. 
         [0017]    The measuring device may be suitable for subtracting the indicated correction distance so as to reduce the threshold value, and the drive unit may be suitable for returning the gear to the starting position, until the drive energy reaches the reduced threshold value or drops below it. This makes it possible to read out the corrected limit value again, directly at the position sensor of the positional control circuit. 
         [0018]    In one alternative development, the measuring device may be provided to determine the information regarding the final position, based on the information regarding the position after the drive energy has reached the threshold value or has exceeded it, or after it has reached the reduced threshold value or has dropped below it. In this way the sensor of the positional control circuit, which feeds back the controlled variable, is able to be used for determining and storing the final position, so that redundancies in the system are avoided. 
         [0019]    The measuring device may be suitable for storing the information regarding the position of the gear prior to the movement back to the starting position, and for performing a plausibility check of the determined information regarding the final position based on a difference between the determined information regarding the final position and the stored information regarding the position. Errors that may occur, for instance, in the drive-energy transmission between a drive energy source, e.g., a motor, and the element of the gear are able to be discovered in this way. 
         [0020]    The measuring device may be suitable for the plausibility check to compare the difference to a difference stored in the measuring device. This difference may be predefined, so that the plausibilization is able to be performed in a simple manner with the aid of the comparison unit, which is already utilized for the purpose of determining the standstill of the drive gear wheel. 
         [0021]    The stored difference may represent the movement of the element in a characteristic curve over the reduced drive energy, the characteristic curve contrasting the drive energy with the information regarding the position of the element when the throttle valve is at standstill. Since the absolute values of the drive energy prior to the correction and following the correction are known, a value for an expected difference is easily able to be found in the characteristic curve, which means that, for the plausibilization, the measured difference simply needs to be compared to the expected difference. 
         [0022]    According to another exemplary aspect of the present invention, a drive for a throttle valve includes:
       a motor;   a gear, moved by the motor, for moving the throttle valve; and   an indicated device for determining information regarding the final position of an element of the gear when the throttle valve strikes a mechanical stop.       
 
         [0026]    The drive may have a butterfly valve shaft, which is connected to the gear, and on which the throttle valve may be mounted. This butterfly valve shaft distorts after it strikes the mechanical stop and is the main cause of the faulty determination of the information regarding the final position. As a result, the present invention may be used to especially good effect in such a device. 
         [0027]    The measuring device is able to be used for determining the information regarding the correction distance, for measuring the indicated position of the element at standstill despite the supply of drive energy, and for rotating the element counter to the direction of the final position until the butterfly valve shaft is no longer distorted, so that the precise information regarding the final position of the element for the stop position of the throttle valve is able to be determined under ideal conditions, without deviations. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    Exemplary embodiments of the present invention are explained in greater detail in the following text with reference to the accompanying drawings. 
           [0029]      FIG. 1  shows a schematic illustration of a throttle valve restricted in its movement. 
           [0030]      FIG. 2  shows a schematic view of a drive having a throttle valve. 
           [0031]      FIG. 3  shows a schematic view of a control circuit for positioning a throttle valve using a device according to a first exemplary embodiment of the present invention. 
           [0032]      FIG. 4  shows a method according to a first exemplary embodiment of the present invention. 
           [0033]      FIG. 5  shows a method according to a second exemplary embodiment of the present invention. 
           [0034]      FIG. 6  shows a characteristic curve, in which the resulting position of a throttle valve having the drive from  FIG. 2  is shown over the drive energy. 
           [0035]      FIG. 7  shows a schematic view of a control circuit for positioning a throttle valve using a device according to a second exemplary embodiment of the present invention. 
           [0036]      FIG. 8  shows a method according to a third exemplary embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0037]    Reference is made to  FIG. 1 , which shows a throttle valve  1 . Throttle valve  1  is pivotably accommodated inside a throttle housing  2  and is able to be freely positioned within a positioning range  5  between a lower stop position  3  and an upper stop position  4 . At lower stop position  3 , the movement of throttle valve  1  is stopped by a first mechanical stop  6 , and at the upper stop position  4 , it is stopped by a second mechanical stop  7 . 
         [0038]    First mechanical stop  6  of lower stop position  3  usually defines a position of throttle valve  1  for an idling state of a vehicle. Second mechanical stop  7  of upper stop position  4  usually restricts a maximally requestable output of the vehicle, e.g., when a motorized bicycle is to be throttled for the driver for reasons of traffic safety, and it therefore defines the full throttle position of throttle valve  1 . 
         [0039]    Throttle valve  1  is driven via a drive pinion  8 . Drive pinion  8  transmits a torque to a drive gear wheel  9 , which is mounted on top of a butterfly valve shaft  10 . In this way throttle valve  1  is able to be pivoted back and forth between lower stop position  3  and upper stop position  4 . 
         [0040]    If throttle valve  1  is positioned with the aid of a control circuit, which is going to be described in the further text, it must, as a minimum, be provided with the information of the location of lower stop position  4 , since the control circuit determines a setpoint position of throttle valve  1  in relation to lower stop position  3 . If lower stop position  3  is incorrect, throttle valve  1  will be positioned at incorrect opening angles and supply an incorrect air quantity to an internal combustion engine, so that inaccurate outputs are called up. For example, this may affect other control circuits that intervene in the engine output of the vehicle, such as the electronic stability program or charge compensation, which is necessary for optimal fuel consumption. 
         [0041]    Lower and upper stop positions  3 ,  4  are usually determined in that the control circuit runs through the full positioning range  5  of throttle valve  1  and checks at which position no further torque is transmittable from drive gear wheel  9  to throttle valve  1 , and drive gear wheel  9  is no longer able to be rotated further. Throttle valve  1  is firmly resting against one of mechanical stops  6 ,  7  in that position. 
         [0042]    However, butterfly valve shaft  7  is not infinitely rigid and is distorted when drive gear wheel  9  positions throttle valve  1  against mechanical stops  6 ,  7 . Drive gear wheel  9  therefore continues to rotate when lower or upper stop position  3 ,  4  has been reached. Lower final position  11  or upper final position  12  of drive gear wheel  9 , starting from which drive gear wheel  9  is no longer rotating, therefore does not correspond to the actual lower or upper stop positions  3 ,  4 , respectively. The problems get worse when the force required to achieve stop positions  3 ,  4  increases due to contamination  13  at mechanical stops  6 ,  7 , and butterfly valve shaft  10  becomes more distorted because of the higher torque. 
         [0043]    In the present invention, lower final position  11  or upper final position  12  of drive gear wheel  9  is therefore recorded and a correction distance  14  is deducted therefrom in order to place lower final position  11  or upper final position  12  of the drive pinion at, respectively, the lower or upper stop positions  3 ,  4  of throttle valve  1 . 
         [0044]      FIG. 2  shows drive system  15  for driving throttle valve  1 . Elements in  FIG. 2  that are identical to elements in  FIG. 1  are denoted by the same reference numerals and not described again. 
         [0045]    In drive system  15 , the torques for throttle valve  1  are transmitted from drive pinion  8  to drive gear wheel  9 , via a gear  16 . A position sensor  17 ,  18  composed of two elements is situated on drive gear wheel  9 . First part  17  of position sensor  17 ,  18  is mounted on drive gear wheel  9 , while second part  18  of position sensor  17 ,  18  is disposed on a housing  119  of drive system  15 . 
         [0046]    In the following text, a potentiometer  17 ,  18  is to be considered for position sensor  17 ,  18 . In this case, first part  17  of position sensor  17 ,  18  may be a slider  17 , and second part  18  of position sensor  17 ,  18  may be a potentiometer track  18 , along which slider  17  is moving while throttle valve  1  is rotating. If a positive potential  19  is applied at slider  17 , which generates a current directed into potentiometer  17 ,  18 , and if a negative potential  20  is applied at potentiometer track  18 , which generates a current directed out of potentiometer  17 ,  18 , a measurable and variable potentiometer voltage  21  drops at potentiometer  17 ,  18 , which is illustrated in  FIG. 3 . As an alternative to potentiometer  17 ,  18 , it is also possible to use a Hall-effect sensor or an incremental sensor for measuring the position of drive gear wheel  9 . 
         [0047]    Lower and upper stop positions  3 ,  4  are determined in a processor  22 , which, similar to drive system  15 , is connected to a supply voltage  24  via a potential line  23  and connected to ground via a ground line  25 . 
         [0048]    Potentiometer voltage  21  indicates the position of drive gear wheel  9  to processor  22 . In the undistorted state of butterfly valve shaft  10 , the position of drive gear wheel  9  corresponds to the position of throttle valve  1 . This allows a check in processor  22  during closed-loop control as to whether throttle valve  1  has reached a predefined setpoint position. If necessary, a positive electrical potential  27  and a negative electrical potential  28  are applied at a motor  26  in order to rotate throttle valve  1  via drive pinion  8  mounted on top of a motor shaft  129  of motor  26 , until the setpoint position has been achieved. The arrows of potentials  27 ,  28  applied at motor  26  indicate the direction of the current produced by potentials  27 ,  28 . 
         [0049]    To measure the deformation of butterfly valve shaft  10 , a second position sensor  29  may be mounted on the side of butterfly valve shaft  10  situated opposite from position sensor  17 ,  18 , which then detects a position of butterfly valve shaft  10  on this side of butterfly valve shaft  10 . The use of second position sensor  29  is discussed in greater detail in  FIGS. 7 ,  8 . 
         [0050]      FIG. 3  shows a schematic view of a control circuit  30  for positioning throttle valve  10  with the aid of a device according to a first exemplary embodiment of the present invention. Elements in  FIG. 3  that are identical to elements in  FIGS. 1 and 2  are denoted by the same reference numerals and not described again. 
         [0051]    In  FIG. 3  the device is realized by a program running in processor  22  of  FIG. 2 , which digitally calculates lower and upper stop positions  3 ,  4 . As an alternative, however, the device may also be implemented as circuit, which determines lower and upper stop positions  3 ,  4  by analog signal conversions. 
         [0052]    Electrical potentials  27 ,  28  applied at motor  26  cause a current  31  through motor  26 , which outputs a torque  32  to drive pinion  8 . Drive pinion  8  moves drive gear wheel  9  via gear  16 , so that torque  32  generated by motor  26  is acting directly on drive gear wheel  9 . This causes drive gear wheel  9  to change its actual position  33 , which is detected by position sensors  17 ,  18  and fed back to processor  22  via potentiometer voltage  21 . 
         [0053]    In processor  22 , potentiometer voltage  21  is compared in a summation unit  34  to a setpoint voltage  35 , which corresponds to the setpoint position of throttle valve  1 , and a system deviation  36  is determined. 
         [0054]    System deviation  36  is output to a controller  37 , which uses it as the basis for calculating electrical potentials  27 ,  28  for motor  26  and applies them to motor  26 . Motor current  31  produced by electrical potentials  27 ,  28  is recorded by a current measuring device  38 , and its value  39  is output to a comparator  40 . 
         [0055]    Setpoint voltage  35  may be output from a control unit  41  and a measuring unit  42 . While control unit  41  is provided to supply setpoint voltage  35  during standard operation of throttle valve  1 , measuring unit  42  is provided to supply setpoint voltage  35  during an initialization phase in which stop positions  3 ,  4  are determined. During standard operation, control unit  41  is able to call up stop positions  3 ,  4  from a control memory  43 , these positions having previously been determined by measuring unit  42  during the initialization phase and stored in control memory  43 . A switch  45 , controlled by measuring unit  42  via an enable signal  44 , can be used to enable standard operation following the initialization phase. 
         [0056]    To determine stop positions  3 ,  4 , measuring unit  42  is able to record potentiometer voltage  21 . To determine stop positions  3 ,  4 , comparator  40  compares current value  39  of motor current  31  to a stop threshold value  46  and outputs a stop signal  47  if current value  39  of motor current  31  exceeds threshold value  46 . Stop threshold value  46  may be specified by measuring device  42 . Stop threshold value  46  defines a current value  39  for motor current  31 , at which drive gear wheel  9  is unable to change its position  33  despite torque  32  supplied by motor  26 . Stop threshold value  46  has been selected high enough so that throttle valve  1  is even able to compress and overcome contamination  13  at mechanical stops  6 ,  7 , and thus is able to rest directly against mechanical stops  6 ,  7 . 
         [0057]    The output of stop signal  47  from comparator  40  indicates that drive gear wheel  9  has attained its lower or upper final position  11 ,  12 , respectively. Measuring unit  42  is able to detect current potentiometer voltage  21  and correct it by a value that corresponds to correction distance  14 . Corrected potentiometer voltage  21  may finally be stored in control memory  43  as a measure of one of stop positions  3 ,  4 . 
         [0058]    The correction of potentiometer voltage  21  will be described in the following text within the framework of an initialization method  48  according to a first exemplary embodiment of the present invention, based on  FIG. 4 . 
         [0059]    In step  49 , measuring unit  42  sets setpoint voltage  35  to an initial value, which corresponds to an initial setpoint position of throttle valve  1  between the two stop positions  3 ,  4 , and throttle valve  1  is moved to the initial setpoint position via control circuit  30 . 
         [0060]    In step  50 , setpoint voltage  35  is varied in order to determine a new position for throttle valve  1 , which position lies closer to one of the two stop positions  3 ,  4 . Depending on whether upper stop position  3  or lower stop position  4  is to be found, measuring unit  42  increases or decreases the value of setpoint voltage  35  by an increment for this purpose. 
         [0061]    In step  51 , control circuit  30  moves throttle valve  1  to the new position and a check takes place as to whether comparator  40  outputs stop signal  47 . If stop signal  47  is not output, then current value  39  of motor current  31  lies below stop threshold value  46  and drive gear wheel  9  is still able to rotate. The search for lower or upper final position  11 ,  12  of drive gear wheel  9  therefore continues with step  50 , and setpoint voltage  35  is varied further. If stop signal  47  is output, then current value  39  of motor current  31  is greater than stop threshold value  46 , and drive gear wheel  9  is no longer able to rotate. Drive gear wheel  9  thus has reached its lower or upper final position  11 ,  12 , and the method proceeds with step  52 . 
         [0062]    In step  52 , measuring device  42  reduces stop threshold value  46  by a correction value that corresponds to correction distance  14 . The correction value may be determined experimentally using a test series of prototypes of control circuit  30 . With the aid of measuring technology, for example, current value  39  of motor current  31  may be determined on each prototype in which throttle value  1  is resting against one of mechanical stops  6 ,  7  while butterfly valve stem  10  is still undistorted. Using individual special current values  39 , it is then possible to form an average value, which can be used as reduced stop threshold value  46 . 
         [0063]    Steps  53  and  54  correspond to steps  50  and  51 , control circuit  30  now repositioning throttle valve  1  until current value  39  of motor current  31  has attained reduced stop threshold value  46 . This makes it possible for position sensor  17 ,  18  to output a corrected potentiometer voltage  21 , which may be used directly as limit value for one of mechanical stops  6 ,  7 . 
         [0064]    After throttle valve  1  has been repositioned, corrected potentiometer voltage  21  thus is able to be detected by measuring device  42  and stored directly in control memory  43 , in step  55 , for further utilization. 
         [0065]    An improved correction of potentiometer voltage  21  will be described in the following text within the framework of an initialization method  56  according to a second exemplary embodiment of the present invention, based on  FIG. 5 . Elements in  FIG. 5  that are identical to elements in  FIG. 4  are denoted by the same reference numerals and not described again. 
         [0066]    In initialization method  56 , all steps up to step  51  are carried out analogously to program  48  from  FIG. 4 . 
         [0067]    Following step  51 , potentiometer voltage  21  is stored in measuring device  42  in step  57 , when drive gear wheel  9  has attained its lower or upper final position  11 ,  12 , respectively. 
         [0068]    Steps  52  to  54  are then carried out as in initialization method  48  from  FIG. 4 . 
         [0069]    Once current value  39  of motor current  31  has reached reduced stop threshold value  46  and the position of drive gear wheel  9  has been corrected, corrected potentiometer voltage  21  is subjected to a plausibility check in step  58 . If corrected potentiometer voltage  21  is obviously free of errors, initialization method  56  is concluded by step  55  of the initialization method from  FIG. 4 . However, if an obvious error is discovered, initialization method  56  is concluded by outputting an error report in step  59 . 
         [0070]    Characteristic curve  60  shown in  FIG. 6 , which plots resulting potentiometer voltage  21  over motor current  31  as a measure of the drive energy supplied to motor  26 , is used to analyze corrected potentiometer voltage  21  for plausibilization purposes regarding obvious errors. The course of characteristic curve  60  may be recorded with the aid of measuring technology, using prototypes once again, for example. 
         [0071]    The characteristic curve essentially has three ranges. A movement range  61  corresponds to a potentiometer voltage range in which the throttle valve is able to move freely within positioning range  5 . Motor current  31  required to move drive gear wheel  9  in this range is essentially constant in all positions of drive gear wheel  9  and thus also constant across potentiometer voltage  21 . Starting with a first limit potentiometer voltage  62 , which corresponds to a potentiometer voltage  21  at which throttle valve  1  is loosely resting against one of the mechanical stops and butterfly valve shaft  10  is not distorted, marks the start of contact range  63  in which drive gear wheel  9  presses throttle valve  1  against one of mechanical stops  6 ,  7  with increasing force. In this range motor current  31  must be increased potentially via potentiometer voltage  21  in order to effect further movement of drive gear wheel  9 . Butterfly valve shaft  10  is distorted in this contact range  63 . However, the distortion of butterfly valve shaft  10  is limited and causes butterfly valve shaft  10  to fracture once a second limit potentiometer voltage  64  has been reached. Starting with the fracture, drive gear wheel  9  once more is able to move freely in a fracture range  65 , in a similar manner as in movement range  61 , without throttle valve  1  itself moving, however. 
         [0072]    Decisive for the plausibilization of corrected potentiometer voltage  21  is contact range  63  of characteristic curve  60 . 
         [0073]    The farther drive gear wheel  9  has rotated beyond one of stop positions  3 ,  4 , the smaller the reduction of potentiometer voltage  21  by a voltage amount  66 ,  67 , through lowering of motor current  31  by a current amount  68 . For example, if motor current  31  is lowered in very close proximity to maximum value  69  at the fracture limit, then a first voltage drop  66  of potentiometer voltage  21  will be smaller than a second voltage drop  67  of potentiometer voltage  21  that results from a lowering of motor current  31  in very close proximity to a minimum value of motor current  31 . 
         [0074]    Using this knowledge and assuming that motor current  31  should be selected very high for positioning throttle valve  1  while finding stop positions  3 ,  4 , in order to overcome contamination  13 , for the plausibilization it is assumed that the change in potentiometer voltage  21  is going to be small when stop threshold value  46  is lowered to correct potentiometer voltage  21  and when throttle valve  1  is repositioned based on lowered stop threshold value  46 . 
         [0075]    In step  58  of initialization method  56  from  FIG. 5 , it is therefore possible to form a difference from potentiometer voltage  21  stored in step  57  and potentiometer voltage  21  corrected in step  54 ; a check may furthermore take place as to whether the difference is small enough to be clearly free of errors. For example, a large difference may occur if gear  16  is also distorted when motor  26  transmits torque  32 . 
         [0076]      FIG. 7  shows a schematic view of a control circuit  30  from  FIG. 3  for positioning throttle valve  1  using a device as recited in a second exemplary embodiment of the present invention. Similar to  FIG. 3 , this device is once again realized by a processor  22 . Elements in  FIG. 7  that are identical to elements in  FIG. 3  are denoted by the same reference numerals and not described again. 
         [0077]    In control circuit  30  of  FIG. 7 , second position sensor  29  on the side of butterfly valve shaft  10  lying opposite first position sensor  17 ,  18  is utilized to determine the point at which the distortion of butterfly valve shaft  10  has been resolved completely. This makes it possible to dispense with a reduction of stop threshold value  46 , so that stop threshold value  46  may be fixedly defined from the outside. 
         [0078]    Second position sensor  29  may likewise be a potentiometer  29 , which has the same design as first potentiometer  17 ,  18 . If a variation of motor current  31  merely leads to a variation of potentiometer voltage  21  from first position sensor  17 ,  18 , butterfly valve shaft  10  is still distorted. However, if a variation of motor current  31  also leads to a variation of a second potentiometer voltage  70  from second position sensor  29 , then this means that butterfly valve shaft  10  rotates at both ends and that the distortion has resolved itself. 
         [0079]      FIG. 8  shows an initialization method  71  according to a third exemplary embodiment. Elements in  FIG. 8  that are identical to elements in  FIG. 4  are denoted by the same reference numerals and not described again. 
         [0080]    Since stop threshold value  46  has been fixedly specified, step  52  for reducing stop threshold value  46  may be omitted in  FIG. 8 . The exemplary embodiments according to  FIGS. 3 and 7  may also be combined with each other, however. 
         [0081]    Step  116  replaces step  54  of initialization method  48  of  FIG. 4 , both steps essentially being executed in the same way. However, instead of checking whether modified stop threshold value  46  has been attained, in step  116  it is checked whether potentiometer voltage  70  varies at second position sensor  29  on the side of butterfly valve shaft  10  lying opposite first position sensor  17 ,  18 . As long as potentiometer voltage  70  does not vary, butterfly valve shaft  10  is still distorted, so that the resetting of the drive energy, such as motor current  31 , for instance, must be continued. 
         [0082]    Corrected potentiometer voltage  21  resulting from step  116  may then be subjected to a plausibility check, once again based on the method according to  FIG. 5 . 
         [0083]    According to the present invention, a measured position of a drive gear wheel while a throttle valve is striking a mechanical stop is shifted by a correction value into the operating position range of the throttle valve, in an effort to cancel the mechanical distortion of the butterfly valve shaft.