Patent Publication Number: US-8522607-B2

Title: Method and device for checking the adjustment of a plurality of actuators driven by a common drive in different mass flow channels

Description:
FIELD OF THE INVENTION 
     The present invention relates to a method and a device for checking the adjustment of a plurality of actuators driven by a common drive in different mass flow channels. 
     BACKGROUND INFORMATION 
     Actuators, for example in the form of throttle valves, are used in internal combustion engines for controlling and/or regulating the rate of the air flow supplied to the internal combustion engine. Standard throttle valves are typically used for this purpose; i.e., a throttle valve controls the rate of the air flow in a mass flow channel that is supplied, for example in the form of a cylindrical inflow, to the internal combustion engine. To be able to maintain the requisite accuracy in the air flow control, the opening angle of the throttle valve must be ascertained as precisely as possible. Angular-position sensors are used for this purpose, for example. However, these sensors must be calibrated to the mechanical limit stops of the throttle valve, to compensate, inter alia, for assembly tolerances. This is accomplished by what is generally referred to as “learning” the limit stops. The throttle valve is adjustable in the position, respectively opening angle thereof, between two mechanical limit stops in the mass flow channel. The throttle valve is fully closed at one of the two limit stops and fully open at the other one of the two limit stops. The process of learning the limit stops entails the throttle valve approaching the limit stops and, depending on the particular limit stop, the throttle valve angles measured upon reaching the limit stops are defined as throttle valve angles for a fully open throttle valve, respectively as throttle valve angles for a fully closed throttle valve. 
     However, for relatively large internal combustion engines, dual- or multi-flow systems are also used, where a plurality of cylinder banks are provided, each having its own air supply and separate throttle valve. Normally, a plurality of standard throttle valves are used in such systems, namely one per inflow path. In the meantime, however, due, inter alia, to discussions that are increasingly focused on installation space, throttle valves are also being used that are connected by a common shaft (in each case, one per inflow path). Throttle valves connected in this manner then have only one common drive, thereby eliminating the need for further drives for the throttle valves. The throttle valves driven via the common drive in the various mass flow channels may then be adjusted between a first mechanical limit stop and a second mechanical limit stop in the particular mass flow channel. 
     SUMMARY 
     In contrast, the method according to example embodiments of the present invention and the device according to example embodiments of the present invention having the features the features described herein have the advantage that the actuators are brought by their common drive to the first limit stop; that a first value of a variable that is characteristic of a position of the common drive of the actuators is ascertained when the first limit stop is reached; that the actuators are brought by their common drive to the second limit stop; that a second value of the variable that is characteristic of the position of the common drive of the actuators is ascertained when the second limit stop is reached; that a difference is determined between the first value and the second value; that the difference is compared in terms of absolute value to at least one predefined threshold value; and that an error in the adjustment of the actuators is recognized in the various mass flow channels when the absolute value of the difference deviates unacceptably from at least one predefined threshold value. In this manner, it is possible to recognize a faulty adjustment of the actuators in the different mass flow channels simply, reliably and with little complexity. In addition, the mentioned difference is a measure of the synchronism of the actuators. 
     It is particularly advantageous that, for the case when the first limit stop is contacted by one of the actuators when the actuators are brought to the first limit stop, and the second limit stop is contacted by the common drive when the actuators are brought to the second limit stop, a faulty adjustment is recognized between the actuators configured, in particular, on a common drive shaft, or a faulty adjustment of the second limit stop is recognized when, in terms of absolute value, the difference is less than a first predefined threshold value. The type of faulty adjustment may be readily inferred in this manner. 
     When a faulty adjustment of the second limit stop is able to be ruled out, it is then possible to uniquely infer a faulty adjustment between the actuators and ascertain a lack of synchronism of the actuators. When the actuators are configured on a common drive shaft, it is then possible in this case to ascertain an unwanted mutual offset of the actuators on the common drive shaft. 
     This is also true for the case when the first limit stop is contacted by one of the actuators when the actuators are brought to the first limit stop, and when the second limit stop is contacted by the common drive when the actuators are brought to the second limit stop; a faulty adjustment of the second limit stop then being recognized when, in terms of absolute value, the difference exceeds a second predefined threshold value. In this case, a faulty adjustment of the second limit stop may then be assumed with certainty. 
     It is also advantageous when the second predefined threshold value is selected to be greater than the first predefined threshold value. In this manner, a tolerance range for the absolute value of the difference is created between the first predefined threshold value and the second predefined threshold value, within which assembly tolerances of the actuators and of the second limit stop are acceptable. 
     It is also advantageous when the first limit stop is configured at a wall of the particular mass flow channel or is formed by the wall of the particular mass flow channel, and when the actuators are in their fully closed position upon reaching the first limit stop. In this manner, the configuration or design of the first limit stop makes it possible to reliably recognize a faulty adjustment of the actuators in the mass flow channels. 
     It is also advantageous when the second limit stop is configured as a limit stop for the common drive, and when the actuators are in their fully open position upon reaching the second limit stop. In this manner, the design of the second limit stop makes it possible to reliably recognize a faulty adjustment of the actuators in the mass flow channels, respectively a faulty adjustment of the second limit stop. 
     It is also advantageous when the actuators reaching one of the limit stops is recognized on the basis of the exceedance in terms of absolute value of a predefined threshold value by a drive current of the actuators. In this manner, a recognition of the actuators reaching one of the limit stops is made possible in a simple, reliable and not very complex process, thereby enhancing the reliability of the checking the adjustment of the actuators in the different mass flow channels is enhanced. 
     Example embodiments of the present invention are represented in the drawing and explained in more detail in the following description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a schematic configuration for controlling and sensing the position of two jointly driven throttle valves in different mass flow channels; 
         FIG. 2  shows a first longitudinal section through a first mass flow channel in accordance with a sectional plane A-A in  FIG. 1  for a fully closed position of the throttle valves; 
         FIG. 3  shows a longitudinal section in accordance with sectional plane A-A in  FIG. 1  through one of the mass flow channels for the case that the throttle valves are in their fully open position; 
         FIG. 4  shows a flow chart for illustrating the design of the device according to an example embodiment of the present invention and the functional sequence of the method according to an example embodiment of the present invention; and 
         FIG. 5  shows a flow chart of an exemplary functional sequence of the method according to an example embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In  FIG. 1 ,  15  denotes a first mass flow channel and  20  a second mass flow channel, as may be provided, for example, for supplying fresh air to a cylinder bank of an internal combustion engine in each case. A first actuator  5 , for example in the form of a throttle valve, is configured in first mass flow channel  15 . A second actuator  10 , likewise in the form of a throttle valve, for example, is configured in second mass flow channel  20 . The two throttle valves  5 ,  10  are driven by a common drive  1  and, in accordance with the example of  FIG. 1 , are configured on a common drive shaft  35 . Common drive  1  is driven by a control device  40  in response to a control signal A. Control signal A is a drive current, for example. A sensor system  80  records the position of throttle valves  5 ,  10 , respectively of common drive shaft  35 , and transmits a measurement signal E to this effect back to control device  40 . Sensor system  80  may be designed in a conventional manner, for example, in the form of a throttle valve potentiometer or also as a contactless system, for example, as an optical, magnetic or inductive system. The position of throttle valves  5 ,  10 , respectively of common drive shaft  35  may be recorded by sensor system  80  in the form of opening angle of throttle valves  5 ,  10 . Since the two throttle valves  5 ,  10  are mounted on common drive shaft  35 , the position of throttle valves  5 ,  10 , respectively of the opening angle of throttle valves  5 ,  10  at the mechanical limit stops may only be learned when the two throttle valves  5 ,  10  have the exact same adjustment on common drive shaft  35 . If the two throttle valves  5 ,  10  have a mutual angular difference, then the opening angle, respectively the position of throttle valves  5 ,  10 , is able to be suitably calibrated by the process of learning the mechanical limit stops of throttle valves  5 ,  10 , as described. The rate of air flow supplied via throttle valves  5 ,  10  through mass flow channels  15 ,  20  of the internal combustion engine is consequently not able to be adjusted accurately enough. 
     Example embodiments of the present invention, therefore, provide for a faulty adjustment of throttle valves  5 ,  10  to be detected in mass flow channels  15 ,  20 . A diagnosis to this effect is performed by control device  40 . For this purpose, control device  40  receives an enable signal F which activates the diagnosis of the adjustment of throttle valves  5 ,  10  in mass flow channels  15 ,  20 . This enable signal F is generated in operating states of the internal combustion engine that do not require a precise adjustment of the air supply to the internal combustion engine. This is the case, for example, in the deceleration fuel-cutoff operating state or also in what is generally referred to as the control unit lag following the switching off of the internal combustion engine. The diagnosis may also be performed after the internal combustion engine is switched off, as long as no load has yet been impressed thereon, for example, by actuation of an accelerator pedal or auxiliary systems, such as air-conditioning systems, a car radio, etc. in the case of a vehicle driven by an internal combustion engine. 
     As a function of the detected faulty adjustment, the control device generates a first error signal F 1  or a second error signal F 2 . Error signals F 1 , F 2  may, for example, be optically and/or acoustically reproduced on a reproduction unit. They may also be entered into a fault memory that may be read out during a workshop visit. Due to error signals F 1 , F 2 , it may also be provided to reduce the power output of the internal combustion engine in the event of a recognized fault or, ultimately, even to completely switch off the same. 
     A longitudinal section through first mass flow channel  15  in accordance with sectional plane A-A marked in  FIG. 1  is sketched in  FIG. 2 . The same reference numerals denote the same elements as in  FIG. 1 . In accordance with the longitudinal section of  FIG. 2 , first throttle valve  5  is in its fully closed position or, in other words, in its fully closed position. In this position, first throttle valve  5  is situated at a first mechanical limit stop  25  that is formed by the wall of first mass flow channel  15 . Alternatively, and as shown by dashed lines in  FIG. 2 , first mechanical limit stop may also be in the form of a projection  26  from the wall of first mass flow channel  15 . In its fully closed position, first throttle valve  5  abuts on first mechanical limit stop  25  or  26 . To bring first throttle valve  5  from any given position to first mechanical limit stop  25 , respectively  26 , first throttle valve  5  is moved by common drive shaft  35  in accordance with the arrow direction marked in  FIG. 2 . To clarify the difficulty of the faulty adjustment of the two throttle valves  5 ,  10 , the position of second throttle valve  10  that is located in second mass flow channel  20 , is additionally sketched in  FIG. 2 . As is apparent in  FIG. 2 , there is an angular offset between first throttle valve  5  and second throttle valve  10 . Thus, located in the fully closed position of first throttle valve  5  is second throttle valve  10 , which is likewise driven by common drive shaft  35 , is not yet in its fully closed position and may not be brought to its fully closed position because common drive shaft  35  is not able to be moved further in the closing direction due to first throttle valve  5  reaching first mechanical limit stop  25 ,  26 . In this context, second mass flow channel  20  also has a corresponding first mechanical limit stop that is ideally configured at the same location and with the same geometry as in first mass flow channel  15 . 
     Also shown in  FIG. 2  is a second mechanical limit stop  30  that is contacted by common drive  1 , respectively common drive shaft  35 , when throttle valves  5 ,  10  are fully open, as is shown in  FIG. 3 .  FIG. 3  shows the longitudinal section along sectional plane A-A of  FIG. 1  in the case of fully open throttle valves  5 ,  10 . Second mechanical limit stop  30  is symbolically illustrated in  FIG. 2  and  FIG. 3  and is normally configured outside of mass flow channels  15 ,  20 , for example, in the gearing of common drive  1 . Thus, drive shaft  35  is directly blocked by second mechanical limit stop  30 , as is illustrated in  FIG. 3  by crosspiece  36  that is connected to the shared drive shaft  35 . Thus, second mechanical limit stop  30  is normally configured in the gearing of common drive  1 . Thus, it is intended that the representation in  FIGS. 2 and 3  only illustrate the action of second mechanical limit stop  30 . Therefore, when second mechanical limit stop  30  is configured in the gearing of shared drive  1 , there is naturally also no need for crosspiece  36 , respectively, it would be configured within the gearing of common drive  1 . In this context, this type of second mechanical limit stop  30  is reasonably well known to one skilled in the art and is, therefore, not clarified in greater detail here. As mentioned, only the description of the functional principle is relevant here. To bring throttle valves  5 ,  10  to their fully open position, they may be brought from any given position by movement in the arrow direction according to  FIG. 3 , the fully open position being reached by the striking of crosspiece  36  on second mechanical limit stop  30 . 
     The angular offset of the two throttle valves  5 ,  10  reduces the angular range that is available for the motion of common drive shaft  35  between first mechanical limit stop  25 ,  26  and second mechanical limit stop  30 . The method according to example embodiments of the present invention and the device according to example embodiments of the present invention make use of this fact for checking the adjustment of throttle valves  5 ,  10  in mass flow channels  15 ,  20 . It is namely provided in accordance with example embodiments of the present invention to determine the angular range that is available for common drive shaft  35  and to ascertain by threshold value comparison whether the available angular range is smaller than a value that is expected for a correct adjustment of throttle valves  5 ,  10 . If this is the case, then a faulty adjustment between the two throttle valves  5 ,  10  is assumed. However, a faulty adjustment of the two throttle valves  5 ,  10  in mass flow channels  15 ,  20  may also be derived from the position of second mechanical limit stop  30  relative to common drive shaft  35 . If second mechanical limit stop  30  is displaced to the right in the representation according to  FIGS. 2 and 3 , the adjustable angular range of shared drive shaft  35  is then likewise reduced. If, on the other hand, second mechanical limit stop  30  is displaced to the left in the representation according to  FIGS. 2 and 3 , the adjustable angular range for common drive shaft  35  is possibly increased beyond a maximum allowable second threshold value. In both cases, the fully open position of throttle valves  5 ,  10  is not adjustable, even when the two throttle valves  5 ,  10  do not have a mutual angular offset. A faulty adjustment of throttle valves  5 ,  10  in mass flow channels  15 ,  20  may also be due to the mutual deviation of the diameters of the normally cylindrical mass flow channels  15 ,  20 , that is inherent to the manufacturing, and/or to the two mass flow channels  15 ,  20  being mutually offset due to the assembly, and or throttle valves  5 ,  10  not being present axisymmetrically to common drive shaft  35 . In all of these cases, the adjustable angular range of common drive shaft  35  may be limited to an undesirable extent. 
     In accordance with example embodiments of the present invention, by evaluating the available angular range of common drive shaft  35 , a faulty adjustment of the two throttle valves  5 ,  10  is recognized in the two mass flow channels  15 ,  20 , whether it be due to a faulty adjustment between the two throttle valves  5 ,  10 , i.e., due to an angular offset between the two throttle valves  5 ,  10 , an asymmetrical configuration of throttle valves  5 ,  10  on the common drive shaft  35 , a mutual offset of mass flow channels  15 ,  20 , a different diameter of mass flow channels  15 ,  20  or a faulty adjustment of second mechanical limit stop  30  relative to throttle valves  5 ,  10 . Moreover, in accordance with example embodiments of the present invention, the latter case of the faulty adjustment of second mechanical limit stop  30  relative to throttle valves  5 ,  10  may be differentiated from the first mentioned cases of the faulty adjustment of throttle valves  5 ,  10 . 
       FIG. 4  shows a functional circuit diagram of control device  40  according to an example embodiment of the present invention. Control device  40  includes a diagnostic unit  130  that controls and coordinates the diagnostic sequence thereof. In terms of software and/or hardware, control device  40  may be implemented in an engine control of the internal combustion engine, for example, or it may be configured as a separate control unit. An enable signal F is fed to diagnostic unit  130 . If this is set during an overrun condition or during a control unit lag, for example, then the diagnostic unit initiates the diagnosis according to the present invention. On the other hand, if enable signal F is reset, for example, in a full-throttle operating state of the internal combustion engine, then no diagnosis is performed by diagnostic unit  130 . The case of set enable signal F is considered in the following. As soon as diagnostic unit  130  receives a positive edge of enable signal F that is used to set enable signal F, it prompts an adjusting unit  45  to generate a control signal A in the form of a drive current, in response to which common drive  1 , in the form of a drive motor, is prompted to bring the two throttle valves  5 ,  10  to the fully closed position. As soon as one of the two throttle valves  5 ,  10  reaches its first mechanical limit stop  25 ,  26 , drive current A begins to increase in order to overcome the obstacle. Drive current A is also fed to a first absolute-value generator  100  which generates the absolute value of drive current A. The generated absolute value of drive current A is fed to a first comparison unit  105  and is compared there to a predefined threshold value for drive current A from a first threshold value memory  110 . If the absolute value of the drive current exceeds the predefined threshold value for the drive current, then first comparison unit  105  transmits a setting signal both to a determination unit  50 , as well as to diagnostic unit  130 . Predefined threshold value for drive current A is applied on a test stand in a way that makes it possible to reliably recognize, for example, at least one of the two throttle valves  5 ,  10  reaching first mechanical limit stop  25 ,  30 . To this end, the predefined threshold value must be selected to be high enough. However, in the sense of a most rapid possible recognition of at least one of the two throttle valves  5 ,  10  reaching first mechanical limit stop  25 ,  30 , and to avoid too high of a drive current A, the predefined threshold value in threshold value memory  110  should not be selected to be too high. Thus, the predefined threshold value for drive current A in first threshold value memory  110  may be selected on the test stand, on the one hand, for example, as a compromise between a greatest possible value for reliably recognizing at least one of the two throttle valves  5 ,  10  reaching first mechanical limit stop  25 ,  30 , and, on the other hand, a smallest possible value for a most rapid possible recognition of at least one of the two throttle valves  5 ,  10  reaching first mechanical limit stop  25 ,  26 , and to avoid too high of a drive current A. The measurement signal of sensor system  80  is fed to determination unit  50 . In this manner, on the basis of measurement signal E supplied thereto, determination unit  50  ascertains the current position of common drive shaft  35  in each instance. As soon as determination unit  50  receives a setting signal from first comparison unit  105 , it retransmits the currently determined position of common drive shaft  35  to a memory unit  85 . In the case that a reset signal is received from first comparison unit  105 , determination unit  50  does not retransmit the currently determined position of common drive shaft  35  to memory unit  85 . The ascertained position of common drive shaft  35  is the angular position thereof, for example. Upon receipt of the first setting signal from first comparison unit  105 , from the time of enabling of the diagnosis, diagnostic unit  130  controls a first memory location  90  of memory unit  85  to receive the current value supplied by determination unit  50 , for the position of common drive shaft  35 . Under the condition that enable signal F continues to be set, diagnostic unit  130  subsequently prompts adjusting unit  45  to bring the two throttle valves  5 ,  10  to their fully open position. To this end, adjusting unit  45  generates a corresponding drive current A, whose sign, in comparison, is inverted in order to bring throttle valves  5 ,  10  to such a fully closed position. As long as second mechanical limit stop  30  is not reached, in terms of absolute value, drive current A falls below the predefined threshold value for drive current A, so that first comparison unit  105  transmits a reset signal both to determination unit  50 , as well as to diagnostic unit  130 . Upon the reaching of second mechanical limit stop  30  by common drive shaft  35 , respectively, as shown in  FIGS. 2 and 3 , by crosspiece  36 , drive current A increases again in terms of absolute value beyond the predetermined threshold value for drive current A, so that first comparison unit  105 , in turn, transmits a setting signal to determination unit  50 , as well as to diagnostic unit  130 . Since, in terms of absolute value, upon the reaching of second mechanical limit stop  30 , drive current A increases similarly to the reaching of first mechanical limit stop  25 ,  26 , the predefined threshold value for drive current A may also be used for detecting the reaching of second mechanical limit stop  30 . Upon receipt of the setting signal from first comparison unit  105 , diagnostic unit  130  controls memory unit  85  such that a second memory location  95  of memory unit  85  is enabled for an overwrite operation. Upon receipt of the setting signal from first comparison unit  105 , determination unit  50  transmits the currently determined position of common drive shaft  35  to memory unit  85 , where it is stored in enabled second memory location  95 . Thus, in the case of a fully closed position of throttle valves  5 ,  10 , the current position of common drive shaft  35  resides in first memory location  90 . In the case of fully open throttle valves  5 ,  10 , the position of common drive shaft  35  resides in second memory location  95 . In the following, the position stored in first memory location  90  is referred to as first position, and the position stored in second memory location  95 , as second position. The first position and the second position are fed to a subtraction unit  55 . Subtraction unit  55  computes the difference between the first position and the second position and transmits the computed difference to a second absolute-value generator  115 . Second absolute-value generator  115  generates the absolute value of the computed difference and transmits it to a second comparison unit  60  and to a third comparison unit  65 . The absolute value of the difference is compared in first comparison unit  60  to a first predefined threshold value from a second threshold value memory  120 . If the absolute value of the difference is less than the first predefined threshold value of second threshold value memory  120 , then first comparison unit  60  transmits a setting signal to a first error detection unit  70 ; otherwise, a reset signal. First predefined threshold value is selected to correspond to the angular difference of common drive shaft  35  between the fully open position and the fully closed position of throttle valves  5 ,  10  for the case of throttle valves  5 ,  10  that have been adjusted without error in mass flow channels  15 ,  20 , minus a permissible tolerance value. If the absolute value of the difference is less than the first predefined threshold value of second threshold value memory  120 , then the angular range of common drive shaft  35  is unacceptably limited, whether it be due to a faulty adjustment, respectively an angular offset between the two throttle valves  5 ,  10 , due to different geometries of the two mass flow channels  15 ,  20 , a different position of common drive shaft  35  in both mass flow channels  15 ,  20 , a lack of symmetry of at least one of throttle valves  5 ,  10  relative to common drive shaft  35 , or due to a faulty adjustment of second mechanical limit stop  30  relative to the position of throttle valves  5 ,  10 , respectively to common drive shaft  35 . 
     In third comparison unit  65 , the absolute value of the difference is compared to a second predefined threshold value of a third threshold value memory  125 . If the absolute value of the difference exceeds the second predefined threshold value of third threshold value memory  125 , third comparison unit  65 , at the output thereof, then transmits a setting signal to a second error detection unit  75 ; otherwise, a reset signal is transmitted. In this context, the second predefined threshold value of third threshold value memory  125  is selected to be greater than the first predefined threshold value of second threshold value memory  120 . It corresponds to the angular range that is covered by common drive shaft  35  between the fully closed and fully open position of throttle valves  5 ,  10  in the case that no faulty adjustment of the two throttle valves  5 ,  10  is present in mass flow channels  15 ,  20 , with the addition of a tolerance value. This tolerance value allows for the tolerances of an assembly-induced offset of second mechanical limit stop  30  relative to the two throttle valves  5 ,  10 , respectively common drive shaft  35 . Therefore, if the absolute value of the difference exceeds the second predefined threshold value of third threshold value memory  125 , then this indicates that, in any case, there must be a faulty adjustment of second mechanical limit stop  30  relative to common drive shaft  35 . 
     Upon receipt of the second setting signal from first comparison unit  105  since receipt of set enable signal F, diagnostic unit  130  also transmits a setting signal to first error detection unit  70  and second error detection unit  75 . Error detection units  70 ,  75  are activated in this manner. In the activated state, in the case of a receipt of a set signal from second comparison unit  60 , first error detection unit  70 , at the output thereof, transmits a set first error signal F 1 . This shows, as described, a faulty adjustment of throttle valves  5 ,  10  in mass flow channels  15 ,  20 , in the case of which the angular range of shared drive shaft  35  was unacceptably limited, in particular, by an angular offset between the two throttle valves  5 ,  10  or a displacement to the right of the top mechanical limit stop  30  relative to common drive shaft  35  in the example according to  FIG. 3  to the right, or due to differences in geometry between first mass flow channel  15  and second mass flow channel  20 , due to a lack of symmetry of at least one of throttle valves  5 ,  10  relative to common drive shaft  35 , due to a different positioning of common drive shaft  35  in first mass flow channel  15  and in second mass flow channel  20 , or due to different geometries of the two throttle valves  5 ,  10 , in particular, different diameters of throttle valves  5 ,  10 . The angular range of common drive shaft  35  may also be reduced by wear to the gearing of common drive  1 . Set first error signal F 1  may, for example, be entered into a fault memory (not shown in  FIG. 4 ) and be read out from there, for example, during a workshop visit. 
     Upon receipt of the set signal from diagnostic unit  130 , second error detection unit  75  is also activated, which, in response to receipt of a set signal from third comparison unit  65  at the output thereof, transmits a set second error signal F 2 ; otherwise, a reset second error signal F 2 . From set second error signal F 2 , it is inferable that there is an unacceptable increase in the angular range that is adjustable from common drive shaft  35 , due to a faulty adjustment of second mechanical limit stop  30  relative to throttle valves  5 ,  10 , respectively relative to common drive shaft  35  in mass flow channels  15 ,  20 . 
     First error signal F 1  is reset when first error detection unit  70  receives a reset signal from first comparison unit  60  or a reset signal from diagnostic unit  130 . Second error signal F 2  of second error detection unit  75  is reset when second error detection unit  75  receives a reset signal from third comparison unit  65  or a reset signal from diagnostic unit  130 . Second error signal F 2  may also be stored in a fault memory (not shown in  FIG. 4 ) and be read out during a workshop visit. Different fault memories may advantageously be used for both error signals F 1 , F 2 , making it possible to differentiate between the two error signals F 1 , F 2 . 
     As a consequence of a set first error signal F 1  and/or of a set second error signal F 2 , a power output of the internal combustion engine may also be reduced, or the internal combustion engine may also be ultimately switched off. 
     Once the described diagnosis is complete, it may be performed repeatedly in the described manner for as long as enable signal F is set. As soon as the diagnosis is started once again, thus, as soon as diagnostic unit  130  prompts adjusting unit  45  to bring throttle valves  5 ,  10  again to the fully closed position, diagnostic unit  130  transmits a reset signal to first error detection unit  70  and to second error detection unit  75 . Error detection units  70 ,  75  are then only enabled again by a corresponding setting signal from diagnostic unit  130  when throttle valves  5 ,  10  have again reached second mechanical limit stop  30 . This ensures that the process of overwriting memory locations  90 ,  95  of memory unit  85  once more until the fully open position of throttle valves  5 ,  10  is reached the next time does not lead to an incorrect diagnosis. 
     With regard to the diagnosis according to example embodiments of the present invention, it was previously described that throttle valves  5 ,  10  are brought to their fully closed position and subsequently to their fully open position. However, the diagnosis may also be carried out in exactly the inverse manner, throttle valves  5 ,  10  being initially brought to their fully open position and subsequently to their fully closed position. Since the absolute value of the difference is generated in second absolute-value generator  115 , it is irrelevant whether throttle valves  5 ,  10  are first brought to their fully closed position for the diagnosis and then to their fully open position or first to their fully open position and then to their fully closed position. 
       FIG. 5  shows a flow chart of an exemplary functional sequence of the method according to an example embodiment of the present invention. 
     Following a program start, for example, when the internal combustion engine is switched on, diagnostic unit  130  checks at a program point  200  on the basis of received enable signal F whether the diagnosis was enabled, i.e., whether enable signal F was set. If this is the case, the program branches to a program point  205 ; otherwise, the program branches to program point  200 . 
     At program point  205 , diagnostic unit  130  prompts adjusting unit  45  to bring throttle valves  5 ,  10  to their fully closed position. The program subsequently branches to a program point  210 . 
     At program point  210 , diagnostic unit  130  checks whether it is receiving a setting signal from first comparison unit  105 , thus, whether the fully closed position of throttle valves  5 ,  10  was reached. If this is the case, the program branches to a program point  215 ; otherwise, the program branches to program point  205 . 
     At program point  215 , determination unit  50  stores the currently determined position of common drive shaft  35  in first memory location  90  of memory unit  85 . The program subsequently branches to a program point  220 . 
     At program point  220 , diagnostic unit  130  prompts adjusting unit  45  to bring throttle valves  5 ,  10  to their fully open position. The program subsequently branches to a program point  225 . 
     At program point  225 , diagnostic unit  130  checks whether it is again receiving a setting signal from comparison unit  105  since controlling of throttle valves  5 ,  10  to reach the fully open position thereof, and thus that the fully open position was reached. If this is the case, the program branches back to a program point  230 ; otherwise, the program branches to program point  220 . 
     At program point  230 , diagnostic unit  130  prompts the storing of the position of common drive shaft currently determined by determination unit  50  in second memory location  95  of memory unit  85 . At program point  230 , the difference between the first position and the second position is then computed, and the absolute value of this difference is subsequently generated in absolute-value generator  115 . The program subsequently branches to a program point  235 . 
     At program point  235 , first comparison unit  60  checks whether the absolute value of the difference is less than the first predefined threshold value of second threshold value memory  120 . If this is the case, the program branches to a program point  240 , otherwise the program branches to a program point  245 . 
     At program point  240 , second comparison unit  60  transmits a setting signal to first error detection unit  70  which then, in response to the receipt of the setting signal, transmits a set first error signal F 1  to diagnostic unit  130 . The program is subsequently exited. 
     At program point  245 , third comparison unit  65  checks whether the absolute value of the difference is less than the second predefined threshold value of third threshold value memory  125 . If this is the case, the program branches to a program point  250 , otherwise the program is exited. 
     At program point  250 , third comparison unit  65 , at the output thereof, transmits a setting signal to second error detection unit  75  which then, in response to the receipt of the setting signal of diagnostic unit  130 , transmits a set, second error signal F 2  to diagnostic unit  130 . The program is subsequently exited. 
     In the case of the no-branching from program point  245 , both first error signal F 1 , as well as second error signal F 2  are reset. The program may be executed repeatedly. 
     The method according to example embodiments of the present invention and the device according to example embodiments of the present invention were described for the case of two mass flow channels  15 ,  20 , each having one throttle valve  5 ,  10 , but may be realized in the same manner for any given number of mass flow channels, each having one throttle valve. 
     In the case of a set first error signal F 1  and/or of a set second error signal F 2 , a component exchange may be initiated in the workshop, in the case of which the entire component, together with mass flow channels  15 ,  20 , common drive shaft  35 , and throttle valves  5 ,  10 , is exchanged. It is thus possible to avoid an imprecise airflow control having negative influences, for example, on the exhaust gas. 
     If the absolute value of the difference falls below the first predefined threshold value of second threshold value memory  120 , then, under the condition of a correctly adjusted second mechanical limit stop  30 , the synchronism of the two throttle valves  5 ,  10  in mass flow channels  15 ,  20  is no longer ensured, whether it be due to manufacturing tolerances, faulty assembly or wear during operation.