Abstract:
A switch is formed by a branch including a measurement resistance and a selectable one of switching resistances having different nominal values such that a switch position depends on which switching resistance is selected. The measurement resistance is connected through the selected switching resistance to a supply voltage whereby a voltage drop dependent on the switch position is across the measurement resistance. A controller identifies the switch position by comparison of a measured value (U M1 ) of the voltage drop with target voltage drops corresponding to switch positions, calculates a voltage drop (Uges) across the branch based on nominal values of the measurement and selected switching resistances and the supply voltage, forms a difference value (U Diff ) between a measured value (U Vcc ) of the supply voltage and the branch voltage drop (Uges), and qualifies the identified switch position as faulty when the difference value (U Diff ) exceeds a difference threshold value (U Diff-S ).

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of International Application No. PCT/EP2011/061780, published in German, with an International filing date of Jul. 11, 2011, which claims priority to DE 10 2010 026 919.0, filed Jul. 13, 2010; the disclosures of which are incorporated in their entirety by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to detecting a switch position of a switch in which the switch position is represented by a value of a physically measured variable. 
       BACKGROUND 
       [0003]    Switching devices are used, for example, in motor vehicles in order to control various vehicle functions. For instance, a steering column module typically has integrated therein a switching device having a plurality of individual switches. The switches are for controlling the windshield wiper and washer assembly, the blinkers, the high-beam lights of the vehicle, etc. 
         [0004]      FIG. 1  illustrates a block diagram of a switch assembly in accordance with embodiments of the present invention. The switch assembly includes a switching device having a plurality of switches (in this example, a first switch SE 1  and a second switch SE 2 ) for controlling respective functions. For instance, first and second switches SE 1 , SE 2  are for controlling first and second vehicle functions respectively. 
         [0005]    Each switch SE 1 , SE 2  is formed by a respective resistance branch. The resistance branch forming first switch SE 1  includes a measurement resistance M 1  and a switchable one of a plurality of switching resistances S 11 , S 12 , S 13 . Switching resistances S 11 , S 12 , S 13  have different nominal resistance values amongst one another. The switch position of first switch SE 1  depends on which switching resistance S 11 , S 12 , S 13  is selected. First switch SE 1  has three potential switch positions respectively corresponding with the three switching resistances S 11 , S 12 , and S 13 . As shown in  FIG. 1 , in this example, switching resistance S 11  is selected such that first switch SE 1  is in the switch position corresponding to switching resistance S 11 . Measurement resistance M 1  is connected at one end to ground potential Gnd and is connected at its other end to a constant supply voltage Vcc through the selected one of the switching resistances S 11 , S 12 , S 13 . As such, in this example, the other end of measurement resistance M 1  is connected to supply voltage Vcc through switching resistance S 11  as first switch SE 1  is in the switch position corresponding to switching resistance S 11 . Thus, in this switch position, the total resistance in the resistance branch forming first switch SE 1  is measuring resistance M 1  and switching resistance S 11 . 
         [0006]    Likewise, the resistance branch forming second switch SE 2  includes a measurement resistance R 2  and a switchable one of a plurality of switching elements S 21 , S 22 , S 23 , S 24 . Switching resistances S 21 , S 22 , S 23 , S 24  have different nominal resistance values amongst one another. The switch position of second switch SE 2  depends on which switching resistance S 21 , S 22 , S 23 , S 24  is selected. Second switch SE 2  has four potential switch positions respectively corresponding with the four switching resistances S 21 , S 22 , S 23 , S 24 . As shown in  FIG. 1 , in this example, switching resistance S 23  is selected such that second switch SE 2  is in the switch position corresponding to switching resistance S 23 . Measurement resistance M 2  is connected at one end to ground potential Gnd and is connected at its other end to supply voltage Vcc through, in this example, switching resistance S 23  as second switch SE 2  is in the switch position corresponding to switching resistance S 23 . Thus, in this switch position, the total resistance in the resistance branch forming second switch SE 2  is measuring resistance M 2  and switching resistance S 23 . 
         [0007]    As shown in  FIG. 1 , the resistance branches of switches SE 1 , SE 2 , including the respective switching resistances (S 11 ; S 23  in this example) according to the respective selected switch positions, are connected in parallel to one another through a common electrical conductor to supply voltage Vcc. 
         [0008]    The switching assembly includes a processor μC having analog-to-digital converter (ADC) inputs. In this example, the processor includes three ADC inputs A/D  1 , A/D  2 , and A/D 3 . 
         [0009]    In an operation for detecting the switch position of first switch SE 1 , the actual voltage drop U M1  across measuring resistance M 1  is measured. The measured voltage drop U M1  is supplied to ADC input A/D  1  for evaluation by the processor Likewise, in an operation for detecting the switch position of second switch SE 2 , the actual voltage drop U M2  across measuring resistance M 2  is measured and supplied to ADC input A/D  2  for the processor. For both operations, the actual voltage U Vcc  of supply voltage Vcc is measured and supplied to ADC input A/D  3  for the processor. 
         [0010]    Measuring resistances M 1 , M 2  and switching resistances S 11 , S 12 , S 13 ; S 21 , S 22 , S 23 , S 24  have known nominal resistance values. For instance, the nominal resistance values of switching resistances S 11 , S 12 , S 13  are 1 k ohms, 10 k ohms, and 100 k ohms. Supply voltage V cc  has a known nominal voltage value such as, for instance, 5V. Expected fixed set-points for the voltage drops across measuring resistors M 1 , M 2  are obtained based on the nominal values. The predetermined fixed set-points are respectively associated with the different switch positions of switches SE 1 , SE 2 , and thus for the measured voltages U M1 , U M2 . 
         [0011]    In the example in which first switch SE 1  is in the switch position in which switching resistance S 11  is selected, the measured voltage drop U M1  occurring across measuring resistance M 1  depends on the actual resistance values of measuring resistance M 1  and switching resistance S 11  and the actual voltage value of supply voltage Vcc. However, the voltage drop expected to across measuring resistance M 1  depends on the nominal resistance values of measuring resistance M 1  and switching resistance S 11  and the nominal voltage value of supply voltage Vcc. Thus, if any of the actual values differ from the corresponding nominal values, then the measured voltage drop U M1  will differ from the expected voltage drop. The same analysis applies to any other one of switching resistances and to second switch SE 2 . 
         [0012]    Deviations of the actual resistance values from the nominal design values arise due to tolerances of the components and characteristic impedances or contact resistances at switches and connectors. This situation affects the entire switching device and can thus give rise to deviations in the measured voltages U M1 , U M2  from the predetermined fixed set-points. If the deviations attain the order of magnitude of the intervals between the measured voltages U M1 , U M2  associated respectively with the different switch positions, then this can lead to erroneous switch position information and thus to defective operation of the components powered by the switching device. 
       SUMMARY 
       [0013]    With reference to  FIG. 1 , embodiments of the present invention are directed to detecting a switching position of a switch SE 1 , SE 2  of a switching device. Each switch SE 1 , SE 2  is formed by a respective resistance branch. Each resistance branch includes a measurement resistance M 1 , M 2  and a switchable one of a plurality of switching resistances S 11 , S 12 , S 13 ; S 21 , S 22 , S 23 , S 24  connected in series. The switching resistances in each resistance branch have different nominal resistance values amongst one another. The switch position of each switch SE 1 , SE 2  depends on which of the switching resistances is selected. In each resistance branch, the measurement resistance M 1 , M 2  is connected at one end to ground potential and is connected at its other end to a supply voltage Vcc through the selected one of the switching resistances (e.g., as shown in  FIG. 1 , switching resistance S 11 , S 23 , respectively). 
         [0014]    The switching position of a switch SE 1 , SE 2  is represented by a respective value of a measured physical variable of the switch. For instance, the measured physical variable of the switch SE 1 , SE 2  is the measured voltage drop U M1 , U M2  across the measurement resistance M 1 , M 2  of the switch. The measured value U M1 , U M2  of the physical variable is supplied via an analog-to-digital converter (ADC) input to a processor for evaluation. 
         [0015]    The operation of detecting the switching position of a switch SE 1 , SE 2  in accordance with embodiments of the present invention includes identifying the switching position of the switch by comparing the measured value U M1 , U M2  of the physical variable to predefined fixed target values of the physical variable. The predefined target values of the physical variable respectively correspond to the possible switching positions of the switch. The operation further includes calculating a deduced value Uges of a comparison physical variable for the identified switch position from a physical model of the switching device. The physical model of the switching device is based on the nominal values of the measuring resistances M 1 , M 2  and the switching resistances S 11 , S 12 , S 13 ; S 21 , S 22 , S 23 , S 24  and the nominal value of the voltage supply Vcc. The operation further includes forming a difference value U Diff  between the deduced value Uges of the physical comparison variable and either the nominal value Vcc or a currently detected actual value Uvcc of the physical comparison variable. The operation further includes comparing the difference value U Diff  to a difference threshold value U Diff-S . The operation further includes qualifying the present switching position detection as being faulty when the difference value U Diff  exceeds the difference threshold value U Diff-S . 
         [0016]    As described, the physically measured variables concern voltage or current values, for example, with the nominal values of measuring resistance M 1 , M 2  and switching resistances S 11 , S 12 , S 13 ; S 21 , S 22 , S 23 , S 24  that determine the measured variables of resistance, capacitance, or inductance, and for the input parameters of the switching device of supply voltage values or input current values. The physical comparison parameters, for example, relate to one of these values, which is calculated as a value derived from other measured values that can be presented as a nominal value or as an actual value, which can be acquired by an actual measurement. 
         [0017]    It is preferable when the acquisition of an existing switch position is qualified as being erroneous that the triggering of the associated vehicle function is thereby suppressed. 
         [0018]    Accordingly, objects of the present invention include having at one&#39;s disposal a possibility for validation of the switch position derived from the measured voltages U M1 , U M2  to at least suppress triggering of the related switch function in case of potentially erroneous switch position information, and correcting erroneous switch position information and triggering the actually intended function. Such a validation of the detection of a switch position is achieved by the embodiments of the present invention directed to detecting a switching position of a switch of a switching device as described above. 
         [0019]    In carrying out at least one of the above and other objects, the present invention provides a switching assembly having a switching device and a controller. The switching device has a switch formed by a resistance branch including a measurement resistance and a selectable one of a plurality of switching resistances having different nominal resistance values amongst one another such that a switch position of the switch depends on which switching resistance is selected. The measurement resistance is connected at one end to ground and connected at another end through the selected switching resistance to a supply voltage whereby a voltage drop dependent on the switch position of the switch occurs across the measurement resistance. The controller is configured to identify the switch position by comparison of a measured value (U M1 ) of the voltage drop across the measurement resistance with predefined target voltage drops respectively corresponding to different switch positions dependent on the switching resistances, calculate a voltage drop (Uges) across the resistance branch based on nominal resistance values of the measurement resistance and the selected switching resistance and a nominal value of the supply voltage, form a difference value (U Diff ) between a measured value (U Vcc ) of the supply voltage and the calculated voltage drop (Uges) across the resistance branch, compare the difference value (U Diff ) to a difference threshold value (U Diff-S ), and qualify the identified switching position as being faulty when the difference value (U Diff ) exceeds the difference threshold value (U Diff-S ). 
         [0020]    Further, in carrying out at least one of the above and other objects, the present invention provides another switching assembly having a switching device and a controller. The switching device has first and second switches formed by respective resistance branches including a measurement resistance and a selectable one of a plurality of switching resistances having different nominal resistance values amongst one another such that a switch position of each switch depends on which switching resistance is selected. In each resistance branch the measurement resistance being connected at one end to ground and connected at another end through the selected switching resistance to a supply voltage whereby a voltage drop dependent on the switch position of the switch occurs across the measurement resistance and whereby the resistance branches are connected in parallel. The controller is configured to identify the respective switch positions of the switches by comparison of measured values (U M1 , U M2 ) of the voltage drops across the measurement resistances with predefined target voltage drops respectively corresponding to different switch positions dependent on the switching resistances, calculate currents (I 1 , I 2 ) flowing in the respective resistance branches from the measured voltages (U M1 , U M2 ) and nominal values of the measuring resistances. The branch currents added together are equal to a total current (Iges) through all of the resistance branches. This controller is further configured to calculate a total resistance (Rges) formed by the parallel connection of the resistance branches from the nominal values of the measuring resistances and the selected switching resistances, calculate a total voltage drop (Uges) across the parallel-connected resistance branches from the calculated values of the total current (Iges) and the total resistance (Rges), form a difference value (U Diff ) between a measured value (U Vcc ) of the supply voltage and the calculated total voltage drop (Uges), compare the difference value (U M ) to a difference threshold value (U Diff-S ), and qualify the identified switching positions as being faulty when the difference value (U Diff ) exceeds the difference threshold value (U Diff-S ). 
         [0021]    Also, in carrying out at least one of the above and other objects, the present invention provides another switching assembly having a switching device and a controller. The switching device is the same switching device noted above with the first and second switches. The controller is configured to identify the respective switch positions of the switches by comparison of measured values (U M1 , U M2 ) of the voltage drops across the measurement resistances with predefined target voltage drops respectively corresponding to different switch positions dependent on the switching resistances, calculate currents (I 1 , I 2 ) flowing in the respective resistance branches from the measured voltages (U M1 , U M2 ) and nominal values of the measuring resistances, calculate branch voltage drops (U 1 , U 2 ) across the respective resistance branches from the respective branch currents (I 1 , I 2 ) and the respective nominal total values of measuring resistances and the selected switching resistances, form a difference value (U Diff ) between a measured value (U Vcc ) of the supply voltage and a largest one of the branch voltage drops (U 1 , U 2 ), compare the difference value (U Diff ) to a difference threshold value (U Diff-S ), and qualify the identified switching positions as being faulty when the difference value (U Diff ) exceeds the difference threshold value (U Diff-S ). 
         [0022]    The above features, and other features and advantages of the present invention are readily apparent from the following detailed description thereof when taken in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  illustrates a block diagram of a switch assembly in accordance with embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0024]    Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the present invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0025]    Referring now to  FIG. 1 , a block diagram of a switch assembly in accordance with embodiments of the present invention is shown. As described above, the switch assembly includes a switching device having switches SE 1 , SE 2  with each switch SE 1 , SE 2  being formed by a respective resistance branch. The resistance branches respectively include a measurement resistance M 1 , M 2  and a switchable one of a plurality of switching resistances S 11 , S 12 , S 13 ; S 21 , S 22 , S 23 , S 24 . Each set of switching resistances have different nominal resistance values amongst one another. The switch position of each switch SE 1 , SE 2  depends on which switching resistance is selected. As shown in  FIG. 1 , in this example, switching resistances S 11 , S 23  are selected such that switches SE 1 , SE 2  are respectively in the switch positions corresponding to switching resistances S 11 , S 23 . Measurement resistance M 1 , M 2  is connected at one end to ground potential Gnd and is connected at its other end to supply voltage Vcc through the selected switching resistances S 11 , S 23 . Thus, in these switch positions, the total resistance in the resistance branch forming first switch SE 1  is measuring resistance M 1  and switching resistance S 11  and the total resistance in the resistance branch forming second switch SE 2  is measuring resistance M 2  and switching resistance S 23 . As shown in  FIG. 1 , the resistance branches of switches SE 1 , SE 2  are connected in parallel to one another through a common electrical conductor to supply voltage Vcc. 
         [0026]    In one embodiment, an operation for detecting the switch positions of switches SE 1 , SE 2  includes the following. The actual voltage drops U M1 , U M2  across the respective measuring resistances M 1 , M 2  in the resistance branches of switches SE 1 , SE 2  are measured. The measured voltages U M1 , U M2  are supplied to respective ADC inputs A/D  1 , A/D  2  for the processor. The actual voltage U Vcc  supplied by supply voltage Vcc is measured and supplied to ADC input A/D  3  for the processor. 
         [0027]    The operation further includes identifying the respective switch positions of switches SE 1 , SE 2  by comparison of measured voltages U M1 , U M2  with predefined fixed target voltage values corresponding to the respective switch positions. The operation further includes calculating branch currents I 1 , I 2  flowing in the respective resistance branches. Branch currents I 1 , I 2  are calculated from measured voltages U M1 , U M2  and the nominal values of measuring resistances M 1 , M 2  according to the following equations: I 1 =U M1 /M 1 ; and I 2 =U M2 /M 2 . 
         [0028]    The branch currents I 1 , I 2  flowing through the respective branches added together are equal to the total current Iges flowing through all of the resistance branches according to the equation: Iges=I 1 +I 2 . The operation further includes calculating the total resistance Rges formed by the parallel connection of the resistance branches between the ground potential Gnd and the supply voltage Vcc. The total resistance Rges is calculated from the nominal values of measuring resistances M 1 , M 2  and the switching resistances in effect for the identified switch positions (in this example, switching resistances S 11 , S 23 ) according to the following equations: 
         [0000]        R 1= M 1+ S 11;  R 2= M 2+ S 23; 
         [0000]      and 
         [0000]        Rges=R 1* R 2/( R 1+ R 2_l ). 
         [0000]    The operation further includes calculating the total voltage drop Uges over the parallel-connected resistance branches. The total voltage drop Uges is calculated from the calculated values of the total current Iges and the total resistance Rges according to the equation: 
         [0000]    
       
      
       Uges=Iges*Rges.  
      
     
         [0029]    The operation further includes calculating a voltage difference value U Diff  between the calculated total voltage drop Uges and the prescribed or measured value of the applied supply voltage Vcc or U Vcc  according to the following equation: 
         [0000]    
       
      
       U 
       Diff 
       =U 
       vcc 
       −Uges.  
      
     
         [0000]    The operation further includes comparing the voltage difference value U Diff  with a difference threshhold value U Diff-S . The operation further includes qualifying the current acquisition of the switching position as being erroneous when the difference threshhold U Diff-S  is exceeded by the current voltage difference value U Diff  per the following equations: 
         [0000]        U   Diff   −U   Diff-S &lt;=0→ i.O.; U   Diff   −U   Diff-S &gt;0→“Error”.
 
         [0030]    As described above, the operation for detecting the switch positions of switches SE 1 , SE 2  of this embodiment is focused on the determination of errors that can occur particularly in the common conductors that affect all the resistance branches uniformly. 
         [0031]    Errors of the type that can occur only in a single resistance branch can be detected by an operation for detecting the switch positions of switches SE 1 , SE 2  in accordance with another embodiment. The switch position detection operation in accordance with this other embodiment further enables compensation for this error so that improved availability of the switching device is achieved. 
         [0032]    In this other embodiment, the operation for detecting the switch positions of switches SE 1 , SE 2  includes: measuring the actual voltage drops U M1 , U M2  across the respective measuring resistances M 1 , M 2 ; identifying the respective switch positions of switches SE 1 , SE 2  by comparison of measured voltages U M1 , U M2  with predefined fixed target voltage drop values corresponding to the respective switch positions; and calculating branch currents I 1 , I 2  from measured voltages U M1 , U M2  and the nominal values of measuring resistances M 1 , M 2 . As such, the initial operation process of this embodiment is the same as the preceding described embodiment. Consequently, the two operation processes can be run completely in parallel. 
         [0033]    The operation for detecting the switch positions of switches SE 1 , SE 2  in accordance with this other embodiment further includes the following. The branch voltage drops U 1 , U 2  over the respective resistance branches are calculated. Branch voltage drops U 1 , U 2  are calculated from the respective branch currents I 1 , I 2  flowing in the resistance branches and the respective nominal total value of measuring resistances M 1 , M 2  and the switching resistances effective in the identified switch positions (S 11 , S 23  in this example) according to the following equations: 
         [0000]        U 1= I 1*( M 1+ S 11);  U 2= I 2*( M 2+ S 23). 
         [0000]    The operation further includes forming a voltage difference value U Diff  between the largest of the branch voltage drops U 1 , U 2  and the prescribed or measured value of the applied supply voltage Vcc or U Vcc  according to the following equations: 
         [0000]        U   Diff   =U   Vcc   −U   max , where  U   max =maximum of  U 1,  U 2). 
         [0000]    The operation further includes comparing the voltage difference value U Diff  with a difference threshhold value U Diff-S . The operation further includes qualifying the present acquisition of the switching position as being erroneous when the difference threshhold U Diff-S  exceeds the existing voltage difference value U Diff  per the following equations: 
         [0000]        U   Diff   −U   Diff-S &lt;=0→ i.O.; U   Diff   −U   Diff-S &gt;0→“Error”.
 
         [0034]    The voltage difference value U Diff  with respect to the applied supply voltage U Vcc  is formed from the largest of branch voltage drops U 1 , U 2 , since this determines the voltage level in all resistance branches through the parallel connection of the resistance branches. Smaller voltage drops in the other branches must thereby be caused by perturbation resistances within this branch. In the case of only a single resistance branch, the next operation process described here is identical to the previously described simpler operation process. 
         [0035]    In order to compensate for perturbations, and thus to be able to correct possible measurement errors, in another embodiment, the sequence of procedural steps described in the next to last step establishes branch voltage drops U 1 , U 2  that are scaled up to the designed or measured supply voltage Vcc or U Vcc . To do this, a scaling factor SF 1 , SF 2  is calculated for each resistance branch, which is formed by the quotients of the prescribed value Vcc or measured value U Vcc  of the applied supply voltage and the respective branch voltage drop U 1 , U 2  according to the following equations: 
         [0000]        SF 1= U   Vcc   /U 1;  SF 2= U   Vcc   /U 2 
         [0036]    Measured voltages U M1 , U M2  in the respective branches are multiplied by the scaling factors SF 1 , SF 2  in the next step. The results obtained are compared as always with the prescribed fixed set point values for the different switch positions according to the following equations: 
         [0000]        U   M1 scal= SF 1* U   M1   ; U   M2  scal= SF 2* U   M2 . 
         [0037]    Scaling enables possible error influences that give rise to deviations in the detected measured voltages U M1 , U M2  to be compensated for the values anticipated based on design principles, so that a positive identification of the actual switch positions is made possible by the scaled measured voltages U M1  scal, U M2  scal. 
         [0038]    Effective monitoring of possible error influences is possible by the continuous use of the methods in accordance with embodiments of the present invention during the acquisition of a switching position. The freely definable difference threshhold U Diff-S  can also be used only for signaling an error situation without intervening in the function. 
         [0039]    Slow or phasewise constant changes in the resistance can be readily compensated on the basis of methods in accordance with embodiments of the present invention. The entire state recognition window is thereby available for sudden resistance changes. This increases the availability. 
         [0040]    While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the present invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the present invention.