Abstract:
The invention relates to a method for determining a position point of a movable element, particularly a window ( 33 ) or a roof of a motor vehicle that can be advanced into at least one elastic receptacle ( 36 ) by means of a drive, comprising the steps of continually determining a spring stiffness in relation to the moving element ( 33 ) in the elastic receptacle ( 36 ) and determining a position point upon exceeding a specified spring stiffness threshold value.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    The invention relates to a method for determining a position point of a movable element, particularly of a window or of a roof of a motor vehicle which can be advanced into at least one elastic receptacle by means of a drive. 
         [0002]    Movable elements, in particular windows or roofs, are used, for example, in motor vehicles as electric activated windows or as electric activated sunroofs. The electric closing devices of the windows or roofs which are provided for this purpose have to ensure both a trapping protection, in order to largely prevent injury to the user as a result of trapping body parts, and move the movable element safely into an elastic receptacle, with the result that the movable element, together with the elastic receptacle, seals off the passenger compartment of the vehicle from external weather influences. 
         [0003]    EP 0 883 724 B1 describes an adjustment drive having trapping protection for movable elements, in which the rotational speed and/or the power of the adjustment drive is lowered according to a predefined mathematical function in a specific adjustment range within a predefined position region before the movable element advances into an elastic receptacle, with the result that the movable element advances into the elastic receptacle at a minimum speed. The position for the stopping of the movable element is determined here from the indirectly measured position thereof. 
         [0004]    The position for the stopping of the movable element is subject to wear, voltage fluctuations in the on-board power system of the vehicle or climatic influences on the closing device, with the result that the desired stopping position often does not correspond to the stopping position which is adopted. In order to avoid this, EP 0 697 305 A1 proposes an adjustment drive for windows and sunroofs having a control system which determines the position of the movable element from the power drain of the motor. Locking of the electric motor of the drive is inferred from an increase in the current profile, and stopping of the drive is initiated. This procedure leads to a situation in which the movable element advances into the elastic element in an unbraked fashion and gives rise to clearly audible noise in this way. 
       SUMMARY OF THE INVENTION 
       [0005]    The object of the invention is to make available a method for determining a position point of a movable element, which method reliably determines the desired position point of the movable element. 
         [0006]    The invention recognizes that the locking of a drive of a drive system of a movable element can be avoided by continuously determining and monitoring a spring stiffness during the movement of the movable element, wherein a position point is determined when a threshold value of the drive is exceeded. 
         [0007]    This ensures that the determined position point of the movable element, for example an electrically activated window or an electrically activated sunroof of a motor vehicle, is reliably determined independently of climatic influences, the wear of the elastic receptacle or of the drive system of the movable element. 
         [0008]    According to one embodiment of the invention, after a defined number of advance processes into the elastic receptacle, the position point is determined once more. This has the advantage that the position point is not only adapted to the wear of the elastic receptacle and of the drive system but also to climatic changes, for example fluctuations in temperature. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention will be explained in more detail below with reference to figures, in which: 
           [0010]      FIG. 1  shows a schematic side view of a window during the advancing into an elastic receptacle; 
           [0011]      FIG. 2  shows the current profile of an electric motor plotted over time; 
           [0012]      FIG. 3  shows a flowchart of the method according to the invention; and 
           [0013]      FIG. 4  shows a schematic design of a control device according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The determination of the position point on the basis of the determination of a stopping position in a soft stop region is demonstrated below, wherein the position point corresponds in its position and in its determination to the stopping point. 
         [0015]      FIG. 1  shows a schematic sectional view of a window  33  as a movable element during the advancing into an elastic receptacle  36 . The window  33  is moved by a window lifter  34 , with the result that the passenger compartment of a motor vehicle is opened or closed. In order to open or close the window  33 , the latter can be moved downward or upward. The window  33  is guided laterally in guides (not illustrated) of the vehicle door here. The elastic receptacle  36  has two sealing lips  32 ,  37 , where the sealing lips  32 ,  37  are separated from one another by a recess  35 . When the window  33  advances into the receptacle  35  during a closing process, the window  33  is sealed at its upper edges  38  by contact and by overlapping with the sealing lips  32 ,  37 . When the window  33  advances into the recess  35 , the drive of the window lifter  34  is switched off as soon as the window  33  advances with its upper edge  38  into a soft stop region  31 . The soft stop region  31  constitutes a tolerance region in which the upper edge  38  of the window  33  comes to a standstill without compressing the elastic receptacle  36 , but at the same time the passenger compartment of the motor vehicle is reliably closed off. The desired soft stop region  31  corresponds approximately to the depth  30  of the recess  35 . Stopping position is understood to be the position of the upper edge  38  of the window  33  in which it comes to a standstill. The stopping position can also be located outside the soft stop region  31 . If the window  33  moves so far into the elastic receptacle  36  that the window  33  compresses the elastic, this gives rise to locking of the electric motor of the window lifter  34  and to unnecessary wear of the window lifter in that the mechanism of the window lifter comes to a standstill under stress. The drive of the window lifter  34  is not usually switched off until the latter is locked or a specific position of the window  33  which has been stored in a control device is passed through. As a result of climatic changes, for example fluctuations in temperature, as well as wear of the window lifter  34 , the desired stopping position of the upper edge  38  of the window  33  changes, with the result that the drive of the window lifter  34  is stopped too late and the window  33  compresses the elastic receptacle  36  in such a way that the closing process generates noise. 
         [0016]    In the embodiment, the force profile for the advancing of the window  33  into the elastic receptacle  36  is observed indirectly. The dip in the rotational speed of the electric motor of the window lifter  34  is used to determine the force. For this purpose, the electric motor has a rotational speed sensor with, for example, a Hall sensor. The number of completed revolutions and therefore the position of the window  33  can also be determined by means of the rotational speed sensor. 
         [0017]    In a further embodiment of the invention, the stopping point is used as a position point for calibrating a further system, in particular an anti-trapping system. This has the advantage that the further system can be adapted to wear, voltage fluctuations of the on-board power system or climatic conditions over the service life of the system. 
         [0018]      FIG. 2  shows a diagram of the current profile plotted over time. In this context, the current profile exhibits, in the left-hand half of the diagram, a virtually horizontal profile which corresponds to the opening process or closing process of the window  33  (shown in  FIG. 1 ) by the window lifter  34 . If the window  33  touches the sealing lip  32 ,  37  with its upper edge  38  during the closing process, an increased application of force is necessary to move the window  33 . The increased application of force results in a relatively low rotational speed of the electric motor of the window lifter  34  and in an increased power drain. As a result, the illustrated profile of the power drain corresponds to the required force profile or to the change in force to close the window  33 . As a result of the movement of the window  33  along the sealing lips  32 ,  37 , the power drain increases in the region  41  owing to the slightly tapering side faces of the recess  35 . 
         [0019]    As soon as the required force for advancing the window  33  into the recess  35  has reached a steady state, the power drain forms a plateau-shaped region  43 . When the window  33  is moved further into the recess  35  by the window lifter  34 , the recess  35  tapers to a greater extent in its upper region, with the result that the application of force to move the window  33  increases in the region  44 . After a specific threshold value of the power drain has been exceeded  45 , the drive is switched off and drops to zero in the region  46  in order to prevent locking of the drive. The increase in the recorded force profile or current profile corresponds to a spring stiffness. The spring stiffness is dependent here on the position of the upper edge  38  in the elastic receptacle  36 . The deeper the extent to which the upper edge  38  advances into the recess  35 , the greater the increase in the spring stiffness. If the spring stiffness exceeds a threshold value, the drive of the window lifter  34  is stopped. Locking and stressing of the window lifter  34  can be avoided by prompt stopping  45  of the drive. 
         [0020]      FIG. 3  shows a flowchart of the method according to the invention, wherein both the stopping position in the soft stop region is detected and a stopping position is re-learnt. In the original state  1 , the control device does not have a stored value of the stopping position of the window  33  of the window lifter  34  which is illustrated in  FIG. 1  but only has the threshold values for force and spring stiffness which are necessary for the method according to the invention but are vehicle specific. When the window lifter  34  is activated, the value zero is assigned to a counter in the state  2  in the control device. When the window lifter  34  is moved for the first time, the stopping positions for a closed window or opened window of the window lifter  34  are not known. The stopping positions are determined, for example, by moving the window  33  into the elastic receptacle  36  shown in  FIG. 1  until the window  33  can no longer be moved and the drive locks at the event  13 . This position is stored in a memory of the control device in the state  3 . The learning of the stopping position is necessary since the stopping position serves as a predefined value for a tolerance range in the rest of the method. 
         [0021]    When the window is moved once more during a further closing process, for example in the state  9  or  17 , the position of the window  33  is monitored by using the number of rotations of the electric motor located in the window lifter  34  to calculate the distance by which the window  33  moved, using the transmission ratio of the window lifter  34 . For this purpose, the electric motor has a sensor which, for example, as a Hall sensor which detects the rotations of the electric motor. By virtue of the detection of the rotations of the electric motor, the control device can also determine the movement speed of the window lifter  34 . 
         [0022]    In state  4 , the control device monitors the position of the upper edge  38  of the window  33  during the movement. If the upper edge  38  of the window  33  is in the soft stop region of the elastic receptacle  36  at the event  16 , the control device starts the force monitoring. In this optional event, the current absolute force of the electric motor is determined. As a result, it is possible, for example, to filter out hard impacting of the window  33  in the elastic receptacle  36 . The soft stop region of the elastic receptacle  36  corresponds to a predefined value, the absolute position of said region being dependent on the stopping position determined by means of the state  3 . The force or the change in force can be determined from the decrease in rotational speed of the electric motor of the window lifter  34 . If the force is determined from the rotational speed, the greater the decrease in the rotational speed of the electric motor the greater the increase in the application of force to move the window  33 . However, the force can also take place on the basis of the power drain of the electric motor or by means of direct force measurement at at least one of the components of the window lifter  34 . If the force at the event  15  exceeds, during the observation of said force in the state  5 , a threshold value which is stored in the control device, the control device thus carries out a test to determine whether the soft stop function is available in the state  6 . The soft stop function is understood to mean that the window lifter advances the window  33  into the elastic receptacle  36 , but stops the electric motor in good time so that the window  33  is not moved at its maximum speed up to the end of the recess  35  and compresses the elastic receptacle. This ensures that the closing of the window  33  is completed without significant noise which occurs if the soft stop function is not available. If the soft stop function is not available owing to disruption at the event  10 , the window  33  is moved into the elastic receptacle  36  and stopped when the electric motor locks, and the electric motor is switched off. 
         [0023]    If the stop soft function is available at the event  11 , the control device, when triggered by the threshold value of the force being exceeded, observes a spring stiffness at the event  15 . The spring stiffness can be determined from the force or from the change in force and the distance moved. In this context, the spring stiffness is locally dependent and can therefore be used to position the window  33 . If the spring stiffness exceeds a threshold value at the event  12  during the observation in the state  7 , the motor is stopped in the state  8 . The stopping position which is determined in the soft stop region of the upper edge  38  of the window  33  has the advantage that the elastic receptacle  36  is not compressed and the upper edge  38  of the window  33  is seated securely in the elastic receptacle  36 . Furthermore, in state  8  the value one is added to the present value of the counter of state  2 . If the new value of the counter corresponds, to a predefined second value and there is a comparison in the state  8 , the counter is reset again to zero at the event  14 , and a new advancing process of the window  33  starts from the state  2 . If the new value of the counter at the event  9  does not correspond to the predefined, second value, the value of the counter remains unchanged. If the window lifter  34  is moved once more, the next advancing process of the window lifter  34  does not start in the state  2  but rather in the state  4 . 
         [0024]    The resetting of the counter has the advantage that the stopping position of the upper edge  38  of the window  33  into the recess  35  is checked at regular intervals. In this way, the window lifter  34  can be adapted automatically to wear or to changed climatic conditions since the stopping position is re-determined at regular intervals. 
         [0025]    In addition it is conceivable that the stopping position which is determined is compared with further, previously determined stopping positions, in order to detect faults or defects in the mechanism of the window lifter. The previous stopping positions can be stored, for example, in a storage unit in the control device in order to compare them with the determined stopping position. 
         [0026]      FIG. 4  shows a schematic design of a control device  61  according to the invention. In this context, various modules of a control device  61  of the window lifter  34  which is shown in  FIG. 1  are illustrated symbolically as rectangles. The control device  61  has here a first module  50  for evaluating the force and the spring stiffness, as well as a fourth module  56  which determines locking of the drive and determines a stopping position of the window  33 . Furthermore, the control device  61  has a third module  58  which checks whether a second module  60  is available. The individual modules  50 ,  56 ,  60 ,  58  can be linked to one another by means of data paths  51  to  55 ,  59  via which information is transmitted. In this context, the dynamic information, for example voltage or motor speed of the electric motor of the drive, is transmitted via the data path  51  to the first and third modules  50 ,  58 . The first module  50  determines from this information the force moving the window  33  and the spring stiffness. The second module  60  determines the stopping position of the window  33  from the available information by comparing the spring stiffness with a threshold value, and stops the drive by means of a data path  57 . Likewise, the second module  60  stops the drive if the fourth module  56  transmits information about a locked state of the drive via the data path  55 . The information as to whether the soft stop function of the third module  58  is available is made available via the data path  59 . Like the first module  50 , the third module  58  receives dynamic information about the drive via the data path  51 . By means of the information which is transmitted via the data paths  51  to  55 ,  59 , the fourth module  60  can determine a stopping position which is in the soft stop region, with the result that the wear of the window lifter and the generation of noise during the advancing into the elastic receptacle  36  are reduced. 
         [0027]    The person skilled in the art is, of course, familiar with the fact that the sequence of the individual method steps is exemplary, but it is essential here that a spring stiffness is used to determine the position point or the stopping point of a movable element in order to determine reliably and independently the position of the movable element during the advancing into an elastic receptacle, for example during the opening and closing of a window of a motor vehicle.