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REFERENCE TO RELATED APPLICATIONS  
         [0001]    The present invention claims the benefit of German Patent Application No. 102 53 643.0, filed Nov. 18, 2002.  
         TECHNICAL FIELD  
         [0002]    The present invention relates to a window lifter control system for a motor vehicle and a method of controlling at least two window lifter motors.  
         BACKGROUND OF THE INVENTION  
         [0003]    When an electric window lifter motor of a window lifter fully closes a window pane, the window lifter motor is rotationally driven to close the window pane until the window pane presses against an associated seal on the window frame with a desirably high amount of force, causing the window pane to come to a stop. The window lifter motor is blocked when the window pane is stopped by the seal, causing a high blocking current (e.g.,  30 A) to flow through the window lifter motor. This is acceptable as long as the blocking current flows through only one window lifter motor in the vehicle.  
           [0004]    However, currently available comfort functions in vehicles are able to close all of the window panes of the vehicle simultaneously. In fact, some consumers find it disturbing when, in spite of identical starting positions, different window panes in the vehicle reach the fully closed position at different times even though the associated window lifters received the instruction to close the window panes at the same time. But if all of the window panes are actually closed at the same time, this can result in as many as four window lifter motors being supplied with the blocking current at the same time. The high amount of blocking current to the window lifter motors leads to a noticeable voltage drop in the power supply of the vehicle. This voltage drop is especially critical if the vehicle is provided with other electric systems which have high power requirements themselves, such as an electrical steering system (“steer-by-wire”) or an electrical brake system (“brake-by-wire”). As soon as a control unit in such systems detects the voltage drop, the system may be momentarily disconnected until the voltage drop is over. Obviously, however, it is undesirable in an electrical steering system or an electrical brake system for a functional interruption to occur.  
           [0005]    There is a desire for a window lifter system in which, on the one hand, can meet the demands in relation to comfort (e.g., simultaneous window closing) made by the ultimate customers and, on the other hand, avoids voltage drops in the on-board supply when meeting those demands.  
         SUMMARY OF THE INVENTION  
         [0006]    One embodiment of the invention is directed to a method of controlling at least two window lifter motors. When at least one of the window lifter motors is instructed to close the window pane associated with the motor to it, the method determines whether the window pane is approaching its fully closed position. The method then checks whether any other window pane is approaching its own fully closed position. If any other window pane is approaching its fully closed position, the original window pane is moved only as far as to an approximately closed position rather than its fully closed position. If, on the other hand, no other window pane is approaching its fully closed position, the window pane is moved to its fully closed position.  
           [0007]    The invention generally prevents a plurality of window lifters from fully closing their respectively assigned window panes at the same time. Instead, only the window lifter that is the first one to close the window pane is allowed to close the window pane fully, causing the window lifter motor to block and blocking current to flow. All other window lifter motors in the vehicle are turned off so that the window pane does not reach its fully closed position and only reaches an approximately closed position in which it contacts its associated seal with a low force. The contact gives a vehicle user the impression that the window pane is already fully closed and that all window panes were closed simultaneously.  
           [0008]    Once the first window pane is fully closed, all the remaining window panes will then also be fully closed, occurring in a staggered relationship with respect to one another so that only one single window lifter motor is blocked at any given time when the window pane presses against its corresponding seal. The short time interval between the time the first window pane closes fully and the time the other window panes closes fully will go unnoticed by the user. The minimum adjustment of the window pane from the approximately closed position to the fully closed position will not be detectable by the user of the vehicle, and as a result the invention will not impair user comfort.  
           [0009]    The moment at which each window pane enters a previously defined end zone portion of its travel distance may be used as a criterion for the decision of which window pane should be allowed to be fully closed. This end zone may cover, for instance, the last 4 mm of the distance traveled before reaching the fully closed position. As soon as a window pane enters this end zone, a blocking signal is transmitted by a controller of the respective window lifter and transferred via a bus system to all other window lifter controllers in the vehicle. If any other controller receives the blocking signal when the window pane assigned to it arrives at the end zone, the other controller will not close the window pane fully, but move it only into the approximately closed position.  
           [0010]    As soon as a window lifter has shifted the window pane into its approximately closed position, it is checked in a loop to see whether the previously received blocking signal continues to be applied. As soon as the blocking signal is no longer applied, a counter starts, initiating a waiting time corresponding to each window controller. After the waiting time has elapsed, the window lifter motor for a given window is driven to move the window pane into its fully closed position while a blocking signal is sent at the same time. This prevents any of the other window lifters from simultaneously shifting their respectively assigned window panes from the approximately closed position to the fully closed position. The blocking signals and waiting times stagger the times at which each window is moved to the fully closed position so that only one window is moved to the fully closed position at a time.  
           [0011]    In one embodiment of the invention, the method suppresses detection of multiple window pane closings when the engine of the vehicle is not running because, in this case, there are no expected negative effects if the multiple window closings create a voltage drop in the on-board voltage supply.  
           [0012]    Another embodiment of the invention is directed to a window lifter control system comprising at least two window lifter motors, at least one controller for driving the window lifter motors, and a sensor that detects the position of a window pane assigned to the window lifter motor. The controller includes a checking circuit that checks whether any other window lifter is a transmitting a blocking signal. The system further includes a blocking signal generator, which generates a blocking signal when the window lifter motor causes its corresponding window pane to approach its fully closed position, and a counter that can detect an expiration of a predetermined waiting time. The description below explains the advantages that may be gained using a window lifter control system of this type in more detail. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The invention will now be described with reference to a preferred embodiment which is illustrated in the accompanying drawings, in which:  
         [0014]    [0014]FIG. 1 is a representative diagram of a window lifter system including two window lifters according to one embodiment of the invention; and  
         [0015]    [0015]FIG. 2 is a representative flow diagram of a method that may be sequenced in one of the window lifters of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0016]    [0016]FIG. 1 is a representative diagram of a window lifter system according to one embodiment of the invention and FIG. 2 is a flow diagram of a method according to one embodiment of the invention. Note that although FIG. 1 shows only two window lifters  5 ,  7  for illustrative purposes, the system may include more than two window lifters without departing from the scope of the invention.  
         [0017]    In the embodiment shown in FIG. 1, each window lifter  5 ,  7  has a window lifter motor  10  which acts on a window pane  14  of a vehicle via an adjustment mechanism  12 . The window pane  14  is adapted to be shifted within a window frame  16 , which is provided at least at its upper edge with a seal  18 , shown schematically in FIG. 1. The window pane  14  can be moved in the window frame  16  by the window lifter motor  10 .  
         [0018]    A controller  20  is provided for driving the window lifter motor  10 . The controller  20  is usually disposed inside the vehicle door in which the window pane  14  is guided and is therefore frequently referred to as a door control module. Each controller  20  drives the window lifter motor  10  by, for example, pulse width modulation. A sensor  22  is provided on the window lifter motor  10  through which a position recognition circuit  24  inside the controller  20  may sense the absolute position of the window pane  14 . In one embodiment, the sensor  22  may be a Hall effect sensor.  
         [0019]    The controller  20  further includes a counter  26  that generates a waiting time. In one embodiment, the counters associated which each controller  20  differ from one another so that each controller  20  in the vehicle each has its own unique waiting time.  
         [0020]    Each controller  20  further contains a blocking signal checking and generating circuit  28 , each of which is able to generate a blocking signal and to sense whether any other controller generates such blocking signal.  
         [0021]    The controllers  20  are connected to a bus system  30 , such as a CAN bus.  
         [0022]    The operation of the window lifter system will now be described when it is intended to close the window panes  14 , reference being also made to the flow chart of FIG. 2.  
         [0023]    When a vehicle user wishes to close a particular window pane  14  such as, for example, the window pane associated with the right-hand window lifter  7  in FIG. 1, the user actuates the appropriate window lifter switch so that the controller  20  drives the window lifter motor  10  in the proper direction for the window pane  14  to be closed. During the closing process of the window pane  14 , the absolute position of the window pane  14  sent to the controller  20  at all times since the sensor  22  continuously supplies information about the position of the window lifter motor  10 .  
         [0024]    When the window pane  14  arrives at an end zone E, which is defined as, for example, the last 4 mm of the closing travel before reaching the fully closed position, the blocking signal checking and generating circuit  28  checks, by way of the bus system  30 , whether any other controller  20  is transmitting a blocking signal  32 . The blocking signal may be, for example, one bit that is encoded in a specific way corresponding to a given controller  20  with the bus system  30 , with each bit encoded in a unique manner to correspond with its associated controller  20 . In the example shown in FIG. 1, the blocking signal checking and generating circuit  28  of the controller  20  of the left-hand window lifter  5  does not send a blocking signal. Therefore, the blocking signal checking and generating circuit  28  of the controller  20  associated with the right-hand window lifter  7  will now generate a blocking signal, which is transmitted to all other controllers  20  in the vehicle via the bus  30 .  
         [0025]    At the same time, since the blocking signal checking and generating circuit  28  of the right-hand window lifter  7  is not currently receiving a foreign blocking signal, the right-hand window lifter motor  10  continues to be supplied with power until the window pane  14  comes up against the seal  18  at full power and comes to a stop. As a result of this, the right-hand window lifter motor  10  is also braked to a standstill and the window lifter motor  10  consumes its blocking current. The high torque produced by the window lifter motor  10  in this condition ensures that the right-hand window pane  14  is pressed against the seal  18  with a desirably high force to ensure that the window pane  14  is fully closed tightly.  
         [0026]    The window pane of the left-hand window lifter  5  is also closed at approximately the same time as the window pane  14  of the right-hand window lifter  7 . However, since the window pane of the left-hand window lifter  5  slightly lags behind the window pane of the right-hand window lifter  7 , the window pane  14  of the left-hand window lifter  5  will enter the end zone slightly later than that of the right-hand window lifter  7 . At the moment the controller  20  detects that the left-hand window pane  14  has arrived at the end zone E, the blocking signal checking and generating circuit  28  detects that a foreign controller  20  is generating a blocking signal, namely the controller  20  of the right-hand window lifter  7 . The left-hand window lifter motor  10  is therefore stopped before the window pane  14  rides up on the seal  18  and is braked by the window pane  14 ; in other words, the left-hand window lifter motor  10  is stopped so that the window pane  14  is in an approximately closed position in which it contacts the seal  18  with a low force.  
         [0027]    The controller  20  subsequently checks whether any foreign blocking signal is continuing to be received. As soon as the controller  20  no longer detects a foreign blocking signal, the counter  26  is activated, which generates a specific time delay or waiting time. After expiration of this time delay, the blocking signal checking and generating circuit  28  transmits its own corresponding blocking signal while the left-hand window lifter motor  10  is at the same time supplied with power so that the left-hand window pane travels from the approximately closed position to the fully closed position until it is braked by the seal  18  and until the left-hand window lifter motor  10  is blocked.  
         [0028]    While only two window lifters are shown in FIG. 1, it is readily apparent that the window panes can be closed in a time-staggered as described above and as shown in FIG. 2 when more than two window lifters are provided. In the case of systems having more than two window panes and more than two associated window lifters, only the window pane that is the first to enter the end zone E is closed fully without interruption, whereas all other window panes will be stopped at the approximately closed position and closed one after the other in a staggered fashion into the fully closed position based on the different waiting times as generated by the counter  26  of each respective controller  20 .  
         [0029]    It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby.

Summary:
A window lifter system and method coordinates closing of multiple windows by detecting when more than one window pane is approaching a fully closed position and moving one window pane to only an approximately closed position while the other window pane is moved to the fully closed position. By staggering the closure of window panes to the fully closed positions, the system and method provides the illusion that all of the window panes are being closed at the same time while avoiding voltage drops in the vehicle power supply caused by excessively high blocking currents generated when multiple window panes are moved to the fully closed position.