Abstract:
The invention relates to a wiper motor control for controlling a wiper motor that moves a wiper arm in a pendulum motion between two turning positions, said wiper motor control being designed to control a speed of the wiper arm dependent on a position of the wiper arm. The speed of the wiper arm in turning regions, which comprise the turning positions, follows a specified progression independent of the speed of the wiper arm between the turning regions.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Wiper systems, as they are used, for example, in motor vehicles, serve to keep a window pane free of moisture and contaminations. To meet this end, a wiper blade on a wiper arm is usually guided across the window pane. The wiper arm is moved in an oscillating manner around a point of rotation so that the wiper blade covers an approximately circularly segmented region of the window pane. 
         [0002]    In order to control a drive motor for the wiper arm, different approaches are known from prior art. Provision is made in the German patent publication DE 10 2006 061 679 A1 to drive the drive motor in such a way that a wiping frequency is dependant on a size of a load on the drive motor. In this way, the window pane is wiped more seldomly by the wiper blade if said window pane is almost dry. 
         [0003]    Provision is made in the German patent publication DE 10 2005 048 343 A1 for the drive motor to be actuated such that a lower region of the window pane is wiped faster by the wiper blade than an upper region. In so doing, a wiper availability can be increased in a visibility region of the window pane. 
         [0004]    In the German patent publication DE 100 24 255 A1, the wiper motor control is designed such that turning positions of the drive motor can be controlled as a function of a wind speed in the region of the wiper blade in such a way that the region of the window pane being wiped by the wiper blade remains constant. 
       SUMMARY OF THE INVENTION 
       [0005]    The aim underlying the invention is to specify a wiper motor control, which facilitates an improved wiping at a lower wiping frequency. 
         [0006]    In order to actuate a wiper motor which moves a wiper arm in a pendulum motion between two turning positions, a wiper motor control is designed to control a speed of the wiper arm dependant on a position of said wiper arm, wherein the speed of said wiper arm in turning regions, which comprise the turning positions, follows a specified progression independent of the speed of said wiper arm between the turning regions. 
         [0007]    A reduction in the speed of the wiper arm in a region between the turning positions can therefore be implemented without a rattling or clattering of a wiper blade attached to the wiper arm being produced as a result of too low a speed of said wiper arm. A very low wiper frequency can thus be achieved in the continuous wiper operation without having to accept noise emissions, a reduction in wiping quality and premature wear to the surface of the window pane or other parts of the wiper system as a result of the rattling or clattering of the wiper blade. 
         [0008]    The progression of the speed in the turning regions can substantially follow a sine function. This speed progression can keep the mechanical stress on one or all of the parts of the wiper system low. 
         [0009]    Between the turning regions, the speed of the wiper arm can be less than the maximum of the sinus function. The advantages of the sinusoidal speed progression in the turning regions can thus be combined with a lower speed between said turning regions. 
         [0010]    The wiper motor can be coupled to the wiper arm by means of a crank mechanism and the wiper motor control can be equipped for the purpose of keeping the rotational speed of the wiper motor constant while the wiper arm is located in one of the turning regions. In this way, conventional wiper mechanics can be used in order to support a sinusoidal speed progression of the wiper arm. 
         [0011]    The wiper motor control can be equipped to keep the rotational speed of the wiper motor at a lower speed between the turning regions than in the turning regions. A sinusoidal speed progression having an extended period of the sinus function results thereby in the region between the turning regions. This type of actuation is simple and cost effective to implement and can contribute to minimizing the mechanical stress on the wiper system. 
         [0012]    The wiper motor control can furthermore comprise a device for determining whether a power consumption of the wiper motor lies above a predetermined threshold value. The control of the speed of the wiper arm can therefore first be carried out in the described manner if, e.g., the concrete danger of rattling exists due to high friction between the wiper blade and the window pane. 
         [0013]    In addition, the wiper motor control can comprise a device for determining whether a time that elapses until the wiper arm is moved from one turning position to the other turning position lies above a predetermined threshold value. The specific speed control in the turning regions is advantageously carried out as a function of the result of the determination of the device only below a predetermined wiper frequency which corresponds to the predetermined time. 
         [0014]    The wiper motor control can furthermore comprise a device for determining whether a wind speed in the region of the wiper arm lies above a predetermined value. The wiper motor control described can thus advantageously determine a concrete rattling tendency using the wind speed and correspondingly carry out the described speed control. 
         [0015]    A method for controlling a wiper motor, which moves a wiper arm in a pendulum motion between two turning positions, furthermore comprises steps for determining whether the wiper arm is situated in one of two turning regions, which lie around the turning positions, and steps for actuating the wiper motor such that a speed of the wiper arm in the turning region follows a rigidly specified progression independently of the speed of the wiper arm between the turning regions. 
         [0016]    The method can advantageously be implemented in an, for example, electronic wiper motor control. The advantages of the described technology can thus be realized in a cost effective manner using existing components of a wiper system. 
         [0017]    In addition, a computer program product comprises program code means for carrying out the described method if the computer program product is stored on a computer-readable data carrier or run on a processing device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The invention is now described in detail with reference to the enclosed figures, in which: 
           [0019]      FIG. 1  shows a wiper system for a window pane of a motor vehicle; 
           [0020]      FIG. 1   a  shows an alternative to the crank mechanism from  FIG. 1 ; 
           [0021]      FIG. 2  shows a progression of a speed of the wiper arm from  FIG. 1 ; 
           [0022]      FIG. 3  shows further progressions of speeds of the wiper arm from  FIG. 1 ; and 
           [0023]      FIG. 4  shows a diagram of a load dependent wiper motor control of the wiper system from  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0024]      FIG. 1  shows a wiper system  100  which is disposed in a motor vehicle  105 . The wiper system  100  is equipped to clean a window pane  110  of the motor vehicle  105 . The window pane can be a front windshield or a rear window of the motor vehicle  105 . 
         [0025]    A wiper blade  115  is fastened to a wiper arm  120 , which moves the wiper blade  115  across the window pane  110  in an oscillating motion about a center of rotation. In so doing, the said wiper blade  115  pushes aside moisture and foreign bodies out of a circularly segmented region so that the window pane is cleaned. Further wiper arms  120  comprising further wiper blades  115  are not depicted in  FIG. 1 , which can be pivoted by the same crank mechanism  125  in order to clean further regions of the window pane  110 . 
         [0026]    The wiper arm  120  is driven by means of a crank mechanism  125  of a wiper motor  130 . The wiper motor  130  supplies a rotational motion which is converted into an oscillating motion. Said wiper motor  130  can, for example, be in a commutated or brushless DC motor comprising or without reduction gears. Said wiper motor  130  is electrically actuated by a wiper motor control  135 . The wiper motor control  135  can, for example, control a voltage, a current or a temporal duty cycle of a pulsating current supply of said wiper motor  130 . The wiper motor  130  can especially control one of the electrical parameters of said wiper motor  130  and scan one or a plurality of additional electrical parameters of the wiper motor  130 . Said wiper motor control  135  can, for example, control the voltage of said wiper motor  130  and thereby scan a current consumption of the wiper motor  130 . 
         [0027]    The wiper motor control  135  is connected to a selector switch  140 , with which a driver of the motor vehicle  105  can select a function of a functional mode of the wiper system  100 . The selector switch  140  can, for example, have a first position for turning the wiper system  100  off, a second position for wiping in the interval operation, a third position for slow continuous operation, a fourth position for fast continuous operation and a fifth position for an automatic operation. 
         [0028]    The wiper motor control  135  is further connected to a rain sensor  145  or an interface to a rain sensor  145 . Signals, which the wiper motor control  135  receives from the rain sensor  145 , can, for example, influence the running of the wiper operation, in particular in positions 2 (interval) and 5 (automatic) of the selector switch  140 . The signals received by the rain sensor  145  can alternatively or additionally control a transition between the operating modes which can be selected by means of the selector switch. 
         [0029]    The wiper motor control  135  is also connected to a speed sensor  150  or to an interface to a speed sensor  150 . Said wiper motor control  135  can, for example, be connected to a data bus or to an integrated control of a part of the motor vehicle  105  in order to receive a speed signal of the motor vehicle  105 . The signals received using the speed sensor  105  are used by the wiper motor control  135  to control the wiping operation of the wiper system  100  as a function of a wind speed in the region of the wiper arm  120  which is associated with the speed of the motor vehicle  105 . 
         [0030]    Finally the wiper motor control  135  is connected to a position sensor  155 , which scans at least one of the positions of the wiper motor  130 , the crank mechanism  125  or the wiper arm  120 . On the basis of the signals received by the position sensor  155 , the wiper motor control  135  actuates accordingly the wiper motor  130  in different positions of the wiper arm  120 . 
         [0031]      FIG. 1   a  shows a continuous gear train assembly in the form of a reduction gear unit  160  as an alternative to the crank mechanism  125  in  FIG. 1 ; the wiper motor  130 , the wiper arm  120  and the position sensor  155  being likewise depicted in  FIG. 1   a.  The reduction gear unit  160  directly actuates the wiper arm  120 , wherein in one embodiment, the axis of rotation of the wiper arm  120  coincides with the output axis of the reduction gear unit  160 . An angular position of the wiper motor  130  is directly proportional to an angular position of the wiper arm  120 . Such an arrangement is called a “direct drive” and is suited to the invention without restrictions. 
         [0032]    The oscillating operation of the wiper arm  120  of  FIG. 1  is achieved by controlling the rotational direction of the wiper motor  130 . A speed control of said wiper motor  130  ensures a harmonic speed progression of the wiper arm  130 , wherein the speed progression at least approximates the substantially sinusoidal speed progression, which is produced by the use of the crank mechanism  125  in  FIG. 1 . The reduction gear unit  160  can comprise a spur gear unit, planetary gear set, worm gear pair or belt drive or any other desired gearing, which produces a scaling factor of the rotational motion of the wiper motor  130  that is independent of the angle of rotation in the rotational motion of the wiper arm  120 . 
         [0033]    In other embodiments of the wiper system  100 , the rain sensor  145 , the speed sensor  150  and/or the position sensor  155  can also be omitted. In addition, the drive motor  130  can also act on the wiper arm  120  via a rotary gear unit, for example a spur gear unit or a planetary gear set, whereby the crank mechanism  125  is omitted. Such a wiper system is also referred to as a “direct drive”. 
         [0034]      FIG. 2  shows a progression of a speed of the wiper arm  120  of the wiper system  100  from  FIG. 1 . A speed v is plotted in a vertical direction. In a corresponding manner, the speed v can represent an angular speed of the wiper arm  120  with respect to the window pane  110  from  FIG. 1  or any desired point of the wiper blade  115  vis-B-vis said window pane  110  from  FIG. 1 . A time t is qualitatively plotted in a horizontal direction. In the contexts described below, a position of the wiper arm  120  could also be used as the reference value instead of the time t because the relationship between the speed v and the position of the wiper arm  120  is of significance. After the relationship between the position of the wiper arm  120  and the time t is clearly defined but is not necessarily linear, the time t is used as the reference value to facilitate understanding. 
         [0035]    A first progression  210  depicts a speed progression of the wiper arm  120  during continuous normal operation. The speed progression  210  has the form of a sine wave, of which only one complete period is depicted. The speed is zero at the turning positions WL of the wiper arm  120 . The first progression  210  occurs, for example, if in  FIG. 1  the wiper motor  130  runs with a constant rotational speed and the crank mechanism  120  provides the oscillating motion of the wiper arm  120  from this uniform rotational motion. At the points, at which the first progression intersects the horizontal axis, said wiper arm  120  is situated at a turning position, i.e. at the upper most or lowest achievable position on the window pane  110  from  FIG. 1 . 
         [0036]    A second progression  220  represents a decelerated operation of the wiper system from  FIG. 1 . The second progression  220  has the form of a sine wave which corresponds to the first progression  210  and of which only one complete period is depicted. The period of the second progression  220  is longer than that of the first progression  210  and the amplitude of the said second progression  220  is less than that of the first progression  210 . 
         [0037]    A critical speed  230  is depicted as a pair of horizontal straight lines. If the amount of speed v lies below the amount of the critical speed  230 , therefore between the straight lines, the wiper blade  115  then tends to rattle. When rattling, said wiper blade  115  executes an uneven motion across the window pane  110  which negatively impacts the wiping performance. When rattling, said wiper blade  115  can be set into vibrational motion, which travels about an attachment point of said wiper blade  115  to the wiper arm  120 . Such a rattling motion is thereby promoted in that the path which is wiped by the lowest point of said wiper blade  115  on the window pane  110  is much shorter than the path of the region of the window pane  110  that is wiped by the upper most point of said wiper blade  115 . The tendency to rattle is additionally dependent on a frictional coefficient of said wiper blade  115  on the window pane  110 . The frictional coefficient is dependent on moisture in a region between said wiper blade  115  and the window pane  110  and on the speed of said wiper blade  115  with respect to said window pane  110 . The frictional coefficient increases exponentially with decreasing speed of said wiper blade  115  with respect to said window pane  110 . 
         [0038]    The first progression  210  passes through the region of the critical speed  230  within a time t 1 , which is substantially less than a time t 2  of the second progression  220 . During the decelerated operation of the second progression  220 , the probability of rattling of the wiper blade  115  on the window pane is accordingly greater. In other words, the slower the wiper motor  130  runs, the more probable is a rattling of said wiper blade  115  in regions around the upper and lower turning position WL. A region, within which one of the speed progressions  210  or  220  lies in the region of the critical speed  230 , is labeled as the turning region WB. The size of the turning regions WB depends on the selection of the critical speed  230 . 
         [0039]      FIG. 3  shows further advantages of speeds of the wiper arms  120  with respect to the window pane  110  from  FIG. 1 . The material depicted in the diagram  300  corresponds to the material depicted in  FIG. 2  including the first progression  210  and the critical speed  230 . In addition, a third progression  310  and a fourth progression  320  are plotted. 
         [0040]    In the three depicted progressions  210 ,  310  and  320 , the time t 1  is identical, during which said progressions  210 ,  310  and  320  are situated in accordance with the amounts thereof below the critical speed  230 . Within the turning regions determined by the times t 1 , the progressions  210 ,  310  and  320  correspond to the sinus function of the first progression  210 . Outside of the turning regions WB, the third progression  310  and the fourth progression  320  are flattened differently with respect to the first progression  210 . The speed of the wiper arm  120  or respectively the wiper blade  115  is reduced with respect to the window pane  110  up to approximately the boundary of the critical speed  230 , whereby a rattling of the wiper blade  115  on the window pane  110  is still not risked. The cycle time or respectively the length of the period of the progressions  310  and  320  is thereby extended; thus enabling a cleaning of the window pane  110 , even wherein few wiper periods per time unit occur, to be carried out during the continuous operation of the wiper system  100 . Such a demand occurs, for example, in the case of fog or very light rain. 
         [0041]      FIG. 4  shows a diagram of a load dependent wiper motor control  135  of the wiper system  100  from  FIG. 1 . A time t is plotted in the horizontal direction in seconds and a number of wiper cycles per minute and a wiper load (without units) is plotted in the vertical direction. A wiper cycle corresponds thereby to a full period of one of the progressions  210 ,  220 ,  310  or  320 . 
         [0042]    The window pane  110  is wet between the points in time A and B. Said window pane  110  gradually dries between the point in time B and the point in time C and then remains approximately dry up to a point in time D. At the point in time D, said window pane  110  quickly becomes wet again and remains wet up to the end of the depicted progression. 
         [0043]    A qualitative progression  410  indicates an average mechanical load on the wiper motor  130  in  FIG. 1 . The load progression  410  can, for example, be determined on the basis of a current measurement of the wiper motor  130  when the voltage stays constant. The dryer the window pane is, the higher the load is in the load progression  410  so that a degree of wetness of the window pane  110  can be determined on the basis of the current measurement, and the wiping frequency can be adapted to the degree of wetness. 
         [0044]    In a wiper system  100  which is controlled as a function of the load progression  410 , the wiping cycle progression  420  results. After it has been determined by the wiper motor control  135  at the point in time C that the window pane  110  is dry, the frequency of the wiping cycles of 40 cycles per minute (cpm) is continuously lowered. With the aid of the procedure described above especially with reference to  FIG. 3 , it is possible to maintain a continuous wiping up to a lower limit of approximately 20 cycles per minute. That means that the wiper system  100  can still be operated in the continuous mode even at very small moisture levels of the window pane  110  instead of having to switch to the interval mode. Conventional wiper systems  100 , which carry out a lowering of the wiper speed corresponding to the progression  220  in  FIG. 2 , do not typically operate below a cycle frequency of 40 cycles per minute while maintaining an acceptable rattle tendency of the wiper blade  115  on the window pane  110 . A slow continuous operation corresponding to the third position of the selection switch  140  in  FIG. 1  typically corresponds to approximately 40 to 45 cpm, a faster continuous operation corresponding to the fourth position of the selection switch  140  in  FIG. 1  to approximately 60 to 70 cpm. 
         [0045]    After the window pane  110  has been wetted at the point in time D, the wiper cycle progression  420  increases correspondingly sharply to a value of approximately 40 cycles per minute. The absolute numbers of cycles that are depicted are used by way of example and should not be seen as a limiting factor. 
         [0046]    The invention is suited to actuating a wiper motor preferably on board of a motor vehicle  105 ; however, use in other means of transportation such as ships or airplanes or in a stationary operation is also possible.