Abstract:
Wiper system, in particular for a motor vehicle, having at least one wiper ( 12 ) supported in a fashion that allows it to swing between two end positions, that can be driven by a—particularly electronically—reversible electric motor ( 20 ) so that the swing angle ( 16 ) enclosed by the two end positions of the wiper ( 12 ) is determined by reversing positions ( 38, 40 ) of the electric motor, wherein at least one reversing position ( 38, 40 ) of the electric motor ( 20 ) can be controlled as a function of vehicle speed.

Description:
BACKGROUND OF THE INVENTION 
   The invention concerns a wiper system, in particular for a motor vehicle, according to the general class of the independent claim. The objective of this wiper system is to achieve a course of wiping that is as uniform as possible. 
   Wiper systems for motor vehicles having controllable wipers have already been made known, e.g., in DE 198 18 173 A1, in which the speed of the wipers is controlled as a function of position and vehicle speed. 
   SUMMARY OF THE INVENTION 
   The wiper system according to the invention has the advantage that the reversal positions or end positions of the wiper can be kept constant independent of the vehicle speed by changing the reversing position of the wiper motor. The elasticities present in the linkage of the wiper system can be compensated for in this fashion by changing the reversal points of the wiper motor. 
   The specified wipe pattern can be maintained exactly without an external sensor, such as a wind speed indicator, because the wind velocity is nearly proportional to the vehicle speed, particularly at the relevant high velocities. 
   Advantageous further developments and improvements of the features indicated in the primary claim result from the measures listed in the subclaims. 
   It is particularly advantageous when the wiper system comprises a memory device in which the reversing positions are stored, e.g., in the form of a table, as a function of the speed of the motor vehicle. In this fashion, the reversing positions can be implemented easily and quickly in the wiper system. 
   It is also advantageous when the wiper system comprises a central processor that determines the reversing positions of the electric motor using the vehicle speed so that more complex algorithms can also be used to control the reversing positions as a function of the vehicle speed. 
   Furthermore, it is advantageous when the wiper system comprises an emergency operation step in which the reversing positions are permanently specified that is triggered when vehicle speed information is missing. If defects occur in the tachometer or a corresponding connecting lead, a sufficiently large wipe pattern can always be guaranteed in this fashion. 
   Since the aerodynamic effects work in opposite directions in conventional wiper systems having wiping angles in the range of 90° between the two end positions, it is particularly advantageous when the reversing positions have the same difference, independent of vehicle speed. 
   It is furthermore advantageous when, if the difference of the reversing positions remains the same, they can be shifted as a function of vehicle speed. Resources can be spared in this fashion while simultaneously ensuring a consistently large wipe pattern, even at high velocities. 
   It is also advantageous when the wiper system comprises a rain sensor, because the wiper system can then be controlled in this fashion as a function of a humidity signal, so that optimal cleaning results can always be achieved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     An exemplary embodiment of the invention is shown in the drawings and explained in greater detail in the description hereinafter. 
       FIGS. 1   a  and  1   b  show a schematic representation of a windshield of a motor vehicle having two wipers, 
       FIGS. 2   a  and  2   b  are schematic representations of one side of a linkage of a wiper system according to the invention, 
       FIG. 2   c  is a diagram in which the motor voltage is plotted as a function of time t, 
       FIG. 3  is a schematic representation of a wiper system according to the invention. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A windshield  10  having the prescribed area of vision  11  and two wipers  12  located in the lower end position is shown in  FIG. 1   a . During operation, the wipers  12  swing between the bottom end position and the top end position  14  around the wiper axles  30 . The wipers  12  enclose a swing angle ( 16 ) between top and bottom end position. 
   During operation, an air stream occurs over the windshield  10  as a result of the motion of the vehicle. The air stream is indicated by the flow arrows  18  in the diagram. As a result of this air stream, the wipers  12  are pushed further and further upward at higher vehicle speeds. The bottom end position of the wipers  12  is therefore shifted upward at higher vehicle speeds due to the elasticities in the wiper system. 
   A windshield  10  having two wipers  12  is also shown in  FIG. 1   b . The two wipers  12  are located in the top end position. The air stream on the windshield  10  is indicated by flow arrows  18  in this drawing as well. 
   Due to the shape of the windshield  10 , the wipers  12  are pushed outward by the air stream at higher vehicle speeds. The top end position of the wipers  12  is therefore pushed outward even further at higher vehicle speeds. 
     FIGS. 2   a  and  2   b  show a schematic representation of a linkage of a wiper system according to the invention. 
   One side of a wiper linkage is shown in the bottom end position in  FIG. 2   a . The wiper axle  30 , to which the wiper  12  is attached, is moved by the oscillating cranks  32 , which are driven by the wiper motor  20  via the cranks  34  and the couple rods  36 . Since the wiper motor  20  is designed as a reversing motor, it can reverse in any position, that is, its direction of rotation and, therefore, the wiping direction, can change at any random point. 
   The solid lines show the wiper linkage in the bottom end position of the wipers  12  when the vehicle is at a stop. The wiper motor  20  is also located in a bottom reversing position  38  in this [drawing]. This bottom reversing position  38  can also be used at low velocities, of course. 
   The reversing position  38  is thereby meant to be understood as the angle of rotation α of the wiper motor  20  relative to a fixed—although random—reference line  37 , at which the direction of motion of the wiper motor  20  is reversed during operation. Due to the elasticities of the cranks  34 , their angle of rotation is not necessarily identical to the angle of rotation of the reversing position. 
   The broken lines represent the wiper linkage during driving at high speeds. The reversing position  38  of the wiper motor  20  for the bottom end position of the wipers  12  is shifted slightly here—in the direction, in fact, where the wiper  12  would reverse at a lower position. Due to the air stream, however, the wiper  12  will never be located in this indicated position, but rather is always pushed into the same bottom end position, which, as a rule, is situated higher up during driving. 
   The wiper linkage is shown in  FIG. 2   b  as in  FIG. 2   a , and the wiper  12  is now located in the top end position  14 . 
   Analogous to  FIG. 2   a , the solid lines show the wiper linkage in the top end position  14  of the wipers  12  when the vehicle is at a stop. In this case, the wiper motor  20  is located in the top reversing position  40 . 
   The broken lines show the wiper linkage during driving at high speeds. The reversing position  40  of the wiper motor  20  for the top end position  14  of the wipers  12  is shifted slightly inward here. The wiper  12  is always pushed into the top end position  14  by the air stream, however. 
   Two diagrams are shown in  FIG. 2   c , in which the electrical voltage at the wiper motor  20  is plotted as a function of time. The top diagram represents a vehicle at a stop. The bottom diagram represents a vehicle travelling at a high rate of speed. 
   The characteristic curve of voltage basically corresponds to a rectangle function with edges  44 , although this curve can also have an entirely different character. A reversal of the polarity of the wiper motor  20  takes place at the edges  44  of the voltage curve in each case. Each edge  44  therefore corresponds to the top or bottom reversing position  38 ,  40  in each case. For purposes of clarification, the wiper motor  20  with the crank  34  was also drawn above each characteristic curve of voltage. 
   The comparison of the two diagrams shows that the wiper motor  20  reverses at earlier points in time when the vehicle is travelling at a high rate of speed, but these points in time can be set at random as necessary. 
   The crank  34  is thereby reversed in other positions, which has an effect on the wipers  12  via the remaining linkage. The displacements of the reversing positions  38 ,  40  of the wiper motor  20  are designed just great that reversal nevertheless takes place by the wipers  12  in the same end positions. 
   A schematic representation of a wiper system according to the invention is shown in FIG.  3 . The wiper motor  20 , which is typically designed as an electronically reversible electric motor, is controlled by control electronics  22 . 
   The wiper motor  20  is thereby provided with a position sensor  21  that is designed as a Hall effect sensor, for example, and the signals of which are sent to the control electronics  22 . The wiper motor  20  can be controlled by the position sensor  21  and the control electronics  22  so that random positions of the wipers  12  can be moved into at any time. In this fashion it is possible to allow the wipers  12  to reverse at any point on the windshield  20  by changing the polarity of the input voltage of the wiper motor  20 , that is, to select the reversing positions  38 ,  40  of the wiper motor  20  at random. 
   The control device  22  receives signals of the vehicle speed  24 , which can be derived from the tachometer available in every motor vehicle, for instance. Furthermore, the control device  22  receives signals from the control lever  26 , which is preferably designed as a switch on a steering column. Further signals, such as signals from a rain sensor  28 , can also be fed to the control device  22 , of course, and incorporated in the processing. The control device  22  comprises a memory device  23  and a central processor  23   a  for this purpose. 
   The function of the wiper system according to the invention is explained hereinafter. 
   When a vehicle is at a stop, that is, when the vehicle speed is zero, the wipers  12  reverse between the top and the bottom end position. A certain reversing positions of the wiper motor  20  correspond to these end positions when the vehicle is at a stop. Since, as illustrated in  FIG. 1   a , the end positions of the wipers  12  would shift upward with increasing vehicle speed due to the elasticities in the wiper system, the reversal positions of the wiper motor  20  are shifted according to the invention so that the end positions of the wipers  12  remain constant at all vehicle speeds. 
   Since the wiper  12  is pushed further and further upward with increasing vehicle speed, the wiper motor  20  moves the wiper  12  further downward, just so far that the end position of the wiper  12  at which it reverses remains constant. For this, the crank  34  is displaced by the wiper motor  20  further than would be necessary if the vehicle were at a stop. That is, with increasing speed of the vehicle, the bottom reversing position  38  of the wiper motor  20  is pushed further downward and, in fact, just so that a displacement of the end position of the wiper  12  is prevented. 
   Conversely, the wipers  12  are pushed further outward in the top end position with increasing vehicle speed. To compensate for this, the top reversing position  40  is shifted inward. This means that the crank  34  is displaced by the wiper motor  20  less far than it would be if the vehicle were at a stop. 
   The elasticities of the wiper system are equalized in this fashion, as a result of which the wiper  12  itself always reverses in the same end positions on the windshield at all speeds. 
   In  FIG. 2   a , the wiper linkage  32 ,  34 ,  36  is shown in the bottom reversing position  38  at a lower vehicle speed using solid lines, and the wiper linkage  32 ,  34 ,  36  is illustrated at a high vehicle speed using broken lines. At a higher vehicle speed, therefore, the bottom reversing position  38  is displaced by the angle δ. 
   In  FIG. 2   b , the top reversing position  40  is shown at a high vehicle speed using broken lines, and at a low vehicle speed using solid lines of the wiper linkage  32 ,  34 ,  36 . Analogous to  FIG. 1   a , the top reversing position  40  is displaced by the angle γ here at a high vehicle speed. 
   In a variant of the wiper system according to the invention, the difference between the bottom reversing position  38  in  FIG. 2   a  and the top reversing position  40  in  FIG. 2   b  can also remain constant. With increasing vehicle speed, the angles δ and γ then become identically greater, which means that the difference of the reversing positions  38 ,  40  remains constant, although they both shift evenly.