Abstract:
The invention relates to a method for controlling the movement of a wiper blade over a wiping surface, including the steps of moving the wiper blade up and down over the wiping surface between a lower turning position and an upper turning position, detecting a requirement to stop the wiper blade, moving the wiper blade downward into a lower end position and from there upward into a first parking position in the event that a reversing signal is present, and stopping the wiper blade. To this end, the wiper blade is moved into the lower end position only if previously thereto low mechanical resistance against the movement of the wiper blade over the wiping surface was determined.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a method and a device for controlling the movement of a wiper blade over a surface. 
     In order to rid a windscreen on a motor vehicle of contaminants and moisture, a wiper blade is moved across the screen in a reciprocal motion. For this purpose the wiper blade is usually mounted on a wiper arm, which is driven about a wiper shaft in an oscillatory motion. The wiper blade comprises a wiper lip, which rests on the windscreen and is pulled across it. The wiper lip is pulled by the wiper blade, so that for each change of direction of the wiper blade or the wiper arm, the wiper lip changes the side with which it is resting on the windscreen. 
     In order to avoid the wiper lip becoming brittle on one side, the wiper blade is moved prior to the wiper system stopping, so that the wiper lip is brought into a predetermined placement position. The placement position can, for example, be changed periodically, either under timer control or after a predetermined number of placements of the wiper lip in the same placement position. The placement positions of the wiper blade on the windscreen are always located in a lower area on the windscreen. 
     Investigations have shown that with dry or very dirty windscreens, a movement carried out by the wiper arm in order to bring the wiper lip into the predetermined placement position can cause the wiper arm to strike a boundary in the lowest area of the windscreen when starting from the placement position, because of elastic tensing of drive elements of the wiper arm. A noise effect connected to this can be perceived as unpleasant by a person near the wiper blade. Moreover, the service life of the wiper blade can be reduced by the impacts. 
     SUMMARY OF THE INVENTION 
     The object of the invention is to specify a method and a device for controlling the movement of a wiper blade across a surface, with which increased noise level during the process of stopping the wiper blade can be prevented. 
     A method according to the invention for controlling the movement of a wiper blade over a wiping surface comprises steps of the movement of the wiper blade up and down across the wiping surface between a lower turning position and an upper turning position. On detecting a request to stop the wiper blade, the wiper blade is moved to a downward movement in the vicinity of the lower turning position according to the above pattern. If there is a reversing signal, then the wiper blade is moved down into a lower end position and from there up into a first park position, before it is stopped. The wiper blade is, however, only then moved down into the lower end position, if a lower mechanical resistance against the movement of the wiper blade across the wiping surface has been previously detected. 
     If the movement of the wiper across the wiping surface has a high mechanical resistance, for example if the wiping surface is dry, then according to the invention the wiper will be prevented when stopping from being brought into a position that is so close to the lower end position that the wiper blade impinges on an external object because of elastic mechanical stresses in a wiper blade drive. An impingement of this type is then particularly probable, if an initially wet wiping surface is dried by means of the wiper blade, whereby moisture still remains in an area of the lower end position. If the wiper blade wipes across this area that is still moist during the stopping process, then the elastic stresses in the drive of the wiper blade will release suddenly, which can lead to striking through or impingement of the wiper blade on the external object. 
     If there is no reversing signal, then the wiper blade can be moved from the downward movement into a second park position and stopped there. The wiper blade can thus be removed from the wiping surface when the wiping movement is ended. Visual and aerodynamic advantages can result therefrom. 
     The first park position is preferably above the lower turning position and this is above the second park position. By means of said stresses and/or a mechanical play in the drive of the wiper blade, the wiper blade can be placed in the first or second park position in this way, whereby in each case the visual impression is given that the wiper blade would be in the same position. This position can coincide with the lower turning position. 
     In an alternative embodiment, the lower turning position corresponds to the second park position. 
     Independently of specific mechanical resistance, the wiper blade can be moved into the lower end position, depending on the reversing signal, if a speed signal lies above a predetermined threshold value. Above a predetermined speed, noise caused by striking through or impingement of the wiper blade can be relatively insignificant, so that the second park position can be approached directly and independently of the specific mechanical resistance. 
     The mechanical resistance of the movement of the wiper blade can be determined on the basis of a current consumption of an electrical drive device driving the wiper blade. A dedicated sensor for recording the mechanical resistance can thus be avoided, enabling cost advantages to result. 
     Upon a request to move the wiper blade again after stopping, the wiper blade can first be moved upwards. Turning of the wiper lip prior to the actual wiping process can thus be avoided and a rapid start-up of the wiper blade across the wiping area is supported, so that a cleaning process can be set going more rapidly. 
     The reversing signal can be switched over following a predetermined number of stopping processes. In particular, the reversing signal can be switched on and off, whereby the number of stopping processes until changeover is adapted to the current status of the reversing signal. Thus, for example, a first number of placement processes of the wiper lip in the upward direction is followed by a second number of placement processes of the wiper lip in the downward direction. 
     A computer program product with a program code means for carrying out the described method can run on a processing means or be stored on a computer-legible data medium. 
     A means according to the invention for controlling the movement of a wiper blade across a wiping surface comprises a drive device for moving the wiper blade up and down across the wiping surface between a lower turning position and an upper turning position, a first input means for detecting a request to stop the wiper blade, a second input means for detecting a mechanical resistance against the movement of the wiper blade across the wiping surface and a control means, which is configured to control the driving means to move the wiper blade downwards into a lower end position and from there upwards into a first park position, if there is a reversing signal. Thereby, the control means is further configured to only then move the wiper blade downwards into the lower end position, if the mechanical resistance lies below a predetermined threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is now described in detail with reference to the accompanying figures, in which: 
         FIG. 1  represents a windscreen wiper system 
         FIG. 2  represents a diagram with locus curves of the wiper blade from  FIG. 1 ; and 
         FIG. 3  represents a process diagram of a method for controlling the windscreen wiper system from  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a windscreen wiper system  100  for use on a motor vehicle. A wiping area  105  of a windscreen  110  essentially has the shape of a circular segment with an opening angle of approx. 90° . A wiper-blade  115  with a wiper lip  120  is attached to a wiper shaft  130  by means of a wiper arm  125 , which shaft can be moved by a drive motor  135 . The drive motor  135  comprises an electric motor  140  with a gearbox  145 . The gearbox  145  usually comprises a reduction gearbox, and in another embodiment additionally or alternatively a coupling gear with a linkage. 
     The electric motor  140  is coupled to a circuit breaker  150 . The circuit breaker  150  is connected to a processing means  155  and is controlled by it. Depending on control signals from the processing means  155 , the circuit breaker  150  provides to the electric motor  140  one or more voltages, which can be influenced in respect of their frequency, phase and/or polarity. A current sensor integrated into the circuit breaker  150  provides a signal to the processing means  155 , which depends on an electric current flowing through the electric motor  140 . The processing means  155  is connected to a position sensor  160 , which senses a position of the wiper arm  125  or the wiper blade  115  on the wiping area  105 . Preferably, the position sensor  160  is located on the gearbox  145  and can, for example, comprise a Hall-Sensor. 
     A wiper switch  165  is connected to the processing means  155 . Using the wiper switch  165 , an operator can turn on and off a movement of the wiper blade  115  across the wiping area  105  of the windscreen  110 . Thereby, using the wiper switch  165 , various movement speeds can be selected. The wiper switch  165  can also comprise an interval switch, so that the wiper arm  125  is moved periodically according to predetermined intervals. In relation to the present invention it is, however, sufficient to assume that by using the wiper switch  165  a continuous wiping movement of the wiper blade  115  can simply be switched on and off. 
     The processing means  155  is also connected to a speed sensor  170 , which provides a signal, which is dependent on a speed of a motor vehicle in which the windscreen wiper system  100  is installed. 
     In another embodiment, the speed sensor  170  provides a signal, which is dependent on a wind speed in the vicinity of the windscreen  110 . The signal provided by the speed sensor  170  can also be determined indirectly, for example on the basis of observation of the current flowing through the electric motor  140 . 
     On the wiping area  105 , various positions are specified qualitatively, which in their sequence from above to below have the following meanings:
         upper end position (OEL): the highest position that can be reached by the wiper blade  115  in the wiping area  105 ;   upper turning position (OWL): that position, in which the wiper blade  115  transitions from an upward movement into a downward movement;   first park position (PL 1 ): the position in which the wiper blade  115  is stopped, when it is in an upward movement;   lower turning position (UWL): in continuous wiping mode, that position in which the wiper blade  115  transitions from a downward movement into an upward movement;   second park position (PL 2 ): that position in which the wiper blade  115  is stopped in a downward movement; and   lower end position (UEL): the lowest achievable position of the wiper blade  115  in the wiping area  105 .       

     Specific distances between the individual positions are not defined, but an angular region between the upper turning position OWL and the lower turning position UWL is usually maximized. Accordingly, the upper turning position OWL is in proximity to the upper end position OEL and the lower turning position UWL is in proximity to the lower end position UEL. An opening angle between the first park position PL 1  and the second park position PL 2  is usually approx. 2 to 3°. 
     Controlled by the wiper switch  165 , in a continuous operation the wiper blade  115  is moved continuously back and forth between the upper turning position OWL and the lower turning position UWL, whereby the drive motor  140  runs in alternating directions. By means of the wiping movement of the wiper blade  115 , a region between the turning positions OWL and UWL is cleaned or dried. The wiper lip  120  is always pulled by the wiper arm  125 . In order to prevent premature wear of the wiper lip  120  when stopping the wiper arm  115 , the wiper arm is stopped in a way that ensures that the wiper lip  120  points up and down alternately, i.e. that the wiper blade  115  is alternately stopped from a downward movement and from an upward movement. The wiper lip  120  is thus loaded less on one side, if the wiper arm  115  is not moving. 
     Should the wiper lip  120  point up after stopping the wiper arm  115 , then following a request expressed via the wiper switch  165  to stop the wiper blade  115 , the oscillating movement of the wiper blade  115  between the upper turning position OWL and the lower turning position UWL is first continued until the wiper blade  115  has reached the lower turning position UWL. From there the wiper blade  115  is moved still further to the second park position PL 2  and is stopped there. 
     By contrast, should the wiper lip  120  on the wiper blade  115  point down after stopping the wiper blade  115 , then after the request to stop expressed through the wiper switch  165 , the wiper blade  115  is moved further as far as the lower turning position UWL, from there downwards to the lower end position UEL and back up to the first park position PL 1 . 
     In one embodiment, the upper park position PL 1  can correspond to the lower turning position UWL. Further, the second park position PL 2  can correspond to the lower end position UEL. 
     These two different stopping processes are controlled by the processing means  155 , in that it senses the present position of the wiper blade  115  using the position sensor  160  and controls the circuit breaker  150 , the direction of rotation and the angular speed of the electric motor  140  accordingly. 
     If by means of the wiper blade  115 , by wiping between the upper turning position OWL and the lower turning position UWL, moisture is removed from the wiping area  105  on the windscreen  110 , then the friction between the windscreen  110  and the wiping lip  120  or the wiper arm  125  increases. As a result, a current consumption of the electric motor  140  also increases. This current consumption is sensed by the processing means  155  via the circuit breaker  150 . The processing means can be configured to regulate the speed of movement of the wiper blade  115  independently of the friction. 
     In the case of high friction, any existing play of the gearbox  145  between the electric motor  140  and the wiper arm  125  acts more strongly on the positioning of the wiper blade  115 . There can also be elastic deformation of the gearbox  145  and/or the wiper arm  125 . If the wiper lip  120  passes into an area underneath the lower turning position UWL, where the screen  110  is still wet, during a stopping operation, then the friction between the wiper lip  120  or the wiper blade  115  and the windscreen  110  suddenly reduces, resulting in the mechanical energy stored in the elastically deformed gearbox  145  and/or wiper arm  125  accelerating the wiper arm  115  downwards. The wiper arm  115  can thereby strike an external object, which can result in a noise nuisance. 
     According to the invention, for this purpose the processing means  155  is configured to detect a high level of friction between the wiper lip  120  or the wiper blade  115  and the windscreen  110  based on the current consumption of the electric motor  140  and to stop the movement of the wiper arm  115  only in such a way that the wiper lip  120  points up, for which purpose the wiper arm  115  is not moved below the lower turning position UWL prior to stopping, or is only moved below the lower turning position UWL to a small extent. 
       FIG. 2  shows a diagram  200  with locus curves of the wiper blade  115  from  FIG. 1 . 
     Time is plotted in the horizontal direction. Positions of the wiper blade  115  relative to the wiping area  105  are plotted according to their positions in  FIG. 1 . 
     The first locus curve  210  shows a movement of the wiper blade  115  for continuous wiping between the upper turning position OWL (not shown in  FIG. 2 ) and the lower turning position UWL. The wiper blade  115  passes through the first park position PL 1  from above, decelerates and reaches a stationary state at the lower turning position UWL at time T 4 . Immediately thereafter, the direction of motion of the wiper blade  115  reverses, the wiper blade  115  overtakes the wiper lip  120  and the wiper blade  115  accelerates upwards above the first park position P 1 . 
     The second locus curve  220  shows a movement of the wiper blade  115  into the second park position PL 2 . The wiper blade  115  approaches from above, first wipes over the first park position PL 1  and then the lower turning position UWL, slows its movement and comes to rest at time T 2  in the second park position PL 2 . The wiper lip  120  pulled by the wiper arm  115  is facing upwards. The wiper arm  115  remains here until a new request for screen cleaning at time T 6 . Then the wiper-blade  115  begins to move upwards again, whereby the wiper blade  115  overtakes the wiper lip  120 , so that the latter folds over and points downwards from the wiper blade  115 . The wiper blade  115  accelerates and moves further upwards. 
     The third locus curve  230  shows a movement of the wiper blade  115  when stopping in the first park position PL 1 . The wiper blade  115  approaches again from above, successively wipes over the first park position PL 1 , the lower turning position UWL and the second park position PL 2 , before it slows its movement and comes to rest at time Ti in the lower end position UEL. Immediately thereafter, the wiper blade  115  accelerates upwards again, whereby the wiper blade  115  overtakes the wiper lip  120 , so that this flips over and faces down from the wiper lip  120 . The wiper blade  115  travels over the second park position PL 2  and the lower turning position UWL, in order to decelerate and to come to rest at time T 3  in the first park position PL 1 . 
     The wiper lip  120  thereby faces down. The wiper blade  115  remains in the first park position PL 1  until a new cleaning request occurs at time T 5 , in order to then accelerate upwards. 
       FIG. 3  shows a process diagram of a method  300  for controlling the windscreen wiper system  100  from  FIG. 1 . In a step  305 , the method  300  is in the starting state. In a following step  310  a check is made as to whether there is a request to move the wiper blade  115 . This step is carried out repeatedly until the request is present, whereupon the wiper blade  115  is controlled in step  315  to perform a periodic movement between the upper turning position OWL and the lower turning position UWL. In a subsequent step  320 , during which the wiper blade  115  is moved, a continuous check is made as to whether a request to stop the wiper blade  115  is present. As long as this request is not present, step  320  is repeated, whereby the wiper blade  115  remains in motion. 
     If the request to stop is present, a check is made in a step  325  as to whether a speed of a motor vehicle, in which the windscreen wiper system  100  is installed, is below a predetermined threshold value. If this is the case, then in a step  330  the electrical load is determined, which represents the electric motor  140  for the circuit breaker  150 . This electric load, which is decisively determined by a current flow through the electric motor  140 , depends on the mechanical load of the electric motor  140 , which in turn is influenced by a coefficient of friction between the wiper blade  115  or the wiper lip  120  and the windscreen  110  in the wiping area  105 . In step  335  a check is made as to whether the load determined in step  330  lies above a predetermined threshold value. This corresponds to an indirect determination of whether the windscreen  110  is dry in the area between the upper turning position OWL and the lower turning position UWL. 
     If this is not the case, then a check is made in step  340  as to whether there is a reversing signal. The reversing signal indicates whether the position of the wiper lip  120  relative to the wiper blade  115  has to be reversed or not, before the wiper blade  115  can be stopped. If the reversing signal is not present, then the wiper blade  115  is brought from above into the first park position P 1  in step  345 , so that the wiper lip  120  points upwards. However, if the reversing signal is present, then the wiper blade  115  is brought from above in step  350  according to the locus curve  230  in  FIG. 2 , first into the lower end position UEL and from there back up into the first park position PL 1 , so that the wiper lip  120  points downwards relative to the wiper arm  115 . 
     Following step  345  or step  350 , the wiper arm  125  is stopped in step  355 . 
     If in step  335 , by contrast, it is determined that the windscreen  110  is dry in the region between the upper turning position OWL and the lower turning position UWL, then step  340  is skipped and the stopping operation of the wiper blade  115  in step  345  is carried out irrespective of the presence or absence of the reversing signal. 
     Steps  330  and  335  are skipped if it is determined in step  325  that the speed of the motor vehicle in which the windscreen wiper system  100  is installed is above the predetermined threshold value. In this case, steps  330  and  335  are not implemented and the method is continued from step  325  in step  340 , so that the reversing signal is again taken into account above a predetermined speed. Following step  355 , the method  300  transitions into an end state  360 .