Abstract:
A wiper device comprising a wiper motor; a storage section storing specific positions at an upper and a lower portions of a region on the window glass where the wiper blade swings as a first upper stop target position and a first lower stop target position, and also storing specific ranges from the first upper stop target position to a lower side and from the first lower stop target position to an upper side as an upper and a lower permissible stop ranges; a detection section that detects rotation speed and rotation angle of the wiper motor; and a control section that identifies the wiper blade position, reduces the rotation speed of the wiper motor as the swinging wiper blade approaches the upper or the lower permissible stop range, and stops the wiper motor rotation when the wiper blade has stopped in the upper or the lower permissible stop range.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority under 35 USC 119 from Japanese Patent Application No. 2012-154843 filed Jul. 10, 2012 and No. 2012-154912 filed Jul. 10, 2012, the disclosures of which are incorporated by reference herein. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Technical Field 
         [0003]    The present invention relates to a wiper device. 
         [0004]    2. Related Art 
         [0005]    In Japanese Patent Application Laid-Open (JP-A) No. 2003-54375 (Publication 1) there is a description of a wiper control device equipped with a switching means that interrupts power supplied to a wiper motor when a wiper blade that is moving towards a return position has reached just-in-front of the return position. 
         [0006]    In the wiper control device of Publication 1, the switching means interrupts power supply to the wiper motor just-in-front of the return position, such that the wiper blade is coasted thereby reducing irregular noise of returning of the wiper blade at the return position. 
         [0007]    A wiper device and wiper control method are described in JP-A No. 2010-159044 (Publication 2) that prevent a wiper from flipping up under wind pressure due to motion wind by increasing the rotation force of a wiper motor when a speed of a vehicle increases to generate a strong motion wind. 
         [0008]    In the wiper device and wiper control method of Publication 2, a sensor is disposed for detecting an rotation angle of an output shaft in a gear housing of a wiper motor, so as to enable detection of current position of a wiper blade that is swinging to-and-fro with forward and reverse rotation of a wiper motor. Moreover, in this wiper device and wiper control method, the rotation force of the wiper motor  18  is controlled according to the speed of the vehicle detected by a vehicle speed sensor so as to maintain the wiper blade in a lower return position. 
         [0009]      FIG. 11  is a diagram illustrating a sensor signal angle that is a rotation angle detected by a sensor and the actual operation angle of an output shaft in an ordinary wiper device, such as that of the wiper device and wiper control method of Publication 2. In  FIG. 11 , configuration is made such that when the sensor signal angle reads 0°, the output shaft actual operation angle is also 0°, and the wiper blade is stopped at a stowing position provided at the lowest portion on the window glass when the output shaft actual operation angle is 0°. 
       SUMMARY 
       [0010]    However, the wiper control device of Publication 1 has an issue in that the wiper blade is abruptly decelerated by interrupting power supplied to the wiper motor, with this being detrimental to the smooth operation of the wiper device and making it more likely that irregular noise is generated. 
         [0011]    Sensors employed in wiper devices and wiper control methods generally have measurable angles of from 0° to 180°. Such a type of sensor is employed in the technology described in Publication 2, leading to a concern that when a stowing position is placed at the position where the sensor signal angle is 0°, as illustrated in  FIG. 11 , in situations in which the wiper blade overruns the 0°, say by swinging an extra 2°, the control unit interprets this as being 178°, and make the swing direction of the wiper blade in an opposite direction. 
         [0012]    In consideration of the above circumstances, the present invention enables suppression of irregular noise generation when a wiper blade returns or stops, and provides a wiper device capable of operating smoothly. 
         [0013]    The present invention provides a wiper device capable of ensuring that the swing direction of the wiper blade is prevented from being wrongly reversed even when the wiper blade overruns a specific position for stopping and returning on the window glass. 
         [0014]    In order to address the above issues, a wiper device of a first aspect of the present invention includes: a wiper motor that rotates forwards and rotates backwards at a specific rotation angle, and swings a wiper blade coupled to the wiper motor through a wiper arm to-and-fro across a window glass; a storage section that is stored with specific positions at an upper portion and a lower portion of a region on the window glass where the wiper blade swings to-and-fro as a first upper stop target position and a first lower stop target position. The first upper stop target position and the first lower stop target position are positions where the wiper blade is intended to stop. And the storage section is stored with specific ranges from the first upper stop target position to a lower side and the first lower stop target position to an upper side on the window glass as an upper permissible stop range and a lower permissible stop range. The upper permissible stop range and the lower permissible stop range are ranges where the wiper blade is allowed to stop. The wiper device further includes a detection section that detects the rotation speed and the rotation angle of the wiper motor; and a control section that refers to the storage means, identifies the position of the wiper blade on the window glass based on the rotation angle of the wiper motor detected by the detection means, reduces the rotation speed of the wiper motor as the to-and-fro swinging wiper blade approaches the upper permissible stop range or the lower permissible stop range, and stops the wiper motor rotation when the wiper blade has stopped in the upper permissible stop range or in the lower permissible stop range. 
         [0015]    According to this wiper device, the rotation speed of the wiper motor is reduced as the wiper blade approaches the upper permissible stop range or the lower permissible stop range, enabling generation of irregular noise to be suppressed when the wiper blade returns or stops, and enabling smooth operation of the wiper device to be assured. 
         [0016]    Moreover, the wiper blade stops in the lower permissible stop range provided towards the bottom of the window glass, whereby wiper blade stopping positions is suppressed to be vary, and a wipeable range by a wiper blade can be set to be a wide range outside of the lower permissible stop range. 
         [0017]    A wiper device of a second aspect of the present invention is the wiper device of the first aspect, wherein the control means reduces the rotation speed of the wiper motor as the swinging wiper blade approaches the first upper stop target position or the first lower stop target position from the vicinity of a midpoint in the to-and-fro swing process, stops the wiper motor rotation when the wiper blade has stopped in the upper permissible stop range or in the lower permissible stop range, and after stopping, rotates the wiper motor in an opposite direction to the direction prior to stopping so as to swing the wiper blade that has stopped in the upper permissible stop range or the lower permissible stop range. 
         [0018]    According to this wiper device, since the rotation speed of the wiper motor is reduced as the wiper blade approaches the stop target position, the wiper blade can be returned even in cases in which the wiper blade has stopped prior to the stop target position, due to sliding resistance arising from friction between the wiper blade and the window glass or wind pressure. 
         [0019]    In such a wiper device, the wiper blade can be returned from the permissible stop range even without re-swinging the wiper blade to the stop target position as long as the stop position of the wiper blade is in the permissible stop range, thereby enabling the wiper blade to swing to-and-fro smoothly. 
         [0020]    A wiper device of a third aspect of the present invention is the wiper device of the first aspect or the second aspect, wherein: the wiper device further includes a wiper switch to input an instruction to operate or stop the wiper motor; the storage section is respectively stored with a lower return position and a stowing position as the first lower stop target position, the lower return position is the position where the to-and-fro swinging wiper blade stops in order to return and the stowing position is provided at a lower portion of the lower return position in order to stow the wiper blade. The storage section is stored with a specific range from the lower return position to an upper side on the window glass as a first lower permissible stop range and a specific range from the stowing position to an upper side on the window glass as a second lower permissible stop range. The first and second lower permissible stop ranges are ranges where the wiper blade is allowed to stop. And the control section reduces the rotation speed of the wiper motor as the wiper blade approaches the lower return position when, during to-and-fro swinging of the wiper blade, an instruction is input from the wiper switch to stop the wiper motor; rotates the wiper motor at a slower speed to that of to-and-fro swinging after the wiper blade has stopped in the first lower permissible stop range including the lower return position; reduces the rotation speed of the wiper motor as the wiper blade approaches the stowing position; and stops the wiper motor rotation when the wiper blade has stopped in the second lower permissible stop range including the stowing position. 
         [0021]    According to this wiper device, when the wiper switch is switched OFF, the wiper blade is rotated to the stop target position for stowing at a slower speed than that of to-and-fro swinging after the to-and-fro swinging wiper blade has been temporarily stopped at the lower return position. Wiper blade overrun due to excessive speed can accordingly be prevented. 
         [0022]    According to this wiper device, the rotation speed of the wiper motor is reduced as the wiper blade approaches the stop target position, thereby enabling the abrupt deceleration of the wiper blade at the stop target position to be avoided, and enabling generation of irregular noise accompanying abrupt deceleration to be suppressed. 
         [0023]    A wiper device of a fourth aspect of the present invention is the wiper device of the first aspect, wherein: a second upper stop target position is provided in the upper permissible stop range; a second lower stop target position is provided in the lower permissible stop range; and the control means reduces the rotation speed of the wiper motor as the swinging wiper blade approaches the second upper stop target position or the second lower stop target position from the vicinity of a midpoint in the to-and-fro swing process. 
         [0024]    According to this wiper device, overrun and abrupt deceleration of the wiper blade at the first upper stop target position or the first lower stop target position can be prevented by reducing the rotation speed of the wiper motor as the wiper blade approaches the second upper stop target position or the second lower stop target position respectively provided in the upper permissible stop range and the lower permissible stop range. 
         [0025]    A wiper device of a fifth aspect of the present invention is the wiper device of the third aspect wherein the control means moves the wiper blade towards the stowing position without stopping in the first lower permissible stop range when, during to-and-fro swinging of the wiper blade, an instruction is input from the wiper switch to stop the wiper motor; reduces the rotation speed of the wiper motor as the wiper blade approaches the stowing position; and stops the wiper motor rotation when the wiper blade has stopped in the second lower permissible stop range including the stowing position. 
         [0026]    According to this wiper device, the wiper blade can be stopped in the stowing position without temporarily stopping the wiper blade in the first lower permissible stop range. 
         [0027]    A wiper device of another aspect of the present invention includes: a wiper motor that rotates forwards and rotates backwards with a specific range of rotation angles, and swings a wiper blade coupled to the wiper motor through a wiper arm to-and-fro across a surface of a window glass; a detection section that detects a rotation angle of the wiper motor in a detection range including the specific range of rotation angles of the wiper motor; and a control section that controls the wiper motor rotation so as to stop or return the wiper blade at a specific position at a lower portion of the window glass when the rotation angle of the wiper motor detected by the detection section is at a specific angle which is equal to or greater than a lower limit value of the detection range, and controls the wiper motor rotation so as to return the wiper blade at a specific position at an upper portion of the window glass when the rotation angle of the wiper motor detected by the detection section is at a specific angle which is equal to or lower than an upper limit value of the detection range. And the specific angle which is equal to or greater than the detection range lower limit value is set such that, even when the wiper blade has passed the specific position at the lower portion, the detected rotation angle of the wiper motor that is corresponds to a position of the wiper blade is at the lower limit value of the detection range or greater. 
         [0028]    According to this wiper device, the wiper blade is returned at the specific position at the lower portion of the window glass when the detected rotation angle of the wiper motor is at a specific angle which is equal to or greater than the detection range lower limit value. 
         [0029]    Moreover, with this wiper device, even when the wiper blade has passed the specific position at the lower portion, the specific angle at the detection range lower limit value or greater is set such that rotation angle of the wiper motor detected by the detection section is at the detection range lower limit value or greater. 
         [0030]    Consequently, according to this wiper device, the wiper blade swing direction can be effectively prevented from wrongly reversed even when the wiper blade overruns the specific position for stopping or returning. 
         [0031]    A wiper device according to still another aspect of the present invention is the wiper device of the above aspect, wherein the control means interprets a central value of the specific range of the rotation angle of the wiper motor as being in the vicinity of a central value of the detection range. 
         [0032]    According to this wiper device, the central value of the wiper motor rotation angle is interpreted as being in the vicinity of the central value of the sensor detection range, thereby enabling a range to be provided that allows the swinging wiper blade to overrun by about the same range at an upper edge position and a lower edge position of a swinging area of the wiper blade. 
         [0033]    Consequently, according to this wiper device, the rotation direction of the wiper blade can be effectively prevented from reversing even when the wiper blade has overrun the specific position for stopping or returning. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    Exemplary embodiments of the present invention will be described in detail based on the following figures, wherein: 
           [0035]      FIG. 1  is a schematic diagram illustrating a configuration of a wiper device according to a first exemplary embodiment of the present invention; 
           [0036]      FIG. 2  is a graph illustrating a speed map of a wiper device according to the first exemplary embodiment of the present invention; 
           [0037]      FIG. 3  is a graph illustrating a modified example of a speed map of a wiper device according to the first exemplary embodiment; 
           [0038]      FIG. 4  is a flow chart illustrating control of a microcomputer in the first exemplary embodiment of the present invention; 
           [0039]      FIG. 5  is a schematic diagram illustrating a configuration of a wiper device according to a second exemplary embodiment of the present invention; 
           [0040]      FIG. 6  is a diagram illustrating an example of a sensor according to the second exemplary embodiment of the present invention; 
           [0041]      FIG. 7  is a graph illustrating an example of output from sensors according to the second exemplary embodiment of the present invention; 
           [0042]      FIG. 8  is a chart illustrating correspondences between sensor signal angle and actual operation angle of an output shaft in the second exemplary embodiment of the present invention; 
           [0043]      FIG. 9  is a graph illustrating an example of a speed map specifying an output shaft rotation speed of a wiper motor in the second exemplary embodiment of the present invention; 
           [0044]      FIG. 10  is a flow chart illustrating sensor signal angle correction and control of rotation of a wiper motor with the corrected sensor signal angle in the second exemplary embodiment of the present invention; and 
           [0045]      FIG. 11  is a chart illustrating correspondences between sensor signal angle and actual operation angle in an ordinary wiper device. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0046]      FIG. 1  is a schematic diagram illustrating a configuration of a wiper device  10  according to the present exemplary embodiment. The wiper device  10  is, for example, employed for wiping a front windshield  12  installed in a vehicle such as a passenger car. The wiper device  10  includes a pair of wipers  14  and  16 , a wiper motor  18 , a link mechanism  20 , and a wiper control circuit  22 . 
         [0047]    The wipers  14  and  16  are respectively configured with wiper arms  24  and  26 , and wiper blades  28  and  30 . A base end portion of each of the wiper arms  24  and  26  is fixed respectively to pivot shafts  42  and  44 , described later, and the wiper blades  28  and  30  are respectively fixed to leading end portions of the wiper arms  24  and  26 . 
         [0048]    In the wipers  14  and  16 , the wiper blades  28  and  30  move to-and-fro over the front windshield  12  accompanying swinging of the wiper arms  24  and  26 , thereby wiping the front windshield  12 . 
         [0049]    The wiper motor  18  includes an output shaft  32  that is forward-reverse rotatable through a speed reduction mechanism  52  configured mainly by a worm gear. The link mechanism  20  includes a crank arm  34 , a first link rod  36 , a pair of pivot levers  38  and  40 , the pair of pivot shafts  42  and  44 , and a second link rod  46 . 
         [0050]    One end side of the crank arm  34  is fixed to the output shaft  32 , and the other end side of the crank arm  34  is connected to a first end side of the first link rod  36  so as to be capable of pivoting. Another end side of the first link rod  36  is connected to a location near to a second end of the pivot lever  38 , opposite to a first end that has the pivot shaft  42 , so as to be capable of pivoting. Two ends of the second link rod  46  are respectively pivotally connected to the second end of the pivot lever  38 , and to an end of the pivot lever  40  that corresponds to the second end of the pivot lever  38 . 
         [0051]    The pivot shafts  42  and  44  are pivotally supported by pivot holders, not shown in the drawings, provided to the vehicle body. The wiper arms  24  and  26  are respectively fixed through the pivot shafts  42  and  44  to the first ends of the pivot levers  38  and  40  where the pivot shafts  42  and  44  are provided. 
         [0052]    In the wiper device  10  according to the present exemplary embodiment, when the output shaft  32  is forward-reverse rotated with a first swing range θ1, the rotation force of the output shaft  32  is transmitted through the link mechanism  20  to the wiper arms  24  and  26 , and the wiper blades  28  and  30  move to-and-fro over the front windshield  12  between a lower return position P 2  and an upper return position P 1  as the wiper arms  24  and  26  swing to-and-fro. 
         [0053]    In the wiper device  10  of the present exemplary embodiment, as illustrated in  FIG. 1 , the crank arm  34  and the first link rod  36  configure a straight line when the wiper blades  28  and  30  are positioned at stowing position P 3 . 
         [0054]    The stowing position P 3  is provided below the lower return position P 2 . The wiper blades  28  and  30  are swung to the stowing position P 3  from the lower return position P 2  by the output shaft  32  rotating through  82 . The value of θ2 may take various values according to such factors as the configuration of the link mechanism of the wiper device, however the value of θ2 may be set so as to enable movement of the wiper blades  28  and  30  in a swing range from the lower return position P 2  to the stowing position P 3  provided from a few cm to 10 cm below the lower return position P 2 . 
         [0055]    Note that when θ2 is “0”, then the lower return position P 2  and the stowing position P 3  are aligned with each other, and the wiper blades  28  and  30  are stopped and stored at the lower return position P 2 . 
         [0056]    In the present exemplary embodiment, a permissible stop position P 4  is provided prior to the stowing position P 3 , with a permissible stop range R 1  provided in a region between the permissible stop position P 4  and the stowing position P 3 . 
         [0057]    The wiper blades  28  and  30  ideally stop accurately at the stowing position P 3  when the wiper blades are stopped. 
         [0058]    However, in order that the wiper blades  28  and  30  do not abruptly stop at the stowing position P 3  without decelerating smoothly even when the rotation speed of the wiper motor  18  is slowed so as to stop the wiper blades  28  and  30  at the stowing position P 3 , in the present exemplary embodiment, the rotation of the wiper motor  18  is gradually slowed as the wiper blades  28  and  30  approach the permissible stop range R 1 . This thereby enables the wiper blades  28  and  30  to be stopped at the stowing position P 3  or inside the permissible stop range R 1  provided prior to the stowing position P 3 . 
         [0059]    A lower permissible return position P 5  is also provided prior to the lower return position P 2 , thereby forming, in a region between the lower return position P 2  and the lower permissible return position P 5 , a lower permissible return range R 2  in which it is possible for the wiper blades  28  and  30  to stop and to return. 
         [0060]    An upper permissible return position P 6  is also provided prior to the upper return position P 1 , thereby forming, in a region between the upper return position P 1  and the upper permissible return position P 6 , an upper permissible return range R 3  in which the wiper blades  28  and  30  are allowed to stop and to return. 
         [0061]    Ideally the wiper blades  28  and  30  stop accurately at the upper return position P 1  or the lower return position P 2  when returning. However, sometimes it is difficult to stop the wiper blades  28  and  30  accurately at a specific position. In the present exemplary embodiment, rotation of the wiper motor  18  is gradually slowed as the wiper blades  28  and  30  approach the upper permissible return range R 3  or the lower permissible return range R 2 , thereby enabling the wiper blades  28  and  30  to be stopped in the upper permissible return range R 3  or in the lower permissible return range R 2 . 
         [0062]    Note that, although the lower return position P 2  is provided higher than the permissible stop range R 1  in  FIG. 1 , the lower return position P 2  may be provided within the permissible stop range R 1  as long as the lower return position P 2  is placed prior to the stowing position P 3 . 
         [0063]    Moreover, the lower return position P 2  and the stowing position P 3  may be aligned with each other. The permissible stop range R 1  and the lower permissible return range R 2  overlap each other in such a case. 
         [0064]    The wiper control circuit  22  is connected to the wiper motor  18  in order to control the rotation of the wiper motor  18 . 
         [0065]    The wiper control circuit  22  of the present exemplary embodiment is, for example, configured including a sensor  54  that detects a rotation speed and rotation angle of the output shaft  32  of the wiper motor  18 , and a drive circuit  56  that generates a current for operating the wiper motor  18  using PWM control, and supplies the current to the wiper motor  18 . 
         [0066]    If the wiper motor  18  is a brushless DC motor, then the drive circuit  56  includes an inverter circuit in which a MOSFET is employed as a switching element, and outputs current with a specific duty ratio under control from a microcomputer  58 , described later. 
         [0067]    The wiper motor  18  according to the present exemplary embodiment includes a speed reduction mechanism  52  as mentioned above, and so the rotation speed and rotation angle of the output shaft  32  are not the same as the rotation speed and rotation angle of the wiper motor body. However, in the present exemplary embodiment, the wiper motor body and the speed reduction mechanism  52  are integrally configured inseparable to each other, and so the rotation speed and rotation angle of the output shaft  32  are taken as respective proxies for the rotation speed and rotation angle of the wiper motor  18  in below description. 
         [0068]    The sensor  54  is provided inside the speed reduction mechanism  52  of the wiper motor  18 , and is configured including an element (for example a Hall IC) to detect a magnetic field (magnetic force) of a magnet that rotates interlockingly with the output shaft  32 . 
         [0069]    The wiper control circuit according to the present exemplary embodiment is also configured including a memory  60  stored with data employed to control the microcomputer  58  and the drive circuit  56 . The wiper switch  50  is connected to the microcomputer  58 . The microcomputer  58  is capable of computing position of the wiper blades  28  and  30  on the front windshield  12  from the rotation angle of the output shaft  32  detected by the sensor  54 , and controls the drive circuit  56  so as to change the rotation speed of the output shaft  32  according to this position. 
         [0070]    The memory  60  is stored with speed maps in which the rotation frequency of the output shaft  32  is specified according to the position of the wiper blades  28  and  30  on the front windshield  12 . 
         [0071]    The microcomputer  58  controls the drive circuit  56  according to speed maps stored in the memory  60  while the wiper switch  50  is ON. 
         [0072]    The wiper switch  50  is an ON/OFF switch for power supplied from a vehicle battery to the wiper motor  18 . 
         [0073]    The wiper switch  50  is switchable between a low speed operation mode selection position that causes the wiper blades  28  and  30  to swing at low speed, a high speed operation mode selection position that causes the wiper blades  28  and  30  to swing at high speed, an intermittent operation mode selection position that causes the wiper blades  28  and  30  to swing intermittently at a specific cycle, and a storage (stationary) mode selection position. The wiper switch  50  outputs to the microcomputer  58  a signal corresponding to the selection position for each mode. 
         [0074]    When the signal corresponding to the selection position for each mode has been output from the wiper switch  50  to the wiper control circuit  22 , the wiper control circuit  22  then performs control according to the output signal from the wiper switch  50 , following the speed map stored in the memory  60 . 
         [0075]      FIG. 2  is a graph illustrating an example of a speed map of the wiper device according to the present exemplary embodiment. The vertical axis of  FIG. 2  is a rotation frequency of the output shaft  32  that varies according to the rotation speed of the wiper motor  18 , and the horizontal axis is a rotation angle of the output shaft  32 . The positions of the wiper blades  28  and  30  on the front windshield  12  are also shown in brackets on the horizontal axis corresponding to the rotation angle of the output shaft  32 . 
         [0076]    Three curves are illustrated in  FIG. 2 , with these being a startup speed map C 1 , a to-and-fro wiping operation speed map C 2  and a stowage operation speed map C 3 . 
         [0077]    The startup speed map C 1  is employed when operation of the wiper motor  18  has been started from a stowed state of the wiper blades  28  and  30  at the stowing position P 3 . In the startup speed map C 1 , the rotation frequency of the output shaft  32  increases as the wiper blades  28  and  30  swing from the stowing position P 3  to the upper return position P 1 , so as to configure a substantially semi-elliptical shaped path that has a maximum rotation frequency of the output shaft  32  in the vicinity of the midpoint between the stowing position P 3  and the upper return position P 1 . 
         [0078]    The to-and-fro wiping operation speed map C 2  is employed when the wiper blades  28  and  30  are swinging to-and-fro between the lower return position P 2  and the upper return position P 1 . In the to-and-fro wiping operation speed map C 2 , the rotation frequency of the output shaft  32  increases as the wiper blades  28  and  30  swing from the lower return position P 2  towards the upper return position P 1 , so as to configure a substantially semi-elliptical shaped path that has a maximum rotation frequency of the output shaft  32  in the vicinity of the midpoint between the lower return position P 2  and the upper return position P 1 . 
         [0079]    The to-and-fro wiping operation speed map C 2  is employed to return the wiper blades  28  and  30  at the upper return position P 1 , namely to return the wiper blades  28  and  30  from the upper return position P 1  to the lower return position P 2 . In such cases, the rotation frequency of the output shaft  32  increases as the wiper blades  28  and  30  swing from the upper return position P 1  to the lower return position P 2 , with the maximum rotation frequency of the output shaft  32  in the vicinity of the midpoint between the upper return position P 1  and the lower return position P 2 . 
         [0080]    Note that the maximum rotation frequency of the output shaft  32  is substantially the same in the startup speed map C 1  and the to-and-fro wiping operation speed map C 2 . Vehicle mounted wiper devices are generally equipped with a low speed operation mode for swinging wiper blades at a low speed and a high speed operation mode for swinging the wiper blades at a high speed, and so configuration may be made with the startup speed map C 1  and the to-and-fro wiping operation speed map C 2  provided for the low speed operation mode and the high speed operation mode, respectively. 
         [0081]    When the intermittent operation mode has been selected with the wiper switch  50 , configuration may be made such that, the wiper blades  28  and  30  are stopped at the lower return position P 2 , then after a specific duration has elapsed, such as a few seconds to ten seconds, the wiper motor  18  is rotated so as to re-swing the wiper blades  28  and  30  according to the to-and-fro wiping operation speed map C 2 . 
         [0082]    The stowage operation speed map C 3  is a speed map employed when the wiper switch  50  is switched to the storage (stationary) mode selection position during operation of the wiper device. 
         [0083]    During operation of the wiper device, the wiper motor  18  is rotated forwards and backwards according to the to-and-fro wiping operation speed map C 2 , and the wiper blades  28  and  30  swing to-and-fro between the upper return position P 1  and the lower return position P 2 . Consequently, the stowage operation speed map C 3  specifies the rotation frequency of the output shaft after the wiper blades  28  and  30  have been returned to the lower return position P 2  and when they are being returned from the lower return position P 2  to the stowing position P 3 . 
         [0084]    In the stowage operation speed map C 3 , the rotation frequency of the output shaft  32  increases as the wiper blades  28  and  30  swing from the lower return position P 2  to the stowing position P 3 , with the stowage operation speed map C 3  configuring a substantially semi-elliptical shaped path with a maximum rotation frequency of the output shaft  32  in the vicinity of the midpoint between the lower return position P 2  and the stowing position P 3 . 
         [0085]    In the present exemplary embodiment, when the wiper switch  50  is switched to the storage (stationary) mode selection position during to-and-fro swinging of the wiper blades, the rotation of the wiper motor  18  is controlled according to the to-and-fro wiping operation speed map C 2  until the wiper blades have reached lower return position P 2 . 
         [0086]    After the wiper blades have reached the lower return position P 2 , the rotation of the wiper motor  18  is then controlled according to the stowage operation speed map C 3 . 
         [0087]    Note that the maximum rotation frequency of the output shaft  32  specified by the stowage operation speed map C 3  is a lower speed than the maximum rotation frequency as specified by each of the startup speed map C 1  and the to-and-fro wiping operation speed map C 2 . This is because the distance from the lower return position P 2  to the stowing position P 3  is short, and so, if the rotation frequency of the output shaft  32  were made high, then the wiper blades  28  and  30  would accelerate and decelerate abruptly on the front windshield  12  to stop at the stowing position P 3 , which would be detrimental to smooth operation. 
         [0088]    Note that preferably the wiper blades  28  and  30  accurately stop at the upper return position P 1 , the lower return position P 2  and the stowing position P 3 . However, it is conceivable that in actual operation, sometimes the wiper blades  28  and  30  will stop prior to the upper return position P 1 , the lower return position P 2  or the stowing position P 3  due to friction between the surface of the front windshield  12  and the wiper blades  28  and  30 . 
         [0089]    In  FIG. 2 , in each of the maps, the rotation speed of the wiper motor  18  is gradually slowed such that the rotation frequency of the output shaft  32  is “0” at the upper return position P 1 , at the lower return position P 2  and at the stowing position P 3 . However, in the present exemplary embodiment, the wiper blades  28  and  30  are allowed to stop in the upper permissible return range R 3 , in the lower permissible return range R 2  or in the permissible stop range R 1  that are provided respectively prior to the upper return position P 1 , the lower return position P 2  and the stowing position P 3 . 
         [0090]    The upper return position P 1 , the lower return position P 2  and the stowing position P 3  are target positions to stop the wiper blades  28  and  30 . In actual operation, the wiper blades  28  and  30  may stop in the specific regions provided prior to the stop target positions where stopping is allowed. 
         [0091]    Namely, when the wiper blades  28  and  30  have stopped in the permissible stop range R 1  then this is interpreted as if the wiper blades  28  and  30  are stored in the stowing position P 3   
         [0092]    Moreover, when the wiper blades  28  and  30  are stopped in the upper permissible return range R 3  or the lower permissible return range R 2 , the wiper blades  28  and  30  are allowed to return from their stopped position. 
         [0093]    Moreover, movement of the wiper blades  28  and  30  is also allowed from the lower permissible return range R 2  to the stowing position P 3  after the wiper blades  28  and  30  has stopped at the range R 2 . 
         [0094]      FIG. 3  is a modified example of a speed map of the present exemplary embodiment. In the modified exemplary embodiment, an upper return target position P 7  is set between the upper return position P 1  and the upper permissible return position P 6 , namely in the upper permissible return range R 3 . 
         [0095]    Moreover, the rotation frequency of the output shaft  32  is specified as “0” at the upper return target position P 7  in the startup speed map C 1  and in the to-and-fro wiping operation speed map C 2 . 
         [0096]    In  FIG. 3 , the upper return target position P 7  is a target position to stop the wiper blades  28  and  30 . By thus controlling the rotation speed of the wiper motor  18  such that the wiper blades  28  and  30  are stopped at the upper return target position P 7 , overrun or abrupt deceleration of the wiper blades  28  and  30  at the upper return position P 1  can be prevented. 
         [0097]    In the to-and-fro wiping operation speed map C 2 , when the wiper blades  28  and  30  swing from the upper return position P 1  to the lower return position P 2 , the rotation frequency of the output shaft  32  is specified so as to be “0” at a lower return target position P 8  provided in the lower permissible return range R 2  prior to the lower return position P 2 . 
         [0098]    In the stowage operation speed map C 3 , the rotation frequency of the output shaft  32  is specified so as to be “0” at a stowage target position P 9  provided in the permissible stop range Rlprior to the stowing position P 3 . 
         [0099]    Thus as described above, target positions for stopping are specified prior to the lower return position P 2  and the stowing position P 3 , and the speed maps specify the rotation frequency of the output shaft  32  as “0” at these stop targets. The wiper blades  28  and  30  can accordingly be prevented from overrunning or decelerating abruptly at the lower return position P 2  or the stowing position P 3 . 
         [0100]    Explanation next follows regarding control in the present exemplary embodiment.  FIG. 4  is a flow chart relating to control of the microcomputer  58  in the present exemplary embodiment. 
         [0101]    The control illustrated in  FIG. 4  is started when the wiper switch  50  is switched from the storage (stationary) mode selection position to the low speed operation mode selection position, the high speed operation mode selection position, or the intermittent operation mode selection position. 
         [0102]    First, at step  400 , rotation of the wiper motor  18  is controlled according to the startup speed map C 1 . 
         [0103]    At step  402 , computation of the position of the wiper blades  28  and  30  on the front windshield  12  is started from the rotation angle of the output shaft  32  detected by the sensor  54 . The rotation frequency of the output shaft  32  is also computed from the rotation angle of the output shaft  32 , and monitoring is performed of whether or not the wiper motor  18  is being controlled under the startup speed map C 1 . 
         [0104]    At step  404 , determination is made as to whether or not the wiper blades  28  and  30  are stopped at the upper permissible return range R 3 . The procedure proceeds to step  408  when affirmative determination is made. However when negative determination is made, then at step  406 , the wiper motor  18  is rotated employing to-and-fro wiping operation speed map C 2 , and the wiper blades  28  and  30  are stopped at the upper permissible return range R 3 . 
         [0105]    Note that although the rotation of the wiper motor  18  is controlled employing the to-and-fro wiping operation speed map C 2  at step  406 , the rotation of the wiper motor  18  may alternatively be controlled according to the startup speed map C 1 . 
         [0106]    At step  408 , the rotation of the wiper motor  18  is controlled using the to-and-fro wiping operation speed map C 2  such that the wiper blades  28  and  30  are swung from the upper permissible return range R 3  to the lower permissible return range R 2 . 
         [0107]    At step  410 , determination is made as to whether or not the wiper blades  28  and  30  are stopped at the lower permissible return range R 2 . The procedure proceeds to step  414  when affirmative determination is made. However when negative determination is made, the wiper motor  18  is rotated at step  412  employing the to-and-fro wiping operation speed map C 2 , and the wiper blades  28  and  30  are stopped at the lower permissible return range R 2 . 
         [0108]    At step  414 , determination is made as to whether or not the wiper switch  50  has been switched to the storage (stationary) mode selection position. When negative determination is made, then at step  416  rotation of the wiper motor  18  is controlled employing the to-and-fro wiping operation speed map C 2  such that the wiper blades  28  and  30  are swung from the lower permissible return range R 2  to the upper permissible return range R 3 , and then the procedure returns to step  404 . 
         [0109]    When affirmative determination is made at step  414 , then at step  418 , the rotation of the wiper motor  18  is controlled according to the stowage operation speed map C 3  such that the wiper blades  28  and  30  are swung from the lower permissible return range R 2  to the permissible stop range R 1 . 
         [0110]    At step  420 , determination is made as to whether or not the wiper blades  28  and  30  have stopped at the permissible stop range R 1 . Processing is ended when affirmative determination is made. However when negative determination is made, then at step  422 , the wiper motor  18  is rotated employing the stowage operation speed map C 3  and the wiper blades  28  and  30  are stopped at the permissible stop range R 1 , then the processing is ended. 
         [0111]    As explained above, according to the present exemplary embodiment, regions where the wiper blades are allowed to stop are provided prior to the stop positions, and regions where the wiper blades are allowed to return are provided prior to the return positions, such that the wiper blades can stop or return in these regions. Overrun of the wiper blade at the stop positions or the return positions can accordingly be prevented, and this also enables irregular noise to be prevented from occurring due to the wiper blades abruptly decelerating at the stop positions or the return positions. 
         [0112]    Note that in the present exemplary embodiment, when the wiper switch  50  is switched OFF, the rotation of the wiper motor  18  is controlled under the to-and-fro wiping operation speed map C 2  as far as the lower return position P 2 , and then the rotation of the wiper motor  18  is controlled from the lower return position P 2  under the stowage operation speed map C 3 . 
         [0113]    However, configuration may be made such that when the wiper switch  50  is switched OFF, the wiper motor  18  is immediately switched from control by the to-and-fro wiping operation speed map C 2  to control by the startup speed map C 1 . 
         [0114]    In such cases, control of the wiper motor  18  is switched from using the to-and-fro wiping operation speed map C 2  to using the startup speed map C 1  illustrated in  FIG. 2 , and the rotation speed of the wiper motor  18  is slowed as the wiper blades  28  and  30  approach the stowing position P 3 . 
         [0115]    Under such control, the wiper blades  28  and  30  can be stopped at the stowing position P 3  without temporarily stopping the wiper blades  28  and  30  at the lower return position P 2 . For example, the wiper blades  28  and  30  can be stopped at the stowing position P 3  or in the permissible stop range R 1  by slowing the rotation speed of the wiper motor  18  as the wiper blades  28  and  30  move from the vicinity of the midpoint of the to-and-fro swinging process so as to approach the stowing position P 3 . 
         [0116]    Explanation next follows regarding the second exemplary embodiment.  FIG. 5  is a schematic diagram illustrating a configuration of a wiper device  110  according to the second exemplary embodiment. The wiper device  110  is similar in structure to the wiper device  10 . Hence similar portions to portions of the wiper device  10  are allocated the same reference numerals and further explanation thereof is omitted. 
         [0117]    In the present exemplary embodiment, a central position P 40  between the upper return position P 1  and the stowing position P 3  of the wiper blades  28  and  30  is employed. 
         [0118]      FIG. 6  is a diagram illustrating an example of a sensor  154  according to the present exemplary embodiment. The sensor  154  illustrated in  FIG. 6  includes an excitation coil  72  that magnetically excites with power supplied from an alternating current source  70 , and includes a rotor  74  that rotates with the output shaft  32 . 
         [0119]    A first detection coil  76  and a second detection coil  78  are provided in the vicinity of the rotor  74  for detecting a magnetic field emitted by the excitation coil  72 . 
         [0120]    The first detection coil  76  and the second detection coil  78  are placed such that a line connecting the center of the second detection coil  78  and the center of the rotor  74 , and a line connecting the center of the first detection coil  76  and the rotor  74  meet at 90°. 
         [0121]    A first voltmeter  80  is provided at the first detection coil  76  and a second voltmeter  82  is provided at the second detection coil  78 . 
         [0122]      FIG. 7  illustrates an example of output of the sensor  154  according to the present exemplary embodiment. The sensor  154  includes the two detection coils that are disposed at 90° to each other, and hence two sine waves are output at phases shifted by 90° from each other, as illustrated in  FIG. 7 . In the present exemplary embodiment, the two sine waves are a sine wave  90  and a cosine wave  92 . The sine wave  90  expresses a voltage value of current detected by the first detection coil  76 , and the cosine wave  92  expresses a voltage value of the current detected by the second detection coil  78 . 
         [0123]    In  FIG. 7 , the sine wave  90  and the cosine wave  92  can be expressed by following Equation (1) and Equation (2), wherein the detection axis angle is denoted by θ. 
         [0000]      sine wave 90 : y =sin θ  Equation (1)
 
         [0000]      cosine wave 92 : y =cos θ  Equation (2)
 
         [0124]    Moreover, the quotient obtained by dividing the sine by the cosine is the tangent expressed by following Equation (3). 
         [0000]      sin θ/cos θ=tan θ  Equation (3)
 
         [0125]    Moreover, the sensor signal angle is computed by processing the inverse tangent function tan −1  of the tangent computed by Equation (3). Thus computed sensor signal angle is illustrated by the zig-zag line  94  in  FIG. 7 . The computed sensor signal angle corresponds to an “output shaft angle” on the horizontal axis of  FIG. 7 . 
         [0126]    Note that in the present exemplary embodiment, the above computation is performed by processing with a dedicated IC based on a trigonometric function. 
         [0127]      FIG. 8  is a diagram illustrating correspondences between a sensor signal angle and actual operation angle of the output shaft  32  in the present exemplary embodiment. 
         [0128]    In the present exemplary embodiment, a central value of the rotation angle of the output shaft  32  of the wiper motor  18 , when the wiper blades  28  and  30  are swinging to-and-fro, is allocated to be in the vicinity of a central value of the angular range detectable by the sensor  154 . 
         [0129]    In  FIG. 8 , the rotation angles of the output shaft  32  when the wiper blades  28  and  30  have swung from the stowing position P 3  to the upper return position P 1  are shown as the output shaft actual operation angle. The output shaft actual operation angle is 0° when the wiper blades  28  and  30  are at the stowing position P 3 , and is 150° when the wiper blades  28  and  30  have reached the upper return position P 1 . 
         [0130]    When the output shaft actual operation angle is 75° which is the central value from 0° to 150°, the wiper blades  28  and  30  are positioned at the central position P 40  at the midpoint between the stowing position P 3  and the upper return position P 1 . 
         [0131]    The sensor signal angle of the rotation angle of the output shaft  32  detected by the sensor  154  is illustrated at the top of  FIG. 8 . The detection range of a sensor that detects rotation angle is generally from 0° to 180°, and the sensor  154  of the present exemplary embodiment also has a detection range of sensor signal angles from 0° to 180°. The central value of the detection range of the sensor  154  in the present exemplary embodiment is accordingly 90°. 
         [0132]    In the present exemplary embodiment, as illustrated in  FIG. 8 , the central value 75° of the output shaft actual operation angle is interpreted as being in the vicinity of the central value 90° of the detection range of the sensor  154 . Setting may then be made to enable the wiper blades to be returned at the lower return position P 2  or to be stored at the stowing position P 3  when the signal angle detected by the sensor  154  is at a specific range of angle which is equal to or greater than the lower limit 0° of the detection range of the sensor  154 . Moreover, settings may be made to enable the wiper blades to be returned at the upper return position P 1  when the sensor signal angle detected by the sensor  154  is a specific range of angle which is equal to or smaller than the upper limit 180° of the detection range of the sensor  154 . Note that the above specific angle range may, for example, be set between 0° and 20° for the return at the lower return position P 2  and between 0° and 15° for the store at the stowing position P 3 . 
         [0133]    At the left side portion of  FIG. 8 , the wiper blades  28  and  30  are illustrated as having gone past the stowing position P 3 , namely illustrated in an overrun situation. Suppose that, as illustrated in  FIG. 8 , even when the wiper blades  28  and  30  overrun by 2° of the output shaft actual operation angle from the stowing position P 3 , the sensor signal angle detected in such a case would be 13°, which would still exceed the lower limit value of the detection range of the sensor  154 , this being 0°, and would lie within the specific angle range. The swing direction of the wiper blades  28  and  30  would accordingly not be controlled wrongly. 
         [0134]      FIG. 9  is a graph illustrating an example of a speed map for designating a rotation frequency of the output shaft  32  of the wiper motor  18  according to the present exemplary embodiment. 
         [0135]    The startup speed map C 1  in  FIG. 9  is a speed map employed when operation of the wiper motor  18  has been started from a stowed state of the wiper blades  28  and  30  at the stowing position P 3 . In the startup speed map C 1 , the rotation frequency of the output shaft  32  increases as the wiper blades  28  and  30  swing from the stowing position P 3  to the upper return position P 1 , so as to configure a substantially semi-elliptical shaped path that has a maximum rotation frequency of the output shaft  32  in the vicinity of midpoint position P 40  that is the midpoint between the stowing position P 3  and the upper return position P 1 . 
         [0136]    On the horizontal axis of  FIG. 9 , in the vicinity of the central position P 40 , the sensor signal angle is set to be the central value of the detection range of the sensor  154 , this being 90°. 
         [0137]    Setting is made such that the wiper blades  28  and  30  are stowed at the stowing position P 3  when the sensor signal angle is 15°, the wiper blades  28  and  30  return at the lower return position P 2  when the sensor signal angle is 20°, and the wiper blades  28  and  30  return at the upper return position P 1  when the sensor signal angle is in 165°. 
         [0138]    Moreover, setting is made such that the wiper blades can be stowed at the stowing position P 3  when the signal angle is in the specific angle range that is the lower limit value of the detection range of the sensor  154 , this being 0°, or greater, even when the signal angle detected by the sensor  154  is smaller than 15° because the wiper blades have overrun. Setting is also made such that the wiper blades can be returned at the lower return position P 2  when the signal angle is in the specific angle range that is the lower limit value of the detection range of the sensor  154 , this being 0°, or greater, even when the signal angle detected by the sensor  154  is smaller than 20° because the wiper blades have overrun. Moreover, setting is made such that the wiper blades can be returned at the upper return position P 1  when the sensor signal angle is in the specific angle range that is the upper limit value of the detection range of the 154, this being 180°, or lower, even when the sensor signal angle detected by the sensor  154  is larger than 165° because the wiper blades have overrun. 
         [0139]    In the present exemplary embodiment, there are various conceivable methods to interpret the central value of the rotation angle of the output shaft  32  of the wiper motor  18  as being in the vicinity of the central value of the detection range of the sensor  154 . 
         [0140]    One conceivable method is to displace attachment position of the sensor  154  by a specific angle from the standard position. 
         [0141]    For example, in the present exemplary embodiment, attachment position of the sensor  154  is adjusted such that the sensor signal angle detected by the sensor  154  is 15° when the wiper blades  28  and  30  are disposed at the stowing position P 3 . 
         [0142]    Another method is to correct the sensor signal angle detected by the sensor  154 , and to control the rotation of the wiper motor  18  according to the post-correction sensor signal angle. 
         [0143]      FIG. 10  is a flow chart illustrating correction of sensor signal angle and control of rotation of the wiper motor  18  according to the corrected sensor signal angle in the present exemplary embodiment. 
         [0144]    The control illustrated in  FIG. 10  is started when the wiper switch  50  is switched over from the storage (stationary) mode selection position to the low speed operation mode selection position, the high speed operation mode selection position, or the intermittent operation mode selection position. 
         [0145]    First, at step  600 , the sensor signal angle is detected. When the sensor  154  is attached in the standard position and the wiper blades  28  and  30  are at the stowing position P 3 , then the rotation angle of the output shaft  32  is 0°, and the sensor signal angle at step  600  is 0°. 
         [0146]    At step  602 , the sensor signal angle is corrected. As an example, in the present exemplary embodiment, the sensor signal angle is corrected so as to be 15° when the wiper blades  28  and  30  are at the stowing position P 3 . The correction angle of 15° is determined according to the present circumstances, as described above, that the central value 75° of the rotation angle of the output shaft  32  is interpreted as being in the vicinity of the central value 90° of the detection range of the sensor  154  under the conditions that the rotation angles of the output shaft  32  of the wiper motor  18  are from 0° to 150°, and the detection range of the sensor  154  is from 0° to 180°. 
         [0147]    The correction angle, that is 15° in the present exemplary embodiment, may be changed by appropriate variation according to the rotation angle of the output shaft  32  of the wiper motor  18  and/or the detection range of the sensor  154 . 
         [0148]    At step  604 , the rotation of the wiper motor  18  is controlled based on the post-correction sensor signal angle and the speed maps stored in the memory  60 . 
         [0149]    At step  606 , determination is made as to whether or not the wiper switch  50  has been switched to the storage (stationary) mode selection position. The procedure returns to step  600  when negative determination is made, however the processing is ended when affirmative determination is made. 
         [0150]    As explained above, according to the present exemplary embodiment, the sensor signal angle detected by the sensor is corrected such that the central value of the rotation angles of the wiper motor is interpreted as being in the vicinity of the central value of the detection range of the sensor. So doing prevents the rotation direction of the wiper blades from being wrongly reversed since the detected sensor signal angles are within an angular range where it is possible for the wiper blades to return or stowage even in cases in which the wiper blades have overrun a specific position for stopping or for returning.