Patent Publication Number: US-2021170993-A1

Title: Reversible motor configured with motion stops for aircraft windshield wiper system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of Indian Application No. 201911050812, filed Dec. 9, 2019, the disclosure of which is incorporated herein by reference in its entirety. 
     BACKGROUND 
     The embodiments herein relate to windshield wiper systems for an aircraft and more specifically to a reversible motor configured with motion stops for such windshield wiper system. 
     A windshield wiper system is used on an aircraft to clean a wind shield of the aircraft, e.g., during rain. One type of windshield wiper system utilizes a crank rocker mechanism. In such a system, continuous rotation of a motor of the windshield wiper system is converted to oscillatory motion at a wiper shaft that is connected the crank rocker mechanism. For such a windshield wiper system, a sweep angle of the crank rocker mechanism is fixed mechanically. From this, the wiper shaft is constrained within the intended sweep angle. Another type of windshield wiper system utilizes a reversible brushless direct-current motor (reversible motor). Through electronic controls, the reversible motor achieves oscillatory motion directly from the motor shaft. 
     BRIEF SUMMARY 
     Disclosed is a windshield wiper system for an aircraft, comprising: a wiper arm; a reversible motor that drives the wiper arm, the reversible motor including: a stator; a rotor configured to rotate relative to the stator; a forward shaft segment, wherein the forward shaft segment is driven by the rotor and is rotationally connected to the wiper arm; an aft shaft segment, wherein the aft shaft segment is driven by the rotor, the aft shaft segment including a forward end and an aft end; a ball nut, wherein the ball nut translates along the aft shaft segment from rotation of the aft shaft segment; a forward stop at a forward end of the aft shaft segment, configured to stop forward translational motion of the ball nut along the aft shaft segment; and an aft stop at an aft end of the aft shaft segment, configured to stop aft translational motion of the ball nut along the aft shaft segment. 
     In addition to one or more of the above disclosed aspects, or as an alternate, the forward shaft segment and the aft shaft segment are segments of a motor shaft. 
     In addition to one or more of the above disclosed aspects, or as an alternate, the motor further includes: a housing, wherein the housing has a forward end wall and an aft end wall, wherein: the stator and the rotor are disposed within the housing; the forward shaft segment extends through the forward end wall of the housing; the aft shaft segment extends through the aft end wall of the housing; and the forward stop surface is formed by the aft end wall of the housing. 
     In addition to one or more of the above disclosed aspects, or as an alternate, the windshield wiper system further includes: an endcap fixed to the aft end wall of the housing, the endcap including an aft end wall spaced apart from the aft end wall of the housing, wherein: the aft shaft segment is disposed within the endcap; and the aft stop surface is defined by the aft end wall of the endcap. 
     In addition to one or more of the above disclosed aspects, or as an alternate: the ball nut includes a flange that defines a first passage; the windshield wiper system further includes: a first guide pin extending from the aft end wall of the housing to the aft end wall of the endcap such that the first guide pin is parallel to the aft shaft, wherein the first guide pin extends through the first passage in the flange of the ball nut and prevents rotation of the ball nut relative to the stator when the aft shaft segment rotates. 
     In addition to one or more of the above disclosed aspects, or as an alternate: a second passage is defined by the flange of the ball nut; and the windshield wiper system further includes: a second guide pin extending from the aft end wall of the housing to the aft end wall of the endcap such that the second guide pin is parallel to the aft shaft segment and is spaced apart from the first guide pin, wherein the second guide pin extends through the second passage in the flange of the ball nut. 
     In addition to one or more of the above disclosed aspects, or as an alternate, the first guide pin and the second guide pin are connected to the aft end wall of the housing. 
     In addition to one or more of the above disclosed aspects, or as an alternate, the reversible motor is a reversible brushless direct-current motor. 
     In addition to one or more of the above disclosed aspects, or as an alternate, the reversible motor is configured to stop responsive to the ball nut contacting the aft stop while the aft shaft segment rotates. 
     In addition to one or more of the above disclosed aspects, or as an alternate, the reversible motor is configured to stop responsive to sensing an increase in current drawn by the motor when the ball nut contacts the aft stop while the aft shaft segment rotates. 
     In addition to one or more of the above disclosed aspects, or as an alternate, the reversible motor is configured to stop responsive to the ball nut contacting the forward stop while the aft shaft segment rotates. 
     In addition to one or more of the above disclosed aspects, or as an alternate, the reversible motor is configured to stop responsive to sensing an increase in current drawn by the motor when the ball nut contacts the forward stop while the aft shaft segment rotates. 
     In addition to one or more of the above disclosed aspects, or as an alternate, the aft shaft segment is threaded, and the system further includes balls within the ball nut that engage the threads on the aft shaft segment, whereby the ball nut translates forward and aft when the aft shaft segment rotates. 
     In addition to one or more of the above disclosed aspects, or as an alternate, the windshield wiper system further includes: a reduction gear that rotationally couples the aft shaft segment to the wiper arm. 
     In addition to one or more of the above disclosed aspects, or as an alternate, a pinion gear is defined by the forward shaft segment, and the pinion gear is rotationally coupled to the reduction gear. 
     Further disclosed is an aircraft including a windshield wiper system having one or more of the above disclosed aspects. 
     Further disclosed is a method of operating a windshield wiper system, comprising: driving a rotor of a reversible motor relative to a stator of the reversible motor; driving an aft shaft segment of a motor shaft with the rotor; translating a ball nut from rotation of the aft shaft segment between a forward stop and an aft stop; and stopping the reversible motor when the ball nut contacts either of the forward stop and the aft stop while the aft shaft segment rotates. 
     In addition to one or more of the above disclosed aspects, or as an alternate, the method further includes: driving a reduction gear with a forward shaft segment of the motor shaft and driving a wiper arm with the reduction gear. 
     In addition to one or more of the above disclosed aspects, or as an alternate, the method further includes: preventing rotation of the ball nut relative to the stator with a guide pin extending through a passage defined in a flange of the ball nut, from the forward stop to the aft stop. 
     In addition to one or more of the above disclosed aspects, or as an alternate, the method further includes: stopping the reversible motor responsive to sensing an increase in current draw by the motor when the ball nut contacts either of the forward stop and the aft stop while the aft shaft segment rotates. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following descriptions should not be considered limiting in any way. With reference to the accompanying drawings, like elements are numbered alike: 
         FIG. 1  is a perspective view of an aircraft that may include a windshield wiper system according to a disclosed embodiment; 
         FIG. 2  shows a detail of section A of  FIG. 1 , showing aspects of a windshield wiper system according to a disclosed embodiment; 
         FIG. 3  shows a motor of the windshield wiper system according to a disclosed embodiment; 
         FIG. 4  shows a cross section of the motor along section lines B-B of  FIG. 3 , showing a ball nut in a forward position, disposed against an aft end of the motor housing; 
         FIG. 5  shows the cross section of the motor along section lines B-B of  FIG. 3 , showing the ball nut in an aft position and disposed against an aft surface of an endcap connected to the motor housing; and 
         FIG. 6  is a flowchart showing a method of operating a windshield wiper system according to a disclosed embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures. 
       FIG. 1  shows an aircraft  2  having a windshield  4 . As shown in  FIG. 2 , the aircraft  2  includes a windshield wiper system  100  for cleaning the windshield  4 , e.g., during rain. The windshield wiper system  100  includes a wiper arm  110  driven by a reduction gear  120  that is powered by a motor  130 . In such systems, the wiper arm  110  can traverse a sweep angle (SA) during operation. According to one non-limiting embodiment the wiper arm  110  is configured to sweep within a sweep angle SA of, e.g., (60) sixty degrees per sweep cycle at a rate of one hundred (100) cycles per minute (CPM). 
     Turning to  FIG. 3-5  the motor  130  includes a motor housing  160 . The motor housing  160  includes forward and aft ends  150   a,    150   b.  As illustrated, the forward and aft ends  150   a,    150   b  of the motor housing  160  are spaced apart along an axis  145 . Within the housing  160 , the motor  130  includes a stator  155   a  with associated coil windings ( FIGS. 4-5 ). A rotor  155   b  ( FIGS. 4-5 ) is configured to rotate relative to the stator  155   a  based on electrical power receive through one or more leads  156  ( FIG. 3 ) extending through the housing  160 . The rotor  155   b  drives a motor shaft  140   a  ( FIGS. 4-5 ), which may be supported on a shaft bearing  155   c  ( FIGS. 4-5 ). The motor shaft  140   a  defines a forward shaft segment  140   b  extending along the axis  145  through the forward end  150   a  of the housing  160 . The motor shaft  140  also defines an aft shaft segment  140   c  ( FIGS. 4-5 ) extending along the axis  145  through the aft end  150   b  of the housing  160 . 
     The motor  130  of the windshield wiper system  100  may be a reversible brushless direct-current motor. Through electronic control of the motor  130 , the motor  130  achieves oscillatory motion with the forward shaft segment  140   b  of the motor shaft  140   a.  As illustrated, the forward shaft segment  140   b  drives the reduction gear  120  ( FIGS. 2-3 ). In addition, the forward shaft segment  140   b  includes a pinion gear profile ( FIG. 3 ) for meshing with the reduction gear  120 . 
     The windshield wiper system  100  includes a ball nut  210 . The ball nut  210  translates along the aft shaft segment  140   c  from rotation of the aft shaft segment  140   c.  This configuration forms a ball screw type linear actuator. A ball screw is a mechanical linear actuator that translates rotational motion, i.e., the aft shaft segment  140   c,  to linear motion of the ball nut  210  with little friction. A ball screw is able to apply or withstand high thrust loads with minimum internal friction and is machinable to close tolerances. The ball screw is therefore is generally suitable for use in situations in which require high precision. The aft shaft segment  140   c  is formed with a helical raceway for engaging ball bearings  200  in the ball nut  210 , which acts as a precision screw. Thus, as the aft shaft segment  140   c  rotates with the motor shaft  140   a,  the rotation of the aft shaft segment  140   c  is converted to linear motion of the ball nut  210  along the axis  145 . 
     As more clearly shown in  FIGS. 4-5 , a forward stop  165   a  is formed by the aft end  150   b  of the housing  160 . The forward stop  165   a  is configured to stop forward translational motion of the ball nut  210  along the aft shaft segment  140   c.  An aft stop  165   b  is located at an aft end  190  of the aft shaft segment  165   b.  The aft stop  165   b  is configured to stop aft translational motion of the ball nut  210  along the aft shaft segment  140   c.  With this configuration, the aft shaft segment  140   c,  the ball nut  210 , and the forward and aft stops  165   a,    165   b  together form a motion limiter located at the aft end  150   b  of the motor housing  160 . This configuration prevents over rotation of the motor shaft  140   a.  This prevents over sweep of the wiper arm  110  ( FIG. 2 ). As a result, damage to the wiper arm  110  and aircraft  2  around the windshield  4  ( FIG. 2 ) is potentially avoided. As disclosed herein, when over rotation of the motor shaft  140   a  in either direction is encountered, the motor  130  is stopped. The windshield wiper system  100  may thereafter be serviced as needed to restore a desired operational state. 
     Rotational motion of the ball nut  210 , e.g., relative to the stator  155   a  is prevented with one or more guide pins  220 . The guide pins  220  extend from the aft end  150   b  of the motor housing  160 , parallel with and along-side the aft shaft segment  140   c.  The ball nut  210  includes a flange  210   a,  which is cylindrical and defines one or more passages  210   b  through which the respective one or more guide pins  220  extend. The one or more guide pins  220  may have a same length as the aft shaft segment  140   c  to prevent run-off of the flange  210   a  as the ball nut  210  moves along the aft shaft segment  140   c.  In the illustrated embodiment a pair of the guide pins  220  are utilized, though this is not intended on limiting the scope of the disclosed embodiments. 
     The aft shaft segment  140   c  with the ball nut  210  and the guide pins  220  are encased against the aft end  150   b  of the motor housing  160  by an endcap  230 . The endcap  230  is cylindrical having a sidewall  240  with an inner diameter that is larger than the flange  210   a  of the ball nut  210 . An aft wall  250  of the endcap  230  is located near or against an aft end  190  of the aft shaft segment  140   c.  The aft wall  250  of the endcap  230  forms the aft stop  165   b.    
     The opposing radial directions in which the motor  130  rotates per wiper sweep cycle are illustrated in  FIGS. 4-5 . The opposing radial directions include a first rotational direction R 1  (as illustrated in  FIG. 4 ) and a second rotational direction R 2  (as illustrated in  FIG. 5 ). The direction of translation D of the ball nut  210  will reverse when rotation of the aft shaft segment  140   c  reverses, e.g., at each wiper sweep cycle. The ball nut  210  translates toward the aft end  150   b  of the motor housing when the motor  130  rotates the aft shaft segment  140   c  in the direction R 1  during one wiper sweep cycle. The ball nut  210  translates toward the aft wall  250  of the endcap  230  when the motor  130  rotates the aft shaft segment  140   c  in the direction R 2  during another wiper sweep cycle. 
     Further, the ball nut  210  translates, during each wiper sweep cycle, by travel distance DT along the aft shaft segment  140   c.  The travel distance DT is a function of on a thread pitch of the aft shaft segment  140   c.  During movement of the ball nut  210 , the aft end  150   b  of the motor housing  160  and the aft wall  250  of the endcap  230 , as indicated above, may respectively form the forward stop and the aft stop (e.g. motion stops). This configuration may prevent over travel of the ball nut  210  against the aft shaft segment  140   c  during each wiper sweep cycle. Preventing the ball nut  210  from traveling beyond the travel distance DT during each wiper sweep cycle may prevent over rotation of the wiper arm  110 . 
     The following non-limiting example demonstrates a process in determining the travel distance DT to restrict the linear travel of the ball nut  210 . The process requires determining the number of complete rotations of the aft shaft segment  140   c  per wiper sweep cycle. This is a function of the gear reduction ratio and the sweep angle SA. The process then requires determining the travel distance DT as a function of the number of complete rotations of the aft shaft segment  140   c  per wiper sweep cycle (calculated) and the thread pitch for the aft shaft segment  140   c.    
     In one non-limiting embodiment the windshield wiper system  100  is configured as follows: a sweep speed of the wiper arm  110  ( FIG. 2 ) is one hundred (100) cycles per minute (CPM); a total sweep angle SA of the wiper arm  110  is sixty (60) degrees ( FIG. 2 ); the reduction gear  120  is configured to provide a reduction gear ratio of fifty to one (50:1); and the aft shaft segment  140   c  is threaded, e.g., with a helical groove, at ten (10) threads per inch (TPI). 
     The number of complete rotations of the aft shaft segment  140   c  per wiper sweep cycle is calculated by a first formula of: 
       (gear reduction x sweep angle)±(360 degrees per rotation).
 
     The gear reduction of fifty to one (50:1) and the sweep angle SA of the wiper arm  110  is sixty (60) degrees. Thus the first formula provides (50×60/360)=eight and a third (8.33) rotations per wiper sweep cycle. 
     The travel distance DT of the ball nut  210  per wiper sweep cycle is calculated by a second formula of: 
       (number of completed rotations of the aft shaft segment  140   c  per wiper sweep cycle (calculated above))±(the thread pitch of the aft shaft segment  140   c ).
 
     The thread pitch on the aft shaft segment  140   c  is ten (10) TPI. Thus the second formula provides (8.33/10)=(0.833) inches of travel for the ball nut  210  per wiper sweep cycle. Therefore, a travel distance DT of the ball nut  210  can be (0.850) inches per wiper sweep cycle, accounting for clearance. 
     To provide the travel distance DT for the ball nut  210 , a height HC of the endcap  230 , and length L of the aft shaft segment  140   c  that extends beyond the aft end  150   b  of the motor housing  160 , are properly sized. The height HC of the endcap  230  may differ from the length L of the aft shaft segment  140   c  by the thickness of the aft wall  250  of the endcap  230 , which may be considered nominal so these two measurements may be substantially the same. Thus, the height HC of the endcap  230  may be a total distance between the aft end  150   b  of the motor housing  160  and the aft wall  250  of the endcap  230 . Thus, the height HC would be the travel distance DT (calculated above), combined with a height HB ( FIG. 5 ) of the ball nut  210 , which may be measured. 
     For design of the motor  130 , it is noted that the speed in revolutions per minute (RPM) of the aft shaft segment  140   c  per wiper sweep cycle is a function of the gear reduction ratio and the sweep speed. That is, the gear reduction ratio is fifty to one (50:1) and the sweep speed of the wiper arm  110  is one hundred (100) CPM. With this, the aft shaft segment  140   c  will have a speed of: 
     gear reduction x sweep speed of wiper arm  110 . 
     This results in (50×100), or five thousand (5000) RPM. 
     With the above configuration, as indicated, the ball nut  210  will be prevented from traveling more than the travel distance DT. The motor  130  will be unable to produce over rotation in either direction R 1  or R 2  and instead will experience an over current draw. An over current trip logic, which may be programmed into the motor  130 , may execute upon sensing an over current draw from the motor  130 , shutting down the motor  130 . 
     Turning to  FIG. 6  a flowchart shows a method of operating the system  100 . As shown in block  510  the method includes driving a rotor  155   b  of a reversible motor  130  relative to a stator  155   a  of the reversible motor  130 . As shown in block  515  the method includes driving a reduction gear  120  with a forward shaft segment  140   b  of the motor shaft  140   a  with the rotor  155   b  and driving a wiper arm  110  with the reduction gear  120 . As shown in block  520  the method includes driving an aft shaft segment  140   c  of a motor shaft  140   a  with the rotor  155   b.  As shown in block  530  the method includes translating a ball nut  210  from rotation of the aft shaft segment  140   c  between a forward stop  165   a  and an aft stop  165   b.  As shown in block  535  the method includes preventing rotation of the ball nut  210  relative to the stator  155   a  with a guide pin  220  extending through a flange  210   a  of the ball nut  210 , from the forward stop  165   a  to the aft stop  165   b.  As shown in block  540  the method includes stopping the reversible motor responsive to sensing an increase in current draw by the motor when the ball nut contacts either of the forward stop and the aft stop while the aft shaft segment rotates. 
     In sum the disclosed embodiments provide for stopping/halting rotation of a motor shaft using ball screw mechanism. The disclosed embodiments utilize an over current-trip of the motor, where the over current-trip is activated at a locked rotor condition that occurs from stoppage of the ball nut. The system is formed and assembled utilizing common manufacturing techniques. The system is relatively easily configurable, depending largely on a sweep angle of the wiper blade arm. One benefit of the disclosed embodiments includes protecting aircraft, wiper components and related hardware from damage that could result from over sweep. A stopping torque required to engage the over current-trip of the motor with the disclosed embodiments is significantly decreased compared with motion limiters located away from the motor. The reduced wear on the motor results in a more reliable system. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, element components, and/or groups thereof 
     Those of skill in the art will appreciate that various example embodiments are shown and described herein, each having certain features in the particular embodiments, but the present disclosure is not thus limited. Rather, the present disclosure can be modified to incorporate any number of variations, alterations, substitutions, combinations, sub-combinations, or equivalent arrangements not heretofore described, but which are commensurate with the scope of the present disclosure. Additionally, while various embodiments of the present disclosure have been described, it is to be understood that aspects of the present disclosure may include only some of the described embodiments. Accordingly, the present disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.