Abstract:
This invention relates to windshield wiper system and method which utilizes a flexible member to account for compression loads in excess of a predetermined load, such as 30 percent, greater than a maximum load for the flexible member. The system utilizes a flexible pultruded composite material having a relatively low modulus of elasticity, yet relatively high elongation characteristics. The flexible arm bends to facilitate preventing damage to components in the wiper system when a compressive load applied to the flexible member reaches a predetermined load as a result of a fatigue condition, such as snow or ice build up on the windshield. In one embodiment, the predetermined load is defined as: 
     
       
         P CR =KE=1.3P link ; where: 
       
     
     P CR =the predetermined load; 
     P link =a maximum normal running load for a comparably-sized steel or rigid link which does not flex; 
     K is a          coefficient   =         π   2        I       L   2         ;                           
     E is the flexural modulus (MPa) 
     and I is a moment of inertia in mm 4    
     and L is a length (mm) of flexible arm 28.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of Ser. No. 09/134,266 filed Aug. 14, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a windshield wiper system and, more particularly, to a windshield wiper system which utilizes at least one flexible member which bends or flexes to compensate for compression loads in excess of a predetermined load. 
     2. Description of the Related Art 
     In the field of windshield wiper systems, wiper arms having wiper blades thereon are driven from a park position, where the blades are often situated at either the bottom of or below a windshield of a vehicle, through an inwipe position, to an outwipe position. During normal wiping operations, the blades oscillate between the inwipe and outwipe positions to clean the windshield of debris or particles, such as ice, snow or other debris. It is not uncommon that snow or ice can accumulate on the windshield and prevent the wiper blades from, for example, fully retracting from the inwipe position to the park position when a user actuates a wiper switch to an off position. 
     When the debris blocks the wiper arms and blades, a considerable amount of stress is imparted on the wiper linkage and drive motor which drives the blades. For example, a motor drive link, which couples the drive shaft of the motor to the drive linkage which drives the wiper arms, often experiences a compressive force. The linkage members of the wiper systems have in the past been stiffened to reduce expansion and shrinkage in order to avoid changing the wipe pattern requirements for the vehicles. However, in freezing, snowy weather, the snow and ice packs at the bottom of the windshield causes a restriction in the movement in the wiper arm and blade. Because of the rigidity of the motor drive link, the housing which houses the drive gears of the drive motor may crack or break. It has also been experienced that one or more drive plates which directly or indirectly couple the drive link to other linkage have been known to fracture or crack. 
     Accordingly, what is needed is a simple, yet effective, linkage system which utilizes one or more linkage arms having a relatively low modulus of elasticity with relatively high elongation and fatigue properties to facilitate avoiding the problems of the past. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of the invention to provide a system and method for driving a windshield wiper blade such that it can accommodate relatively high loads resulting from undesired fatigue conditions. 
     It is another object of the invention to provide a wiper blade linkage system which utilizes at least one flexible arm which is capable of flexing when a compressive load exceeds a predetermined amount, such as 30 percent higher than a maximum working load. 
     It is another object of the invention to provide a system and method which can accommodate for compressive loads on linkage components resulting from fatigue conditions, such as snow or ice situated on a windshield. 
     In one aspect, this invention comprises a windshield wiper drive linkage for use in a wiper system comprising a plurality of linkage arms, at least one of the plurality of linkage arms comprising a flexible arm which bends to facilitate preventing damage to components in the wiper system when a compressive load applied to at least one of the plurality of linkage arms exceeds a predetermined load as a result of a fatigue condition. 
     In another aspect, this invention comprises a wiper system comprising a first wiper, a second wiper, a windshield wiper drive linkage coupled to the first and second wipers, a drive motor coupled to the windshield wiper drive linkage and the windshield wiper drive linkage comprising a plurality of linkage arms coupled to the first and second wipers and the drive motor, at least one of the linkage arms comprising a flexible arm which bends to facilitate preventing damage to components in the wiper system when a compressive load applied to one linkage arms exceeds a predetermined load as a result of a fatigue condition. 
     In yet another aspect, this invention comprises a method of driving at least one wiper blade in a windshield wiper system comprising the steps of providing a drive motor for driving the at least one wiper blade, providing linkage for linking at least one wiper blade to the drive motor, the linkage comprising a flexible arm which bends to facilitate preventing damage to components in the wiper system when a compressive load applied to at least one linkage arms exceeds a predetermined load as a result of a fatigue condition. 
     Other objects and advantages of the invention will be apparent from the following description, the accompanying drawings, and the appended claims. 
    
    
     BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS 
     FIG. 1 is a general schematic view of a wiper blade drive and linking system in accordance with one embodiment of the invention; 
     FIGS. 2A-2D are illustrations of the wiper blade assembly of FIG. 1 as it is driven from an outwipe position towards inwipe and park positions; 
     FIG. 3 is a perspective view of a flexible member in accordance with one embodiment of the invention; 
     FIG. 4 is a front view of the flexible member shown in FIG. 3; 
     FIG. 5 is a plan view of the flexible member shown in FIG. 3; 
     FIG. 6 is a fragmentary sectional view of an end cap situated on the flexible member; 
     FIG. 7 is a view similar to FIG. 6 showing a plurality of shear areas to enable the cap to separate from the flexible member when a shear stress exceeds a predetermined amount; 
     FIG. 8A is a sectional view taken along the line  8 A— 8 A in FIG. 6; 
     FIG. 8B is a sectional view similar to FIG. 8A showing a flexible member with rounded corners; 
     FIG. 9 is graphical representation of a relationship between a compressive load for the flexible member relative to the length of the member as it shortens and flexes when the compression load exceeds a predetermined amount; 
     FIG. 10 is an illustration of another flexible member in accordance with another embodiment of the invention; 
     FIG. 11 is a illustration of the flexible member shown in FIG. 10 showing a shortened length L 4 ; 
     FIG. 12 is a sectional view taken along the line  12 — 12  in FIG. 10; and 
     FIG. 13 is a sectional view taken along the line  13 — 13  in FIG.  11 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIGS.  1  and  2 A- 2 D, a windshield wiper system  10  is shown comprising a first wiper  12  and a second wiper  14  for wiping a windshield  16 . The wiper  12  comprises a wiper arm  12   a  and blade  12   b , and wiper  14  comprises a wiper arm  14   a  and blade  14   b.    
     The wiper system  10  further comprises a windshield wiper drive linkage or linking means  18  comprising a first link arm  18  on which a drive motor  20  is fastened thereto by conventional means, such as a weld, nut and bolt, or the like. Notice that the frame link  18  comprises a first pivot housing  21  and a second pivot housing  21  which is secured thereto. The pivot housings  20  and  22  comprise a first rotatable pivot housing shaft  21   a  and a second rotatable pivot housing shaft  22   a  which are drivingly coupled to wiper arms and  14   a  (shown in phantom in FIG.  1 ), respectively. 
     The first rotatable pivot housing shafts  21   a  is coupled to a first end  24   a  of a drive plate  24 . Likewise, the pivot housing shaft  22   a  is secured to a first end  26   a  of a second drive plate  26 , as best illustrated in FIG.  1 . An operating or “slave” link  23  couples a second end  24   b  of first drive plate  24  to a second end  26   b  of second drive plate  26  such that the drive plates  24  and  26  operate synchronously to rotatably drive the pivot housing shafts  21   a  and  22   a  in the direction of arrow A, thereby driving the wiper blades  12   b  and  14   b.    
     The linkage or linking means  18  further comprises a motor drive link or flexible arm  28  having a first end  28   a  coupled to the second end  24   b  of the drive plate  24 . The motor drive link or flexible arm  28  further comprises a second end  28   b  which is coupled to an output shaft  20   a  of motor  20  via a crank arm  30 . In this regard, the crank arm  30  comprises a crank arm ball (not shown) and the drive plate  24  comprises a drive plate ball (not shown). 
     The arm  28  comprises an elongated rectangular member  29  (FIGS. 3-5) comprising a socket  32  and socket  34  which are over-molded thereon. As best illustrated in FIGS. 3-6, the first end  28   a  of motor drive link or flexible arm  28  comprises the socket  32  for mounting onto the drive plate ball (not shown) on drive plates  24 , and second end  28   b  of motor drive link or flexible arm  28  comprises the socket  34  for receiving crank arm ball (not shown) on crank arm  30 . As best illustrated in FIGS. 3-7, the first and second ends  28   a  and  28   b  comprise the sockets  32  and  34 , respectively. Notice that socket  32  (FIG. 6) defines a socket area  40 , respectively. It has been found that it is desirable to align the centerline CL (FIG. 5) with the axis of shafts  20   a ,  22   a  and  24   a  when the wipers  12  and  14  are in the park position. 
     As best illustrated in FIGS. 2A-2C and  3 , flexible arm  28  defines a length L 1 , which in the embodiment being described is in excess of 250 mm. During a fatigue condition, when the compressive load applied to the arm  28  exceeds a predetermined load (such as at least 30 percent of a maximum working load of flexible member  28  as defined below), the flexible arm  28  begins to flex or bend. This causes the flexible arm  28  to shorten to a length L 2 , illustrated in FIG. 2D, and this length L 2  is shorter than length L 1 . As illustrated in the graphs shown in FIG. 9 which are referred to and described later herein, the compressive load remains substantially constant as the flexible arm  28  continues to bend or flex and shorten for at least 5 mm after the compressive load achieves the predetermined load. 
     As illustrated in FIGS. 3-5, the flexible arm  28  is preferably made from a composite material of the type described later herein relative to Table 1. As best illustrated in FIG. 8A, the flexible arm  28  is generally rectangular in cross-section and is generally elongated (FIGS.  3 - 5 ). It should be appreciated that the member  28  could be elliptical, circular or of some other geometry as desired. In the embodiment being described, the length L 1  (FIGS. 2A and 3) of flexible arm  28  is on the order of at least 250 mm, but it could be any suitable length depending on the application. 
     FIG. 7 illustrates another embodiment of the invention where the flexible member  28  may be provided with sockets  32  and  34  with shear relief areas  50  and  52  which enable the end caps  32  and  34  to shear away or separate from member  29  when a predetermined stress applied to the flexible member  28 . Preferably, the predetermined stress is selected to be just slightly below a break point or maximum load of the member  29  so that, when the member  29  is about to reach its break point, one or more of the sockets  32  or  34  are permitted to shear and separate themselves from member  29  to avoid breakage. 
     As illustrated in FIG. 7, line C defines a shear plane (A s =lW) and a minimal cross section (AC=HW), as shown by line D in FIG.  7 . The shear stress along shear plane should not exceed the shearing strength which is defined as follows:        T   =       P     A   s       =       P   lW     ≤     T   y                                
     where: 
     A s=lW;    
     L=a length of shear plane (line C); 
     W=a width of member  28 ; 
     P=a tensile load on member  28  as measured experimentally; 
     T=shear stress of member  28 ; and 
     T y =yield shear stress of member  28 . 
     A tensile stress on the minimum cross section should not exceed a yield stress as follows:        S   =       P     A   c       =       P   HW     ≤     S   y                                
     Where: 
     S=a tensile stress of member  28 ; 
     S y =a yield stress of member  28 ; 
     P=a tensile load on member  28  as measured experimentally; 
     H=a height of member  28 ; and 
     W=a width of member  28 . 
     The general operation of the linkage  18  will now be described relative to FIGS.  1  and  2 A- 2 D. When a user actuates a wiper switch (not shown) the drive motor  20  is energized to cause the wipers to move from a park position (PP) through an inwipe position (IWP) towards an outwipe position (OWP), back to the inwipe position and so on. When the user turns the switch to an off position (not shown), the drive motor  20  drives the crank arm  30  to drive the motor drive link or flexible arm  28  to attempt to drive wipers  12  and  14  from the inwipe position to the park position. The motor  20  rotatably drives crank arm  30  which, in turn, drives the motor drive link or flexible arm  28  to drive the second end  24   b  of drive plate  24  in the direction of arrow B in FIG.  1 . The operating link  23  responds by directly driving second end  26   b  of drive plate  26 . The movement of drive plates  24  and  26 , in turn, rotatably drive the pivot housing shafts  21   a  and  22   a , respectively, to drive the first and second wipers  12  and  14  across the face of windshield  16  in response to rotation of the motor drive shaft  20   a.    
     As best illustrated in the FIGS. 2C and 2D, a fatigue condition may occur when snow, ice or some other material or condition (illustrated as  49  in FIGS. 2C and 2D) prevents the wiper blades from moving, for example, from the inwipe position to the park position. However, the motor  20  continues to drive the motor drive link or flexible arm  28 . Consequently, a compressive force or load is applied to the arm  28 . The flexible arm  28  bends or flexes to facilitate preventing damage to the various components in the wiper system  10  when the load applied to the flexible arm  28  exceeds a predetermined load described later herein. Thus, it should be appreciated, that the flexible arm  28  flexes to accommodate the compressive force or load mentioned earlier when the compressive force or load exceeding the predetermined load as a result of the fatigue condition. 
     In the embodiment being described, it was determined empirically that, when the predetermined load was established is at least 130 percent or more of a maximum normal running load, the arm  28  remained rigid enough to handle the normal wiping, yet flexible enough to bend during fatigue conditions. Thus, when the predetermined load exceeds about 130 percent of the maximum normal running load for the flexible arm  28 , the wiper system  10  was able to operate with maximum efficiency, while protecting the components of the system  10 . In the embodiment described, the predetermined load is defined as follows: 
     
       
         P CR =KE=1.3P link ; where: 
       
     
     P CR =the predetermined load; 
     P link =a maximum normal running load for a comparably-sized steel or rigid link which does not flex; 
     K is a          coefficient   =         π   2        I       L   2         ;                          
     E is the flexural modulus (MPa) 
     and I is a moment of inertia in mm 4    
     and L is a length (mm) of flexible arm  28 . 
     If the cross-sectional shape of member  28  is rounded on its edges as shown in FIG. 8B, then the formula for the area moment of inertia (I) is calculated using the following equation:              I   =                    1   12                       w        (     h   -     2      r       )       3       +       1   6                       r   3          (     b   -     2      r       )         +       1   2                       r        (     h   -   r     )       2          (     b   -     2      r       )       +                                  1   4                   π                     r   2          [       r   2     +       (     h   -     2      r       )     2       ]         ;                                  
     where W, H and R are width, height and fillet radius, respectively, of the cross-section of member  28  shown in FIG.  8 B. 
     Eight samples of composite material with dimensions as shown in Table 1 below were made and tested using an Instron testing machine. The load and displacement were recorded and the testing results are shown in Table 1 and in the graph illustrated in FIG. 9 
     
       
         
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                   
                 L1 (mm) 
                 b (mm) 
                 h (mm) 
                 Pcrit- 
                 Pcrit- 
               
               
                 Material 
                 (FIG. 3) 
                 (FIG. 4) 
                 (FIG. 8) 
                 Exp. (N) 
                 Theory (N) 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1. Glastic 
                   
                   
                   
                   
                   
               
               
                  Laminate 
               
               
                 1a. 
                 253 
                 12.7 
                 3.3 
                 61.71 
                 68.74 
               
               
                 1b. 
                 253 
                 19.09 
                 3.3 
                 94.96 
                 103.33 
               
               
                 1c. 
                 253 
                 25.32 
                 3.3 
                 131.91 
                 137.05 
               
               
                 2. Epoxy 
               
               
                  Resin (IP) 
               
               
                 2a. 
                 253 
                 12.7 
                 3.18 
                 106.23 
                 97.69 
               
               
                 2b. 
                 253 
                 19.09 
                 3.18 
                 206.52 
                 146.85 
               
               
                 2c. 
                 253 
                 25.32 
                 3.18 
                 290.02 
                 238.47 
               
               
                 3. Polyester 
                 300 
                 20 
                 3.4 
                 290.02 
                 238.47 
               
               
                  (NCC) 
               
               
                 4. Fiberglass 
                 305 
                 31.7 
                 2.42 
                 237.98 
                 219.10 
               
               
                   
               
             
          
         
       
     
     As illustrated in Table 1, the four different composite materials included a molded glass laminate provided by Red Seal Electric Company of Cleveland, Ohio; a molded epoxy resin provided by International Paper of Hampton, South Carolina; a protruded polyester with oriented glass fibers provided by National Composite Center of Dayton, Ohio; and a protruded polyester with uni-directional glass fibers provided by Polygon Company of Walkerton, Indiana. 
     It should be apparent from the Table 1 that the actual loads (Pcrit-Exp.) compared vary favorably to theoretical loads (Pcrit-Theory). 
     FIG. 9 graphically illustrates the Instron testing machine results. Notice that, as the load on compressive arm  18  increased to in excess of 300 Newton, the flexible arm  18  began to bend or flex (as shown in FIG.  2 D), thereby causing the load to be distributed across the flexible member  28 . Notice that the load remains substantially constant even while the motor  20  (FIG. 1) continues to apply torque to the flexible arm  28 . 
     FIGS. 10-13 illustrate another embodiment of the invention with like parts being identified with the same part numbers, except that a “prime” mark (“′”) has been added thereto. In this embodiment, the flexible arm  28 ′ is generally circular in cross-section (as shown in FIG. 13) and comprises a plurality of areas of flex  62 ′ at areas where the flexible member  28 ′ defines an oval shape in cross section, as shown in FIG.  12 . The points of weakness permit the flexible member  28 ′ to flex at the areas  62 ′ when the compressive load exceeds the predetermined load, such as  30  percent higher than a maximum working load of the flexible member  28 ′. Notice that the flexible member  28 ′ defines a length L 3  (FIG. 10) which is greater than the length L 4  shown in FIG.  11 . It has been found that the difference between the length L 3  and length L 4 , as well as the difference between length L 1  and length L 2  referred to in the embodiment described above, is directly proportional to the arcuate distance the drive motor  20  continues to drive the drive plate  24  (FIG.  1 ). 
     While the method herein described, and the forms of apparatus for carrying these methods into effect, constitute preferred embodiments of this invention, it is to be understood that the invention is not limited to these precise methods and forms of apparatus, and that changes may be made in either without departing from the scope of the invention, which is defined in the appended claims.