Abstract:
A wiper arm has a fastening element and a cap which surrounds the fastening element and is supported via a bearing face in the form of a closed C radially continuous about a toggle joint covering an angle of more than 180° to maintain the cap on the fastening element so that it can be hinged open to the joint.

Description:
BACKGROUND OF THE INVENTION 
     The invention is based on a wiper arm. 
     Known windshield wipers have a wiper arm which is constructed of a fastening element, secured to a drive shaft, that has a joint head; a joint part connected to the joint head via a toggle joint; and a wiper rod rigidly adjoining the joint part. The windshield wiper also has a wiper blade, which has a support bracket system and a wiper strip held by the support bracket system. The wiper blade is pivotably connected to the wiper arm in that a hooklike end of the wiper rod engages between two support cheeks of the support bracket system and surrounds a pivot pin. The joint thus formed guides the wiper blade with the wiper strip over a motor vehicle window; the joint part and the support bracket system make it possible for the wiper strip to adapt to a curvature of the vehicle window. A requisite contact pressure of the wiper strip on the vehicle window is attained with at least one tension spring, which braces the fastening element and the joint part jointly with the wiper rod via the toggle joint. 
     The fastening element is as a rule made from aluminum or die-cast zinc and is embodied as largely solid in its head and cone regions. A middle region of the fastening element has a U-shaped cross section, open toward the vehicle window, with reinforcing ribs. 
     To prevent the wiper arm in the preassembled state, before it is mounted on the motor vehicle, from collapsing in response to the spring force and thus to prevent the tension spring from coming unfastened, two side walls of the joint head extend in the longitudinal direction via the toggle joint and form two support faces, by way of which the joint part can be supported in the direction of the wiping area. 
     In known wiper arms, the fastening elements are often covered with a plastic cap that has a top wall and side walls, so as to protect the fastening element and its bearing points against soiling and corrosion and to obtain an attractively shaped component. 
     In order to make the cap in the hinged-open state secure against being lost and yet easily mountable and unmountable, the cap is pivotably supported on bearing faces that are closed over more than 180° on bearing protrusions on the joint head. The bearing faces are formed by the face ends of the side walls. If the fastening element or the wiper arm is to be mounted on the motor vehicle or unmounted or adjusted, the cap can be hinged open on the side of the bearing point for the drive shaft. Via the more than 180° closed bearing face, the cap is supported secure against being lost in the hinged-open state and can easily be slipped on by its open side or pulled off again. 
     To allow folding the cap open far enough, there is a recess in each of the side walls of the joint head that extend along the toggle joint; the cap can dip into this recess with its top wall when it is opened. 
     In the installed state on the motor vehicle, the tension spring generates the contact pressure of the wiper blade on the windshield. In the preassembled state, this force must be absorbed via a far shorter lever, from the toggle joint to the support face, and as a result a strong force acts on the support face. To allow securely absorbing this force in the joint head, the side walls must be made sufficiently high. In the region of the recesses, the cross section is weakened by the recesses and is more heavily loaded by notch stresses, which must be compensated for by a sufficiently high side wall below the recess. As a result, there are especially high side walls around the recesses. 
     Furthermore, the side walls of the joint head are made thicker than those of the remainder of the fastening element, so that the stresses around the toggle joint can be reliably absorbed. The greater material thickness, because of a uniform transition suitable for casting, extends up to the support faces. 
     ADVANTAGES OF THE INVENTION 
     According to the invention, the joint head has a round face end, and as a result with little expenditure of material, uniform wall thickness and thus a shape suitable for casting is attained for absorbing the stresses around the toggle joint. The joint head can be manufactured in a casting operation jointly with the fastening element or can be mounted afterward. 
     The face end of the joint head serves simultaneously as a guide for the cap. The bearing face at the cap is formed In keeping with these objects, one feature of present invention, resides, briefly stated, in a wiper arm which avoids the disadvantages of the prior art. over a first part of the angle by the face ends of the side walls of the cap, which are guided on bearing protrusions disposed laterally on the joint head. The remainder of the angle is formed by the inside of the preferably curved top wall of the cap, which is guided on the face end of the joint head. One support cheek is disposed on each side of the joint head and extends in the longitudinal direction, and its top side acts as a support face. 
     The top wall is embodied as narrower than the inside clearance between the support cheeks, so that the top wall can be thrust between the support cheeks when the cap is opened. Recesses in the support cheeks can be avoided as a result, and thus the support cheeks can be made triangular or in the form of truncated triangles in the longitudinal direction, with little expenditure of material, in a way that suits the course of the moment. The joint head can be made from little material and thus can be made light in weight. This makes the construction especially suitable for fastening elements or joint heads of zinc, so that despite the heavy yet economical material, an acceptable weight can be achieved. 
     Without recesses, the casting mold for the fastening element or the joint head also becomes simpler, because pushers or similar emplacement parts for the recesses can be dispensed with. 
     The construction according to the invention also assures that the bearing face on the cap, which overall encloses an angle of more than 180°, can be distributed over a plurality of planes, each encompassing less than 180°. As a result, the cap can be made in a casting process without pushers. The casting molds become narrower as a result, and thus more molds can be placed side by side. They are also less expensive, and the production cost becomes less. 
     In a further feature of the invention, it is proposed that the bearing protrusions on the joint head have a greater radius than the outer contour of the joint head. Given a favorable pivot point, the cap can be hinged upward by more than 90° (in the prior art, only about 60° was possible). 
     The strains can also be better absorbed by the entire width of the joint head, including the height of the bearing protrusions; that is, an axially larger effectively usable bearing face is created, which in particular is reinforced in its outer region by the large radius of the bearing protrusions. Over the service life, there is less bearing play. In addition, an attractively shaped cap can be formed that covers the fastening element except for the bearing protrusions and the support cheeks. 
     Further advantages will become apparent from the ensuing description of the drawing. The drawing shows one exemplary embodiment of the invention. The drawing, description and claims include numerous characteristics in combination. One skilled in the art will expediently consider each of the characteristics individually as well and combine them into appropriate additional combinations. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1, a fastening element from below; 
     FIG. 2, a fastening element of FIG. 1 from the side; 
     FIG. 3, a cap from below; 
     FIG. 4, a cap of FIG. 3 from the side; 
     FIG. 5, an enlarged detail V of FIG. 2; 
     FIG. 6, an enlarged detail VI of FIG. 4; 
     FIG. 7, a detail of a fastening element with a mounted cap in the opened state; 
     FIG. 8, a fastening element with a mounted cap of FIGS. 1 and 3 from below; and 
     FIG. 9, a fastening element with a mounted cap and part of a joint part from the side. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1 and 2 show a fastening element  10  of a wiper arm, which on a first end  12  has a bearing point  14  for a drive shaft of a wiper arm. On the other end of the fastening element  10  is a joint head  16 , with which the fastening element  10  is connected via a toggle joint  20  to a joint part  18  (FIG.  9 ). The fastening element  10  and the joint part  18  are braced via a tension spring  22 , which in the mounted state of the wiper arm on the motor vehicle presses a wiper blade against a windshield. 
     The wiper arm is supplied to the automobile manufacturer in the preassembled state. To prevent the wiper arm from collapsing by the tensile strength of the tension spring  22  and thus to prevent the tension spring  22  from possibly coming loose, support faces  26 ,  28  are disposed on the joint head  16 , by way of which the joint part  18  in the preassembled state can be braced in the direction of the wiping area  24  (FIG.  9 ), so that the tension spring  22  is always under a tension. 
     To protect the fastening element  10  against dirt and corrosion and to attain an attractively shaped component that is favorable in terms of the wind attack face, the fastening element  10  is surrounded with a plastic cap  30  that has a top wall  32  and side walls  34 ,  36 . In FIGS. 3 and 4, the cap  30  is shown from below and from the side in the as yet unmounted state. FIGS. 8 and 9 show the fastening element  10  with the mounted cap  30 . 
     In the mounted state of the wiper arm, the cap  30  must reliably cover the fastening element  10  and is intended to be capable of being hinged open on the side of the bearing point  14  so that the wiper arm can be installed. To that end, the cap  30  is pivotably supported on the joint head  16 , and in the mounted state of the wiper arm, with protrusions  60 ,  62 , it engages recesses  64 ,  66  on the fastening element  10  on the side of the bearing point  14  (FIGS.  1  and  3 ). 
     According to the invention, the joint head  16  is embodied as round on its face end  40  in the pivoting direction  38  of the cap  30 , as can be seen in FIG.  2  and in the detail V of FIG. 5, which is enlarged compared with FIG.  2 . As a result, it can be embodied with a uniform material thickness easily and in a way appropriate for casting. In addition, the face end  40  can be used as a bearing face for the cap  30 . The support faces  26 ,  28  are formed by two support cheeks  42 ,  44 , which extend in the longitudinal direction  46  laterally of the joint head  16 . 
     To assure that in the hinged-open state the cap  30  will be joined in captive fashion to the fastening element  10 , this cap is supported on the joint head  16  on a C-shaped bearing face  48 ,  50 ,  52  that is closed over more than 180°, and as a result at the same time simple mounting and unmounting is made possible, because the cap  30  can be slipped onto the joint head  16  and pulled off by way of the open side of the bearing face  48 ,  50 ,  52  (FIG.  6 ). 
     The bearing face  48 ,  50 ,  52  is formed, over a first part of the angle  72 , by the face ends  48 ,  50  of the side walls  34 ,  36  of the cap  30 , which are guided on bearing protrusions  54 ,  56  disposed laterally on the joint head  16  (FIGS.  6  and  1 ). The remainder of the angle  74  is formed by the inside  52  of the top wall  32  of the cap  30 , which wall is curved in this region (FIG.  6 ). The bearing face  48 ,  50 ,  52  of 180° is distributed over a plurality of planes, each of less than 180°. As a result, the cap  30  can be produced in a casting process in a simple way, without pushers. 
     The top wall  32  of the cap  30  is narrower, in the region of the joint head  16 , than an inside clearance  58  between the two support cheeks  42 ,  44  disposed laterally on the joint head  16 ; as a result, the top wall  32  can be pushed between the support cheeks  42 ,  44  while being guided on the joint head  16 , when the cap  30  is hinged open (FIG.  7 ). The height of the support cheeks  42 ,  44  can be adapted in a targeted way to the moment course, by being embodied triangularly in the longitudinal direction  46 , so that recesses for the cap  30  are not required. 
     The bearing protrusions  54 ,  56  disposed laterally on the joint head  16 , together with the support cheeks  42 ,  44 , have approximately the same shape as a camshaft in section, and as a result an attractive shape appropriate for casting is achieved. In addition, the radius  76  of the bearing protrusions  54 ,  56  is greater than the radius  68  of the face end  40  of the joint head  16 . The total width  70  of the joint head  16 , including the height of the bearing protrusions  54 ,  56 , can be utilized for bearing the joint part  18 . The width  70  of the joint head  16  that can be effectively used for bearing becomes greater, and as a result the bearing play that occurs over the service life becomes less.