A wiper blade for windshields of motor vehicles, has an elongated wiper strip having a constant diameter, which is held by a support frame and loaded toward the windshield to be wiped is movable over the windshield transversely to its longitudinal extension, wherein, viewed in cross section, the wiper strip has a tip held by a support frame and consisting of synthetic caoutchouc and a skirting strip connected with it, on whose side facing away from the tip a movable wiper lip strip resting on the windshield is attached by means of an elongated tilting bar. A wiper blade, which is dependable in operation over time and can be produced in a cost-effective manner results in that at least a portion of the areas forming the outer contour of the skirting strip consists of natural caoutchouc with a low coefficient of friction.

BACKGROUND OF THE INVENTION 
The invention relates to a wiper blade for cleaning windshields of motor 
vehicles. 
The wiper strips which are a part of the wiper blade which serves to remove 
water drops from the windshield of a motor vehicle, for example, and which 
are attached to the wiper blades of a wiper blade device that move back 
and forth in front of the windshield, are customarily produced, in that a 
previously compounded and vulcanized initial rubber material, therefore an 
un-vulcanized synthetic caoutchouc, is shaped in a metal mold and 
vulcanized. Subsequently the surface of the thus obtained rubber wiper 
strip is post-treated in order to reduce the friction resistance on the 
windshield to be wiped in accordance with the requirements, or to improve 
the slidability of the rubberized wiper strip on the windshield to be 
wiped. At a temperature t of 23.degree..+-.5.degree. C. and a relative 
humidity of 50.+-.3%, the desired coefficient of friction A may not exceed 
the value of 2.0. This post-treatment of the surface consists for example 
of a hardening of the surface of the rubberized wiper strip by 
chlorination or of a coating, in order to achieve a surface layer of the 
wiper strip which contains a fine, lubricating powder, for example 
powder-like molybdenum sulfide. Even though the chlorination reduces the 
friction resistance and improves the slidability, the necessary durability 
for wear and tear is still missing. The application of a lubricating 
surface layer containing powder presents the disadvantage in that it is 
scraped off after the wiper strip has been in use for a short period of 
time, thus lacking the necessary durability. 
Incidentally, it should be considered that the improvement of the sliding 
properties of the wiper strips because of the reduced friction coefficient 
between the wiper strip and the glass surface of the windshield presents 
difficulties in that they do not tilt in the tilting bar when the wiper 
blade reverses directions during the operation of the wiper blade device 
which is normally embodied as pendular wiping device, so that the wiper 
strip is not dragged but pushed. A flawless, noiseless operation of the 
wiper blade device is thus ruled out. 
To overcome this problem, in connection with a known wiper blade (DE 34 40 
677 A1) of the species in question, the areas of the wiper strip which 
come into contact with the windshield during the wiper blade operation 
were made of a lubricating synthetic rubber, for example urethane rubber, 
styrene butadiene rubber, fluoro rubber, chlorinated sulfonized rubber or 
a mixture of these materials. However, such wiper strips are not, or are 
only insufficiently halogenizable, so that the desired coefficient of 
friction can hardly be reached. 
SUMMARY OF THE INVENTION 
It is the object of the invention to develop a rubber wiper blade, which is 
distinguished by superior sliding properties, in particular by a very low 
friction resistance remaining constant over the long-term and which can be 
produced in a cost effective way. It is also intended to provide areas of 
the wiper strip with an advantageous; coefficient of friction, which 
occasionally come into contact with the surface of the windshield to be 
cleaned. 
In the inventive rubber wiper blade the desired coefficient of friction 
between both sliding components of wiper lip strip and vehicle windshield 
is practically maintained indefinitely. However, a certain friction is 
necessary in order to achieve the tilting motion of the wiper lip strip. 
This tilting motion occurs in the reversed pendular movements of the wiper 
strip and assures the required drag position of the wiper lip strip which 
is necessary in both pendular directions for proper achievement of the 
wiping operation. 
A further improvement in attaining the object results if at least a portion 
of the areas forming the outer contour of the wiper lip strip consists of 
a natural caoutchouc with a low coefficient of friction, because in this 
way the coefficient of friction of the wiper lip strip which has to 
perform the main portion of the cleaning is matched to the coefficient of 
friction of the skirting strip. 
The wiper strip areas equipped in this way are hardenable, wherein their 
shape can be kept constant, even under difficult wiping conditions. In 
this way an improved and secure holding of the wiper strip in the claws of 
the support frame is assured and the required mobility of the wiper strip 
in the claws is guaranteed. 
A particularly cost effective production of the wiper strip results, if the 
wiper strip has a base component made of synthetic caoutchouc enveloping 
the tip, of which a core area of the skirting strip and the tilting bar 
are a part, if in addition two wings are arranged, made of natural 
caoutchouc with a low coefficient of friction, extending away from the 
core area consecutively in different directions and which are a part of 
the skirting strip, and finally, if the tilting bar makes a transition 
into a connector strip, on which the wiper lip strip consisting of natural 
caoutchouc with a low coefficient of friction is arranged. 
The natural caoutchouc areas of the wiper strip are hardened by 
halogenization, while the other wiper strip areas remain soft and pliable. 
Depending on the degree of halogenization, the hardenable areas can be 
adjusted in accordance with the requirements. This also applies to the 
desired coefficient of friction. 
Additional advantages of the invention are to be taken from the following 
description, which relates to an exemplary embodiment of the invention 
represented in the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
A wiper blade 10, represented partially and in a plan view, in FIG. 1 has a 
support frame 12 consisting of several support bracket parts, holding an 
elongated wiper strip 16 made of an elastic material by means of holding 
claws 14. 
In FIG. 2 the structure of the wiper strip 16 is shown in cross-section. 
Since the wiper strip 16 has a constant diameter over its entire length, 
it can be produced by extrusion, for example. It has a tip 20, which is 
held by the holding claws 14 of the support frame 16. In its longitudinal 
direction, the tip 20 is penetrated by a longitudinal conduit 22, in which 
a runner-like spring element 24 is housed, which at least approximately 
extends over the entire length of the wiper strip 16 and provides the 
proper distribution of the wiper blade bearing force. On the side facing 
away from the support frame, the tip 20 has two longitudinal grooves 26 
located opposite each other, into which the holding claws 14 dip with 
their end sections 28. Between the two longitudinal grooves 26 a base 
component 30 of the wiper strip 16 making a transition into the tip 
remains. On the side of the base component 30 facing away from the tip 20 
a narrow tilting bar 32 is joined, which is formed by narrow longitudinal 
slots 34, which are spaced apart from the longitudinal grooves 26. The 
tilting bar 32 remains between the base surfaces of the opposing and 
oppositely arranged longitudinal slots 34. Between the longitudinal 
grooves 26 and the longitudinal slots 34 wing-like widenings 36 remain, 
which form a skirting strip 38 extending over the entire width of the 
wiper strip 16. On its end facing away from the skirting strip 38, the 
tilting bar 32 makes a transition into a wiper lip strip 40, which during 
operation of the wiping device rests at least at its free end on the 
windshield to be wiped and takes over the cleaning. 
As shown by FIG. 2, the greater portion of the wiper lip strip 40 is made 
of a different materials then the tip 20, the base component 30 and the 
tilting bar 32. The wiper lip strip 40 is connected to the tilting bar 32 
by a connector strip 42 connected in one piece with the latter. This 
connector strip 42 also extends over the entire length of the wiper strip 
16. It has a curved end contour 44 facing the wiper lip strip 40, on which 
an opposite contour 46 is matched to the wiper lip strip 40, which is 
almost wedge-shaped the cross-section. This results in a relatively large 
connecting surface between the tilting bar 32 and the wiper lip strip 40. 
Further, FIG. 2 shows that the two widenings or wings 36 of the wiper 
strip 16 are made from a different material than the tip 20 and the base 
component 30. Those two areas 20, 30 of the wiper strip 16 as well as the 
tilting bar 32 and the connector strip 42 consist of synthetic caoutchouc. 
The wings 36 of the wiper strip 16 however, or at least their areas which 
form the outer contour of the skirting strip, are made of natural 
caoutchouc with a low coefficient of friction. This also applies to the 
wiper lip strip 40, which is made of the same material as the wings 36 of 
the skirting strip 38. In certain cases it can be advantageous, too, if 
the corner areas 47, which form the outer contour of the tip 20 and which 
are facing the windshield 60 (FIG. 3), are also made of natural caoutchouc 
with a low coefficient of friction. Because of this the wiper strip can 
more easily move in the holding claws of the support frame, which is 
particularly necessary when passing over variously curved windshield 
areas. In addition, the danger of a disadvantageous deformation of the 
corner areas 47 is ruled out. The areas 40, 36, 47 of the wiper strip 16 
consisting of the said natural caoutchouc can be extruded in one 
production step and vulcanized in one single piece, along with the areas 
20, 30, 32, 42 of the wiper strip 16 which consist of synthetic 
caoutchouc. 
In what follows, the mode of functioning of the wiper blade 10 on the 
windshield 60 will be explained by means of in FIG. 3, in which the wiper 
strip 40 is shown in an extremely slanted position in respect to the 
windshield 60. Such extreme positions can result under certain conditions, 
known to the expert-for example a severe curvature of the windshield, high 
bearing pressure on the windshield by the wiper blade, deformed wiper arms 
etc. In order to obtain a cleansing effect, the wiper strip 16 has to be 
loaded toward the windshield. This is suggested by the arrow 62 shown in 
FIG. 3. Thus, if the wiper blade is moved over the surface of the 
windshield 60 in the direction suggested by the arrow 64, the wiper lip 
strip 40 tilts into a so-called drag position, in which it is dragged over 
the windshield 60. In this case, under the disadvantageous operating 
condition already described, the one wing 36 of the skirting strip 38 
which is facing the windshield 60, can touch the surface of the windshield 
60 to be wiped with its end area. With the known, already mentioned wiper 
blades with wings made of synthetic caoutchouc--whose coefficient of 
friction is too high--undesirable, braking and vibration causing side 
effects develop, which in addition adversely influence the wiping quality. 
In addition, FIG. 3 shows that the wiper lip strip 40 is supported with a 
corner edge 66 on the skirting strip 38, so that the bearing force (arrow 
62) is properly put into effect. When the wiper blade 10 gets into its 
reverse position and it reverses its direction of movement, it is moved in 
the opposite direction (arrow 68) over the windshield 60. In the process, 
the wiper lip strip 40 tilts over into its other operating position in the 
tilting bar 32, indicated by the dashdotted line in FIG. 3, so that the 
wiper lip strip 40 also is dragged over the windshield and not pushed. To 
assure a safe tilt of the wiper lip strip 40 in its respective drag 
position, a certain amount of friction between the windshield and the 
wiper lip strip 40 is required. The coefficient of friction of the natural 
caoutchouc material must take this requirement into account. However, this 
coefficient of friction necessary for the tilt into the respective drag 
position should not be substantially exceeded, so that the fundamental 
object of the invention can be attained. 
It is therefore provided by the concept of the invention that at least a 
portion of the areas constituting the outer contour of the skirting strip 
38, or the areas constituting the outer contour of the wiper lip strip 40, 
consist of natural caoutchouc with a low coefficient of friction. This 
preferably refers to the areas which could bear on the windshield 60 
during the wiping operation (FIG. 3). 
The desired coefficient of friction p to be attained, measured at a 
temperature of 23.+-.5.degree. C. and at a humidity of 50.+-.3% should be 
approximately 2.0, or preferably lower than 2.0.