Abstract:
A wiper brush arm for a motor vehicle includes a rigid molded plastic single-piece body having a generally elongated shape whereof one end is driven in reciprocating wiping movement, and the other end bears a wiper brush or a wiper blade. The body is coated at least partly with a protective layer protecting the body against external environmental attacks, such as ultraviolet radiation. The protective layer is made of plastic material.

Description:
BACKGROUND  
         [0001]    The invention concerns a wiper arm. The invention concerns more specifically a wiper arm for a motor vehicle also forming a brush, which is called a wiper brush.  
           [0002]    The wiper arms are of a generally elongated shape and allow transmission of a reciprocating wiping movement of a drive head situated, for example, near the lower base of the front windshield or the rear window of a vehicle, to a wiper brush equipped with a wiping scraper.  
           [0003]    The wiper arms must be sufficiently rigid in order to be able to transmit the reciprocating wiping movement without undergoing significant distortions. They are situated on the exterior of the vehicle and are visible, in particular, during the reciprocating wiping movement. Their aesthetics have a significant influence on the general exterior aspect of the vehicle.  
           [0004]    A wiper arm can be made up of a metal profile, for example, a reverse U cross-section, which allows transmission of the wiping effort. However, exterior stresses, such as humidity and rain, can damage it, for example, by provoking the appearance of oxidation, in particular, rust. In such a manner as to protect the metallic profile, it is common knowledge to cover it with a protective layer such as paint.  
           [0005]    The fabrication of such a wiper arm is costly. In effect, it contains a significant number of steps such as cutting a metallic side, its folding and its painting. In addition, a metallic wiper arm is heavy.  
           [0006]    Another solution proposes creating a wiper brush arm comprising a single-piece body in a molded plastic material. The necessary mechanical rigidity necessitates the use of a reinforced material.  
           [0007]    The exterior attacks, in particular, ultraviolet rays emitted by the sun, provoke a modification of the coloration of certain of these materials. For example, when a wiper arm is created in a thermoplastic material reinforced with fiberglass, the ultraviolet rays cause whitening of the piece. Such a phenomenon is unacceptable.  
         SUMMARY  
         [0008]    With the goal of remedying these inconveniences, the invention proposes a wiper arm, in particular, a motor vehicle brush arm of the type comprising a single-piece rigid body in a molded plastic material and having a generally elongated shape, an end of which is driven in reciprocating wiping movement and the other end bears a wiper brush or wiper blade, characterized in that the body is, at least in part, coated by a layer protecting the body against exterior attacks, such as ultraviolet rays, and in that the protective layer is made of a plastic material.  
           [0009]    According to other characteristics of the invention:  
           [0010]    the body comprises reinforcement means;  
           [0011]    the reinforcement means consist of fibers, in particular, fiberglass;  
           [0012]    the surfaces of the body and the protective layer in mutual contact include means for the mechanical coupling of the protective layer onto the body;  
           [0013]    the coupling means consist of, at least in part, a chemical and/or physicochemical bond between the surfaces in mutual contact;  
           [0014]    the coupling means consist of, at least in part, a coupling zone of one of the two elements, the shape of which cooperates with a second coupling zone complementary to the other element;  
           [0015]    the protective layer envelopes the body at least in part;  
           [0016]    the body is created in a reinforced material;  
           [0017]    the reinforced material is, for example, polybutadene;  
           [0018]    the protective layer is produced in a material resistant to climatic aging; and  
           [0019]    the material resistant to climatic shift is acrylonitrile styrene acrylate;  
           [0020]    The invention also proposes a process for making a wiper brush arm of the type described above characterized in that the body and the protective layer are produced simultaneously via molding, in particular, via injection molding, in only one mold impression in such a way that the protective layer envelopes the body at least in part.  
           [0021]    According to other characteristics of the process, the invention proposes:  
           [0022]    that the body and the protective layer be created in only one operation according to the technique of co-molding or bi-material molding;  
           [0023]    that the body is produced at least in part with gas blowing during the injection in such a way as to form a hollow body;  
           [0024]    that one makes the brush arm in two steps, in particular, via molding of the body during a first step, and by casting the protective layer around the body during a following step; 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0025]    Other characteristics and advantages of the invention will appear in the detailed description which follows and for which one will refer to the attached drawings in which:  
         [0026]    [0026]FIG. 1 is a schematic perspective view of a wiper comprising a brush arm in a plastic material made up of a body covered with a protective layer produced conforming to a first production method of the invention;  
         [0027]    [0027]FIG. 2 is a transversal cross-section view of the brush arm wiper according to line  2 - 2  in FIG. 1;  
         [0028]    [0028]FIG. 3 is a view similar to that represented in FIG. 2, the body and the protective layer comprising complementary coupling means;  
         [0029]    [0029]FIG. 4 is a detailed view at a larger scale of a part of FIG. 3;  
         [0030]    [0030]FIGS. 5 a  and  5   b  are views similar to that represented in FIG. 4, the coupling means being produced according to a another aspect of the invention;  
         [0031]    FIGS.  6  to  9  represent, in a transversal cross-section, an injection mold of two brush arm wipers during different phases of fabrication of one of the brush arms; and  
         [0032]    [0032]FIG. 10 is a view similar to that represented in FIG. 2, the brush arm wiper being produced according to a second production method of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0033]    A plastic material can satisfy two required principal conditions with difficulty for a brush arm wiper, that is to say, a sufficient rigidity to limit the deformation of the brush arm during the reciprocating wiping movement and stability to the exterior attacks such as, for example, humidity and ultraviolet rays.  
         [0034]    In order to do this, the invention proposes producing a wiper  10 , in particular for a motor vehicle, comprising a brush arm  12  that is made up of a single-piece rigid body  14  molded in a plastic material and which is covered by a cover  16  protecting against exterior environmental attacks, which is also made of a polymer.  
         [0035]    The body  14  allows transmission of the reciprocating wiping efforts of a first free end  18 , that is, for example, linked to a drive bearing (not represented) in reciprocating rotation of a second free end  20 , near which is attached a wiper brush  22  that supports a scraper  24  made of a polymer material that allows wiping of the window during wiping.  
         [0036]    The body  14  can be produced in polybutadene terephtalate (PBT) which comprises reinforcement means. The reinforcement means can be fibers, such as fiberglass, that presents advantages, in particular, to improve the mechanical resistance of the PBT and to be inexpensive. However, the reinforcement means modify the appearance of the body  14 , for example, by whitening under the climatic aging.  
         [0037]    The protective layer  16  that covers at least in part the body  14  and which avoids the modification of its appearance, can be for example, produced in acrylonitrile styrene acrylate (ASA) or a base in an polybutadene terephtalate alloy. This is a stable material in relation to exterior attacks, in particular, ultraviolet rays.  
         [0038]    According to a first method of production, conforming to FIGS.  1  to  5   b , the protective cover  16  covers only the sides or the exterior faces of the single-piece body  14  of the brush arm wiper  12 .  
         [0039]    It is thus necessary that the exterior side  26  of the body  14  and the internal side  28  of the protective cover  16 , which are in mutual contact, comprise means for the mechanical coupling of the protective cover  16  onto the body  14 . The coupling means can comprise a layer of glue which allows the adhesion of the exterior side  26  of the body  14  of the internal side  28  of the protective cover  16 .  
         [0040]    The coupling means can also consist at least in part of a chemical and/or physicochemical coupling between the sides  26  and  28  of the body  14  and of the protective layer  16  which are in mutual contact. That is to say, the plastic material constituents of the body  14  and of the protective envelope  16  present a good chemical compatibility in such a way so that during the fabrication of the brush arm  12 , the chemical links are established between the materials of the body  14  and of the protective envelope  16  in such a way as to produce their coupling.  
         [0041]    In this way, the polybutadene terephtalate-acrylonitrile styrene acrylate couple, for the body  14  and the protective envelope  16 , respectively, present a good chemical compatibility.  
         [0042]    In addition, conforming to FIGS. 3 and 4, the coupling means consist of, at least in part, in a first coupling zone  30  of the body  14  that reaches towards the exterior of the exterior side  26  in order to cooperate with a second coupling zone  32  in a complementary form produced in the internal side  28  of the protective cover  16 . In this way, the contact surface between the exterior  26  and internal  28  sides is augmented which optimizes the coupling of the body  14  and of the protective layer  16 . In addition, the penetration of the first coupling zone  30  of the body  14  in the second coupling zone  32  of the layer  16  improves the attachment of the two elements  14  and  16  to one another.  
         [0043]    According to variations conforming to FIGS. 5 a  and  5   b , the first coupling zone  30  presents a counter-cast  34  in a hollow form in which cooperate complementary projecting forms  36  from the protective layer  16 . The mechanical coupling thus produced allows the protective layer  16  to be attached to the body  14 . In a similar manner, FIG. 5 b  represents a transversal cross-section of the brush arm  12 . The second coupling zone  32  reaches towards the exterior of the internal side  28  of the protective layer  16  in order to cooperate with the first coupling zone  30 , in complementary shape, created in the external side  26  of the body  14 .  
         [0044]    The wiper brush arm  12  according to the first method of production can be obtained via molding, in two steps in the same mold or in two separate molds.  
         [0045]    This molding technique is also called casting of plastic material.  
         [0046]    A mold  50  represented on FIGS.  6  to  9  comprises an upper part  52  and a lower part  54  in which are created two hollow impressions  56  and  58  which are linked to the exterior by two injection canals  60  and  62 , respectively.  
         [0047]    The impression form  56  corresponds to that of the body  14 , and that of the impression  58  corresponds to the brush arm wiper  12  made up of the body and the protective cover  16 .  
         [0048]    The lower part  54  comprises a first and second, identical, ribs  57  and  59  which initially define the lower sides of the impressions  56  and  58  respectively.  
         [0049]    During the first step, a device not represented allows heating of the plastic material, in particular granules of polybutadene terphtalate, reinforced by fiberglass, at a temperature set by transformation, in such a way as to “liquefy” it. The material is thus pressed to fill the first impression  56  of the mold  50 , by a process that can be an injection method. The heating and injection of the plastic material are produced by a specific device called the plasticization screw.  
         [0050]    The melted material is introduced in the mold  50  via the first injection canal  60  in such a way so that it fills the first impression  56 , conforming to FIG. 7. A cooling device, not represented, which is produced in the upper  52  and the lower  54  parts of the mold  50  allows acceleration of the solidification of the injected material. The body  14  is thus completed.  
         [0051]    The mold  50  is open, that is to say, that the lower part  54  is translated towards the bottom according to a vertical axis A. The body  14  stays attached to the lower part  54 . In addition, conforming to FIG. 8, the core situated in the first injection canal  60  is removed. A rotation of 180 degrees around the vertical axis A is thus produced in such a way so that the body  14  and the rib  57  are vertically aligned with the second impression  58 . Then, the mold  50  is closed again. During the second step, the protective “skin”  16  is molded onto the body  14 .  
         [0052]    As the plastic material, such as the acrylonitrile styrene acrylate is carried to its transformation temperature, when the mold  50  is closed, it is injected in the second injection canal  62  in order to fill the second impression  58 , conforming to FIG. 9, in a similar manner as the first step. After cooling, the second impression  58  thus contains a wiper  10  brush arm  12  produced according to the invention.  
         [0053]    The mold  50  is opened, and the wiper  10  and the brush arm  12  are separated from the rib  57 . Another brush arm  12  can then be fabricated.  
         [0054]    Advantageously, the first impression  56  is filled simultaneous with the filling of the second impression  58 . In this way, a wiper  10  and a brush arm  12  is produced at each opening in the mold  50 .  
         [0055]    The casting technique allows, in particular, obtaining great precision as for the thickness of the protective layer  16  and the thickness of the body  14  over the length of the arm  10 .  
         [0056]    The above description of the first production method is not limited to the described steps. In effect, according to variants, the body  14  can be molded onto the protective layer  16 , and/or the upper part  52  of the mold  50  can be mobile, and/or the injection of plastic can be created by injection canals situated in the upper part  54  of the mold  50 .  
         [0057]    The first production method can be obtained without rotation of part of the mold  50 , but via transfer of the first part injected into the second impression.  
         [0058]    According to a second method of production, the protective layer  16  entirely envelopes the body  14 , conforming to the transversal section of the brush arm  14  represented on FIG. 10. The body  14  and the protective cover  16  can be simultaneously produced via molding, in particular, via injection of plastic materials in one single impression of a mold, not represented. The brush arm  12  is thus produced in only one operation, according to the co-molding, bi-molding or “sandwich” type of injection techniques. The two materials of the body  14  and the protective layer  16  are injected simultaneously during the same “shot” or injection. The dosage of the two materials is thus made in a shared plasticization screw.  
         [0059]    Advantageously, during molding of the brush arm  12 , gas can be blown into the mold simultaneously to the injection  12  of at least one of the two materials of the body  14  and/or of the protective layer  16  in such a way as to form a hollow brush arm  12 .