DE-ICING DEVICE FOR WINDSHIELD WIPERS

Abstract: A device for de-icing windshield wipers and the like, and takes the form of an electric heating element (10) shaped as an elongate strip with substantially the same outside dimensions, and also to advantage with the same resiliency characteristics, as one of the spring strips normally inserted in longitudinal grooves on either side of a wiper blade to give it the necessary lateral stiffness and vertical springiness. This strip-like electrical heating element is intended for inserting in one of said grooves in the blade instead of the normal spring strip. The heating element is built up from an outer metal casing (13) having said strip shape and resiliency characteristics, and being provided with an internal axial duct in which an insulated (12) electric resistance wire (11) is disposed. At its one end, this resistance wire is connected to an electric supply lead at one end of the casing, while at its other end the wire is electrically connected to the casing in the vicinity of the other end of the latter, so that the casing can function as ground or return lead for the heating element. The outer metal casing can to advantage consist of a metal tube flattened to the rectangular shape of a normal strip.

Description: DE-ICING DEVICE FOR WINDSHIELD WIPERS The present invention relates to a device for de- icing windshield wipers of the kind disclosed in the preamble to the accompanying claim 1. The problem of removing ice from windshields on cars and other vehicles has been satisfactorily solved in the majority of cases a long while ago, usually by hot air being blown against the inside of the wind¬ shield. It is, however, well known that under certain weather conditions there is often heavy ice formation on the wipers, partly on the wiper blade of rubber or similar material, and partly on the articulated holder retaining the wiper blade along its spine and which is attached to the wiper arm. This ice formation causes the wiper blade itself to become stiff and to loose its required flexibility, deterioration in the necessary articulation of the holder, and deterio¬ ration in the necessary mutual ovability between wiper blade and holder in the longitudinal direction of the blade, all of this leading to the wiper blade no longer shaping itself to the windshield surface, which is usually curved, and the function of the wiper thus being seriously deteriorated. It may also occur that the iceformation on the wiper blade is so heavy that the latter is completely or partially lifted up from the windshield surface, the wiper function thus being disabled. It is also well known that the wiper blades on a stationary vehicle often freeze solid against the windshield. If the driver then loosens the frozen-on blades by hand before starting, it often occurs that the narrow edge of the blade is damaged, with sub¬ sequent deteriorated wiper function. A very large number of devices have been suggested for de-icing windshield wipers, primarily by using electrical heating. These previously proposed devices are burdened with many serious disadvantages, however, and none of them appears to have been put to any practical use either. 5.. In some of the previously proposed devices (those of the US Patent specifications 2 865 040, 3 201 818 and 3 428 993, for example) one or more electrical resistance wires are molded into .or inserted in longitudinal ducts inside the wiper blade itself. 0 This arrangement makes the manufacture of the wiper blades more complicated and thereby more expensive, which is a substantial disadvantage, since these blades are a consumption part which usually needs replacing comparatively often. The resistance wires 5 molded or inserted into the wiper blade also reduce the flexability of the wiper blade, which is necessary for a good wiping function. A device of this kind also results in that the heat is generated inside the blade itself, which is not what is really desired, 0 and which can also disadvantageously affect the rubber material in the blade. In other previously proposed devices (those in accordance with the US Patent specifications 2 686 247. 2 746 007 and 3 530 525, for example) insulated 5 electrical resistance wires or the like are fitted in exterior grooves on the wiper blade or on different parts of the holder means for the blade. These devices are, however, comparatively complicated to install, and they are furthermore easily subjected 0 to damage due to the small dimension of the resistance wires, especially when replacing a wiper blade which, as pointed out above, must take place relatively often and which is something that should preferably be possible for the vehicle owner himself to do. It has further been proposed in the German Published Specification 2 309 902 that the metal spring strips, which in a very common type of wiper blades are inserted in grooves formed on either side of the wiper blade along its spine in order to provide the blade with sufficient lateral stiffness and required springiness in height, are also utilized as electrical heating elements by having a current passed directly through these strips. Such an arrangement is not practically realizable, however, since it is difficult to. provide the necessary electrical insulation of these spring strips in a way that is simple and reliable at the same time. Furthermore, these strips have an electrical resistance which is much too low for them to be used as electrical resistance-heating elements. If the strips are con¬ nected to the normal voltage supply on the vehicle, which is usually 6 or 12 volt, very large current values are obtained and the generated power will be many times greater than what is necessary for the purpose. The object of the present invention is therefore to provide an improved device for de-icing a wind¬ shield wiper, which has a wiper blade of rubber or similar material and of the very usual type which is provided with a groove on either side of its spine, these grooves being intended to accommodate spring strips, substantially rectangular in cross section, for giving the wiper blade the necessary lateral stiffness and necessary vertical springiness. What primarily distinguishes the device in accordance with the invention is apparent from the characterizing portion of the accompanying claim 1. Advantageous embodiments and improvements of this device have the characterizing features disclosed in claims 2-13. The invention is thus based on the idea that at least one of the spring strips normally inserted in the grooves on either side of the wiper blade along its spine is exchanged for a strip-shaped electric heating element having substantially the same outside dimensions as said spring strip, and having the structure disclosed in the claims with a central, insulated electric resistance wire disposed in an outer strip-shaped metal sleeve or casing, which is preferably electrically connected at one end to the adjacent end of the resistance wire and which serves as a mechanical protection against damage to the insulated resistance wire and also as a ground or return conductor for the current through the resistance wire. Such a heating element in accordance with the invention can be manufactured very simply and cheaply and is also very resistant to outside damage. It is also just as easy to mount and remove as the normal spring strip which it is in¬ tended to replace, the exchange of wiper blades thus not being made more difficult in any way. If so desired, during seasons when there is no danger of ice formation, the heating element can easily be removed and the normal spring strip inserted instead. The heating element in accordance with the invention will also have such a location on the wiper that the heat generation occurs at the desired place, i.e. on the outside of the wiper blade and close to the most adjacent portions of the blade holder. The heating element can be easily manufactured in dimensions suited to different wiper blades, and by selecting the area of the resistance wire, it is easy to adjust the resistance of the element to a desired value. The invention will now be described in detail with reference to the accompanying drawing, on which there are shown as examples some embodiments of the invention, and where Figure 1 is a schematic side view, of a common design of a windshield wiper, Figure 2 shows a portion of the wiper in Figure 1 to a larger scale, Figure 3 is a section along the line III-III in Figure 2, Figure 4 is a -side view of an embodiment of a heating element in accordance with the invention, Figure 5 is a sectional perspective view showing the construction of the heating element accord-. ing to Figure 4, Figure 6 is an axial section through one end of the element in Figure 4 at a certain stage of its manufacture, Figure 7 is an axial section through the other end of the heating element in Figure 4, at a certain stage of its manufacture, Figure 8 is an axial section similar o the one in Figure 7, but showing a somewhat different arrangement of the connections for the • current supply lead and the ground lead, Figure 9 is a schematic side view of another embodi¬ ment of a heating element in accordance with the invention, in which embodiment the metal casing is formed from two halves joined together, one of these halves being removed on the drawing, Figure 10 is a cross section through a heating element according to Figure 9 , with both halves of the outer metal casing shown spaced apart, Figure 11 is a view similar to the one in Figure 9 illustrating a further embodiment of the invention, and Figure 12 is an axial section through one end of a heating element in accordance with the invention, with a suitable form for the connection between the current supply lead and the resistance wire. Figures 1-3 show by way of example a very common design of a windshield wiper. This wiper comprises an elongate wiper blade 1 of soft rubber or similar material, and a holder assembly generally designated by the numeral 2, which is attached to the outer end of the wiper arm 3, only partially shown in Figure 1, and which retains the blade 1 along its spine. The holder 2 usually comprises, as in the example shown, a number of yokes 4 hinged to each other. The number of yokes can vary and is essentially dependent of the length of the blade 1. The outermost of these yokes 4 are provided with claws 5 grasping round the rear edge or spine of the blade 1, and with their tips gripping into two grooves 6 formed on either side of the blade 1. So that the very soft and easily deformable wiper blade 1 will have sufficient lateral stiffness, i.e. in the direction of the arrow 7 in Figure 3, and at the same time the necess¬ ary springiness or resiliency in vertical direction, i.e. in the direction indicated by the arrow 8 in Figure 3, there are two elongate spring strips 9 of substantially rectangular cross section and usually made of metal, inserted in corresponding grooves on either side of the blade 1 in the vicinity of its spine. These strips 9 have substantially the same length as the blade 1. In order that the blade 1 will be able to adopt itself to the varying curva¬ ture of the windshield when the wiper is in operation, so that the blade has the total length of its scraping edge engaging against the windshield the-whole time, the blade 1 must be movable in its longitudinal direction relative to all the claws 5 on the yokes 4 with the exception of one such claw. The blade 1 is usually formed with stops filling out the groove 6 at one end, these stops coacting with the claw 5 at the same end of the blade so that the blade is kept in place in its longitudinal direction at this claw. The blade 1 is freely movable in its longitu¬ dinal direction relative to all the remaining claws 5. In a corresponding way, the grooves in the-blade 1 accommodating the spring strips 9 are formed with a tap or the like which coacts with a notch in the strips 9, so that the strips are locked in their longitudinal direction. The strips are otherwise loose in their grooves in the blade 1 and are retained in these grooves by their being surrounded by the holder claws 5. In a de-icing device in accordance with the invention, at least one of said strips 9 is replaced by an elongate strip-like electric heating element 10, having substantially the same outside dimensions as the spring strip 9. Figures 4 and 5 show a first embodiment of such a heating element as an example. This element 10 consists of a central electric resistance wire 11 surrounded by an insulation consisting in the illu¬ strated ' embodiment of a tube 12 of a pliant plastic material, e.g. polytetrafluorethene, and an outer flattened metallic casing 13. All these parts of the - heating element extend for substantially the whole length of the element. At one end 10a of the ele¬ ment 10, the resistance wire 11 is electrically connected to the outer metallic casing 13. At the other end 10b of the element, the resistance wire 11 extends together with the insulation tube 12 out of the casing 13 for being connected in a suitable way (not shown in the drawing) to the supply lead from a current source. At this end 10b of the element there is also a return or ground lead 14, which is inserted into the end of the casing 13 between it and the insulation tube 12, and is in electrical contact with the casing 13, as will be more closely described in the following. At the end 10a, the element 10 can be formed with a notch 10c for fixing the position of the element in the groove in the wiper blade 1 in the same way as is described hereinbefore with respect to the normal spring strips 9. The desired resistance value for the heating element, and thus the value of the current flowing through it and its generated power, is determined by selecting the area of the resistance wire in re¬ lation to the length of the heating element, i.e. the length of the appropriate wiper blade. The di¬ mensions of the outer flattened metal casing 13 are selected so that the cross-sectional form of the heating element 10 substantially coincides with that of the normal spring strip 9, which the heating element is intended to replace. The casing 13 should naturally consist of a metallic material which is a good heat conductor and -also a good electrical conductor. Practically all conceivable metallic materials are satisfactory from this point of view. The casing 13 should further consist of a metallic material which is sufficiently resistant to corrosion, or alterna¬ tively it can be provided with a corrosion resistant surface layer. The casing 13 can to advantage be manufactured from a resilient metallic material so that the heating element 10 is given substantially the same resiliency characteristics as the normal spring strip 9 which the element is intended to replace. If only one spring strip 9 in the wiper blade 1 is replaced by a heating element in accord¬ ance with the invention, which in most cases is sufficient for the de-icing, the casing 13 in the heating element does not necessarily need to consist of a particularly resilient material, since the remaining normal spring strip 9 in the wiper blade will provide it with the necessary resiliency, and the casing 13 can consist of a comparatively pliant and flexible metallic material, advantageous from other points of view, such as aluminium. The heating element according to Figures 4 and 5* can to advantage be manufactured such that a resistance wire 11 is thrust into an insulation tube 12 so that one end of the resistance wire 11 projects a distance outside one end of said tube'. The resist¬ ance wire 11 together with the insulation tube 12 is then thrust into a circular metallic tube of a length corresponding to the finished length of a heating element and with a suitable diameter and wall thick¬ ness , it being ascertained that the uninsulated end of the resistance wire 11 is within one end of the metal tube while the other end of the resistance wire 11 together with the insulation tube 12 projects out from the other end of the metal tube. The metal tube is then flattened along its entire length into the cross-sectional shape desired for the heating element, so that the resistance wire 11 together with the insulation tube 12 are clamped inside the flatten¬ ed metal casing 13 and so that the uninsulated end * of the resistance wire 11 is brought into electrical contact with the casing 13 at one end thereof. As illustrated in Figure 6, before compressing the casing 13 a short piece of metallic tube 14 can be pushed into said end of casing 13 round the un¬ insulated portion of the resistance wire 11. At the subsequent compression of the casing 13 this tubular piece 14 contributes to a secure electrical contact between the resistance wire 11 and the casing 13. The outer end 10a of the heating element 10 is furthermore reinforced by this means, so that the notch 10c shown in Figure 4 can be cut out of the heating element without detriment. At the other end of the heating element, an end of the return or ground lead 14, from which the in¬ sulation has been removed, can be thrust into the outer casing 13, between it and the insulation tube 12 surrounding the resistance wire 11, before com- pressing the casing 13 so that when this compression subsequently takes place the ground lead 14 is clamped firmly and brought into secure electrical contact with the casing 13. It will be observed that the outer metal casing 13 of the heating element will serve as a return conductor for the current through the resistance wire 11. Since the resistance of the casing 13 is very much less than the resistance of the resistance wire 11, the voltage drop across the casing 13 will be very small, and therefore electrical insulation of it is not required.- The casing 13 will naturally be able to come into contact with* the retaining claws 5 on the yokes 4 which are generally made of metal. There will thus be a certain amount of current flowing from the casing 13 to the retainer claws 5 and the holder yokes 5, but this does not constitute any essential disadvantage. For secure grounding of the casing 13 and secure return flow of the current through the heating element, it is, however, prefer¬ able that said element is provided with a return or ground lead 14 connected to the casing. In the embodiment of a heating element in accord- ance with the invention shown in Figures 4, 5 and 7 and described above, there is a certain risk of mechanical damage to the insulated wire 11/12, and even to the ground lead 14 at the end of the casing 13, since the resistance wire 11 and the ground lead 14 are subjected to such fatigue stresses due to vibrations that rupture or at least insulation damage may occur. This risk is substantially reduced in the embodiment schematically shown in Figure 8, where the outer metal casing 13 is not flattened into the shape of the flat strip over a short portion 13B outermost at the end 10B of the heating element, where the casing 13 is thus allowed to retain its substantial¬ ly circular cross-sectional form. Within this end postion 13B of the casing 13, the resistance wire 11 is joined in a suitable way, e.g. by soldering with an insulated electric supply lead 15 of a conventional kind, which extends a dis- tance into the end of the casing 13. The joint bet¬ ween the resistance wire 11 and the supply lead 15 can to advantage be insulated by a sleeve of plastics tube 16, as in the illustrated embodiment, and this tube can extend a distance outside the end of the casing as shown on the drawing, whereby the plastics sleeve 16 will serve to protect against mechanical damage and as an insulation reinforcement at the outer end of the casing 13, where the risk for insu¬ lation damage and fatigue rupture to the electrical conductor is greatest. In this embodiment of a hetaing element in accordance with the invention, the ground lead 14 is attached in a suitable manner, e.g. by soldering or welding, to the outside of the casing 13 close to its end, so that both electrical leads 14 and 15 for the heating element can be extended parallel and together from the wiper blade. In the embodiments of a heating element in accord¬ ance with the invention described above, the outer metallic casing has consisted of a metal tube, which has been flattened to the desired strip shape after insertion of the insulated resistance wire. This appears to be a simple and advantageous method of manufacturing a heating element according to the in- vention. However, there is nothing to prevent the outer metal casing of a heating element in accordance with the invention being manufactured with the desired strip shape from the beginning, it then being provided with one or more internal axial ducts in which the insulated resistance wire is inserted. Such a strip¬ like metallic casing could be manufactured by ex¬ trusion, for example. It is also possible to form the outer strip- shaped metal casing from two halves which are put together as shown by way of example in Figures 9 and 10. In the embodiment of a heating element in accord¬ ance with the invention shown here as an example, the outer metal casing consists of two strip-shaped halves 13a and 13b, which can be joined in the way shown in Figure 10, and of which at least one is formed with a groove 17 to provide an axial duct when both strip halves are put together, in which duct the insulated resistance wire 11, 12 can be inserted. Both strip halves 13a and 13b can further¬ more be formed with complementary recesses and pro¬ jections 18 as well as guide pins 19 and mating holes, which facilitate the assembling of the strip halves. They can be kept together by welding or by glueing. As shown in Figure 11,. a heating element of this kind can also be provided with a notch 10c at one end, for locking the heat element in the wiper blade groove. Figure 11 also shows how the electric supply lead 15 can project a distance into the central duct 17 in the outer strip-shaped metal casing and be joined here to the electric resistance wire 11. Figure 12 shows schematically how the junction 19 between the lead 15 and the resistance wire 11 can be accommodated in an expanded portion 13B of • the strip-shaped casing 13. This expanded portion 13B can be formed in one piece with the two strip halves 13a and 13b. Other embodiments of a heating element in accord¬ ance with the invention are naturally possible further to those described hereinbefore. Thus, the materials for the resistance wire 11, the resistance wire insulation 12 and the casing 13 can be varied and selected differently depending on different require¬ ments. One can naturally use an electric resistance wire which has already been provided with suitable insulation during manufacture. A device in accordance with the invention can of course also be used for de-icing wiper blades on headlights, vehicle rear windows and the like.

Claims: C L A I M S :- 1. A device for de-icing a windshield wiper, which has a wiper blade (1) made from rubber or similar material and formed with two grooves substantially extending the entire length of the blade one on either side thereof, in which elongate spring strips (9) with a substantially rectangular cross section are intended to be inserted for providing the blade with sufficient lateral (7) stiffness and sufficient vertical (8) resiliency, said device comprising an electric heating element (10) which can be mounted on the wiper blade (1), characterized in that said heating element (10) is formed as an elongate strip having substantially the same outside dimensions as said spring strips and intended for insertion in one of said grooves in the wiper blade (1) instead of such spring strip, this strip-shaped heating element (10) being built up from an outer metallic casing (13) with said strip-shape, said casing having at least one interior duct extending axially at least over the greater portion of the casing length, in said duct there being disposed an electric resistance wire (11) provided with insulation (12), said wire being electrically connected at one end to an electric supply lead (15) and at its other end to a ground connection. 2. A device as claimed in claim 1, characteriz¬ ed in that the outer metal casing (13) consists of a resilient metal material so that it has substantial the same resiliency characteristics as said spring strip (9). 3. A device as claimed in claim 1 or 2 , characteriz¬ ed in that the resistance wire (11) is electrically connected to the electric supply lead (15) at, or in the vicinity of, one end (10B) of the outer metal casing, while at its other end it is electrically connected to the casing (13) at the other end ( 10A) thereof, so that the casing serves as a part of the ground connection. 4. A device as claimed in any of claims 1-3, characterized in that an electric ground lead (14) is connected to the outer metal casing (13) at its said one end (10B). 5. A device as claimed in any of claims 1-4, characterized in that the casing consists of a metal pipe (13) flattened to a substantially rectangular cross sectional shape after inserting the insulated resistance wire (11). 6. A device as claimed in claim 3 or 5, characteriz¬ ed in that the electrical connection between said second end of the electric resistance wire (11) and the outer metal casing (13) at said other end (10A) of the latter consists of a short piece (14) of metal pipe surrounding the uninsulated end of the resistance wire, said pipe piece (14) being inserted and firmly clamped in the end of the casing (13). 7. A device as claimed in claim 5 or 6 , characteriz¬ ed in that an electric ground lead (14) is inserted a distance into the outer metal casing (13) at said one end (10b) of the latter and clamped firmly therein. 8. A device as claimed in any of claims 1-4, characterized in that the outer metal casing is put together from two strip-shaped halves (13a, 13b) substantially rectangular in cross section, of which at least one is formed with a longitudinal groove (17) in its flat side facing towards the other half, said groove (17) forming said duct for the insulated (12) resistance * ire (11). 9. A device as claimed in claim 8, characterized in that both strip halves (13a, 13b) are formed in their opposing and connected sides with complementary recesses and projections (18) engaging each other and contributing to the union of both strip halves. 10. A device as claimed in any of claims 1-9, characterized in that the insulation of the resistance wire (11) consists of a tube (12) of plastics material surrounding said wire. 11. A device as claimed in any of claims 1-10, characterized in that said one end of the insulated resistance wire (11) extends out from the outer metal casing (13) at said one end (10B) of the latter and is electrically connected to the electric supply lead outside the casing. 12. A device as claimed in any of claims 1-10, characterized in that the electric supply lead (15) projects a distance into the outer metal casing (13) at said one end (10B) of the latter, and is electircal- ly connected to said one end of the resistance wire (11) inside the casing (13). 13. A device as claimed in claim 12, characterized in that the inner duct in the outer metal casing (13) has an expanded portion (13B) therein accommodating the joint between the resistance wire (11) and the electric supply lead (15).

Inventors: OHLSSON A, OLANI L
Applicants: OHLSSON A, OLANI L
Application year: 1978
Main classification: B60S1
IPC codes: B60S1