AN ELECTRICALLY HEATED WIPER BLADE

Abstract: At low temperatures, it is desirable to be able to heat up a wiper blade in windscreen wipers on a vehicle so as to prevent ice formation on the wiper blades and the windscreen. Within the wiper blade, there is disposed an elongate heating device (4) in thermal contact with the profile (1) of the wiper blade. The heating device (4) extends along the entire wiper profile (1) and is connected to a current source. The heating device (4) includes a temperature sensor (9, 16) which extends substantially along the entire heating device (4) and which is connected to the current source. The material in the temperature sensor (9, 16) has a temperature-dependent resistivity. Suitably, this material is a so-called NTC material, whose resistivity falls when the temperature rises. The current source includes a regulator for regulating the current supply to the heating device (4) in response to the temperature which is registered in the temperature sensor (9). In one embodiment, the NTC material (9, 16) is disposed hose-shaped about a central conductor (8), while an element wire (10) is helically wound around the NTC material. The temperature sensor, i.e. the NTC material, is connected to the regulator at the conductor (8) and the element wire (10).

Description: AN ELECTRICALLY HEATED WIPER BLADE TECHNICAL FIELD The present invention relates to an apparatus for electrically heating a wiper profile of rubber or rubber-like material included in a windscreen wiper blade, and comprising an elongate electric heating device which has thermal contact with the wiper profile and which extends therealong, and means for power supply to the heating device. BACKGROUND ART A plurality of different types of electrically heated windscreen wiper blades are previously known in the art. In one category of such electrically heated windscreen wiper blades, use is made of a resistor wire which forms an electric element and which is embedded in the profile produced from rubber or rubber-like material and which abuts against the windscreen. The resistor wire is supplied with current, and heating of the material of the wire takes place. Theoretically, it may conceivably be expected that such a design and construction would function. However, in practice serious problems are encountered which render the above-outlined design and construction unusable. On driving in temperatures around zero degrees centigrade, the need for heated windscreen wiper blades begins to make itself felt. If this temperature level is combined with low driving speeds, only minor amounts of heat are transported away from the wiper blade, i.e. the element disposed in the wiper blade can only develop a very limited output if the wiper blade and the element are not to be overheated and destroyed. If, on the other hand, the vehicle is driven at low temperatures, for example of the order of -15 to -20°C or lower and at high speeds, the amount of heat which per unit of time is transported away from the wiper blade is multiplied. This operational situation places extreme demands on developed output in the wiper blade. The above-outlined operational situations are not compatible with each other, for which reason the solution closest to hand will be to employ dimensions in such a manner that more or less reliable security against overheating of the element and the wiper profile will be obtained. With such dimensioning however, function becomes poor at higher driving speeds and at lower temperatures. Patent specification DE 2 807 330 discloses a wiper blade of the above - outlined basic type. According to this patent specification, use is, however, made of a regulator circuit which is controlled by a temperature sensor. According to this publication, the purpose of this temperature sensor is to render the apparatus fully automatic so that it is switched on and off as necessary. No output adaptation to meet differing operational conditions is permitted with this design and construction. Another attempt to solve the above-considered problems involved in greatly varying operational conditions is disclosed in CA 2 114 058. According to this publication, use is made in the element of a material which has a positive temperature coefficient for the resistivity (PTC material). A material of this type behaves such that, according as the temperature in the material rises, the resistance also increases, for which reason the output which is developed is reduced with increasing temperature if the voltage across the element is kept constant. An element manufactured from such material would, therefore, theoretically assume a state of continuity where the temperature could not rise any further. Theoretically, an element produced from PTC material could be made self- governing so that the output development is great when the need is great and vice versa the output development is slight when the need is slight. In practice however, there are no possibilities of producing an electric heating element with PTC properties and of such dimensions that it can be placed interiorly in a wiper profile included in a windscreen wiper blade. This applies if the operating voltage is to be kept low, e.g. 12 or 24 V, which are the normal voltages employed in vehicles. If, on the other hand, the voltage is increased, safety risks arise. In addition, the PTC material will be so hard and rigid that it would prevent the necessary flexural movements in the wiper profile. PROBLEM STRUCTURE The present invention has for its object to design the apparatus intimated by way of introduction such that it affords satisfactory function both at low temperatures and high output requirements, i.e. both at low speed and high temperature and at high speed and low temperature. The present invention further has for its object to design the apparatus such that it may readily be accommodated in a wiper profile included in a wiper blade without appreciably affecting the deformation and movement properties of the wiper blade. Finally, the present invention has for its object to realise an apparatus displaying a high degree of operational reliability, an apparatus which may be manufactured at low cost and which does not require any other operational voltage than that which is normally available in a vehicle, i.e. 12 or 24 volts. SOLUTION The objects forming the basis of the present invention will be attained if the apparatus intimated by way of introduction is characterized in that the heating device includes a temperature sensor and that the means for current supply include a regulator for regulating the temperature of the heating device, the temperature sensor being connected to the regulator. In one particularly advantageous embodiment, it moreover applies that the temperature sensor is elongate and extends along substantially the entire length of the heating device. Suitably, the temperature sensor is a resistive sensor and comprises material with a negative temperature coefficient for the resistivity of the material (NTC material). Further advantages will be attained according to the present invention if the apparatus is also given one or more of the characterizing features as set forth in appended Claims 4 to 10. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS The present invention will now be described in greater detail here nbelow, with particular reference to the accompanying Drawings, in which: Fig. 1 schematically illustrates an end portion of a heating device included in the apparatus according to the present invention; Fig. 2 shows in principle how the heating device according to Fig. 1 is electrically connected; Fig.3 shows an alternative embodiment of a heating device; Fig. 4 shows in principle how the heating device according to Fig. 3 is electrically connected; Fig. 5 is an end elevation of a wiper profile included in the windscreen wiper blade according to the present invention; and Fig.6 shows a side elevation of the wiper profile of Fig. 5. DESCRIPTION OF PREFERRED EMBODIMENT Figs. 5 and 6 show a wiper profile 1 included in a windscreen wiper blade and being of rubber or rubber-like material. The wiper profile has longitudinal grooves 2 along opposing sides for securing the wiper profile in the wiper blade. In its end facing towards a vehicle windscreen, the wiper profile has a scraper portion 3 which abuts against the windscreen and which, with a scraper surface 5, scrapes against the windscreen when the windscreen wiper sweeps across the windscreen. The material in the wiper profile is such that the profile is deformed during its movements so that the scraper portion 3 is constantly bent rearwards in the direction of travel. On driving at temperatures about 0°C or just below, in particular in rain, sleet or snowfall, it often occurs that water, slush or wet snow adheres to the windscreen wiper and the wiper blade and freezes to ice there. In such situations, the movements of the wiper profile are impeded, for which reason its clean-scraping action against the windscreen greatly deteriorates. Furthermore, a cold wiper profile (which moreover may be feared to be in poor contact with the windscreen) is not capable even of removing a very thin film of ice. On the other hand, a warm wiper profile follows the contour of the windscreen perfectly and may be expected to have a melting effect on the film of ice. The wiper profile has, according to the present invention, a longitudinal heating device 4 which is electrically heated and which is located interiorly in the wiper profile and is in thermal contact with the wiper profile for heating it. In one practical embodiment, the heating device has the appearance of a thin electric conductor which extends along substantially the entire length of the wiper profile. A method of applying the heating device 4 in the wiper profile entails that the wiper profile is provided with a longitudinal slot 6 which is at right angles, or approximately at right angles, to the scraper surface 5 of the scraper portion 3. At the end of the slot 6 most proximal the scraper portion, the slot discharges into a channel 7 in which the heating device is accommodated. In one practical embodiment, both the heating device 4 and the channel 7 are of circular cross section. For achieving good thermal contact between the heating device 4 and the material of the wiper profile 1, the fit between the heating device 4 and the channel 7 is relatively tight. Suitably, the channel may be complementary in relation to the heating device, and possibly slightly under dimensioned. The heating device 4 includes an electric element which may consist of an electric resistor wire which extends along substantially the entire length of the heating device 4. Possibly, the resistor wire may be helically disposed in the heating device so that the extended or electric length of the resistor wire will thereby be considerably greater than the physical length of the heating device. The heating device 4 further includes a temperature sensor which is elongate and which extends substantially throughout the entire length of the heating device. This avoids the risk that the heating device may locally be heated or cooled without the temperature sensor reacting. The heating device 4 is connected to means for the supply of electric current so that the resistor wire included in the heating device may thereby be heated. In such means for supplying electric current there is also included a regulator which is designed, in response to the temperature registered in the temperature sensor, to control the current supply to the heating device in such a manner that at least a predetermined maximum temperature in the material of the wiper profile or in the heating device proper is not exceeded. Suitably, the regulator may also be designed in such a manner that it increases the output development in the heating device if the temperature in this device or in the material of the wiper profile were to fall below the maximum temperature. An even more far-reaching purpose with the regulator is to maintain the temperature in the heating device or in the material of the wiper profile at a constant and predetermined level regardless of how much heat is transported away from the wiper profile, i.e. regardless of whether the vehicle is advanced at low speed at high temperature or at high speed at low temperature. According to the present invention, the temperature sensor is resistive and comprises a material whose resistivity depends upon the temperature. This material is disposed to extend along the entire length of the temperature sensor and thereby also along substantially the entire length of the heating device and the wiper profile 1. It has proved to be particularly advantageous if the material under consideration here has a negative temperature coefficient for its resistivity, a so-called NTC material. An NTC material has the property that its resistivity is reduced with increasing temperature. The resistivity is relatively high and varies according to an approximately logarithmic cycle, whereby the resistivity first falls rapidly with increasing temperature in order subsequently to level out towards an approximately constant and temperature-independent value. As an example of NTC materials, mention might be made of plastic material which has embedded carbon particles or fibres in it. Fig. 1 shows an example of the design and construction of a first embodiment of the heating device 4. It will be apparent from the Figure that the heating device is of cylindrical cross section and that, in the radial direction, it consists of a plurality of different components. In the centre, the heating device has a core 8 which is electrically conductive and which thereby serves the function of a central electric conductor. The core 8 further has for its object to stabilise the heating device 4 so that this will have a certain steadiness and, above all, the necessary tensile strength. Surrounding the core 8, there is disposed a casing of NTC material, and this casing may be characterized as hose-shaped or tubular. The core 8 extends through a channel in the casing 9 and is in electric contact with the casing throughout the entire length of the core. On the outside of the casing 9 of NTC material, there is helically wound an electric resistor wire 10 which constitutes a part of the electric element of the heating device 4. The resistor wire 10 is further in electric contact with the peripheral surface of the casing 9, throughout all of its length. The resistor wire 10 is intended to lead current in order thereby to be heated. Despite the electric contact with the casing 9 of NTC material, the different turns of the resistor wire will not be short-circuited, since the NTC material has high resistance, of the order of magnitude of several KΩ from the peripheral surface into the core 8, while, on the other hand, at an operational voltage of 12 or 24 volts, the resistor wire 10 only has a resistance of the order of magnitude of a few Ω. The short-circuiting effect which occurs between closely adjacent turns of the resistor wire 10 via the NTC material may be entirely disregarded because of the high resistance of the NTC material. On the outside of the resistor wire 10, there is disposed a layer 11 of electrically insulating material. This insulator 11 may also be described as hose-shaped or tubular and consists of a suitable plastic material. On the outside of the insulator 11, there is disposed an additional resistor wire 12 and preferably helically wound around the peripheral surface of the insulator 11. Since the wiper profile 1 of the wiper blade consists of rubber or rubber-like material, an additional insulation on the outside of the resistor wire 12 could be dispensed with, but in order to improve the handling of the heating device 4, it is appropriate to provide an additional insulation which surrounds the outer resistor wire 12. This outer insulator is not shown in Fig. 1. In Fig. 4, the broken line may be considered as representing a heating device. This heating device has terminals 13, 14 and 15 which, via suitable conductors, are connected to the means for current supply and the regulator. In the heating device 4, reference numeral 16 represents the elongate NTC material, and reference numerals 17 and 18 electric conductors. Reference numerals 19 and 20 represent the resistances which in total are embodied in the resistor wires 10 and 12, respectively, i.e. the element resistances in the heating device. It will be apparent from the Figure that the terminal 13 is connected to the conductor 17, i.e. with the one side of the elongate NTC material. In Fig. 1, this implies that the core 8, as shown with broken lines, is connected to the terminal 13 and to the NTC material. It is further apparent from Fig. 2 that the terminal 14 is connected to the resistance 19, which constitutes the total resistance of the resistor wire 10. The opposite end of the resistance 19 is connected to the conductor 18 which extends along the elongate NTC material 16 and is in electric conductive communication therewith. In Fig. 1, this has its counterpart in that the free end 21 of the resistor wire 10 (as intimated by broken lines) is connected to the terminal 14, and that the resistor wire 10 is electrically connected to the casing 9. It will finally be apparent from Fig. 2 that the terminal 15 is connected to the resistance 20, which represents the total resistance of the resistor wire 12. Further, the opposite end of the resistance 20 is connected to the conductor 18 and the resistance 19. In Fig. 1, this has its counterpart in that the free end 22 of the resistor wire 12 as intimated by broken lines is connected to the terminal 15. The distal ends (not shown in Fig. 1) of the two resistor wires 10 and 12 are connected to each other, which, in Fig. 2, has its counterpart in the interconnection of the one ends of the resistances 19 and 20 with one another and with the conductor 18. When the heating device 4 according to Figs. 1 and 2 is put into use, the terminals 14 and 15 are supplied with the current which is employed for heating the elements formed by the resistor wires 10 and 12. The output signal from the temperature sensor, i.e. from the casing 9 of NTC material is taken out between the terminal 13 and one of the terminals 14 and 15 and is led to the regulator for output control of the elements 10 and 12. By the interconnection of the distal ends of the resistor wires 10 and 12 in Fig. 1, the heating device 4 needs only three terminals for realising both current supply and emitting measurement signals. Figs. 3 and 4 show an alternative version of the heating device 4. In these Figures, the same reference numerals have been employed as in Figs. 1 and 2 as long as direct counterparts between the relevant components exit. Thus, reference numeral 8 in Fig. 3 refers to an electrically conductive core which is disposed interiorly in a casing 9 of NTC material. On the outside of the casing 9, there is helically disposed a resistor wire 10 which forms an electric heating element in the heating device 4. The arrangement of the terminal 13, the conductors 17 and 18, as well as the elongate NTC material 16 corresponds in Fig. 4 entirely with that described above. Furthermore, the resistance 19 corresponds to the total resistance in the resistor wire 10, hence full agreement with the embodiment according to Figs. 1 and 2. The difference in relation to the embodiment according to Figs. 1 and 2 is that only one resistor wire is employed and that instead of the omitted resistor wire 12, use is made of a return conductor 23 which is connected to the terminal 15. The return conductor 23 is, in Fig. 3, connected to the distal end portion 24 of the resistor wire. The return conductor 23 can, in a practical embodiment, be a separate conductor which is disposed on or in the heating device 4 in a manner which is not specified in Figs. 3 and 4. Another method of arranging the return conductor 23 implies that the free end 24 of the resistor wire 10 is quite simply earthed (grounded) in the metal parts of the windscreen wiper blade and that these in turn are earthed (grounded) in the body of the vehicle. In this alternative, the terminal 15 will consist of earth (ground) or the vehicle body. Also in the embodiment according to Figs. 3 and 4, it may be appropriate to arrange, on the outside of the resistor wire 10, an electrically insulating protective casing such that the heating device 4 runs no risk of being damaged during assembly or use. DESCRIPTION OF ALTERNATIVE EMBODIMENTS In the embodiment according to Figs. 3 and 4, the return conductor 23 may possibly be arranged in such a manner that two resistor wires are heHcally wound on the outside of the casing or sleeve 9 of NTC material and which are spaced apart from one another in the axial direction. These two resistor wires are electrically connected to one another at a point which corresponds to the free end 24 of the resistor wire 10. In this case, the electrical diagram will be identical to that of Fig. 2 although the physical appearance may be given the same small dimensions as in the embodiment according to Fig. 3. In yet a further modification, it is possible to manufacture the electrically conductive components in the core 8 of resistor material so that the core will also have the function of an electric element. The present invention may be modified further without departing from the scope of the appended Claims.

Claims: WHAT IS CLAIMED IS: 1. An apparatus for electrically heating a wiper profile (1) of rubber or rubber-like material included in a windscreen wiper blade, and comprising an elongate electric heating device (4) which has thermal contact with the wiper profile (1) and which extends therealong, and means for power supply to the heating device, characterized in that the heating device (4) includes a temperature sensor (9, 16); and that said means for current supply include a regulator for regulating the temperature of the heating device (4), said temperature sensor being connected to said regulator. 2. The apparatus as claimed in Claim 1, characterized in that said temperature sensor (9, 16) is elongate and extends along substantially the entire length of the heating device (4). 3. The apparatus as claimed in Claim 1 or 2, characterized in that said temperature sensor (9, 16) is a resistive sensor and comprises a material with negative temperature coefficient for the resistivity of the material (NTC material). 4. The apparatus as claimed in Claim 3, characterized in that said NTC material is in the form of a tube or a hose (9) with one inner (8, 17) and one outer (10, 18) electric conductor, said conductors extending along substantially the entire length of the NTC material. 5. The apparatus as claimed in Claim 3 or 4, characterized in that a resistor wire (10) forming a heating element in the heating device (4) is disposed along or is helically wound around said NTC material (9). 6. The apparatus as claimed in Claim 4 or 5, characterized in that the outer conductor (10, 18) consists of a resistor material and constitutes a heating element included in the heating device (4). 7. The apparatus as claimed in Claim 4 or 5, characterized in that the inner conductor (8, 17) consists of a resistor material and constitutes a heating element included in the heating device (4). 8. The apparatus as claimed in any of Claims 4 to 7, characterized in that a second outer conductor (12) is discrete from the first by the intermediary of an electrically insulating material (11); and that both of the outer conductors (10, 12) form a heating element in the heating device (4). 9. The apparatus as claimed in Claim 8, characterized in that the second outer conductor (12) is helically arranged concentrically with the first (10); and that the electrically insulating material (11) between them is in the form of a hose or a tube. 10. The apparatus as claimed in Claim 9, characterized in that both of the outer conductors (10, 12) are electrically united at one end of the heating device (4); and that the point of union is in electric communication (18) with said NTC material (9, 16) along substantially all of its length.

Inventors: LUNDSTROEM MIKAEL, LUNDSTROEM, MIKAEL
Applicants: EXQVISITA AB, LUNDSTROEM MIKAEL, LUNDSTROEM, MIKAEL
Application year: 1998
Main classification: B60S1
IPC codes: B60S1