Patent Publication Number: US-2013248513-A1

Title: Heater element for vehicle

Description:
BACKGROUND 
     1. Technical Field 
     The invention relates to a heater element for a vehicle. 
     2. Background Art 
     As a heater element mounted on a vehicle, Patent Document 1 discloses a heater element provided in a steering wheel. 
     The heater element disclosed in Patent Document 1 includes a heating wire, an inner cover provided on an outer side of the heating wire, an outer cover provided on an outer side of the inner cover, and a heat conduction sheet (heat-equalizing foil) welded on the outer cover and made of aluminum. In the heater element, electrical insulation between the heating wire and the heat conduction sheet, which are conductors, is secured by the insulation layer such as the inner cover or outer cover. 
     Patent Document 1: JP-Y2-63-11029 
     SUMMARY 
     When the insulation layer is damaged at two or more portions thereof, the current that should normally flow through the heating wire is allowed to flow to the heat conduction sheet between the damaged portions. Thereby, a resistance value of the entire heating wire is reduced, and an amount of heat generation of the heating wire increases. 
     The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a heater element for vehicle which can suppress an increase in an amount of heat generation of a heating wire due to a damage of an insulation layer. 
     In a first aspect of the invention, a heater element for vehicle includes: a non-conductive base material; a conductive heat conduction sheet laminated on the base material; a heating wire which is arranged between the base material and the heat conduction sheet and which generates heat by energization; and an insulation layer which electrically insulates the heating wire from the heat conduction sheet. The heat conduction sheet is separated in an extending direction of the heating wire. 
     According to the first aspect, the heat conduction sheet is separated in the extending direction of the heating wire, whereby the conduction of electricity does not occur between separated heat conduction sheet parts. Therefore, even when the insulation layer is damaged below the different heat conduction sheet parts, the current of the heating wire does not flow between the corresponding heat conduction sheet parts. Hence, a resistance value of the whole heating wire does not change, and an amount of heat generation of the heating wire due to the damage of the insulation layer does not increase. 
     Even when the insulation layer is damaged at two or more portions below one heat conduction sheet part, the current flowing through the heating wire flows through the one heat conduction sheet part. Hence, regarding the whole heat conduction sheet separated into the plurality of heat conduction sheet parts, the current of the heating wire flows to only a part of the heat conduction sheet, and a distance of the heating wire at which a short circuit occurs is relatively small. Thus, it is possible to suppress a decrease in the resistance value of the whole heating wire. Thereby, it is possible to suppress an increase in an amount of heat generation of the heating wire due to the damage of the insulation layer. 
     For the above reasons, it is possible to suppress an increase in an amount of heat generation of the heating wire due to the damage of the insulation layer. 
     In a second aspect of the invention, the heat conduction sheet is separated by a slit extending in a direction intersecting with the extending direction of the heating wire. 
     According to the second aspect, since the heat conduction sheet can be separated simply by forming the slits at the heat conduction sheet, it is possible to separate the heat conduction sheet by the simple configuration. 
     The insulation layer may cover an outer periphery of the heating wire in a third aspect of the invention, and may be formed on a surface of the heat conduction sheet facing the base material in a fourth aspect of the invention. 
     In a fifth aspect of the invention, the heater element includes a heater element provided in a steering wheel. 
     A driver always touches the steering wheel provided in a vehicle interior during the vehicle traveling. Thus, if an amount of heat generation of the heating wire increases when the heater element is provided in the steering wheel, the driver may feel uncomfortable for a relatively long time. In the fifth aspect, it is possible to suppress the increase in the amount of heat generation of the heating wire in the heater element provided in the steering wheel. Hence, it is possible to suppress the problem that the driver feels uncomfortable for a relatively long time. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a steering wheel with a heater element for vehicle according to an illustrative embodiment of the invention; 
         FIG. 2  shows the steering wheel seen from an arrow C in  FIG. 1 ; 
         FIG. 3  is a partial sectional view (partial sectional view taken along a line  3 - 3  of  FIG. 4 ) of the heater element of the illustrative embodiment; 
         FIG. 4  is a plan view of the heater element of the illustrative embodiment; 
         FIG. 5  is a schematic diagram showing a separated state of a heat conduction sheet of the illustrative embodiment; 
         FIG. 6  is a partial sectional view (partial sectional view taken along an extending direction of a heating wire) of a related-art heater element; 
         FIG. 7  is a partial sectional view (partial sectional view taken along an extending direction of a heating wire) of the heater element of the illustrative embodiment; 
         FIG. 8  is a partial sectional view (partial sectional view taken along an extending direction of a heating wire) of the heater element of the illustrative embodiment; and 
         FIG. 9  is a partial sectional view (partial sectional view taken along an extending direction of a heating wire) of a heater element according to a modified embodiment of the illustrative embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an illustrative embodiment of a heater element for vehicle of the invention will be described with reference to  FIGS. 1 to 8 . 
     As shown in  FIGS. 1 and 2 , a steering shaft  11  that rotates about a rotational axis line L 1  is arranged at the front (the left in  FIG. 1 ) of a driver seat of a vehicle with being upwards inclined toward the driver seat (the right in  FIG. 1 ). A steering wheel  12  is rotatably integrated with a rear end portion of the steering shaft  11 . 
     The steering wheel  12  includes a rim part (which is also referred to as a handle part or ring part)  13 , a pad part  14  and spoke parts  16  (refer to  FIG. 2 ). The rim part  13  is gripped and rotation-operated (steered) by a driver, and has a substantially circular ring shape about the rotational axis line L 1  (refer to  FIG. 2 ). 
     The pad part  14  is disposed in a space surrounded by the rim part  13 . A front side part of the pad part  14  includes a lower cover  15  (refer to  FIG. 1 ). The plurality of spoke parts  16  (three spoke parts, in this illustrative embodiment) is provided between the rim part  13  and the pad part  14 . 
     In order to specify a circumferential position of the rim part  13  that is rotation-operated (steered), the ‘upper’, the ‘lower’, the ‘left’ and the ‘right’ are defined based on a state (neutral state) where a vehicle travels straight, in this illustrative embodiment. 
     In the rim part  13 , the spoke parts  16  and the pad part  14  of the steering wheel  12 , core bars made of iron, aluminum, magnesium or alloys thereof are arranged, respectively. Among the core bars, a core bar positioned in the rim part  13  configures a framework of the rim part  13  and has a substantially circular ring shape as viewed from the driver side. The core bar in the rim part  13  is referred to as a rim part core bar  20 . 
     As shown with the broken line in  FIG. 2 , heater elements  40  are incorporated in left and right side parts that most of drivers grip with respect to the circumferential direction of the rim part  13 . More specifically, the heater element  40  is adhered so that it covers the rim part core bar  20 . 
     Hereinafter, a structure of the heater element  40  of this illustrative embodiment is described. 
       FIG. 3  shows a sectional structure of the heater element  40 , and  FIG. 4  is a plan view of the heater element  40  at a developed state. 
     As shown in  FIGS. 3 and 4 , the heater element  40  includes a heat insulation sheet  41 , a heat conduction sheet  43 , a heat generation member  45  and an adhesive layer  47 . In this illustrative embodiment, the heat conduction sheet  43  includes a plurality of heat insulation sheet parts, more specifically, first to tenth heat conduction sheet parts  43   a  to  43   j.    
     As shown in  FIG. 3 , the heat insulation sheet  41  is made of a non-conductive insulation material having flexibility, and has a plate shape of a uniform thickness (2 to 3 mm, in this illustrative embodiment). As the insulation material, an elastic and flexible resin material such as urethane and rubber may be preferably used. In the meantime, the heat insulation sheet  41  preferably includes a foamed member, from a standpoint of an increase in heat insulation properties. Thus, in this illustrative embodiment, the heat insulation sheet  41  is made of foamed urethane. The heat insulation sheet  41  serves as the base material. 
     The heat conduction sheet  43  is provided so as to rapidly spread the heat generated from the heat generation member  45 . The heat conduction sheet  43  is thinner than the heat insulation sheet  41 , and is made of a material having a high thermal conductivity. Since the heat conduction sheet  43  is bent along the rim part core bar  20  as well as the heat insulation sheet  41 , the heat conduction sheet is preferably thin. In this illustrative embodiment, the heat conduction sheet  32  is made of a conductive aluminum foil. The heat conduction sheet  43  is laminated on the heat insulation sheet  41 , and is fixed to the heat insulation sheet  41  by a fixing means such as adhesion. 
     The heat generation member  45  includes: a hating wire  45   a  arranged between the heat insulation sheet  41  and the heat conduction sheet  43  and generates heat by energization and an insulation layer  45   b  which electrically insulates between the heating wire  45   a  and the heat conduction sheet  43 . 
     The heating wire  45   a  is sufficient to generate the heat only by the energization, and is made of a wire rod material having high electric resistance and generating heat by energization. Also, as shown in  FIG. 4 , the heat generation member  45  (heating wire  45   a ) is repeatedly bent and arranged so that it forms a waveform in a longitudinal direction of the heater element  40  (in the upper-lower direction in  FIG. 4 ). 
     The insulation layer  45   b  is made of a non-conductive resin and the like and covers an outer periphery of the heating wire  45   a.    
     The adhesive layer  47  has a uniform thickness on a whole surface of the heat insulation sheet  41  opposite to the heat generation member  45 . 
     As shown in  FIG. 4 , the heater element  40  has a long shape at a developed state. The heater element  40  has a pair of opposing edge parts  48  extending in a longitudinal direction with opposing each other. In the heater element  40 , the heat insulation sheet  41  and the heat conduction sheet  43  include cut portions  49  extending from a plurality of portions of each opposing edge part  48  toward the other opposing edge part  48 . Each of the cut portions  49  has a width narrower as the distance from the opposing edge part  48  increases. The cut portions  49  can avoid a wrinkle in the heater element  40  in a state where the heater element  40  is adhered to the rim part core bar  20 . 
     The heat insulation sheet  43  laminated on the heat insulation sheet  41  is provided with a first slit  61  formed in the longitudinal direction of the heater element  40  around a center of the heater element  40  and second to fifth slits  62  to  65  formed in a direction perpendicular to the longitudinal direction of the heater element  40 . The second to fifth slits  62  to  65  are provided between the cut portions  49  facing each other, and formation intervals of the second to fifth slits  62  to  65  in the longitudinal direction of the heater element  40  are substantially equal. 
     As schematically shown in  FIG. 5 , the heat conduction sheet  43  is separated into the ten heat conduction sheet parts, i.e., the first to tenth heat conduction sheet parts  43   a  to  43   j  by the first to fifth slits  61  to  65 . More specifically, the heat conduction sheet  43  is separated in an extending direction of the heat generation member  45  (heating wire  45   a ) by the slits intersecting with the heat generation member  45  (heating wire  45   a ), i.e., the slits (first to fifth slits  61  to  65 ) extending in a direction intersecting with the extending direction of the heat generation member  45  (heating wire  45   a ). Specifically, the first heat conduction sheet part  43   a  is a heat conduction sheet part from which the heat generation member  45  is taken out to the outside. Based on the first heat conduction sheet part  43   a , the second heat conduction sheet part  43   b,  the third heat conduction sheet part  43   c,  the fourth heat conduction sheet part  43   d,  the fifth heat conduction sheet part  43   e,  the sixth heat conduction sheet part  43   f,  the seventh heat conduction sheet part  43   g,  the eighth heat conduction sheet part  43   h,  the ninth heat conduction sheet part  43   i  and the tenth heat conduction sheet part  43   j  are provided in a clockwise direction toward the extending direction of the heat generation member  45 . 
     Next, operations of the heater element  40  of this illustrative embodiment in which the heat conduction sheet  43  is separated into the plurality of heat conduction sheet parts are described with reference to  FIGS. 6 to 8 . Meanwhile, a heater element  400  shown in  FIG. 6  is a heater element in which the heat conduction sheet  43  is not separated, contrary to the heater element  40  of this illustrative embodiment. 
     As shown in  FIG. 6 , in the heater element  400  in which the heat conduction sheet  43  is not separated, when the insulation layer  45   b  is damaged at two portions and the heat insulation sheet  43  contacts the heating wire  45   a  at the first damaged part S 1  and the second damaged portion S 2 , the current that should normally flow through the heating wire  45   a  is allowed to flow to the heat conduction sheet  43  between the first and second damaged portions S 1 , S 2 . When a part of the hearing wire  45   a  is shorted by the heat conduction sheet  43  accordingly, a resistance value of the whole heating wire  45   a  is reduced, so that an amount of heat generation of the heating wire  45   a  may be increased. Such increase in the amount of heat generation of the heating wire  45   a  may be caused when the insulation layer  45   b  is damaged at two or more portions. 
     In contrast, according to the heater element  40  of this illustrative embodiment, the heat conduction sheet  43  is separated in the extending direction of the heating wire  45   a , as described above. The conduction of electricity does not occur between the separated heat conduction sheet parts. 
     When the insulation layer  45   b  is damaged below the different heat conduction sheet parts, for example as shown in  FIG. 7 , the insulation layer  45   b  is damaged below the fourth heat conduction sheet part  43   d,  and the heat conduction sheet  43  contacts the heating wire  45   a  at the first damaged portion S 1 . Also, when the insulation layer  45   b  is also damaged below the eighth heat conduction sheet part  43   h,  the heat conduction sheet  43  contacts the heating wire  45   a  at the second damaged portion S 2 . Even in this case, the current of the heating wire  45   a  does not flow between the fourth heat conduction sheet part  43   d  and the eighth heat conduction sheet part  43   h  because the heat conduction sheet  43  is separated. Therefore, the resistance value of the whole heating wire  45   a  does not change, and the increase in the amount of heat generation of the heating wire  45   a  due to the damage of the insulation layer  45   b  is not caused. Also, even when the insulation layer  45   b  is damaged at one portion below each of three or more heat conduction sheet parts, the current of the heating wire  45   a  does not flow between the heat conduction sheet parts, so that the resistance value of the whole heating wire  45   a  does not change, and the increase in the amount of heat generation of the heating wire  45   a  due to the damage of the insulation layer  45   b  is not caused. 
     When the insulation layer  45   b  is damaged at two or more portions below the one heat conduction sheet part, for example as shown in  FIG. 8 , when the insulation layer  45   b  is damaged at two portions below the second heat conduction sheet part  43   b  and the heat conduction sheet  43  contacts the heating wire  43   a  at the first damaged portion S 1  and the second damaged portion S 2 , the current flowing through the heating wire  45   a  flows through the one heat conduction sheet part only, i.e., the second heat conduction sheet part  43   b . Hence, with respect to the whole heat conduction sheet  43  separated into the plurality of heat conduction sheet parts, the current of the heating wire  45   a  flows to only a part of the heat conduction sheet, and a distance of the heating wire  45   a  at which a short circuit occurs is relatively small. Thus, it is possible to suppress the decrease in the resistance value of the whole heating wire  45   a . Thereby, it is possible to suppress the increase in the amount of heat generation of the heating wire  45   a  due to the damage of the insulation layer  45   b . When the insulation layer  45   b  is damaged at two or more portions below the one heat conduction sheet part (for example, when the insulation layer  45   b  is damaged at three portions below the second heat conduction sheet part  43   b ), the current of the heating wire  45   a  flows between the two damaged portions having the longest distance at which a short circuit occurs. Therefore, even when the insulation layer  45   b  is damaged at three or more portions below the one heat conduction sheet part, it is possible to realize the substantially same operational effects as the case where the insulation layer  45   b  is damaged at two portions below the one heat conduction sheet part. 
     The driver always touches the steering wheel  12  provided in a vehicle interior during the vehicle traveling. Thus, if an amount of heat generation of the heating wire  45   a  increases when the heater element is provided in the steering wheel  12 , the driver may feel uncomfortable for a relatively long time. According to this illustrative embodiment, it is possible to suppress the increase in the amount of heat generation of the heating wire  45   a  in the heater element  40  provided in the steering wheel  12 . Hence, it is possible to suppress the problem that the driver feels uncomfortable for a relatively long time. 
     As described above, according to this illustrative embodiment, the following effects are realized. 
     (1) The heater element  40  for vehicle includes the insulation layer  45   b  that electrically insulates the heating wire  45   a  from the heat conduction sheet  43 . The heat conduction sheet  43  is separated in the extending direction of the heating wire  45   a . Therefore, even when the insulation layer  45   b  is damaged below the different heat conduction sheet parts, the current of the heating wire  45   a  does not flow between the different heat conduction sheet parts. Hence, the resistance value of the whole heating wire  45   a  does not change, and the amount of heat generation of the heating wire  45   a  due to the damage of the insulation layer  45   b  does not increase. 
     Even when the insulation layer  45   b  is damaged at two or more portions below one heat conduction sheet part, the current flowing through the heating wire  45   a  just flows through the one heat conduction sheet part. Hence, it the decrease in the resistance value of the whole heating wire  45   a  can be suppressed. Thereby, it is possible to suppress the increase in the amount of heat generation of the heating wire  45   a  due to the damage of the insulation layer  45   b.    
     According to this illustrative embodiment, it is possible to suppress the increase in the amount of heat generation of the heating wire  45   a  due to the damage of the insulation layer  45   b.    
     (2) The heat conduction sheet  43  is separated by the slits (first to fifth slits  61  to  65 ) extending in the direction intersecting with the extending direction of the heating wire  45   a.  Therefore, since the heat conduction sheet  43  can be separated simply by forming the slits at the heat conduction sheet  43 , it is possible to separate the heat conduction sheet  43  by the simple configuration. 
     (3) The heat conduction sheet  43  of the heater element  40  provided in the steering wheel  12  is separated. Therefore, it is possible to suppress the driver&#39;s uncomfortable feeling for a relatively long time due to the increase in the amount of heat generation of the heating wire  45   a.    
     The invention can be also implemented by other illustrative embodiments described below. 
     Although the heat conduct sheet  43  is separated into the ten sheet parts, the number of separated sheet parts may be appropriately changed. 
     The heat conduction sheet  43  is separated by the slits provided in the heat conduction sheet  43 . As another embodiment, a plurality of heat conduction sheets  43  may be prepared in advance, and the heat conduction sheets  43  may be provided to be spaced from one another on the heat insulation sheet  41 , so that the heat conduction sheets  43  are separated in the extending direction of the heating wire  45   a.    
     As the base material on which the heat conduction sheet  43  is laminated, the material other than the heat insulation sheet  41  may be applied. For example, the sheet configuring the adhesive layer  47  may be used as the base material. 
     The insulation layer  45   b  is provided to cover the outer periphery of the heating wire  45   a.  However, other arrangement may be implemented so long as the insulation layer  45   b  electrically insulates the heating wire  45   a  from the heat conduction sheet  43 . 
     For example, as shown in  FIG. 9 , the insulation layer  45   b  may be omitted from the heat generation member  45 , and the heat generation member  45  may include the heating wire  45   a  without the insulating layer  45   b . Then, an insulation layer  100  having the equivalent function to the insulation layer  45   b  may be formed on a surface of the heat conduction sheet  43  facing the heat insulation sheet  41  (the base material). Also in this configuration, it is possible to suppress the increase in the amount of heat generation of the heating wire  45   a  due to the damage of the insulation layer  100 . 
     The heat conduction sheet  43  may be a member made of a material different from the aluminum foil so long as the member can rapidly spread the heat generated by the heat generation member  45 . For example, the heat conduction sheet  43  may be made of a copper foil. 
     The heat generation member  45  may be a member different from the heating wire  45   a  so long as the member can generate the heat by the energization. For example, a member having a resistance layer formed on an insulation sheet may be used as the heat generation member  45 . 
     The heat generation member  45  may be arranged between the heat insulation sheet  41  and the heat conduction sheet  43 , differently from the above illustrative embodiment. For example, the heat generation member  45  may be repeatedly bent and arranged so that it forms a waveform in a width direction of the heater element  40 . 
     The adhesive layer  47  may be omitted from the heater element  40 . In this case, the heater element  40  may be adhered to the rim part core bar  20  by an adhesive, for example. 
     In the above illustrative embodiment, the second to fifth slits  62  to  65  are provided between the cut portions  49  facing each other. However, the slits may be provided at other positions, so long as the slits are formed in the heat conduction sheet  43  in a direction intersecting with the extending direction of the heating wire  45   a.    
     The cut portions  49  may have a different shape from the above illustrative embodiment. Also, the cut portions  49  may be omitted. 
     The heater element of the invention is not limited to the steering wheel  12  and may be applied to other heater elements for vehicle such as shift knob, seat, etc.