Patent Publication Number: US-2011073582-A1

Title: Steering wheel

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a steering wheel incorporating in the rim a heat generating member that generates heat when electrified. 
     When a vehicle is parked in extremely cold weather in winter, the temperature in the passenger compartment is lowered. Accordingly, the temperature of the rim of the steering wheel is lowered. The rim is also referred to as the handle portion or ring portion. When the driver gets in the vehicle in this state and starts driving, he/she needs to grip the cold rim. This can make the steering operation uncomfortable. 
     In this regard, various types of steering wheels have been known that incorporate in the rim a heat generating member that generates heat when electrified.  FIG. 24(A)  illustrates one such steering wheel  70  disclosed in Japanese Laid-Open Patent Publication No. 2003-317905 (first prior art device). Specifically,  FIG. 24(A)  shows the cross-sectional structure of a rim  71 . The steering wheel  70  includes a rim metal core  72 , which forms the framework of the rim  71 . The rim metal core  72  is coated with a rigid coating portion  73  made, for example, of rigid urethane. A sheet-like heat generating member  74  covers the outer surface of the coating portion  73 . As shown in  FIG. 24(B) , the sheet-like heat generating member  74  includes a base fabric sheet  75  formed, for example, by woven fabric or nonwoven fabric, and heating wires  76  arranged on the base fabric sheet  75 . The heating wires  76  generate heat when electrified. The heating wires  76  are sewn to the base fabric sheet  75  by means of upper threads  77  and lower threads  78 . The sheet-like heat generating member  74  is coated by an elastic member (support body)  79  made of a soft (elastic) material, which is for example, a foam resin as shown in  FIG. 24(A) . Further, a cover  81  made of leather is wound about the elastic member  79 . 
     Unlike the case where a cover  81  is directly wound about the sheet-like heat generating member  74 , asperities of the outer surface of the sheet-like heat generating member  74  hardly stand out on the outer surface  810  of the cover  81  (the ornamental surface of the rim  71 ). The external appearance is therefore hardly degraded by the sheet-like heat generating member  74 . 
     However, in the above described steering wheel  70 , heat generated by the heating wires  76  in the sheet-like heating element is easily transferred through the rigid coating portion  73  to the rim metal core  72 , which has good heat conductivity. Accordingly, the amount of heat transferred to the cover  81  is reduced, and the temperature of the cover  81  is not raised as intended. It is therefore desired that a greater proportion of the heat generated by the heating wires  76  be efficiently transferred to the cover  81 , so that its temperature is increased. 
     Further, since the heating wires  76  are sewn to the base fabric sheet  75  by means of the upper and lower threads  77 ,  78 , the manufacture thereof is difficult and costly. This increases the costs of the steering wheel  70 . 
       FIG. 25  illustrates the cross-sectional structure of a rim  171  of a steering wheel  170  according to a second prior art device. The steering wheel  170  includes a rim metal core  172 , which forms the framework of the rim  171 . The rim metal core  172  is coated with a coating portion  173  made of soft (elastic) material such as foamed polyurethane. A flexible heating element  174  is arranged on the outer surface  173   o  of the coating portion  173 , and a cover  175  is wound about the heating element  174 . 
       FIG. 26  shows one example of the heating element  174 , which is formed by arranging heating wires (heat generating members)  177  on a soft fabric sheet  176  as shown in  FIG. 26 . The heating wires  177  generate heat when electrified (refer to, for example, Japanese National Phase Laid-Open Patent Publication No. 2002-502759). 
     However, in the steering wheel  170 , which employs the prior art heating element  174 , parts of the cover  175  that correspond to the heating wires  177  are pushed from below, causing the pattern of the heating wires  177  to stand out. This degrades the external appearance. The parts of the cover  175  that correspond to the heating wires  177  are locally heated and thus contracted. Due to repeated contraction over years, wrinkles will be conspicuous, degrading the external appearance. 
     Such a problem can be dealt with by providing an elastic member made of rubber such as chloroprene rubber (neoprene rubber) between the heating element  174  and the cover  175 . In this case, at positions where the elastic member covers the heating wires  177 , only the parts on the inner surface are elastically deformed, so that asperities on the outer surface  174   o  of the heating element  174  are absorbed. At positions where the elastic member covers the heating wires  177 , the parts on the outer surface are hardly influenced by the asperities on the outer surface  174   o  of the heating element  174 . Therefore, the outer surface of the elastic member is smooth. Accordingly, the outer surface of the cover  175  wound about the elastic member is smooth. 
     However, since the elastic member is used in this configuration, the number of components in the steering wheel is increased. This increases the number of assembly steps, and thus increases manufacturing costs. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an objective of the present invention to provide a steering wheel that efficiently increases the temperature of a cover, and particularly a steering wheel that efficiently increases the temperature of a cover without increasing the costs. 
     To achieve the foregoing objective and in accordance with one aspect of the present invention, a steering wheel is provided that includes a rim, a rim metal core that forms the framework of the rim, a rigid covering member, a heating element, and a coating layer. The rigid covering member is provided about at least a part of the rim metal core in the circumferential direction of the rim metal core. The covering member has an outer surface. The heating element is formed by a flexible sheet having a heat generating member that generates heat when electrified. The heating element is arranged along the outer surface of the covering member and has an outer surface. The coating layer is provided on the outer surface of the heating element. The coating layer is softer than the covering member. A hollow portion is formed between the rim metal core and a part of the covering member at which the heat generating member of the heating element is located. 
     Other aspects and advantages of the present invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention, together with objects and advantages thereof, may best be understood by reference to the following description of the presently preferred embodiments together with the accompanying drawings in which: 
         FIG. 1  is a front view showing a steering wheel according to a first embodiment of the present invention; 
         FIG. 2  is a front view showing a metal core of the steering wheel of  FIG. 1 ; 
         FIG. 3  is a schematic side view showing the steering wheel of  FIG. 1  as viewed from the left; 
         FIG. 4  is an enlarged partial front view illustrating a section X in  FIG. 1 ; 
         FIG. 5  is a cross-sectional view taken along line  5 - 5  of  FIG. 4 , illustrating the rim; 
         FIG. 6  is a cross-sectional view taken along line  6 - 6  of  FIG. 4 , illustrating the steering wheel; 
         FIG. 7  is a cross-sectional view taken along line  7 - 7  of  FIG. 4 , illustrating the rim; 
         FIG. 8  is an exploded cross-sectional view illustrating components of the rim shown in  FIG. 7 ; 
         FIG. 9  is a front view illustrating a heating element, from which the insulation layer and adhesive layers on both sides are omitted; 
         FIG. 10  is a partially enlarged cross-sectional view of the heating element; 
         FIG. 11  is a partial cross-sectional view illustrating a state before the heating element is adhered to a covering member; 
         FIG. 12  is a front view showing a steering wheel according to a second embodiment of the present invention; 
         FIG. 13  is a front view showing a metal core of the steering wheel of  FIG. 12 ; 
         FIG. 14  is a schematic side view showing the steering wheel of  FIG. 12  as viewed from the left; 
         FIG. 15  is an enlarged partial front view illustrating a section X in  FIG. 12 ; 
         FIG. 16  is a cross-sectional view taken along line  16 - 16  of  FIG. 15 , illustrating the rim; 
         FIG. 17  is a cross-sectional view taken along line  17 - 17  of  FIG. 15 , illustrating the steering wheel; 
         FIG. 18  is a cross-sectional view taken along line  18 - 18  of  FIG. 15 , illustrating the rim; 
         FIG. 19  is an exploded cross-sectional view illustrating the rim metal core, support member, and covering member shown in  FIG. 18 ; 
         FIG. 20  is a front view illustrating a heating element, from which the insulation sheet is omitted; 
         FIG. 21  is a partially enlarged cross-sectional view of the heating element; 
         FIG. 22  is a cross-sectional view illustrating a state in which a steering wheel intermediate is set in a molding apparatus; 
         FIG. 23  is a partial cross-sectional view taken along line  23 - 23  of  FIG. 22 . 
         FIG. 24(A)  is a cross-sectional view of a rim in a steering wheel according to a first prior art; 
         FIG. 24(B)  is an enlarged cross-sectional view illustrating the sheet-like heat generating member in the steering wheel shown in  FIG. 24(A) ; 
         FIG. 25  is a cross-sectional view of a rim in a steering wheel according to a first prior art; and 
         FIG. 26  is a cross-sectional view illustrating a heating element incorporated in the steering wheel shown in  FIG. 25 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment 
     A vehicle steering wheel according to a first embodiment of the present invention will now be described with reference to  FIGS. 1 to 11 . 
     As shown in  FIGS. 1 and 3 , a steering shaft  11  is provided in front of the driver&#39;s seat of a vehicle (on the left side of  FIG. 3 ). The steering shaft  11  is inclined so that its height increases toward the driver&#39;s seat (toward the right side of  FIG. 3 ). A steering column cover  12  is provided about the steering shaft  11 . The rear end of the steering shaft  11  is coupled to a steering wheel  13  of the present embodiment. The steering wheel  13  is integrally rotatable with the steering shaft  11 . The steering wheel  13  includes a rim (also, referred to as a handle portion or a ring portion)  14 , a pad  15 , spokes  16 , and a lower cover  17 . 
     The rim  14  is formed to be annular with its center coinciding with the steering shaft  11  (see  FIG. 1 ). Since the steering shaft  11  is inclined as described above, the steering wheel  13  is inclined so as to approach the driver&#39;s seat toward the lower end (see  FIG. 3 ). 
     The pad  15  is arranged in the space surrounded by the rim  14 . The number of spokes  16 , which connect the rim  14  and the pad  15  together, is three in the present embodiment. The lower cover  17  is arranged forward of the pad  15  and the spokes  16 . 
     In the present embodiment, the steering shaft  11  is used as a reference when describing each part of the steering wheel  13 . A direction along the steering shaft  11  is defined as the front-rear direction of the steering wheel  13 . Among directions along a plane perpendicular to the steering shaft  11 , a direction in which the steering wheel  13  rises is defined as an up-down direction. Thus, the front-rear direction and the up-down direction of the steering wheel  13  are slightly inclined relative to the front-rear direction (horizontal direction) and the up-down direction (vertical direction) of the vehicle. 
     To identify the circumferential position of the rim  14 , which is rotated during operation, the upward, downward, leftward, and rightward directions are defined with reference to the state when the vehicle is traveling forward in a straight line (the neutral state). 
     As shown in  FIGS. 1 and 2 , a metal core  18  is arranged in a space surrounded by the rim  14  of the steering wheel  13 , the spokes  16 , the pad  15 , and the lower cover  17 . The metal core  18  is formed, for example, of iron, aluminum, magnesium, or an alloy thereof. The metal core  18  includes a rim metal core  19  located in the rim  14 . The rim metal core  19  forms the framework of the rim  14  and has an annular shape as viewed from an occupant (driver). The rim metal core  19  is substantially located at a center in a cross section of the rim  14  along a plane that is perpendicular to the elevation of the drawing and includes the rotational axis of the steering shaft  11  (see  FIG. 5 ). 
     In addition to the rim metal core  19 , the metal core  18  includes a boss metal core  21 , which is located slightly forward of the space surrounded by the rim metal core  19 . The metal core  18  includes a plurality of (three) spoke metal cores  22 , each corresponding to one of the spokes  16 . The boss metal core  21  is attached to and rotates integrally with the steering shaft  11 . Each spoke metal core  22  includes one end coupled to the boss metal core  21  and another end coupled to the rim metal core  19 . Parts at which the left and right spoke metal cores  22  and the rim metal core  19  are coupled together are referred to as coupling portions. Each coupling portion includes a spoke-side coupling portion  22 A, which is a part of the spoke metal core  22  that is coupled to the rim metal core  19 , and a rim-side coupling portion  19 A, which is a part of the rim metal core  19  that is coupled to the spoke metal core  22 . Each rim-side coupling portion  19 A has an arcuate shape in the front view. Each spoke-side coupling portion  22 A is bent in the front-rear direction at positions spaced from each other in the longitudinal direction of the spoke  16  (see  FIG. 6 ). 
     The structure of the rim  14  is different between a part corresponding to the rim-side coupling portion  19 A and a part corresponding to the remaining parts of the rim metal core  19 . 
       FIG. 4  is an enlarged view of a section X of  FIG. 1 .  FIG. 5  is a cross-sectional view taken along line  5 - 5  of  FIG. 4 .  FIG. 6  is a cross-sectional view taken along line  6 - 6  of  FIG. 4 .  FIG. 7  is a cross-sectional view taken along line  7 - 7  of  FIG. 4 . In  FIGS. 5 to 7 , the upper side generally corresponds to the rear side in the vehicle (driver&#39;s seat), and the lower side generally corresponds to the front side in the vehicle.  FIGS. 5 to 7  show the cross-sectional structure of the left part of the rim  14 . The right side has the same cross-sectional structure. Therefore, in the present embodiment, the cross-sectional structure of the left part is described, and description of that of the right part is omitted. 
     As shown in  FIGS. 4 and 5 , parts of the rim metal core  19  except for the rim-side coupling portion  19 A is coated with a rigid coating portion  23  made of a rigid resin. 
     As shown in  FIGS. 4 ,  7  and  8 , a support member  25  is arranged at each end of the rim-side coupling portion  19 A with respect to the circumferential direction of the rim  14  (see  FIG. 4 ). Each support member  25  is divided into two members. To distinguish these members, the member located at the rear will be referred to as a support piece  26 , and the member located at front will be referred to as a support piece  27 . The support pieces  26 ,  27  are each formed by an elastic member made, for example, of rubber or silicone. The support piece  26  is fitted from the rear to each end of the rim-side coupling portion  19 A with respect to the circumferential direction of the rim  14 , and the support piece  27  is fitted from the front. A separating surface of the support piece  27  and a separating surface of the support piece  26  are brought into contact. In this contacting state, the support pieces  26 ,  27  both closely contact each end of the rim-side coupling portion  19 A with respect to the circumferential direction of the rim  14 , so as to make the annular support member  25  about each end (see  FIG. 7 ). 
     As shown in  FIGS. 6 to 8 , a rigid covering member (also, referred to as a bezel)  30  is attached to the rim metal core  19  and the spoke metal core  22 . The covering member  30  is formed to be hollow and made of a rigid resin. The covering member  30  covers the entire rim-side coupling portion  19 A and the spoke-side coupling portion  22 A. In this attached state, an inner end portion  30 A of the covering member  30  covers a part  22 B of the spoke metal core  22  that is closer to the boss metal core  21  than the spoke-side coupling portion  22 A (right side as viewed in  FIG. 6 ). 
     The covering member  30  is divided into two members. To distinguish these members, the member located at rear will be referred to as a covering piece  31 , and the member located at front will be referred to as a covering piece  32 . An inner surface  31   i  of the covering piece  31  and an inner surface  32   i  of the covering piece  32  form the inner surface of the covering member  30 . Also, an outer surface  310  of the covering piece  31  and an outer surface  32   o  of the covering piece  32  form the outer surface of the covering member  30 . 
     An engaging portion  31 A is formed on the separating surface of the covering piece  31 , and an engaging portion  32 A is formed on the separating surface of the covering piece  32 . The engaging portions  32 A are engageable with the engaging portions  31 A. The covering piece  32  is fitted from the front to the support piece  27 , and the covering piece  32  is fitted to the support piece  26  from rear. The engaging portions  31 A of the covering piece  31  are engaged with the engaging portions  32 A of the covering piece  32 . The engagement causes the covering member  30  to be attached to the rim-side coupling portion  19 A and the spoke-side coupling portion  22 A with the pair of support members  25  in between. The region surrounded by the rim-side coupling portion  19 A, the spoke-side coupling portion  22 A, the covering member  30 , and the support members  25  defines a hollow portion  35  (see  FIG. 6 ). 
     As shown in  FIG. 11 , two through holes  33  (only one is shown in  FIG. 11 ) are formed in the rear covering piece  31 . The through holes  33  connect the exterior and interior of the covering member  30  to each other. The through holes  33  are located in a part that covers the spoke-side coupling portion  22 A and are separated from each other with respect to the circumferential direction of the rim  14  (the direction perpendicular to the elevation of the drawing). A first connector  34  is inserted in and fixed to each through hole  33 . A part of each fixed first connector  34  is exposed to the outside of the covering piece  31 . 
     Two second connectors  36  (only one is shown in  FIG. 11 ) are fixed to the inner end portion  30 A of the covering member  30 . More specifically, the two second connectors  36  are inserted and fixed to the part between an end of the covering piece  31  facing the boss metal core  21  (the right end in  FIG. 11 ) and the spoke metal core  22 . The two second connectors  36  are separated from each other along the circumferential direction of the rim  14 . 
     Two conductive wire rods are arranged in the covering member  30  to extend along the inner surface  31   i  of the covering piece  31 . In the present embodiment, the wire rods are first electric wires  37 , which are formed by coating lead wires with insulating material such as soft resin. One end of each first electric wire  37  (left end as viewed in  FIG. 11 ) is connected to one of the first connectors  34 . The other end (right end as viewed in  FIG. 11 ) is connected to one of the second connectors  36 . Each first electric wire  37  is used for supplying electricity or signals to a heat generating member of a heating element  40 , which will be discussed below, from the outside of the rim  14 . Each first electric wire  37  is arranged while being curved along the inner surface  31   i  of the covering piece  31 . 
     A resin receiving portion  38  for receiving the first electric wires  37  is provided inside the covering piece  31 . The receiving portion  38  is formed by a component separate from the covering piece  31  and attached to the covering piece  31  from inside. In most part, the receiving portion  38  is spaced from the inner surface  31   i  of the covering piece  31  by a constant distance except for the sections that are attached to the covering piece  31 . The receiving portion  38  entirely covers the first connectors  34  and the curved first electric wires  37  from front. The receiving portion  38  restricts movement (for example, shaking) of the electric wires  37  and maintains the first electric wires  37  in shapes conforming to the inner surface  31   i  of the covering piece  31 . 
     The first connectors  34 , the first electric wires  37 , the second connectors  36 , and the receiving portion  38  are attached to the covering piece  31  before the covering piece  31  are placed over the support pieces  26 . The receiving portion  38  may receive the first electric wires  37  at several positions that are spaced from each other along the longitudinal direction. 
     As shown in  FIG. 6 , a sheet-like heating element  40  is arranged on the covering member  30  at a part corresponding to the hollow portion  35 . The heating element  40  is spread along the outer surfaces  31   o ,  32   o  of the covering member  30 .  FIG. 9  shows the heating element  40  as viewed from front, and  FIG. 10  is an enlarged cross-sectional view of the heating element  40 .  FIG. 9  shows the heating element  40  with adhesive layers  45 ,  47  and an insulation layer  46 , which are discussed below, omitted. 
     As shown in  FIGS. 9 and 10 , the main portion of the heating element  40  is a flexible sheet having a sheet-like heat generating member that generates heat when electrified. The heating element  40  of the present embodiment has a slightly greater rigidity than the sheet-like heat generating member  74  of Japanese Laid-Open Patent Publication No. 2003-317905, in which the heating wires  76  are sewn to the base fabric sheet  75  (see  FIGS. 24(A) ,  24 (B)). When receiving force, the heating element  40  is flexed, and returns to the original shape when the force is removed. The heating element  40  has a thickness T 1 , which is 0.2 to 0.3 mm, as a whole. 
     The heating element  40  includes a sheet-like heating main body  40 A, heating a sheet-like extension  40 B, and a pair of first terminals  48 ,  49  (see  FIG. 9 ). The heating main body  40 A is arranged on the covering member  30  at a part corresponding to the hollow portion  35 . The heating main body  40 A is spread along the outer surfaces  31   o ,  32   o  of the covering member  30  (see  FIG. 6 ). The extension  40 B is located at a position facing the boss metal core  21  (right side in  FIG. 9 ) and overlaps and surrounds the through holes  33 . The extension  40 B is integrally formed with the main body  40 A. 
     Each of the heating main body  40 A and the extension  40 B include an insulation sheet  41  serving as an insulative substrate, a resistor layer  44 , a pair of electrodes  42 ,  43 , an adhesive layer  45 , an insulation layer  46 , and an adhesive layer  47 . 
     The insulation sheet  41  is a member that forms one side of the heating element  40  (upper side as viewed in  FIG. 10 ). The insulation sheet  41  is formed by an insulation film such as a polyester film, and has flexibility as a whole. The outer surface  410  of the insulation sheet  41  forms the outer surface of the heating element  40 . 
     The resistor layer  44  forms a heat generating member and is formed substantially over the entire insulation sheet  41 . The resistor layer  44  is formed by, for example, printing the following ink and subjecting the printed ink to high temperature baking. The ink is formed by dispersing conductive particles such as carbon particles to insulating organic polymer by means of solvent. The resistor layer  44  may have a positive temperature coefficient (PTC) so that the resistance value increases as the temperature increases. Alternatively, the resistor layer  44  does not need to have the PTC. If the resistor layer  44  has the PTC, its temperature is relatively low and the resistance value is small when electricity starts being supplied. Accordingly, a large current flows through the resistor layer  44 , generating a great amount of heat. The resistor layer  44  has high heat conductivity like the electrodes  42 ,  43 , which will be discussed below. 
     The electrode  42  functions as a positive electrode and has a wide main electrode portion  42 A, which extends along the circumferential direction of the rim  14  (up-down direction of  FIG. 9 ) on the resistor layer  44 . The other electrode  43  functions as a negative electrode and has a wide main electrode portion  43 A, which extends along the circumferential direction of the rim  14  at a position on the resistor layer  44  that is different from the main electrode portion  42 A. Comb-like auxiliary electrode portions  42 B, which are narrower than the main electrode portion  42 A, extend from the main electrode portion  42 A toward the other main electrode portion  43 A. Likewise, comb-like auxiliary electrode portions  43 B, which are narrower than the main electrode portion  43 A, extend from the main electrode portion  43 A toward the other main electrode portion  42 A. The auxiliary electrode portions  42 B,  43 B are spaced by constant intervals along the circumferential direction of the rim  14 . The electrodes  42 ,  43  are arranged such that the auxiliary electrode portions  42 B,  43 B are alternately arranged along the circumferential direction of the rim  14 . Each adjacent pair of the auxiliary electrodes  42 B,  43 B function as opposing electrodes. 
     The electrodes  42 ,  43  are formed by a printing method, in which conductive ink containing, for example, silver or copper, is applied onto the resistor layer  44 . Alternatively, the electrodes  42 ,  43  can be formed by etching metal foil adhered to the resistor layer  44 . In this case, aluminum foil or copper foil is used as the metal foil. 
     The insulation layer  46  is formed by an insulation film such as a polyester film, and has flexibility. The insulation layer  46  coats and protects the resistor layer  44  and the electrodes  42 ,  43 . 
     The adhesive layer  45  is formed on one surface (the upper surface as viewed in  FIG. 10 ) of the insulation layer  46 , and the adhesive layer  47  is formed on the other surface (the lower surface as viewed in  FIG. 10 ) of the insulation layer  46 . The adhesive layers  45 ,  47  are formed of insulating adhesive compound. The insulation layer  46  is adhered to the resistor layer  44  and the electrodes  42 ,  43  by means of the adhesive layer  45 . 
     As shown in  FIGS. 9 to 11 , the first terminals  48 ,  49  form ports through which currents flow between the electrodes  42 ,  43  and the outside. The first terminals  48 ,  49  protrude from the heating element  40  toward the covering member  30  (see  FIG. 11 ). The first terminal  48  functions as a positive terminal and is electrically connected to the electrode  42  by means of a fastener such as a grommet. The first terminal  49  functions as a negative terminal and is electrically connected to the electrode  43  by means of a fastener such as a grommet. The first terminals  48 ,  49  are connected to the first connectors  34  through the through holes  33  in the covering piece  31 . Accordingly, the electrodes  42 ,  43  are electrically connected to the first electric wires  37  through the through holes  33 . This connection determines the position of the heating element  40  in relation to the covering member  30 . 
     An electronic control unit (not shown), which controls electricity supplied to the heating element  40 , is provided in the space between the pad  15  (see  FIG. 1 ) and the lower cover  17 . As shown in  FIG. 6 , two second electric wires  51  extend from the electronic control unit (only one is shown in  FIG. 6 ). The second electric wires  51  are formed by coating leading wires are formed by coating lead wires with insulating material such as soft resin. Second terminals  52 , which are connectable to the second connectors  36 , are connected to the second electric wires  51 . The second terminals  52  are detachably connected to the second connectors  36 . 
     The first terminals  48 ,  49  are connected to the first connectors  34  in the above described manner. In this state, the heating main body  40 A is adhered to the outer surfaces  31   o ,  32   o  of the covering pieces  31 ,  32  (see  FIG. 6 ) by means of the adhesive layer  47  (see  FIG. 10 ), while being flexed along the covering pieces  31 ,  32 . Also, the extension  40 B is adhered to the outer surface  310  of the covering piece  31  (see  FIG. 6 ) by means of the adhesive layer  47 , while being flexed along the covering piece  31 . 
     Although the heating main body  40 A and the extension  40 B of the present embodiment both have flexibility, the heating main body  40 A and the extension  40 B are less flexible than the sheet-like heat generating member  74  (see  FIG. 24(B) ) disclosed in Japanese Laid-Open Patent Publication No. 2003-317905, in which the heating wires  76  are sewn to the base fabric sheet  75 . Therefore, compared to the sheet-like heat generating member  74 , the heating main body  40 A and the extension  40 B can be easily and reliably adhered to predetermined positions of the covering member  30  without making wrinkles. Once adhered, the heating main body  40 A and the extension  40 B are not peeled or displaced and are maintained at the initial positions unless significantly great force is applied. 
     A cover  62  made of, for example, leather, is wound about the above described rigid coating portion  23  (see  FIG. 5 ) and the heating element  40  (see  FIG. 6 ) by means of a sheet-like elastic member  61 , which is made of, for example, rubber (such as neoprene rubber). The outer surface  62   o  of the cover  62  forms an ornamental surface of the rim  14 . The elastic member  61  and the cover  62  form a coating layer that is softer than the covering member  30 . 
     In the steering wheel  13  configured as described above, the electronic control unit outside of the rim  14  supplies electricity and signals to the heating element  40  through the second electric wires  51 , the second terminals  52 , the second connectors  36 , the first electric wires  37 , the first connectors  34 , and the first terminals  48 ,  49 . 
     When the vehicle starts being driven in the winter under a low outside temperature condition, a current is supplied to the heat generating member (the resistor layer  44 ), so that the heat generating member (the resistor layer  44 ) generates heat. That is, as shown in  FIGS. 9 and 10 , when the pair of electrodes  42 ,  43  is electrified through the first terminals  48 ,  49 , current flows in the resistor layer  44  from the auxiliary electrode portions  42 B to the auxiliary electrode portions  43 B as indicated by arrows in  FIG. 10 . Accordingly, the resistor layer  44  between the auxiliary electrode portions  42 B,  43 B generates heat. The resistor layer  44  and the auxiliary electrode portions  42 B,  43 B both have good heat conductance, the temperature of wide areas on the surfaces increases. 
     The heat generated by the resistor layer  44  is transferred to the cover  62  through the elastic member  61  coating the heating element  40 . The heat transfer uniformly increases the temperature of contacting parts of the elastic member  61  and the cover  62  about the heating element  40 , so that the temperature is quickly increased to an adequate level for being gripped by the driver. 
     The rim metal core  19  is made of metal and has good heat conductivity. Therefore, if the covering member  30  is in direct contact with the rim metal core  19 , or the covering member  30  indirectly contacts the rim metal core  19  via the rigid coating portion  173  as in Japanese Laid-Open Patent Publication No. 2003-317905 (see  FIG. 24  (A)), the heat generated by the heat generating member (the resistor layer  44 ) is likely to transferred to the rim metal core  19  through the covering member  30 , or through the covering member  30  and the rigid coating portion  173 . If heat is transferred to the rim metal core  19 , the amount of heat transferred from the heat generating member (the resistor layer  44 ) to the elastic member  61  and the cover  62  is reduced accordingly. 
     However, in the present embodiment, the hollow portion (an air layer)  35  between the covering member  30  and the rim-side coupling portion  19 A and the spoke-side coupling portion  22 A functions as a heat-insulating layer. The hollow portion  35  prevents the heat generated by the heat generating member (the resistor layer  44 ) of the heating element  40  from being transferred to the rim metal core  19  through the covering member  30 . As a result, most of the heat generated by the heat generating member (the resistor layer  44 ) of the heating element  40  is transferred to parts of the elastic member  61  and the cover  62  that surround the heating element  40 . 
     As shown in  FIG. 6 , the outer surface  62   o  of the cover  62  forms the ornamental surface of the rim  14 . If the asperities on the outer surface  410  of the heating element  40  (see  FIG. 10 ) stand out on the ornamental surface, the external appearance is degraded. However, in the present embodiment, the elastic member  61  located between the heating element  40  and the cover  62  elastically deforms in accordance with the asperities of the heating element  40  on the inner side, thereby absorbing the asperities on the outer surface of the heating element  40  (the outer surface  410  of the insulation sheet  41 ). Accordingly, the outer surface of parts of the elastic member  61  that covers the heat generating member (the resistor layer  44 ) is less likely to be influenced by the asperities of the outer surface of the heating element  40  (the outer surface  410  of the insulation sheet  41 ), and smooth or substantially smooth. The outer surface  62   o  of the cover  62  outside the elastic member  61  becomes smooth or substantially smooth, so that the external appearance is prevented from being degraded by the heating element  40 . 
     If the cover  81  is wrapped about the sheet-like heat generating member  74 , which is formed by sewing the heating wires  76  to the base fabric sheet  75 , as disclosed in Japanese Laid-Open Patent Publication No. 2003-317905, parts of the cover  81  that cover the heating wires  76  are locally heated and contracted. Due to repeated contraction over years, wrinkles will be conspicuous, degrading the external appearance. 
     However, according to the present embodiment, the resistor layer  44  between the adjacent auxiliary electrode portions  42 B and  43 B generates heat as shown in  FIG. 10 . Since the auxiliary electrode portions  42 B,  43 B and the resistor layer  44  both have good heat conductivity, the temperature is increased in large area on the surface. Therefore, the elastic member  61  covering the heating element  40  and the cover  62  is unlikely to be locally heated and contracted. This prevents the external appearance from being degraded. 
     The present embodiment described above has the following advantages. 
     (1) The rigid covering member  30  is provided about the rim metal core  19 , and the heating element  40  is arranged along the outer surfaces  31   o ,  32   o  of the covering member  30 . Further, the cover  62  is wrapped about the heating element  40 . Also, the hollow portion (air layer)  35  is formed between the rim metal core  19  and a part of the covering member  30  at which the heat generating member (the resistor layer  44 ) of the heating element  40  is arranged (see  FIG. 6 ). The heat insulating effect of the hollow portion  35  hinders heat transfer from the heat generating member (the resistor layer  44 ) to the rim metal core  19 . Accordingly, an increased proportion of the heat of the heat generating member (the resistor layer  44 ) is transferred to the cover  62 . 
     (2) The elastic member  61  is located between the heating element  40  and the cover  62  (see  FIG. 6 ). The elastic member  61  prevents the shape of the outer surface of the heating element  40  (the outer surface  410  of the insulation sheet  41 ) from standing out on the outer surface  62   o  of the cover  62 . Also, when the driver grips the rim  14 , the soft elastic member  61  is elastically deformed. Thus, the touch of the cover  62  is improved compared to a case where the cover  62  is directly wrapped about the heating element  40  without using the elastic member  61 . 
     (3) The support members  25  for supporting the covering member  30  to the rim metal core  19  are located between the covering member  30  and the rim-side coupling portion  19 A, and at positions where the hollow portion  35  does not exist ( FIGS. 4 and 7 ). The support members  25  allow the covering member  30  to be attached to the rim-side coupling portion  19 A, while determining the position of the covering member  30  such that the hollow portion  35  is defined between the covering member  30  and the rim-side coupling portion  19 A. 
     (4) The two support members  25  are located at positions that are between the rim-side coupling portion  19 A of the rim metal core  19  and the covering member  30  and at both ends of the covering member  30  along the circumferential direction of the rim  14 . The hollow portion  35  is formed between the rim-side coupling portion  19 A and the covering member  30  and between the support members  25  ( FIGS. 4 and 7 ). Therefore, when the covering member  30  is attached to the rim-side coupling portion  19 A by means of the support members  25 , the hollow portion  35  is formed at the same time as the covering member  30  is attached. The formation of the hollow portion  35  is therefore simplified. 
     (5) The heating element  40  has as its main part the insulation layer  46  and the pair of electrodes  42 ,  43 , which is formed by the insulation sheet  41 , the resistor layer  44 , the main electrode portions  42 A,  43 A, and the auxiliary electrode portions  42 B,  43 B ( FIG. 10 ). Therefore, unlike the sheet-like heat generating member  74  of Japanese Laid-Open Patent Publication No. 2003-317905, in which the heating wires  76  are sewn to the base fabric sheet  75  by means of the upper and lower threads  77 ,  78  ( FIGS. 24  (A) and  24 (B)), troublesome sewing operation is not required. The manufacturing costs are therefore reduced. 
     The temperature of the heating element  40  is increased in a large area on the surface. Therefore, the cover  62  covering the heating element  40  is prevented from being locally heated and contracted. This prevents the external appearance from being degraded. 
     (6) One surface of the heating element  40  is formed by the adhesive layer  47 . Before the elastic member  61  and the cover  62  are wound, the heating element  40  is adhered to the outer surfaces  31   o ,  32   o  of the covering member  30  at the adhesive layer  47  ( FIGS. 10 and 11 ). Once adhered, the heating element  40  is not peeled off the covering member  30  or displaced and is maintained at the initial position unless significantly great force is applied. This facilitates the winding of the elastic member  61  and the cover  62 . 
     Second Embodiment 
     Hereinafter, a steering wheel according to the second embodiment will be described with reference to  FIGS. 12 to 23 , focusing on differences from the steering wheel according to the first embodiment. The steering wheel according to the second embodiment is different from the steering wheel according to the first embodiment in the structure of the covering portion that covers the heating element  40 . Like or the same reference numerals are given to those components that are like or the same as the corresponding components of the steering wheel according to the fifth embodiment. 
     As shown in  FIGS. 12 and 13 , the entire rim metal core  19  including both rim-side coupling portions  19 A, and the spoke-side coupling portions  22 A in the left and right spoke metal cores  22  are directly or indirectly covered with the soft coating portion  20 . The soft coating portion  20  is formed of a soft (elastic) material such as foamed polyurethane. The soft coating portion  20  is softer than the covering member  30 . 
     The rim metal core  19  is directly coated with the soft coating portion  20  in parts except for the rim-side coupling portions  19 A. The rim metal core  19  is indirectly coated with the soft coating portion  20  in rim-side coupling portions  19 A and the spoke-side coupling portions  22 A of the spoke metal cores  22 . To distinguish the parts that directly coat the metal core and the parts that indirectly coat the metal core in the soft coating portion  20 , the latter is referred to as a first coating portion  28 , while the former is referred to as a second coating portion  29 . 
     As shown in  FIGS. 15 and 16 , the second coating portion  29  contacts the rim metal core  19  so as to directly coats the rim metal core  19  at positions spaced from the rim-side coupling portion  19 A (see  FIG. 13 ) along the circumferential direction of the rim  14  (upward and downward in  FIG. 15 ). The second coating portion  29  is thicker than the first coating portion  28 . 
     The manner in which the first coating portion  28  coats the coupling portions (the rim-side coupling portions  19 A and the spoke-side coupling portions  22 A) will now be described. The first coating portion  28  functions as the coating layer of the present invention. 
     As shown in  FIGS. 17 to 19 , the covering member  30  covers a part of the rim metal core  19  and a part of the spoke metal core  22 . Therefore, the covering member  30  has an opening  30 C at the boundary between the rim-side coupling portion  19 A and the remaining portion in the rim metal core  19 , that is, at each end of the rim  14  in the circumferential direction (see  FIGS. 15 and 18 ). Also, the covering member  30  has an opening  30 B at the boundary between the spoke-side coupling portion  22 A and the remaining portion in the spoke metal core  22 , that is, at an end closer to the boss metal core  21  (right side as viewed in  FIG. 17 ). 
     At both ends of the covering piece  32  with respect to the circumferential direction of the rim  14 , the inner surface  32   i  closely contacts the outer surface  27   o  of the support piece  27 , and the inner surface  31   i  of the covering piece  31  closely contacts the outer surface  26   o  of the support piece  26 . The closely contacting support pieces  26 ,  27  close the openings  30 C of the covering member  30 . At the opening  30 B in the vicinity of the boss metal core  21  of the covering member  30 , an end face  31 E of the covering piece  31  and an end face  32 E of the covering piece  32  closely contact the spoke metal core  22  (see  FIG. 17 ). The region surrounded by the rim-side coupling portion  19 A, the spoke-side coupling portion  22 A, the covering member  30 , and the support members  25  defines a hollow portion  35  (see  FIG. 17 ). 
     A sheet-like heating element  40  is arranged on the covering member  30  at a part corresponding to the hollow portion  35 . The heating element  40  is spread along the outer surfaces  31   o ,  32   o  of the covering member  30 .  FIG. 20  shows the heating element  40  as viewed from rear, and  FIG. 21  is an enlarged cross-sectional view of the heating element  40 .  FIG. 20  shows the heating element  40 , without illustrating an insulation sheet  41 , which will be discussed below. 
     As shown in  FIGS. 20 and 21 , the main portion of the heating element  40  is a flexible sheet having a sheet-like heat generating member that generates heat when electrified. The heating element  40  of the present embodiment has a slightly greater rigidity than the heating element  174  of the second prior art, in which the heating wires  177  are arranged on the fabric sheet  176  (see  FIG. 26 ). The heating element  40  includes an insulation sheet  41  serving as an insulative substrate, a pair of electrodes  42  and  43 , a resistor layer  44 , an adhesive layer  45 , and an insulation layer  46 , and has a thickness of 0.2 to 0.3 mm as a whole. 
     The insulation sheet  41  forms the outermost layer of the heating element  40 . The insulation sheet  41  is formed by an insulation film such as a polyester film, and has flexibility as a whole. The outer surface  410  of the insulation sheet  41  forms the outer surface of the heating element  40 . 
     A pair of power supply terminals  57 ,  58  is fixed to the insulation sheet  41  by means of fasteners such as grommets. The power supply terminals  57 ,  58  are each electrically connected to the corresponding one of the electrodes  42 ,  43  by means of the grommet. The power supply terminals  57 ,  58  are arranged in the pad  15  and connected to an electronic control unit (not shown), which controls electricity supplied to the heating element  40 . 
     The insulation layer  46  is formed by an insulation film such as a polyester film, and has flexibility. The insulation layer  46  coats and protects the resistor layer  44 . 
     The adhesive layer  45  forms the innermost layer of the heating element  40  and is provided, for example, over the entire insulation layer  46 . The adhesive layer  45  is formed of insulating adhesive compound. The adhesive layer  45  adheres the heating element  40  to the outer surfaces  31   o ,  32   o  of the covering member  30  (see  FIG. 17 ). 
     As illustrated in  FIG. 17 , at the rim-side coupling portion  19 A and the spoke-side coupling portion  22 A, the entire covering member  30  and most of the heating element  40  are coated with a first coating portion  28 , which is made of a soft (elastic) material such as foamed polyurethane. The first coating portion  28  indirectly coats the rim-side coupling portion  19 A of the rim metal core  19  and the spoke-side coupling portion  22 A of the spoke metal core  22 . The outer surface  28   o  of the first coating portion  28  has no visible asperities and is a smooth surface. 
     The first coating portion  28  preferably has a thickness of 3 to 4 mm. The reason for this is as follows. If the thickness is less than 3 mm, the first coating portion  28  can be no longer elastically deformed even if the driver grips it with a slightly strong force (which gives the driver hard-surface-contacting sensation). Therefore, the tactile sensation is deteriorated. In addition, if the molding material, which will be discussed below, can be insufficiently supplied to parts in a cavity  50 A of a molding apparatus  50  for forming the first coating portion  28 , defective molding may occur. If the thickness is greater than 4 mm, it takes a relatively long time from when the heating element  40  starts being electrified to when the temperature of the first coating portion  28  is increased to a predetermined level. 
     The manufacture of the steering wheel  13  having the above described configuration will now be described with reference to  FIGS. 18 ,  22 , and  23 . First, the support piece  27  is fitted from the front to each end of the rim-side coupling portion  19 A with respect to the circumferential direction of the rim  14 , and the support piece  26  is fitted from the rear. The separating surface of the support piece  27  and the separating surface of the support piece  26  are brought into contact. The contact forms the annular support member  25  at either end of the rim-side coupling portion  19 A with respect to the circumferential direction of the rim  14 . 
     Subsequently, the covering piece  32  is fitted from the front to each support piece  27 , and the covering piece  31  is fitted to each support piece  26  from rear. The engaging portions  31 A of the covering piece  31  are engaged with the engaging portions  32 A of the covering piece  32 . The engagement causes the covering member  30  to be attached to the rim-side coupling portion  19 A and the spoke-side coupling portion  22 A with the pair of support members  25  in between. At this time, the pair of support members  25  forms the hollow portion  35  (see  FIG. 22 ) between the rim metal core  19  and the covering member  30 , and supports the covering member  30  while determining the position of the covering member  30  relative to the rim metal core  19 . Thus, by using the support members  25 , the covering member  30  is attached to the rim-side coupling portion  19 A and the spoke-side coupling portion  22 A, with the hollow portion  35  defined therebetween. The hollow portion  35  is formed at the same as when the covering member  30  is attached to the pair of support members  25 . Specifically, the hollow portion  35  is formed at a position between the rim-side and spoke-side coupling portions  19 A,  22 A of the metal core and the covering member  30 , and between the support members  25 . 
     Further, as shown in  FIGS. 22 and 23 , the heating element  40  is adhered to the outer surfaces  31   o ,  32   o  of the covering member  30  and the spoke metal core  22  at the innermost adhesive layer  45  (see  FIG. 21 ), while being flexed to conform to the covering pieces  31 ,  32  and the spoke metal core  22 . Although the heating element  40  of the present embodiment has flexibility, the heating element  40  is less flexible than the heating element  174  (see  FIG. 26 ) of the second prior art, in which the fabric sheet  176  and the heating wires  177  are combined. Therefore, compared to the prior art shown above, the heating element  40  can be easily and reliably adhered to predetermined positions of the covering member  30  and the spoke metal core  22  without making wrinkles. Once adhered, the heating element  40  is not peeled off the covering member  30  and the spoke metal core  22  or displaced and is maintained at the initial position unless significantly great force is applied. 
     The steering wheel  13  at this state will be referred to as a steering wheel intermediate  13 A. 
     The steering wheel intermediate  13 A is set in the molding apparatus  50  for Reaction Injection Molding (RIM) as illustrated in  FIG. 22 . The molding apparatus  50  is clamped so that a molding space (cavity  50 A) for forming the soft coating portion  20  is defined in the molding apparatus  50  mainly about the rim metal core  19  of the steering wheel intermediate  13 A. In this state, since the heating element  40  is adhered to a predetermined part of the covering member  30  and the spoke metal core  22 , no operation is required for determining the position of the heating element  40 . 
     Subsequently, liquid molding material, which is made by mixing predetermined ingredients, is supplied to the cavity  50 A. The supplied molding material undergoes reaction (foams) to form the soft coating portion  20  at a part of the steering wheel intermediate  13 A, mainly at a part corresponding to the rim metal core  19 . More specifically, in parts of the rim metal core  19  that are away from the rim-side coupling portions  19 A with respect to the circumferential direction of the rim  14 , the second coating portion  29  is formed to contact the rim metal core  19  (see  FIG. 16 ). At the rim-side coupling portion  19 A and the spoke-side coupling portion  22 A, the first coating portion  28  is formed to contact large areas of the covering member  30  and the heating element  40  (see  FIG. 17 ). The first coating portion  28  is formed not to contact the rim-side coupling portion  19 A and the spoke-side coupling portion  22 A, which are covered with the covering member  30 . 
     The covering member  30 , which is formed by engaging the pair of covering pieces  31 ,  32  together, has the opening  30 C at either end with respect to the circumferential direction of the rim  14  (see  FIG. 15 ). If the openings  30 C are not closed, molding material in a liquid or gel state can flow into the covering member  30  through the openings  30 C. 
     However, in the present embodiment, the support member  25  is placed between each end of the covering member  30  and the end of the rim-side coupling portion  19 A with respect to the circumferential direction of the rim  14 , so that the openings  30 C are closed (see  FIG. 18 ). Further, the support member  25  is formed of rubber or silicone, and closely contacts the outer surface of the rim-side coupling portion  19 A as well as the inner surfaces  31   i ,  32   i  of the covering member  30 . The end faces  31 E,  32 E of the covering piece  31 ,  32  closely contact the spoke metal core  22 , so that the opening  30 C, which is located close to the boss metal core  21  of the covering member  30 , is closed (see  FIG. 17 ). Therefore, the support members  25  prevent the molding material from flowing into the covering member  30  through the openings  30 B,  30 C. This allows the hollow portion  35  to be reliably formed between the rim-side and spoke-side coupling portions  19 A,  22 A and the inner surfaces  31   i ,  32   i  of the covering member  30 . 
     Since the heating element  40  is adhered to the outer surfaces  31   o ,  32   o  of the covering member  30  at the adhesive layer  45 , the molding material hardly enters between the covering member  30  and the heating element  40 . Therefore, the heating element  40  is unlikely to be peeled off or displaced on the covering member  30  due to entering molding material. 
     After the soft coating portion  20  is molded, the molding apparatus  50  is opened and the steering wheel  13  is removed. When the vehicle starts being driven in the winter under a low outside temperature condition, the heat generating member (the resistor layer  44 ) of the heating element  40  in the steering wheel  13  is electrified and generates heat. That is, as shown in  FIGS. 20 and 21 , when the pair of electrodes  42 ,  43  are electrified through the power supply terminals  57 ,  58 , current flows from the auxiliary electrode portions  42 B to the auxiliary electrode portion  43 B as indicated by arrows in FIG.  21  in the resistor layer  44 , which is formed on the insulation sheet  41  to cover both of the adjacent auxiliary electrode portions  42 B,  43 B. Accordingly, the resistor layer  44  between the auxiliary electrode portions  42 B,  43 B generates heat. The resistor layer  44  and the auxiliary electrode portions  42 B,  43 B both have good heat conductance, the temperature of wide areas on the surfaces increases. 
     The heat generated by the resistor layer  44  is transferred to the first coating portion  28 , which contacts and covers the heating element  40 . The heat transfer uniformly increases the temperature of the first coating portion  28  at any part that contacts the heating element  40 , so that the temperature is quickly increased to an adequate level for being gripped by the driver. 
     The rim metal core  19  has good heat conductivity. Thus, if the covering member  30  contacts and covers the rim metal core  19 , the heat generated by the heat generating member (the resistor layer  44 ) of the heating element  40  is likely to be transferred to the rim metal core  19  through the covering member  30 . If heat is transferred to the rim metal core  19 , the amount of heat transferred to the first coating portion  28  is reduced, accordingly. 
     However, in the present embodiment, the hollow portion  35  between the covering member  30  and the rim-side coupling portion  19 A and the spoke-side coupling portion  22 A functions as a heat-insulating layer. The hollow portion  35  prevents the heat generated by the heat generating member (the resistor layer  44 ) of the heating element  40  from being transferred to the rim metal core  19  through the covering member  30 . As a result, a greater amount of heat generated by the heat generating member (the resistor layer  44 ) of the heating element  40  is transferred to the first coating portion  28 . 
     As shown in  FIG. 17 , the outer surface  28   o  of the first coating portion  28 , which contacts and coats the heating element  40 , forms a part of the ornamental surface of the rim  14 , or in other words, the ornamental surface of the steering wheel  13 . If the shape of the outer surface  410  of the heating element  40  (see  FIG. 21 ) stand out on the ornamental surface, the external appearance is degraded. However, according to the present embodiment, the first coating portion  28  is formed into a desired shape about the heating element  40  through the Reaction Injection Molding. Therefore, unlike the second prior art, in which the cover  175  is wound about the heating element  174  (see  FIG. 25 ), the shape of the outer surface  410  of the heating element  40  hardly stands out on the outer surface  28   o  of the first coating portion  28 . 
     Further, since the first coating portion  28  is made of foamed polyurethane, which is soft material, and the heating element  40  is a flexible sheet, the shape of the outer surface  410  of the heating element  40  hardly stands out on the outer surface  28   o  of the first coating portion  28 . That is, even if there are conspicuous asperities on the outer surface  410  of the heating element  40 , only the inner surface of the first coating portion  28  is formed in accordance with the shape of the outer surface  410  of the heating element  40 . Thus, the first coating portion  28  absorbs such asperities and prevents the shape of the outer surface  410  from standing out on its outer surface  280 . In the first place, since the outer surface  410  of the insulation sheet  41  of the heating element  40  is smooth (see  FIG. 21 ), asperities due to the heating element  40  are unlikely to be formed on the outer surface  28   o  of the first coating portion  28 . 
     In the steering wheel  170  according to the second prior art, in which the cover  175  is wound about the heating element  174 , which is made by placing the fabric sheet  176  on the heating wires  177  (see  FIG. 26 ), parts of the cover  175  that covers the heating wires  177  are locally heated and contracted. Due to repeated contraction over years, wrinkles will be conspicuous, degrading the external appearance. 
     However, according to the present embodiment, the resistor layer  44  between the adjacent auxiliary electrode portions  42 B and  43 B generates heat as shown in  FIG. 21 . Since the auxiliary electrode portions  42 B,  43 B and the resistor layer  44  both have good heat conductivity, the temperature is increased in large area on the surface. Therefore, the elastic member  1  covering the heating element  40  and the cover  28  are unlikely to be locally heated and contacted. This prevents the external appearance from being degraded. 
     Accordingly, unlike the steering wheel  170  according to the second prior art in which the cover  175  is wound, an elastic member made of, for example, rubber does not need to be placed between the heating element  40  and the first coating portion  28 . 
     The present embodiment described above has the following advantages. 
     (1) The rigid covering member  30  is provided about the rim metal core  19 , and the heating element  40  is arranged along the outer surfaces  31   o ,  32   o  of the covering member  30 . Further, the first coating portion  28  made of soft resin is formed about the heating element  40  and contacts the heating element  40 . The heating element  40  is formed through the Reaction Injection Molding and has an outer surface  28   o , which serves as an ornamental surface ( FIG. 17 ). Accordingly, the external appearance is prevented from degraded by the heating element  40 , and without increasing the number of components. Also, the steering wheel  13  can be assembled from a smaller number of components. This reduces the manufacturing steps required and costs. 
     (2) The heat insulating effect of the hollow portion  35  hinders heat transfer from the heat generating member (the resistor layer  44 ) to the rim metal core  19 . Accordingly, a greater amount of the heat of the heat generating member (the resistor layer  44 ) is transferred to the first coating portion  28 , so that the rim  14  is efficiently heated. 
     (3) Prior to the Reaction Injection Molding of the first coating portion  28 , each support member  25  is placed between the rim-side coupling portion  19 A of the rim metal core  19  and the covering member  30  while closely contacting the outer surface of the rim-side coupling portion  19 A and the inner surfaces  31   i ,  32   i  of the covering member  30 . Therefore, the support members  25  function as sealing members during the Reaction Injection Molding of the soft coating portion  20 , so as to prevent the molding material from entering the covering member  30 . 
     (4) The heating element  40  is formed by laminating the insulation sheet  41 , the pair of electrodes  42 ,  43  formed by the main electrode portions  42 A,  43 A and the auxiliary electrode portions  42 B,  43 B, and the resistor layer  44  ( FIG. 21 ). Therefore, the first coating portion  28  covering the heating element  40  is prevented from being locally heated and contracted. This prevents the external appearance from being degraded. 
     (5) The innermost layer of the heating element  40  is formed by the adhesive layer  45 . Prior to the Reaction Injection Molding of the first coating portion  28 , the heating element  40  is adhered to the outer surfaces  31   o ,  32   o  of the covering member  30  at the adhesive layer  45  ( FIGS. 21 and 22 ). When the steering wheel intermediate  13 A is set in the molding apparatus  50 , the heating element  40  is placed at a predetermined position in the cavity  50 A. Therefore, in the Reaction Injection Molding, additional operation for determining the position of the heating element  40  is not required when setting the steering wheel intermediate  13 A in the molding apparatus  50 . This facilitates the preparation (mainly, setting of the steering wheel intermediate  13 A in the molding apparatus  50 ) performed before the molding material is supplied to the molding apparatus  50 . 
     The present invention may be modified as follows. 
     &lt;Regarding Support Members  25 &gt; 
     In each of the above embodiments, the covering member  30  may be fixed to the rim metal core  19  without using the support members  25 . In such a case, the fixation may be achieved by, for example, fastening with screws. 
     &lt;Regarding Covering Member  30 &gt; 
     In each of the above embodiments, the part of the covering member  30  to which the heating element  40  is adhered may have a shape that gradually changes, instead of a shape that abruptly changes. This modification allows the heating element  40  to be easily flexed along and adhered to the covering member  30 . 
     In each of the above embodiments, it is sufficient if the covering member  30  is provided about at least a part of the rim metal core  19  in the circumferential direction. Thus, the length of the covering member  30  along the rim metal core  19  may be changed to be longer or shorter. 
     In each of the above embodiments, the positions of the covering member  30  and the heating element  40  in the rim  14  may be changed on the condition that the covering member  30  and the heating element  40  are embedded in the rim  14  at parts gripped by an occupant (driver). For example, the heating element  40  may be embedded in a part that is separated away from the coupling portion between the rim  14  and the spoke  16  or from the vicinity of the rim  14  and the spoke  16 . 
     &lt;Regarding Hollow Portion  35 &gt; 
     In each of the above embodiments, the hollow portion  35  may be provided only about the rim-side coupling portion  19 A, which is, among the rim-side coupling portion  19 A and the spoke-side coupling portion  22 A, the one surrounded by the heat generating member (the resistor layer  44 ). 
     &lt;Regarding Heating Element  40 &gt; 
     In each of the above embodiments, the adhesive layers  45 ,  47  on the heating element  40  may be omitted, and the heating element  40  may be attached to the covering member  30  by means of other means such as adhesive agent or screws. The heating element  40  can be attached to the covering member  30  by providing an engaging portion on the covering member  30  and fitting the engaging portion into the peripheral portion of the heating element  40 . 
     &lt;Regarding Elastic Member  61 &gt; 
     In the first embodiment, the elastic member  61  may be omitted if the shape of the heating element  40  does not stand out excessively conspicuously on the cover  62  or when such appearance is not a problem. 
     Other Modification 
     The present invention may be applied not only to the steering wheel of vehicles, but also to steering wheels of the steering device in other transport vehicles such as airplanes and ships. In this case, such vehicles include not only private automobiles, but also various kinds of industrial vehicles. 
     Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalence of the appended claims.