Handgrip with built-in heater having chamfered surface

A handgrip with a built-in heater for a motorcycle constituted by a hollow cylindrical handgrip body, wherein a flexible printed circuit heater is wound around an outer periphery of a synthetic resin inner piece of a substantially hollow cylindrical shape with a hollow cylindrical or peripheral portion slotted, and a cladding rubber layer is integrally molded thereon to cause the heater to extend between the inner piece and the cladding rubber layer. The heater is wound over a range covering a half circumference or more but less than a full circumference of the inner piece. The cladding rubber layer is molded in such a form that a region where the heater is not wound faces parting positions of mold halves for forming the cladding rubber layer so as to prevent the occurrence of turn-ups and creases. In addition, an outer peripheral portion of the inner piece facing the parting positions is chamfered, whereby the thickness of the cladding rubber layer at a chamfered portion is made large to force any crease which occurs to be formed in the chamfered portion of the heater.

BACKGROUND OF THE INVENTION 
The present invention relates to a handgrip with a built-in heater for a 
motorcycle or the like, and more particularly to a handgrip with a 
built-in flexible printed circuit heater (hereafter simply referred to as 
the FPC heater), which is a planar heater. 
Conventionally, it has been known to incorporate a planar heater in the 
handgrips of a handlebar of a motorcycle to heat the handgrips as 
required. 
FIG. 12 is a vertical cross-sectional view illustrating an example of a 
handgrip with a built-in heater of this type (See Japanese Utility Model 
Application Laid-Open No. 60996/1993). Reference numeral 1 denotes a 
handgrip body which can be integrally fitted over and secured to a handle 
pipe 2 as the handle pipe 2 is inserted into the handgrip body 1. The 
handgrip body 1 has a structure in which a soft rubber cladding layer 5 is 
molded integrally over the outer periphery of a synthetic resin inner 
piece 3 which has appropriate rigidity and around which an FPC heater 4 is 
wound. The inner piece 3, which excels in heat insulation, has a 
substantially cylindrical shape in which a peripheral portion 3a is formed 
with slots. The FPC heater 4 extends over the outer periphery of the inner 
piece 3 over a range covering half the circumference or more but less than 
the full circumference thereof, so as to efficiently warm the hand of the 
rider who holds the handgrip. Reference numeral 3b denotes slits formed in 
the inner peripheral surface of the inner piece 3, and a rubber layer 5a 
for making pressure contact with the pipe and formed integrally with the 
soft rubber cladding layer 5 is filled in each slit 3b. 
To mold the handgrip body 1, the FPC heater 4 is first wound around the 
inner piece 3, and a raw rubber sheet 6 is then wound thereon to 
tentatively secure the FPC heater 4. Then, a core 7 is inserted into the 
inner piece 3, and this assembly is placed in a fixed mold half 8a, as 
shown in FIG. 13. Subsequently, a movable mold half 8b is moved toward the 
fixed mold half 8a, and the mold is closed, as shown in FIG. 14. Then, 
once the mold halves 8a and 8b have been heated to a predetermined 
temperature and molten rubber injected into the mold halves 8a and 8b, the 
raw rubber sheet 6 which tentatively secures the FPC heater 4 is melted by 
the heat, and is molded integrally with the rubber in the molten state 
which has flowed into the mold halves 8a and 8b, thereby forming the 
cladding layer 5 and the rubber layer 5a for making pressure contact with 
the pipe. 
However, with the above-described conventional handgrip with a built-in 
heater, in light of the fact that the cladding layer 5 is molded by 
placing the assembly in the mold in a state in which the region indicated 
at reference character A where no portion of the FPC heater is wound faces 
the movable mold half 8b, as shown in FIGS. 13 and 14, during the closing 
of the mold when the movable mold half 8b is engaged with (moved toward) 
the fixed mold half 8a (see FIGS. 13 and 14), the raw rubber sheet 6 at 
positions shown at reference characters B.sub.l and B.sub.2 is brought 
into contact with the vicinities of a parting position of a molding 
surface between the mold halves 8a and 8b, and is pressed downward in 
FIGS. 13 and 14. Consequently, there has been a problem in that corner 
portions at side edges of the FPC heater 4 are turned up, or the FPC 
heater 4 slides downward along the outer peripheral surface of the inner 
piece 3, possibly causing a crease in a central portion of the FPC heater 
in its winding direction, as shown at reference numeral 4b. 
FIG. 15 is a development of the FPC heater for showing turned-up portions 
4a and the creases 4b occurring during the molding of the cladding layer 
5. The turned-up portions 4a and the creases 4b not only constitute direct 
causes of damage to the FPC heater 4, but also degrade the external 
appearance of the product if they project outside the cladding layer 5. 
Hence, it is desirable to ensure that the turned-up portions 4a and the 
creases 4b do not occur. 
SUMMARY OF THE INVENTION 
The present invention has been made in view of the above-described problems 
of the conventional art, and an object thereof is to provide a handgrip 
with a built-in heater for a motorcycle in which the FPC heater extends 
positively along the outer peripheral surface of the inner piece. 
To attain the above-described object, in accordance with the present 
invention, there is provided a handgrip with a built-in heater for a 
motorcycle constituted by a hollow cylindrical handgrip body in which a 
flexible printed circuit heater is wound around the outer periphery of a 
synthetic resin inner piece of a substantially hollow cylindrical shape 
with a hollow cylindrical or peripheral portion having an opening, and a 
cladding rubber layer is integrally molded thereon to cause the flexible 
printed circuit heater to extend between the inner piece and the cladding 
rubber layer, wherein the flexible printed circuit heater is wound over a 
range covering half the circumference or more but less than the full 
circumference thereof, and wherein the cladding rubber layer is molded in 
such a form that a region where the flexible printed circuit heater is not 
wound faces a parting position of a mold for forming the cladding rubber 
layer. 
Moreover, the outer peripheral surface of the inner piece facing the 
parting position of the mold for forming the cladding rubber layer in a 
region where the flexible printed circuit heater is wound is chamfered, 
and the thickness of the cladding rubber layer at a chamfered portion of 
the inner piece is made greater than the thickness of the cladding rubber 
layer at other portions. 
Further, the flexural rigidity of the flexible printed circuit heater in a 
region corresponding to a chamfered region of the inner piece is made 
smaller than the flexural rigidity in other regions. 
Since the FPC heater is wound over a range covering half the circumference 
or more but less than the full circumference thereof, when the mold is 
closed (when the movable mold half moves toward the fixed mold half), the 
raw rubber sheet which tentatively secures the FPC heater is pressed in 
the mold-closing direction upon being brought into contact with the mold. 
However, since the region where the FPC heater is not wound faces the 
parting position of the mold, forces acting on the FPC heater from the raw 
rubber sheet act in the direction in which the side edges of the FPC 
heater are pressed against the inner piece (in the direction in which the 
FPC heater is wound), so that there is no likelihood of corner portions of 
the side edges of the FPC heater becoming turned up. In addition, during 
the closing of the mold, substantially laterally symmetrical portions of 
the raw rubber sheet (see reference characters C.sub.1, C.sub.2 in FIG. 
8), located close to the movable mold half in the vicinity of the parting 
position of the mold, i.e., the abutment plane of the mold halves, are 
pressed in the mold-closing direction substantially simultaneously. 
However, since the forces acting on the FPC heater offset each other 
(FC.sub.1 =FC.sub.2), the FPC heater is not shifted along the inner piece, 
and hence no crease is formed in the FPC heater. 
In addition, should the FPC heater slide along the outer peripheral surface 
of the inner piece as the raw rubber sheet comes into contact with the 
mold, since the forces acting on the FPC heater offset each other as 
described above, the force which tends to slide the FPC heater is very 
small (the amount of sliding of the FPC heater along the inner piece is 
small). Accordingly, even if a crease occurs in the FPC heater, the size 
(height) of the crease is very small as compared with a crease occurring 
in the conventional handgrip with a built-in heater. 
Since the outer peripheral surface of the inner piece facing the 
mold-parting position in the region where the FPC heater is wound is 
chamfered, the FPC heater is liable to be lifted up in this chamfered 
portion. That is, in the case where a crease is formed in the FPC heater, 
the crease appears in the chamfered portion of the inner piece facing the 
mold-parting position. However, since the thickness of the cladding rubber 
layer at the position where the crease is likely to occur is made greater 
than the thickness of the cladding rubber layer in other regions, the 
possibility of the crease projecting outside the cladding rubber layer is 
small. 
Moreover, since the flexural rigidity of a portion of the FPC heater 
corresponding to the chamfered region of the inner piece is smaller than 
at other regions, in case a crease does occur in the inner piece, the 
crease will always occur at the chamfered region of the inner piece where 
the thickness of the cladding rubber layer is large.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings, a description will be provided of preferred 
embodiments of the present invention. 
FIG. 1 is a perspective view illustrating an embodiment of a handgrip with 
a built-in heater for a motorcycle. FIG. 2 is a vertical cross-sectional 
view of a handgrip body, which is an essential portion of the handgrip. 
FIGS. 3 to 5 are horizontal cross-sectional views of the handgrip body 
(cross-sectional views taken along lines III--III, IV--IV, and V--V shown 
in FIG. 2). FIG. 6 is an enlarged perspective view of an inner piece. FIG. 
7 is a diagram illustrating a flexible printed circuit heater prior to 
winding around the inner piece, as well as the electric circuit thereof. 
FIGS. 8 and 9 are explanatory diagrams illustrating the manner in which 
the handgrip body is molded. FIG. 10 is an explanatory diagram 
illustrating the slackening of the FPC heater at the position of a 
chamfered flat surface. 
In these drawings, reference numeral 10 denotes a handgrip body of a hollow 
cylindrical type whose surface is clad with rubber. This handgrip body 10 
is exteriorly fitted and secured to a handle pipe or throttle pipe of a 
motorcycle. The handgrip body 10 is structured such that a flexible 
printed circuit heater (hereafter referred to as the FPC heater) 20 is 
wound on the outer side of a synthetic resin inner piece 12 of a hollow 
cylindrical shape, and a cladding rubber layer 16 is integrally molded 
thereon to cause the FPC heater 20 to extend between the inner piece 12 
and the cladding rubber layer 16. 
A belt-shaped rubber layer 14 (including rubber layer portions 14a 
extending circumferentially and rubber layer portions 14b extending 
axially) for making pressure contact with the pipe, which is coupled 
integrally to the cladding rubber layer 16 and extends circumferentially 
and axially, is formed on the inner peripheral surface of the inner piece 
12. This rubber layer 14 is filled in grooves 13 (grooves 13a extending 
circumferentially and grooves 13b extending axially) which communicate 
with notches 15 (15a, 15b) provided in a side wall of the inner piece 12. 
The rubber layer 14, which is formed flush with the inner peripheral 
surface of the inner piece 12, serves to increase the adhesive strength 
between the handgrip body 10 and the handle pipe (or throttle pipe) by 
being brought into pressure contact with the handle pipe inserted in the 
inner piece 12. 
The rubber layer 14 may be formed to a height at which the rubber layer 14 
projects slightly inward from the inner peripheral surface of the inner 
piece 12. In this case, a small air layer is formed between the inner 
peripheral surface of the inner piece and the handle pipe (or throttle 
pipe). In this case, the structure is such that heat on the handgrip body 
10 side can be prevented form escaping to the handle pipe (or throttle 
pipe) side. 
In addition, the rubber layer 14 is filled in the grooves 13 with an 
adhesive agent applied thereto, and is firmly bonded and secured to the 
grooves 13. Therefore, when the handle pipe or the throttle pipe is 
inserted into the handgrip body 10, there is no danger of the rubber layer 
14 being torn by the inserting end of the handle pipe (throttle pipe). 
Since the inner piece 12 has a hollow cylindrical shape, it is very 
difficult to form the grooves 13 for receiving the rubber layer on the 
inner peripheral surface of the inner piece. In this embodiment, however, 
the inner piece 12 has a structure whereby it is split into two parts in 
the circumferential direction (split into an upper split piece 12a and a 
lower split piece 12b). Hence, it is easy to form the grooves 13 (13a, 
13b) for forming the rubber layer on the respective inner peripheral 
surfaces of the split pieces 12a and 12b each having a semicircular cross 
section. Namely, it is easy to mold the split pieces 12a and 12b of the 
synthetic resin-made inner piece by injection molding or press molding 
using a mold provided with protrusions for forming the grooves 13 on its 
molding surface, or to form the grooves 13 on the inner peripheral surface 
of the split pieces of the synthetic resin-made inner piece by cutting. 
The notches 15 (15a, 15b) are respectively formed in left- and right-hand 
side edges of the lower split piece 12b, which is a constituent member of 
the inner piece. As the lower split piece 12b and the upper split piece 
12a are engaged with each other to form the inner piece 12 of the hollow 
cylindrical type, the notches 15a form openings H which are communicating 
holes for allowing the outer side and the inner side of the inner piece 12 
to communicate with each other during the molding of the rubber layer. 
That is, the cladding rubber layer 16 and the rubber layer 14 for making 
pressure contact with the pipe are integrally coupled to each other by a 
rubber layer 50 filled in the openings H. Consequently, since offset 
between the cladding rubber layer 16 and the inner piece 12 can be 
reliably suppressed, there is no drawback in that the FPC heater 20, the 
cladding rubber layer 16, and the rubber layer 14 for making pressure 
contact with the pipe are peeled off the inner piece 12, thereby ensuring 
a structural strength sufficient to withstand extended periods of use. 
In addition, although the inner piece 12 is formed into a hollow 
cylindrical shape, the structure provided is such that chamfered flat 
surfaces 12c (12c.sub.1, 12c.sub.2) are formed at portions of the inner 
piece 12 along the split position of the outer peripheral surface thereof 
(in regions along the joining portions of the split pieces 12a, 12b), and 
that the FPC heater 20 extends over the entire peripheral region of the 
inner piece excluding one flat surface 12c.sub.2 of the opposing left- and 
right-hand flat surfaces 12c.sub.1 and 12c.sub.2, so as to warm the entire 
handgrip body 10. 
In addition, the present inventors took note of the fact that in a case 
where a flat surface 42 is formed on an arcuate surface 40 by partially 
chamfering the arcuate surface 40, as shown in FIG. 10, if the FPC heater 
20 wound around the arcuate surface 40 slackens, the FPC heater 20 is 
liable to become separated at the position of the flat surface 42, as 
shown by phantom lines (i.e., the FPC heater 20 slackens and a crease is 
liable to be formed in the FPC heater 20). However, in accordance with the 
invention, control is provided to cause the crease always to be formed 
only at the position of this flat surface 12c.sub.1, and the thickness of 
the cladding rubber layer 16 at the position of the flat surface 12c.sub.1 
is set to a thickness sufficient to conceal the crease, as will be 
described in detail later. 
In addition, the FPC heater 20 extending between the cladding rubber layer 
16 and the inner piece 12 has a cross-sectional structure in which a 
copper foil strip pattern 30 is sandwiched between a base film and an 
overlay film. If the FPC heater 20 is unrolled, it is substantially 
square, as shown in FIG. 7. A lead portion 21 for connection to a power 
supply and which is led outside the handgrip is formed at one side edge of 
the FPC heater 20, as shown in FIGS. 2, 3, and 7. Formed on this lead 
portion 21 are two lands R.sub.1 and R.sub.2 where copper foils, connected 
to copper foil strips 32 arranged in a meandering manner and serving as a 
heat source, are exposed. Two terminals 27 of a male connector 26 (see 
FIGS. 2 and 3) abut the respective lands R1 and R2, while a female 
connector 29, provided at a distal end of a power cord 28 extending from a 
battery, i.e., the power supply, is connected to the terminals 27. 
The male connector 26 engages the upper split piece 12a of the inner piece 
12, and is molded integrally with the handgrip body 10 by means of the 
cladding rubber layer 16 covering the inner piece 12. When the cladding 
rubber layer 16 is molded on the outer side of the inner piece 12, the 
male connector 26 is also formed integrally with the inner piece 12. 
Reference numeral 38 denotes circular holes provided at regular pitches in 
the FPC heater 20 at positions where a reinforcing copper foil strip 34 is 
formed. Exfoliation of the FPC heater 20 is prevented since the cladding 
rubber layer 16 on the FPC heater 20 is made to adhere directly to the 
inner piece 12 in the circular holes 38. 
In addition, the meandering copper foil strips 32 which constitute the heat 
source in the copper foil strip pattern 30 extend in the Y-direction, 
corresponding to the circumferential direction (the direction in which the 
FPC heater is wound) of the handgrip body perpendicular to the 
X-direction. This arrangement enhances the flexural rigidity of the copper 
foil strips 32 with respect to external forces acting in the 
circumferential direction of the handgrip body. Thus, in the process of 
molding the cladding rubber layer 16, a crease is unlikely to occur in the 
copper foil strips 32, which perform the heat-generating action of the FPC 
heater 20. 
Around the copper foil strips 32, the reinforcing copper foil strip 34 
extends along the outer edges of the FPC heater 20, and the reinforcing 
copper foil strip 34 (indicated by oblique lines in FIG. 7) has portions 
extending in the Y-direction in the region where the copper foil pattern 
32 is formed. As a result, the flexural rigidity of the FPC heater 20 is 
enhanced, thereby providing a structure in which the FPC heater 20 is 
unlikely to be deformed. 
In addition, elongated holes 22, which are aligned with the openings H in 
the inner piece 12, are formed in a central portion, as viewed in the 
Y-direction, of the FPC heater 20. The FPC heater 20 is wound around and 
held on the inner piece 12 in a state in which the elongated holes 22 are 
aligned with the openings H, and the structure is such that in a case 
where a crease is formed in the FPC heater 20, the crease is concentrated 
in a position P.sub.1 where the elongated holes 22 are formed. That is, 
the modulus of section at the position P.sub.1 where the elongated holes 
are formed in the FPC heater 20 is smaller than the modulus of section at 
other positions parallel with the X-direction since the elongated holes 22 
are provided. Accordingly, in the case where an external force sufficient 
to produce a crease in the FPC heater 20 occurs, a crease is produced only 
at the position P.sub.1 where the elongated holes are formed. 
Since the outer configuration of the cladding rubber layer 16 is circular, 
the thickness of the cladding rubber layer 16 at the positions of the 
chamfered flat surfaces 12c (12c.sub.1, 12c.sub.2) of the inner piece 12 
is greater than the thickness of the cladding rubber layer 16 at other 
portions (nonchamfered portions) of the outer peripheral surface of the 
inner piece. The position P.sub.1 where the elongated holes 22 are formed 
in the FPC heater 20 (the portion where a crease is liable to occur due to 
the small flexural rigidity in the FPC heater 20) is located at the 
position of this flat surface 12c.sub.2. Hence, in the case where a crease 
is formed in the FPC heater 20, the crease occurs at the position of the 
flat surface 12c.sub.1 where the thickness of the cladding rubber layer 16 
is sufficiently large. Therefore, even if a crease is fairly large (having 
a large height), the crease is concealed in the cladding rubber layer 16, 
so that the crease is not exposed outside the cladding rubber layer 16. 
Furthermore, a copper foil strip 36 for reinforcing peripheral edge 
portions of the elongated holes 22 is provided, extending in the same 
direction as the elongated holes 22. Also, a belt-shaped region 37 where 
no copper foil is present is provided in parallel with the copper foil 
strip 36 so as to guide any crease occurring in the FPC heater 20 to the 
position where the elongated holes are formed. Namely, since the 
belt-shaped region 37 where no copper foil is formed and which extends in 
the direction of the elongated holes 22 is provided in the transverse 
central portion of the copper foil strip 36, the flexural rigidity at a 
position along the region 37 where no copper foil is formed at the 
position where the elongated holes 22 are formed is minimized. Hence, in a 
case where a crease 20b (see FIG. 9) occurs in the FPC heater 20, the 
crease will always be formed at the position P.sub.1 along the elongated 
holes. The thickness t.sub.1 (see FIGS. 4 and 5) of the cladding rubber 
layer 16 at this position P.sub.1 is the largest in the thickness of the 
cladding rubber layer 16 corresponding to the flat surface 12c.sub.1, with 
the result that the crease is guided to the thickest portion of the 
cladding rubber layer 16, thereby making it possible to conceal the crease 
20b. 
In addition, to mold the cladding rubber layer 16 on the outer side of the 
inner piece 12 and the rubber layer for making pressure contact with the 
pipe on the inner side thereof, the cladding rubber layer 16 is molded 
such that the region where the FPC heater is not wound faces the 
mold-parting position, as shown in FIGS. 8 and 9. Consequently, a crease 
is unlikely to occur in the FPC heater 20 which extends along the inner 
piece 12. Namely, the FPC heater 20 is first wound around the inner piece 
12 in which the upper and lower split pieces 12a and 12b are integrally 
engaged with each other, and a raw rubber sheet 19 is wound therearound 
before the FPC heater 20 is tentatively secured. Then, a core 17 is 
inserted into the inner piece 12, and this assembly is placed in a fixed 
mold half 18a. 
As for the raw rubber sheet 19 used for tentatively securing the FPC heater 
20, if a rubber-layer forming material (the raw rubber sheet 19) is 
accommodated in advance in the mold halves 18a and 18b, it is effective in 
forming the cladding rubber layer 16 and the pipe pressure-contacting 
rubber layer 14 with sufficient thicknesses to compensate for a shortage 
of molten rubber cast into the mold. Then, the movable mold half 18b is 
engaged with the fixed mold half 18a, and the mold is closed. During the 
closing of the mold, as shown in FIG. 8, portions of the raw rubber sheet 
19 indicated by reference characters C.sub.1 and C.sub.2 are pressed by 
the movable mold half 19, so that a pair of external forces, indicated by 
reference characters FC.sub.1 and FC.sub.2 in FIG. 8, act on the FPC 
heater 20. However, these two external forces FC.sub.1 and FC.sub.2 acting 
on the FPC heater 20 are oriented in mutually opposite directions so that 
they offset each other. For this reason, the FPC heater 20 does not slide 
along the inner piece 12, thereby preventing a crease from occurring in 
the FPC heater 20. Additionally, this external force FC.sub.2 acts in a 
direction opposite to the direction in which a side edge 20a of the FPC 
heater 20 is turned up, i.e., in the direction in which the side edge 20a 
is pressed along the surface of the inner piece 12 (in the direction in 
which the FPC heater is wound). Hence, the side edge 20a is held in close 
contact with the outer surface of the inner piece 12. Hence, a drawback 
does not occur in that a corner portion of the side edge 20a is turned up 
in a conventional manner. 
Upon completion of the closing of the mold, molten rubber is injected into 
the mold halves 18a and 18b through a gate (not shown) provided in the 
mold. The rubber in a molten state, which is supplied between the molding 
surface of the mold and the outer peripheral surface of the inner piece 
12, passes through the openings H provided in the side wall of the inner 
piece 12, and flows smoothly into all portions of the grooves 13 (13a, 
13b) on the inner side of the inner piece 12. Hence, since the mold 
temperature is sufficiently transmitted to the rubber filled in the 
grooves 13, the rubber layer 14 for making pressure contact with the pipe 
has no possibility of being insufficiently heated. Then, after the rubber 
is allowed to cool and set for a predetermined period of time, the mold is 
opened, thus obtaining a handgrip body 10 in which the cladding rubber 
layer 16 is integrally molded on the outer side of the inner piece 12, and 
the rubber layer 14 for making pressure contact with the pipe is 
integrally formed on the inner side thereof. 
Although, in the above-described embodiment, the hollow cylindrical inner 
piece 12 is split into two portions as viewed in the circumferential 
direction, the inner piece may be a single hollow cylindrical type which 
is not split, or a substantially hollow cylindrical type having a C-shaped 
cross section in which a part 50 of a peripheral portion is slotted, as 
shown in FIG. 11. 
Reference character H.sub.1 in FIG. 11 denotes an opening formed in the 
side wall (a position corresponding to the position where the slot 50 is 
formed) of the inner piece 12. 
Although the chamfered portions (flat surfaces) 12c (12c.sub.1, 12c.sub.2) 
of the inner piece 12 are provided as a pair in the side surfaces of the 
inner piece 12 in face-to-face relation to each other, it suffices if the 
chamfered portion (flat surface) 12c is provided at least on the side 
where the FPC heater 20 is wound, and it need not be provided on the side 
of the region where the FPC heater 20 is not wound. Namely, the flat 
surface 12c.sub.2 on the side where the FPC heater is not wound may be 
omitted. 
In addition, although in the above-described embodiments the FPC heater 20 
is wound around a region covering substantially one circumference of the 
inner piece 12 excluding the flat surface 12c.sub.2, it suffices if the 
FPC heater 20 is wound around the inner piece 12 in a range covering half 
the circumference or more but less than the entire circumference thereof. 
As is apparent from the foregoing description, according to the handgrip 
with a built-in heater for a motorcycle of the present invention, when the 
mold is closed in the process of molding the handgrip body, the raw rubber 
sheet which tentatively secures the FPC heater is pressed in the 
mold-closing direction by being brought into contact with the mold. 
However, since the mold is closed in a state in which the region where the 
FPC heater is not wound faces the mold-parting position, these pressing 
forces cause the side edges of the FPC heater to be pressed in the 
direction in which the FPC heater is wound, and since these pressing 
forces offset each other, the FPC heater does not slide along the outer 
peripheral surface of the inner piece during the closing of the mold. 
Hence, the cladding rubber layer is formed in a state in which the FPC 
heater is positively held in close contact with the inner piece. 
Consequently, it is possible to obtain a handgrip with a built-in heater 
in which turning-up or creasing does not occur in the FPC heater. 
In addition, in a case where a crease does occur in the FPC heater, the 
crease occurs in the FPC heater at a chamfered portion of an outer 
peripheral surface of the inner piece where the thickness of the cladding 
rubber layer is particularly large. However, since the crease is concealed 
by the cladding rubber layer, the appearance of the handgrip body is not 
disturbed. 
Yet further, since the flexural rigidity of the portion of the FPC heater 
corresponding to the chamfered portion of the outer peripheral portion of 
the inner piece is made particularly small, in a case where a crease 
occurs in the FPC heater, the crease unfailingly occurs at the chamfered 
portion of the outer peripheral surface of the inner piece where the 
thickness of the cladding rubber layer is large. Since the crease is 
positively concealed by the cladding rubber layer, the appearance of the 
handgrip body is further improved.