Title of Invention

THROTTLE VALVE APPARATUS FOR INTERNAL COMBUSTION ENGINE

Abstract

A throttle valve apparatus for an internal combustion engine is disclosed, in which a metal member for reinforcing a resin molded portion (6) of a throttle shaft (4) is divided into two parts including a metal shaft portion (7) and a metal pipe portion (8), which are set in the same resin molding die for integral molding to fabricate the throttle shaft (4). In the process, the molten resin is supplied from a cylindrical gap formed between the outer peripheral surface of a small-diameter portion (54) of the metal shaft portion (7) and the inner peripheral surface of the metal pipe portion (8). The cylindrical gap can be used as a cylindrical film gate and, therefore, the weld is prevented from being generated in a valve fixing resin portion (31) thereby to prevent both a deterioration in appearance and a reducation in strenqth.

Full Text

THROTTLE VALVE APPARATUS FOR INTERNAL COMBUSTION ENGINE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a throttle valve apparatus, for an internal combustion engine, to control the engine torque or the engine speed by changing the intake air amount of the internal combustion engine in accordance with the accelerator pedal angle or, in particular, to a throttle valve apparatus for the internal combustion engine comprising, in an integrally resin molded form, a throttle shaft, a valve fixing resin portion for fixing the throttle valve, a resin lever portion for transmitting the accelerator pedal angle set by the driver to the valve fixing resin portion and a resin shaft portion for connecting the valve fixing resin portion and the resin lever portion. The invention also relates to a throttle valve apparatus, for an internal combustion engine, wherein the resin shaft portion of the throttle shaft and the resin cylindrical portion of the throttle valve are fixed by thermal welding. 2. Description of the Related Art A conventional throttle valve apparatus for the internal combustion engine has been proposed and comprises a metal pipe 107, for reinforcing a valve fixing resin portion 104 and as shown in Figs. 7 and 8A to 8C, for the purpose of securing a sufficient strength without changing the outer diameter of an acceleration lever-integrated shaft (throttle shaft) 10 6 having the valve fixing resin portion 104 for fixing a throttle valve 103 accommodated openably in a cylindrical bore wall portion 102 of a throttle body 101 and an acceleration resin lever portion 105 for rotationally driving the throttle valve 103. The metal pipe 107, as shown in Figs. 7 and 8A to 8C, is arranged in such a manner that bearing slide portions 113, 114 supported rotatably on the inner periphery of cylindrical bearing portions 111, 112 arranged in opposed relation to each other in the direction substantially perpendicular to the direction of intake air flow in the bore wall portion 102 are exposed to the outer peripheral surface of the throttle shaft 106 more than to the valve fixing resin portion 104 on both sides in axial direction. Also, a resin shaft portion 108 for connecting the valve fixing resin portion 104 and the resin acceleration lever portion 105 is arranged on the inner periphery of the metal pipe 107. The axial ends of the resin shaft portion 108 are filled in the openings formed at the two axial ends of the metal pipe 107 in such a manner as to be exposed outside. The metal pipe 107 is formed with a plurality of round holes 115 to 117 to cause the molten thermoplastic resin (molten resin) to circumvent to the valve fixing resin portion 104 and the resin acceleration lever 105 from the internal space formed in the resin shaft portion 108. In the conventional throttle valve apparatus for the internal combustion engine, the metal pipe 107 in the shape shown in Fig. 8C is inserted into a resin molding die and the molten resin is injected into the internal space of the metal pipe 107 from the direction of arrow A in Fig. 8A. In this way, the molten resin is filled up in the space formed by the resin shaft portion 108, The molten resin, after being filled up in the internal space, flows to the outer periphery from the internal space by way of the plurality of the round holes 115 to 117 formed in the metal pipe 107. In this way, the molten resin is filled up in the space formed by the valve fixing resin portion 104 and the resin acceleration lever portion 105. After that, the resin molded product is removed from the resin molding die and cooled into solid state at normal temperature. In this way, the valve fixing resin portion 104, the resin acceleration lever portion 105 and the resin shaft portion 108 are integrally formed of resin. In the case where the valve fixing resin portion 104 and the resin acceleration lever portion 105 are formed in such a manner that the molten resin is recovered through the round holes 115 to 117 formed in -the metal pipe 107, however, a weld is generated in the valve fixing resin portion 104 and the resin acceleration lever 105. As a result, in the case where the valve fixing resin portion 104 and the resin acceleration lever 105 are subjected to heating and cooling cycles, the weld is liable to crack thereby often deteriorating the dimensional accuracy of the throttle shaft 106. Another conventional throttle valve apparatus for the internal combustion engine has been proposed, comprising a resin throttle body having a cylindrical bore wall portion forming an intake path for sending the intake air into the internal combustion engine, a throttle shaft having first and second metal bearing slide portions at the two ends thereof slidably supported on the first and second bearing supporting portions of the throttle body and a valve fixing resin portion between the first and second metal bearing sliding portions, and a throttle valve having a cylindrical resin portion fixed on the outer periphery of the valve fixing resin portion of the throttle shaft. In this throttle valve apparatus, the resin cylindrical portion of the throttle valve is fitted on the outer periphery of the valve fixing resin portion of the throttle shaft, after which the fitting portion between the valve fixing resin portion and the cylindrical resin portion is fixed by laser welding. Generally, the welding strength for thermally welding the fitting portion between the valve fixing resin portion and the cylindrical resin portion using the laser welding is larger, the narrower the welding space (welding gap) between the valve fixing resin portion and the cylindrical resin portion. In terms of the welding strength alone, therefore, the valve fixing resin portion and the cylindrical resin portion are fitted with each other, preferably with a welding space smaller than a predetermined value, as in the case where the fitting welding portion is press-fitted over the entire axial length. Taking the assembly of the throttle valve on the throttle shaft into consideration, however, the cylindrical resin portion of the throttle valve is required to be fixed on the valve fixing resin portion while aligning the axis of the fitting hole of the cylindrical resin portion with the axis of the shaft through hole of the cylindrical bore wall portion of the throttle body. As a result, a structure is desired in which the throttle valve can be fixedly assembled while allowing freedom in the direction perpendicular to the bore axis (radial direction) of the throttle shaft. SUMMARY OF THE INVENTION An object of this invention is to provide a throttle valve apparatus for the internal combustion engine in which a weld is not easily developed in the valve fixing resin portion, the resin is not easily cracked by heating and cooling cycles of the valve fixing resin portion and the rotational driving resin portion, and the dimensional accuracy of the throttle shaft is easily secured. Another object of the invention is to provide a throttle valve apparatus for the internal combustion engine, wherein the welding strength is secured in thermally welding the shaft portion of the throttle shaft and the cylindrical portion of the throttle valve while at the same time improving the mount ability of the cylindrical portion of the throttle valve on the throttle shaft. Still another object of the invention is to provide a throttle valve apparatus of the internal combustion engine in which the structure of the fitting portion between the shaft portion of the throttle shaft and the cylindrical portion of the throttle valve, i.e. the structure of the fitting welding portion is optimized. According to a first aspect of the invention, there is provided a throttle valve apparatus for an internal combustion engine, comprising a valve fixing resin portion for fixing a throttle valve on a throttle shaft rotationally driven in accordance with the accelerator pedal angle set by the driver, a rotational drive resin portion for transmitting the accelerator pedal angle to the throttle valve through the valve fixing resin portion, and a divided-type metal member for reinforcing the valve fixing resin portion and the rotational drive resin portion, which metal member is divided into a member arranged at about the axial center and a member arranged on the outer peripheral portion of the shaft, wherein the valve fixing resin portion hardly develops a weld and the resin of the valve fixing resin portion and the rotational drive resin portion is not easily cracked in heating and cooling cycles, thereby easily securing the dimensional accuracy of the throttle shaft. According to a second aspect of the invention, there is provided a throttle valve apparatus for an internal combustion engine, wherein the divided-type metal member includes two members, i.e. an axial rod-like metal shaft portion and a tubular metal pipe portion, and the metal pipe portion is arranged only on the surface of the throttle shaft between the valve fixing resin portion and the rotational drive resin portion. As a result, the molten resin is supplied from the cylindrical gap formed between the axial rod-like metal shaft portion and the tubular metal portion, so that the valve fixing resin portion can be formed on the outer periphery of the metal shaft portion while suppressing the generation of a weld or a resin cracking. Also, the rotational drive resin portion can be formed on the outer periphery of the metal shaft portion while suppressing the generation of weld or resin cracks. According to third and fourth aspects of the invention; there is provided a throttle valve apparatus for an internal combustion engine, wherein a cylindrical resin shaft portion connecting the valve fixing resin portion and the rotational drive resin portion is interposed in the cylindrical gap formed between the axial rod-like metal shaft portion and the tubular pipe portion, and wherein the molten resin is supplied into the cylindrical gap from one direction thereby to integrally resin-mold the valve fixing resin portion, the rotational drive resin portion and the resin shaft portion. According to a fifth aspect of the invention, there is provided a throttle valve apparatus for an internal combustion engine, further comprising a divided-type metal member, i.e. an axial rod-like metal shaft portion extending axially of the throttle valve, wherein the diametrical size of the throttle valve is not increased even by the provision of a cylindrical fitted portion fitted on the outer periphery of the valve fixing resin portion at the rotational center of the throttle valve and a peripheral position determining portion on the valve fixing resin portion for stopping the rotation of the fitted portion in the peripheral direction of the throttle valve. According to a sixth aspect of the invention, there is provided a throttle valve apparatus for an internal combustion engine, wherein an exposed portion of the metal shaft portion constitutes a first bearing slide portion rotatably supported on the inner periphery of a first bearing support portion of the throttle body, and an exposed portion of the metal pipe portion constitutes a second bearing support portion rotatably supported on the inner periphery of the second bearing support portion of the throttle body, thereby leading to a structure advantageously resistant to wear and requiring no bearing member to reduce the number of parts and assembly steps as well as the production cost. According to a seventh aspect of the invention, there is provided a throttle valve apparatus for an internal combustion engine, wherein a coating material is applied on the outer peripheral portion of the throttle valve or the inner wall surface of the throttle body in such a manner as to fill the gap formed between the outer peripheral portion of the throttle valve and the inner wall surface of the throttle body, thereby reducing the air leakage in idling mode, and wherein a trap gap for trapping the coating material is formed between the inner periphery of the first bearing support portion or the second bearing support portion and the first bearing slide portion or the second bearing slide portion, thereby preventing the coating material from intruding into the gap between the inner periphery of the first bearing support portion and the outer periphery of the first bearing slide portion or between the inner periphery of the second bearing support portion and the outer periphery of the second bearing slide portion• According to an eighth aspect of the invention, there is provided a throttle valve apparatus for an internal combustion engine, wherein the fitting portion between the shaft portion of the throttle shaft and the cylindrical portion of the throttle valve is formed with a press-fitting portion in such a manner that the maximum size of the shaft portion and the minimum size of the fitting hole formed in the cylindrical portion are substantially equal to each other and the welding gap between the shaft portion and the cylindrical portion is as small as not more than a predetermined value, and wherein the fitting portion, except for the press-fitting portion, between the shaft portion of the throttle shaft and the cylindrical portion of the throttle valve is formed with a gap fitting portion in such a manner that the maximum size of the shaft portion is smaller than the minimum size of the fitting hole and the welding gap between the shaft portion and the cylindrical portion is larger than a predetermined value. The provision of the press-fitting portion in a part of the fitting portion between the shaft portion of the throttle shaft and the cylindrical portion of the throttle valve reduces the welding gap between the shaft portion and the cylindrical portion of the press-fitting portion to less than a predetermined value. Thus, welding strength can be secured by thermally welding the shaft portion of the throttle shaft and the cylindrical portion of the throttle valve. Also, the provision of the gap fitting portion in the remaining part of the fitting portion between the shaft portion of the throttle shaft and the cylindrical portion of the throttle valve increases the welding gap between the shaft portion and the cylindrical portion of the gap fitting portion to more than a predetermined value, thereby improving the workability of assembling the cylindrical portion of the throttle valve on the shaft portion of the throttle shaft. According to a ninth aspect of the invention, there is provided a throttle valve apparatus for an internal combustion engine, wherein the press-fitting portion of the fitting portion and the gap fitting portion in the neighborhood of the press-fitting portion, with the inner periphery of the cylindrical portion fitted on the outer periphery of the shaft portion, constitute a fitting welding portion for fixing the outer periphery of the shaft portion and the inner periphery of the cylindrical portion to each other by thermal welding, so that the welding gap of the fitting welding portion is reduced for an improved welding strength. According to a tenth aspect of the invention, there is provided a throttle valve apparatus for an internal combustion engine, wherein the use of the laser welding for thermal welding and the radiation of a laser beam on the outer wall surface of the cylindrical portion from outside radially of the cylindrical portion of the throttle valve, for example, thermally welds the outer periphery of the shaft portion and the inner periphery of the cylindrical portion to each other. As a result, the fitting welding portion of the fitting portion between the resin shaft portion and the cylindrical resin portion is firmly fixed. According to an eleventh aspect of the invention, there is provided a throttle valve apparatus for an internal combustion engine, wherein the maximum size of the welding gap is set to 75 ^im or less to permit laser welding, thereby firmly fixing the fitting welding portion of the fitting portion between the resin shaft portion and the cylindrical resin portion. According to a twelfth aspect of the invention, there is provided a throttle valve apparatus for an internal combustion engine, wherein the cylindrical portion of the throttle valve is formed with a substantially conical tilted cylindrical wall having an outer diameter or an inner diameter progressively increasing toward the end of the cylindrical portion from the press-fitting portion, so that the press-fitting portion and the gap fitting portion can be resin-molded continuously thereby easily securing the dimensional accuracy of the cylindrical portion of the throttle valve. According to a thirteenth aspect of the invention, there is provided a throttle valve apparatus for an internal combustion engine, wherein the press-fitting portion may be arranged at an axial end of the fitting portion. As another alternative, the press-fitting portion may be formed at about the axial center of the fitting portion. In this case, the press-fitting portion can be formed at about the center between the shaft portion of the throttle shaft and the cylindrical portion of the throttle valve subjected to the largest stress by a backfire and the intake pressure. Thus, the maximum strength of the fitting welding portion can be secured at the fitting welding portion of the fitting portion between the resin shaft portion and the cylindrical resin portion. According to a fourteenth aspect of the invention, there is provided a throttle valve apparatus for an internal combustion engine, wherein the exterior of the shaft portion of the throttle shaft and the interior of the fitting hole of the cylindrical portion of the throttle valve are noncircular, so that the cylindrical portion of the throttle valve can be stopped along the peripheral direction of the shaft portion of the throttle shaft. According to a fifteenth aspect of the invention, there is provided a throttle valve apparatus for an internal combustion engine, wherein the exterior of the shaft portion of the throttle shaft and the interior of the fitting hole of the cylindrical portion of the throttle valve are noncircular, and wherein the outer wall surface of the shaft portion is formed with a shaft-side two-transverse-surface portion and the wall surface of the fitting hole is formed with a valve-side two-transverse-surface portion corresponding to the shaft-side two-transverse-surface portion, thereby making it possible for the cylindrical portion to move in a radial direction substantially perpendicular to the axial direction of the shaft portion. The present invention may be more fully understood from the description of preferred embodiments of the invention set forth below, together with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. lA is a front view of a throttle valve apparatus for the internal combustion engine, and Fig. IB a sectional view taken in line A-A in Fig. lA. Fig. 2 is a sectional view of a throttle valve apparatus the internal combustion engine. Fig. 3A is a front view of a throttle shaft and Fig. 3B a side view of the throttle shaft. Fig. 4A is a sectional view taken in line B-B in Fig. 3A, and Fig. 4B a sectional view taken in line C-C in Fig 3A. Fig. 5 is an enlarged sectional view of a first annular gap formed between a first bearing support portion and a first bearing slide portion. Fig. 6 is an enlarged sectional view of a second annular gap formed between a second bearing support portion and a second bearing slide portion. Fig. 7 is a sectional view of the conventional throttle valve apparatus for the internal combustion engine. Fig. 8A is a sectional view of the conventional throttle valve apparatus. Fig. 8B a side view of a throttle shaft, and Fig. 8C a perspective view of a metal pipe. Fig. 9A is a plan view of a fitting portion between the throttle shaft and the throttle valve. Fig. 9B a side view of the fitting portion between the throttle shaft and the throttle valve. Fig. 9C a sectional view taken in line B-B in Fig. 9A, and Fig. 9D a sectional view taken in line C-C in Fig. 9C. Fig. lOA is a plan view of a fitting portion between the throttle shaft and the throttle valve. Fig. lOB a side view of the fitting portion between the throttle shaft and the throttle valve, and Fig. IOC a sectional view taken in line D-D in Fig. lOA. DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the invention is explained below. Figs. lA to 6 show the embodiment of the invention, in which Figs. lA, IB and 2 are diagrams showing a throttle valve apparatus for an internal combustion engine. The throttle valve apparatus for the internal combustion engine according to this embodiment is for controlling the engine speed or the engine torque by changing the amount of the intake air flowing into an internal combustion engine (such as for a two-wheeled vehicle engine, hereinafter sometimes referred to as an engine) based on the angle of the accelerator pedal operated by the driver. This throttle valve apparatus for the internal combustion engine is an intake air throttle valve unit comprising a throttle body 2 having a cylindrical bore wall portion 1 in which the intake air flows toward the engine, a throttle valve 3 accommodated openably in the bore wall portion 1 of the throttle body 2, a throttle shaft 4 driven and integrally rotated with the throttle valve 3 in accordance with the amount of the accelerator pedal operation (such as the accelerator pedal angle) set by the driver, and a return spring 5 for restoring the rotational position of the throttle valve 3 and the throttle shaft 4 to the initial position in engine idle mode. The throttle body 2 is a resin molded product integrally formed of a heat resistant resin (polyphenylene sulfide (PPS), polybutylene terephthalate containing 30 % glass fiber (PBTG30, etc.), and constitutes a device for holding the throttle valve 3 and the throttle shaft 4. An intake air path 10 for sending the intake air into the engine is formed in the bore wall portion 1 of the throttle body 2, and the throttle valve 3 and the throttle shaft 4 are rotatably incorporated in the central portion of the intake air path 10. The intake air path 10 includes an air inlet for sucking the intake air through an intake pipe (not shown) from an air cleaner (not shown) and an air outlet for supplying the intake air to the surge tank or the intake manifold (not shown) of the engine. On the left end surface, in the drawing, of the bore wall portion 1, a cylindrical first bearing support portion 11 for rotatably supporting an axial end of the throttle shaft 4 is integrally formed in such a manner as to project leftward, in the drawing, from the inner wall surface of the bore wall portion 1. The left end, in the drawing, of the first bearing support portion 11 is closed. Also, on the right end surface, in the drawing, of the bore wall portion 1, a cylindrical second bearing support portion 12 for rotatably supporting the other axial end of the throttle shaft 4 is integrally formed in such a manner as to project rightward, in the drawing, from the inner wall surface of the bore wall portion 1. The right end, in the drawing, of the second bearing support portion 12 is closed. The first and second bearing support portions 11, 12 are formed with first and second shaft slide holes 13, 14, respectively, having a circular cross section along which the throttle shaft 4 is adapted to slide. A cylindrical spring inner peripheral guide 15 fitted with the return spring 5 is integrally arranged on the outer periphery of the second bearing support portion 12. An oil seal 16 is mounted between the forward end (right end in the drawing) of the second bearing support portion 12 and the outer periphery of the throttle shaft 4. On the right end surface, in the drawing, of the bore wall portion 1, a body side hook 17 adapted to engage a spring-side hook of the return spring 5 is integrally formed. The throttle valve 3 is a resin molded product integrally formed of a heat resistant resin (polyphenylene sulfide (PPS), polybutylene terephthalate containing 30 % glass fiber (PBTG30), etc. ) , and constitutes a butterfly-shaped rotary valve for controlling the amount of the intake air sucked into the engine. The throttle valve 3 is formed with a substantially cylindrical fitted portion 21 having a through hole (not shown) adapted to be fitted on the outer peripheral portion (surface portion) of the throttle shaft 4, two semicircular tabular portions 22, 23 extended from the fitted portion 21 to close the intake air path 10, etc. The fitted portion 21 is arranged substantially at the center of rotation of the two semicircular tabular portions 22, 23, and fixed on the outer peripheral portion (surface portion) of the throttle shaft 4 by a laser, or the like, thermal welding process. Reference numerals 24, 25 designate reinforcing ribs for reinforcing the throttle valve 3. Next, the structure of the throttle shaft 4 according to this embodiment is explained briefly with reference to Figs. lA to 6. Figs. 3A, 3B, 4A, 4B are diagrams showing the throttle shaft 4. The throttle shaft 4 includes a resin molded portion 6 integrally formed of a heat resistant resin (for example, a resin shaft of such as polyphenylene sulfide (PPS), polybutylene terephthalate containing 30 % glass fiber (PBTG30), etc.), and a divided-type metal member (for example, a metal shaft of stainless steel of SUS304, etc.) insert-molded for reinforcing the resin molded portion 6. The resin molded portion 6 of the throttle shaft 4 is configured of an integral mold of a heat-resistant resin including a valve fixing resin portion 31 for fixing the fitted portion 21 of the throttle valve 3, a resin lever portion (rotary driving resin portion) 32 for transmitting the accelerator pedal operation amount to the throttle valve 3 through the valve fixing resin portion 31, and a resin shaft portion 33 connecting the valve fixing resin portion 31 and the resin lever portion 32. The resin shaft portion 33 is formed as a cylinder to connect the inner periphery of the valve fixing resin portion 31 and the inner periphery of the resin lever portion 32. The valve fixing resin portion 31 is formed as a cylinder on the left side, in the drawing, of the resin shaft portion 33. The outer peripheral surface of the valve fixing resin portion 31 is formed with two flat surfaces (two transverse surfaces or peripheral direction determining portion) for stopping the rotation of the fitted portion 21 of the throttle valve 3 in the peripheral direction of the throttle shaft 4, as shown in Figs. 3A and 4B. The inner peripheral surface of the fitted portion 21 of the throttle valve 3 is formed with two flat surfaces (two transverse surfaces, not shown) corresponding to the two flat surfaces 34. The resin lever portion 32 is formed as an annular plate on the right side, in the drawing, of the resin shaft portion 33. The resin lever portion 32 is formed with a cylindrical portion 35 on the outer periphery of the right end, in the drawing, of the metal member, and an annular portion 36 extending diametrically from the outer periphery of the cylindrical portion 35. The outer periphery of the annular portion 36 is formed with substantially V-shaped peripheral grooves 37 wound with a valve open/close wire cable (not shown) operatively interlocked with the accelerator pedal operated by the driver. Also, the outer periphery of the annular portion 36 is formed with valve open/close cable mounting grooves 38, 39 for mounting each end of the valve open/close wire cable, respectively. On the left end surface, in the drawing, of the resin lever portion 32, a cylindrical inner peripheral guide 41 having substantially the same outer diameter as the spring inner peripheral guide 15 of the throttle body 2 and fitted with a return spring is integrally formed. On the left end surface, in the drawing, of the annular portion 36, on the other hand, a lever-side hook 42 for engaging the spring-side hook of the return spring 5 is formed integrally. The resin lever portion 32 has a plurality of grooves 43 for equalizing the thickness. A reinforcing rib 44 is arranged between each two adjoining grooves 43. The divided-type metal member is divided into an axial rod-like metal shaft portion 7 extending in axial direction from one end surface to the other end surface of the throttle shaft 4 and a cylindrical metal pipe portion 8 partially fitted, through a cylindrical gap, on the outer periphery of the metal shaft portion 7. The metal shaft portion 7 is formed as an axial rod of a metal material such as stainless steel, and is integrated with the resin molded portion 6 of the throttle shaft 4 by insert-molding. The metal shaft portion 7 is extended over the entire axial direction from the left end surface to the right end surface, in the drawing. In the metal shaft portion 7, the surface portion at an axial end is exposed, more than the valve fixing resin portion 31, to the outer peripheral surface of the throttle shaft 4, and the exposed portion makes up the first bearing slide portion 51 rotatably supported on the inner peripheral surface of a first shaft slide hole 13 of the first bearing support portion 11 of the throttle body 2. The right end, in the drawing, of the metal shaft portion 7 is exposed (projected) more outward than the right end surface, in the drawing, of the resin lever portion 32. The metal shaft portion 7 has a solid cylindrical large diameter portion 53 at the left end portion in the drawing and a solid cylindrical small diameter portion 54 on the right side, in the drawing, of the large diameter portion 53. The small diameter portion 54 has a smaller outer diameter than the large diameter portion 53 • That outer peripheral surface of the central portion of that part of the small diameter portion 54 arranged in the intake path 10 of the bore wall 1 of the throttle body 2 which corresponds to the valve fixing resin portion 31 is formed with a notch 55 to improve the connection with the inner peripheral surface of the valve fixing resin portion 31. Also, the outer peripheral surface of the small diameter portion 54 projected rightward, in the drawing, from the right end, in the drawing, of the resin shaft portion 33 is formed with a notch 56 for improving the connection with the inner peripheral surface of the resin lever portion 32. The metal pipe portion 8 is cylindrically formed of a metal material such as stainless steel only on the surface portion of the throttle shaft 4 between the valve fixing resin portion 31 and the resin lever portion 32. The metal pipe portion 8 is fitted, through a cylindrical gap (where the heat-resistant resin is filled to make up the resin shaft portion 33), on the outer periphery of the metal shaft portion 7 partially, i.e. only on the outer periphery of the metal shaft portion 7 arranged on the inner periphery of the first bearing support portion 11 of the throttle body 2. In this metal pipe portion 8, the surface portion at the axial other end is exposed more than the valve fixing resin portion 31 to the outer peripheral surface of the throttle shaft portion 7. The exposed portion constitutes the second bearing support portion 52 supported rotatably on the inner periphery of the oil seal 16 and the inner peripheral surface of the second shaft slide hole 14 of the second bearing support portion 12 of the throttle body 2. According to this embodiment, on the outer peripheral portion of the throttle valve 3 or the inner wall surface of the bore wall portion 1 of the throttle body 2, a coating material (such as tetrafluoroethylene resin, fluoro resin, molybdenum disulfide, or the like, semi-solid or liquid coating material) is applied in such a way as to fill the gap between the outer peripheral portion of the throttle valve 3 and the inner wall surface of the bore wall portion 1 of the throttle body 2, which coating material is then solidified into a powder form. As shown in Fig. 5, therefore, a first annular gap (trap gap) 61 for trapping the intruding coating material is formed between the inner periphery of the first bearing support portion 11 of the throttle body 2 and the outer periphery of the first bearing slide portion 51 of the throttle shaft 4. According to this embodiment, the first annular gap 61 is formed as an annular part along the peripheral direction of the outer peripheral surface of the large diameter portion 53 of the metal shaft portion ?• Also, as shown in Fig. 6, a second annular gap (trap gap) 62 for trapping the intruding coating material is formed between the inner periphery of the second bearing support portion 12 of the throttle body 2 and the outer periphery of the second bearing slide portion 52 of the throttle shaft 4. Next, a method of fabricating the throttle valve apparatus for the internal combustion engine according to this embodiment is briefly explained with reference to Figs, lA to 6. First, a heat-resistant resin in a heated and molten state (hereinafter referred to as a molten resin) is injected by way of one or more gates into a cavity formed by a resin molding die including a cutting die for forming the intake path 10 and a cutting die for forming the first and second shaft slide holes 13, 14, thereby filling the molten resin into the cavity of the resin molding die. The molten resin filled in the cavity is removed from the resin molding die, cooled and hardened (solidified). As an alternative, a cooling medium such as cooling water is circulated around the cavity of the resin molding die thereby to cool and harden (solidify) the molten resin filled in the cavity more than the resin molding die. Then, the throttle body 2 having the bore wall portion 1 and the first and second bearing support portions 11, 12 is integrally molded with the heat-resistant resin. On the other hand, the axial rod-like metal shaft portion 7 is formed by cutting a metal material such as stainless steel. In the process, the outer periphery of the metal shaft portion 7 may be partially knurled (with notches 55, 56, for example, as shown in Fig. 2) in order to improve the ability of the valve fixing resin portion 31 and the resin lever portion 32 to bite the metal shaft portion 7. Also, the cylindrical metal pipe portion 8 is formed by cutting a metal material such as stainless steel. Next, a heat-resistant resin in a heated and molten state (hereinafter referred to as a molten resin) is injected by way of one or more gates into a cavity formed by a resin molding die including a cutting die for forming a through hole in the fitted portion 21, for example, thereby filling the molten resin in the cavity of the resin molding die* The molten resin filled in the cavity is recovered from the resin molding die, and cooled and hardened (solidified). As an alternative, a cooling medium such as cooling water is circulated around the cavity of the resin molding die thereby to cool and harden (solidify) the molten resin filled in the cavity more than the resin molding die. Then, the throttle valve 3 having the fitted portion 21 and the two semicircular tabular portions 22, 23 is integrally molded with the heat-resistant resin. Next, the outer peripheral surface of the large diameter portion 53 of the metal shaft portion 7 is fitted and fixedly held on the inner peripheral surface of the first bearing support portion (not shown) of the resin molding die. The outer peripheral surface of the metal pipe portion 8 is fitted and fixedly held on the inner peripheral surface of the second bearing support portion (not shown) of the resin molding die in such a manner that the metal pipe portion 8 is fitted, through a cylindrical gap, on the outer periphery at a predetermined position of the small diameter portion 54 of the metal shaft potion 7. As a result, the metal shaft portion 7 formed of a metal material such as stainless steel and the metal pipe portion 8 formed of a metal material such as stainless steel are inserted and fixedly held in the cavity formed by the resin molding die. The heated and molten heat-resistant resin (hereinafter referred to as the molten resin) is injected by way of one or more gates leftward, in the drawing. from the right end portion of the cylindrical gap formed between the outer peripheral surface of the small diameter portion 54 of the metal shaft portion 7 and the inner peripheral surface of the metal pipe portion 8 and also toward the outer periphery from the right end, in the drawing, of the small diameter portion 54 of the metal shaft portion 7, thereby filling the molten resin in the cavity of the resin molding die. In the process, preferably, the resin molding gate is arranged on the resin lever portion 32, so that the molten resin is injected through the narrow cylindrical gap formed between the outer peripheral surface of the small diameter portion 54 of the metal shaft portion 7 and the inner peripheral surface of the metal pipe portion 8 (film gate method). The molten resin poured into the cylindrical gap forming the resin shaft portion 33 flows directly into the valve fixing resin portion 31 from the cylindrical gap. On the other hand, the molten resin injected into the cavity formed between the outer peripheral surface at the right end, in the drawing, of the small diameter portion 54 of the metal shaft portion 7 and the inner peripheral surface of the resin molding die flows directly into the resin lever portion 32. The molten resin filled in the cavity is recovered from the resin molding die, and cooled and hardened (solidified). As an alternative, a cooling medium such as cooling water is circulated around the cavity of the resin molding die thereby to cool and harden (solidify) the molten resin filled in the cavity more than the resin molding die. Then, the small diameter portion 54 of the metal shaft portion 7 is insert-molded in the valve fixing resin portion 31 and the resin shaft portion 33, on the one hand, and the resin molded portion 6 of the throttle shaft 4 integrally formed with the metal pipe portion 8 is integrally formed by resin molding by the heat-resistant resin on the outer periphery of the resin shaft portion 33, on the other hand. Next, the spring-side hook of the return spring 5 is assembled on the body-side hook 17 formed on the outer wall surface (the right end surface in the drawing) of the bore wall portion 1 of the throttle body 2, and the left side portion, in the drawing, of the return spring 5 is fitted on the outer periphery of the cylindrical spring inner peripheral guide 15 formed on the outer wall surface (the right end surface in the drawing) of the bore wall portion 1 of the throttle body 2. In this way, the return spring 5 is assembled on the outer wall surface (on the right end surface in the drawing) of the bore wall portion 1 of the throttle body 2. The throttle valve 3 is inserted in the intake path 10 formed in the bore wall portion 1 of the throttle body 2 in such a manner as to align the axial center of the through hole formed in the fitted portion 21 of the throttle valve 3 and the first and second shaft slide holes 13, 14 formed in the first and second bearing support portions 11, 12, respectively, of the throttle body 2. Then, the second shaft slide hole 14, the through hole and the first shaft slide hole 13 of the throttle shaft 4 are inserted in that order from the right end, in the drawing, of the second bearing support portion 12 of the throttle body 2. In this way, the throttle shaft 4 is assembled on the throttle body 2. Next, the spring-side hook of the return spring 5 is assembled on the lever-side hook 42 formed on the outer wall surface (the left end surface in the drawing) of the resin lever portion 32 of the throttle shaft 4, and the right end portion, in the drawing, of the return spring 5 is fitted on the outer periphery of the cylindrical spring inner peripheral guide 41 formed on the outer wall surface (the left end surface in the drawing) of the resin lever portion 32. Thus, the return spring 5 is mounted between the outer wall surface (the right end surface in the drawing) of the bore wall portion 1 of the throttle body 2 and the outer wall surface (the left end surface in the drawing) of the resin lever portion 32 of the throttle shaft 4, Using a thermal welding method, such as laser welding, in the bore wall portion 1 of the throttle body 2, the fitted portion 21 of the throttle valve 3 is fixed on the outer periphery of the valve fixing resin portion 31 of the throttle valve 4 held at a predetermined position in the intake path 10. As a result, a throttle valve apparatus for the internal combustion engine comprising the throttle body 2, the throttle valve 3, the throttle shaft 4 and the return spring 5 is fabricated. The employment of the fabrication method and the fabrication steps described above effectively contributes to the reduction in the number of the parts and the fabrication steps. Next, the operation of the throttle valve apparatus for the internal combustion engine according to this embodiment is explained briefly with reference to Figs. lA to 6. Upon depression of the accelerator pedal by the driver, the resin lever portion 32 mechanically connected to the accelerator pedal through a wire cable is rotated by an angle corresponding to the amount of the accelerator pedal depression against the force of the return spring 5. The rotation of the resin lever portion 32 is transmitted through the resin shaft portion 333 to the valve fixing resin portion 31, and with the rotation of the valve fixing resin portion 31, the throttle valve 3 is rotated by the same angle as the resin lever portion 32, i.e. the same angle as the throttle shaft 4. As a result, the intake path 10 to the engine is opened by a predetermined throttle opening degree, and therefore the engine speed is changed to a value corresponding to the accelerator pedal angle. Once the driver releases his/her foot from the accelerator pedal, on the contrary, the throttle valve 3 and the throttle shaft 4 are returned to the initial position (idling position) by the force of the return spring 5. Thus^ the intake path 10 to the engine is closed (fully closed state), and the engine enters the idling mode. The effects of the throttle valve apparatus for the internal combustion engine according to this embodiment are explained. In the throttle valve apparatus for the internal combustion engine according to this embodiment, the resin molded portion 6 of the throttle shaft 4 includes the metal shaft portion 7 made up of a rod member and a metal core metal of the cylindrical metal pipe portion 8. Without increasing the diametrical size of the throttle shaft 4 to an unnecessary degree, therefore, the strength of the throttle shaft 4 is increased. Specifically, in the throttle shaft 4 according to this embodiment, the valve fixing resin portion 31 is reinforced by the small diameter portion 4 of the metal shaft portion 7 and, therefore, as compared with an all-resin throttle shaft configured entirely of a heat-resistant resin, has a sufficient resistance to the excessive load of the negative pressure of the intake pipe imparted to the throttle valve 3 accommodated in the intake path 10. Even in the case where the negative pressure of the intake pipe generated in the engine is imparted to the throttle valve 3, therefore, the valve fixing resin portion 31 for fixing the throttle valve 3 is not warped or distorted, and a sufficient strength is secured without excessively changing the outer diameter of the valve fixing resin portion 31 molded of resin. Thus, the size of the intake path of the intake pipe which otherwise might be increased with the outer diameter of the valve fixing resin portion 31 is not increased, thereby making it possible to reduce the space occupied by the intake pipe around the engine. The first and second bearing slide portions 51, 52 on the two sides of the throttle shaft 4 slide in such a manner that the first bearing slide portion 51 (SUS304, for example) of the metal shaft portion 7 slides with the first bearing support portion 11 (PBTG30, for example) of the throttle body 2, and the second bearing slide portion 52 (SUS304, for example) of the metal pipe portion 8 slides with the second bearing support portion 12 (PBTG30, for example) of the throttle body 2. Without arranging a bearing member such as a ball bearing or a thrust bearing, therefore, bearing slide portions with high wear resistance are formed. Specifically, the large diameter portion 53 of the metal shaft potion 7 and the metal pipe portion 8 formed of a metal material such as stainless steel are formed integrally with the first and second bearing slide portions 51, 52 rotatably supported on the first and second bearing support portions 11, 12, respectively, of the throttle body 2. This is very advantageous in respect to wear resistance. According to this embodiment, the bearing members such as the ball bearing and the thrust bearing are not required, and therefore the number of parts and assembly steps is reduced for a lower production cost. A "weld" is a discontinuous portion of the resin polymer formed in the boundary surface of the resin integrated at the time of reintegration and solidification of divided portions while filling the molding resin in a die, and is lower in strength than the portion continuously formed of polymer. Especially, in the case where the weld is generated in the direction transverse to the axis when molding in axial form, the strength in the bending direction of the shaft is reduced. According to this invention, on the other hand, a divided-type metal member is used as a reinforcing member configured of a member arranged in the neighborhood of the axial center and a member arranged in the outer peripheral portion of the shaft. Therefore, the resin material making up the outer peripheral portion and the resin material making up the central portion can be molded without being divided in the transverse direction of the shaft. Thus, the strength, which otherwise might be reduced by a weld, is not decreased. Especially, in the case where a gate is arranged at least in one of the positions indicated by arrows A and B in Fig, 4A, for example, the resin can flow to the end without being divided transversely to the shaft in the molding process, and therefore no weld transverses the shaft and reduces the strength. The positions indicated by the arrows in Fig. 4A are not intended to limit the configuration of the invention. In the throttle valve apparatus for the internal combustion engine according to this embodiment, a metal member for reinforcing the resin molded portion 6 of the throttle shaft 4 is divided into two parts including the metal shaft portion 7 and the metal pipe portion 8, and can be set and integrally molded by resin in the same resin molding die for fabricating the throttle shaft 4. In the process, the molten resin is poured from the cylindrical gap formed between the outer peripheral surface of the small diameter portion 54 of the metal shaft portion 7 and the inner peripheral surface of the metal pipe portion 8. Specifically, as the cylindrical gap can be used as a cylindrical film gate (according to what is called the film gate method), the generation of the weld in the valve fixing resin portion 31 is suppressed, thereby making it possible to prevent a deterioration in appearance and a reduction in the strength of the particular part. Also, by suppressing the generation of the weld in the valve fixing resin portion 31, resin cracking due to the heating and cooling cycles of the resin molded portion 6 of the throttle shaft portion 4 can be suppressed, and the dimensional accuracy of the resin molded portion 6 of the throttle shaft 4, after annealing, is improved. The annealing is defined as a heat treatment for slowly cooling a product after holding it at an appropriate temperature for a predetermined length of time for the purpose of removing the residual stress generated in the resin molded portion 6 by thermal or mechanical stress. According to the prior art, as shown in Figs. 7 and 8A to 8C, the shaft diameter of the throttle shaft 106 is constant, and therefore the insertion length into the resin molding die is so large that the metal pipe 107 cannot be assembled (set) easily in the cavity of the resin molding die. According to this embodiment, in contrast, the metal member for reinforcing the resin molded portion 6 of the throttle shaft 4 is divided into two parts and, therefore, the metal shaft portion 7 and the metal pipe portion 8 can be very easily built (set) in the cavity of the resin molding die, thereby reducing the production cost. Also, in the throttle valve apparatus for the internal combustion engine according to this embodiment, two flat surfaces (two-transverse-surface portion or peripheral position determining portion) 34 for stopping the rotation of the fitted portion 21 of the throttle valve 3 along the peripheral direction of the throttle shaft 4 are formed on the outer peripheral surface of the valve fixing resin portion 31. In the prior art, as shown in Figs. 7 and 8A to 8C, a structure with the two-transverse-surface portion formed on the outer peripheral surface of the valve fixing resin portion 104 makes it necessary to secure a space in the metal pipe 107 to inject the molten resin, which in turn requires a correspondingly increased shaft diameter of the throttle shaft 106. According to this embodiment, however, the molten resin need not be poured into the small diameter portion 54 of the metal shaft portion 7 and, as compared with the conventional structure, the throttle shaft 4 can be reduced in diameter and made less bulky. Other embodiments of the invention are explained below. In the aforementioned embodiments, the resin lever portion 32 for transmitting the accelerator pedal angle to the throttle valve 3 through the valve fixing resin portion 31 and the resin shaft portion 33 is integrally molded with resin on the outer periphery at an end of the small diameter portion 54 of the metal shaft portion 7 for reinforcing the resin molded portion 6 of the throttle shaft 4, As an alternative, a resin valve-side gear portion for transmitting the accelerator pedal angle to the throttle valve 3 through the valve fixing resin portion 31 and the resin shaft portion 33 may be integrally molded by resin on the outer periphery at an end of the small diameter portion 54 of the metal shaft portion 7 for reinforcing the resin molded portion 5 of the throttle shaft 4. In this case, the throttle valve 3 is rotated by an electric motor integrally with the resin valve-side gear portion through a reduction gear mechanism. In the aforementioned embodiments, the metal pipe portion 8 is formed as a cylinder. As an alternative, the metal pipe portion 8 may be configured of a plurality of arcuate metal pieces arranged, in the axial direction, substantially into the shape of cylinder. As another alternative, a plurality of metal rings may be arranged in axial direction to make up the metal pipe portion. Also, in the aforementioned embodiments, the fitted portion 21 of the throttle valve 3 is fixed by thermal welding on the outer periphery of the valve fixing resin portion 31 of the throttle shaft 4. Instead, the fitted portion 21 of the throttle valve 3 may be fixed by use of a fastening tool on the outer periphery of the valve fixing resin portion 31 of the throttle shaft 4. A second embodiment of the invention is explained below. Figs. 9A to 9D show the second embodiment of the invention, in which the fitting portion between the throttle shaft and the throttle valve is illustrated. The valve fixing resin portion 31 is formed as a no cylindrical member and arranged on the left side, in the drawing, of the resin shaft portion 33. The valve fixing resin portion 31 includes a fitting portion 121 in which the throttle valve 3 is fitted under pressure. The outer peripheral surface of the valve fixing resin portion 31 is formed with two flat surfaces {two-transverse-surf ace portion or peripheral position determining portion) 34 for stopping the rotation of the throttle valve 3 along the peripheral direction of the throttle shaft 4. Specifically, the two-transverse-surface portion 34 is a noncircular portion for preventing relative rotational motion of the throttle shaft 4 and the throttle valve 3. The resin lever portion 32 is formed as an annular plate on the right side, in the drawing, of the resin shaft portion 33. The outer periphery of the resin lever portion 32 is formed with a substantially V-shaped peripheral groove 37 wound with a valve open/close wire cable (not shown) operatively interlocked with the accelerator pedal operated by the driver. The outer periphery of the resin lever portion 32, on the other hand, is formed with a valve open/close wire mounting groove (not shown) for mounting an end of the valve open/close wire cable. The throttle valve 3 is a resin molded product integrally molded of a heat-resistant resin (such as polyphenylene sulfide (PPS), polybutylene terephthalates containing 30% glass fiber (PBTG30), etc.), and constitutes a rotary valve of butterfly type operably accommodated in the bore wall portion 1 of the throttle body 2 to control the amount of the engine intake air. The throttle valve 3 is formed with an outer peripheral portion (surface portion) of the throttle shaft 4, i.e. a no cylindrical fitted portion (cylindrical resin portion) 21 fixedly fitted on the outer periphery of the valve fixing resin portion 31 by laser welding or the like, and two semicircular tabular portions 22 extended from the fitted portion 21 in such a manner as to close the intake path 10. The fitted portion 21 is arranged at about the rotational center of the two semicircular tabular portions 22, and is fixed, by laser welding, onto the outer peripheral portion (surface portion) of the throttle shaft 4. Also, the fitted portion 21, as shown in Figs 9A to 9D, has a reduction unit 141 fixedly fitted on the outer periphery of the fitting portion 121 of the valve fixing resin portion 31 of the throttle shaft 4 at the central portion of the fitting portion with the valve fixing resin portion 31 of the throttle shaft 4, On both axial sides of the reduction unit 141, substantially conical tilted cylindrical walls 142, 143 having an outer diameter or an inner diameter progressively increasing toward the two axial ends (two open ends) of the fitted portion 21 from the reduction unit 141, An elliptic through hole (fitting hole) 144 is formed axially through the fitted portion 21. The inner peripheral surface and the outer peripheral surface of the fitted portion 21, corresponding to the contour of the throttle shaft 4, i.e. the two-transverse-surface portion 34 formed on the outer peripheral surface of the valve fixing resin portion 31, are formed with two flat surfaces (two-transverse-surface portion) 145 for stopping the rotation of the throttle shaft 4 along the peripheral direction of the throttle valve 3. The portion of the inner peripheral surface and the outer peripheral surface of the fitted portion 21 except for the two-transverse-surface portion 145 has a radius of curvature in arcuate form centered on the axis of the fitted portion 21. Next, the structure of the fitting portion between the valve fixing resin portion 31 of the throttle shaft 4 and the fitted portion 21 of the throttle valve 3 according to this embodiment is explained with reference to Figs. 9A to 9D. A part of the fitting portion, or especially, the central part of the fitting portion is formed with a press-fitting portion 151 having a welding gap of not more than a predetermined size between the fitting portion 121 of the valve fixing resin portion 31 and the reduction unit 141 of the fitted portion 21. The maximum size of the valve fixing resin potion 31 and the minimum size of the through hole (fitting hole) 144 are substantially equal to each other. The fitting portion, except for the press-fitting portion 151, which is such that the maximum size of the valve fixing resin portion 31 is smaller than the minimum size of the through hole (fitting hole) 144, is formed with a gap fitting portion 152 having a welding gap larger than a predetermined value between the two tilted cylindrical walls 142, 143 of the fitted portion 21 and the valve fixing resin portion 31. The press-fitting portion 151 of the fitting portion and the gap fitting portion 152 in the neighborhood of the press-fitting portion 151, with the inner periphery of the fitted portion 21 of the throttle valve 3 fitted on the outer periphery of the valve fixing resin portion 31 of the throttle shaft 4, make up a fitting welding portion 153 for fixing the outer periphery of the valve fixing resin portion 31 and the inner periphery of the fitted portion 21 to each other by laser welding. The maximum size of the welding gap (welding space) of the fitting welding portion 153 is set to not more than a predetermined value (say, 75 ) permitting laser welding. Taking the welding strength of the fitting welding portion 153 into consideration, the maximum size of the welding gap (welding space) of the fitting welding portion 153 is desirably set to not more than a predetermined value S (say, 25 ) . As described above, a part of the fitting portion between the valve fixing resin portion 31 of the throttle shaft 4 and the fitted portion 21 of the throttle valve 3 makes up the press-fitting portion 151/ and the two-transverse-surface portion 34 and the two-transverse-surface portion 145 are arranged along the lateral direction in Fig. 9D. In this way, the position of the fitted portion 21 of the throttle valve 3 can be restricted in the vertical direction in Fig. 9D, i.e. in the direction perpendicular to the axis of the valve fixing resin portion 31 of the throttle shaft 4. The whole fitting portion including the press-fitting portion 151 has a gap between the valve fixing resin portion 31 of the throttle shaft 4 and the fitted portion 21 of the throttle valve 3, and the two-transverse-surface portions 34, 145 are arranged in the horizontal direction in the drawing. Thus, the fitted portion 21 of the throttle valve 3 can be moved in the direction perpendicular to the axis of the valve fixing resin portion 31 of the throttle shaft 4, i.e. in the horizontal direction in Fig. 9D. Next, a method of fabricating the throttle valve apparatus for an internal combustion engine according to this embodiment is explained briefly with reference to Figs. 9A to 9D. First, the spring-side hook of the return spring 5 is assembled on the body-side hook 17 formed on the outer wall surface (on the right end surface in the drawing) of the bore wall portion 1 of the throttle body 2, and the left side portion, in the drawing, of the return spring 5 is fitted on the outer periphery of the cylindrical spring inner peripheral guide 15 formed on the outer wall surface (on the right end surface in the drawing) of the bore wall portion 1 of the throttle body 2. In this way, the return spring 5 is assembled on the outer wall surface (on the right end surface in the drawing) of the bore wall portion 1 of the throttle body 2. Next, the throttle valve 3 is inserted into the intake path 10 formed in the bore wall portion 1 of the throttle body 2 in such a manner that the axes of the through hole (fitting hole) 144 of the fitted portion 21 of the throttle valve 3 and the first and second shaft sliding holes formed in the first and second bearing support portions 11, 12 of the throttle body 2 are aligned with each other. Then, the throttle shaft 4 is assembled on the throttle body 2 by inserting the throttle shaft 4 into the second slide hole, the through hole (fitting hole) 144 and the first shaft slide hole, in that order, from the right end in Fig. 12 of the second bearing support portion 12 of the throttle body 2. The spring-side hook of the return spring S is assembled on the lever-side hook 42 formed on the outer wall surface (on the left end surface in the drawing) of the resin lever portion 32 of the throttle shaft 4, and the right side portion, in the drawing, of the return spring 5 is fitted on the outer periphery of the cylindrical spring inner peripheral guide 41 formed on the outer wall surface (on the left end surface in the drawing) of the resin lever portion 3. In this way, the return spring 5 is mounted between the outer wall surface (the right end surface in the drawing) of the bore wall portion 1 of the throttle body 2 and the outer wall surface (the left end surface in the drawing) of the resin lever portion 32 of the throttle shaft 4. In the bore wall portion 1 of the throttle body 2, while fitting the fitted portion 21 of the throttle valve 3 on the outer periphery of the valve fixing resin portion 3 of the throttle shaft "4, the throttle body assembly is assembled on the jig of a laser welding device not shown. This jig can be reciprocated within a predetermined range, and has the laser device arranged above it. The laser device focuses the laser beam output from a laser source by a lens or the like, and radiates it onto the outer wall surface of the fitted portion 21 of the throttle valve 3 in the bore wall portion 1. A semiconductor laser source having a laser output of about 20 W to 30 W is used for the laser device. Alternatively, a pulse YAG (yttrium aluminum garnet) laser, a CO2 laser or the like may be used as a laser source. The feed rate of the jig is set to about 10 mm/sec. While radiating the laser beam on the outer wall surface of the fitted portion 21 of the throttle valve 3 from the laser source of the laser device, the jig is moved in axial direction of the throttle shaft 4 while at the same time reciprocally swinging back and forth in the direction perpendicular to the axis of the throttle shaft 4. In the process, the laser beam enters the fitted portion 21 of the throttle valve 3 and, passing through it, reaches and is absorbed into the outer peripheral surface of the valve fixing resin portion 31 of the throttle shaft 4. The laser thus radiated melts the outer peripheral surface of the valve fixing resin portion 31 as shown in Fig. 9A, and the same heat melts the inner wall surface of the fitted portion 31, thereby thermally welding the outer peripheral surface of the valve fixing resin portion 21 and the inner wall surface of the fitted portion 21 to each other. According to this embodiment, as shown in Figs. 9A and 9B, the laser welding is carried out along the axial direction of the throttle shaft 4 with the press-fitting portion 151 as a center on the two-transverse-surface portion 34 of the valve fixing resin portion 31 and the two-transverse-surface portion 145 of the fitted portion 21. Specifically, the laser welding is conducted two ways, on the obverse and reverse surfaces, respectively, of the two-transverse-surface portion 145 of the fitted portion 21 of the throttle valve 3. As a result, the press-fitting portion 151 of the fitting portion between the valve fixing resin portion 31 of the throttle shaft 4 and the fitted portion 21 of the throttle valve 3, and the gap fitting portion 152 in the neighborhood of the press-fitting portion 151 make up the fitting welding portion 153 as shown in Fig. 9C. As described above, a throttle valve apparatus for the internal combustion engine, comprising the throttle body 2, the throttle valve 3, the throttle shaft 4 and the return spring 5 is fabricated. The employment of this fabrication method and the fabrication steps contributes to a decreased number of parts and fabrication steps. Next, the effects of the throttle valve apparatus for the internal combustion engine according to this embodiment are explained. As explained above, in the throttle valve apparatus for the internal combustion engine according to this embodiment, the press-fitting portion 151 is arranged as a part of the fitting portion between the valve fixing resin portion 31 of the throttle shaft 4 and the fitted portion 21 of the throttle valve 3- Specifically, the welding space between the valve fixing resin portion 131 and the fitted portion 21 of the press-fitting portion 151 can be reduced below a predetermined value, and therefore a sufficient welding strength is secured for laser welding the valve fixing resin portion 1 of the throttle shaft 4 and the fitted portion 21 of the throttle valve 3 to each other. Especially, in the case where the throttle valve apparatus for the internal combustion engine is mounted on a vehicle and operated by the engine, the press-fitting portion 151 is arranged at the central part of the fitting portion between the valve fixing resin portion 31 of the throttle shaft 4 and the fitted portion 21 of the throttle valve 3 subjected to the largest stress due to the negative intake pipe pressure (intake air pressure) or a backfire when the engine is running. In this way, the fitting welding portion 153 having a gap of a value permitting the laser welding is formed at about the central part of the fitting portion. As a result, the maximum strength can be secured of the fitting welding portion 153 between the outer periphery of the valve fixing resin portion 31 of the throttle shaft 4 and the fitted portion 21 of the throttle valve 3, thereby improving the welding quality of the fitting welding portion 153. Even in the case where the negative pressure of the intake pipe or a backfire is applied to the throttle valve 3, the valve fixing resin portion 31 of the throttle shaft 4 for fixing the throttle valve 3 by laser welding is not warped or distorted, and a sufficient strength can be secured without much changing the outer diameter of the resin-molded valve fixing resin portion 31. Thus, the diameter of the air path of the intake pipe is prevented from being increased by the increase in the outer diameter of the valve fixing resin portion 31, thereby making it possible to reduce the space occupied by the intake pipe around the engine. Also, as the gap fitting potion 152 is arranged in the remaining part of the fitting portion between the valve fixing resin portion 31 of the throttle shaft 4 and the fitted portion 21 of the throttle valve 3 except for the press-fitting portion 151, the welding space between the valve fixing resin portion 31 and the fitted portion 21 of the gap fitting portion 152 can be increased beyond a predetermined value. Therefore, the fitted portion 21 of the throttle valve 3 can be assembled more easily on the valve fixing resin portion 31 of the throttle shaft 4. A third embodiment of the invention is explained below. Figs. lOA to IOC show the fitting portion between the throttle shaft and the throttle valve according to the third embodiment of the invention. The left end, in the drawing, of the fitted portion 21 of the throttle valve 3 according to this embodiment is formed with a diaphragm 141 press-fixed on the outer periphery of the fitting portion 121 of the valve fixing resin portion 31 of the throttle shaft 4, On the right side, in the drawing, in axial direction of the diaphragm 141, on the other hand, is formed with a substantially conical tilted cylindrical wall 143 with the outer diameter or the inner diameter thereof progressively increasing from the diaphragm 141 toward the right end portion in the drawing (the open end on the right side in the drawing) in the axial direction of the fitted portion 21. Also, according to this embodiment, a part of the fitting portion between the valve fixing resin portion 31 of the throttle shaft 4 and the fitted portion 21 of the throttle valve 3, or especially the right end, in the drawing, of the fitting portion is formed with a press-fitting portion 151 having a welding space smaller than a predetermined value between the fitting portion 121 of the valve fixing resin portion 31 and the diaphragm 141 of the fitted portion 21 in such a manner that the maximum size of the valve fixing portion 31 is substantially equal to the minimum size of the through hole (fitting hole) 144. Also, the fitting portion other than the press-fitting portion 151 is formed with a gap fitting portion 152 with the welding space larger than the predetermined value between the tilted cylindrical wall 143 of the fitted portion 21 and the valve fixing resin portion 31 in such a manner that the maximum size of the valve fixing resin portion 31 is smaller than the minimum size of the through hole (fitting hole) 144, The pressure fitting portion 151 and the gap fitting portion 152 in the neighborhood of the press-fitting portion 151 of the fitting portion, while fitting the inner periphery of the fitted portion 21 of the throttle valve 3 on the outer periphery of the valve fixing resin portion 31 of the throttle shaft 4, is formed with a fitting welding portion 153 for fixing the outer periphery of the valve fixing resin portion 31 and the inner periphery of the fitted portion 21 by laser welding to each other. The maximum size of the welding gap (welding space) of the fitting welding portion 153 is set to not larger than a predetermined value S (say, 75 |Am) permitting laser welding. As described above, the press-fitting portion 151 is arranged at the left end, in the drawing, other than the central portion of the fitting portion between the valve fixing resin portion 31 of the throttle shaft 4 and the fitted portion 21 of the throttle valve 3. In spite of this configuration, the fitting welding portion 153 can be formed at about the central portion of the fitting portion between the valve fixing resin portion 31 of the throttle shaft 4 and the fitted portion 21 of the throttle valve 3 subjected to the maximum stress under the intake air pressure or a backfire and, therefore, the same advantage as the second embodiment is achieved. Specifically, this configuration can sufficiently stand the excessive load of the negative pressure of the intake pipe imparted to the throttle valve 3 in the intake path 10. Finally, other embodiments are explained. In the embodiments described above, the outer peripheral side of an end of the metal shaft portion 7 for reinforcing the resin molded portion of the throttle shaft 4 is resin molded integrally with the resin lever portion 32 for transmitting the accelerator pedal angle to the throttle valve 3 through the valve fixing resin portion 31 and the resin shaft portion 33. Nevertheless, the resin lever portion 32 is not necessarily molded integrally with the valve fixing resin portion 31. Also, the resin lever portion 32 may be formed as a resin valve-side gear portion for transmitting the accelerator pedal angle to the throttle valve 3 through the valve fixing resin portion 31 and the resin shaft portion 33, on the outer periphery of an end of the metal shaft portion 7 for reinforcing the resin molded portion of the throttle shaft 4. In this case, the throttle valve 3 is driven by an electric motor through a reduction gear mechanism integrally with the resin valve-side gear portion. In the embodiments described above, the valve fixing resin portion (axial resin portion) 31 of the throttle shaft 4, the resin lever portion 32 and the resin shaft portion 33 are integrally molded by a heat-resistant resin. As an alternative, only the shaft portion of the throttle shaft 4 may be molded of a heat-resistant resin. Also, in the embodiments described above, the fitted portion (cylindrical resin portion) 21 of the throttle valve 3 and the two semicircular tabular portions 22 are integrally molded of a heat-resistant resin. Alternatively, only the cylindrical portion of the throttle valve 3 may be molded of a heat-resistant resin. Also, a thermal welding method other than laser welding may be employed. According to the embodiments described above, the resin molded portion (especially, the valve fixing resin portion 31) of the throttle shaft 4 is reinforced by a divided-type metal member, i.e. the metal shaft portion 7 and the metal pipe portion 8. Instead, the resin molded portion (especially, the valve fixing resin portion 31) of the throttle shaft 4 may be reinforced by either an axial rod-like metal material or a cylindrical metal material. Also, the metal pipe portion 8 may be configured of a plurality of arcuate metal pieces arranged in axial direction to form a substantial cylinder. Further, a plurality of annular metal members may be arranged in axial direction. While the invention has been described by reference to specific embodiments chosen for purposes of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention. CLAIMS 1. A throttle valve apparatus for an internal combustion engine, comprising: A throttle valve accommodated openably in a throttle body for changing the amount of the intake air flowing toward an engine in accordance with the rotational angle of the valve; and a throttle shaft driven in accordance with the accelerator pedal angle set by the driver and rotated integrally with said throttle valve; Wherein said throttle shaft includes a valve fixing resin portion for fixing said throttle valve, a rotational driving resin portion for transmitting the accelerator pedal angle to said throttle valve through said valve fixing resin portion, and a divided-type metal member having a member arranged in the neighborhood of the axial center and a member arranged on the outer peripheral part of the shaft for reinforcing said valve fixing resin portion and said rotational driving resin portion, 2. A throttle valve apparatus for an internal combustion engine according to claim 1, wherein said divided-type metal member is divided into an axial rod-like metal shaft portion extending in axial direction of said throttle shaft and a tubular metal pipe portion partially fitted, through a cylindrical space, on the outer periphery of said metal shaft portion, and wherein said metal pipe portion is arranged only on the surface portion of said throttle shaft between said valve fixing resin portion and said rotational driving resin portion, 3. A throttle valve apparatus for an internal combustion engine according to claim 2, wherein a cylindrical resin shaft portion for connecting said valve fixing resin portion and said rotational driving resin portion is arranged in said cylindrical space, 4. A throttle valve apparatus for an internal combustion engine according to claim 3, wherein said fixing valve resin portion and said resin shaft portion are integrally molded with said rotational driving resin portion by supplying molten resin from said cylindrical space and solidifying, by cooling, said molten resin. 5. A throttle valve apparatus for an internal combustion engine according to claim 1, wherein said throttle valve includes a cylindrical fitted portion adapted to be fitted on the outer periphery of said valve fixing resin portion at the rotational central portion, and wherein said valve fixing resin portion has a peripheral position determining portion for stopping the rotation of said fitted portion in the peripheral direction of said throttle shaft. 6. A throttle valve apparatus for an internal combustion engine according to claim 1, wherein said throttle body includes a cylindrical first bearing support portion for rotatably supporting an axial end of said throttle shaft and a cylindrical second bearing support portion for rotatably supporting the other axial end of said throttle shaft, wherein the surface portion at an axial end of said metal shaft portion is exposed to the outer peripheral surface of said throttle shaft more than said valve fixing resin portion, and said exposed portion constitutes a first bearing slide portion rotatably supported on the inner periphery of said first bearing support portion, and Wherein the surface portion at the other axial end of said metal pipe portion is exposed to the outer peripheral surface of said throttle shaft more than said valve fixing resin portion, and said exposed portion constitutes a second bearing slide portion rotatably supported on the inner periphery of said second bearing support portion. 7. A throttle valve apparatus for an internal combustion engine according to claim 6, wherein a coating material for reducing the air leakage at the time of idling operation is applied on selected one of the outer peripheral portion of said throttle valve and the inner wall surface of said throttle body in such a manner as to fill the gap between the outer peripheral portion of said throttle valve and the inner wall surface of said throttle body^ and wherein a gap for trapping the intruding part of said coating material is formed between the inner periphery of selected one of said first bearing support potion and said second bearing support portion and the outer periphery of selected one of said first bearing slide portion and said second bearing slide portion. 8. A throttle valve apparatus for an internal combustion engine, comprising: a throttle body with the intake air flowing therein toward the internal combustion engine; a throttle shaft rotatably supported on said throttle body and having a shaft portion of resin in axial direction thereof; and a throttle valve including a cylindrical resin portion openably accommodated in said throttle body and fitted on the outer periphery of said shaft portion, and a fitting hole through which said cylindrical portion is arranged in axial direction; wherein with the inner periphery of said cylindrical portion fitted on the outer periphery of said shaft portion, the outer periphery of said shaft portion and the inner periphery of said cylindrical portion are fixed to each other by thermal welding; wherein the fitting portion between said shaft portion and said cylindrical portion, which is such that the maximum size of said shaft portion is substantially equal to the minimum size of said fitting hole, is formed with a press-fitting portion with the welding space between said shaft portion and said cylindrical portion smaller than a predetermined value; and wherein said fitting portion except for said press-fitting portion, which is such that the maximum size of said shaft portion is smaller than the minimum size of said fitting hole, is formed with a gap fitting portion with the welding space between said shaft portion and said cylindrical portion larger than said predetermined value. 9. A throttle valve apparatus for an internal combustion engine according to claim 8, wherein said press-fitting portion of said fitting portion and said gap fitting portion in the neighborhood of said press-fitting portion, with the inner periphery of said cylindrical portion fitted on the outer periphery of said shaft portion, constitute a fitting welding portion for fixing the outer periphery of said shaft portion and the inner periphery of said cylindrical portion by thermal welding. 10. A throttle valve apparatus for an internal combustion engine according to claim 8, wherein the laser welding is used for said thermal welding. 11. A throttle valve apparatus for an internal combustion engine according to claim 10, wherein the maximum size of said welding gap is set to not more than 75 ^m to permit laser welding. 12. A throttle valve apparatus for an internal combustion engine according to claim 8, wherein said cylindrical portion has a substantially conical tilted cylindrical wall having selected one of the outer diameter and the inner diameter thereof progressively increasing toward the end of said cylindrical portion from said press-fitting portion. 13. A throttle valve apparatus for an internal combustion engine according to claim 8, wherein said press-fitting portion is arranged at selected one of the positions at an axial end of said fitting portion and at about the axial central portion of said fitting portion, 14. A throttle valve apparatus for an internal combustion engine according to claim 8, Wherein the exterior of said shaft portion and the interior of said fitting hole assume a noncircular shape capable of stopping the rotation of said cylindrical portion in the peripheral direction of said shaft portion. 15. A throttle valve apparatus for an internal combustion engine according to claim 8, wherein the exterior of said shaft portion and the interior of said fitting hole assume such a noncircular shape that said cylindrical portion is movable in a radial direction substantially perpendicular to the axis of said shaft portion. 16. A throttle valve apparatus for an internal combustion engine substantial as herein described with reference to the accompanying drawings.

Documents:

139-che-2004-abstract.pdf

139-che-2004-claims filed.pdf

139-che-2004-claims granted.pdf

139-che-2004-correspondnece-others.pdf

139-che-2004-correspondnece-po.pdf

139-che-2004-description(complete) filed.pdf

139-che-2004-description(complete) granted.pdf

139-che-2004-drawings.pdf

139-che-2004-form 1.pdf

139-che-2004-form 19.pdf

139-che-2004-form 26.pdf

139-che-2004-form 3.pdf

139-che-2004-form 5.pdf