Manufacturing method for a throttle body of an internal combustion engine and a related throttle apparatus

Abstract: A worker inserts a correcting pin into bearing members. Then, a cylindrical portion and retaining portions are molded together into an integrated resin unit. After finishing the molding operation, the worker extracts the correcting pin from the bearing members and subsequently inserts a throttle shaft into the bearing members. Accordingly, an axial center of the bearing member accurately agrees with an axial center of the bearing member. Then, the worker fixes a throttle valve to the throttle shaft.

Description: BACKGROUND OF THE INVENTION The present invention relates to a manufacturing method for a throttle body defining therein an air passage of an internal combustion engine (hereinafter, referred to as engine). From recent requirements of weight reduction as well as cost reduction, there is known a throttle body whose housing is made of a resin. However, the throttle body is generally configured into a complicated shape with protrusions and recesses for providing bearing members of a throttle shaft and for installing an opening degree sensor. More specifically, the housing of the throttle body supports both ends of the throttle shaft via the bearing members. The housing has two recesses formed for receiving the bearing members (at portions where the throttle shaft is supported). A method comprising the features summarized in the precharacterizing clause of claim 1 is known from document JP-A-11294203 (Figures 1 to 4). In this known method, the two bearing members are separately placed in molding spaces of the molding dye. After the molding step, the retaining portions of the housing firmly hold the bearing members. Thereafter, the throttle shaft is inserted into the bearing members, and the valve member is fixed to the throttle shaft. In this known method, it is necessary to accurately set the molding dye parts on which the bearing members are placed for accurately adjusting the axial centres of the bearing members. Otherwise, the axial centers of the bearing members resulting through the resin molding operation will not agree with each other. For example, even if the throttle shaft can be inserted into the bearing members, disagreement of the axial centers of the bearing members will undesirably increase a rotational torque of the throttle shaft. This will generate an excessive drive loss when the throttle shaft is driven. Furthermore, requiring high accuracy in the setting of the separate molding dies will increase the manufacturing cost. Furthermore, even if setting of the separate molding die parts is accurately done, the axial centers of the bearing members may disagree with each other due to product tolerance of the bearing members themselves. Unexamined Japanese patent publication No. 11-173227 proposes a manufacturing method for a throttle body. According to this method, a housing of the throttle body is formed by a composite material with a matrix of synthetic resin. Retaining portions of a throttle shaft are formed independent of the housing. The retaining portions are connected to a cylindrical portion of the housing by welding or the like so that deformation of the intake passage can be prevented. According to this manufacturing method, the above-described molding dies are not used for forming the retaining portions of the throttle shaft. However, this conventional technique will encounter with the similar problems. For example, the separately formed retaining portions may not be accurately connected to the cylindrical portion of the housing. In this case, the axial centers of the bearing members disagree with each other. Furthermore, even if connection of the retaining portions with the cylindrical portion of the housing is accurately done, the axial centers of the bearing members may disagree with each other due to tolerances of respective bearing members. Furthermore, the above-described conventional technique requires a step of forming the retaining portions of the throttle shaft independent of the cylindrical portion of the housing and a step of connecting the retaining portions to the cylindrical portion. Thus, the total number of required manufacturing steps increases and the manufacturing cost increases. SUMMARY OF THE INVENTION In view of the foregoing problems of the prior art, a primary object of the present invention is to provide a method for manufacturing resinous or resin-made throttle body for an engine throttle apparatus which is free from disagreement of axial centers of bearing members supporting both ends of a throttle shaft. To accomplish the above and other related objects, the present invention provides the manufacturing method according to claim 1. With this method, it becomes possible to support the throttle shaft by the bearing members whose axial centers accurately agree with each other. Furthermore, integrally forming the cylindrical portion and the retaining portions makes it possible to eliminate a step of connecting the cylindrical portion with the separately formed retaining portions. Thus, it becomes possible to facilitate the manufacturing process and reduce the manufacturing cost. According to the manufacturing method for an engine throttle body of the present invention, it is preferable that the features of claim 2 are provided. This enhances the effect of preventing the valve member from freezing due to icing phenomenon or from sticking due to accumulation of deposition, compared with a case where both of the bearing members are constituted by the sleeve bearing. Furthermore, in the molding step of the throttle body, an axial end of the anti-friction bearing is covered by a covering member. Thus, it becomes possible to conceal the rotational portion of the bearing against the resin material so as to assure smooth rotation of the bearing. According to the manufacturing method for an engine throttle body of the present invention, it is also preferable that the features of claim 3 are provided. Thus, it becomes possible to conceal the rotational portion of the bearing against the resin material so as to assure smooth rotation of the bearing. Furthermore, a locking means is provided on the cylindrical wall for preventing rotation of the bearing. Thus it becomes possible to prevent the bearing from rotating in the resin during the molding operation. Thus, the bearing does not shift in the shaft thrust direction. According to the manufacturing method for an engine throttle body of the present invention, it is preferable that the throttle shaft has a smaller outer diameter at a portion accommodated in the cylindrical portion and a larger outer diameter at another portions accommodated in the retaining portions. Thus, it becomes possible to eliminate frictional contact between the throttle shaft and the cylindrical portion. The throttle shaft smoothly rotates without causing frictional loss. Accordingly, the opening degree of the valve member can be controlled properly. Adjustment of air flow amount in the air passage can be performed adequately. According to the manufacturing method for an engine throttle body of the present invention, it is preferable that the correcting shaft member is extracted in a predetermined direction in the extracting step of the correcting shaft member. Thus, the axial opposed end of the retaining portion can be closed. The rotational portion of the throttle shaft or the like is not exposed to the outside of the throttle body. Accordingly, it becomes possible to enhance the airtightness and fluid-tightness of the bearing member. No special plug or the like is required. Therefore, it becomes possible to simplify the arrangement, reduce the total number of parts constituting the throttle body, and reduce the manufacturing cost. BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description which is to be read in conjunction with the accompanying drawings, in which: Fig. 1 is a cross-sectional view showing a molding process of a housing, explaining a manufacturing method for a throttle body in accordance with a first embodiment of the present invention; Fig. 2 is a cross-sectional view showing the throttle body in accordance with the first embodiment of the present invention; Fig. 3 is an enlarged cross-sectional view showing an essential part of the molding process of a housing, explaining a manufacturing method for a throttle body in accordance with a second embodiment of the present invention; Fig. 4 is a perspective view showing a collar in accordance with the second embodiment of the present invention; Fig. 5 is an enlarged cross-sectional view showing an essential part of the molding process of a housing, explaining a manufacturing method for a throttle body in accordance with a third embodiment of the present invention; Fig. 6 is a cross-sectional view showing a molding process of a housing, explaining a manufacturing method for a throttle body in accordance with a fourth embodiment of the present invention; and Fig. 7 is a cross-sectional view showing the throttle body in accordance with the fourth embodiment of the present invention. DESCRIPTION OF PREFERRED EMBODIMENTS Hereinafter, a plurality of embodiments of the present invention will be explained with reference to attached drawings. First Embodiment Fig. 2 shows a throttle body of an engine in accordance with a first embodiment of the present invention. A throttle body 10 shown in Fig. 2 is attached to an inlet side of a surge tank (not shown) constituting part of an intake passage of an engine. The throttle body 10 comprises a housing 11, a throttle shaft 13, and a throttle valve 14 serving as a valve member adjusting an intake air amount of the engine. The housing 11 consists of a cylindrical portion 20 and retaining portions 31 and 32 which are integrally formed as a resin product through resin molding with a shaping die. The cylindrical portion 20 has a smooth and simplified cylindrical shape with no protrusions or recessed portions formed on the inner cylindrical surface thereof. An inside hollow space of the cylindrical portion 20 defines an intake passage 12. The throttle valve 14 adjusts an opening degree of the intake passage 12. The throttle valve 14 is fixed to the throttle shaft 13 by means of screws 15. The throttle shaft 13 is rotatably supported in the throttle body 10. More specifically, the cylindrical portion 20 has through-holes 21 and 22 opened at opposed portions corresponding to the retaining portions 31 and 32. The axial ends of the throttle shaft 13 are rotatably inserted in the through-holes 21 and 22. The clearance between the inner cylindrical portion 20 and the throttle valve 14 must be accurately maintained. To this end, roundness and inner diameter of the cylindrical portion 20 are very accurately administrated in the manufacturing process of the cylindrical portion 20. The throttle shaft 13 has a first large-diameter portion 16, a smaller-diameter portion 17, and a second large-diameter portion 18. The first large-diameter portion 16 is provided at one end of the throttle shaft 13 and supported by a later-described bearing member 41. The smaller-diameter portion 17 is interposed between the first large-diameter portion 16 and the second large-diameter portion 16. The throttle valve 14 is securely fixed to the smaller-diameter portion 17 by means of the screws 15. The second large-diameter portion 18 is connected to the smaller-diameter portion 17 at one end and connected to a lever 19 at the other end. A later-described bearing member 42 supports the second large-diameter portion 18. The outer diameter of the first large-diameter portion 16 is substantially the same as that of the second large-diameter portion 18. The smaller-diameter portion 17 has an outer diameter smaller than those of the larger-diameter portions 16 and 18. In other words, the throttle shaft 13 has a smaller outer diameter at a portion accommodated in the cylindrical portion 20 and a larger outer diameter at another portions accommodated in the retaining portions 31 and 32. The lever 19, connected to the second large-diameter portion 18, is provided at the other end of the throttle shaft 13. The lever 19 is connected to one end of a cable (not shown). The other end of the lever 19 is connected to an accelerator pedal (not shown). Each of the retaining portions 31 and 32 protrudes from the outer surface of the cylindrical portion 20 in the radial outward direction. The retaining portions 31 and 32 have bores 33 and 34 formed therein. The bearings members 41 and 42, supporting the axial ends of the throttle shaft 13, are placed in the bores 33 and 34, respectively. The bores 33 and 34 are continuous or communicate with the through-holes 21 and 22, respectively. The bearing member 41 is a sleeve bearing held by the inside wall of the bore 33 for rotatably supporting the first large-diameter portion 16 of the throttle shaft 13. The bearing member 42 is constituted by an anti-friction bearing 44, such as a ball bearing or a needle bearing, held by the inside wall of the bore 34 for rotatably supporting the second large-diameter portion 18 of the throttle shaft 13. Next, a manufacturing method of the throttle body 10 will be explained with reference to Figs. 1 and 2. 1: Prior to the molding operation of the housing 11, a worker inserts a correcting pin 50 into the bearing members 41 and 42 as shown in Fig. 1. Then, the worker places an integrated assembly of the correcting pin 50 and the bearing members 41 and 42 to a predetermined position in a molding space of a resin molding die 100. Alternatively, it is possible that the worker places the correcting pin 50 and the bearing members 41 and 42 separately in the molding space of the resin molding die 100. In this case, the worker first places the bearing members 41 and 42 in position, and next inserts the correcting pin 50 into the bearing members 41 and 42 placed in the molding space of the resin molding die 100. Thereafter, the cylindrical portion 20, the retaining portions 31 and 32 are molded together into an integrated unit. The correcting pin 50, serving as a correcting shaft member, has a uniform outer diameter and entirely extends in the axial direction from the first large-diameter portion 16 to the second large-diameter portion 18 as shown in Fig. 2. Accordingly, the outer diameter of the correcting pin 50 is larger than that of the smaller-diameter portion 17 of the throttle shaft 13. 2: After finishing the molding operation of the housing 11, the worker extracts the correcting pin 50 from the bearing members 41 and 42 and then press fits the oil sealing (not shown) into the bores 33 and 34 of the retaining portions 31 and 32. 3: Thereafter, the worker inserts the throttle shaft 13 into the through-holes 21 and 22 of the cylindrical portion 20 so that the first large-diameter portion 16 and the second large-diameter portion 18 of the throttle shaft 13 are supported by the bearing members 41 and 42, respectively. Then, the worker engages the throttle valve 14 with the throttle shaft 13 and fixes them by means of the screws 15. Next, an operation of the throttle body 10 manufactured through the above-described steps 1 to 3 will be explained. When a driver depresses the accelerator pedal, the cable shifts by an amount corresponding to a depression amount of the accelerator pedal. The lever 19 and the throttle shaft 13 rotate together in response to the shift movement of the cable. The throttle valve 14 rotates correspondingly with the same rotational angle as that of the throttle shaft 13. Intake air corresponding to the opening degree of the throttle valve 14 flows in the intake passage 12 and is introduced into a cylinder of the engine due to pumping function of an engine piston. As described above, the throttle shaft 13 has a smaller outer diameter at the portion accommodated in the cylindrical portion 20 and a larger outer diameter at another portions accommodated in the retaining portions 31 and 32. Thus, it is possible to eliminate frictional contact between the throttle shaft 13 and the resinous or resin-made housing 11. The throttle shaft 13 smoothly rotates without causing frictional loss. Accordingly, the opening degree of the throttle valve 14 can be controlled properly. Adjustment of air flow amount in the intake passage 12 can be performed adequately. Furthermore, the bearing member 42 is constituted by an anti-friction bearing 44. This enhances the effect of preventing the throttle valve 14 from freezing due to icing phenomenon or from sticking due to accumulation of deposition, compared with a case where both of the bearing members 41 and 42 are constituted by the sleeve bearing. According to the above-described first embodiment of the present invention, the correcting pin 50 is inserted into the bearing members 41 and 42. Then, the cylindrical portion 20 and the retaining portions 31 and 32 are integrally molded by a resin material. After finishing the molding operation, the correcting pin 50 is extracted from the bearing members 41 and 42. Then, the throttle shaft 13 is inserted into the bearing members 41 and 42. Finally, the throttle valve 14 is fixed to the throttle shaft 13. Performing the resin molding operation by using the correcting pin 50 temporarily inserted into the bearing members 41 and 42 is advantageous in that the bearing members 41 and 42 are accurately held in the retaining portions 31 and 32 so that the condition the axial center of the bearing member 41 agrees with the axial center of the bearing member 42 throughout the molding operation. Accordingly, it becomes possible to accurately equalize the axial centers of the bearing members supporting the both ends of the throttle shaft 13. If the axial centers of the bearing members 41 and 42 disagree with each other, the throttle shaft 13 will be subjected to a large rotational torque caused by this disagreement. The increased rotational torque induces a drive loss of a motor or the like which drives the throttle shaft 13. Furthermore, according to the first embodiment, the cylindrical portion 20 and the retaining portions 31 and 32 are integrally molded. If the cylindrical portion 20 is formed separately from the retaining portions 31 and 32, a step of connecting the cylindrical portion 20 to the retaining portions 31 and 32 is additionally required. Thus, the first embodiment provides an excellent manufacturing method capable of reducing the total number of manufacturing steps of the throttle body 10. The manufacturing process becomes easy and the manufacturing cost reduces. Second Embodiment Figs. 3 and 4 cooperatively show a second embodiment of the present invention. The second embodiment differs from the first embodiment in that a cover member is provided to cover an axial inner end and a cylindrical side surface of the anti-friction bearing 44 shown in Fig. 1. The components identical with those disclosed in the first embodiment are denoted by the same reference numerals. According to the second embodiment, prior to the molding operation of the housing 11, the worker attaches a collar 60 to the anti-friction bearing 44 so that the axial inner end and the cylindrical side wall of the anti-friction bearing 44 are covered by the collar 60 as shown in Fig. 3. Then, the worker inserts the correcting pin 50 into the bearing member 42 and the collar 60. Subsequently, the worker integrally molds the housing 11. The collar 60, serving as a covering member, has a cylindrical shape with a side wall 61 and a cylindrical wall 62 as shown in Fig. 4. The side wall 61 has an circular opening 65 whose inner diameter is substantially identical with or slightly larger than the outer diameter of the correcting pin 50. Accordingly, the side wall 61 covers the axial inner end of the bearing 44. The cylindrical wall 62 has grooves 63 formed on an outer surface thereof which serve as knurling capable of preventing the bearing 44 from rotating in the resin during the molding operation. In other words, the collar 60 has a locking means for preventing the rotation of the bearing. The cylindrical wall 62 covers a cylindrical side surface of the bearing 44. After finishing the molding operation of the housing 11, the worker performs the same steps as the above-described steps 2 and 3 explained in the first embodiment, thereby manufacturing the engine throttle body. According to the second embodiment, the axial inner end of the bearing 44 is covered by the side wall 61 of the collar 60 before starting the molding operation. Thus, it becomes possible to conceal the rotational portion of the bearing 44 against the resin material so as to assure smooth rotation of the bearing 44. According to the second embodiment, the cylindrical side surface of the bearing 44 is covered by the cylindrical wall 62 of the collar 60 before starting the molding operation. Thus, it becomes possible to conceal the rotational portion of the bearing 44 against the resin material so as to assure smooth rotation of the bearing 44. Furthermore, according to the second embodiment, the knurling is provided on the outer surface of the cylindrical wall 62 of the collar 60 so as to prevent the bearing 44 from rotating in the resin during the molding operation. Thus, the bearing 44 does not shift in the shaft thrust direction. Third Embodiment Fig. 5 shows a third embodiment of the present invention. The third embodiment differs from the second embodiment in that the collar 60 shown in Fig. 3 is modified so as to cover only the axial inner end of the anti-friction bearing 44. The components identical with those disclosed in the second embodiment are denoted by the same reference numerals. According to the third embodiment, prior to the molding operation of the housing 11, the worker attaches a collar 70 to the anti-friction bearing 44 so that the axial inner end of the anti-friction bearing 44 is covered by the collar 70 as shown in Fig. 4. Then, the worker inserts the correcting pin 50 into the bearing member 42 and the collar 70. Subsequently, the worker integrally molds the housing 11 with a gate placed at a side opposed to the bearing 44. The molding pressure acts on the collar 70 so that the collar 70 airtightly contacts with the axial inner end of the bearing 44. Thus, it becomes possible to conceal the rotational portion of the bearing 44 against the resin material. The collar 70, serving as a covering member, has a disk shape with a circular opening 75 whose inner diameter is substantially identical with or slightly larger than the outer diameter of the correcting pin 50. According to the third embodiment, the axial inner end of the bearing 44 is covered by the collar 70 before starting the molding operation. Thus, it becomes possible to conceal the rotational portion of the bearing 44 against the resin material so as to assure smooth rotation of the bearing 44. Fourth Embodiment Figs. 6 and 7 cooperatively show a fourth embodiment of the present invention. The fourth embodiment differs from the first embodiment in that the retaining portion 31 shown in Figs. 1 and 2 is modified into a sealed type. The components identical with those disclosed in the first embodiment are denoted by the same reference numerals. According to the fourth embodiment, as shown in Fig. 7, a retaining portion 131 has a bore 133. The bearing member 41, supporting one axial end of the throttle shaft 13, is placed in the bore 133. The hollow space 133 is continuous or communicates with the through-hole 21. The bore 133 is closed by a sealing portion 45 at an axial outer end. Prior to the molding operation of a housing 111, the worker inserts the correcting pin 50 into the bearing members 41 and 42 as shown in Fig. 6. Then, the worker places an integrated assembly of the correcting pin 50 and the bearing members 41 and 42 to a predetermined position in a molding space of a resin molding die 200. Alternatively, it is possible that the worker first places the bearing members 41 and 42 in position, and next inserts the correcting pin 50 into the bearing members 41 and 42 placed in the molding space of the resin molding die 200. Thereafter, the cylindrical portion 20, the retaining portions 131 and 32 are molded together into an integrated unit. After finishing the molding operation of the housing 111, the worker extracts the correcting pin 50 from the bearing members 41 and 42 in the right direction, i.e., in a predetermined one direction. Then, the worker press fits the oil sealing (not shown) into the bore 34 of the retaining portion 32. Thereafter, the worker performs the same step as the above-described step 3 explained in the first embodiment, thereby manufacturing the engine throttle body 110. According to the above-described forth embodiment, the correcting pin 50 is extracted from the bearing members 41 and 42 in the predetermined one direction opposed to the retaining portion 131. Thus, the axial outer end of the retaining portion 131 can be closed by the sealing portion 45. The rotational portion of the throttle shaft 13 or the like is not exposed to the outside of the throttle body. Accordingly, it becomes possible to enhance the airtightness and fluid-tightness of the bearing member. No special plug or the like is required. Therefore, the fourth embodiment provides an excellent manufacturing method capable of simplifying the arrangement, reducing the total number of parts constituting the throttle body, and reducing the manufacturing cost. According to the above-described first and fourth embodiments, one bearing member 41 is constituted by a sleeve bearing and the other bearing member 42 is constituted by the anti-friction bearing 44. However, the present invention is not limited to this combination. It is therefore possible to constitute both of the bearing members 41 and 42 by the same sleeve bearing or by the same anti-friction bearing. Furthermore, according to the first and fourth embodiments, the throttle shaft 13 has a stepped shape consisting of the first large-diameter portion 16, the smaller-diameter portion 17, and the second large-diameter portion 18. However, the present invention is not limited to this configuration. It is therefore possible to configure the throttle shaft 13 so as to extend entirely in the axial direction with a uniform outer diameter.

Claims: A method for manufacturing a throttle body (10, 110) of an internal combustion engine which adjusts an air flow amount in an air passage (12) formed therein, said throttle body (10, 110) comprising a throttle shaft (13), bearing members (41, 42) rotatably supporting said throttle shaft (13), a valve member (14) for controlling an opening degree of said air passage (12), said valve member (14) being fixed to said throttle shaft (13), and a housing (11, 111) having a cylindrical portion (20) defining said air passage (12) and retaining portions (31, 32, 131) supporting said bearing members (41, 42), said method comprising a step of placing said bearing members (41, 42) in a molding space of a molding die (100, 200), thereafter, a step of molding integrally in said molding space said cylindrical portion (20) and said retaining portions (31, 32, 132) of said housing (11, 111) by a resin material, after said molding step, a step of inserting said throttle shaft (13) into said bearing members (41, 42), and a step of fixing said valve member (14) to said throttle shaft (13), said method being characterized by a step of inserting a correcting shaft member (50) into said bearing members (41, 42) before said molding step, and, after finishing said molding step and prior to the step of inserting said throttle shaft (13), a step of extracting said correcting shaft member (50) from said bearing members (41, 42). The method in accordance with claim 1, wherein one of said bearing member (41, 42) is constituted by an anti-friction bearing (44) and, in said molding step, an axial end of said anti-friction bearing (44) is covered by a covering member (60, 70). The method in accordance with claim 2, wherein said covering member (60) comprises a cylindrical wall (62) covering a cylindrical side surface of said anti-friction bearing (44) and a locking means (63) provided on said cylindrical wall for preventing the rotation of said anti-friction bearing (44). The method in accordance with any one of claims 1, 2 and 3, wherein said throttle shaft (13) has a smaller outer diameter at a portion (17) accommodated in said cylindrical portion (20) of said housing (11, 111) and a larger outer diameter at another portions (16, 18) accommodated in said retaining portions (31, 32). The method in accordance with any one of claims 1 to 5, wherein said correcting shaft member (50) is extracted in a predetermined direction in said extracting step of said correcting shaft member (50).

Inventors: MIURA YUICHIRO, TORII KATSUYA, MIURA, YUICHIRO, TORII, KATSUYA
Applicants: DENSO CORP, DENSO CORPORATION
Application year: 2001
Main classification: F02D9
IPC codes: F02D9