Patent Publication Number: US-2006000997-A1

Title: Throttle device for internal combustion engine

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
      This application is based upon and claims benefit of priority of Japanese Patent Application No. 2004-193916 filed on Jun. 30, 2004, the content of which is incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a throttle device for controlling an amount of air supplied to an internal combustion engine. A rotational angle of a throttle valve disposed in the throttle body is controlled by a motor which is driven according to operation of an acceleration pedal by a driver. The present invention also relates to a method of manufacturing such a throttle device.  
      2. Description of Related Art  
      A throttle device having a throttle valve driven by an electric motor that is controlled according to operation of an acceleration pedal by a driver has been known hitherto. A throttle body forming the throttle device is made of a resin material, as exemplified in JP-A-11-294203 and JP-A-2000-202866. As shown in  FIG. 4  attached hereto, the resin-made throttle body  101  is molded together with a pair of bearing bushes  103 ,  104  that rotatably support a throttle shaft  102 . The bearing bushes  103 ,  104  are held in shaft-supporting bosses  106 ,  107  of the throttle body  101 . The throttle body  101  includes a cylindrical wall  105  forming an air passage therein.  
      In a molding process of the throttle body  101 , the throttle shaft  102  and the bearing bushes  103 ,  104  are set at predetermined positions in a molding die, and then molten resin is injected into a cavity of the molding die. Then, the molten resin is further pressurized and maintained at that pressure for a while. Then, the molten resin is solidified by cooling the molding die. Thus, the throttle shaft  102  and the bearing bushes  103 ,  104  are molded together with the throttle body  101 .  
      In the conventional throttle device, however, there has been a problem that the throttle shaft  102  does not smoothly rotate. This is because the bearing bushes  103 ,  104  may be deformed by a pressure of injection molding if the bearing bushes  103 ,  104  are not sufficiently strong, compared with the pressure of injection molding. The pair of bearing bushes  103 ,  104  may not be maintained at a coaxial relation due to shrinkage of the resin material after the injection molding. In addition, there has been a possibility that molten resin inters into a small gap between the throttle shaft  102  and the bearing bushes  103 ,  104  in the molding process. If this happens, smooth rotation of the throttle shaft  102  is prevented. In the case where an oil-impregnated sintered metal is used as the bearing bushes  103 ,  104 , the impregnated oil may be permeated into the molten resin in the molding process. This results in decrease in mechanical strength of the resin-made throttle body.  
      DE 10105526 A1 also shows a throttle device in which bearings are directly insert-molded in a throttle body. JP-A-2003-522869 shows a resin throttle body in which a metallic member forming a cylindrical air passage and bearings for supporting a throttle shaft is insert-molded. It is not easy, however, to insert-mold the metallic member having a complex shape.  
     SUMMARY OF THE INVENTION  
      The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide an improved throttle device, in which bearings supporting a throttle shaft are press-fitted in bearing holders after the molding process is completed.  
      The throttle device is used for supplying air into an internal combustion engine in a controlled manner. The throttle device includes a throttle body, a throttle shaft rotatably supported in the throttle body and a throttle valve connected to the throttle shaft. A cylindrical air passage is formed in the throttle body made of a resin material. The throttle valve connected to the throttle shaft is rotated in the air passage, and thereby an amount of air passing through the air passage is controlled.  
      In manufacturing the throttle device, a pair of bearing holders are set in a molding die at predetermined positions in the molding die, and the throttle shaft is positioned in the molding die so that a predetermined space for inserting a bearing is formed between an inner bore of the bearing holder and the throttle shaft. Then, molten resin is injected into the cavity in the molding die, so that the throttle body and the throttle valve connected to the throttle shaft are formed at the same time. After the molten resin is solidified by cooling, the throttle body is taken out of the molding die. Then, each bearing is press-fitted into the inner bore of each bearing holder embedded in the throttle body, so that the throttle shaft is rotatably supported by the pair of bearings.  
      In order to secure coaxial relation between the bearing holders embedded in the throttle body and the throttle shaft, the throttle shaft may be positioned in the molding die at a position to compensate deformation of the throttle body in the molding process. The coaxial relation may be adjusted before press-fitting the bearings into the bearing holders by machining the bearing holders and/or the bearings, if necessary to secure smooth rotation of the throttle shaft.  
      According to the present invention, the bearings are press-fitted into the bearing holders after the molding process is completed. Therefore, deformation of the bearings by the molding pressure is avoided, and the molten resin is prevented from entering into a space between the inner bore of the bearings and the throttle shaft. Accordingly, smooth rotation of the throttle shaft is secured. In addition, the manufacturing process of the throttle device is simplified since the throttle body and the throttle valve connected to the throttle shaft are formed at the same time by injection molding.  
      Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a cross-sectional view showing a throttle device of the present invention;  
       FIG. 2  is a cross-sectional view showing the throttle body, in which bearing holders are embedded and a throttle shaft is positioned in the bearing holders;  
       FIG. 3A  is a cross-sectional view showing a position of a throttle shaft in the throttle body immediately after molding;  
       FIG. 3B  is a cross-sectional view showing a position of the throttle shaft in the throttle body after a molding distortion is generated; and  
       FIG. 4  is a cross-sectional view showing a conventional throttle body in which bearing bushes are embedded. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      A preferred embodiment of the present invention will be described with reference to  FIGS. 1, 2 ,  3 A and  3 B. First, referring to  FIG. 1 , an entire structure of a throttle device according to the present invention will be described. The throttle device is used for supplying air to an internal combustion engine in a controlled manner. The throttle device includes a throttle body  1  made of a thermoplastic resin material, a throttle valve  2  disposed in the throttle body  1 , and a throttle shaft  3  supporting the throttle valve  2  thereon. The throttle shaft  3  is driven by a motor (not shown) which is in turn controlled by operation of an acceleration pedal by a driver. An angular position of the throttle valve  2  is fed-back to an electronic control unit (ECU).  
      An air passage  15  is formed in the throttle body  1 , and the throttle valve  2  connected to the throttle shaft  3  is disposed in the air passage  15 , so that an amount of air flowing through the air passage  15  is controlled according to an angular position of the throttle valve  2 . The throttle shaft  3  is connected to an electric motor via a speed-reduction device and is driven by the motor in a direction for opening the air passage  15 . The throttle shaft  3  is biased by a return spring in a direction to close the air passage  15 . An angular position of the throttle valve  2  is detected by a throttle position sensor, and an electrical signal representing the angular position is fed to the electronic control unit. The electronic control unit drives the motor so that a difference between the signal representing the angular position of the throttle valve  2  and a signal representing an accelerator pedal position becomes minimal.  
      The throttle position sensor is connected to the right side axial end of the throttle shaft  3 , and is composed of a member for generating a magnetic field and a sensor element (such as a Hall element, a Hall IC or a magneto-resistive element) for detecting changes in the magnetic field. The member for generating a magnetic field is composed of permanent magnets  11  and yoke  12  connected to an inner periphery of a valve gear  13  that constitutes the speed-reduction device.  
      The throttle body  1  is made of a thermoplastic resin material, such as polyphenylene sulfide (PPS), polyamide (PA), polypropylene (PP), polyether amide (PEI) and is formed by injection molding. The air passage  15  surrounded by a cylindrical wall  14  is formed in the throttle body  1 . Air cleaned by an air cleaner is fed to the air passage  15  from an upside thereof and fed to each cylinder of an engine through a surge tank or an intake manifold connected to a bottom of the air passage  15 .  
      In the throttle body  1 , a pair of shaft-supporting bosses  16 ,  17  are formed so that their axial direction becomes perpendicular to an axial direction of the air passage  15 . A pair of bearing holders  6 ,  7  are embedded in holes  21 ,  22  formed in the shaft-supporting bosses  16 ,  17 . An outer circumference  19  of the shaft-supporting boss  16  (formed at the right side of the throttle body  1 ) functions as a spring guide for supporting an inner circumference of the return spring. At the right side end of the bearing holder  6 , an oil seal  8  for liquid-tightly closing the opening of the bearing holder  6  is disposed. At the left side end of the bearing holder  7 , a hermetic plug  9  for hermetically closing the opening of the bearing holder  7  is disposed.  
      A gear box  23  for containing the speed-reduction device therein is formed integrally with the cylindrical wall  14  at the right side of the shaft-supporting boss  16 . A stopper for stopping the throttle valve  2  at its fully closed position is formed in the gear box  23 . A stopper for stopping the throttle valve  2  at its fully open position may be formed in the gear box  23 .  
      The throttle shaft  3  is composed of a connecting portion  30  to which the throttle valve  2  made of resin is connected by molding and a pair of end portions supported by a pair of bearings  4 ,  5  press-fitted in the bearing holders  6 ,  7 . The throttle valve  2  is composed of a round disc portion having reinforcing ribs and a cylindrical portion. The cylindrical portion is connected to the throttle shaft  3  by molding. On the outer circumference of the connecting portion  30  of the throttle shaft  3 , knurls are formed so that the cylindrical portion of the throttle valve  2  is firmly connected to the throttle shaft  3 . Alternatively, the connecting portion  30  may be formed in a non-round cross-section having a pair of parallel surfaces to further improve connecting force between the throttle valve  2  and the throttle shaft  3 . The throttle valve  2  rotates in the air passage  15  according to rotation of the throttle shaft  3 , and thereby an amount of air passing through the air passage  15  is controlled.  
      The throttle shaft  3  further includes a pair of flanges  31 ,  32 , each having a diameter larger than that of its end portion supported in the bearing  4 ,  5 . Axial end surfaces of the flanges  31 ,  32  abut the axial ends of the respective bearings  4 ,  5 , and thereby movement of the throttle shaft  3  in the axial direction is restricted.  
      The valve gear  13  constituting the speed-reduction device for transferring a motor torque to the throttle shaft  3  at a reduced speed is connected to the axial end of the throttle shaft  3  (at the right side end in  FIG. 1 ). The valve gear  13  is made of a resin material or a metallic material and has gears  41  formed on its outer flange. The outer periphery  42  of the valve gear  13  functions as a spring guide for supporting an inner diameter of the return spring. A stopper for stopping the throttle valve  2  at its fully closed position is formed on the outer periphery of the valve gear  13 . Another stopper for stopping the throttle valve  2  at its fully opened position may be formed on the outer periphery of the valve gear  13 . Such stoppers may be directly formed on the inner circumference of the air passage  15 .  
      A metallic disc  44  having a hole  43  is connected to the valve gear  13 . When the valve gear  13  is formed by molding, the metallic disc  44  is insert-molded. An end  33  of the throttle shaft  3  is inserted into the hole  43  of the metallic disc  44  and staked to firmly connect the valve gear  13  to the throttle shaft  3 . In order to connect the valve gear  13  to the throttle shaft  3  with a predetermined angular relative position, a pair of parallel surfaces to be coupled to the metallic disc  44  may be formed on the end  33  of the throttle shaft  3 .  
      The bearings  4 ,  5  are made of a metallic material (such as brass, oil-less metal or copper) or a resin material and formed in a cylindrical shape. The bearings  4 ,  5  are press-fitted in the respective bearing holders  6 ,  7 . The inner bores  51 ,  52  of the bearings  4 ,  5  rotatably support both ends of the throttle shaft  3 , and a movement of the throttle shaft  3  in the axial direction is restricted by abutment between axial ends  53 ,  54  of the bearings  4 ,  5  and the flanges  31 ,  32  of the throttle shaft  3 .  
      The bearing holders  6 ,  7 , each having an inner bore  61 ,  62  and an axial inner end  63 ,  64 , are insert-molded in holes  21 ,  22  of the shaft-supporting bosses  16 ,  17 . Thus, the bearing holders  6 ,  7  are embedded in the throttle body  1 . The bearings  4 ,  5  press-fitted in the bearing holders  6 ,  7  abut the axial inner ends  63 ,  64  of the bearing holders  6 ,  7 , and thereby axial positions of the bearings  4 ,  5  are defined. An outer end of the inner bore  61  of the bearing holder  6  is enlarged, and an oil seal  8  is press-fitted in the enlarged portion to liquid-tightly close the outer end of the inner bore  61 . Similarly, an outer end of the inner bore  62  of the bearing holder  7  is enlarged, and a hermetic plug  9  is press-fitted in the enlarged portion to hermetically close the outer end of the inner bore  62 . The hermetic plug  9  not only prevents air leakage from the air passage  15  to the outside but also prevents outside dusts from entering into the air passage  15 .  
      Now, a method of manufacturing the throttle device will be described with reference to  FIGS. 1, 2 ,  3 A and  3 B. A molding die for molding the throttle body  1  by injection molding is composed of a stationary die and a movable die. First, the throttle shaft  3  and the bearing holders  6 ,  7  are placed in the molding die at predetermined respective positions. The throttle shaft  3  is placed in the bearing holders  6 ,  7  so that spaces for the bearings  4 ,  5  to be inserted after the molded throttle body  1  is solidified are secured. As shown in  FIG. 3A , an axis of the throttle shaft  3  and an axis of either one of the bearing holders  6 ,  7  or both are placed to become a little off-centered (non-coaxial), considering a distortion in the molding process. In other words, the throttle shaft  3  and the bearing holders  6 ,  7  are placed in the molding die so that they become co-axial after completion of the injection molding process, as shown in  FIG. 3B .  
      Then, molten resin (such as PPS, PBT resin) is injected into the cavity of the molding die to fill the cavity with the molten resin. Then, the injection pressure of the molten resin is gradually increased to a level higher than an original injection pressure, and the molten resin pressure is kept at the increased level for a while. In this manner, additional resin required due to shrinkage of the resin by cooling the molding die by supplying cooling water to passages in the molding die is fed to the cavity. Thus, the throttle body  1 , in which the bearing holders  6 ,  7  are embedded and the throttle valve  2  is connected to the throttle shaft  3 , is formed as shown in  FIG. 2 .  
      After the molded resin is solidified, the throttle body  1  is taken out of the molding die. Then, the throttle body  1  is further cooled down at a room temperature. At this stage, the throttle shaft  3  is loosely disposed in the bearing holders  6 ,  7  as shown in  FIG. 2 . Then, the bearings  4 ,  5  are press-fitted into the respective inner bores  61 ,  62  of the bearing holders  6 ,  7 . At the same time, both ends of the throttle shaft  3  are supported in the bearings  4 ,  5 . Thus, the throttle shaft  3  is rotatably supported in the throttle body  1 . When the bearings  4 ,  5  are forcibly inserted into the bearing holders  6 ,  7 , the bearing  4  is pushed until its axial end  53  abuts the axial inner end  63  of the bearing holder  6 , and the bearing  5  is pushed until its axial end  54  abuts the axial inner end  64  of the bearing holder  7 . In this manner, both bearings  4 ,  5  are correctly positioned in the throttle body  1  not to move in the axial direction.  
      Then, the hermetic plug  9  is forcibly inserted into the outer opening of the bearing holder  7  (at the left side of  FIG. 1 ). Similarly, the oil seal  8  is inserted into the outer opening of the bearing holder  6  (at the right side).  
      As described above, the pair of bearing holders  6 ,  7  are integrally molded with the throttle body  1 , and the throttle valve  2  is formed and connected to the throttle shaft  3  at the same time. Then, the pair of bearings  4 ,  5  are press-fitted into the bearing holders  6 ,  7  so that the throttle shaft  3  is rotatably supported in the throttle body  1 . Therefore, the throttle body  1  having the throttle valve  2  is manufactured in a simple process, and thereby the throttle device can be manufactured at a low cost.  
      Now, operation of the throttle device will be briefly explained. Upon pressing the accelerator pedal, an electrical signal representing a position of the accelerator pedal is sent to the electronic control unit. The electronic control unit drives the motor so that the motor rotates the throttle shaft  3  by an angle corresponding to the electrical signal representing the position of the accelerator pedal. The throttle shaft  3  is rotated to a direction to open the throttle valve  2  against the biasing force of the return spring.  
      On the other hand, when the accelerator pedal returns to the original position, the throttle shaft  3  is rotated in a direction to close the throttle valve  3  by the biasing force of the return spring. The throttle valve  2  is rotated up to its fully closed position where the stopper members formed on the valve gear  13  and the gear box  23  abut each other. When the throttle valve  2  is at the fully closed position, an amount of air corresponding to an idling speed is supplied to the engine. Alternatively, the throttle shaft  3  may be driven by the motor in the direction to close the throttle valve  2  under the control of the electronic control unit. Thus, the opening degree of the throttle valve  2 , i.e., the amount of air supplied to the engine is controlled according to operation of the acceleration pedal.  
      Advantages of the present invention will be summarized as follows. The bearing holders  6 ,  7  are integrally molded with the throttle body  1  by injection molding, and after the molded throttle body  1  is solidified, the bearings  4 ,  5  are press-fitted in the bearing holders  6 ,  7  to rotatably support the throttle shaft  3 . Therefore, deformation of the bearings  4 ,  5  due to the pressure of the injection molding can be avoided. Further, it is avoided that molten resin enters into a clearance between the throttle shaft  3  and the bearings  4 ,  5  in the molding process. Thus, smooth rotation of the throttle shaft  3  is secured.  
      When the throttle shaft  3  and the bearing holders  6 ,  7  are set in the molding die, they are positioned in the die so that the throttle shaft  3  becomes co-axial with the bearing holders  6 ,  7  after the molding process is completed. In other words, they are positioned in the molding die, taking into consideration a small amount of positional displacement due to resin deformation in and after the molding process. In this manner, the rotational axis of the throttle shaft  3  and the bearing holders  6 ,  7  are kept in a co-axial relation.  
      The bearings  4 ,  5  and/or the inner bore of the bearing holders  6 ,  7  may be machined before press-fitting the bearings  4 ,  5  into the bearing holders  6 ,  7  if it is necessary to further secure the co-axial relation between the bearings  4 ,  5  and the throttle shaft  3 . Clearance between the inner bores  61 ,  62  of the bearing holders  6 ,  7  and the outer circumference of the bearings  4 ,  5  may be a little enlarged to eliminate an adverse affect on the co-axial relation due to deformation of the bearing holders  6 ,  7  by the molding pressure.  
      The bearings  4 ,  5  are press-fitted into the bearing holders  6 ,  7  after the molding process of the throttle body  1  is completed. Therefore, if an oil-impregnated sintered metal is used as the bearings  4 ,  6 , it is avoided that oil permeates into the molten resin to thereby decrease rigidity of the resin.  
      Movement of the throttle shaft  3  in the axial direction is restricted by abutment between the flanges  31 ,  32  and the axial ends  53 ,  54  of the bearings  4 ,  5 . An axial position of the magnetic field (composed of the magnets  11  and yokes  12  connected to the valve gear  13  fixed to the throttle shaft  3 ) relative to the sensor element (carried on a sensor cover to face the magnetic field) is correctly kept. Therefore, the angular position of the throttle valve  2  is correctly detected by the sensor element. Further, the throttle valve  2  can be smoothly rotated in the air passage  15  without contacting the inner wall of the air passage  15  because the throttle shaft  3  is correctly and fixedly positioned in the axial direction.  
      The axial end of the throttle shaft  3  is closed by the hermetic plug  9 , so that the air passage  15  does not communicates with the outside and the outside dusts are prevented from entering into the air passage  15 . An amount of air passing through a gap between the throttle valve  2  and the inner wall of the air passage  15  when the throttle valve  2  is at the fully closed position is kept constant at a predetermined level. Therefore, an idling speed of the engine can be kept at a predetermined speed, and fuel consumption at the idling speed can be minimized.  
      The present invention is not limited to the embodiment described above, but it maybe variously modified. For example, the present invention may be applied to a throttle device that is not driven by an electric motor but directly driven by a wire connected to an accelerator pedal. Though the throttle valve  2  is made of resin and connected to the throttle shaft  3  by molding in the foregoing embodiment, it is also possible to mechanically connect a resin valve or a metallic valve to the throttle shaft  3  with screws or the like. Further, the throttle shaft  3  may be installed in the throttle body  1  after the throttle body  1  having the embedded bearing holders  6 ,  7  is formed by injection molding.  
      The cylindrical wall  14  forming the air passage  15  may be made as a double cylinder structure having a coaxial two cylindrical walls. A compound resin material having a filler material (such as glass fibers, carbon fibers, aramid fibers or boron fibers) may be used as the molding resin. For example, polybutylene telephthalate including 30% of glass fibers (PBTG30) may be used as the molding resin. The throttle body  1  having high strength and high rigidity as well as high heat resistivity can be manufactured by injection molding at a low cost, using a compound resin material.  
      In order to firmly embed the bearing holders  6 ,  7  in the throttle body  1 , knurls, or small depressions and projections, may be formed on the outer circumference of the bearing holders  6 ,  7 . Further, in order to prevent the bearing holders  6 ,  7  from being rotated in the holes  21 ,  22  of the shaft-supporting bosses  16 ,  17 , two parallel surfaces may be formed on the outer circumference of the bearing holders  6 ,  7 . Alternatively, the outer circumference of the bearing holders  6 ,  7  may be shaped in a polygonal surface.  
      While the present invention has been shown and described with reference to the foregoing preferred embodiment, it will be apparent to those skilled in the art that changes in form and detail may be made therein without departing from the scope of the invention as defined in the appended claims.