Patent Publication Number: US-2021164419-A1

Title: Limiting cap

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of priority to Japanese Patent Application No. 2019-215042 filed on Nov. 28, 2019, the disclosures of all of which are hereby incorporated by reference in their entireties. 
     FIELD 
     The present disclosure relates to a limiting cap used for adjusting an air-fuel ratio of an air-fuel mixture. 
     BACKGROUND 
     A carburetor of an internal combustion engine includes needle valves for adjusting an air-fuel ratio of an air-fuel mixture. Each needle valve is screwed into a thread groove formed in an adjustment hole which communicates with a flow path in the carburetor. The needle valve is rotated about the axis to adjust a protrusion amount thereof into the flow path, to allow for increasing or decreasing a flow rate of fuel flowing through the flow path. 
     A limiting cap in a cylindrical shape for restricting rotation of the needle valve is fitted onto the needle valve in a related art (see, Japanese Patent No. 2919305, for example). The limiting cap includes a fixing part and an engagement part, and a first splined part is formed in the inner peripheral surface of the engagement part. 
     A flange of the needle valve is press-fitted into the fixing part of the limiting cap, and the first splined part of the limiting cap is engaged with a second splined part of the needle valve. 
     Further, a rising part is formed on the outer peripheral surface of the limiting cap. The rising part is inserted into a recess formed in the outer surface of the carburetor, and movement of the rising part is restricted by the recess. Therefore, rotation of the needle valve is restricted. 
     The limiting cap as described above in a related art includes the fixing part formed on an inner side (closer to the carburetor) and the engagement part formed on an outer side (away from the carburetor), and the fixing part is formed to have a larger diameter than the engagement part. The needle valve assembled into the limiting cap described above includes the second splined part formed on an outer side of the flange. 
     When the limiting cap described above in a related art is fixed onto the needle valve, with the engagement part being located on the outer side and the fixing part being located on the inner side, the fixing part is located away from an operator at the time of fixing operation, to have a problem that it is difficult to assemble the limiting cap onto the needle valve. 
     The present disclosure is intended to solve the problem described above, and to provide a limiting cap which restricts rotation of a needle valve and is easily assembled onto the needle valve. 
     SUMMARY 
     To solve the problem described above, the present disclosure provides a limiting cap assembled onto a needle valve which is screwed into an adjustment hole of a fuel adjuster. The limiting cap includes a main body in a cylindrical shape to be arranged onto a protruding part of the needle valve which protrudes from the adjustment hole, and a rising part, which is inserted into a recess formed in the fuel adjuster for restricting rotation of the needle valve, is formed on an outer peripheral surface of the main body. The main body includes an engagement part on an inner side and a fixing part on an outer side. A first hubbly part formed in an inner peripheral surface of the engagement part is engageable in a circumferential direction of the main body with a second hubbly part formed in an outer peripheral surface of the needle valve. The needle valve is fixed into the fixing part. The fixing part is formed to have a smaller inner diameter than the engagement part. 
     The limiting cap of the present disclosure is assembled onto the needle valve, and the rising part of the main body is inserted into the recess of the fuel adjuster. Movement of the rising part is restricted by the recess. Therefore, rotation of the needle valve is restricted. 
     When the limiting cap of the present disclosure is fixed onto the needle valve, with the engagement part being located on the inner side and the fixing part being located on the outer side. The fixing part is fixed on the outer side of the fuel adjuster at the time of fixing operation, while the limiting cap is easily positioned to engage with the needle valve. Therefore, the limiting cap is easily assembled onto the needle valve. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a carburetor assembled with a limiting cap according to an embodiment of the present disclosure; 
         FIG. 2  is a side cross-sectional view of the limiting cap according to the embodiment of the present disclosure, a needle valve, and a carburetor; 
         FIG. 3  is an exploded perspective view of the limiting caps according to the embodiment of the present disclosure, the needle valves, and the carburetor; 
         FIG. 4  is a front view of the limiting caps according to the embodiment of the present disclosure, the needle valves, and the carburetor; and 
         FIG. 5  is a front view of adjustment holes formed in the carburetor associated with the limiting caps according to the embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     A description will be given in detail of an example of an embodiment of the present disclosure, with reference to the drawings as appropriate. 
     As shown in  FIG. 1 , a limiting cap  10  of the present embodiment is used for a carburetor  1  (intake device) as an example of a fuel adjuster for an internal combustion engine of small outdoor power equipment such as a chain saw and a blower. 
     The carburetor  1  is formed therein with flow paths to generate a fuel-air mixture of fuel and air. The carburetor  1  includes a peripheral wall part  3  cross-sectionally in an elliptical shape protruding from an outer surface of the carburetor  1 . 
     As shown in  FIG. 5 , two adjustment holes  5  are open in an inner region of the peripheral wall part  3  on the outer surface of the carburetor  1 . The adjustment holes  5  are formed side by side. Each adjustment hole  5  is a through hole having a circular cross section and communicates with the flow path through which the fuel flows. A thread groove is formed in the inner peripheral surface of the adjustment hole  5 . 
     In the carburetor  1  of the present embodiment, the adjustment hole  5  formed on the left side in  FIG. 5  is a hole to be used for adjusting an air-fuel ratio of an air-fuel mixture when the output shaft of the internal combustion engine rotates at low speed. Further, the adjustment hole  5  formed on the right side in  FIG. 5  is a hole to be used for adjusting the air-fuel ratio of the air-fuel mixture when the output shaft of the internal combustion engine rotates at high speed. 
     In the present embodiment, structures of the adjustment holes  5  and components assembled to the adjustment holes  5  are the same. Therefore, in the following description, the adjustment hole  5  formed on the left side in  FIG. 5  and each component assembled to the adjustment hole  5  will be described, whereas descriptions of the said adjustment hole  5  formed on the right side in  FIG. 5  and components assembled to the said adjustment hole  5  are omitted. 
     As shown in  FIG. 2 , a needle valve  50  for adjusting the air-fuel ratio of the air-fuel mixture is inserted into the adjustment hole  5 . 
     As shown in  FIG. 3 , the needle valve  50  is a straight member having a circular cross section. A thread groove is formed in the outer peripheral surface of a portion near the inner end (left side in  FIG. 2 ) of the needle valve  50 . As shown in  FIG. 2 , the portion near the inner end of the needle valve  50  is screwed into the thread groove of the adjustment hole  5 . 
     The needle valve  50  is rotated about the axis to increase or decrease an insertion amount of the needle valve  50  into the adjustment hole  5 . Adjusting a protrusion amount of the needle valve  50  into the flow path allows for adjusting the flow rate of the fuel flowing through the flow path. Thus, the air-fuel ratio of the air-fuel mixture is adjusted by the rotation of the needle valve  50  about the axis. 
     A protruding part  51  of the needle valve  50 , which protrudes from the adjustment hole  5  to the outer side of the carburetor  1 , is accommodated in the peripheral wall part  3 . 
     As shown in  FIG. 4 , a groove  56  is formed in the outer end surface of the needle valve  50 , so as to be used for rotating the needle valve  50  about the axis with a tool such as a screwdriver. 
     Note that, in the present embodiment, the groove  56  is formed straight to be engaged with the tip of a straight-head screwdriver, but the tool for rotating the needle valve  50  is not limited thereto. For example, a cross-shaped groove may be formed in a base end surface of the needle valve  50  to correspond to a cross-head screwdriver, or a hexagonal hole may be formed in the base end surface of the needle valve  50  to correspond to a hexagonal-head wrench. 
     As shown in  FIG. 3 , the outer peripheral surface of the protruding part  51  of the needle valve  50  is formed with a second engagement part  52  formed with a second splined (bubbly) part  53 , and a needle valve fixed part  55 . The needle valve fixed part  55  is a part to be press-fitted into a fixing part  15 , which is described below, of the limiting cap  10 . 
     The outer peripheral surface of the second engagement part  52  is applied with knurling (straight knurling) to have the second splined part  53  by knurling over the entire surface thereof. The second splined part  53  is formed with straight grooves extending in the axial direction of the needle valve  50  and is arranged at equal intervals in the circumferential direction of the second engagement part  52 . 
     Note that, in the present embodiment, the second splined part  53  is formed in the second engagement part  52  by knurling, but the forming method is not limited thereto. For example, the second engagement part  52  may be cut, assembled with other components, molded, or the like to form the second splined part  53 . 
     As shown in  FIG. 2 , the needle valve fixed part  55  is continuously formed closer to the outer end of the needle valve  50  than the second engagement part  52 . The outer peripheral surface of the needle valve fixed part  55  is not knurled. The needle valve fixed part  55  is formed to have a smaller outer diameter than the second engagement part  52 , and further, than the minimum outer diameter of the second engagement part  52 . 
     The limiting cap  10  includes a main body  11  in a cylindrical shape fitted onto the protruding part  51  of the needle valve  50 . The main body  11  has the inner end surface and the outer end surface fully opened in a circular shape (see  FIG. 3 ). 
     As shown in  FIG. 3 , the main body  11  includes a first engagement part  12  on the inner side (closer to the carburetor  1 ) and the fixing part  15  on the outer side (away from the carburetor  1 ). The first engagement part  12  and fixing part  15  are separate members, and the outer end of the first engagement part  12  is coupled to the inner end of the fixing part  15 . 
     The first engagement part  12  of the present embodiment is a metal member, and the fixing part  15  is a resin member. Therefore, the first engagement part  12  is harder than the fixing part  15 . 
     The first engagement part  12  and fixing part  15  are integrally molded by insert molding to form a single component. 
     A rising part  16  extending axially is formed on the outer peripheral surface of the main body  11 . The rising part  16  has an axial cross section in a square shape. The rising part  16  extends straight from the inner edge of the first engagement part  12  to the middle in the axial direction of the fixing part  15 . 
     The inner peripheral surface of the first engagement part  12 A has a first splined part  13  formed over the entire surface thereof. The first splined part  13  is formed with straight grooves extending in the axial direction of the main body  11  and arranged at equal intervals in the circumferential direction of the first engagement part  12 . 
     As shown in  FIG. 2 , in a state where the main body  11  is fitted onto the protruding part  51  of the needle valve  50 , the first splined part  13  of the first engagement part  12  is engaged with the second splined part  53  of the needle valve  50  in the circumferential direction of the needle valve  50  and the main body  11 . Accordingly, the main body  11  rotates about the axis in conjunction with the needle valve  50  rotating about the axis. 
     As shown in  FIG. 4 , a recess  6 , into which the rising part  16  of the main body  11  is inserted, is formed in the inner peripheral surface of the peripheral wall part  3  of the carburetor  1 . Note that  FIG. 4  shows a state that a guide member  30  to be described below is removed from the peripheral wall part  3 . 
     As shown in  FIG. 5 , the recess  6  is formed in the inner peripheral surface of the peripheral wall part  3 , and extends straight in a protruding direction of the peripheral wall part  3 . Further, the axial cross section of the recess  6  is curved in an arc shape along the rim of the adjustment hole  5 . The axial cross section of the recess  6  of the present embodiment is curved in an arc subtending a central angle of approximately 90 degrees. 
     As shown in  FIG. 4 , in the present embodiment, a length in the circumferential direction of the recess  6  is set such that the rising part  16  inserted into the recess  6  is rotatable about the axis of the adjustment hole  5  in a range of rotation angle of 90 degrees. Accordingly, the main body  11  is rotatable by a quarter turn about the axis. Further, the needle valve  50  assembled in the main body  11  is also rotatable by a quarter turn about the axis. 
     As shown in  FIG. 2 , the fixing part  15  is a cylindrical part into which the needle valve fixed part  55  of the needle valve  50  is press-fitted. The fixing part  15  is formed to have a smaller inner diameter than the first engagement part  12 . More specifically, the fixing part  15  is formed to have a smaller inner diameter than the minimum inner diameter of the first engagement part  12 . 
     The needle valve fixed part  55  of the needle valve  50  is press-fitted into the fixing part  15  of the main body  11 , and hence the needle valve  50  and the limiting cap  10  are axially fixed. 
     As shown in  FIG. 1 , the guide member  30  is fitted in the peripheral wall part  3 . Guide holes  31 , which communicate with the adjustment holes  5  (see  FIG. 5 ), are formed in the guide member  30 . A guide groove  32  extending axially is formed in the inner peripheral surface of each guide hole  31 . 
     As shown in  FIG. 3 , the guide groove  32  is a part through which the rising part  16  of the main body  11  passes when the main body  11  is inserted into the guide hole  31  from the outer side. 
     In a state where the inner edge of the main body  11  is in contact with the outer surface of the carburetor  1 , the entire rising part  16  is arranged on the inner side (closer to the carburetor  1 ) with respect to the guide groove  32  (see  FIG. 1 ). Accordingly, the main body  11  is rotatable about the axis without engaging with the guide groove  32 . 
     When the main body  11  is inserted into the guide hole  31  from the outer side, orientation about the axis of the main body  11  is adjusted to allow the rising part  16  of the main body  11  to pass through the guide groove  32 . Thus, when the main body  11  is assembled into the guide hole  31 , as shown in  FIG. 4 , the rising part  16  is arranged at one end in the circumferential direction of the axial cross section of the recess  6 . 
     Next, a description is given of a procedure to assemble the guide member  30 , the needle valve  50 , and the limiting cap  10  to the adjustment hole  5  of the carburetor  1 , as shown in  FIG. 2 . 
     At first, the inner end portion of the needle valve  50  is inserted in the adjustment hole  5  to screw the thread groove of the needle valve  50  into the thread groove of the adjustment hole  5 . 
     Then, the needle valve  50  is rotated about the axis to increase or decrease the insertion amount of the needle valve  50  into the adjustment hole  5 . Adjusting the protruding amount of the inner end of the needle valve  50  into the flow path allows for adjusting the air-fuel ratio of the air-fuel mixture. 
     After or before the air-fuel ratio of the air-fuel mixture is properly adjusted, the guide member  30  is fitted into the peripheral wall part  3 , as shown in  FIG. 1 . Then, the main body  11  of the limiting cap  10  is inserted into the guide hole  31  of the guide member  30  from the outer side. At this time, the rising part  16  of the main body  11  is passed through the guide groove  32  of the guide member  30 . 
     As shown in  FIG. 2 , when the main body  11  is moved, the first splined part  13  of the main body  11  is axially moved to mesh with the second splined part  53  of the needle valve  50 . Accordingly, the first engagement part  12  of the main body  11  is circumferentially engaged with the second engagement part  52  of the needle valve  50 . Note that, before the first splined part  13  meshes with the second splined part  53 , the air-fuel ratio of the air-fuel mixture may be adjusted with the needle valve  50 . 
     Further, the needle valve fixed part  55  of the needle valve  50  is press-fitted into the fixing part  15  of the main body  11 , to cause the needle valve  50  and the main body  11  to be fixed axially. 
     Thus, once the limiting cap  10  is assembled on the protruding part  51  of the needle valve  50 , as shown in  FIG. 4 , the rising part  16  of the main body  11  is disposed at one end in the circumferential direction, in the axial cross section, of the recess  6 . 
     The rising part  16  is rotatable clockwise by a quarter turn in  FIG. 4  in the recess  6  from a reference position where the rising part  16  is disposed at the one end in the circumferential direction in the axial cross section of the recess  6 . 
     Thus, the limiting cap  10  and the needle valve  50  are rotatable clockwise by a quarter turn in  FIG. 4  from the reference position where the needle valve  50  has been assembled into the adjustment hole  5  and the air-fuel ratio of the air-fuel mixture has been properly adjusted. 
     In the present embodiment, when the needle valve  50  is rotated clockwise from the reference position in  FIG. 4 , fuel concentration of the air-fuel mixture decreases. 
     The rising part  16  cannot be rotated counterclockwise in  FIG. 4  from the reference position due to the recess  6 , and hence the needle valve  50  cannot be rotated counterclockwise in  FIG. 4  from the reference position. Thus, in the present embodiment, the fuel concentration does not become higher than the air-fuel ratio of the air-fuel mixture at the reference position of the needle valve  50 . 
     As shown in  FIG. 2 , the limiting cap  10  as described above is assembled onto the needle valve  50  which is screwed into the adjustment hole  5  of the carburetor  1  (fuel adjuster). The limiting cap  10  includes the main body  11  in a cylindrical shape to be arranged on the protruding part  51  of the needle valve  50  which protrudes from the adjustment hole  5 . 
     As shown in  FIG. 4 , the rising part  16  is formed on the outer peripheral surface of the main body  11 , which is inserted into the recess  6  formed in the carburetor  1  to restrict the rotation of the limiting cap  10 . 
     As shown in  FIG. 2 , the main body  11  includes the first engagement part  12  on the inner side and the fixing part  15  on the outer side. The first splined part  13  formed in the inner peripheral surface of the first engagement part  12  is engageable in the circumferential direction of the main body  11  with the second splined part  53  formed in the outer peripheral surface of the needle valve  50 . Further, the needle valve fixed part  55  of the needle valve  50  is fixed in the fixing part  15 . The fixed part  15  is formed to have a smaller inner diameter than the first engagement part  12 . Still further, the fixing part  15  may be formed to have a smaller inner diameter than the minimum inner diameter of the first engagement part  12 . 
     As shown in  FIG. 4 , the rising part  16  formed on the main body  11  of the limiting cap  10  of the present embodiment is arranged in the recess  6  of the carburetor  1 . Therefore, the movement of the rising part  16  is restricted by the recess  6 , to restrict the rotation of the needle valve  50 . Accordingly, the fuel concentration of the air-fuel mixture is kept within an appropriate range. 
     The main body  11  of the limiting cap  10  of the present embodiment has the outer end surface fully opened. With this structure, the tip of a general-purpose tool such as a screwdriver is inserted inside the main body  11  from the outer end to engage with the needle valve  50 . Therefore, the air-fuel ratio of the air-fuel mixture is easily adjusted. In other words, the outer end surface of the main body  11  is widely open, requiring no special tool (tool with a thin tip, for example). Further, the tip of the tool is easily inserted accurately into the groove  56  of the needle valve  50 , and hence the groove  56  is less likely to be deformed. 
     As shown in  FIG. 2 , when the limiting cap  10  is fixed onto the needle valve  50 , the limiting cap  10  of the present embodiment includes the first engagement part  12  positioned on the inner side and the fixing part  15  positioned on the outer side. At the time of the fixing operation, the fixing part  15  is fixed on the outer side of the carburetor  1  while the limiting cap  10  is easily engaged with the needle valve (for example, when an operator pushes the limiting cap  10  in a press-fitting operation, if the needle valve fixed part  55  is located closer to the operator, the limiting cap  10  is easily assembled). 
     When the operator pushes the limiting cap  10  onto the needle valve  50 , the fixing part  15  of the limiting cap  10  of the present embodiment is located close to the position where the operator holds and pushes the limiting cap  10  onto the needle valve  50 . Therefore, the press-fitting operation of the limiting cap  10  onto the needle valve  50  is easily performed. 
     As shown in  FIG. 3 , the needle valve  50 , onto which the limiting cap  10  of the present embodiment is fixed, includes the needle valve fixed part  55  on the outer side of the second engagement part  52 , and the needle valve fixed part  55  has a smaller diameter than the second engagement part  52 . 
     The needle valve  50  described above includes the second engagement part  52  having a larger diameter than the needle valve fixed part  55 . Therefore, the second splined part  53  of the second engagement part  52  is easily formed when the second engagement part  52  is processed. For example, when concave parts are to be processed in the surface of the second engagement part  52 , if the needle valve fixed part  55  has a larger diameter than the second engagement part  52 , the concave parts are not easily processed. Especially, when the second engagement part  52  is adjacent to the needle valve fixed part  55 , it is remarkably difficult to process the second engagement part  52 . 
     The needle valve  50 , onto which the limiting cap  10  of the present embodiment is fixed, includes the needle valve fixed part  55  formed on the outer side of the second engagement part  52  with a smaller diameter than the second engagement part  52 . Further, the second splined part  53  is processed by knurling in the second engagement part  52 . 
     The needle valve  50  described above includes the second engagement part  52  having a larger diameter than the needle valve fixed part  55 . Therefore, the second engagement part  52  is easily formed when the second engagement part  52  is processed. 
     The needle valve  50  applied with the limiting cap  10  of the present embodiment includes the needle valve fixed part  55  formed on the outer side of the second engagement part  52 , and the needle valve fixed part  55  has a smaller diameter than the second engagement part  52 . 
     In the manufacturing method of the needle valve  50  described above, firstly, the second splined part  53  is formed in the outer peripheral surface of the shaft member. At this time, the second splined part  53  may be also formed in the outer peripheral surface of a portion to be formed as the needle valve fixed part  55 . Secondly, the outer peripheral surface of the portion to be formed as the needle valve fixed part  55  in the shaft member is machined to have a reduced diameter, to form the needle valve fixed part  55  on the outer side of the second engagement part  52 . With the manufacturing method, the second engagement part  52  and the needle valve fixed part  55  are easily processed in the needle valve  50 . Further, the second engagement part  52  has a larger diameter than the needle valve fixed part  55  so that the second engagement part  52  is easily processed. Accordingly, the second splined part  53  of the second engagement part  52  may be formed after the needle valve fixed part  55  is processed. 
     The first engagement part  12  and the fixing part  15  of the limiting cap  10  of the present embodiment are separate members. With the structure, the first engagement part  12  and the fixing part  15  are made of materials suitable therefor, respectively. 
     The first engagement part  12  is harder than the fixing part  15  of the limiting cap  10  of the present embodiment. 
     With the structure, the first engagement part  12  of the main body  11  is not easily deformed so that the first splined part  13  is securely engaged with the second splined part  53  of the needle valve  50 . 
     Further, the fixing part  15  of the main body  11  is a soft and deformable member suitable for being fixed onto the needle valve  50 , as compared with the first engagement part  12 . For example, the fixing part  15  of the main body  11  is suitable for fixing by press-fitting or snap-fitting. 
     The limiting cap  10  of the present embodiment includes the first engagement part  12  made of metal and the fixing part  15  made of resin. Thus, the first engagement part  12  is a member harder than the fixing part  15 . 
     With the structure, the first engagement part  12  of the main body  11  is not easily deformed and is less likely to slip with respect to the second engagement part  52  of the needle valve  50 . Therefore, the first splined part  13  is securely engaged with the second splined part  53  of the needle valve  50 . 
     Further, the fixing part  15  of the main body  11  is made of resin which is more flexible than metal. Therefore, the fixing part  15  is easily fixed onto the needle valve fixed part  55  of the needle valve  50 . This prevents the needle valve  50  from being rotated about the axis due to displacement, deformation, or slipping of the engagement parts when the needle valve fixed part  55  is fixed onto the fixing part  15 . This prevents deviation of a reference value of the fuel-air ratio of the fuel-air mixture. Still further, resin is lighter in weight than metal, to contribute to weight reduction of the limiting cap  10 . 
     The first engagement part  12  is integrally molded with the fixing part  15  of the main body  11  by insert molding in the limiting cap  10  of the present embodiment. The integration of the first engagement part  12  with the fixing part  15  as described above improves production efficiency of the carburetor  1  (fuel adjuster) (the number of assembly steps is reduced). 
     The embodiment of the present invention has been described above, but the present invention is not limited thereto and can be appropriately modified within the scope of the present invention. 
     As shown in  FIG. 3 , the first engagement part  12  and the fixing part  15  of the main body  11  of the limiting cap  10  of the present embodiment are separate members, but the entire main body  11  may be made of resin or metal. 
     Further, in the present embodiment, the limiting cap  10  is fixed onto the needle valve  50  by press-fitting, but the fixing method is not limited thereto, and various methods may be used, such as adhesion and snap-fitting which those skilled in the art can think of. 
     As shown in  FIG. 1 , the present embodiment is directed to the limiting cap  10  which is applied to the carburetor  1  (fuel adjuster) of an internal combustion engine of small outdoor power equipment such as a chain saw or a blower, but a device, to which the limiting cap of the present disclosure is applicable, is not limited thereto. 
     The limiting cap  10  of the present embodiment is assembled onto the needle valve  50  for adjusting the flow rate of fuel, but may also be assembled onto a needle valve for adjusting a flow rate of air. 
     REFERENCE NUMERALS 
       1 : carburetor (fuel adjuster),  3 : peripheral wall part,  5 : adjustment hole,  6 : recess,  10 : limiting cap,  11 : main body,  12 : first engagement part,  13 : first splined part,  15 : fixing part,  16 : rising part,  30 : guide member,  31 : guide hole,  32 : guide groove,  50 : needle valve,  51 : protruding part,  52 : second engagement part,  53 : second splined part,  55 : needle valve fixed part,  56 : groove