JP2009008175A - Automatic tensioner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic tensioner capable of discharging air mixed in engine oil from a discharge hole to the outside in a short period of time. <P>SOLUTION: A plunger 15 and a plunger spring 1 are assembled in a cylinder chamber 12 of a housing 11. A serrate female screw 18 is formed on the inner periphery of a rod insertion hole 17 formed in the plunger 15, and a male screw 20 formed on the outer periphery of a screw rod 19 is screwed into the female screw 18. The screw rod 19 is provided with a spring storage hole 23 and an oil passage 24. A return spring 25 is assembled between closed ends of the spring storage hole 23 and the rod insertion hole 17. An air introduction passage 27 in the radial direction penetrating the oil passage 24 from the outer periphery is formed at a rear end of the screw rod 19. When oil is fed by starting of the engine from an oil supply passage 13 of the housing 11 to the oil passage 24, air mixed in the oil is made to flow into the cylinder chamber 12 from the air introduction passage 27 and is discharged to the outside from the discharge hole 28 formed in the rear end of the housing 11. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an auto tensioner that keeps the tension of a timing chain or timing belt for driving a cam shaft constant.

  In general, in a chain transmission that uses a timing chain or timing belt (hereinafter simply referred to as a chain) to transmit the rotation of the crankshaft to the camshaft, the adjustment force of the auto tensioner is applied to the slack side of the chain to increase the chain tension. I try to keep it constant.

As the auto tensioner, the one described in Patent Document 1 is known.
FIG. 7 shows an auto tensioner described in Patent Document 1, in which a plunger 15 is incorporated in a cylinder chamber 12 formed in the housing 11, and a plunger spring 16 that imparts outward protrusion to the plunger 15 is incorporated. A rod insertion hole 17 is formed in the plunger 15, and a sawtooth male screw 20 formed on the outer periphery of the screw rod 19 is screwed into a sawtooth female screw 18 provided on the inner periphery of the opening end of the rod insertion hole 17. A spring accommodating hole 23 that engages and opens at the front end surface of the screw rod 19 and an oil passage 24 that penetrates from the rear end surface to the spring accommodating hole 23 are provided, and the closed end of the spring accommodating hole 23 and the rod insertion hole 17 is provided. A return spring 25 is incorporated between the plunger 15 and the screw rod 19 so as to press in the extending direction. That.

  Further, an oil supply passage 13 communicating with the closed end of the cylinder chamber 12 is provided in the housing 11, a check valve 14 for preventing backflow of oil is provided at the oil outlet portion of the oil supply passage 13, and an oil pump is connected to the oil supply passage 13. The engine oil to be fed is caused to flow from the oil passage 24 into the spring accommodating hole 23, and chained by the engine oil flowing from the rod insertion hole 17 into the cylinder chamber 12 through the screw clearance between the female screw 18 and the male screw 20. Thus, the pushing force applied to the plunger 15 is buffered, and the pushing force is received by the pressure side flank 21 of the female screw 18 and the male screw 20.

  When the chain is slack, the plunger 15 is protruded outward by pressing the plunger spring 16 to absorb the slack of the chain. At this time, when the screw rod 19 is moved together with the plunger 15 and is separated from the check valve 14, the screw rod 19 is moved backward while being rotated by the pressing of the return spring 25, and moved backward to a position where the screw rod 19 contacts the check valve 14. I try to let them.

  In the oil supply type auto tensioner as described above, when the engine is stopped, the engine oil in the housing 11 and the oil supply passage 13 returns to the oil pump side. For this reason, when the engine is restarted, air is sent together with the supply of engine oil. If this air stays in the cylinder chamber 12, the hydraulic damper effect is reduced, and if it takes time to eliminate the air, if tension changes in the chain until the inside of the cylinder chamber 12 is filled with engine oil, The chain will flutter and generate abnormal noise.

  Therefore, in the oil supply type auto tensioner, it is necessary to quickly remove the air fed together with the engine oil from the inside of the cylinder chamber 12 to the outside. To eliminate the air, the cylinder chamber 12 is blocked at the upper outer periphery of the housing 11. An exhaust hole 28 communicating with the end portion is provided, and the protruding direction of the plunger 15 is obliquely downward so that air is smoothly removed from the exhaust hole 28, and the exhaust hole 28 is used as an inclined attachment disposed at the upper part. Is extremely effective.

JP 2001-124159 A

  By the way, in the conventional autotensioner shown in FIG. 7, the engine oil fed into the oil supply passage 13 is 180 from the state where it has once flowed into the closed end of the rod insertion hole 17 of the plunger 15 as indicated by the arrow in FIG. Since the direction is changed and the air flows into the cylinder chamber 12, it takes time to exhaust the air mixed into the engine oil from the exhaust hole 28 to the outside.

  An object of the present invention is to provide an auto tensioner capable of exhausting air mixed in engine oil from the exhaust hole to the outside in a short time.

  In order to solve the above-mentioned problem, in the first invention, an oil supply passage is provided at a closed end of a cylinder chamber formed in the housing, and an oil backflow prevention provided at an oil outlet portion of the oil supply passage is provided. A check valve is press-fitted into the closed end portion of the cylinder chamber, a valve seat in which a cylinder portion is formed on the end surface on the subsequent side in the press-fitting direction, and a check ball that opens and closes a valve hole formed in the valve seat; A retainer that is press-fitted into the cylindrical portion and regulates the opening and closing amount of the check ball, and includes a plunger that is slidable in the cylinder chamber and a plunger spring that imparts outward protrusion to the plunger, A serrated female screw is formed on the inner periphery of the open end of the rod insertion hole extending in the axial direction from the rear end surface of the plunger, and the outer serrated male screw is engaged with the female screw. A direction in which the spring and the rod are extended between the spring receiving hole and the closed end of the rod insertion hole provided with a spring receiving hole opened at the front end surface of the screw rod and an oil passage penetrating from the rear end surface to the spring receiving hole. The housing has a return spring that pushes it into the housing, and the housing has an exhaust hole that penetrates from the upper part of the outer periphery to the closed end of the cylinder chamber. In the auto tensioner, an air introduction path is formed in the rear end portion of the screw rod so as to guide the air mixed into the oil from the oil passage into the closed end portion of the cylinder chamber.

  In the auto tensioner according to the first aspect of the present invention, the air introduction path may be a through-hole penetrating from the outer peripheral surface of the screw rod to the inner peripheral surface, or formed on the rear end surface of the screw rod. It may consist of radial grooves. When the air introduction path is a radial groove, air in the cylinder portion of the valve seat can be surely extracted from the air introduction path into the closed end of the cylinder chamber regardless of the rotational position of the screw rod.

  In the case of an air introduction path composed of a through hole, if the through hole is a single one, when the screw rod rotates and stops, the through hole is arranged at the lower part of the screw rod and the air mixed into the oil is cylinder There are cases where it cannot be introduced into the chamber. For this reason, when the air introduction path is composed of a through hole, a plurality of the through holes are formed, and the plurality of through holes are formed at equal intervals in the circumferential direction of the screw rod. It is preferable that the air vent hole is positioned at the upper position.

Here, if the oil passage is a tapered hole having a small diameter end on the oil outlet side, it is possible to prevent the oil flow from being disturbed due to the collision with the rear end surface of the screw rod and generating bubbles. In addition, the air mixed into the oil becomes difficult to flow to the outlet side of the oil passage due to the throttle effect on the oil outlet side and the inclination of the inner peripheral surface of the oil passage,
Air can be smoothly guided into the air introduction path.

  In order to solve the above problems, in the second invention, an oil supply passage is provided at a closed end portion of a cylinder chamber formed in the housing, and an oil backflow prevention provided at an oil outlet portion of the oil supply passage is provided. A check valve is press-fitted into the closed end portion of the cylinder chamber, a valve seat in which a cylinder portion is formed on the end surface on the subsequent side in the press-fitting direction, and a check ball that opens and closes a valve hole formed in the valve seat; A retainer that is press-fitted into the cylindrical portion and regulates the opening and closing amount of the check ball, and includes a plunger that is slidable in the cylinder chamber and a plunger spring that imparts outward protrusion to the plunger, A serrated female screw is formed on the inner periphery of the open end of the rod insertion hole extending in the axial direction from the rear end surface of the plunger, and the outer serrated male screw is engaged with the female screw. A direction in which the spring and the rod are extended between the spring receiving hole and the closed end of the rod insertion hole provided with a spring receiving hole opened at the front end surface of the screw rod and an oil passage penetrating from the rear end surface to the spring receiving hole. The housing has a return spring that pushes it into the housing, and the housing has an exhaust hole that penetrates from the upper part of the outer periphery to the closed end of the cylinder chamber. In the auto tensioner, an air introduction path is formed in the upper part of the cylinder part of the valve seat so as to guide the air mixed into the oil from the cylinder part into the closed end of the cylinder chamber.

  Here, the air introduction path may be formed of a through hole penetrating from the outer peripheral surface of the cylindrical portion to the inner peripheral surface, or in the radial direction formed at the upper portion of the screw rod contact surface of the cylindrical portion. It may consist of grooves.

  As described above, in the auto tensioner according to the first aspect of the present invention, the air introduction path that guides the air mixed into the oil from the oil passage into the closed end of the cylinder chamber is formed at the rear end of the screw rod. When the engine oil supplied from the passage flows in the oil passage of the screw rod, the air mixed in the engine oil flows into the cylinder chamber from the air introduction passage and is discharged to the outside through the exhaust hole. Can be eliminated in a very short time.

  In the autotensioner according to the second aspect of the present invention, an oil introduction path is formed in the upper part of the cylinder part of the valve seat to guide the air mixed into the oil from the cylinder part into the closed end of the cylinder chamber. When the engine oil supplied from the passage flows through the check valve through the check valve, the air mixed into the engine oil flows into the cylinder chamber from the air introduction path and is discharged outside through the exhaust hole. Air can be eliminated in a very short time.

  Further, since the air introduction path is formed in the cylinder portion of the valve seat, the air in the cylinder portion can be reliably guided from the air introduction path into the closed end portion of the cylinder chamber regardless of the rotational position of the screw rod.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 3. FIG. 1 shows a chain tension adjusting device employing an auto tensioner according to the present invention. As shown, a chain 5 is stretched between a sprocket 2 attached to the end of the crankshaft 1 and a sprocket 4 attached to the end of the camshaft 3.

  A chain guide 6 is provided on one side of the slack side chain 5 a of the chain 5. The chain guide 6 is swingable about a shaft 7, and an auto tensioner 10 for applying an adjustment force to the chain 5 via the chain guide 6 is provided on one side thereof.

  As shown in FIG. 2, the auto tensioner 10 has a housing 11, in which a cylinder chamber 12 and an oil supply passage 13 that opens at the closed end of the cylinder chamber 12 are formed. A check valve 14 is provided at the oil outlet.

  The check valve 14 is press-fitted into the closed end portion of the cylinder chamber 12, and includes a valve seat 14a in which a cylindrical portion 14b is formed on the end surface on the downstream side in the press-fitting direction, and a valve hole 14c formed in the valve seat 14a. A check ball 14d that opens and closes and a retainer 14e that is press-fitted into the cylindrical portion 14b and restricts the opening and closing amount of the check ball 14d. The check valve 14 prevents engine oil (hereinafter simply referred to as oil) fed from the oil pump through the oil supply passage 13 into the housing 11 from flowing back into the oil supply passage 13.

  In the cylinder chamber 12, a plunger 15 and a plunger spring 16 that imparts outward protrusion to the plunger 15 are incorporated. The plunger 15 is formed with a rod insertion hole 17 that opens at the rear end surface. A female screw 18 is provided on the inner periphery of the opening end of the rod insertion hole 17, and a male screw 20 formed on the outer periphery of the screw rod 19 is threadedly engaged with the female screw 18.

  The screw threads of the female screw 18 and the male screw 20 have a sawtooth shape in which the flank angle of the pressure side flank 21 receiving the pushing force when the plunger 15 is pushed is larger than the flank angle of the play side flank 22. A lead angle is provided for the plunger 15 to move outward while rotating by the pressing of the plunger spring 16.

  The flank angle of the pressure side flank 21 is such that when the pushing force applied to the plunger 15 is a dynamic load, the plunger 15 retreats while rotating, and in the case of a static load, the plunger receives the load. The size is set to prevent 15 backward movements.

  The screw rod 19 is provided with a spring accommodation hole 23 that opens at the front end surface, and an oil passage 24 that penetrates from the closed end of the spring accommodation hole 23 to the rear end of the screw rod 19.

  A return spring 25 and a spring seat 26 are assembled between the closed ends of the spring accommodation hole 23 and the rod insertion hole 17, and the return spring 25 urges the plunger 15 and the screw rod 19 in the extending direction.

  As shown in FIGS. 2 and 3, an air introduction path 27 that guides the air in the oil passage 24 into the closed end of the cylinder chamber 12 is formed at the rear end of the screw rod 19. The air introduction path 27 includes a plurality of through holes penetrating from the outer peripheral surface of the rear end portion of the screw rod 19 to the oil passage 24, and the plurality of through holes are formed at equal intervals in the circumferential direction of the screw rod 19. . On the other hand, the housing 11 is provided with an exhaust hole 28 penetrating from the upper outer periphery of the rear end portion to the closed end portion of the cylinder chamber 12.

  The auto tensioner 10 configured as described above is assembled so as to press the chain guide 6 shown in FIG. 1 by the plunger 15 to which the outward projecting property is imparted by the plunger spring 16. At this time, the housing 11 is attached in an inclined manner in which the protruding direction of the plunger 15 is obliquely downward and the exhaust hole 28 is positioned at the upper position.

  In the assembled state of the auto tensioner 10 as described above, the chain 5 vibrates due to the change in the angular velocity during one rotation of the crankshaft 1 or the torque fluctuation of the camshaft 3, and the slack side chain 5a of the chain 5 is slack. When this occurs, the plunger 15 moves outward due to the pressing force of the plunger spring 16 and absorbs the slack of the chain 5.

  At this time, the screw rod 19 moves in the same direction together with the plunger 15, and when the screw rod 19 moves away from the check valve 14, the screw rod 19 is moved backward while rotating by the pressing of the return spring 25, and is moved to the check valve 14. Return to the abutting position.

  Further, since the pressure inside the housing 11 decreases due to the outward movement of the plunger 15 and the backward movement of the screw rod 19, the check valve 14 is opened and the oil supplied to the oil supply passage 13 enters the inside of the housing 11. Inflow.

  On the other hand, when the tension of the chain 5 increases and the plunger 15 is pressed, the pressing force is received by the oil sealed in the cylinder chamber 12 and the rod insertion hole 17 and the spring accommodating hole 23, The plunger 15 is not retracted by being received by the pressure side flank 21 of the male screw 20. When the pressing force is stronger than the elasticity of the plunger spring 16 and the return spring 25, the plunger 15 moves backward while rotating.

  At this time, the check valve 14 closes the oil supply passage 13, and the oil in the rod insertion hole 17 and the spring accommodation hole 23 flows into the cylinder chamber 12 from the screw engaging portion of the female screw 18 and the male screw 20, and in the cylinder chamber 12. The oil flows between the sliding surfaces of the cylinder chamber 12 and the plunger 15 and leaks to the outside, and the plunger 15 is slowly retracted to a position where the elastic forces of the plunger spring 16 and the return spring 25 are balanced with the pressing force. To maintain a constant tension.

  When the engine is stopped, the oil in the housing 11 and the oil supply passage 13 returns to the oil pump side, and the amount of oil in the housing 11 decreases. For this reason, when the engine is restarted, air is sent together with oil from the supply passage 13 into the oil passage 24.

  At this time, since an air introduction path 27 penetrating the oil passage 24 is formed on the outer periphery of the rear end portion of the screw rod 19, when the oil supplied to the oil passage 24 flows through the oil passage 24, the oil The air mixed in the air flows into the cylinder chamber 12 from the air introduction path 27 and is discharged to the outside through the exhaust hole 28.

  In this way, the air mixed into the oil flows into the cylinder chamber 12 from the air introduction path 27 and is directly discharged to the outside through the exhaust hole 28, so that the air can be effectively eliminated and the housing 11 The inside is filled with oil in a short time, and the occurrence of the hydraulic damper is accelerated, so that the generation of noise due to the flapping of the chain 5 can be prevented.

  As shown in the embodiment, a plurality of air introduction passages 27 are formed, and the plurality of air introduction passages 27 are formed at equal intervals in the circumferential direction of the screw rod 19, so that even if the screw rod 19 rotates, there is always one. The two air introduction paths 27 are arranged at the upper position, and the air mixed into the engine oil can be reliably guided from the air introduction path 27 into the cylinder chamber 12.

  In the embodiment shown in FIG. 2, the oil passage 24 has a straight hole, but the shape of the oil passage 24 is not limited to this. For example, as shown in FIG. 4, it is good also as a taper hole which makes an oil exit side a small diameter end.

  When the oil passage 24 is a tapered hole, it is possible to prevent the oil flow from being disturbed by the collision with the rear end surface of the screw rod 19 and generating bubbles. In addition, the air mixed into the oil hardly flows to the outlet side of the oil passage 24 due to the throttle effect on the oil outlet side and the inclination of the inner peripheral surface of the oil passage 24, and the air can be smoothly guided into the air introduction path 27. .

  2 shows that the air introduction path 27 is formed of a through hole. As shown in FIG. 4, a radial groove is formed on the rear end surface of the screw rod 19, and the radial groove is formed as an air introduction path. 27 may be used. When the air introduction path 27 is a radial groove, the air in the cylindrical portion 14b of the valve seat 14a can be surely extracted from the air introduction path 27 into the closed end of the cylinder chamber 12 regardless of the rotational position of the screw rod 19. it can.

  2 and 4, the air introduction path 27 is formed at the rear end of the screw rod 19. However, as shown in FIG. 5, the air introduction path 27 is formed in the cylindrical portion 14b of the valve seat 14a. May be.

  Here, in FIG. 5 (I), a through hole penetrating from the outer peripheral surface of the cylindrical portion 14b to the inner peripheral surface is used as the air introduction path 27, and in FIG. 5 (II), the screw rod 19 of the cylindrical portion 14b contacts. A groove directed in the radial direction is formed in the upper portion of the tapered surface 14 f, and the groove is used as an air introduction path 27.

  As shown in FIG. 5, by forming an air introduction path 27 in the cylinder portion 14 b, air in the cylinder portion 14 b is transferred from the air introduction path 27 into the closed end of the cylinder chamber 12 regardless of the rotational position of the screw rod 19. Since the through hole and the groove can be single, the machining can be easily performed as compared with the case where the air introduction path 27 is machined in the screw rod 19.

  Here, in recent years, motor oil (friction modifier oil, hereinafter referred to as FM oil) containing organic molybdenum has been generally used for automobile engines in order to reduce friction and reduce direct contact of sliding parts. ing. When FM oil is used, a coating with a very low coefficient of friction is generated by the tribochemical reaction in the iron-based sliding part, and the sliding resistance of each part is reduced. it can.

  By the way, in the engine incorporating the auto tensioner shown in the embodiment, when the FM oil is used, a film having a very low friction coefficient is generated on the thread surfaces of the internal thread 18 of the plunger 15 and the external thread 20 of the screw rod 19. There is a risk of being. When a film is formed on the screw surface, the friction coefficient of the screw engaging portion is extremely reduced. Therefore, when the engine is stopped, when the chain 5 is tensioned due to the cam stop position, the plunger 15 is pushed into the cylinder chamber. There is a problem that the chain 5 retreats greatly and the chain 5 vibrates greatly when the engine is restarted, generating abnormal noise.

  In order to prevent the occurrence of such a problem, in FIG. 6, a film 30 that does not react with the oil additive of FM oil is formed on the surface of the male screw 20 in the screw rod 19. Examples of the film 30 include a carbon film, a ceramic film, and a film formed by plating.

  As described above, by forming the film 30 that does not react with the oil additive of FM oil on the surface of the male screw 20 of the screw rod 19, it is possible to suppress a decrease in the frictional resistance of the screw surface due to the tribochemical reaction. For this reason, it is possible to prevent the plunger from being pushed in when the engine is stopped, and it is possible to prevent the chain 5 from vibrating when the engine is restarted.

Front view showing a chain tension adjusting device using an auto tensioner according to the present invention. 1 is a longitudinal front view of the auto tensioner shown in FIG. Sectional view along line III-III in FIG. Sectional view showing another example of screw rod (I) is a sectional view showing a state in which an air introduction path is formed in the cylinder portion of the valve seat, and (II) is a sectional view showing another example of the air introduction path formed in the cylinder portion of the valve seat. Sectional view showing another example of screw rod Sectional view showing a conventional auto tensioner

Explanation of symbols

11 Housing 12 Cylinder chamber 13 Oil supply passage 14 Check valve 14a Valve seat 14b Tube portion 14c Valve hole 14d Check ball 14e Retainer 15 Plunger 16 Plunger spring 17 Rod insertion hole 18 Female screw 19 Screw rod 20 Male screw 23 Spring housing hole 24 Oil passage 25 Return Spring 27 Air introduction path 28 Exhaust hole

Claims (8)

The housing is provided with a cylinder chamber and an oil supply passage that opens at the closed end of the cylinder chamber, and a check valve that prevents backflow of oil is provided at the oil outlet of the oil supply passage. A valve seat that is press-fitted into the closed end portion and has a cylindrical portion formed on the end face on the downstream side in the press-fitting direction, a check ball that opens and closes a valve hole formed in the valve seat, and a press-fit into the cylindrical portion It consists of a retainer that regulates the opening and closing amount of the check ball, and incorporates a plunger slidable in the cylinder chamber and a plunger spring that imparts outward protrusion to the plunger, and opens at the rear end surface of the plunger. A rod insertion hole is formed and formed on the outer periphery of the screw rod on the sawtooth female screw provided on the inner periphery of the open end of the rod insertion hole. A spring receiving hole that engages with the saw-toothed male screw and opens at the front end surface of the screw rod, and an oil passage that penetrates from the rear end surface to the spring receiving hole. The closed end of the spring receiving hole and the rod insertion hole A return spring that presses the plunger and screw rod in the extending direction is installed between them, and the housing is provided with an exhaust hole that penetrates from the upper part of the outer periphery to the closed end of the cylinder chamber. In an auto tensioner that applies adjustment force to the chain or belt with the direction inclined downward,
An auto-tensioner characterized in that an air introduction path is formed at the rear end of the screw rod to guide air mixed into the oil from the oil passage into the closed end of the cylinder chamber.   The auto tensioner according to claim 1, wherein the air introduction path includes a through hole penetrating from the outer peripheral surface of the screw rod to the inner peripheral surface.   The auto tensioner according to claim 2, wherein a plurality of the through holes are provided, and the plurality of through holes are formed at equal intervals in a circumferential direction of the screw rod.   The auto tensioner according to claim 1, wherein the air introduction path includes a radial groove formed in a rear end surface of the screw rod.   The auto tensioner according to any one of claims 1 to 4, wherein the oil passage includes a tapered hole having an oil outlet as a small diameter end. The housing is provided with a cylinder chamber and an oil supply passage that opens at the closed end of the cylinder chamber, and a check valve that prevents backflow of oil is provided at the oil outlet of the oil supply passage. A valve seat that is press-fitted into the closed end portion and has a cylindrical portion formed on the end face on the downstream side in the press-fitting direction, a check ball that opens and closes a valve hole formed in the valve seat, and a press-fit into the cylindrical portion It consists of a retainer that regulates the opening and closing amount of the check ball, and incorporates a plunger slidable in the cylinder chamber and a plunger spring that imparts outward protrusion to the plunger, and opens at the rear end surface of the plunger. A rod insertion hole is formed and formed on the outer periphery of the screw rod on the sawtooth female screw provided on the inner periphery of the open end of the rod insertion hole. A spring receiving hole that engages with the saw-toothed male screw and opens at the front end surface of the screw rod, and an oil passage that penetrates from the rear end surface to the spring receiving hole. The closed end of the spring receiving hole and the rod insertion hole A return spring that presses the plunger and screw rod in the extending direction is installed between them, and the housing is provided with an exhaust hole that penetrates from the upper part of the outer periphery to the closed end of the cylinder chamber. In an auto tensioner that applies adjustment force to the chain or belt with the direction inclined downward,
An auto tensioner, characterized in that an air introduction path is formed in the upper part of the cylinder part of the valve seat to guide the air mixed into the oil from the cylinder part into the closed end of the cylinder chamber.   The auto tensioner according to claim 6, wherein the air introduction path includes a through hole penetrating from the outer peripheral surface of the cylindrical portion to the inner peripheral surface.   The auto tensioner according to claim 6, wherein the air introduction path includes a radial groove formed in an upper portion of a screw rod contact surface of the cylindrical portion.

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