JP2008106842A - Automatic tensioner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an automatic tensioner which prevents the generation of a crack in bellows for sealing hydraulic oil in a cylinder. <P>SOLUTION: An automatic tensioner stores working fluid in a bottomed cylinder 10, contains a sleeve 12 in the cylinder 10, partitions the inside of the cylinder 10 into a pressure chamber 14 and reservoir chamber 15 by slidably inserting a rod 13 in the sleeve 12, communicates with the pressure chamber 14 and reservoir chamber 15 through the medium of a leak clearance 16 forming a throttle, includes a check valve 18 which allows only a flow of working fluid from the reservoir chamber side to the pressure chamber side in a passage 17 for communicating with the pressure chamber 14 and reservoir chamber 15 and has a return spring 20 for biasing the rod 13 between the cylinder 10 and a spring seat 19 fixed to a protruded part of the rod 13 from the cylinder 10. One end 22 of the bellows 21 is fixed to the cylinder 10. The other end 23 is fixed to the spring seat 19. Hydraulic oil in the cylinder 10 is sealed by the bellows 21, which is formed of a thermoplastic elastomer. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an auto tensioner used for maintaining the tension of a belt for driving an automobile auxiliary machine such as an alternator.

  An auxiliary machine of an automobile, for example, an alternator, a car air conditioner, a water pump, or the like has a rotating shaft connected to a crankshaft of an engine by a belt, and is driven by the engine through the belt. In order to keep the tension of this belt within an appropriate range, generally, a pulley arm that is swingable about a fulcrum shaft, a tension pulley that is rotatably attached to the pulley arm, and a direction in which the tension pulley is pressed against the belt. A tension adjusting device including an auto tensioner that biases the pulley arm is used.

  As an auto tensioner built into this tension adjusting device, hydraulic oil is stored in a bottomed cylinder, a sleeve is provided coaxially with the cylinder, and a rod is inserted into the sleeve so as to be slidable in the axial direction. The inside of the cylinder is divided into a pressure chamber and a reservoir chamber, a spring seat is fixed to the protruding portion of the rod from the cylinder, and the rod is urged between the spring seat and the cylinder in the direction of expanding the volume of the pressure chamber. A device provided with a return spring is known (Patent Document 1).

  In this auto tensioner, the rod moves to a position where the urging force of the return spring balances with the belt tension, thereby absorbing the belt tension fluctuation and keeping the belt tension within an appropriate range.

  In addition, the pressure chamber and the reservoir chamber communicate with each other through a first passage that forms a throttle. When the rod moves in a direction in which the volume of the pressure chamber decreases, the hydraulic oil in the pressure chamber passes through the first passage. leak. At this time, since the flow rate of the hydraulic oil is limited by the throttle, the rod moves slowly and absorbs the tension while keeping the belt in a stable state.

  In addition, the auto tensioner is provided with a second passage that allows the pressure chamber and the reservoir chamber to communicate with each other, and a check valve that allows only the flow of hydraulic oil from the reservoir chamber side to the pressure chamber side is provided in the second passage. When the rod moves in the direction in which the volume of the pressure chamber increases, the hydraulic oil flows from the reservoir chamber side to the pressure chamber side through the second passage. Therefore, the rod quickly moves in the direction in which the volume of the pressure chamber expands, and the belt slack is absorbed quickly.

In addition, this auto tensioner has a cylindrical bellows that can expand and contract in the axial direction to seal the hydraulic oil in the cylinder, and one end of the bellows is fixed to the cylinder, and the other end is fixed to the spring seat. Has been.
JP 2006-125448 A

  However, in this auto tensioner, since the bellows is formed of a rubber material such as nitrile rubber, the rigidity of the bellows is low. For this reason, when the rod moves in the direction of expanding the volume of the pressure chamber and the pressure in the reservoir chamber is greatly reduced, a dent is formed in the peak portion of the bellows, an excessive stress is generated, and the bellows may be cracked. It was. Further, when stress was repeatedly generated in the bellows, cracks due to fatigue were likely to occur in the bellows.

  The problem to be solved by the present invention is to provide an auto tensioner in which the bellows sealing the hydraulic oil in the cylinder is less likely to crack.

  In order to solve the above problems, the bellows was formed of a thermoplastic elastomer.

  In the autotensioner according to the present invention, since the bellows is formed of a thermoplastic elastomer, the bellows has higher rigidity than that of the bellows formed of a rubber material. Therefore, even when the rod moves in the direction of expanding the volume of the pressure chamber and the pressure in the reservoir chamber is greatly reduced, the accordion peak portion is not likely to be depressed, and the bellows is not easily cracked. Further, since the bellows has higher durability than the bellows formed of a rubber material, when stress is repeatedly generated in the bellows, fatigue cracks are unlikely to occur in the bellows.

  1 and 2 show a tension adjusting device for a belt 1 for driving an automobile auxiliary machine. This tension adjusting device has a tension pulley 2 that contacts the belt 1 and a pulley arm 3 that rotatably supports the tension pulley 2, and the pulley arm 3 is attached to a fulcrum shaft 5 that is fixed to the engine block 4 shown in FIG. It is supported so that it can swing.

  One end of an auto tensioner 6 according to an embodiment of the present invention is rotatably connected to the pulley arm 3 around a connecting shaft 7, and the other end of the auto tensioner 6 is rotatable to a connecting shaft 8 fixed to the engine block 4. It is connected to. The auto tensioner 6 biases the pulley arm 3 to press the tension pulley 2 against the belt 1.

  As shown in FIG. 2, the auto tensioner 6 has working oil stored in a cylinder 10 having a bottom 9. A sleeve 12 coaxial with the cylinder 10 is press-fitted into a sleeve fitting recess 11 formed in the bottom 9, and a rod 13 is inserted into the sleeve 12 so as to be slidable in the axial direction. Here, the sleeve 12 and the rod 13 partition the inside of the cylinder 10 into a pressure chamber 14 and a reservoir chamber 15.

  Between the sliding surfaces of the sleeve 12 and the rod 13, a leak gap 16 that connects the pressure chamber 14 and the reservoir chamber 15 is formed. The leak gap 16 is very small and constitutes a throttle that restricts the flow rate of the hydraulic oil flowing from the pressure chamber 14 to the reservoir chamber 15.

  In addition, a passage 17 is formed between the sleeve 12 and the fitting surface of the sleeve fitting recess 11 to communicate the pressure chamber 14 and the reservoir chamber 15, and the reservoir chamber 15 side is formed at the end of the passage 17 on the pressure chamber 14 side. A check valve 18 is provided that allows only the flow of hydraulic oil from the pressure chamber 14 to the pressure chamber 14 side.

  A spring seat 19 is fixed to a protruding portion of the rod 13 from the cylinder 10. A return spring 20 is incorporated between the spring seat 19 and the bottom 9 of the cylinder 10, and the return spring 20 urges the rod 13 in the direction of expanding the volume of the pressure chamber 14.

  An annular opening formed between the spring seat 19 and the cylinder 10 is closed by a cylindrical bellows 21 that can be expanded and contracted in the axial direction, whereby the hydraulic oil in the cylinder 10 is sealed. The bellows 21 has one end 22 fitted and fixed to the outer periphery of the cylinder 10 and the other end 23 fitted and fixed to the outer periphery of the spring seat 19. Further, between the end portion 22 and the end portion 23, a ridge portion 24 protruding to the outer diameter side and continuing in the circumferential direction and a valley portion 25 recessed to the inner diameter side and continuing in the circumferential direction are alternately arranged in the axial direction. Is formed.

  The bellows 21 is made of a thermoplastic elastomer. Examples of thermoplastic elastomers include thermoplastic polyester elastomers, thermoplastic polyurethane elastomers, thermoplastic polyamide elastomers, and thermoplastic polyolefin elastomers.

  Next, an operation example of the auto tensioner 6 will be described.

  When the tension of the belt 1 increases, the tension is transmitted to the rod 13 through the tension pulley 2, the pulley arm 3, and the spring seat 19, and the pressure in the pressure chamber 14 increases. When the pressure in the pressure chamber 14 becomes higher than the pressure in the reservoir chamber 15, the hydraulic oil flows through the leak gap 16 from the pressure chamber 14 side to the reservoir chamber 15 side. At this time, since the check valve 18 is closed, the hydraulic oil does not flow through the passage 17. The hydraulic oil thus flows through the leak gap 16, so that the rod 13 moves, and the tension pulley 2 moves to a position where the tension of the belt 1 and the urging force of the return spring 20 are balanced. At this time, since the flow rate of the hydraulic oil flowing through the leak gap 16 is limited and a damper action is generated, the tension pulley 2 moves slowly and absorbs the tension while keeping the belt 1 in a stable state.

  On the other hand, when the tension of the belt 1 decreases, the pressure in the pressure chamber 14 decreases due to the urging force of the return spring 20. When the pressure in the pressure chamber 14 becomes lower than the pressure in the reservoir chamber 15, the check valve 18 is opened, and hydraulic oil flows through the passage 17 from the reservoir chamber 15 side to the pressure chamber 14 side. The rod 13 is moved by the flow of the hydraulic oil, and the tension pulley 2 is moved to a position where the tension of the belt 1 and the biasing force of the return spring 20 are balanced. At this time, the tension pulley 2 moves quickly and absorbs the slack of the belt 1 quickly.

  Here, when the rod 13 moves in the direction of expanding the volume of the pressure chamber 14, the bellows 21 expands and the pressure in the reservoir chamber 15 decreases, so that the ridges 24 of the bellows 21 are likely to be recessed. However, in this auto tensioner 6, since the bellows 21 is formed of a thermoplastic elastomer, the rigidity of the bellows 21 is higher than that of the bellows 21 made of a rubber material such as nitrile rubber. It is hard to produce a dent. Therefore, the bellows 21 is not easily cracked, and the hydraulic oil is less likely to leak.

  Further, when the tension of the belt 1 is periodically increased and decreased and the bellows 21 is repeatedly expanded and contracted, stress is repeatedly generated in the bellows 21 and a state in which cracks due to fatigue are likely to occur. Since the bellows 21 is made of a thermoplastic elastomer, the bellows 21 is more durable than the bellows 21 made of a rubber material such as nitrile rubber, and fatigue cracks are less likely to occur in the bellows 21.

The front view which shows the tension adjustment apparatus incorporating the auto tensioner of embodiment of this invention Sectional view along the line II-II in FIG.

Explanation of symbols

10 cylinder 12 sleeve 13 rod 14 pressure chamber 15 reservoir chamber 16 leak gap 17 passage 18 check valve 19 spring seat 20 return spring 21 bellows 22, 23 end

Claims (1)

  The hydraulic oil is stored in the bottomed cylinder (10), a sleeve (12) is provided in the cylinder (10) coaxially with the cylinder (10), and the rod (13) is axially disposed in the sleeve (12). The cylinder (10) is slidably inserted to partition the pressure chamber (14) and the reservoir chamber (15), and the pressure chamber (14) and the reservoir through a first passage (16) forming a throttle. A second passage (17) is provided for communicating the chamber (15) and the pressure chamber (14) and the reservoir chamber (15), and pressure is applied to the second passage (17) from the reservoir chamber (15) side. A check valve (18) that allows only the flow of hydraulic oil to the chamber (14) side is provided, and a spring seat (19) is fixed to a protruding portion of the rod (13) from the cylinder (10). Between the seat (19) and the cylinder (10), One end (22) of a cylindrical bellows (21) that is provided with a return spring (20) that urges the rod (13) in the direction of enlarging the volume of the force chamber (14) and can be expanded and contracted in the axial direction. Is fixed to the cylinder (10) and the other end (23) is fixed to the spring seat (19), and the hydraulic oil in the cylinder (10) is sealed by the bellows (21). An auto tensioner, wherein the bellows (21) is formed of a thermoplastic elastomer.

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