JPH084850A - Damper device for automatic tensioner - Google Patents

Abstract

PURPOSE:To prevent the performance of a damper device from being deteriorated, by preventing bubbles from entering the lower side of a piston due to the cavitation while securing the extending speed at a low temperature. CONSTITUTION:When the tension of a belt is increased, a piston 19 is lowered in viscous liquid 17 while a check valve 27 is closed. Viscous liquid having viscosity of 10000cSt or less at minus 20 deg.C, and viscosity of 100cSt or less at plus 40 deg.C is used as this viscous liquid 17.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The damper device for an autotensioner according to the present invention is a timing belt for an automobile engine or a belt for driving an auxiliary machine such as an alternator and a compressor (hereinafter, these are simply referred to as "belt"). It is used to suppress the vibration of the belt by incorporating it in an auto tensioner that gives an appropriate tension.

[0002]

2. Description of the Related Art A tension applying device called an auto tensioner is known to apply an appropriate tension to a belt.
The structure and operation of this auto tensioner will be described with reference to FIG. 2, which shows the structure described in Japanese Patent Application No. 4-67543. A base end portion of a swing member 3 is rotatably supported around a fixed shaft 2 provided on a fixed member 1 fixed to the front surface of a cylinder block or the like. A pivot 4 parallel to the fixed shaft 2 is provided at the tip of the swing member 3. A pulley 5 is rotatably supported around the pivot 4, and a belt 6 to which tension is applied to the pulley 5.
Are handed over. A coil portion 8 of a torsion coil spring 7 is arranged around the fixed shaft 2. Further, a pair of locking portions 9a and 9b provided at both ends of the torsion coil spring 7 are locked to the fixed member 1 and the rocking member 3, respectively, so that the rocking member 3 has the pulley. Elasticity is applied in the direction of pressing 5 toward the belt 6.

The fixed arm piece 1 provided on the fixing member 1
0 and the rocking side arm piece 11 provided on the rocking member 3, the damper device 12 which is the object of the present invention is provided so as to be stretched between these arm pieces 10 and 11. . The damper device 12 includes a cylinder tube 13 and a plunger 14. In the case of the structure shown in the figure, the lower portion of the cylinder tube 13 is fitted and fixed to the tip of the fixed arm piece 10, and the plunger 14 is attached to the lower surface of the receiving block 15 fixed to the tip of the swing arm piece 11. Abutting the upper end. In the state shown in FIG. 2, the stopper pin 16 blocks the displacement of the swinging member 3 with respect to the fixed member 1. The stopper pin 16 is pulled out after the automatic tensioner is assembled to the engine, the belt 6 is stretched over the pulley 5.

Japanese Patent Application No. 5-29569 describes an auto tensioner as shown in FIG. This figure 3
In the auto tensioner shown in FIG. 2, the fixing member 1 is omitted from the structure shown in FIG. Then, the damper device 12 is supported at the tip of the swing-side arm piece 11, and the damper device 12 is supported.
A portion of the lower end of the rocking side arm piece 11 that projects from the lower surface of the rocking side arm piece 11 can freely abut against a protrusion (not shown) formed in a fixed portion such as the front surface of the cylinder block of the engine.
The locking portion 9a of the torsion coil spring 7 is locked to the fixed portion.

In the case of an auto tensioner having any structure, the damper device 12 is constructed as shown in FIG. 4 or 5. The cylinder cylinder 13 in which a viscous liquid 17 such as silicon oil is enclosed has a bottomed cylindrical shape with an open upper end and a closed lower end. This cylinder cylinder 13
A piston 19 is fitted in the lower half of the inside of the above so as to be able to move up and down. There is a minute gap between the inner peripheral surface of the cylinder cylinder 13 and the outer peripheral surface of the piston 19. Piston 1 above
The viscous liquid 17 existing on the upper side and the lower side of 9 flows slowly through this minute gap. Also, the piston 19
An urging spring 20 which is a compression coil spring is provided between the lower surface of the piston 1 and the upper surface of the bottom of the cylinder cylinder 13.
9 is biased upward. Further, a base portion 21 of the plunger 14 is fitted in an upper inner half portion of the cylinder cylinder 13 so as to be vertically movable. Inner peripheral surface of cylinder cylinder 13 and base 2
A seal ring 22 is provided between the outer peripheral surface and the outer peripheral surface of No. 1 to maintain liquid-tightness between the both peripheral surfaces. In addition, a plurality of notches 23, 23 are formed on the upper end surface of the piston 19, and through the notches 23, 23, the inner space 24 existing inside the abutting portion of the base 21 and the piston 19 and the minute gap are formed. And communicate with.

On the other hand, the partition wall 2 which constitutes the piston 19
5, a through hole 26 is formed in the central portion of the piston 19.
Constitutes a passage that connects the upper and lower sides of the. The check valve 2 that opens and closes the through hole 26 is provided in the lower portion of the partition wall 25.
7 are provided. The check valve 27 is formed by elastically pressing the ball 29 toward the lower end opening of the through hole 26 by the elastic force of the spring 28, and the piston 19 is displaced upward by the elastic force of the biasing spring 20. It has the function of opening only when.

Further, the damper device 1 of the first example shown in FIG.
In the case of 2, the outer diameter of the front half portion 30 of the plunger 14 is made sufficiently smaller than the inner diameter of the cylinder cylinder 13. The viscous liquid 17 is also injected into the lower half of the upper space 31 between the outer peripheral surface of the first half 30 and the upper inner peripheral surface of the cylinder cylinder 13. And
Communication hole 3 provided in a continuous portion of the base portion 21 and the first half portion 30.
2 and 32, the upper space 31 and the inner space 24
The viscous liquid 17 can freely flow between and. A seal ring 33 is provided between the inner peripheral surface of the upper end portion of the cylinder cylinder 13 and the outer peripheral surface of the front half portion 30 to close the upper end opening portion of the upper space 31.

On the other hand, the damper device 1 of the second example shown in FIG.
In the case of 2, the first half portion 30a has a relatively large diameter, and instead of increasing the internal volume of the first half portion 30a, the communication holes 32, 32 (FIG. 4) through which the inside and the outside of the plunger 14 are passed are omitted. . When the damper device 12 shown in FIG. 5 is incorporated in the auto tensioner shown in FIG. 3, in the example shown in the drawing, the cylinder cylinder 13 is projected from the lower surface of the rocking side arm piece 11 and The end surface can be abutted against the upper surface of a protrusion formed on a fixed portion such as the front surface of the cylinder block of the engine. Incidentally, FIG. 5A shows the contracted state of the damper device, and FIG. 5B shows the expanded state.

The autotensioner of the prior invention constructed as described above by incorporating the damper device 12 constructed as described above is incorporated into an engine as shown in FIG. 6, for example, and is used as a belt for driving a camshaft. Appropriate tension is applied to 6. In the example shown in FIG. 6, the auto tensioner shown in FIG. 2 is shown. However, the auto tensioner shown in FIG. To do. In the use state of the auto tensioner as shown in FIG. 6, the swinging member 3 swings based on the elastic force of the torsion coil spring 7, and the swinging member 3 is rotatable about the pivot shaft 4 at the tip thereof. The pulley 5 supported by is elastically pressed toward the belt 6. By pressing the pulley 5 against the belt 6, the rocking of the rocking member 3 is restricted.
In this state, it is provided between the fixed side arm piece 10 (in the case of the structure of FIG. 2) or the protrusion (in the case of the structure of FIG. 3) formed on the fixed portion such as the cylinder block and the swing side arm piece 11. The damper device 12 is in a state of being stretched between the fixed side arm piece 10 or the protrusion and the swing side arm piece 11 based on the elasticity of the biasing spring 20.

When the belt 6 loosens from this state, the swinging member 3 swings due to the elastic force of the torsion coil spring 7, causing the pulley 5 to follow the movement of the belt 6. At this time, the displacement of the plunger 14 which constitutes the damper device 12 is slightly delayed. Therefore, the tip of the plunger 14 and the lower surface of the receiving block 15 (in the case of the structure shown in FIG. 2), or the lower surface of the cylinder tube 13 and the upper surface of the protrusion (in the structure shown in FIG. 3). Case), separate from each other. Therefore, when the belt 6 is loosened, the damper device 12 does not become a resistance against rotating the swinging member 3 so that the pulley 5 follows the movement of the belt 6. As a result, the pulley 5 can be made to quickly follow the movement of the belt 6, and the tension of the belt 6 can be prevented from decreasing. Due to the elastic force of the biasing spring 20, the damper device 12 extends slightly later than the movement of the swing member 3.

As described above, when the damper device 12 extends due to the elasticity of the biasing spring 20, the check valve 27 opens. That is, the ball 29 descends against the elasticity of the spring 28 and opens the lower end opening of the through hole 26 formed in the partition wall 25. As a result, the viscous liquid 1 from the upper side to the lower side of the partition wall 25
7 is smoothly moved, the piston 19 and the plunger 14 are moved up relatively quickly, and after a very short time, the damper device 12 causes the fixed side arm piece 10 or the protrusion and the swing side arm to move. Stretch between the pieces 11.

On the contrary, when the tension of the belt 6 increases, the swing member 3 tends to rotate against the elastic force of the torsion coil spring 7. In this state, the swing-side arm piece 11 presses the damper device 12 in the compression direction. Therefore, in this case, in order to rotate the swinging member 3, the plunger 14 and the piston 19 must be pushed into the cylinder cylinder 13 against the elastic force of the biasing spring 20. At this time, since the check valve 27 remains closed, the viscous liquid 17 present on the lower side of the piston 19 is moved to the upper side of the piston 19 in order to lower the piston 19. It must be performed through a minute gap existing between the inner peripheral surface of the cylinder 13 and the outer peripheral surface of the piston 19. Since the amount of the viscous liquid 17 flowing through the minute gap is limited, the piston 19 and the plunger 14 are displaced only slowly. As a result, the displacement of the pulley 5 supported by the swinging member 3 is only slowly performed by the action of the damper device 12, and the belt 6 moves the pulley 5
The vibration of the belt 6 does not grow because it is suppressed by. In FIG. 6, reference numeral 42 is a drive pulley which is rotationally driven by the crankshaft of the engine, 43 is a driven pulley which is fixed to the end of the camshaft, and 44 is a guide pulley which guides the belt 6.

As a damper device that can be incorporated in the above-mentioned auto tensioner, in addition to the structure shown in FIGS. 4 to 5, the structure shown in FIG.
It is conventionally known as described in Japanese Patent No. 41. In the case of the structure shown in FIG. 7, the cylinder liner 35 is fitted in the cylinder case 34 to form the cylinder cylinder 13. The lower end of the rod-shaped plunger 14 is connected to the piston 19 slidably fitted inside the cylinder liner 35. Further, the lower surface of the upper retaining ring 36 engaged with the middle portion of the plunger 14 and the lower retaining ring 3 engaged with the upper edge of the cylinder liner 35.
7, a compression spring 38 is provided. Therefore, the plunger 14 is provided with the urging spring 2 provided below the check valve 27.
Not only the elastic force of 0 but also the elastic force in the ascending direction is given by the compression spring 38. The action itself for suppressing the growth of the vibration of the belt is almost the same as the structure shown in FIGS. In addition, although not shown in the drawing, the actual development 60-
Japanese Patent No. 182553 also describes a similar structure.

[0014]

However, in the case of the damper device for an autotensioner which is constructed as described above and operates as described above in a state of being incorporated in the autotensioner,
The desired performance may not always be obtained. this is,
This is because the viscous liquid 17 that becomes a resistance against the movement of the piston 19 that constitutes the damper device 12 is required to have opposite characteristics.

When the tension of the belt 6 (FIGS. 2 to 3) suddenly rises, the damper device 12 contracts the belt 6 and shortens its overall length. At this time, the damper device 12 is reduced in length by a predetermined length dimension. The so-called leakdown time required for a predetermined amount of viscous liquid 17 to flow from the lower side to the upper side of the piston 19 in order to contract is the piston 19 that constitutes the damper device 12.
Is greatly influenced by the size of the minute gap between the outer peripheral surface of the cylinder and the inner peripheral surface of the cylinder tube 13 (the cylinder liner 35 in the structure of FIG. 7).

For example, the axial length dimension of the portion of the outer peripheral surface of the piston 19 facing the inner peripheral surface of the cylinder cylinder 13 is L.
(Mm) and the outer diameter of the piston 19 in this part is D
(Mm) and the viscosity coefficient of viscous liquid 17 is μ (kgf · s / mm
² ), the thickness of the minute gap in the state where the cylinder cylinder 13 and the piston 19 are not eccentric is ε (mm), and the pressure in the space below the piston 19 due to the increase in the tension of the belt 1 is P (Kgf / mm ² ) and the atmospheric pressure is P ₀ (1 × 1
0 ^-2 kgf / mm ²⁾ and then, when the eccentric coefficient and K (the cylinder barrel 13 the piston 19 is in the case when concentric and K = 1, the most eccentric was K = 2.5), the leak down The time T (sec / mm) is expressed by the following equation. T = {24 μ · L · D} / {K · ε ³ (P−P ₀ ) · 1
0 ⁴ }

As is clear from this equation, the leakdown time T is proportional to the viscosity coefficient μ of the viscous liquid 17, and the larger the viscosity coefficient μ, the longer the leakdown time T.
In the end, the effect of preventing the vibration of the belt 6 becomes large.

For this reason, conventionally, as the viscous liquid 17, silicon oil or the like having a large viscosity coefficient μ and a high viscosity index (the degree to which the viscosity changes with temperature is small) has been used. However, the viscous liquid 17 having a high viscosity coefficient μ
When flows between the upper side and the lower side of the piston 19, cavitation is likely to occur during the flow. And
When air bubbles generated as a result of cavitation accumulate below the piston 19, the piston 19 can be moved up and down by the elastic deformation of the gas even when the check valve 27 is closed, and the effect of preventing the vibration of the belt 6 can be obtained. Be damaged. As a result, for example, when the belt 6 is a timing belt for driving a camshaft, the so-called tooth jump where the meshing position between the teeth formed on the inner peripheral surface of the belt 6 and the teeth formed on the outer peripheral surface of the pulley is displaced. May occur.

In order to eliminate such inconvenience, conventionally, the viscous liquid 17 is defoamed by vacuuming and then injected into the cylinder cylinder 13. By using the viscous liquid 17 that has been degassed in advance as described above, it is possible to prevent the occurrence of cavitation associated with the above inconvenience, but equipment for evacuation is required and the manufacturing process of the damper device 12 becomes complicated, Since it causes a high cost, improvement is desired. The damper device for an automatic tensioner of the present invention was invented in view of such circumstances.

[0020]

DISCLOSURE OF THE INVENTION A damper device for an autotensioner according to the present invention comprises a cylinder cylinder containing a viscous liquid therein, and a piston fitted inside the cylinder cylinder so as to be displaceable axially. An urging spring that is provided between the piston and the cylinder cylinder and urges the piston in one direction, and the amount of protrusion from the cylinder cylinder that accompanies the displacement of the piston based on the elastic force of the urging spring. It is provided with an increasing plunger, a passage that connects both axial end surfaces of the piston, and a check valve that opens and closes the passage. The check valve has a function of opening only when the piston is displaced based on the elastic force of the biasing spring.

Particularly, in the damper device for an automatic tensioner of the present invention, the viscosity of the viscous liquid is 1 at -20 ° C.
It is 0000 cSt or less and 100 cSt or less at 40 ° C.

[0022]

The action of the damper device for an autotensioner of the present invention constructed as described above when the displacement of the swinging member supporting the pulley is limited in order to suppress the vibration of the belt in the state of being incorporated in the autotensioner. The structure itself is the same as that of the damper device incorporated in the autotensioner of the previous invention or the conventional damper device described above.

In particular, in the damper device for an autotensioner of the present invention, since the viscosity of the viscous liquid is lowered to some extent, cavitation is less likely to occur in the viscous liquid, and the damper is generated by the generation of bubbles. It is possible to prevent the performance of the device from deteriorating. The viscosity of the viscous liquid is set to 10,000 cSt or less at −20 ° C. in order to secure the extension speed of the damper device to some extent even at a low temperature. Again 4
It is necessary to set it to 100 cSt or less at 0 ° C. in order to make it difficult for cavitation to occur after the temperature rises.

Further, in order to secure (longen) the leak down time to some extent or more, the viscosity of the viscous liquid is preferably 10 cSt or more at 40 ° C. The viscosity at -20 ° C is
Since it always exceeds the viscosity at 40 ° C., it is not necessary to regulate it.

[0025]

1 is a longitudinal sectional view showing an embodiment of the present invention, in which the left half portion shows the most contracted state and the right half portion shows the most extended state. A viscous liquid 17 is enclosed in a cylinder cylinder 13 having a bottomed cylindrical shape with an open upper end, and a piston 19 is vertically movable. And
A biasing spring 20 is provided between the lower surface of the piston 19 and the upper surface of the bottom portion of the cylinder tube 13 to give the piston 19 upward resilience. Also, the piston 19
A plunger 14a is provided on the upper side of the.

The viscosity of the viscous liquid 17 is 1 at -20.degree.
0000 cSt or less, 10 cSt or more at 40 ° C., 10
It is less than 0 cSt. Viscous liquid 17 having such viscosity
For example, highly refined mineral oil can be used.

Further, the cylinder cylinder 1 of the plunger 14a.
The amount of protrusion from 3 increases as the piston 19 rises due to the elastic force of the biasing spring 20. Further, a through hole 26 is formed in the central portion of the partition wall 25 of the piston 19 so that the upper side and the lower side of the piston 19 (both axial end faces).
It is a passage that communicates. Further, a check valve 27 including a spring 28 and a ball 29 is provided on the lower side of the partition wall 25. The check valve 27 opens only when the piston 19 rises due to the elastic force of the biasing spring 20.

In the lower half of the plunger 14a,
Cylindrical portion 39 that is in sliding contact with the inner peripheral surface of the cylinder tube 13
A rod-shaped portion 40 having an outer diameter dimension sufficiently smaller than the inner diameter dimension of the cylinder cylinder 13 is formed in the upper half portion. The rod-shaped portion 40 is a solid body unlike the prior invention structure shown in FIG. Further, communication holes 32, 32 are provided in a continuous portion of the cylindrical portion 39 and the rod-shaped portion 40 to communicate the upper space 31 and the inner space 24.

Further, in the case of the damper device 12 of this embodiment, the difference (= R ₁₃ -D ₁₉ ) between the inner diameter dimension R ₁₃ of the cylinder tube ₁₃ and the outer diameter dimension D ₁₉ of the piston 19 is desired. Accurately finished as expected. For example, this difference is 40 ± 2μ
When the cylinder cylinder 13 and the piston 19 are concentric with each other, the thickness dimension ε of the minute gap existing between these peripheral surfaces is about 20 ± 1 μm. Therefore, when assembling the damper device 12 of this embodiment, first, the inner diameter dimension R ₁₃ of the cylinder cylinder ₁₃ and the outer diameter dimension D _{19 of the} piston 19 are measured. Then, the cylinder barrel 13 and the piston 19 having the inner diameter R ₁₃ is a predetermined size (40 ± 2 [mu] m) only larger such inner diameter R ₁₃ or outer diameter D ₁₉ than the outer diameter D ₁₉
Combine with.

In the illustrated embodiment, the cylinder cylinder 13
The upper end opening of the boot is closed by a boot 18 made of a flexible material such as oil resistant rubber. As a result of closing the upper end opening with the boots 18 as described above, the upper space 31 existing above the cylinder tube 13 is irrespective of changes in ambient temperature.
The pressure change inside is suppressed. As a result, the air mixed in the viscous liquid 17 as the pressure increases does not deposit when the pressure decreases.

Further, in the case of the illustrated embodiment, a part of the cored bar 41 provided at the base of the boot 18 is projected inward in the diameter direction from the inner peripheral surface of the cylinder cylinder 13,
It has a function as a stopper for preventing the plunger 14a from coming off. That is, the inner diameter dimension R of the core metal 41
_41, smaller than the inner diameter R ₁₃ of the cylinder tube 13 with (R ₄₁ <R ₁₃₎ to and covers the bent corner portion opposed to the shoulder portion of the plunger 14a of an elastic member such as the oil-resistant rubber . Therefore, when the plunger 14a rises, the shoulder portion abuts against the elastic body and prevents the plunger 14a from coming out of the cylinder cylinder 13.

In the state in which the damper device for an automatic tensioner of the present invention constructed as described above is incorporated in the automatic tensioner as shown in FIG. 2 or 3, the belt 6 (FIG.
The action itself when restricting the displacement of the rocking member 3 supporting the pulley 5 in order to suppress the vibrations of 3 to 3) is the same as that of the damper device incorporated in the above-described autotensioner of the previous invention.

In particular, in the damper device for an autotensioner of the present invention, the viscosity of the viscous liquid 17 is lowered to some extent, so that the following operational effects can be obtained. First, since the viscosity of the viscous liquid 17 is set to 10,000 cSt or less at −20 ° C., the extension speed of the damper device 12 can be secured to some extent even at a low temperature. That is, when the viscosity becomes excessive,
Even when the check valve 27 is open, the piston 19
The viscous liquid 17 does not move smoothly from the upper side to the lower side. If the tension of the belt 6 suddenly loosens in this state, the tip of the plunger 14a and the receiving block 15 of the swinging member 3
The lower surface (see FIG. 2) (in the case of the structure shown in FIG. 2), or the lower surface of the cylinder tube 13 and the protrusion formed on the fixed portion such as the cylinder block (in the case of the structure shown in FIG. 3) ) Separate. As a result, the function of suppressing the belt 6 by the damper device 12 does not work. Partially loosening the tension of the belt 6 always occurs when the engine is started.
It is important to secure the extension speed of the damper device 12 at low temperatures.

With respect to this point, the present inventor has made the viscous liquid 17
The following experiment was conducted while changing the viscosity of. First,
A viscous liquid 17 (silicon oil) having a viscosity of 20,000 cSt at 20 ° C. was enclosed in a damper device 12 having a structure as shown in FIG. And, this damper device 12 is -2
In the state of being cooled to 0 ° C., the speed at which the damper device 12 contracted as shown in the left half of FIG. 1 extends as shown in the right half of FIG. 1 was measured. The through hole 26 formed in the piston 19 has an inner diameter of 2.8 mm and a length of 2.5 mm.
The Young's modulus of 0 was 0.23 kgf / mm. As a result, the expansion speed of the damper device 12 in which the viscous liquid 17 having a viscosity of 20000 cSt was enclosed was 0.95 mm / sec. Further, the damper device 12 is incorporated into an auto tensioner as shown in FIG. 2, and the auto tensioner is further incorporated into an engine as shown in FIG. 6 to suppress the timing belt of the engine and start the engine at −20 ° C. As a result, the tooth skipping as described above occurred.

Next, a similar experiment was conducted using a viscous liquid 17 (silicon oil) having a viscosity of 8000 cSt at −20 ° C., and the extension speed of the damper device 12 was 2.0.
No tooth skipping occurred at mm / sec. Furthermore, -20 ℃
When a similar experiment was conducted using a viscous liquid 17 (silicon oil) having a viscosity of 2000 cSt, the extension speed of the damper device 12 was 7.5 mm / sec and tooth skipping did not occur.

From these experiments, if the viscosity of the viscous liquid 17 is set to 10,000 cSt or less at -20 ° C., -20
Even if the engine is started at a low temperature of about ℃, the damper device 1
It can be seen that 2 follows the movement of the belt 6 sufficiently and does not cause tooth jump. The viscosity of 10,000 cSt is
Although the viscosity of the viscous liquid 17 for the damper device 12 is high, the extremely low temperature of −20 ° C. is only for an extremely short time immediately after the engine is started. That is, since the temperature of the viscous liquid 17 rises immediately after the engine is started, a sufficiently practical autotensioner can be obtained if the viscosity is such that tooth jumping does not occur at the time of starting at -20 ° C.

Further, the viscosity of the viscous liquid 17 is 10 at 40.degree.
Since it is set to 0 cSt or less, even if the viscous liquid 17 moves above and below the piston 19 as the piston 19 moves, cavitation hardly occurs in the viscous liquid 17. As a result, it is possible to prevent the performance of the damper device 12 from deteriorating due to the generation of bubbles due to cavitation.

With respect to this point, the present inventor has made the viscous liquid 17
The following experiment was conducted while changing the viscosity of. First, 4
A viscous liquid 17 (silicon oil) having a viscosity of 700 cSt at 0 ° C. has a structure as shown in FIG.
Enclosed in. Then, with the damper device 12 kept at 40 ° C., the tip of the plunger 14 has a frequency of 50 Hz,
By vibrating with an amplitude of ± 0.3 mm, the presence or absence of cavitation in the viscous liquid 17 was observed. As a result, the occurrence of cavitation was observed.

Next, when a similar experiment was conducted using a viscous liquid 17 (silicon oil) having a viscosity of 150 cSt at 40 ° C., cavitation was also observed. Next, a viscous liquid 1 having a viscosity of 200 cSt at 40 ° C.
When a similar experiment was carried out using 7 (mineral oil), the occurrence of cavitation was also observed.

Further, when a similar experiment was conducted using a viscous liquid 17 (mineral oil) having a viscosity of 100 cSt at 40 ° C., no cavitation was observed. Through these experiments, the viscosity of the viscous liquid 17 at 1
It can be seen that if the pressure is set to 00 cSt or less, cavitation that will lead to performance deterioration of the damper device 12 will not occur.

Further, in the case of the illustrated embodiment, since the boot 18 is provided, the pressure change in the upper space 31 existing in the upper portion of the cylinder cylinder 13 is suppressed, and it is mixed in the viscous liquid 17 as the pressure rises. The generated air does not precipitate when the pressure drops. Therefore, as a result of more surely preventing the bubbles from entering the lower side of the piston 19, the damper device 12
The performance deterioration prevention function can be secured more reliably.

Further, in the illustrated embodiment, the cylinder tube 13
It is possible to accurately regulate the difference between the inner diameter R ₁₃ of the piston and the outer diameter D ₁₉ of the piston 19 as desired. Therefore, when the tension of the belt 6 increases, when the piston 19 is pushed into the cylinder tube 13, the inner peripheral surface of the cylinder tube 13 and the piston 19 are pushed.
The amount of the viscous liquid 17 flowing in a minute gap between the outer peripheral surface of the product and the outer peripheral surface of the product does not vary from product to product. As a result, it is possible to stabilize the leak down time of the damper device 12 and the vibration preventing function of the belt 6 affected by the leak down time.

[0043]

The damper device for an autotensioner of the present invention is constructed and operates as described above. However, while ensuring performance at low temperatures, cavitation is prevented from occurring when the temperature rises, and a damper device is provided. The automatic tensioner with built-in can stabilize the function to prevent the vibration of the belt.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of the present invention.

FIG. 2 is a front view showing a first example of the automatic tensioner according to the previous invention.

FIG. 3 is a front view showing the second example.

FIG. 4 is a vertical cross-sectional view showing a first example of a damper device incorporated in the auto tensioner according to the previous invention.

FIG. 5 is a longitudinal sectional view showing the second example in a contracted state and an expanded state.

FIG. 6 is a state 1 of use of the auto tensioner according to the previous invention.
The front view which shows an example.

FIG. 7 is a vertical sectional view showing an example of a conventional damper device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixed member 2 Fixed shaft 3 Swing member 4 Pivot 5 Pulley 6 Belt 7 Torsion coil spring 8 Coil part 9a, 9b Locking part 10 Fixed side arm piece 11 Swing side arm piece 12 Damper device 13 Cylinder cylinder 14, 14a Plunger 15 receiving block 16 stopper pin 17 viscous liquid 18 boot 19 piston 20 biasing spring 21 base 22 seal ring 23 notch 24 inner space 25 partition wall 26 through hole 27 check valve 28 spring 29 ball 30, 30a tip half 31 upper space 32 Communication hole 33 Seal ring 34 Cylinder case 35 Cylinder liner 36 Upper retaining ring 37 Lower retaining ring 38 Compression spring 39 Cylindrical portion 40 Rod-shaped portion 41 Core bar 42 Drive pulley 43 Driven pulley 44 Guide pulley

Claims (1)

[Claims] 1. A cylinder cylinder having a viscous liquid sealed therein, a piston displaceably fitted in the cylinder cylinder axially, and a piston provided between the piston and the cylinder cylinder. The urging spring that urges the piston in one direction, and the plunger that increases the amount of protrusion from the cylinder cylinder due to the displacement of the piston based on the elastic force of the urging spring and the both axial end surfaces of the piston communicate with each other. In a damper device for an autotensioner having a function of opening only when the piston is displaced based on the elastic force of the biasing spring. The viscosity of the viscous liquid is 10,000 cSt or less at -20 ° C and 100 cSt at 40 ° C.
A damper device for an auto tensioner characterized by the following.