JP2009168159A - Shock absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a target temperature characteristic when a piston and a piston rod are connected to each other by being press-fitted. <P>SOLUTION: In a shock absorber 1, a cylinder 3 and the piston 7 are formed of materials having different expansion coefficient, and an interval (d) between the cylinder and the piston 7 is changed according to a change in temperature of working fluid. The piston 7 is integrally formed with a cylindrical press-fit portion 23 press-fitting and connecting the piston rod 5 to the piston with a predetermined press-fit margin, and a circulating first space portion 35 absorbing expansion of the press-fit portion 23 caused by the press-fit margin is formed between the press-fit portion 23 and the cylinder 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a shock absorber.

  As a conventional shock absorber, there is one in which a piston is disposed through a piston rod in a cylinder filled with a working fluid (see, for example, Patent Document 1).

  In such a shock absorber, the piston and the piston rod may be connected by press-fitting from the viewpoint of simplifying the structure.

  On the other hand, in recent shock absorbers, the cylinder and piston are made of materials having different linear expansion coefficients, and the desired temperature characteristics are obtained by changing the distance between the cylinder and piston according to the temperature change. Attempts have been made.

  However, when the piston and the piston rod are connected by press-fitting as described above, the expansion of the piston accompanying the press-fitting affects the gap, and the desired temperature characteristics cannot be obtained.

JP 2002-54675 A

  The problem to be solved is that the target temperature characteristic cannot be obtained when the piston and the piston rod are connected by press fitting.

  In order to obtain a desired temperature characteristic when a piston and a piston rod are connected by press-fitting, the present invention is arranged in a cylinder filled with a working fluid via a piston rod, and the inside of the cylinder is connected to a pressure chamber side and a non-pressure. A piston partitioned into a chamber side, a flow path communicating the pressure chamber side and the non-pressure chamber side is provided in the piston, and the cylinder and the piston are formed of materials having different expansion coefficients, A shock absorber that changes a distance between the cylinder and the piston in accordance with a temperature change of the working fluid, and a cylindrical press-fit portion that press-fits the piston rod with a predetermined press-fit allowance to the piston. And a first circular space portion that can absorb expansion of the press-fitting portion due to the press-fitting allowance is formed between the press-fitting portion and the cylinder. And features.

  In the shock absorber according to the present invention, since the cylindrical press-fitting portion for press-fitting the piston rod with a predetermined press-fitting allowance is integrally formed on the piston, the piston and the piston rod can be press-fitted and joined while the press-fitting portion is expanded.

  And since the 1st space part which absorbs expansion | swelling of the press-fit part accompanying the press-fit is provided between the press-fit part and the cylinder, the expansion by the press-fit affects the distance between the cylinder and the piston. Can be suppressed.

  Therefore, in the shock absorber, the interval can be reliably changed according to the expansion coefficients of the cylinder and the piston, and the desired temperature characteristic can be obtained with certainty.

  When connecting the piston and piston rod by press-fitting, a cylindrical press-fit part is provided on the center side of the piston and a groove is formed on the outer periphery of the press-fit part for the purpose of obtaining the desired temperature characteristics. Realized by doing.

  1 is a cross-sectional view of a shock absorber according to a first embodiment of the present invention, FIG. 2 shows a piston used in the shock absorber of FIG. 1, (a) is an enlarged cross-sectional view, and (b) is a cross-sectional view of (a). 3 is an enlarged cross-sectional view showing an outline of the main part, FIG. 3 shows a piston used in the shock absorber of FIG. 1, (a) is a plan view, and (b) is a bottom view.

  The shock absorber 1 of this embodiment has a temperature characteristic (target temperature characteristic) that suppresses a change in the damper effect when a temperature change occurs in the working fluid. As shown in FIG. 1, the shock absorber 1 includes a cylinder 3 and a piston 7 disposed in the cylinder 3 via a piston rod 5.

  The cylinder 3 is made of a material having a predetermined linear expansion coefficient. In this embodiment, it is made of PPS (polyphenylene sulfide) resin. The cylinder 3 has a cylindrical shape with an open end closed by a cap 9, and a fluid chamber 11 in which a working fluid having viscosity such as silicon oil is sealed is formed. The fluid chamber 11 is divided into a pressure chamber 13 side and a non-pressure chamber 15 side, with the piston 7 movably inserted into the cylinder 3.

  The piston 7 is made of a material having a linear expansion coefficient different from that of the cylinder 3. In this embodiment, it is made of POM (polyacetal) resin and has a larger linear expansion coefficient than that of the cylinder 3. The piston 7 is formed in a substantially cylindrical shape as shown in FIGS. 1 to 3, and the outer peripheral surface 17 forms a predetermined interval (clearance) d between the piston 7 and the inner peripheral surface 19 of the cylinder 3.

  The interval d communicates the pressure chamber 13 side and the non-pressure chamber 15 side separately from the flow path 21 described later, and allows the working fluid to flow. The dimension of the space | interval d changes according to the temperature change of a working fluid by the difference in the linear expansion coefficient of the cylinder 3 and the piston 7. FIG. In this embodiment, since the linear expansion coefficient of the piston 7 is larger than that of the cylinder 3, when the temperature of the working fluid decreases, the piston 7 contracts relative to the cylinder 3 and the dimension of the interval d increases. . Conversely, when the temperature of the working fluid rises, the piston 7 expands relative to the cylinder 3 and the dimension of the distance d decreases.

  A cylindrical press-fitting portion 23 for press-fitting the piston rod 5 is integrally formed at one central portion of the piston 7. The press-fit portion 23 is configured to press-fit the inner end portion 25 of the piston rod 5 with a predetermined press-fitting allowance. That is, the inner diameter of the press-fit portion 23 is formed to be smaller than the outer diameter of the inner end portion 25 of the piston rod 5, and the difference in the diameter serves as a press-fitting allowance for press-fitting.

  On the inner peripheral surface of the press-fit portion 23, a circumferential protrusion 29 that engages with a circumferential groove 27 provided in the inner end portion 25 of the piston rod 5 is formed. A groove 31 is formed on the outer peripheral side of the press-fit portion 23.

  The groove 31 is formed in a circular shape around the entire press-fit portion 23. The groove portion 31 defines an outer peripheral wall portion 33 that forms a gap d on one outer periphery of the piston 7 with the cylinder 3 on the outer diameter side, and defines the press-fit portion 23 on the inner diameter side. Further, a circular first space 35 is defined in the groove 31.

  The first space portion 35 is adapted to absorb the expansion of the press-fit portion 23 accompanying the press-fit of the piston rod 5. That is, when the inner end portion 25 of the piston rod 5 is press-fitted into the press-fit portion 23, the first space portion 35 causes the press-fit portion 23 to expand within the range. Thereby, it is suppressed that the one side of piston 7 expand | swells as a whole by the said press injection, and the space | interval d is ensured on the one side outer periphery of piston 7. FIG.

  A flow path 21 is formed through the bottom of the groove 31 to the other side of the piston 7. Therefore, the flow path 21 communicates the pressure chamber 13 side and the non-pressure chamber 15 side via the groove 31. The flow path 21 is formed to have a smaller diameter than the width between the inner and outer diameters of the groove 31, and has a stepped shape between the groove 21. In other words, the width between the inner and outer diameters of the groove 31 is formed to be larger than the diameter of the flow path 21, and the pressure chamber 13 side and the non-pressure chamber 15 side can be reliably communicated even if the press-fit portion 23 expands. It is like that. A plurality of the flow paths 21 are formed for each predetermined pitch in the circumferential direction of the piston 7. In this embodiment, they are arranged every 45 ° of the central angle.

  On the other outer periphery of the groove portion 31, a circular step portion 37 is formed. The stepped portion 37 is formed by making the outer periphery of the other side smaller than the outer periphery of the one side. The step portion 37 forms a circular second space 39 between the inner peripheral surface 19 of the cylinder 3.

  The second space 39 absorbs expansion on the other side of the piston 7 due to press-fitting. That is, when the inner end 25 of the piston rod 5 is press-fitted into the press-fit portion 23, the other side of the piston 7 expands as a whole together with the press-fit portion 23, but this expansion is performed within the range of the second space portion 39. Thereby, even if the piston 7 other side expand | swells, the space | interval d is ensured on the other side outer periphery of the piston 7.

  The other end face 41 of the piston 7 is provided with an orifice 43 formed from the flow path 21 to the stepped portion 37. The orifice 43 communicates the flow path 21 and the pressure chamber 13 with the flow path 21 closed by a valve body 47 described later.

  A valve body 47 is provided on the other side of the piston 7 via a guide bar 45. The valve body 47 is inserted through the guide bar 45 so as to be movable in the axial direction. The valve body 47 moves close to and away from the piston 7 by the resistance of the working fluid according to the movement of the piston 7. The valve body 47 opens and closes the flow path 21 by this close and separate movement.

  In the non-pressure chamber 15 of the cylinder 3, an elastic film 49 that is elastically deformed in response to the pressure fluctuation in the non-pressure chamber 15 is disposed. The elastic film 49 is a membrane made of a rubber film, and is attached to a guide 51 inserted into the cylinder 3.

  The guide 51 is fitted in an accommodation step portion 37 formed on the open end side of the cylinder 3. The axial center portion of the guide 51 is provided with an insertion hole 53 through which the piston rod 5 is inserted. A concave portion 55 that accommodates and arranges the elastic film 49 is formed in an intermediate portion of the guide 51. A space 57 is formed between the elastic membrane 49 and the guide 51.

  At both ends of the guide 51, flange portions 59 and 61 that are fitted to the inner peripheral surface of the cylinder 3 are formed. The flange portions 59 and 61 are formed with a concave groove 67 on the outer periphery to engage the circumferential end portions 63 and 65 on both sides of the elastic film 49. Therefore, the circumferential end portions 63 and 65 of the elastic film 49 are nipped and fixed between the flange portions 59 and 61 of the guide 51 and the inner peripheral surface of the cylinder 3.

  The flange portion 61 on the open end side stores the packing 71 in the circumferential groove 69 and prevents the working fluid in the cylinder 3 from leaking from the periphery of the piston rod 5 to the outside. The flange portion 59 on the side opposite to the open end includes a communication hole 73 and communicates the non-pressure chamber 15 and the space 57.

The elastic membrane 49 improves the performance of the shock absorber 1 by improving the flow of the working fluid between the non-pressure chamber 15 and the pressure chamber 13 due to its elastic deformation.
[Action of shock absorber]
The shock absorber 1 of this embodiment operates when the outer end 75 of the piston rod 5 receives an external force.

  When the outer end 75 receives an external force in the pushing direction with respect to the cylinder 3, the piston 7 moves to the pressure chamber 13 side in conjunction with the piston rod 5. In response to this movement, the valve body 47 that has received the resistance of the working fluid moves close to the piston 7 side, and each flow path 21 is closed. At this time, the closed flow path 21 communicates with the pressure chamber 13 via the orifice 43 and moves the working fluid to the non-pressure chamber 15 side. At the same time, the working fluid moves toward the non-pressure chamber 15 through the distance d between the inner peripheral surface 19 of the cylinder 3 and the outer peripheral surface 17 of the piston 7. By the movement of these working fluids, the shock absorber 1 can exhibit a predetermined damper effect.

  When the outer end 75 receives an external force in the pulling direction with respect to the cylinder 3, the piston 7 moves to the non-pressure chamber 15 side and the valve body 47 receives the resistance of the working fluid and moves to the anti-piston 7 side. It moves away and each flow path 21 is opened. Therefore, the working fluid moves to the pressure chamber 13 side through the opened flow path 21 and the interval d.

  In addition, since the outer peripheral wall part 33 arrange | positioned at the outer peripheral side of the piston 7 is thin by the 1st space part 35, it can be made to function as a relief valve, and can suppress the damage at the time of high load. it can.

  During the operation, the viscosity may change with the temperature of the working fluid depending on the surrounding environment, usage time, and the like. Even in this case, the shock absorber 1 of the present embodiment can suppress the change in the damper effect by changing the dimension of the distance d.

  That is, when the temperature of the working fluid rises, the piston 7 is relatively expanded with respect to the cylinder 3 and the dimension of the distance d is reduced. Therefore, the shock absorber 1 suppresses the change in resistance to the movement of the entire piston 7 regardless of the temperature rise, because the flow resistance of the interval d increases even if the viscosity of the working fluid decreases as the temperature rises. Can be prevented.

  On the other hand, when the temperature of the working fluid is lowered, the piston 7 is relatively contracted with respect to the cylinder 3 and the dimension of the interval d is increased. Therefore, the shock absorber 1 suppresses the change in resistance to the movement of the entire piston 7 regardless of the temperature decrease, because the flow resistance of the interval d decreases even if the viscosity of the working fluid increases in response to the temperature decrease. Can be prevented.

  Here, the shock absorber 1 press-fits the inner end portion 25 of the piston rod 5 into a press-fit portion 23 formed integrally with the central portion on one side of the piston 7, and a first space formed around the entire press-fit portion 23. The portion 35 absorbs the expansion of the press-fitting portion 23 accompanying the press-fitting. For this reason, the one side of the piston 7 is expanded by press-fitting, that is, the influence of the press-fitting is suppressed, and the expansion and contraction according to the linear expansion coefficient can be reliably performed in accordance with the temperature change of the working fluid.

  On the other hand, a second space 39 that absorbs expansion on the other side of the piston 7 due to press-fitting is formed on the outer periphery of the other side of the piston 7. For this reason, also on the other side of the piston 7, the influence (expansion due to the press-fitting) due to the press-fitting is suppressed, and the expansion and contraction according to the linear expansion count can be reliably performed in accordance with the temperature change of the working fluid.

  Thus, in the shock absorber 1 of the present embodiment, the expansion and contraction according to the linear expansion coefficient is surely performed from one side of the piston 7 to the other side as the working fluid changes in temperature, and the damper effect is improved. The temperature characteristic that suppresses the change can be obtained with certainty.

  FIG. 4 is a table showing changes in the damper effect accompanying changes in the temperature of the shock absorber. 5A and 5B are graphs showing changes in FIG. 4, in which FIG. 5A shows a change in operating time accompanying a temperature change, and FIG. 5B shows a change rate accompanying a temperature change. 4 and 5 show changes at −10 ° C. (low temperature) and 50 ° C. (high temperature) relative to the damper effect at 23 ° C. (normal temperature). Further, in FIG. 5, ▲ indicates the shock absorber 1 of the present embodiment having the first and second space portions 35 and 39, and ■ indicates that the first and second space portions 35 and 39 are not included. A comparative example is shown.

As is apparent from FIGS. 4 and 5, the shock absorber 1 of this embodiment significantly reduces the change and rate of change in the operating time at each of the low temperature and high temperature times as compared with the comparative example, thereby reducing the fluctuation of the damper effect. Suppressed temperature characteristics could be obtained.
[Modification]
The shock absorber 1 has a temperature characteristic that suppresses a change in the damper effect accompanying a change in the temperature of the working fluid. However, the shock absorber 1 has a temperature characteristic that positively changes the damper effect in accordance with a change in the temperature of the working fluid. Is also possible.

  For example, by setting the distance d between the inner peripheral surface 19 of the cylinder 3 and the outer peripheral surface 17 of the piston 7 and the orifice 43, the operation time is shortened at low temperatures and the operation is performed at high temperatures as shown in x in FIGS. It is possible to obtain a temperature characteristic (target temperature characteristic) with a longer time.

  Contrary to this temperature characteristic, it is also possible to have a temperature characteristic in which the operating time is lengthened at low temperatures and the operating time is shortened at high temperatures.

In addition, the same temperature characteristics as described above can be obtained by selecting materials for the cylinder 3 and the piston 7.
[Effect of Example]
In the shock absorber 1 of this embodiment, since the cylindrical press-fit portion 23 that press-fits the inner end portion 25 of the piston rod 5 with a predetermined press-fitting allowance is integrally formed in the piston 7, The piston rod 5 can be press-fitted and the structure can be simplified.

  A first space 35 is formed between the cylinder 3 and the press-fitting portion 23. The first space 35 is formed of a groove 31 formed around the entire press-fitting portion 23 and absorbs expansion of the press-fitting portion 23 caused by the press-fitting. Yes. For this reason, the expansion of the press-fitting portion 23 by the press-fitting is performed within the range of the first space portion 35, and the influence of the press-fitting on the interval d can be suppressed.

  Therefore, in the shock absorber 1, the piston 7 can be surely expanded and contracted according to the linear expansion coefficient in accordance with the temperature change of the working fluid, and the desired temperature characteristic can be obtained with certainty.

  A second space 39 is formed on the outer periphery of the piston 7 to absorb expansion of the piston 7 due to press-fitting. For this reason, the influence of press-fitting on the distance d can be more reliably suppressed, and the target temperature characteristic can be obtained more reliably.

  The shock absorber 1 according to the present embodiment is provided with a valve body 47 that opens and closes the flow path 21 close to and away from the piston 7 and has an orifice 43 that communicates the pressure chamber 13 and the flow path 21 in a closed state of the flow path. Since it is provided, a damper effect can be obtained easily and reliably.

  In addition, as the design of the piston 7 and the cylinder 3, etc., by appropriately selecting any one or any combination of the material selection of the piston 7 and the cylinder 3, the setting of the distance d, and the setting of the orifice 43. Thus, the desired temperature characteristic can be obtained more easily and reliably.

(Example 1) which is sectional drawing of a shock absorber. The piston used for the shock absorber of FIG. 1 is shown, (a) is sectional drawing, (b) is an expanded sectional view which shows the principal part outline of (a) (Example 1). The piston used for the shock absorber of FIG. 1 is shown, (a) is a top view, (b) is a bottom view (Example 1). It is a graph which shows the change of the damper effect accompanying the temperature change of a shock absorber (Example 1). 5A and 4B are graphs showing changes in FIG. 4, in which FIG. 4A shows a change in operating time accompanying a temperature change, and FIG. 4B shows a change rate accompanying a temperature change. (Example 1).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shock absorber 3 Cylinder 5 Piston rod 7 Piston 11 Fluid chamber 13 Pressure chamber 15 Non-pressure chamber 21 Channel 23 Press fit part 31 Groove part 35 First space part 37 Step part 39 Second space part

Claims (5)

Provided in the cylinder filled with the working fluid is a piston that is arranged via a piston rod and divides the cylinder into a pressure chamber side and a non-pressure chamber side,
The piston is provided with a flow path communicating the pressure chamber side and the non-pressure chamber side,
A shock absorber, wherein the cylinder and the piston are formed of materials having different expansion coefficients, and a distance between the cylinder and the piston is changed according to a temperature change of the working fluid,
The piston is integrally provided with a cylindrical press-fitting portion that press-fits the piston rod with a predetermined press-fitting allowance,
Between the press-fitting part and the cylinder, a circular first space part capable of absorbing expansion of the press-fitting part due to the press-fitting allowance was formed.
Shock absorber characterized by that. The shock absorber according to claim 1,
On the outer periphery of the piston, a circular second space portion that can absorb expansion of the piston due to the press-fitting allowance was formed.
Shock absorber characterized by that. The shock absorber according to claim 1 or 2,
The first space portion is composed of a circumferential groove formed around the entire press-fit portion.
Shock absorber characterized by that. The shock absorber according to claim 2 or 3,
The second space portion comprises a circular step formed on the outer periphery of the piston.
Shock absorber characterized by that. The shock absorber according to any one of claims 1 to 4,
Provided with a valve body that opens and closes the flow path close to and away from the piston, and provided with an orifice that communicates the pressure chamber and the flow path in a closed state of the flow path.
Shock absorber characterized by that.

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