Damping valve for shock absorber

A damping valve includes a valve disk, a retainer, an inner peripheral side flow passage configured to include a valve disk through hole formed in an inner peripheral side of the valve disk and a retainer through hole formed in the retainer and allowing communication between one and other chambers, an outer peripheral side flow passage formed in an outer peripheral side of the valve disk and allowing communication between the one and the other chambers, and a leaf valve in the form of an annular plate arranged on a side of the retainer opposite to the valve disk and configured to openably close the inner peripheral side flow passage by an outer peripheral part. A flow passage area of the retainer through hole is not smaller than that of the valve disk through hole.

TECHNICAL FIELD

The present invention relates to a damping valve for shock absorber.

BACKGROUND ART

A damping valve for shock absorber is applied, for example, to a piston unit or the like of a shock absorber for vehicle and is provided with a piston (valve disk) partitioning one chamber and another chamber for storing working fluid in the shock absorber, a flow passage formed in this piston to allow communication between the one and the other chambers, and a damping force generating element such as a leaf valve for applying resistance to the working fluid passing in this flow passage.

When the piston moves toward the one or the other chamber, the one or the other chamber is pressurized and the working fluid moves between the one and the other chambers through the flow passage. In this way, the shock absorber generates a damping force due to the resistance of the damping force generating element.

Since the damping force generated by the shock absorber for vehicle largely affects the ride quality of a vehicle, it is preferable to provide a damping valve capable of realizing various damping characteristics so that the shock absorber can realize a desired damping characteristic (change in damping force in relation to piston speed).

For example, JP2008-138696A discloses a damping valve for shock absorber in which a retainer is provided to be placed on a piston partitioning one chamber and another chamber.

The above damping valve is provided with an inner peripheral side flow passage configured to include a valve disk through hole formed in an inner peripheral side of the piston and a retainer through hole formed in the retainer and allowing communication between the one and the other chambers, and an outer peripheral side flow passage formed in an outer peripheral side of the piston and allowing communication between the one and the other chambers.

In the above damping valve, even if the flow passages are formed in the inner and outer peripheral sides of the piston, a diameter of a valve seat on which a leaf valve corresponding to the inner peripheral side flow passage is seated can be increased by laminating the leaf valve via the retainer. Thus, it is possible to use the leaf valve having a large diameter and easily deflectable.

Accordingly, a damping coefficient (ratio of the amount of change in damping force to the amount of change in piston speed) of a valve characteristic due to resistance produced when the working fluid passes through a clearance between an outer peripheral part of the leaf valve and the valve seat can be decreased.

Further, a damping force characteristic can be variously changed by replaceably mounting retainers having various dimensions and shapes.

SUMMARY OF INVENTION

A shock absorber to which the above damping valve is applied generates a damping force with a port characteristic due to resistance produced during the passage of the working fluid in the inner peripheral side flow passage when the leaf valve is opened to a certain extent. Further, the damping force with the port characteristic can be changed by a replacement with a retainer having a different flow passage area of a retainer through hole.

However, in order to enable the generation of a damping force with a port characteristic dependent on the flow passage area of the retainer through hole, it is necessary not to throttle the working fluid passing in the inner peripheral side flow passage by the valve disk through hole.

Accordingly, it is necessary to prepare a special piston formed with a valve disk through hole having a large flow passage area in order to use the piston in combination with retainers having various dimensions and shapes. In the case of singly using this special piston, there is a problem of being difficult to increase the damping coefficient of the port characteristic since the flow passage area of the valve disk through hole is large.

The present invention was developed in view of the above problem and aims to provide a damping valve for shock absorber which enables a piston (valve disk) to be used in combination with a retainer and can increase a damping coefficient of a port characteristic also in the case of singly using the piston and change a damping force with a port characteristic.

According to one aspect of the present invention, a damping valve for shock absorber includes a valve disk partitioning the interior of a cylinder into one chamber and another chamber, a retainer provided to be placed on the valve disk, an inner peripheral side flow passage configured to include a valve disk through hole formed in an inner peripheral side of the valve disk and a retainer through hole formed in the retainer and allowing communication between the one and the other chambers, an outer peripheral side flow passage formed in an outer peripheral side of the valve disk and allowing communication between the one and the other chambers, and a leaf valve in the form of an annular plate arranged on a side of the retainer opposite to the valve disk and configured to openably close the inner peripheral side flow passage by an outer peripheral part, wherein a flow passage area of the retainer through hole is not smaller than that of the valve disk through hole.

An embodiment and advantages of the present invention are described in detail below with reference to the accompanying drawings.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present invention is described with reference to the drawings. It should be noted that the same reference signs given through several drawings denote the same or corresponding components.

As shown inFIG. 1, a damping valve according to the present embodiment is applied to a piston unit of a shock absorber D and provided with a piston (valve disk)1partitioning one chamber A and another chamber B, a retainer2provided to be placed on the piston1, an inner peripheral side flow passage3aconfigured to include valve disk through holes10formed in an inner peripheral side of the piston1and retainer through holes20formed in the retainer2and allowing communication between the one chamber A and the other chamber B, outer peripheral side flow passages3bformed in an outer peripheral side of the piston1and allowing communication between the one chamber A and the other chamber B, and leaf valves4ain the form of annular plates arranged on a side of the retainer2opposite to the piston and configured to openably close the inner peripheral side flow passage3aby outer peripheral parts. A flow passage area of the retainer through holes20is set to be not smaller than the flow passage area of the valve disk through holes10.

Further, the shock absorber D is configured to be provided with a cylinder5for storing working fluid composed of liquid such as water, aqueous solution or oil, an annular head member (not shown) for sealing an one-side opening of the cylinder5, a piston rod6rotatably supported on the head member and slidably penetrating through the head member, the piston1held on a mounting portion60of the piston rod6, a sealing member (not shown) for closing an other-side opening of the cylinder5, and a reservoir (not shown) or an air chamber (not shown) for compensating for a volumetric change in the cylinder caused by the volume of the piston rod6entering the cylinder5.

Further, the interior of the cylinder5is partitioned by the piston1into the one and the other chambers A, B filled with the working fluid, and the one and the other chambers A, B communicate via the inner peripheral side flow passage3aand the outer peripheral side flow passages3b.

When the piston1vertically moves together with the piston rod6relative to the cylinder5, the working fluid flows between the one and the other chambers A, B via the inner and outer peripheral side flow passages3a,3b. Resistance is applied to those flows of the working fluid respectively by corresponding leaf valves4a,4bto generate a predetermined pressure loss, whereby a predetermined damping force is generated in the shock absorber D.

The damping valve is described in detail below.

A plurality of leaf valves4bin the form of annular plates, a spacer7and a valve stopper8are laminated in this order from the piston1side on a side of piston (valve disk)1in the one chamber A. The retainer2, a shim9in the form of an annular plate, a plurality of leaf valves4ain the form of annular plates, and a spacer7are laminated in this order from the piston1side on a side of the piston1in the other chamber B.

The mounting portion60having a smaller outer diameter than the piston rod6is formed on a tip part of the piston rod6holding the piston1, and a step portion61is formed between parts having different outer diameters. Further, a screw groove with which a nut N is to be threadably engaged is formed on a tip part60aof the mounting portion60.

Accordingly, by threadably engaging the nut N with the tip part60ain a state where the mounting portion60of the piston rod6penetrates through axial center portions of the piston1, the retainer2, the leaf valves4a,4b, the spacers7, the valve stopper8and the shim9, these can be sandwiched between the step portion61and the nut N and held on the piston rod6.

At this time, inner peripheral sides of the leaf valves4a,4bare fixed to the piston rod6, but outer peripheral sides thereof can be deflected in a direction away from the piston. Further, the leaf valves4alaminated on the retainer2are initially deflected, and this deflection amount can be adjusted by using a shim9having a different thickness or changing the number of laminated shims9.

The piston1is provided with a piston main body1bformed into an annular shape by including a mounting hole1athough which the mounting portion60of the piston rod6penetrates, and a slide contact portion1cwhich is mounted along the outer periphery of the piston main body1band slides in contact with the inner peripheral surface of the cylinder5. Further, an outer peripheral part of the piston main body1bextends toward the retainer2, thereby forming a tubular skirt portion1d.

The outer peripheral side flow passages3ballowing communication between the one and the other chambers A, B are formed in an outer peripheral side of the piston main body1band at an inner side of the skirt portion1d, and the exits of the outer peripheral side flow passages3bare openably closed by the leaf valves4b. Further, the inner peripheral side flow passage3ais formed in an inner peripheral side of the piston main body1band the retainer2and the exit of the inner peripheral side flow passage3ais openably closed by the leaf valves4a.

Further, cuts40which function as orifices are respectively formed on outer peripheral parts of the leaf valves4a,4blocated closest to the piston1(retainer2).

The outer peripheral side flow passage3bpenetrates through the piston1in a direction of a central axis of the shock absorber D and a plurality of the outer peripheral side flow passages3bare formed along a circumferential direction in the outer peripheral side of the piston1. Further, the inner peripheral side flow passage3ais configured to include a plurality of valve disk through holes10penetrating through the piston1in the direction of the central axis of the shock absorber D and formed along the circumferential direction in the inner peripheral side of the piston1and a plurality of retainer through holes20penetrating through the retainer2in the direction of the central axis of the shock absorber D and formed along a circumferential direction of the retainer2.

As shown inFIG. 2A, windows11continuous with the respective outer peripheral side flow passages3band windows12continuous with the respective valve disk through holes10are alternately formed in the circumferential direction on a surface of the piston1opposite to the retainer2. These windows11,12are partitioned by a petal-shaped valve seat13surrounding the outer peripheries of the windows11. Accordingly, when the leaf valves4bare seated on the valve seat13, sides of the outer peripheral side flow passages3bnear the one chamber A are closed by the leaf valves4b, but sides of the valve disk through holes10near the one chamber A are not closed by the leaf valves4b.

It should be noted that although a projection14for supporting the leaf valves4bfrom below is provided in each window12, the projections14are not shown inFIG. 1. Further, a cross-section of the piston1shown inFIG. 1is an X-X cross-section ofFIG. 2A.

Further, as shown inFIG. 2B, an annular window15continuous with the valve disk through holes10, an annular valve seat16surrounding the outer periphery of the window15and an annular seat portion17raised at an inner peripheral side of the window15are formed on a surface of the piston1near the retainer2. Further, the outer peripheral side flow passages3bare open at an outer peripheral side of the valve seat16.

As shown inFIG. 1, the retainer2is provided with a small outer diameter portion2aand a large outer diameter portion2bhaving a larger outer diameter than the small outer diameter portion2aand formed on a side of the retainer2opposite to the piston1coaxially with the small outer diameter portion2a, and is inserted into the inside of the skirt portion1dof the piston1.

The small outer diameter portion2ais formed to have the outer diameter smaller than an inner diameter of the skirt portion1dand a side thereof opposite to the piston1projects from the skirt portion1d. Further, there is a clearance between the outer periphery of the large outer diameter portion2band the cylinder5so as not to prevent the working fluid in the other chamber B from flowing into the outer peripheral side flow passages3b.

As shown inFIGS. 3A and 3B, the plurality of retainer through holes20formed in the retainer2are respectively formed into arcuate shapes and arranged at equal intervals along the circumferential direction of the retainer2. Deformable elastic deforming portions21are formed between the plurality of retainer through holes20. It should be noted that a cross-section of the retainer shown inFIG. 1is a Y-Y cross-section ofFIG. 3A.

A flow passage area of the retainer through holes20is set to be not smaller than that of the valve disk through holes10. The flow passage area of the retainer through holes20is the sum of opening areas of the retainer through holes20. Since each retainer through hole20is identically shaped in the present embodiment, the flow passage area of the retainer through holes20can be obtained by a product of the opening area per retainer through hole20and the number of the retainer through holes20. Further, the flow passage area of the valve disk through holes10is the sum of opening areas of the valve disk through holes10. Since each valve disk through hole10is also identically shaped in the present embodiment, a total opening area of the valve disk through holes10can be obtained by a product of the opening area per valve disk through hole10and the number of the valve disk through holes10.

It should be noted that since a cross-sectional area of each of the retainer through holes20and the valve disk through holes10cut along a plane perpendicular to the central axis of the shock absorber D is set to be equal from the entrance to the exit in the present embodiment, the cross-sectional area of each of the retainer through holes20and the valve disk through holes10is equal to the opening area thereof. However, if either the retainer through holes20or the valve disk through holes10or both the retainer through holes20and the valve disk through holes10are partly reduced in diameter, cross-section areas of narrowest parts are equivalent to opening areas.

As shown inFIG. 3A, an annular window22continuous with the retainer through holes20, an annular outer peripheral seat surface23surrounding the outer periphery of the window22and an annular inner peripheral seat surface24raised at an inner peripheral side of the window22are formed on a surface of the retainer2near the piston1. Further, the outer and inner peripheral seat surfaces23,24are formed to meet the valve seat16and the seat portion17of the piston1when the retainer2is placed on the piston1(FIG. 1).

By bringing the outer peripheral seat surface23into close contact with the valve seat16, the leakage of the working fluid in the middle of the inner peripheral side flow passage3aconfigured to include the valve disk through holes10and the retainer through holes20can be prevented.

It should be noted that although a known method can be appropriately adopted as a method for bringing the outer peripheral seat surface23into close contact with the valve seat16, setting is made such that a clearance is formed between the inner peripheral seat surface24and the seat portion17in a state where the outer peripheral seat surface23is held in contact with the valve seat16without tightening the nut N in the present embodiment. Then, by tightening the nut N, the elastic deforming portions21are elastically deformed and the inner peripheral seat surface24is parallelly moved in a direction toward the seat portion17. Since the outer peripheral seat surface23is brought into close contact with the valve seat16in this way, the leakage of the working fluid in the middle of the inner peripheral side flow passage3acan be prevented.

As shown inFIG. 3B, an annular window25continuous with the retainer through holes20and a valve seat26in the form of a ring having a large diameter and surrounding the outer periphery of the window25are formed on a surface of the retainer2opposite to the piston1. In a state where the leaf valves4aare seated on the valve seat26, a side of the inner peripheral side flow passage3ain the other chamber B is closed by the leaf valves4a.

Next, functions and effects of the damping valve according to the present embodiment are described with reference to a comparative example of the present invention.

When a piston speed is in a low speed region during extension of the shock absorber D in which the piston rod6comes out of the cylinder5, the pressurized working fluid in the one chamber A moves to the other chamber B through the cuts40of the leaf valves4a,4b. Thus, the shock absorber D generates a damping force with a square-law characteristic by the orifices.

When the piston speed increases beyond the low speed region and reaches a middle speed region during extension of the shock absorber D, the pressurized working fluid in the one chamber A deflects outer peripheral parts of the leaf valves4aand moves to the other chamber B through a clearance formed between the valve seat26of the retainer2and the outer peripheral parts of the leaf valves4a. Thus, the shock absorber D generates a damping force with a proportional characteristic by the leaf valves4a.

When the piston speed further increases and reaches a high speed region and the leaf valves4aare opened to a certain extent during extension of the shock absorber D, the shock absorber D generates a damping force with a port characteristic by resistance produced when the working fluid passes in the inner peripheral side flow passage3a.

When the piston speed is in the low speed region during contraction of the shock absorber D in which the piston rod6enters the cylinder5, the pressurized working fluid in the other chamber B moves to the one chamber A through the cuts40of the leaf valves4a,4b. Thus, the shock absorber D generates a damping force with a square-law characteristic by the orifices.

When the piston speed increases beyond the low speed region and reaches the middle speed region during contraction of the shock absorber D, the pressurized working fluid in the other chamber B deflects outer peripheral parts of the leaf valves4band moves to the one chamber A through a clearance formed between the valve seat13of the piston1and the outer peripheral parts of the leaf valves4b. Thus, the shock absorber D generates a damping force with a proportional characteristic by the leaf valves4b.

When the piston speed further increases and reaches the high speed region and the leaf valves4bare opened to a certain extent during contraction of the shock absorber D, the shock absorber D generates a damping force with a port characteristic by resistance produced when the working fluid passes in the outer peripheral side flow passages3b.

FIG. 5is a sectional view showing a piston unit of a shock absorber to which a damping valve of a comparative example is applied.

A shock absorber D1to which the damping valve of the comparative example is applied is provided with a piston100partitioning one chamber A and another chamber B, and a retainer200provided to be placed on the piston100as shown inFIG. 5.

Further, the shock absorber D1is provided with an inner peripheral side flow passage300aconfigured to include a valve disk through hole110formed in an inner peripheral side of the piston100and a retainer through hole210formed in the retainer200and allowing communication between the one and the other chambers A, B, and an outer peripheral side flow passage300bformed in an outer peripheral side of the piston100and allowing communication between the one and the other chambers A, B.

A window101continuous with the outer peripheral side flow passage300band a valve seat102surrounding the outer periphery of the window101are formed on a surface of the piston100opposite to the retainer200. Further, a window201continuous with the inner peripheral side flow passage300aand a valve seat202surrounding the outer periphery of the window201are formed on a surface of the retainer200opposite to the piston100. The outer peripheral parts of leaf valves4a,4bin the form of annular plates are respectively seated on the valve seats202,102and openably close the exits of the inner and outer peripheral side flow passages300a,300b.

In the shock absorber D1, the leaf valves4ahaving a large diameter and easily deflectable can be used since a diameter of the valve seat202on which the leaf valves4acorresponding to the inner peripheral side flow passage300aare seated can be made larger by laminating the leaf valves4avia the retainer200even if the flow passages are formed in the outer and inner peripheral sides of the piston100.

Accordingly, it is possible to decrease a damping coefficient (ratio of the amount of change in damping force to the amount of change in piston speed) of a valve characteristic due to resistance produced when the working fluid passes through a clearance between the outer peripheral parts of the leaf valves4aand the valve seat202.

Further, a damping force characteristic can be variously changed by replaceably mounting retainers200having various dimensions and shapes.

Further, the shock absorber D1generates a damping force with a port characteristic due to resistance during the passage of the working fluid in the inner peripheral side flow passage300awhen the leaf valves4aare opened to a certain extent. The damping force with the port characteristic can be changed by a replacement with a retainer200having a different flow passage area of the retainer through hole210.

However, in order to enable the generation of a damping force with a port characteristic dependent on the flow passage area of the retainer through hole210, it is necessary not to throttle the working fluid passing in the inner peripheral side flow passage300aby the valve disk through hole110.

Accordingly, it is necessary to prepare a special piston formed with a valve disk through hole110having a large flow passage area in order to use the piston in combination with retainers200having various dimensions and shapes. In the case of singly using this special piston, there is a problem of being difficult to increase the damping coefficient of the port characteristic since the flow passage area of the valve disk through hole110is large.

Contrary to this, since the flow passage area of the retainer through holes20is set to be larger than that of the valve disk through holes10in the present embodiment, the working fluid having passed through the valve disk through holes10is not throttled by the retainer through holes20. Thus, the damping force with the port characteristic can be set by the flow passage area of the valve disk through holes10and the damping force characteristic can be changed by a replacement with a piston1having a different flow passage area.

Further, since the flow passage area of the valve disk through holes10only has to be not smaller than that of the retainer through holes20, the damping coefficient of the port characteristic can be increased and an existing piston can be utilized even in the case of singly using the piston1. When it is desired to increase the damping force due to the resistance of the leaf valves4a, the piston1may be singly used without providing the retainer2.

Accordingly, if three types of pistons1having different flow passage areas of valve disk through holes10are prepared, the piston1including the valve disk through holes10having a largest flow passage area is the piston1A, the piston1including the valve disk through holes10having a second largest flow passage area is the piston1B and the piston1including the valve disk through holes10having a smallest flow passage area is the piston1C, the flow passage area of the retainer through holes20formed in the retainer2to be combined with the pistons1A,1B and1C is set to be not smaller than the flow passage area of the valve disk through holes10of the piston1A. In this way, six kinds of damping characteristics shown inFIG. 4can be realized.

P1, P2and P3shown in solid line inFIG. 4represent damping characteristics when the three types of pistons1A,1B and1C are respectively used in combination with the retainer2including the retainer through holes20having a flow passage area set to be not smaller than that of the valve disk through holes10of the piston1A. P1indicates a case where the piston1A is used, P2indicates a case where the piston1B is used and P3indicates a case where the piston1C is used.

Further, P4, P5and P6shown in broken line inFIG. 4represent damping characteristics when the three types of pistons1A,1B and1C are singly used. In this case, P1changes to P4, P2changes to P5and P3changes to P6.

According to the present embodiment, by preparing n types of pistons1having different flow passage areas of valve disk through holes10and one retainer2including retainer through holes20having a flow passage area set so as not to throttle the working fluid passing through the valve disk through holes10of the piston1having a largest flow passage area of the valve disk through holes10out of the n types of pistons1, n damping force characteristics in the case of singly using the piston and n damping force characteristics in the case of using the retainer2and the piston1in combination, i.e.2ndamping force characteristics can be realized. That is, according to the present embodiment, various damping force characteristics can be realized by a small number of components.

Further, since the piston1is formed with the inner peripheral side flow passage3ain the inner peripheral side and the outer peripheral side flow passages3bin the outer peripheral side, the diameter of the leaf valves4abecomes smaller and the damping coefficient when the piston speed is in the middle speed region becomes larger when the leaf valves4afor closing the exit of the inner peripheral side flow passage3aare directly seated on the valve seat16formed on the piston1.

Accordingly, as in the present embodiment, it is preferable to enable the use of the leaf valves4ahaving a large diameter and easily deflectable and enable the damping coefficient when the piston speed is in the middle speed region to be decreased by increasing the diameter of the valve seat26on which the leaf valves4afor closing the inner peripheral side flow passage3aare seated in the configuration provided with the retainer2.

Further, since the valve disk through holes10and the retainer through holes20communicate via the windows15,22in the present embodiment, it is not necessary to position the valve disk through holes10and the retainer through holes20in the circumferential direction.

Further, since the valve disk through holes10and the outer peripheral side flow passages3bpenetrate through the piston1in the direction of the central axis of the shock absorber D and the retainer through holes20penetrate through the retainer2in the direction of the central axis of the shock absorber D, the valve disk through holes10, the outer peripheral side flow passages3band the retainer through holes20can be easily formed.

Further, since the piston main body1bis provided with the skirt portion1dand the small outer diameter portion2aof the retainer2is inserted into the skirt portion1d, it is possible to ensure the width of the slide contact portion1cin the direction of the central axis of the shock absorber D, shorten the width when the piston1and the retainer2are assembled and miniaturize the shock absorber D.

Embodiments of this invention were described above, but the above embodiments are merely examples of applications of this invention, and the technical scope of this invention is not limited to the specific constitutions of the above embodiments.

For example, although the damping valve in the above embodiment is applied to the piston unit of the shock absorber D, it may be applied to a base valve unit of the shock absorber D.

Further, although the shock absorber D is a hydraulic shock absorber using liquid as the working fluid, it may be a pneumatic shock absorber using gas as the working fluid.

Further, although the valve disk through holes10and the retainer through holes20communicate via the windows15,22formed on each mating surface of the piston1and the retainer2, positioning in the circumferential direction is not necessary if a window is formed on either one of the piston1and the retainer2. Further, if positioning is possible, the valve disk through holes10and the retainer through holes20may communicate without via the windows15,22.

The shapes of the piston1and the retainer2, the shapes and the numbers of the valve disk through holes10, the outer peripheral side flow passages3band the retainer through holes20are not limited to the above ones and can be changed as appropriate.

Further, the retainer2in the above embodiment includes the elastic deforming portions21between adjacent ones of the retainer through holes20, whereby the leakage of the working fluid in the middle of the inner peripheral side flow passage3acan be prevented. However, the elastic deforming portions21may not be included if this effect can be achieved.

With respect to the above description, the contents of application No. 2012-056846, with a filing date of Mar. 14, 2012 in Japan, are incorporated herein by reference.