GB2122305A - Fluid spring or damper with slidable piston - Google Patents

Abstract

A cylinder device such as a hydraulic damper or gas spring has a cylinder 1, a piston 25 slidably disposed in the cylinder which partitions the interior of the cylinder into two chambers B, C, and at least one passage 26 extending through the piston to communicate the two chambers. A piston rod 21 extends through at least one of the two chambers to extend out of the cylinder, and a control device for controlling fluid flow through the passage is provided, the control device comprising an annular disc 23, 38, 79 cooperating with one side surface of the piston. The piston is mounted on the piston rod and is axially displaceable relative thereto by a limited amount. In Figure 3, the stops 23, 24 which limit movement of the piston also control flow thro' the passage. In Figure 11, the passage is controlled by resiliently deflectable valve discs 38, 39. In Figure 30, the passage is controlled by an elastomeric ring 79 with a port (79B) which closes when the ring is compressed. The ring may be relaced by a deflecting valve disc (60, Figure 16). <IMAGE>

Description

SPECIFICATION Cylinder device This invention relates to a cylinder device such as a gas spring our a hydraulic damper which includes a cylinder, a piston partitioning the interior of the cylinder into two chambers and slidably disposed in the cylinder, and a piston rod connected to the piston and extending out of the cylinder.

Usually, a damping force generating mechanism is incorporated in the cylinder device to generate damping force when the piston moves reciprocatingly in the cylinder or in extension and contraction strokes of the cylinder device. Various proposals have been make with respect to the damping force generating valve mechanism. Such prior art mechanisms operate generally satisfactorily but, there are shortcomings such that it is complicated in the construction and/or assembling operation, and it is difficult to obtain desired damping force characteristics, particularly, the ratio between the damping force in the contraction and extension strokes.

An object of the invention is to provide a cylinder device having a novel damping force generating mechanism.

According to the invention, the piston is axially displaceably mountd on the piston by a limited amount, and the damping force generating mechanism comprises at least one passage extending through the piston to communicate the two chambers defined on opposite sides of the piston and control means including an annular disc cooperates with one side surface of the piston for controlling the fluid flow in the passage.

Figure 1 shows a typical prior art cylinder device acting as a hydraulic damper which comprises a cylinder 1 with one end thereof being closed by a cap 2 and the other end thereof being fitted with a rod guide 3 and a seal member 4. A piston 5 is slidably disposed in the cylinder 1, and a piston rod 3 is secured to the piston and extends through the rod guide 3 and the seal member 4. A free piston 7 is slidably disposed in the cylinder to define a gas chamber A between the free piston 7 and the cap 2 in the cylinder 1 for compensating the change in volume of the cylinder 1 which is caused of the ingress or exit of the piston rod. The gas chamber A contains therein gas under a predetermined pressure.Two oil chambers B and C containing therein oil are defined in the cylinder 1 and between the free piston 7 and the piston 5 and between the piston 5 and the seal member 4. A through hole or a passage 8 constituting an orifice extends through the piston 5 to permanently connect chambers B and C. Seal members 9 and 10 are respectively provided on the piston 5 and the free piston 7, and mounting members 11 and 12 are mounted respectively on the outer end of the piston rod 6 and on the cap 2 to mount the cylinder device in such as a suspension system of an automotive vehicle.

The hydraulic damper illustrated in Figure 1 operates as follows. When force acts on the piston 5 or the piston rod 6 to displace the same in arrow a direction, the piston rod 6togetherwith the piston 5 displaces in extending direction, and the pressure in the chamber C increases as compared with that in the chamber B with the oil in the chamber C flowing into the chamber B through the orifice 8, thereby generating a damping force as shown in line OR in Figure 2. While, in the contraction stroke of the damper, the piston rod 6 together with the piston 5 displaces in arrows direction with the oil in the chamber B flowing into the chamber C through the orifice 8, thereby generating a damping force as shown in line OR' in Figure 2.

The construction of the damper shown in Figure 1 is very simple, however, since the cross-sectional area of the orifice 8 provided in the piston 5 is a constant the damping force characteristics with respect to the speed of the piston 5 are the same both in the extension and contraction strokes. Further, the damping force is very large in the high speed range of the piston.

Various proposals have been made with respect to damping force generating mechanism of the hydraulic damper for attaining desired damping forces in respective extension and contraction strokes of the damper.

For example, a resiliently deformable annular disc is mounted on one side of the piston and the disc normally engages with a large diameter valve seat one side of the disc and with a small diameter valve seat at the other side of the disc. When the piston moves in one direction the disc separates from one of valve seats to permit the fluid flow across the piston in one direction, and when the piston moves in the other direction the disc resiliently deflects and separates from the other valve seat and the fluid flows across the piston in the other direction. The construction is relatively simple, but it is difficult to obtain a large ratio in the damping force between the extension and contraction strokes.

It has also been proposed to provide on opposite sides of the piston resiiiently deformable discs for acting respectively in extension and contraction strokes. The damping force in either one of extension and contraction strokes can be determined independently of the other strokes. However, it is usually required to form two sets of through bores in the piston which are inclined with respect to the axis of the cylinder thereby complicating machining procedure of the piston.

An object of the invention is to provide a novel damping force generating mechanism for use in a cylinder device such as a gas spring or a hydraulic damper having a simple construction with the damping force characteristics in extension and conraction strokes can easily be adjusted for respective extension and contraction strokes.

The present invention provides a cylinder device comprising a cylinder, a piston slidabiy disposed in the cylinder and partitioning the interior of the cylinder into two chambers, at least one passage extending through the piston to communicate the two chambers, a piston rod connected to the piston and extending through at least one of the two chambers to extend out of the cylinder, and a control device for controlling fluid flow through the passage.

The piston is axially displaceably mounted on the piston rod and being displaceable by a limited amount, and the control device comprises an annular resiliently deformable disc cooperating with one side surface of the disc.

According to the invention, the construction of the piston is very simple and the damping force in respective extension and contraction strokes of the cylinder device can be adjusted as desired.

The piston according to the invention is mounted on the piston rod and is displaceable relative thereto by a limited amount. Thus, the cylinder device according to the invention is particularly advantageous when the piston rod moves relative to the cylinder at severe vibrating or reciprocating movements since the piston rod can move relative to the cylinder by a limited amount without displacing the piston and without generating any substantial damping force. It will be understood that when the piston rod reciprocatingly moves irrespective to the movement of the piston the damping force generating mechanism is not actuated but a force corresponding to the pressure of the fluid enclosed in the cylinder acts on the piston rod.

Further objects and advantages of the invention will become apparent from following detailed descriptions taken in conjunction with the accompanying drawings exemplifying some preferred embodiments of the invention, in which: Figure 1 is a schematic longitudinal sectional view of a prior art cylinder device; Figure 2 is a diagram showing damping force characteristics of the cylinder devices according to prior art and to present invention; Figure 3 is a longitudinal sectional view of a cylinder device according to a first embodiment of the invention; Figure 4 - Figure 6 are enlarged partial half sectional views of the device of Figure 3 in respective operational conditions; Figure 7 is a longitudinal sectional view of a cylinder device according to a second embodiment of the invention;; Figure 8- Figure 11 are enlarged partial half sectional views of the device of Figure 7 in respective operational conditions; Figure 12-Figure 15 are partial longitudinal sectional views of a cylinder device according to a third embodiment of the invention and showing respective operational conditions; Figure 16Figure 19 are partial longitudinal half sectional views of a cylinder device according to a fourth embodiment of the invention and showing respective operational conditions; Figure 20 is a partial longitudinal half sectional view of a cylinder device according to a fifth embodiment of the invention; Figure 21 is a plan view of a resiliently deformable annular disc incorporated in the device of Figure 20;; Figure 22 is a partial longitudinal half sectional view of a cylinder device according to a sixth embodiment of the invention; Figure 23 is a plan view of a resiliently deformable annular disc incorporated in the device of Figure 22; Figure 24 is a view similar to Figure 22 but showing a seventh embodiment of the invention; Figure 25 is a plan view of an annular disc incorporated in the embodiment of Figure 24; Figure 26 and Figure 27 are partial longitudinal half sectional views of a cylinder device according to an eighth embodiment of the invention and showing respective operational conditions; Figure 28 is a plan view of an annular disc incorporated in the device of Figures 26 and 27; Figure 29 and Figure 30 are partial longitudinal half sectional views of a cylinder device according to a ninth embodiment of the invention and showing respective operational conditions;; Figure 31 is a partial view showing a rubber ring being assembled in the device of Figures 29 and 30; Figure 32 is a cross-sectional half view of the rubber ring in Figure 29 and Figure 31; Figure 33 and Figure 34 are partial longitudinal half views of a cylinder device according to a tenth embodiment of the invention and showing respective operational conditions; Figure 35 is a plan view of an annular disc incorporated in the device of Figures 33 and 34; Figure 36 and Figure 37 are partial longitudinal half sectional views of a cylinder device according to an eleventh embodiment of the invention and showing respective operational conditions; Figure 38 is a plan view of an annular disc incorporated in the device of Figures 36 and 37; and Figure 39 is a view similar to Figure 36 but showing a modified form.

Figures 3-6 show the first embodiment of the invention wherein parts corresponding to Figure 1 are depicted by the same reference numerals and detailed description therefor is omitted. A piston 25 is slidably mounted in the cylinder 1 and is also slidably mounted on a piston rod 21. The piston rod 21 has on the inner end a small diameter portion 21A, and retainer 23 and 24 and a collar or sleeve 22 are mounted on the small diameter portion 21A and retained by a projecting portion 21C which is preferably formed by caulking the tip end of the small diameter portion 21A. The piston 25 has central bore 25A fitted on the sleeve 22, thus, the piston 25 can displace on the sleeve 22 between the retainers 23 and 24. Coil springs 29 and 30 extends between the retainers 23 and the piston 25 and between the retainer 24 and the piston 25 respectively. The piston 25 has on the opposite side surfaces annular projecting portions 25B and 25C near to the outer diameter portion thereof, and one or more axially extending holes 26 constituting a passage according to the invention. The passage 26 normally communicates chambers B and C, but when the piston 25 is displaced axially against the spring force of the spring 29 or 30 to abut with the retainer 23 or 24, the fluid flow through the passage 26 stops. The piston 25 further has orifice passages 27 and 28 which are branched from the passage 26 and are permanently communicated with chambers C and B respectively. Coil springs 29 and 30 coact to determine the neutral position of the piston 25 with respect to the piston rod 21 as shown in Figure 4 whereat desired distances ea and f bare defined between the retainers 23 and 24 and the piston 25 respectively.

The cylinder device according to the first embodiment operates as follows. Firstly, when an external force acts on the piston rod 21 to move the same in arrow a direction in Figure 3, the piston 25 tends to move with the piston rod 21 and the oil in the chamber C flows into the chamber B through the passage 26. The cross-sectional area of the passage 26 in larger than that of the orifice passage 27 which is larger than that of the orifice passage 28. The fluid flow through the passage 26 generates a relatively small damping force as shown in line OM in Figure 2.

The piston 25 displaces toward the retainer 24 against the spring force of the spring 30. When the speed of the piston 25 further increases, the piston 25 abuts with the retainer 30 as shown in Figure 5, and the passage 26 is closed by the retainer 30. The oil in the chamber C flows into the chamber B through the orifice passage 28 solely. A large damping force as shown in line M N in Figure 2 generates.

While, in the contraction stroke, the piston rod 21 moves in arrow b direction. When the piston speed is low, a damping force is generated from the fluid flow through the passage 26 which is depicted by line OM' in Figure 2. When the piston speed increases further, the pressure difference between the chambers B and C overcomes the spring force of the coil spring 29 and the piston 25 abuts with the retainer 23 thereby closing adjacent end of the passage 26, as shown in Figure 6. The fluid in the chamber B flows into the chamber C through the orifice passage 27, which generates damping force as shown in line M'N' in Figure 2.

As clearly be shown in lines OMNand OM'N' in Figure 2, in the low speed range of the piston 25, the damping force is solely determined by the passage 26 both in the extension and contraction strokes, and the damping force gradually increases in response to the piston speed. In the high speed range of the piston 25, the passage 26 is closed and the damping forces are determined in respective extension and contraction strokes by the orifice passages 28 and 27 respectively. The damping force can easily be adjusted by adjusting the cross-sectional area of the orifice passage which can be performed independently on either of extension and contraction strokes. Further, by changing the spring force of the springs 29 and 30, the points M and M' can be changed as desired.

Figures 7 - 11 show the second embodiment of the invention, wherein parts corresponding to the first embodiment are depicted by the same reference numerals and detailed description therefor is omitted. The second embodiment differs from the first embodiment in that a spacer 40, an annular resiliently deformable disc 40 and an annular rigid disc 36 are interposed between the retainer 23 and the sleeve 22, and in that an annular rigid disc 37, an annular resiliently deformable disc 39 and a spacer 41 are interposed the sleeve 22 and the retainer 24 as shown in the drawings. The resiliently deformable discs 38 and 39 may consist of one or more mutually overlapping thin discs respectively. In the drawings the disc 38 consists of a single disc and the disc 39 consists of two mutually overlapping discs.The rigid discs 36 and 37 has axially extending openings 36A and 37A as shown in the drawings. A piston 35 generally similar to the piston 25 is slidably mounted on the sleeve 22 and the axial displacement thereof is restricted by rigid discs 36 and 37. The springs 29 and 30 extend respectively between the piston 35 and the discs 36 and 37. The flexible discs 38 and 39 normally abut with rigid discs 36 and 37 respectively to close respective openings 36A and 37A, but the outer circumferential portions thereof can resiliently flex in the direction separating from respective rigid discs 36 and 37. The piston 35 has, similarly to the piston 25 in the first embodiment, the passage 26 and orifice passages 27 and 28, and the passage 26 normally communicate the two chambers C and B.

In operation, when the piston rod 21 displaces in arrow a direction in the extension stroke, the piston 35 displaces toward the rigid disc 37 against the spring force of the spring 30. At a predetermined piston speed, the cylinder device takes the condition of Figure 8 which is similar to Figure 5 in the first embodiment, namely, the fluid in the chamber C flows into the chamber B solely through the orifice passage 27. When the piston speed further increases, the resilient disc 39 is flexed by the pressure in the chamber C acting through the passage 26 in the piston 35 and through the opening 37A in the disc 37, and the outer circumference thereof separates from the disc 37 as shown in Figure 9. An annular passage S2 is formed between the disc 37 and the resilient disc 37. The damping force characteristics of the device in the extension stroke are defined by line OMPO in Figure 2.

Similarly, in the contraction stroke, in the low speed range of the piston, the passage 26 acts to determine the damping force. Thereafter, the piston 35 engages with the rigid disc 36 as shown in Figure 10 which is similar to Figure 6 in the first embodiment. The fluid in the chamber B flows into the chamber C solely through the orifice passage 27 to define an intermediate speed range of the piston, which is depicted by line M'P' in Figure 2. At high speed range of the piston, the flexible disc 38 separates from the rigid disc 36 as shown in Figure 11, and the fluid in the chamber B flows into the chamber C through the passage 26 in the piston 35, the opening 36A in the rigid disc 36 and an annular passage S1 formed between the discs 36 and 38. As the result, the damping force characteristics in the contraction stroke are depicted by line OM'P'Q' in Figure 2.

Figures 12 - 15 show the third embodiment of the invention, and portions not shown in the drawings are similar to preceding embodiments, and the same reference numerals are applied to parts similar to the preceding embodiments. The piston rod 21 has on the inner end portion thereof a small diameter portion 21Adefining inwardly facing shoulder 21 B.

The small diameter portion 21A of the piston rod 21 slidably mounts thereon a piston 55 and a retainer 24 is secured on the tip end portion of the small diameter portion 21A by an annular groove and a projecting portion 21 C. Further to the piston 55, two resiliently deflectable annular discs 59 and 60 are slidably mounted on the small diameter portion 21A at the opposite sides of the piston 55. The disc 59 can displace between the shoulder 21 B and the piston 55, and the disc 60 can displace between the piston 55 and the retainer 24. There are provided in the piston 55 a first passage 57 extending axially through the piston 55, a second passage 56 indepen dentlyfrom the first passage 57 and opening only toward the chamber C, and an orifice passage 58 branched from the second passage 56 to open to the chamber B.In the drawing, the second passage 56 is integrally formed with the central bore 55A of the piston 55 which slidably engages with the small diameter portion 21A of the piston rod, however, the passage 56 may be formed independently of the central bore 55A. In the embodiment, the piston 55 is directly mounted on the piston rod 21, however, a sleeve similar to the sleeve 22 in the preceding embodiments may be interposed therebetween. The piston 55 has in opposite side surfaces thereof annular grooves or recesses which define, on radially outer portions axially projecting portions 55B and 55C, and on radially inner portions axially projecting portions 55D and 55E as shown.The projecting portion 55C toward the retainer 24 such that when the inner circumference of the disc 60 is clamped between the retainer 24 and the projecting portion 55E as shown in Figures 12 and 13, a small clearance S2 is formed between the projecting portion 55C and the disc 60. Similarly, the projecting portion 55D projects toward the disc 59 as compared with the projecting portion 55B such that when the inner circumferential portion of the disc 59 is clamped between the shoulder 21 B on the piston rod 21 and the projecting portion 55D of the piston 55 as shown in Figures 14 and 15, a small clearance Si is formed between the outer circumferential portion of the disc 59 and the projecting portion 55B of the piston 55.

Further, a cut-out 59A is formed in the disc 59 to communicate the chamber C with the passage 56 at the condition of Figures 14 and 15.

In operation, when the piston rod 21 moves in arrow a direction in the extension stroke of the damper, the piston 55 and the disc 59 move rightward relative to the piston rod 21 in the initial stage and takes the condition of Figure 12, at that condition, it will be understood that the fluid in the chamber C can flow into the chamber B through the cut-out 59A in the disc 59, the passage 56 and the orifice passage 58 on one hand, and through annular spaces S1 between the disc 59 and the projecting portion 55B, the passage 57 and the annular space S2 between the disc 60 and the projecting portion 55C.The flow is substantially defined by the passage 57 acting as an orifice passage since the effective cross-sectional area thereof is larger than that of the orifice passage 58 and is smaller than the annular space S, or 52 When the piston speed in the extension stroke increases, the resilient disc 59 deflects toward the projecting portion 55B and the outer circumference thereof engages therewith as shown in Figure 13. The fluid flow through the orifice passage 57 stops and the orifice passage 58 acts to define the damping force. The damping force characteristics in the extension stroke are generally similarto line OMN in Figure 2.

In the contraction stroke, the piston rod 21 moves in arrow b direction, and the device takes the condition shown in Figure 14 in the initial stage.

Similar to the condition of Figure 2, the passages 57 and 58 define the damping force. When the piston speed increases to a predetermined level, the outer circumference of the resilient disc 60 deflects toward and engages with the projecting portion 55C of the piston 55 thereby closing the orifice passage 57, as shown in Figure 15. The damping force is defined by the fluid flow through the orifice passage 58. Thus, the damping force characteristics in the contraction stroke is generally similar to line OM'N' in Figure 2.

The damping force characteristics can be determined as desired by changing the rigidity of the discs 59 and 60 and the effective cross-sectional area of orifice passages 57 and 58.

Figures 16 - 19 show the fourth embodiment of the invention with the construction thereof being simplified as compared with the third embodiment. Namely, a piston 65 having a through passage 56 and a branched orifice passage 58 is slidably mounted on the small diameter portion 21A of the piston rod 21, and a generally dish shaped annular disc 60 is interposed between the retainer 24 and adjacent side surface of the piston 65. An annular peojecting portion 65C is formed on the side surface of the piston 65 to cooperate with the outer circumferential portion of the disc 60. The disc 59 in the third embodiment is omitted and the leftward movement of the piston 65 relative to the piston rod 21 is restricted by the shoulder 21 B on the piston rod 21.

In the extension stroke of the device, the device takes the condition shown in Figure 16 in the initial stage wherein the outer circumferential portion of the disc 60 contacts with the retainer 24 and the inner circumferential portion thereof contacts with the piston 65, and an annular clearance S2 is formed between the projecting portion 65C and the disc 60.

The effective cross-sectional area of the clearance S2 is substantially larger than the orifice passage 58 and the damping force is relatively low. When the piston speed increases, the disc 60 is gradually deflected with the clearance S2 being gradually decreased until the disc 60 engages with the projecting portion 65C as shown in Figure 17. Thereafter, the damping force is determined by the orifice passage 58. The damping force characteristics are generally similar to line OMN in Figure 2, with the sharp corner M not being observed.

Figures 18 and 19 show the conditions in the contraction stroke which are generally similar to Figures 16 and 17 respectively and, accordingly, the detailed description therefor is omitted. It will be noted that the damping force characteristics of the fourth embodiment are identical with respect to the extension and contraction strokes.

Figures 20 and 21 show the fifth embodiment of the invention, which is modified from the fourth embodiment to change the damping force in the contraction stroke from that in the extension stroke.

For the end, there are provided cut-outs 60A in resiliently deformable disc 60' in the inner circumferential portion thereof. The cut-outs 60A do not have any effect in the extension stroke, but in the contraction stroke, the cut-outs 60 communicates the chamber B with the passage 56 irrespective to the deflection of the disc 60'. Thus, the damping force in the contraction stroke is depicted by line OT in Figure 2.

Figures 22 and 23 show the sixth embodiment of the invention which also is modified from the fourth embodiment and is generally similar to the fifth embodiment. The disc 60' in Figure 21 is modified to disc 60" having further a cut-out 60B in the outer circumferential portion. The configuration of the piston 65, particularly the configuration of the projecting portion 65C thereof or the inclination of the disc 60" are determined such that, in the initial stage of the extension stroke, the device takes the condition of Figure 21 whereat the disc 60" contacts with the projecting portion 65C of the piston 65 and the fluid in the chamber C flows through the passage 56 and the orifice passage 58 into the chamber B and through the passage 56, the cut-outs 60A in the disc 60" and the cut-out 60B into the chamber B.

Figures 24 and 25 show the seventh embodiment of the invention which is generally similar to the embodiments of Figures 20 and 21 and Figures 22 and 23. A resiliently flexible disc 60' generally similar to the disc 60' in Figure 20 is interposed between the piston 65 and the retainer 25, but the disc 60' in this embodiment is inclined in the direction opposite to the embodiment of Figure 20. The operation and function are generally similar to the fifth and sixth embodiments.

Figures 26 - 28 show the eighth embodiment of the invention generally similar to preceding three embodiments. The disc 60' shown in Figure 28 is generally similar to the disc 60' in Figure 28 in the plan view, but the former is normally flat while the latter is normally dish shaped. The retainer 24 in the preceding embodiments is substituted by a retainer 64 which has projecting portions 64A and 64B and a recessed portion 64C on the surface facing the piston 65'. Further, there is provided a resilient ring such as rubber ring 66 on the small diameter portion 21A of the piston rod 21 for absorbing the shock between the piston 65' and the annular shoulder 21 B on the piston rod 21 and suppressing the generation of foreign sounds.When the piston rod 21 moves in arrow a direction or in the extension stroke, the piston 65' takes the position shown in Figure 26 in the initial stage, whereat the fluid in the chamber C flows into the chamber B through the orifice passage 58 and through a portion of the cut-out 60A in the disc 60' (which portion is designated at 61, and remaining portion 62 of the cut-out 60A is covered by the projecting portion 64A of the retainer 64 as shown in Figure 28). The fluid flow through the cut-out 60A is gradually reduced in response to the increase of the piston speed. The disc 60' gradually deflects and the circumferential clearance between the projecting portion 64B and the disc 60' gradually decreases.

Figures 29 - 32 show the ninth embodiment of the invention which also is generally similar to preceding four embodiments. The resiliently flexible disc in the preceding embodiments is substituted by an annular rubber ring 79 interposed between a piston 75 and a retainer 74. The piston 75 is generally similar to the piston 55 in Figures 16 - 27 although distinct reference numerals are applied to corres ponding parts. Preferably, the rubber ring 79 is secured to the piston 75. The rubber ring 79 has a circumferential groove 79A in the outer circumfer encethereofto define a generally U-shaped cross section. In the bottom wall of the U-shaped rubber ring 79, there is provided at least one radial hole 79B to define an orifice passage.The retainer 74 has a plurality of angularly spaced and axially extending arms 74A for preventing the deformation of the rubber ring 79 in compressing axially the rubber ring. In the initial stage of the extension stroke, the piston 75 moves toward the retainer 74 and the fluid in the chamber C flows into the chamber B through the orifice passage 78 in the piston 75 which is generally similar to the orifice passage 58 in such as Figure 27, and through the orifice passage 79B in the rubber ring 79. When the piston speed in arrow b direction increases, the rubber ring 79 is compressed between the piston 75 and the retainer 74 with the effective cross-sectional area of the passage 79B decreasing gradually. At a predetermined piston speed, the passage 79B closes as shown in Figure 30.Thereafter, the fluid in the chamber C flows solely through the orifice passage 78 and into the chamber B.

Figures 33 - 35 show the tenth embodiment of the invention which is slightly modified from the ninth embodiment of Figures 26 - 28. The disc 60' shown in Figure 28 is substituted by a disc 80 as shown in Figure 35. The disc 80 is fixedly mounted on the piston rod 21, thus, in the contraction stroke shown in Figure 33, the fluid in the chamber B relatively freely flows into the chamber C and any substantial damping force does not generate. In the initial stage of the extension stroke, the piston 85 takes the condition shown in Figure 34 which is generally similar to Figure 26, and the cylinder device acts similarly thereto.

Figures 36 - 38 show the eleventh embodiment of the invention which is modified from the tenth embodiment. Namely, retainers 93 and 94 similar to the retainer 84 and resiliently flexible discs 90 and 91 generally similar to the disc 80 are fixed mounted on the small diameter portion 21A of the piston rod 21 and on the opposite sides of a piston 95. A sleeve 22 generally similar to the sleeve 22 in Figure 3 is interposed between the inner circumferential portions of the discs 90 and 91 and on the small diameter portion 21A of the piston rod and slidably mounts thereon the piston 95. Each disc 90 or 91 has in the outer circumferential portion at least one cut-out 90A or 91A acting as an orifice passage. The retainers 93 and 94, the discs 90 and 91 and the sleeve 22 are secured on the piston rod 21 by a nut 97 engaging with external screw threads formed on the tip end portion of the small diameter portion 21A of the piston rod 21. Figure 36 shows the condition in the initial stage of the extension stroke, whereat an annular projecting portion 95C formed on the outer circumferential portion of the piston 95 contacts with the outer circumferential portion of the disc 91. The radially outward portion 98 (Figure 38) of the cut-out 91A is covered by the projecting portion 95C, and the radially inward portion 99 (Figure 38) defines the area of the orifice passage. It will be noted that the axial clearance between the disc 91 and the radially outward portion 94B of the retainer 94 is larger than the orifice passage 99.When the piston speed increases, the disc 91 gradually deflects toward the portion 94B of the retainer 94 and, finally, takes the condition shown in Figure 37. At that condition, the fluid flow from the chamber C to the chamber B is restricted by a generally rectangular orifice and the two sides of which are defined by the width of the cut-out 90A and the thickness of the disc 91, and which orifice corresponds to the orifice 88 in Figures 33 and 34.

In the contraction stroke the piston 95 moves leftward in Figure 36 and cooperates with the disc 90. It will be noted that the discs 90 and 91 consist respectively of single discs, however, each or either one disc may be formed of two or more mutually overlapping discs such as shown in the disc 39 in Figure 7.

Figure 39 shows a modified form of the embodiment of Figure 36 - 39 wherein the disc 90, the retainer 93 and the sleeve 22 in Figure 36 are removed. A piston 95' is directly mounted on the small diameter portion 21A of the piston rod 21, and disc91 similar to the disc 91 in Figure 38 and a retainer 94 similar to the retainer 94 in Figure 36 are secured on the piston rod 21. In the initial stage of the extension stroke the device takes the condition as shown in Figure 39 which is similar to the condition of Figure 36. The damping force characteristics in the extension stroke are substantially similar to the embodiment of Figure 36 and that in the contraction stroke is substantially zero.

As described heretofore, according to the invention, the piston is mounted on the pistion rod and is displaceable axially relative thereto by a limited small amount such as about 1 - 2 mm. In other word, the piston is connected to the piston rod with a lost-motion connection and, as the result, the piston rod can reciprocatingly move relative to the cylinder by a limited small amount with the damping force generating mechanism being inactuated and only a force corresponding to the pressure of the fluid enclosed in the cylinder acting on the piston rod.

Various types of damping force generating mechanisms may easily be incorporated in the cylinder device, and the construction of the piston can be simplified.

The invention is not limited to or by details of construction of particular embodiments thereof illustrated in the drawings, as various other forms of the device will of course be apparent to those skilled in the art without departing from the spirit of the invention.

For example, the cylinder devices shown in the embodiments are single tube type hydraulic dampers but may be gas springs or dual tube type.

Further, the effective cross-sectional area of orifice passages such as passages 27 and 28 in Figures 3 - 6 may be changed as desired, and various components such as the sleeve 22, springs 29 and 30, discs 38,39,59,60,80,90 and 91 and the like shown in respective embodiments may be combined with other embodiments. Further, the configuration and the construction of the piston and the piston rod may be changed as desired.

Claims (9)

1. A cylinder device including a cylinder, a piston slidably disposed in the cylinder and partitioning the interior of the cylinder into two chambers, at least one passage extending through the piston to communicate said two chambers, a piston rod connected to the piston and extending through at least one of said two chambers to extend out of the cylinder, and control means for controlling fluid flow through said passage, wherein the piston is mounted on the piston rod and is displaceable relative thereto in the axial direction by a limited amount, and the control means comprises an annular disc cooperating with one side surface of the piston.

2. A cylinder device according to claim 1 wherein said passage comprises a main passage and an orifice passage, and the annular disc is a rigid member secured to the piston rod and restricts the fluid flow through said main passage when the disc abuts with one side surface of the piston.

3. A cylinder device according to claim 2 wherein a coil spring extends between the annular disc and the piston.

4. A cylinder device according to claim 1 wherein said passage comprises a main passage and an orifice passage, and the annular disc comprises a resiliently deflectable disc which, in response to the movement of the piston rod in the cylinder and in one axial direction, firstly closes one end of said main passage and, thereafter, resiliently deflects to permit the fluid flow through said main passage.

5. A cylinder device according to claim 1 wherein said passage comprises a main passage and an orifice passage, and the annular disc comprises a resiliently deflectable dish shaped disc which is axially displaceable together with the piston and resiliently closes said main passage in response to the increase of the moving speed of the piston and the piston rod in the cylinder in one axial direction.

6. A cylinder device according to claim 5 wherein a cutout is formed in the resiliently deflectable disc for controlling the fluid flow through the disc.

7. A cylinder device according to claim 1 wherein said passage comprises a main passage and an orifice passage, and the annular disc comprises an elastomeric ring having an orifice opening for controlling fluid flow through said main passage, and said elastomeric ring resiliently deflects to close said orifice opening in response to the increase in the moving speed of the piston and piston rod in the cylinder in one axial direction.

8. A cylinder device according to claim 1 wherein said annular disc is a resiliently deflectable disc with the inner circumference thereof being secured to the piston rod and the outer circumference thereof being adapted to engage with the piston in response to the movement of the piston relative to the piston rod in one axial direction.

9. A cylinder device substantially as herein de scribed with reference to and as shown in Figures 3-6; 7-11; 12-15; 16-19; 20, 21; 22,23; 24,25; 26-28; 29-32; 33-35; 36-38; 39.