Vibration damper for a vehicle

Abstract

A vibration damper for a vehicle, includes at least one cylinder tube forming a fluid chamber, in which a piston assembly is axially and slidingly arranged and divides the cylinder tube into two working chambers, an upper and a lower working chamber, and wherein the piston assembly has an axially moveable main piston which is axially fixed to a piston rod that can move axially relative to the cylinder tube, and which has a piston valve influencing the fluid flow between the upper and lower working chambers, and wherein a further stroke-dependent piston is arranged on an axial extension of the piston rod in the direction of the cylinder base, which operates once a determined damper stroke is achieved. The stroke-dependent piston has a smaller diameter than the main piston and only operates when plunging into a smaller diameter of an inner casing surface. The stroke-dependent piston therefore has a stroke-dependent valve, and the stroke-dependent piston also has a frequency-dependent valve in addition to the stroke-dependent valve.

Claims

1. A vibration damper for a vehicle, comprising: at least one cylinder tube which forms a fluid chamber; and a piston assembly disposed in the cylinder tube so as to slide axially and divide the cylinder tube into two working chambers, an upper and a lower working chamber; wherein the piston assembly comprises an axially displaceable primary piston which is axially established on a piston rod that is movable axially relative to the cylinder tube, and a piston valve which influences the flow of fluid between the upper working chamber and the lower working chamber, wherein a stroke-dependent piston which acts upon reaching a specific damper stroke is disposed in an axial extension of the piston rod in the direction of a cylinder base of the cylinder tube, wherein the stroke-dependent piston has a smaller diameter than the primary piston and only operates when plunging into a smaller diameter of a cylinder-internal shell face, on account of which a stroke-dependent valve of the stroke-dependent piston is formed, and wherein a damping action of the stroke-dependent valve takes place as a function of a plunging depth of the stroke-dependent piston into the cylinder tube, wherein the stroke-dependent piston comprises a frequency-dependent valve in addition to the stroke-dependent valve, wherein the frequency-dependent valve is disposed so as to be coaxial with the stroke-dependent piston and is disposed in an interior of the stroke-dependent piston, wherein the piston rod at a position in the upper working chamber comprises a bypass for flow of fluid from the upper working chamber into the lower working chamber, and the flow is through the piston rod and the extension of the piston rod directly into the frequency-dependent valve which is disposed in the interior of the stroke-dependent piston.

2. The vibration damper according to claim 1, wherein a cup-shaped socket is disposed on a lower end of the cylinder tube so as to be coaxial with the latter, an external diameter of the socket is smaller than an internal diameter of the cylinder tube, and the stroke-dependent piston upon reaching a specific damper stroke plunges into the socket and is active.

3. The vibration damper according to claim 2, wherein the vibration damper is a twin-tube damper having an internal and an external cylinder tube, and the cup-shaped socket is disposed within the internal cylinder tube.

4. The vibration damper according to claim 2, wherein the cup-shaped socket, at least on an internal shell face, has an axially extending conical groove which from a socket entry runs axially in the direction of a socket base and narrows in a conical manner.

5. The vibration damper according to claim 4, wherein the at least one groove does not extend up to the socket base.

6. The vibration damper according to claim 2, wherein the stroke-dependent piston comprises an annular seal, and the annular seal has a same diameter as an internal shell face of the socket.

7. The vibration damper according to claim 1, wherein the stroke-dependent piston comprises at least one through bore for flow of fluid from the upper working chamber into the lower working chamber in a tension stage of the vibration damper.

8. The vibration damper according to claim 1, wherein the stroke-dependent valve acts in a compression stage of the vibration damper, and the frequency-dependent valve acts in a tension stage of the vibration damper.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1, in a schematic manner, shows a longitudinal section through a cylinder tube of a shock absorber of a vehicle, having a stroke-dependent piston according to an embodiment of the invention.

(2) FIGS. 2 and 3 are more detailed views of the sectional view from FIG. 1, wherein the flow of fluid and the functional mode of the stroke-dependent piston are shown individually in a compression stage and in a tension stage.

DETAILED DESCRIPTION OF THE DRAWINGS

(3) A sectional view through the longitudinal axis of an exemplary fluid-filled cylinder tube 1 of a shock absorber of a vehicle is schematically shown in FIG. 1. The cylinder tube 1 in FIG. 1 herein is oriented so as to be at least approximately in the installed state thereof in the vehicle, specifically at least approximately in the vehicle vertical direction H.

(4) A piston assembly which is movable axially up and down in relation to the cylinder tube 1 is disposed in the interior of the cylinder tube 1, said piston assembly having a piston 3 (also referred to as the primary piston) which is likewise able to slide axially in the cylinder tube 1 and which is fixedly connected to a piston rod 2 which is movable axially in the cylinder tube 1. An operating fluid is located in the cylinder tube 1.

(5) A base valve 5 which enables a flow of fluid between the cylinder tube 1 and the exterior of the cylinder tube 1 (such as in a twin-tube damper, for example) is disposed on the cylinder base 4.

(6) The diameter of the primary piston 3 herein corresponds to the diameter of the internal shell face of the cylinder tube 1, on account of which the primary piston 3 forms an upper working chamber 7 and a lower working chamber 8. On account of suitable bypasses or through bores, respectively, (not illustrated) through the primary piston 3, a flow of fluid from the upper working chamber 7 into the lower working chamber 8 can be achieved, and damping can be achieved on account of specific variations of the cross sections of the bypasses, as is already known from the prior art.

(7) In one preferred embodiment of the invention, this however not being depicted in this example, the cylinder tube 1 is surrounded by a further cylinder tube, wherein the shock absorber in this instance represents a so-called twin-tube shock absorber.

(8) A further piston 6, here referred to as the stroke-dependent piston 6, is disposed at the lower end of an extension 2.1 of the piston rod 2, the stroke-dependent piston 6 sliding axially in the cylinder tube 1 having the extension 2.1. The stroke-dependent piston 6 herein is screw-fitted to the extension 2.1 of the piston rod. To this end, the extension 2.1 of the piston rod 2 on the lower end thereof preferably has a thread (not shown) on which the stroke-dependent piston 6 is screwed in and thus fastened.

(9) With the aid of this stroke-dependent piston 6, additional damping in the compression stage and frequency-dependent or frequency-selective, respectively, controlling or adjusting, respectively, of the damping are to be implemented as a function of the piston stroke and of the vibration frequency, or the frequency of the movement, respectively, of the damper in the tension stage of the shock absorber.

(10) These additional damping actions, or this frequency-dependent or frequency-selective, respectively, controlling, respectively, herein is in each case possible in different operating situations or (operating) stages, respectively, of the shock absorber. The stroke-dependent damping herein can be implemented in a compression stage of the damper, and the frequency-dependent, or frequency-selective, respectively, damping herein can be implemented in a tension stage of the damper.

(11) The damper in this instance is in a compression stage when the piston assembly 2, 3 moves in the direction of the cylinder base 4 and thus pushes downward. The telescopic shock absorber herein is displaced so as to axially inherently compress and the operating fluid flows from the lower working chamber 8 into the upper working chamber 7.

(12) In contrast, the piston assembly 2, 3 in a tension stage moves away from the cylinder base 4, upward in the axial direction of the cylinder tube 1. The telescopic shock absorber is displaced so as to axially inherently expand, wherein the operating fluid flows from the upper working chamber 7 into the lower working chamber 8.

(13) In order for the mentioned two additional functions, specifically frequency-dependent or frequency-selective, respectively, damping in a tension stage and stroke-dependent damping in a compression stage of the damper to be implemented, the stroke-dependent piston 6 is furthermore configured as follows.

(14) In order to enable frequency-dependent or frequency-selective, respectively, damping, a frequency-dependent or frequency-selective, respectively, a valve 9 known from the prior art is disposed in the interior of the stroke-dependent piston 6, the valve 9 not being illustrated in more detail in FIG. 1.

(15) FIG. 3 describes in more detail the functional mode of this frequency-selective valve 9 by illustrating arrows along the flow direction of the fluid in a tension stage of the damper. A detailed view of the sectional view from FIG. 1 of the stroke-dependent piston 6 which has plunged into the socket 16 is shown here.

(16) The frequency-selective valve 9 is configured such that a bypass 10 of the upper working chamber 7 into the lower working chamber 8, through the piston rod 2 and the extension 2.1 of the piston rod 2, is disposed directly into the interior of the frequency-selective valve 9.

(17) As is illustrated in FIG. 3, the frequency-selective valve 9 comprises an extra volume 11 which, by way of a constricted inlet duct 12, is connected to the mentioned bypass 10 in the piston rod 2, 2.1. The frequency-selective valve 9 furthermore comprises an intervening deformable diaphragm 13 which mutually separates the bypass 10 and the extra volume 11, as well as a plurality of outlet ducts 14 which fluidically connect the bypass 10 and the lower working chamber 8 of the damper to one another.

(18) The outlet ducts 14 in a non-stressed state of the frequency-selective valve 9 (thus in a compression stage of the damper, for example) are closed by a flat disk 15.

(19) When the shock absorber is thus now in a tension stage, the shock absorber by means of the frequency-selective valve 9 is thus capable of enabling frequency-selective damping in the stroke-selective piston 6.

(20) This frequency-selective damping is to be explained in more detail by means of the arrow arrangement in FIG. 3. FIG. 2 and FIG. 3 herein show a detailed view of the socket 16 and the stroke-selective piston 6 in the same sectional view as in FIG. 1. The damper herein is depicted in a compression stage in FIG. 2, and in a tension stage in FIG. 3. The stroke-dependent valve of the stroke-dependent damper 6 does not act in a tension stage, while the frequency-selective valve 9 of the independent damper 6 does not act in a compression stage.

(21) For example, when the piston assembly 2, 3 moves axially away from the cylinder base 4 at a low frequency of movement, an at least approximately constant quantity of operating fluid thus flows from the upper working chamber 7 into the bypass 10 (cf. P1). Pressure thus prevails for a comparatively long duration on the inlet duct 12 and on the flat disk 15. This prevailing pressure leads to the operating fluid which is located in the bypass 10 to flow through the inlet duct 12 into the extra volume 11 below the diaphragm 13 (cf. P2). The operating fluid accumulating there generates a specific pressure in the extra volume 11, this specific pressure leading to a specific force acting on the diaphragm 13 (cf. P3). This force herein is configured in such a manner that the force pushes the diaphragm 13 upward, on account of which the flat disk 15 is also pushed or pressed upward, respectively. The outlet ducts 14 are closed. On account thereof, an outflow of the operating fluid from the extra volume 11 of the frequency-selective valve 9 is prevented. The damping force is not reduced.

(22) When the frequency of movement of the lifting piston, or of the primary piston 3, respectively, increases (in a tension stage), for example on account of travel of the vehicle on a rough carriageway, abrupt flows of the operating fluid through the bypass 10 are thus created (cf. P1). These abrupt flows likewise generate abrupt pressure variations which act on the flat disk 15, the diaphragm 13, and the inlet duct 12. By virtue of the intense variations and thus of the excessively fast movement of the fluid toward the inlet duct 12 which in terms of the cross section thereof is too narrow for this purpose, no fluid can flow through the inlet duct 12, and no operating fluid either can thus accumulate in the extra volume 11. The fluid is distributed on the diaphragm 13 (cf. P4). The pressure variations prevailing on the flat disk 15 lead to a deformation of this flat disk 15 in the direction of the extra volume 11. The outlet ducts 14 are opened on account of this deformation (cf. P5). The fluid in this instance flows from the stroke-dependent piston 6 (in which the extra volume 11 is located) into the lower working chamber 8 (cf. P6). The damping force is reduced.

(23) Besides the just described frequency-dependent or frequency-selective, respectively, damping function the stroke-dependent piston 6 moreover enables a stroke-dependent damper function of the shock absorber in a compression stage. To this end, a cup-shaped socket 16 at the lower end of the cylinder tube 1 is disposed so as to be coaxial with the cylinder tube 1 and so as to bear on the cylinder base 4. The closed end of the socket 16 herein bears on the cylinder base 4. The diameter of the external shell face of the socket 16 herein is significantly smaller than the diameter of the internal shell face of the cylinder tube 1, on account of which a radial gap 17 which permits a flow of fluid between the base valve 5 and the cylinder tube 1 is formed between the socket 16 and the cylinder tube 1.

(24) The diameter of the internal shell face of the socket 16 herein corresponds exactly to the external diameter of the stroke-dependent piston 6, the latter as from a specific damper stroke (thus in a compression stage) plunging into the socket 16. The external diameter of the stroke-dependent piston 6 herein is determined by an annular seal 21 which is capable of bearing in a sealing manner on the internal shell face of the socket 16.

(25) On account of the stroke-dependent piston 6 plunging into the socket 16 at a specific damper stroke which is predefined by the height or the position, respectively, of the socket within the cylinder tube 1, an extra chamber 18 is formed in which operating fluid is compressed in a compression stage (upon reaching the specific damper stroke).

(26) In order for suitable stroke-dependent damping to be achieved, bypasses may be disposed in the stroke-dependent piston 6, said bypasses according to the principle of the primary piston 3 causing or initiating damping, respectively.

(27) As can in particular be seen in FIG. 1, it is alternatively or else additionally possible for the socket 16 on the internal shell face to be provided with one or a plurality of conically running grooves 19. These grooves 19 are distributed radially across the shell face of the socket 16 and disposed in the axial direction of the socket 16, and when viewed in the direction of the socket base, run in a tapered or conical manner, respectively.

(28) As can likewise be readily seen in FIG. 1, it is furthermore possible for the grooves not to run up to the base of the socket 16 but to already terminate ahead of said base.

(29) Such a conical configuration of the grooves has the advantage that damping is not abrupt in manner on account of the abrupt diameter difference between the socket 16 and the cylinder tube 1, but that a gradual transition, or increased damping associated with the continuing damper stroke, respectively, takes place. The damping is thus more or increased as the stroke increases, or as the stroke-dependent piston 6 plunges further into the socket 16, respectively, until the operating fluid in the region without grooves 19 is simply increasingly compressed.

(30) In order for the operating fluid during a tension stage of the damper to be able to flow from the lower working chamber 8 into the extra chamber 18, through bores 20 are provided in the stroke-dependent piston 6.

(31) The functional mode of the stroke-dependent damping is to be explained in more detail hereunder by means of FIG. 2. In a compression stage of the damper, thus when the piston assembly 2, 3 moves axially in the direction of the cylinder base 4, operating fluid from the lower working chamber 8 first flows through the bypasses or valves, respectively, of the primary piston 3 into the upper working chamber 7. The damping in this instance at least is largely handled by the properties of the primary piston 3. The stroke-dependent piston 6 at this point participates in damping only to a negligible extent since the operating fluid flows laterally through the radial gap which is created on account of the difference in the diameter of the stroke-dependent piston 6 and that of the cylinder tube 1.

(32) However, when the stroke-dependent piston 6 reaches the socket 16, the damper stroke thus having progressed in such a manner that the socket 16 has been reached, the stroke-dependent piston 6 thus handles a large share of the damping. As is illustrated in FIG. 2, the operating fluid in this instance flows through the grooves 19, passing the stroke-independent piston 6, or the annular seal 21, respectively, in a radially external manner.

(33) By virtue of the conical shape of the grooves 19, the flow cross section decreases as the stroke increases, or as the stroke-dependent piston 6 increasingly plunges into the socket 16, and the damping force is thus increased.

(34) Upon reaching the end of the grooves 19, no more operating fluid can flow from the extra chamber 18 into the lower working chamber 8. The operating fluid as from this stroke, or as from this point in time, respectively, is simply increasingly compressed as the stroke increases.

(35) When the damper is then again in a compression stage, the operating fluid thus flows by way of the bypasses, or the through bores 20 of the stroke-dependent piston 6, respectively, into the extra chamber 18, as can be seen by the arrows in FIG. 3.

LIST OF REFERENCE SIGNS

(36) 1 Cylinder tube 2 Piston rod 2.1 Extension of the piston rod 3 Primary piston 4 Cylinder base 5 Base valve 6 Stroke-dependent pistons 7 Upper working chamber 8 Lower working chamber 9 Frequency-selective valves 10 Bypass 11 Extra volume 12 Inlet duct 13 Diaphragm 14 Outlet duct 15 Flat disk 16 Socket 17 Gap 18 Extra chamber 19 Groove 20 Through bore 21 Annular seal H Vehicle vertical direction P1 Arrow 1 P2 Arrow 2 P3 Arrow 3 P4 Arrow 4 P5 Arrow 5 P6 Arrow 6 P7 Arrow 7