ADJUSTABLE VIBRATION DAMPER FOR MOTOR VEHICLES

Description

[0001] The present invention relates to an adjustable vibration damper according to the preamble of claim 1. STATE OF THE ART

[0002] Such a vibration damper is known from DE 44 41 047 C1. Pressure-dependent damping valves are provided on a piston guided axially within a cylinder barrel for the exchange of fluid between two working chambers during the rebound and compression stages. A pilot control acts in such a way that a controllable pressure is built up in the pilot chambers. The pilot pressure acts on the valve discs of the damping valves in their closed position. Fluid is guided from the working chambers into the pilot chambers through a bypass channel system, thus increasing the pressure there. The pilot pressure is regulated by means of an externally adjustable pilot valve arranged in the bypass channel system. An elastic element forms the separation between the pilot chamber and the working chamber.

[0003] Another vibration damper operating according to the same principle is known from DE 101 04 640 C1. In this case, the pilot chambers are formed by pressure chambers. These pressure chambers are each formed by a pressure chamber housing and a seal that movably rests on a damping valve. A pilot valve controls the pressure in the pilot chambers. An outlet of the pilot valve opens into the working chambers.

[0004] The valve discs typically provide the vibration damper with a degressive damping behavior at high piston speeds, where the valve discs lift off the valve seat. The opening cross-section increases with increasing speed, triggering this degressive behavior.

[0005] In parallel to the damping via the valve discs, one or more bypass channels in the piston form a throttle between the working chambers, which imparts a progressive component to the damping behavior of the vibration damper. The influence of this progressive component is particularly important at low piston speeds, where the valve discs are still fully in contact with the valve seat. Such a bypass channel can be formed by a notch in the valve disc or in the valve seat, so that fluid flow through the passages from one working chamber to the other is possible despite the valve discs being fully in contact with the valve seat. However, such a bypass channel is fundamentally effective for both flow directions, so that the progressive component can only be adjusted to the same extent for both flow directions.

[0006] The dimensioning of the bypass cross-sections through the notches on the valve disc or the valve seat requires adapted valve discs or pistons, which requires the provision of a large number of different discs and pistons.

[0007] WO 2010 / 122102 A1 discloses a vibration damper characterized by particularly smooth valve disc opening. For each valve disc, several valve seat areas are configured for the compression and tension sides, each of which can be supplied with hydraulic fluid to varying degrees. In the static state, the same hydraulic pressure is applied to all valve seat areas, so that the valve disc opens quickly upon further pressure application. In the dynamic state, the pressure cannot be maintained in some valve seat areas due to a smaller inflow cross-section of the associated hydraulic channel. While these valve seat areas support rapid opening of the valve disc, once the disc is open, they have little or no influence on the further opening of the valve. The vibration damper does not provide any bypass channels in the piston.

[0008] US 2014 / 0262655 A1 discloses a shock absorber with a bypass channel within the piston, wherein the bypass channel has a combination of a perforated disc and a check disc on the output side for flow velocity-dependent adjustment of the bypass cross-section. GB2222227A discloses an adjustable vibration damper with the features of the preamble of claim 1.

[0009] It is the object of the present invention to further develop the generic vibration damper in such a way that the damping behavior at low piston speeds can be adjusted separately for both flow directions in a very simple manner. DISCLOSURE OF THE INVENTION

[0010] The object underlying the invention is achieved by an adjustable vibration damper, in particular for a vehicle chassis, comprising a cylinder tube having a hydraulic fluid sealed therein, a piston which is axially movable within the cylinder tube along a cylinder tube axis and which divides the cylinder tube into two working chambers, a piston rod which is aligned parallel to the cylinder tube axis and is connected to the piston, wherein the piston has at least two fluid passages through which one working chamber is connected to the other working chamber, wherein a first valve assembly for damping the piston movement in a first actuation direction is arranged on a first fluid passage and wherein a second valve assembly for damping the piston movement in a second actuation direction is arranged on a second fluid passage, wherein each valve assembly has at least one valve disc,which, in a closed valve position, rests on a valve seat and thus at least partially covers the associated fluid passage, and which, in an open valve position, is at least partially spaced from the valve seat. The valve seat, the associated valve disc, and the piston each define an atrium into which the respective fluid passage opens on the outlet side. In addition to the fluid passages, a bypass channel with different flow cross-sections for both flow directions is provided in the piston, or several bypass channels are provided, the total flow cross-sections of which are different for both flow directions. According to the invention, a fluid connection is formed by means of the one bypass channel, or several fluid connections are formed by means of the several bypass channels between the two working chambers, bypassing both atriums, wherein openings of the bypass channel(s) are formed by a check disc,which is formed separately from the valve discs, are at least partially covered, wherein a non-return disc for limiting the flow cross-section is arranged coaxially and axially offset from a valve disc, wherein the non-return disc and the valve disc are arranged on the same side of the piston, wherein the non-return disc does not completely cover the inlet of the bypass channel to reduce the bypass cross-section, and wherein the flow cross-section is reduced at least in one flow direction by a non-return disc, wherein the non-return disc has at least one, preferably several, radially projecting bypass flaps. Furthermore, the different flow cross-sections for both flow directions are realized in that an opening of the bypass channel or openings of the bypass channels on the two sides of the piston are covered to different degrees by corresponding non-return discs.

[0011] This arrangement allows for different bypass cross-sections to be realized without requiring any special design of the valve discs or valve seat. A standard piston without application-specific notches in the valve seats can be used as the piston; standard discs without application-specific notches or other passages can now also be used as the valve discs. Thus, the different flow cross-sections of the bypass channels allow the damping behavior of the vibration damper to be adjusted separately for both flow directions, especially for low piston speeds.

[0012] Preferably, an opening of one or more bypass channels is or are at least partially covered by a non-return disc which is designed separately from the valve discs. Instead of the valve discs, a specific non-return disc is used to set a defined, freely flow-through bypass channel inlet cross-section. Since the non-return disc only reduces the cross-section of the bypass channel in one flow direction, the flow cross-sections for both flow directions can be set separately by selecting suitable non-return discs. Such non-return discs can be made of plastic and are therefore very inexpensive to manufacture. Preferably, the flow cross-sections which are different for both flow directions are achieved by having an opening in the bypass channel orOpenings of the bypass channels on both sides of the piston are covered to different degrees by corresponding check discs. This means that the openings (or only one opening) of the bypass channel that face one working chamber are covered by a check disc to a different extent than the other openings (or only one opening) that face the other working chamber. By varying the degree of coverage of the openings, the free inflow cross-section and thus also the flow resistance or the pressure loss occurring during flow can be individually adjusted for both flow directions. In the context of the invention, the sides of the piston are understood to be the side of the piston closest to the piston rod and the side farther from the piston rod.The side closest to the piston rod faces the working space on the piston rod side, while the side remote from the piston rod faces the working space remote from the piston rod.

[0013] This mode of operation is preferably further achieved by providing an inlet opening for the first or second fluid passage on one side of the piston, which is enclosed by one of the valve seats, and by providing an inlet opening for the bypass on this side of the piston, which is not enclosed by the valve seat. Therefore, for the fluid to flow into the bypass channel, flow through the valve seat and thus the atrium is not necessary. This also applies in particular to all inlets of possibly multiple bypass channels.

[0014] Preferably, a check disc is arranged coaxially and axially offset from a valve disc to limit the flow cross-section of the bypass channel, with the check disc and the valve disc being arranged on the same side of the piston. This allows for easy installation of the check disc. Furthermore, the use of such discs allows the vibration damper to be easily adapted to other applications. However, the check disc does not have to completely cover the inlet of the bypass channel; partial coverage is sufficient to reduce the bypass cross-section.

[0015] Preferably, on one side (the side near the piston rod and / or the side remote from the piston rod) of the piston, a plurality of circumferential regions are formed, distributed in the circumferential direction, of which at least a first region is enclosed by a valve seat and at least a second region is not enclosed by the valve seat. The openings of the fluid passages and / or those of the bypass channels can be arranged in the second, unenclosed region, thus bypassing the atria. The outlets of the fluid passages are arranged in the first enclosed region, so that the fluid passages open into the atria.

[0016] Preferably, the flow cross-section is reduced at least in one flow direction by a check disc, wherein the check disc has at least one, preferably several, radially projecting bypass flaps. The bypass flaps partially reduce the freely flowable cross-section of the bypass channel. The geometric design of the bypass flaps allows the freely flowable cross-section of the bypass channel to be adjusted and thus the pressure loss occurring during flow. The number of bypass flaps in one / more check discs corresponds at least to the number of bypass channel inlet openings to be covered. When flowing in the respective flow directions, a different pressure loss occurs for both flow directions if the bypass channels are covered to different extents by the bypass flaps.

[0017] The check disc is preferably designed such that the check disc can be mounted on the piston with either side in such a way that the bypass flap or the multiple bypass flaps reduce the flow cross-section of the bypass channel or the flow cross-sections of the bypass channels. This can be achieved by arranging an even number, in particular two or four, bypass flaps, with essential parts of the bypass flaps arranged rotationally symmetrically around a rotation axis. This can significantly simplify assembly, since the check disc can be mounted in any orientation. Incorrect assembly can be virtually eliminated.

[0018] Preferably, the bypass valves are provided with contact surfaces to correctly align the check disc relative to a positioning element of the piston. This facilitates installation in the correct position relative to the piston.

[0019] The invention is particularly applicable to vibration dampers in which each valve assembly comprises a pilot chamber, wherein the valve disc can be preloaded into the closed valve position by pressurizing the pilot chamber, wherein the pressure in the respective pilot chambers can be adjusted by at least one pilot valve. In such vibration dampers, any backpressure at the inlets of the bypass channels does not affect the pressure structure in the atria due to the bypassing of the atria by the claimed arrangement. This ensures that the pressure in the atria continues to be primarily influenced by the pressure in the pilot chambers and, of course, the piston speed. Any distortion caused by the throttling effect of the bypass channels is avoided. PREFERRED EMBODIMENTS OF THE INVENTION

[0020] Further measures further developing the invention are presented in more detail below, together with the description of preferred embodiments of the invention, with reference to the figures. It shows: Fig. 1 shows a part of a conventional vibration damper with a valve assembly in cross section; Fig. 2 shows the piston of a vibration damper according to the invention in detail in a perspective view; Fig. 3 shows the check disc of a vibration damper according to the invention in detail in plan view; Fig. 4 shows the piston according to Figure 2 with two non-return discs mounted on it Figure 4 in perspective view; Fig. 5 the arrangement according to Figure 4 in cross section; Fig. 6 the arrangement according to Figure 4 in plan view. Fig. 7 shows the piston of an alternative embodiment of the invention in cross section, with bypass flaps arranged in the bypass channel.

[0021] Figure 1shows a section of a conventional vibration damper 1 as described in the not yet published German patent application 10 2013 114 169.2.

[0022] The vibration damper 1 comprises a cylinder tube 10 in which a piston 2 is slidably mounted along a cylinder tube axis A. The piston 2 has an annular seal 28 on its outer circumference, so that the piston 2 sealingly divides the cylinder tube 10 into a first working chamber 11 (away from the piston rod) and a second working chamber 21 (on the piston rod side). The piston 2 is attached to a mounting pin 42, which in turn is firmly connected to a piston rod 3. When the piston rod 3 is actuated in a first actuation direction RI toward the first working chamber 11 (also called the "pressure direction"), the pressure in the first working chamber 11 increases. Fluid present in the first working chamber 11 then flows through a first fluid passage 12 in the piston 2 into the second working chamber 21.The fluid passage opens on the piston rod side into an atrium 18, which is separated from the second working chamber 21 by the associated valve seat 15 and the valve disk 16. When the fluid is conveyed through the first fluid passage 12, the fluid flows through a first valve assembly 13 with a pressure relief valve 14. The pressure relief valve 6 can be formed, for example, from one or more flexible valve disks 14. When a minimum pressure of the fluid in the first working chamber 11 is reached, the first pressure relief valve 14, which sits with preload on a first valve seat 15, is at least partially released from the first valve seat 15. The valve disk 14 is thus moved from the closed position into the open position lifted from the valve seat. A hydraulic connection is thus established between the first working chamber 11 and the second working chamber 21.The first pressure relief valve 14 in interaction with the first valve seat 15 generates the damping force.

[0023] The pressure relief valve 14 is acted upon by a pressure prevailing in a pilot chamber 16 (hereinafter referred to as the "pilot pressure") in the direction of the valve seat 15. This pilot pressure in the first pilot chamber 16 can be adjusted during operation. It is evident that the higher the pressure in the first pilot chamber 16, the greater the damping force provided by the first valve assembly 13. This is because the pressure that must be built up in the atrium 18 accordingly to release the pressure relief valve 14 from the valve seat 15.

[0024] The vibration damper 1 further comprises a second valve assembly 23, which is identically designed to the first valve assembly 13. The second valve assembly is intended to slow the flow of the fluid when the piston 2 is moved in a second actuation direction R2 (also called the "pulling direction"). In this case, the fluid flows from the second working chamber 21 via a second fluid passage 22 into the first working chamber 11 (distant from the piston rod). A second pilot chamber 26 is similarly formed by a base 4, a cylindrical side wall 5, and a second valve disc 24 of a second pressure relief valve 6. The second valve disc 24 and a second valve seat 25, as well as the arrangement of the atrium 18, are identical to the first valve assembly 13.

[0025] The two bases 4 each have fluid passages 17 and 27, respectively, and check valves 20. If the piston 2 is moved in the compression direction R1, damping fluid flows from the working chamber 11 remote from the piston rod through the fluid passage 27 into the second pilot chamber 26. If the piston 2 is moved in the retraction direction R2, damping fluid flows from the working chamber 21 on the piston rod side through the fluid passage 17 into the first pilot chamber 16.

[0026] The two pilot chambers 16, 26 are hydraulically connected to one another via a connecting passage 9. The connecting passage 9 comprises an axial bore in the fastening pin 42 and two radial connecting bores in the fastening pin 42, which connect the axial bore and the pilot chambers 16, 26. Essentially, the same pressure always prevails in both pilot chambers 16, 26. When the piston 2 is moved in the first actuating direction R1, the pressure in the first working chamber 11 increases and the damping fluid flows through a fluid passage 27 between the first working chamber 11 and the second pilot chamber 26 from the first working chamber 11 into the second pilot chamber 26, thereby increasing the pilot pressure in the second pilot chamber 26. The pilot pressure built up in the second pilot chamber 26 is also propagated into the first pilot chamber 16 through the connecting passage 9.This generates the pilot pressure in the first pilot chamber 16, which influences the damping behavior of the first valve assembly 13. The same applies to actuation in the second actuation direction R2. In this case, the fluid flows from the second working chamber 21 through a fluid passage 17 between the second working chamber 21 and the first pilot chamber 16 into the first pilot chamber 16. The pilot pressure thus generated in the first pilot chamber 16 is in turn propagated through the connecting passage 9 into the second pilot chamber 26. To prevent the fluid from flowing through the fluid passages 17, 27 from the first pilot chamber 16 directly into the second working chamber 21 or from the second pilot chamber 26 into the first working chamber 11, one-way valves 20, which are designed, for example, as check valves, are installed in the fluid passages 17, 27.

[0027] The pilot pressure in the two pilot chambers 16 and 26 can be regulated. For this purpose, a pilot valve 31 is provided, which has a valve body 32. The valve body is movable along the cylinder tube axis A and can sit on a fixed (relative to the mounting pin) valve seat 33. When the valve body 32 sits on the valve seat 33, fluid can largely be prevented from flowing out through the pilot valve 31. During such a phase, the pilot pressure can be built up or maintained. If the valve body 32 is released from the valve seat 33, fluid can flow out of the connecting passage through the pilot valve 31; during this phase, the pilot pressure can be reduced. The valve body 32 is acted upon in the first actuation direction R1 by means of a magnetic actuator 40. In the second actuation direction R2, the valve body 32 is acted upon by the pilot pressure.Depending on the force ratios caused by the magnetic actuator 40 and the pilot pressure, the position of the valve body 32 relative to the valve seat 33 is determined.

[0028] Typically, the valve disks 16, 26 and / or valve seats 15, 25 are provided with notches or bores to create a free flow cross-section that is not obstructed by the valve disk 14 or the valve seat 15. This defines a bypass cross-section that is used to shape the damping characteristics. However, the aforementioned measures only achieve a bypass cross-section that applies equally to both stages, i.e., the compression stage and the rebound stage. In some applications, however, it is desirable to design bypass cross-sections differently in the compression stage than in the rebound stage. This could be achieved using one-way valves within the fluid passage 12, 22 in the piston 2. However, if such a one-way valve is present in the fluid passage, this would cause backflow into the upstream atrium 18.However, this backpressure in the atrium in turn affects the pilot chamber 16, 26, increasing the pressure there, even though a pressureless phase currently prevails there. This leads to a malfunction in the pressure regulation in the pilot chamber, so this option is not realized.

[0029] The vibration damper according to the invention now has a piston 2, as can be seen from the Figures 2 to 6 described. In Figure 2 The piston 2 can be seen in detail. In addition to the fluid passages 12, 22, two further openings are provided between the two sides of the piston 2, each forming a bypass channel 7.

[0030] Such a bypass channel 7 is at least partially covered by a non-return disc 19, which is Figure 3shown in detail. The check disc has several bypass flaps 8, each of which can be folded away in exactly one direction when it is placed on a corresponding opening of the bypass channels 7. Such a check disc 190 is placed on top of the piston 2; another check disc 19u is placed on the bottom of the piston 2. Two bypass flaps 8 of the respective check disc 19 are in partial overlap with the two openings of the bypass channel 7, as shown for the top side in Figure 4 shown and also from Figure 5 in cross-section is visible for both sides. If, as in Figure 5 As can be seen on the right side, fluid flows from bottom to top through the bypass channels (first flow direction B1), the bypass flaps 8 of the upper check disc 190 fold upwards and do not reduce the flow cross-section of the bypass channels in this flow direction. However, if, as in Figure 5As can be seen on the left side, fluid flows from top to bottom through the bypass channels 7 (second flow direction B2), the bypass flaps 8 of the upper check disc 190 at least partially block the opening and reduce the flow cross-section of the bypass channels in this flow direction. This is because the bypass flaps 8 can be folded away from the piston, but not toward the piston 2.

[0031] Accordingly, the bypass flaps 8 of the lower check disc 19u fold downward and do not reduce the flow cross-section of the bypass channels when fluid flows in the second flow direction B2. However, when fluid flows through the bypass channels 7 in the first flow direction B1, the bypass flaps 8 of the lower check disc 19u at least partially block the opening and reduce the flow cross-section of the bypass channels.

[0032] Due to the different designs of the upper and lower bypass flaps 8, the flow cross-sections of the bypass channels can be adjusted separately for different flow directions. Figure 6 shows piston 2 from above. The upper check disc 190 is clearly visible; the lower check disc 19u is less clearly visible, as it is largely concealed by piston 2 and the upper check disc 190. Therefore, the visible part of the lower check disc 19u is highlighted in black in this figure. The bypass flaps 8 of the lower check disc 19u are larger than the bypass flaps 8 of the upper check disc 190, resulting in the smaller flow cross-section in the first flow direction B1 (out of the image plane).

[0033] To prevent the back pressure created by the bypass valve 8 from propagating into the atria 18, the atria 18 are now (as shown in Figure 2can be seen) on the sides of the piston 2, on the one hand, first regions 34 are formed, which are enclosed by the valve seat 15 (shown here with a strong border), and on the other hand, second regions, namely the remaining regions 35, which are not enclosed by the valve seats 15. These first regions 34 enclosed by the valve seat 15 define the position of the atria 18 on the sides of the piston 2; the fluid passages 12, 22 open downstream into these atria 18 or first regions 34. In the other, second regions 35 of the side, which are not enclosed by the valve seat 15, the fluid passages 12, 22 open on the inlet side, i.e. upstream. Furthermore, the inlets and outlets of the bypass channels 7 also open into the second areas 35. In this respect, the inlets of the bypass channel 7 can now communicate directly with the working spaces 11, 21 upstream in the bypass flow direction, without the atrium 18 being flowed through by the bypass volume flow.

[0034] In Figure 5The axial arrangement of the check discs 19 relative to the valve seats 15, 25 and the valve discs 14, 24 is visible. The positions of the valve discs 14, 24 are indicated by the dashed lines. The valve discs 14, 24 rest against the raised area formed by the valve seats 15, 25. The valve discs are arranged axially further outward relative to a piston center than the check disc 19 arranged on the same side of the piston 2.

[0035] In Figure 4A top side of the piston 2 with a check disc 19 adjacent thereto is shown. The check disc 19 has four bypass flaps 8, although the piston 2 only has two bypass channels 7 to be covered. Two of the bypass flaps 8 each cover a bypass channel 7; two others cover areas of the outlets of the fluid passages 12, 22, which, however, has no significant effect due to the large cross-section of the fluid passages 12, 22, especially since these two bypass flaps 8 can be folded away with the flow in both directions. This results in a rotationally symmetrical x-shaped arrangement of the bypass flaps 8 relative to an imaginary rotation axis S ( Figure 3This design ensures that the check disc 19 is always correctly mounted, regardless of its orientation. The check disc 19 can therefore also be placed upside down on the piston 2. Accordingly, the check disc is positioned on the underside of the piston 2.

[0036] In addition, the check disc 19 has defined contact surfaces 36 in the area of the bypass valves 8 ( Figure 3 and 4 ), which in turn interact with defined contact surfaces 37 on the piston ( Figure 3 ) to determine the exact position and alignment relative to the piston. Since the defined contact surfaces 36 are provided on all four bypass valves 8, incorrect insertion of the check disc 19 is impossible. The contact surfaces 36 on the check disc 19, in conjunction with the contact surfaces 37 on the piston, act as a stop for correct positioning in the radial and circumferential directions.

[0037] Figure 7 shows an alternative embodiment of the present invention. In contrast to the embodiment described above, the bypass flaps 8 do not cover an entrance of the bypass channel 7; rather, the bypass flaps 8 are arranged inside the bypass channel 7. The bypass flaps 8 rest in the bypass channel 8 on a contact projection 44, which only allows the bypass flaps 8 to fold away in one direction (namely away from the contact projection 44), but prevents them from folding in the other direction (namely toward the contact projection 44). The bypass flaps 8 can be fixed in the bypass channel 7 by suitable prestressing means (not shown). List of reference symbols

[0038] 1 Vibration damper 2 Piston 3 Piston rod 4 Base 5 Cylindrical side wall 6 Dimensionally stable movable cover 7 Bypass channel 8 Bypass flap 9 Connection between the two pilot chambers 10 Cylinder tube 11 First working chamber 12 First fluid passage 13 First valve assembly 14 First valve disc 15 First valve seat 16 First pilot chamber 17 Connection between second working chamber 21 and first pilot chamber 16 18 Atrium 19 Check disc 20 One-way valve 21 Second working chamber 22 Second fluid passage 23 Second valve assembly 24 Second valve disc 25 Second valve seat 26 Second pilot chamber 27 Fluid passage between first working chamber 11 and second pilot chamber 26 28 Ring seal 31 Pilot valve 32 Valve body 33Valve seat 34First side area enclosed by valve seat 35Second side area not enclosed by valve seat 36Contact surface on bypass flap 37Contact surface on piston 40Magnetic actuator 42Mounting pin43'piston rod side of the piston 43"piston rod remote side of the piston 44support projections arranged in the bypass channel AZylinder tube axis RBactuation direction BFlow direction through bypass channel SRotation axis

Claims

1. Regulable vibration damper (1), in particular for a vehicle chassis, comprising a cylinder barrel (10) which has a hydraulic fluid received therein in a sealed-off manner, comprising a piston (2) which is axially movable within the cylinder barrel (10) along a cylinder-barrel axis (A) and which subdivides the cylinder barrel (10) into two working chambers (11, 21), comprising a piston rod (3) which is oriented parallel to the cylinder-barrel axis (A) and which is connected to the piston (2), wherein the piston (2) has at least two fluid leadthroughs (12, 22) by way of which one working chamber (11, 21) is connected to the other working chamber (21, 11), wherein a first valve assembly (13) for damping the piston movement in a first actuation direction (R1) is arranged at a first fluid leadthrough (12), and wherein a second valve assembly (23) for damping the piston movement in a second actuation direction (R2) is arranged at a second fluid leadthrough (22), wherein each valve assembly (13, 23) has at least one valve disc (14, 24) which, in a closed valve position, is seated on a valve seat (15, 25) and thus at least partially covers the associated fluid leadthrough (12, 22) and which, in an open valve position, is at least partially spaced apart from the valve seat (15, 25), wherein the valve seat (15, 25), the associated valve disc and the piston (2) in each case delimit a vestibule (18) into which the respective fluid leadthrough (12, 22) opens at an outlet side, and, in the piston (2), in addition to the fluid leadthroughs (12, 22), there is provided a bypass duct (7) with throughflow cross sections of different size for the two throughflow directions (B1, B2), or there are provided multiple bypass ducts (7) whose throughflow cross sections are, in sum total, of different size for the two throughflow directions (B1, B2), wherein, by means of the single bypass duct (7), a fluidic connection, or by means of the multiple bypass ducts (7), multiple fluidic connections, is or are formed between the two working chambers (11, 21), bypassing the vestibules (18), wherein openings of the bypass duct (7) or of the bypass ducts (7) are at least partially covered by a non-return disc (19) which is formed separately from the valve discs (14, 24), wherein a non-return disc (19) for limiting the throughflow cross section is arranged coaxially and axially offset with respect to a valve disc (14), wherein the non-return disc (19) and the valve disc (14) are arranged at the same side (43', 43'') of the piston (2), characterized in that the non-return disc, for reducing the bypass cross section, does not completely cover the inlet of the bypass duct, wherein the throughflow cross section (7) is reduced, at least in one throughflow direction (B1, B2), by a non-return disc (19), wherein the non-return disc (19) has at least one, preferably multiple radially, projecting bypass flaps (8), wherein the throughflow cross sections of different size for the two throughflow directions (B1, B2) are realized in that an opening of the bypass duct (7) or openings of the bypass ducts (7) at the two sides (43', 43'') of the piston (2) are covered to different extents by corresponding non-return discs (19).

2. Regulable vibration damper (1) according to the preceding claim, characterized in that, at a piston-rod-facing and / or a piston-rod-averted side (43', 43'') of the piston (2), there is provided an opening of the first or second fluid leadthrough (12, 22), which opening is surrounded by one of the valve seats (15, 25), and in that, at said side (43', 43'') of the piston (2), there is provided an inlet opening of the bypass duct (7), which inlet opening is not surrounded by the valve seat (15, 25).

3. Regulable vibration damper (1) according to either of the preceding claims, characterized in that, on one side (43', 43'') of the piston, multiple circumferential regions are formed in a manner distributed in a circumferential direction, of which circumferential regions at least one first region (34) is surrounded by a valve seat (15) and at least one second region (35) is not surrounded by the valve seat (15), wherein the openings of the bypass ducts (7) are arranged in the second regions (35).

4. Regulable vibration damper (1) according to the preceding claim, characterized in that the non-return disc (19) is designed in such a way that the non-return disc (19) can be mounted selectively by way of both sides on the piston (2) in such a way that the single bypass flap (8) or the multiple bypass flaps (8) reduce the throughflow cross section of the bypass duct (7) or the throughflow cross sections of the bypass ducts (7).

5. Regulable vibration damper (1) according to one of the preceding claims, characterized in that, on the bypass flaps (8), there are formed abutment surfaces (36) for correct orientation of the non-return disc (19) with respect to a positioning element (37) of the piston (2).

6. Regulable vibration damper (1) according to one of the preceding claims, characterized in that each valve assembly (13, 23) comprises a pilot-control chamber (16, 26), wherein the valve disc (14, 24) is able to be preloaded into the closed valve position by pressurization of the pilot-control chamber (16, 26), wherein the pressure in the respective pilot-control chambers (16, 26) is able to be set by way of at least one pilot-control valve (31).