HYDRAULIC SHOCK ABSORBER

Abstract

A hydraulic shock absorber comprising a shock absorber tube enclosing a hollow piston rod which moves in an oscillating manner corresponding to successive compression stages and rebound stages. The piston rod connects to a working piston that divides the interior of the shock absorber tube into two working areas. A bypass connects the two working areas of the shock absorber tube. The piston slide valve which is used to block and release the bypass is actuated by the pressure of a control pressure medium. The piston slide valve contains a piston slide which can be displaced by the control pressure medium against the force of a restoring spring, and which blocks or releases the bypass. The shock absorber is configured to be switched to a lower damping effect of the rebound stage by means of a controlled pressure application and without changing the damping effect of the compression stage.

Claims

1. A hydraulic shock absorber, the damping effect of which can be changed by means of the pressure medium pressure of a control pressure medium, having a shock absorber tube that contains a shock absorption fluid, into which tube a piston rod configured to be hollow is plunged while oscillating, corresponding to successive compression stages and rebound stages, which rod is connected, at its free end, to a working piston that divides the interior of the shock absorber tube into two working areas, and contains at least two throttle passages that allow flow through non-return valves assigned to them, in each instance, alternatively and in opposite directions, wherein a bypass that additionally connects the two working areas of the shock absorber tube runs through the working piston, in the progression of which bypass a piston slide valve that serves to block and release this bypass and is activated by the pressure of the control pressure medium is arranged, to which valve the control pressure medium is supplied by way of the cavity of the piston rod, and wherein the piston slide valve contains a piston slide that can be displaced counter to the force of a reset spring by means of the control pressure medium, which slide blocks or releases the bypass, wherein the piston slide of the piston slide valve has blocking positions for error mode, on the one hand, and heavy load mode, on the other hand, which positions block the bypass, at the beginning and at the end of the displacement path of the slide, and wherein the slide is provided, in the length region of its displacement path, with at least one release position that releases the bypass, wherein a non-return valve is additionally assigned to the bypass, which valve prevents the passage of damping fluid through the bypass during the compression stage of the shock absorber, and allows it during the rebound stage of the shock absorber.

2. The shock absorber according to claim 1, wherein the piston slide of the piston slide valve has two or more release positions having different passage cross-sections, which positions release the bypass, in the length region of its displacement path, at a distance from one another.

3. The shock absorber according to claim 1, wherein the piston slide valve has one or more additional reset springs that are shorter than its reset spring, and which only act on the piston slide, in each instance, when the slide has reached a release position.

4. The shock absorber according to claim 3, wherein the additional reset springs are arranged, in each instance, in spring chambers of the piston slide, and act, in a spring-loaded manner, on displaceable support fingers that project in the displacement direction of the piston slide and support themselves on the housing of the piston slide valve, as soon as the piston slide of the valve reaches the assigned release position.

5. The shock absorber according to claim 4, wherein the reset spring of the piston slide and/or the additional reset springs of the support fingers are spring-loaded in the moving-out direction.

6. The shock absorber according to claim 1, wherein the release position extends over a partial region of the displacement path of the piston slide, and wherein the piston slide simultaneously activates a needle valve that lies in the bypass, the passage cross-section of which valve becomes continuously smaller over this partial region of the displacement path until the heavy load blocked position is reached.

Description

[0017] Exemplary embodiments of the invention will be explained in greater detail in the following, using the attached drawing. The figures show:

[0018] FIG. 1: schematically, a longitudinal section through the shock absorber tube of a shock absorber according to the invention, and the piston rod that plunges into this shock absorber tube, with the working piston attached to it, during the rebound stage of the shock absorber in the comfort mode;

[0019] FIG. 2: the shock absorber tube according to FIG. 1 during the compression stage in the comfort mode;

[0020] FIG. 3: the shock absorber tube according to FIG. 1 during the rebound stage in the heavy load mode;

[0021] FIG. 4: the shock absorber tube according to FIG. 1 during the rebound stage in the error mode;

[0022] FIG. 5: an outer view of the working piston and of the piston slide valve connected to it;

[0023] FIG. 6: an exploded view related to FIG. 5;

[0024] FIG. 7a/7b: in the same representation as FIG. 1, a modified embodiment of a shock absorber according to the invention, in which the piston slide of the piston slide valve has two release positions that have different passage cross-sections;

[0025] FIG. 8: the shock absorber according to FIGS. 7a and 7b, during the compression stage in the comfort mode;

[0026] FIG. 9: the shock absorber according to FIGS. 7a and 7b, during the rebound stage in the heavy load mode;

[0027] FIG. 10: the shock absorber according to FIGS. 7a and 7b, during the rebound stage in the error mode;

[0028] FIG. 11: an outer view of the working piston that proceeds from FIGS. 7a and 7b and of the piston slide valve connected to it;

[0029] FIG. 12: an exploded view related to FIG. 11;

[0030] FIG. 13: schematically, in longitudinal sectionin a representation similar to FIG. 1a modified embodiment of the devices that control the passage through the bypass;

[0031] FIG. 14: an outer view of the working piston that proceeds from FIG. 13 and of the piston slide valve connected to it.

[0032] In the drawing, a partial section of a shock absorber tube filled with a damping fluid is designated with the reference symbol 1. A piston rod 2 that is configured to be hollow plunges into this shock absorber tube 1, in an oscillating manner; this rod is connected, for example, to the unsprung mass of a vehicle, not shown in the drawing, which in turn is connected to the shock absorber tube 1.

[0033] In all the figures of the drawing, the movement possibilities of the damping fluid, in each instance, are indicated by movement arrows, and all of the passages that are blocked for the passage of damping fluid, in each instance, are indicated with (x). Furthermore, the movement directions of the piston rod 2 relative to the shock absorber tube 1 are indicated with an arrow (Z) in the rebound stage (Z) and with an arrow (D) in the compression stage (D).

[0034] The cavity 2a of the piston rod 2, which is configured to be hollow, serves for supplying a gaseous or liquid control pressure medium (S), which serves for pressure-controlled switching of the shock absorber to its different modes, as will still be explained in detail below. The control pressure medium (S) used for switching is derived either from the hydraulically or pneumatically assisted suspension system of the vehicle itself, but it can also be generated by other control pressure sources.

[0035] The free end of the piston rod 2, which plunges into the shock absorber tube 1 in an oscillating manner, is screwed onto a multi-part fastening apparatus 3, which carries a working piston 4. This working piston 4 is guided in the shock absorber tube 1, sealed off at its periphery, and divides the interior of the shock absorber tube 1 into two working areas, namely a working area 1a below the working piston 4 and a working area 1b above the working piston 4.

[0036] Furthermore, the working piston 4 is provided with throttle passages 5a and 5b, which connect the working areas 1a and 1b to one another. These throttle passages 5a and 5b have non-return valves 6a and 6b assigned to them, which allow flow in the opposite direction, and bring about the result that the throttle passage 5a allows flow exclusively in the direction toward the working area 1a, which lies below the working piston 4, and the throttle passage 5b allows flow exclusively in the direction toward the working area 1b, which lies above the working piston 4. The cross-sections of the two throttle passages 5a and 5b are different, so that different flow resistances occur for the damping fluid passing through, in the rebound stage Z (upward movement of the working piston 4) and the compression stage D (downward movement of the working piston 4).

[0037] A bypass that additionally connects the two working areas 1a and 1b runs through the fastening apparatus 3 of the working piston 4, in the progression of which bypass a piston slide valve 7 that serves for blocking and release, activated by the pressure of the control pressure medium (S), is arranged, to which valve the gaseous or liquid control pressure medium (S) that serves to activate it is supplied by way of the cavity 2a of the piston rod 2.

[0038] This piston slide valve 7 has a cylindrical valve housing 7a, in which a piston slide 7b can be displaced, in a sealed-off manner, which slide is impacted, in one direction, by the pressure of the control pressure medium (S), and, in the opposite direction, by the force of a reset spring 8 that is supported on the underside of the valve housing 7a, which spring presses the piston slide 7b against the top side of the valve housing 7a when no pressure is applied.

[0039] The bypass mentioned above, which bridges the working piston 4, runs, by way of a passage 9, into the holding apparatus 3 of the working piston 4, the interior of the valve housing 7a of the piston slide valve 7, and a passage opening 10 in the cylindrical wall of the piston slide 7b of this piston slide valve 7. Corresponding to this passage opening 10, there is a passage opening 11 in the cylindrical wall of the valve housing 7a of the piston slide valve 7, which opening leads into the working area 1b of the shock absorber tube 1. Furthermore, a non-return valve 12 is arranged in the bypass, which valve is oriented in such a manner that the bypass can only be traversed in the direction toward the lower working area 1b of the shock absorber tube 1. In the exemplary embodiment, this non-return valve 12 is situated at the lower end of the passage opening 9, but it can also be arranged elsewhere in the bypass. This non-return valve 12 ensures that the bypass can fundamentally be activated only during the rebound stage Z of the shock absorber.

[0040] As is evident from the exemplary embodiments shown in the drawing, the piston slide valve 7 only releases the bypass when the piston slide 7b is moved into a position, relative to the valve housing 7a, in which the two corresponding passage openings 10 and 11 lie opposite one another (release position). In this release position, which is shown in FIG. 1, for example, the bypass is open and ensures a reduction of the damping effect in the rebound stage Z shown in FIG. 1, and this is significant for the comfort mode of the shock absorber. During the rebound stage Z shown in FIG. 1, the working piston 4 moves upward relative to the shock absorber tube 1, as indicated by the arrow Z. As is furthermore indicated by movement arrows of the damping fluid in FIG. 1, the damping fluid, in the rebound stage Z shown, passes through both the throttle passage 5a and, parallel to it, through the bypass, in the direction toward the working area 1a.

[0041] In contrast, during the compression stage D shown in FIG. 2, during which no reduction in the damping effect is supposed to occur, the working piston 4 moves downward relative to the shock absorber tube 1, as indicated by an arrow D. During this compression stage D, the bypass can easily remain open in the region of the corresponding passage openings 10 and 11, because the through-flow through the bypass is blocked in the direction toward the working area 1b, by means of the non-return valve 12, so that during the compression stage D, the full damping effect is fundamentally maintained, without any change in control being necessary.

[0042] According to the teaching of the invention, the corresponding passage openings 10 and 11 are arranged in the cylindrical wall of the piston slide 7b and the cylindrical wall of the valve housing 7a, in the length region of the displacement path of the piston slide 7b, in such a manner that when the piston slide 7b is displaced in the direction toward the underside of the valve housing 7a, blocking positions, i.e., positions in which the passage opening in 10 and 11 do not overlap, occur both before the release position is reached and after the release position has been traversed. As a result, two blocking positions, in which the bypass is interrupted, occur aside from the release position mentioned above, namely a first blocking position (cf. FIG. 3) when the control pressure medium (S) has a high pressure (heavy load mode), or a second blocking position (cf. FIG. 4) when no control pressure is applied at all (error mode), due to an error in the control system.

[0043] Furthermore, it is provided, in the exemplary embodiments shown in the drawing, that spring chambers 13 are arranged in the side of the piston slide 7b that faces the underside of the valve housing 7a, in which chambers additional reset springs 14 are arranged, which are configured to be shorter than the reset spring 8, run parallel to the reset spring 8, and act, in a spring-loaded manner, on displaceable support fingers 15 that project in the direction toward the underside of the valve housing 7a. These support fingers 15 support themselves on this underside of the valve housing 7a, as soon as the piston slide 7b, moved by the control pressure medium (S), reaches the release position.

[0044] The effect of these additional reset springs 14 essentially consists in that relatively great pressure increases are required in the control pressure medium for the transition from comfort mode (release position) to heavy load mode (blocking position), because the reset forces that act on the piston slide 7b suddenly become great, with a very steep increase, if a departure from the release position is supposed to occur. For this reason, when the piston slide is displaced at the boundary between comfort mode (release position) and heavy load mode (blocking position), there is no hysteresis of any kind between these two switching states. Furthermore, it is easily possible, during mass production of shock absorbers, to replace the additional reset springs for the purpose of adaptation to different control pressures.

[0045] The exemplary embodiments of the invention shown in FIGS. 7-12 corresponds, to the greatest possible extent, to the exemplary embodiment of FIGS. 1-6, so that the same reference symbols can be used for the parts that correspond to one another.

[0046] The significant difference as compared with the exemplary embodiment of FIGS. 1-6 consists in that here, two release positions are provided between the two blocking positions situated at the beginning and at the end of the displacement path of the piston slide 7b, instead of only one release position, which positions are arranged at a distance from one another in the displacement direction of the piston slide 7b and have different passage cross-sections.

[0047] For this purpose, in the exemplary embodiment of FIGS. 7-12, two passage openings 11a and 11b, arranged at a distance from one another in the displacement direction of the piston slide 7b, are provided in the cylindrical wall of the cylinder housing 7b, instead of only one passage opening, wherein the passage 11a has a greater passage cross-section than the passage 11b. In this way, it is possible to set the flow resistance in the bypass and thereby the damping effect during the rebound stage Z to two different values. Thus, FIG. 7a shows the first release position with softer damping (=greater passage cross-section), and FIG. 7b shows the second release position with stronger damping (=smaller cross-section).

[0048] Of course, if necessary, additional release positions can also be inserted in the region between the two blocking positions instead of just two release positions, for the purpose of an even finer gradation.

[0049] In order to be able to control the different release positions reliably and with sufficient precision, additional reset spring 14 and support fingers 15 are provided in the exemplary embodiment of FIGS. 7-12, as well, the length of which is adapted, in each instance, to the positions of the additional release positions. These additional reset springs 14 are spring-loaded in the moving-out directionjust like the reset spring 8 of the piston slide 7bso as to achieve the least possible hysteresis during all the switching processes.

[0050] In the exemplary embodiment of the invention shown in FIGS. 12 and 13, once again only one release position is provided between the two blocking positions situated at the beginning and at the end of the displacement path of the piston slide 7b, but here, this release position extends over a partial region of the displacement path of the piston slide 7b. For this purpose, as is evident from FIGS. 13 and 14, a passage opening 11c that is widened over its length, in the displacement direction, is provided in the cylindrical wall of the valve housing 7a, and extends over the partial region of the displacement path mentioned above. In order to be able to change the flow resistance in the bypass here, as well, a needle valve 16 that is activated by the piston slide 7b is arranged in the bypass, with the passage cross-section of the valve becoming continuously smaller until the heavy load blocking position is reached.

REFERENCE SYMBOL LIST

[0051] Z rebound stage; [0052] D compression stage; [0053] S control pressure medium; [0054] x passage blocked; [0055] 1 shock absorber tube; [0056] 1a lower working area; [0057] 1b upper working area; [0058] 2 piston rod; [0059] 2a cavity in the piston rod; [0060] 3 fastening apparatus; [0061] 4 working piston; [0062] 5a throttle passage; [0063] 5b throttle passage; [0064] 6a non-return valve; [0065] 6b non-return valve; [0066] 7 piston slide valve; [0067] 7a valve housing; [0068] 7b piston slide; [0069] 8 reset spring; [0070] 9 passage; [0071] 10 passage opening; [0072] 11 passage opening; [0073] 11a passage opening wide; [0074] 11b passage opening narrow; [0075] 11c passage opening elongated; [0076] 12 non-return valve; [0077] 13 spring chamber; [0078] 14 additional reset spring; [0079] 15 support finger; [0080] 16 needle valve;