Piston-cylinder unit with path-dependent damping characteristics

p0001The invention relates to a piston-cylinder assembly according to the preamble of claim. 1

p0002DE 42 12 078 A1, a piston-cylinder assembly is known, which is designed as a final dampers. This end position damper comprises a cylindrical pressure tube, which is bounded on one side by a bottom and on the other hand by a seal guide unit axially. Furthermore, part of the piston-cylinder assembly, a piston system that divides the pressure tube into two working chambers, said piston system flow channels has, which are fitted with non-return valves. The piston-cylinder assembly has a working range, which is formed by the relative position between the piston rod and the pressure tube, is present in the respective no damping. In the end regions of each Kolbenstangenhubes acts only one piston of the piston system, since the pistons each having a check valve, so that a piston for movement towards a damping force and for the other through-flow direction does not generate the damping force due to the check valve.

p0003The DE-PS 12 51 165 describes a shock absorber having a piston on a piston rod, wherein the piston consists of two piston heads. The piston cooperates with a rod which is fixed to the bottom of the shock absorber together. The piston rod holding the piston at the outer diameter, so that in the middle a central aperture can be formed for each piston head. These central openings cooperate with the rod as throttles, wherein check valves are arranged on the piston heads, which ensure Dar is generated from the respective end positions no damping. In a middle stroke range of the shock absorber also generates no damping force, because the rod has at a defined length, a diameter reduction, so that the central apertures can practically not generate damping forces.

p0004Overall, the damping force is generated only on the instantaneous cross-section which results from the overlapping of a center openings with the rod. The piston heads are not involved by their non-return valves in the damping force.

p0005The DE 34 46 133 discloses a shock absorber having a variable damping force, in which a bypass within a damping valve device by means of an adjusting device can be switched in such a way so that one Dämpfventilsystem generates a damping force or within the damping valve device both Dämpfventilsysteme are effective.

p0006Object of the present invention is to realize a piston-cylinder unit that independently of an external controller generates a load-dependent damping force.

p0007According to the invention the object is achieved by the two pistons are spaced relative to the bypass, so that depending on the stroke position of both pistons, a piston or none of the piston a damping force produced / produce, the two piston outside of the bypass in both directions of travel attenuate. Depending on the stroke position or compression travel, the damping force is adapted to the requirements without resorting to expensive fillers. Here both pistons for both flow directions are provided with damping valves. A different Dämpfventilausgestaltung, a more or less asymmetrical damping force can be achieved.

p0008Here is the bypass of at least one bead with a substantially axial alignment in the cylinder tube. This type of the bypass can be relatively easily and sufficiently precise shaping. In consistent development is / the bead (s) are stepped in cross-section, depending on the stroke position run. The grading of the bypass cross-section in conjunction with the differently designed damping valves allows a wide variability in terms of the desired Dämpfkraftkennfeldes. Especially when the cross-section sizes of the bead (s) are carried out with transition sections, which cause a continuous change in cross section, are virtually unlimited possibilities.

p0009Use the following figure description, the invention is illustrated.

p0010It shows:<dl id="dl0001" compact="compact"><dt>Fig. 1</dt><dd>Piston-cylinder assembly in longitudinal section</dd><dt>FIG. 2</dt><dd>Cylinder as item</dd><dt>Fig. 3</dt><dd>Dämpfkraftkennfeld as a function of the way</dd></dl>

p0011The FIG. 1 shows a piston-cylinder unit 1 by way of example in the execution of a single-tube shock absorber, but other designs are also conceivable. The piston-cylinder assembly comprises, inter alia, a cylinder 3, which is closed at one end by a bottom 5 and at the other end of a piston rod guide 7 from the environment. Inside the cylinder 3 is a piston rod 9 is arranged with a first piston 11 and a second piston thirteenth The two pistons 11; 13 are held by a sleeve 15 to a distance A, whereby three working spaces 17; 19; 21 arise. The two working chambers 17; 21 depend on the current stroke position of the piston rod 9 in its spatial size while the working space 19 having between the pistons 11, 13 is a constant volume. Starting from the bottom 5 extends a gas-filled compensation chamber 23 which is separated by a floating piston 25 from the working space 21st

p0012The pistons are each on both sides with damping valves 27; 29; 31; 33 is provided so that in both directions of flow, the piston 11; 13 can generate a damping force. With regard to the concrete design of the piston and the damping valves refer to the entire circumference of the DE-44 10 996 C1.

p0013To generate a path-dependent damping force hublagen- or the piston-cylinder unit 1 has at least one bypass 35, which is formed by at least one substantially axially extending bead 37th

p0014In FIG. 2, the cylinder 3 is shown as an individual part in a number of views and callouts. It is clear that the bead (s) is carried out 37 graded depending on the stroke position / are. In the description, a bead is always described, but should be considered tacitly assumed that even more beads with this configuration are possible.

p0015To avoid Dämpfkraftstößen form the beads transition sections 39, wherein the transition cross sections are formed by a sloping contour of at least one bead edge.

p0016In FIG. 3, the relationship of the piston position to the bypass is easy to understand with the travel-dependent damping force. It is assumed that the bypass is longer than the distance of the two pistons 11; 13 or its piston seals. to being both pistons within the bypass, then there is the most minimal damping force of the piston-cylinder unit, for the damping medium can between the working spaces 17; 21 exchanged, without the damping valves must be traversed. The damping force is not necessarily equal to zero. But you shall in any case a very comfortable damping force adjustment, this point being the stroke position of the piston rod at a normal or reduced loading of the motor vehicle corresponds.

p0017Moves to the piston rod in either direction F_D, Equal damping force in the compression direction or F_Z So affects only the piston, which is located outside of the bypass. Here, the damping valves 29; 33 in their damping force L_Z and B_Z more run than the damping valves 27; 31 with the damping force L_D and B_D, One assumes that a stronger damping effect with a larger loading, the driving safety of the vehicle advantageously influenced. In Dämpfkraftkennfeld of Fig. 3, this relationship can be clearly seen on the vertical extent of Dämpfkraftflächen.

p0018to being both pistons outside the bypass, then the effective damping forces of the pistons overlap each case based on the tensile and compressive direction to a hydraulic pressure stop HDA and HZA, as the pistons are arranged hydraulically in series. The damping medium has, for example, flow in pressure direction from the working chamber 21 via the damping valve 31 in the working space 19 and from there via the damping valve 27 in the working space 17th

p0019As can be seen from the Dämpfkraftkennfeld, no Dämpfkraftsprünge must occur between the individual Dämpfkraftkennfelder when the bypass has appropriately adapted transition sections. The influence of the transition cross-sections is illustrated by the dotted lines.