Electrically adjustable shock absorber.

The invention relates to a shock absorber, compris­ing a cylinder with damping fluid, a piston with piston rod displaceable in said cylinder, a sleeve disposed in the piston and having at least two openings or series of open­ings, while at least two duct systems of differing damping characteristic are disposed in the piston, and each duct system connects to an opening or series of openings in the sleeve, and where electrically operated control means are present to close off or release one or more of the openings in the sleeve as desired.

Such a shock absorber is known from DE-A-3.434,566.

The object of such an electrically adjustable shock absorber is to permit adaptation of the absorption to the type of road surface; where there is a good-quality road surface little shock absorption is selected, while a high shock absorption setting of the shock absorbers is chosen where the road surface is poor.

In the known shock absorber the control means con­sist of a rotatable cylinder with openings which can be placed in register with openings of differing size in the sleeve. Through their relatively small dimensions, these latter openings have a great influence on the damping characteristic, at least at relatively low speed of the piston. If this speed exceeds a certain value, the damping fluid will flow via a non-return valve essentially round the sleeve and control means from one side of the piston to the other, so that the switch position of the rotatable cylinder now has only a very small influence on the damping characteristic. In other words, the shock absorption in this known construction is hardly adjustable at higher pis­ton speeds.

The object of the invention is to avoid these disad­vantages and produce a shock absorber of the type mentioned in the preamble, whose shock absorption is electrically ad­justable over the entire speed range of the piston, and in which the form of sleeve and control means has no essential influence on the shock absorption.

According to the invention, the shock absorber is to this end characterized in that said openings in the sleeve are so large that they do not essentially affect the shock absorption, while both at high and at low piston speeds the control means alone determine via which duct system the damping fluid can flow through the piston.

In the switch positions in which the damping medium flows only through one or more of the damping duct systems, the damping characteristic is determined both at high and at low suction speed entirely by the damping properties of the particular duct systems. The possibility is not ex­cluded that in a particular switch position of the control means the damping medium does not flow through the duct systems to be shut off or released by the control means, but takes a different route through the piston. However, in that case also this selection is determined by the switch position of the control means, and the damping characteris­tics are adjustable even at high piston speed.

An easily operable design of the control means con­sists of a slide which is axially displaceable inside the sleeve and has axial throughflow channels which do not af­fect the shock absorption, while the length of the slide is smaller than the distance between the openings or series of openings in the sleeve.

This slide can close off or release the openings disposed in the axial direction in the sleeve at various levels. The sleeve can be designed so that it is in line with the hollow piston rod and is provided with an opening near the connection to the hollow piston rod.

The invention will now be explained in greater detail with reference to an embodiment shown in the figures.

The figures each show a cross section through a shock absorber, in which the control means are at various positions corresponding to differing damping characteris­tics.

Solid arrows show the direction of movement of the piston and the corresponding direction of flow of the damp­ing medium on the outward stroke, and dotted arrows show the direction of movement of the piston and the corresponding direction of flow of the damping medium on the inward stroke.

Only the part of the shock absorber which is impor­tant for the invention is shown in the three figures. The shock absorber comprises a cylinder 1 with shock absorber piston rod 2 and attached thereto a piston. ChassiS or wheel suspension parts of the particular vehicle may be at­tached to the ends of cylinder and piston rod. In the cylinder/piston assembly is a damping medium which is known per se. In the piston rod 2 is a magnetic device 3, com­prising a coil 4 and a core 5 moving therein. This core 5 projects via a sealing assembly into a cylindrical sleeve 7 which is in line with the piston rod 2, and around which the piston is fastened. This cylindrical sleeve 7 is provided with three sets of openings 8, 9 and 10 respec­tively. Disposed in this sleeve 7 is a slide 11 which can slide in the axial direction. This slide is provided with axial openings 12 through which the medium can flow unimpeded. The slide 11 is connected to the core 5. The wall 13 of the slide can on displacement come to rest in front of the openings 9 or the openings 10. The openings 9 are connected via a first chamber 14 to an opening 15, against which a spring-loaded one-way valve 16 rests. This opening 15 is disposed in a body 17 on which rests a seal­ing element 18. The latter is also provided with a one-way valve 19 which can open and close a duct 20. The element 18 with the sealing element 21 forms the actual seal between cylinder and piston rod. The opening 10 is connected to a second chamber 22 which is provided with one-way valves 23 and 24. One-way valve 24 is loaded by a conical spiral spring 25, while one-way valve 23 is loaded by a spring packet 26 in the rest position. This spring packet 26 also serves to push the one-way valve 16 back to the initial position. The body 27 bounding the second chamber is at such a distance from the shock absorber cylinder 1 that damping medium can flow freely between them. The sleeve 7 is bounded on the under side by a floor 28.

The shock absorber works as follows: In the top position of the slide 11 shown in Fig. 1, on the outward movement of the shock absorber, indicated by a solid arrow, the damping medium is displaced from the space 29 to the space 30. The medium thereby flows unimpeded through the openings 8 to the inside of the piston rod. Since the wall 13 is in front of the openings 9, no medium can flow through them. The one-way valve 19 also impedes the passage of the medium. The medium is consequently forced to move through the opening 10 to the space 30 and thereby to pass through a duct system causing shock absorption. When it ar­rives in the second chamber 22, the one-way valve 24 im­pedes further throughflow, but the one-way valve 23, against the pressure of the spring packet 26, permits out­flow of the medium as shown by the solid arrow. On the in­ward stroke, where the medium has to be displaced from space 30 to space 29, the medium flows via the one-way valve 24, the opening 10, the opening 12 and the opening 8 to the space 29. The valve 19 requires so much force to be opened that it remains shut in the position shown in Fig. 1.

In the intermediate position shown in Fig. 2, the damping medium on the outward stroke flows out of the space 29 to the space 30, where this medium can flow not only in the above-described manner through the openings 8, 12, 10, the second chamber 22 and the one-way valve 23 but also, because the opening 9 is now released via the chamber 14 and the one-way valve 16 to the space 30. This means that the shock absorption is considerably less than that in the embodiment shown in Fig. 1.

If the piston moves inwards in the intermediate position of the slide shown in Fig. 2, which is indicated by dotted lines, the fluid can flow via the one-way valve 24 and the openings 10, 12, 8 from the space 30 into the space 29. Releasing the opening 9 has no effect on the damping characteristic of the inward stroke. For the one-­way valve 16 does not allow any medium through in that direction of flow.

Fig. 3 shows the bottom position of the slide 11. Here the opening 10 is shut off by the wall 13 of the slide 11. On the outward stroke of the piston the medium flows from the space 29 to the space 30, as shown by solid lines. Since the opening 10 is shut off, flow through the one-way valve 23 is no longer possible. The medium can now only flow through the one-way valve 16 to the outside. On the inward stroke of the shock absorber the flow route through the one-way valve 24 is made impossible through the fact that the opening 10 is shut off. The medium can only flow through the duct 20 to the space 29 through opening of the valve 19. The shock absorption in the two directions of flow is very great.

It can be seen from the above that the construction shown produces three different damping characteristics for the outward stroke and two different damping characteris­tics for the inward stroke. Through the use of a slide in conjunction with separate throttling openings and one-way valves which form the actual shock absorber devices, the accuracy of positioning of the slide 12 can be limited to sealing or otherwise of the relevant openings.

An ordinary bottom valve can be present in the bot­tom of the shock absorber to prevent overloading.

Many modifications are possible within the scope of the invention. For example, it is not out of the question for electrically operated valves to be used instead of the slide 11 for each of the series of openings 9 and 10 in­dividually, in which case, as in the case shown in the drawings, a choice can be made from three possibilities: <ul id="ul0001" list-style="none"><li>1) closing of openings 9 and releasing of openings 10,</li><li>2) releasing of openings 9 and closing of openings 10,</li><li>3) releasing of both openings 9 and openings 10.</li></ul> Of course, more than two series of openings 9 and 10 are possible, in which case the shock absorption can be more finely adjusted to the road surface.

Important for the invention is that the medium flows at all piston speeds are determined by the position of the slide or equivalent control means and that consequently the shock absorption is adjustable at all piston speeds. The openings 8, 9, 10 and 12 are so large that they exert no appreciable influence on the shock absorption.