Adjustable shock absorber, especially for motor vehicles

An adjustable shock absorber for motor vehicles has a cylinder containing damping fluid, a piston rod arranged to be axially displaceable in the cylinder, and a damping piston secured to the inner end of the piston rod. The damping piston divides the cylinder chamber into two working chamber compartments and is provided with fluid flow passages which produce damping forces, the effective cross-section of these flow passages being controllable by a throttling member and an electromagnetic drive controlling the throttling member, with the electromagnetic drive including a coil winding which is mounted in the damping piston. In order to achieve improved control of the damping force the throttling member is under the influence on the one hand of the fluid pressure difference between the two working chamber compartments and on the other hand of a restoring force which is created by the electromagnetic drive. Preferably, a hydraulic compensating device which reinforces this restoring force is provided between the throttling member and the electromagnetic drive which counteracts the hydraulic displacement of the throttling member.

FIELD OF THE INVENTION 
This invention relates to an adjustable shock absorber, particularly for 
motor vehicles, comprising a cylinder containing a damping fluid, 
especially a damping liquid, a piston rod axially displaceable in the 
cylinder and extending in sealed manner into the cylinder, and a damping 
piston which divides the cylinder chamber into two working chamber 
compartments and is provided with fluid flow passages which produce 
damping forces. The effective cross-section of these passages is 
controllable by means of a throttling member and by means of an 
electromagnetic drive comprising a magnetic circuit and a coil winding 
which acts upon the throttling member, and the electromagnetic drive is 
mounted in the damping piston immediately adjacent to the fluid flow 
passages and the throttling member. 
BACKGROUND OF THE INVENTION 
Adjustable shock absorbers for motor vehicles having electromagnetically 
displaceable throttling members are known from West German patent 
specification No. 10 84 528, West German published patent application No. 
32 15 614 and West German published patent application No. 32 41 984. In 
these shock absorbers a throttling plate mounted to be rotationally 
displaceable in the damping piston, is used as a throttling member. 
The throttling plate is provided with appropriately positioned holes 
therethrough which can be brought into alignment to a greater or lesser 
degree with through-flow passages provided in the piston body. Alternately 
a through-flow hole lying in the bypass to the fluid flow passages of the 
piston is freed to a greater or lesser extent. 
The displacement of the throttling plate is effected by means of a control 
rod which is connected rigidly to the plate and which extends through the 
full length of the piston rod, which is hollow. The control rod can be 
brought into different rotational set positions by means of an 
electromagnet mounted at the free end of the piston rod in a suitably 
projecting piston rod head. 
In another known adjustable shock absorber for motor vehicles, as described 
in West German published patent application No. 29 11 768, an 
electromagnet coil is mounted at the outer end of a hollow piston rod, and 
a control rod which serves as an armature for the coil extends through the 
full length of the piston rod and is axially displaceable therein. The 
inner end of the control rod permits bypass openings in the piston rod in 
the vicinity of the damping piston to be closed off to a greater or lesser 
degree. 
In these known electromagnetically adjustable shock absorbers it is a 
common feature that in spite of far-reaching objectives it is only 
possible to achieve a coarse presetting of the throttling member and thus 
also of the desired variable damping force behavior, since, in respect of 
their setting means, these shock absorbers are very sluggish in terms of 
their inertia. The fact that the control rod extends through the hollow 
piston rod to its full length and lies between the electromagnetic drive 
means on the one hand and the throttling member on the other hand 
contributes to this to a substantial degree. 
Electromagnetically adjustable shock absorbers of the type referred to 
above are also already known from French patent specification Nos. 
1094025, 1095506 and 1130621. In these shock absorbers, electromagnetic 
drive means comprising magnetic circuits and coil windings and acting upon 
the throttling member are mounted in the damping piston immediately 
adjacent to the fluid flow passages and the throttling member. The 
throttling member is in all these cases formed as a throttling piston 
which is mounted to be displaceable in the longitudinal direction of the 
piston rod against a spring bias. The throttling piston is set to a fully 
defined throttling position in dependence upon the particular current flow 
in the coil winding and is maintained in that position, and indeed 
independently of the changing fluid pressures arising in the working 
chamber compartments, since those pressures are compensated by the equal 
size fluid pressure reaction surfaces provided on the throttling piston, 
whereby the changing pressures have no effect on the position of the 
throttling piston. Consequently, it is still only possible to achieve a 
comparatively coarse damping setting, with throttling holes of constant 
cross-section producing a characteristic exponential damping force curve 
in dependence upon the piston speed. 
OBJECT OF THE INVENTION 
It is therefore an object of the present invention to provide an 
electromagnetically adjustable shock absorber of the type described to 
above whose damping characteristic is essentially linear in nature, yet 
which can be set and/or adjusted steplessly and over the widest range 
desired, and wherein the damping force adjustment can be carried out with 
the maximum sensitivity, even within the individual phases of movement of 
the shock absorber, and desirably with adjustment of the electrical 
control current being capable of being effected either manually or 
automatically, for example under the control of a computer. 
SUMMARY OF THE INVENTION 
This object is achieved in accordance with the present invention in that 
the throttling member is provided with suitably positioned fluid pressure 
reaction surfaces to cause displacement thereof in dependence on the fluid 
pressure difference between the two working chamber compartments, and in 
that the electromagnetic drive exerts on the throttling member an 
adjustable restoring force acting in opposition to the aforesaid 
displacement. 
By this means a highly sensitive, yet stepless setting of the desired 
damping force curve, linearly dependent on the piston speed, is possible, 
since the throttling member on the one hand attempts to move under the 
effect of the hydraulic driving pressure to an appropriate open or 
alternative setting in the sense of opening the fluid flow passages to a 
greater or lesser extent, yet on the other hand is prevented more or less 
strongly from doing so by the counteracting restoring force of the 
electromagnetic drive. The electromagnetic control extends preferably to 
the whole throttling member of the piston and to all its throttling 
elements forming the throttling member, i.e. not just to a bypass provided 
in the piston. 
The electromagnetic drive is preferably so arranged that its restoring 
force is equal to zero in the rest position of the throttling member and 
increases with increasing hydraulic displacement of the throttling member. 
In the rest setting of the throttling member the electromagnetic restoring 
force is thus zero and ineffective regardless of the control current 
flowing through the coil winding; it increases however with the departure 
of the throttling member from the zero or rest setting, with the amount of 
the increase in the restoring force being dependenent upon the current 
flowing through the coil winding. 
Thus, one can achieve not only adjustability of the shock absorber, but 
also an ability to control the shock absorber without complex control 
means and using only direct-current based displacement. Even without 
regulation of the damping force the shock absorber has a defined damping 
characteristic and can be set to different hardnesses by predetermined 
changes in the current supply. It can also be used as a normal shock 
absorber if one dispenses with the current supply and control means. 
Insofar as the shock absorber is provided with a throttling member mounted 
to be rotationally displaceable in the damping piston and is also provided 
with throughflow holes in the throttling member, these holes being brought 
into greater or lesser alignment with flow passages in the fixed piston 
body, for the hydraulic displacement of the rotationally displaceable 
throttling member at least two flow inlet holes are provided between the 
throttling member and the fixed piston body which are in communication 
with the one and with the other working chamber compartment respectively, 
and in each of which holes, viewed in the direction of rotational 
displacement of the throttling member, there are opposed fluidpressure 
reaction surfaces, one provided on the throttling member and the other on 
the piston body. Preferably, the throttling member is formed as a ring 
armature provided with alternate differently poled permanent magnets, the 
armature being mounted rotatably in the piston body and encircling a coil 
winding of an electromagnet forming the electromagnetic drive. The coil 
winding is mounted centrally of the piston body and is provided with a 
plurality of radial pole pieces. 
Insofar as the shock absorber is provided with valve plates as throttling 
members, especially valve spring plates, closing off the fluid flow 
passages in the damping piston, one can secure rod armatures on the valve 
plates or on support plates provided on the rearward side of the valve 
plates, these rod armatures projecting into coil windings set in 
corresponding receiving holes in the damping piston, the coil windings 
being part of an electromagnet forming the electromagnetic drive. However, 
this arrangement requires a comparatively strong electromagnetic drive. 
It is extremely advantageous if, in accordance with a further preferred 
feature of the invention, a hydraulic compensating device reinforcing the 
restoring force is provided between the valve plate and the 
electromagnetic drive which acts in opposition to its hydraulic 
displacement. One such compensating device preferably has at least one 
support member engaging the rear side of the valve plate and hydraulically 
drivable in opposition to the valve plate, the support member being 
mounted displaceably in a pressure reaction chamber from which there 
branches off a liquid supply line leading to the working chamber 
compartment which lies on the inflow side with reference to the associated 
valve plate and also a relief passage leading to the other working chamber 
compartment, the mouth of the relief passage being closable by an 
auxiliary valve plate which is arranged to flex under liquid pressure and 
on which the electromagnetic drive acts with adjustable restoring force. 
In this way it is possible, even with very weak electromagnetic drive and 
restoring forces, to control the valve plate in a sensitive manner, since 
the comparatively strong liquid pressure present at its inflow side is 
compensated to a substantial degree by the counterpressure of the 
oppositely acting hydraulically drivable support member. 
In most cases one can use as the electromagnetic drive an electromagnet 
provided with a coil winding, a magnetic circuit and a movable armature. 
However, it is basically possible also, and in order to achieve a 
particularly rapid and sensitive control of the throttling member setting 
of real advantage, if as the electromagnetic drive for the control of the 
auxiliary valve plate one uses a moving coil mounted on the auxiliary 
valve plate and which moves in an appropriately dimensioned annular gap of 
a permanent magnet provided in the piston. Using this moving coil 
principle one can achieve an extremely rapid adjustment of the damping 
force properties, so that in consequence damping characteristics of any 
desired type can be obtained. 
According to a further preferred feature of the invention, for both the 
compression and expansion phase damping, one need provide only one single 
throttling valve member with a pressure reaction chamber and 
electromagnetically energizable control valve, with these components being 
mounted tightly and compactly in the damping piston. For this purpose the 
throttling valve member on its pressurization side lying opposite to the 
pressure reaction chamber comprises, in addition to its first pressure 
reaction surface which closes off the fluid flow passages, a second 
pressure reaction surface of approximately the same size which is 
subjected to the fluid pressure in the working chamber compartment 
surrounding the valve member, with control throttles being incorporated in 
both fluid connecting passages leading from the pressure reaction chamber 
to the two working chamber compartments. These throttles are controllable 
reciprocally by the control valve which is displaceable in dependence upon 
the pressure difference between the two working chamber compartments, in 
such a manner that they connect the pressure reaction chamber with the 
working chamber compartment which is at the then lower fluid pressure to a 
lesser, throttled degree, whereas they connect the pressure reaction 
chamber to the working chamber compartment which is at the then higher 
fluid pressure to a stronger, throttled degree. 
It is in consequence essential that a total of three different pressure 
reaction surfaces are provided on the throttling valve member, namely the 
active surfaces lying on one side of the valve member and subjected to the 
different pressures in the two working chamber compartments, and the 
reaction surface facing the pressure reaction chamber and lying on the 
other side of the throttling valve member and which in its dimensions 
corresponds substantially to the total surface area of the two oppositely 
disposed reaction surfaces. Thus, in the rest position of the shock 
absorber, the equal pressures in all three chambers mutually balance out 
in their effect on the throttling valve member, so that the latter remains 
in its closed position in which it completely closes off the fluid flow 
passages. However, as soon as the piston performs a movement, and indeed 
whether this is in the compression direction or in the expansion 
direction, the pressure reaction chamber is connected with greater 
freedom, i.e. is less throttled, to the working chamber compartment which 
is then at the lower pressure, and additionally is more strongly throttled 
off from the other working chamber compartment, so that this leads in each 
case to a corresponding pressure drop in the reaction chamber and 
consequently to an opening movement of the throttling valve member which 
is always directed in the same sense. The throttling valve member thus 
always opens in the same direction independently of the direction of 
movement of the piston. 
Preferably, feedback spring elements are provided between the throttling 
valve member and the control valve which, in dependence upon the opening 
displacement movement of the throttling valve member, exert a restoring 
force on the control valve which is in opposition to the particular 
hydraulic displacement force. By this means, in the event of any possible 
electric current failure in the electromagnet which energizes the control 
valve, a satisfactory damping force curve can still be achieved, i.e. a 
suitable emergency function of the shock absorber results, both in the 
expansion phase and also in the compression phase. Furthermore, it has 
been found that oscillations in the damping piston, especially of its 
control valve, can be avoided by this arrangement. 
The damping piston is preferably provided with an insert member containing 
the control valve and its control throttles as well as the fluid 
connecting passages leading from the pressure reaction chamber to the two 
working chamber compartments. At its periphery the insert member carries 
the annular pressure reaction chamber as well as the throttling valve 
member which closes off the pressure reaction chamber in the manner of a 
cap and which is also of annular configuration. The throttling valve 
member is guided on both sides of the pressure reaction chamber at the 
periphery of the insert member to be axially displaceable and sealed in 
relation thereto, and the throttling valve member also comprises an 
annular shoulder separating its two circumferential reaction surfaces from 
each other, with the shoulder being engageable with a closure edge 
positioned on the piston body adjacent to its through-flow passages and 
extending around the piston body. In this way one has a modular unit 
containing the essential functional components and which can easily be 
mounted in the damping piston body.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The adjustable shock absorber which is illustrated in FIG. 1 and which is 
particularly suitable for motor vehicles is of conventional design insofar 
as it comprises a cylinder 1 partially filled with damping liquid and with 
pressurized gas, an axially movable piston rod 3 which extends into and is 
guided into the cylinder through a seal 2, and a damping piston 4 which is 
secured to the inner end of the piston rod 3 and which divides the 
cylinder space filled with the damping liquid into two working chamber 
compartments 5 and 6. The lower working chamber compartment, 6 is divided 
from a chamber 7 filled with pressurized gas by a separating piston 8 
which is guided sealingly within the cylinder 1. 
As is shown particularly well in FIG. 2, the damping piston 4 includes a 
piston body which consists of two plates 9 and 10 which are secured to the 
lower end 3' of the piston rod 3 and through which liquid flow passages 11 
are formed. Between the two piston plates 9,10 is mounted a throttling 
plate 12 which is rotationally displaceable and which is provided with 
through-flow apertures 12' therethrough which can be brought to a greater 
or lesser extent into overlapping relationship with the flow passages 11 
in the fixed piston plates 9 and 10. The throttling plate 12 is rigidly 
connected by means of entraining pins 13 which are secured in the 
throttling plate to a ring armature 15 mounted to be rotationally movable 
in a piston head 14. The armature 15 is part of a rotary electromagnet 
which forms the electromagnetic drive. A coil winding 16 of the 
electromagnet lies in the piston head 14 which is of ferromagnetic 
material. The ring armature 15, which is likewise made of ferromagnetic 
material, is provided, in just the same way as the piston head 14, with 
pole pieces which when positioned opposite each other produce the maximum 
possible magnetic flux. The current supply to the coil winding 16 is 
effected through the piston rod 3 which is provided with a suitable bore 
3" therethrough for this purpose, and the electrical leads are then taken 
to a setting or control device provided on the vehicle side of the piston 
rod. Springs 13' bias the throttling plate 12 into the closed setting, 
i.e. its central rest position, so that in the event of any loss of 
current the shock absorber will always still exert a damping force. 
In order to be able to achieve a greater range of adjustment and 
simultaneously to achieve a greater sensitivity, a permanent magnet 14' 
may be inset into the piston head 14. The restoring force produced by the 
permanent magnet 14' ensures a normal or average damping without any 
current supply. The control current then increases or reduces the 
restoring force of the magnet and thus also the damping force. In this 
case the springs 13' are not used. 
In addition to its through-flow apertures 12' the throttling plate 12 is 
also provided with two crescent-shaped holes 12" therethrough, through 
each of which a respective one of two pins 17 extends, with the pins 17 
connecting the two fixed piston plates 9 and 10 together. Cylindrical 
collar-like bosses 17' are provided at the middle of each of the 
connecting pins 17. These bosses 17' engage sealingly on opposite sides 
thereof in the crescent-shaped holes 12", with the result that each 
crescent-shaped hole 12" is divided into two flow inlet holes. The one 
flow inlet hole is in communication with the upper working chamber 
compartment 5 and the other flow inlet hole is in communication with the 
lower working chamber compartment 6, in each case by way of holes 11' 
provided in the fixed plates 9 and 10. By this means the throttling plate 
12 is rotated in one sense or the other, according to the direction of 
movement of the piston rod 3, by the hydraulic driving force resulting on 
the particular flow inlet side, and, by means of the rotary electromagnet 
14 to 16, a restoring force which is adjustable and is opposed to this 
rotary displacement can be exerted on the throttling plate 12. 
Consequently, by appropriate adjustment or regulation of the electrical 
control current, a particular damping characteristic can be achieved. 
The illustration shown in FIGS. 3 and 4 should make the aforementioned 
control principle somewhat clearer. The damping piston shown in FIG. 3 
corresponds essentially with the damping piston shown in FIGS. 1 and 2. As 
before, it comprises a rotationally displaceable throttling plate 12 
arranged between two fixed piston plates 9 and 10. Flow passages 11 and 
holes 11' are provided in the fixed piston plates 9 and 10. The 
through-flow apertures 12' which can be brought into greater or lesser 
overlapping relationship with the flow passages 11 are arranged in the 
throttling plate 12. Additionally, there are provided in the throttling 
plate. 12 at least two flow inlet holes 12"' respectively in communication 
by way of the holes 11' with the one or the other of the working chamber 
compartments 5 and 6. The flow inlet holes 12"' are defined by 
face-to-face opposed pressure reaction surfaces A,A', seen in the 
direction of rotary displacement of the throttling plate 12, one on the 
plate 12 and the other on a piston bridging piece 4'. 
As will be clearly apparent from the associated schematic illustration in 
FIG. 4, with a downward movement of the damping piston, i.e. with the 
insertion movement of the piston rod, the liquid pressure arising at the 
flow inlet hole 12.sub.a "' causes the throttling plate 12 to be displaced 
rotationally in the direction of the arrow 18, whereas, in the event of an 
extension movement of the piston plate, the pressure increase in the flow 
inlet chamber 12.sub.b "' arising therefrom causes the throttling plate to 
be rotationally displaced in the opposite direction. By controlling the 
current flowing through the coil winding 16 of the electromagnet the 
aforementioned rotary displacement movement can be appropriately 
counterbalanced and thereby the particular amount of rotary displacement 
of the throttling plate 12 can be controlled with considerable 
sensitivity, whereby again the liquid flow through the piston passages and 
consequently also the damping force can be correspondingly adjusted. 
The adjustable shock absorber shown in FIGS. 5 and 6 is also provided with 
a rotationally displaceable throttling member, but here this is in the 
form of a ring armature 21 which is provided with alternating, 
oppositely-poled permanent magnets 20 and which by virtue of its low 
weight and space-saving construction is integrated directly into the 
piston body 4" of the damping piston 4. The piston body 4" is made 
appropriately hollow and is provided with a bottom cover 4"'. The ring 
armature 21 here encircles the coil winding 23 of an electromagnet, the 
coil winding being provided with a plurality of radial pole pieces 22 and 
being positioned centrally of the piston body. The coil winding 23 can be 
connected by means of a switch 24 alternately to one or other of two 
control current supply leads 25 and 26 for the expansion and compression 
phase damping, the connection being synchronized with the alternating 
direction of rotary movement of the ring armature 21. Both current supply 
leads 25,26 are guided up through the piston rod 3 to operating or control 
means at the vehicle side of the piston rod. 
As can be seen from FIG. 6, an arcuate flow inlet groove 27 is machined 
into the inner wall of the piston body 4" which surrounds the ring 
armature 21. The flow inlet groove 27 defines two flow inlet holes 
27',27". The two flow inlet holes 27',27" are in communication by way of a 
connecting passage 28' or 28" with the one or other working chamber 
compartment 5 or 6. A projection 21' provided on the external periphery of 
the ring armature 21 and defining fluid pressure reaction surfaces A' on 
each side thereof projects sealingly into the flow inlet groove 27. In 
this way, here again, the ring armature 21 is rotationally displaced to a 
greater or lesser degree in the one or other direction in accordance with 
the direction of movement of the damping piston 4 and the hydraulic 
pressure difference arising therefrom. This rotational displacement can be 
opposed by energizing the coil winding 23 of the electromagnet to a 
greater or lesser degree, and consequently a corresponding effect can be 
created on the damping behaviour of the damping piston. The switch 24 
comprises a fork 24'. The switch is appropriately reversed by the ring 
armature in its alternating direction of rotation by an entraining pin 21" 
secured to the ring armature 21 and projecting into the fork 24' striking 
the fork. By means of the switch the coil winding 23 can be energized with 
the control current desired for the particular expansion and compression 
phase damping, so that thereby any desired damping force diagram can be 
achieved, since the liquid flow through the passages 11,12' and 4.sup.IV 
can be allowed to flow more or less freely or be throttled in both 
directions, corresponding to the indicated double arrows. For the rest, it 
will be understood that in the event of current failure the damping piston 
4 here also, as in the other embodiments, is not blocked but is opened for 
the through flow of liquid by the hydraulic pressurization of the 
throttling plate 12 and of the ring armature 21 arising through the flow 
inlet holes, with the result that only the force of the permanent magnet 
controls the particular damping. 
Instead of the ring armature 21 fitted with permanent magnets 20 as 
provided in the embodiment shown in FIGS. 5 and 6, a suitably designed 
axially displaceable throttling member can alternatively be used, in which 
the flow passages and flow inlet holes are suitably modified. By making 
the throttling member axially displaceable, the electromagnetic drive can 
be further simplified. 
The adjustable shock absorber shown in FIGS. 7 and 8 is of particularly 
simple construction. The damping piston 4 is here provided with respective 
pairs of liquid flow passages 31,31' for the compression phase and 
expansion phase damping. The passages are each offset by 90.degree. 
relative to each other and are covered, in respective pairs, by valve 
spring plates 32 and 32' which are secured centrally on the piston rod end 
3' and which are arranged on the opposite end faces of the damping piston 
4. Backing the substantially rhombic-shaped valve spring plates 32 are 
support plates 33 and 33' which are essentially H-shaped. Rod armatures 34 
positioned to lie on both sides of the valve spring plates 32 and 32' are 
secured to these support plates 33 and 33', the rod armatures projecting 
into coil windings 35 of an electromagnet set into appropriately 
positioned pocket recesses 36 of the damping piston 4. The coil windings 
35 are connected by way of a current supply conductor 37 with an adjusting 
or control member provided on the vehicle side of the shock absorber. The 
rod armatures 34 project almost down to the base 36' of the pocket 
recesses 36 and, like the damping piston 4 are made of ferromagnetic 
material so that here also corresponding electromagnetic force effects 
result. When the piston rod 3 moves inwards, the damping piston 4 moves 
downwards, so that the valve spring plate 32 and also its support plate 33 
is bent upwards to a greater or lesser degree by the hydraulic pressure 
arising in the liquid flow passages 31. This bending deformation can be 
opposed to a greater or lesser extent by appropriate adjustment of the 
control current in the electromagnet coils 35 and thus of the restoring 
force exerted by the rod armature 34 on the plates 32 and 33, so that here 
also a damping diagram of any characteristic can be achieved by the use of 
the electromagnet coils incorporated directly into the piston 4. In this 
embodiment the electromagnetic restoring force has to be comparatively 
large, in order to be able to oppose directly the fairly high liquid 
reaction pressures. 
Substantially more favorable control and adjustment possibilities for the 
damping force curve can be achieved with the embodiment illustrated in 
FIG. 9, in which the liquid flow through the flow passages 31 provided in 
the damping piston 4 is controlled likewise by one or more valve spring 
plates 32 set centrally on the end 3' of the piston rod. A difference 
between this embodiment and the embodiment shown in FIGS. 7 and 8 is the 
fact that here, between the valve spring plate 32 and the electromagnetic 
drive opposing its hydraulic displacement, there is provided a hydraulic 
compensating device which reinforces this restoring force. This 
compensating device comprises, in the present embodiment, support members 
38 which engage with the rear side of the valve plate 32 and which are 
hydraulically pressurizable in opposition thereto, the support members 38 
being axially displaceably mounted in a pressure reaction chamber 40 
within a piston cover 39. This reaction chamber 40 is in permanent 
communication with the working chamber compartment which is positioned on 
the inflow side with reference to the valve spring plate 32, in the 
present case the lower chamber 6, by way of liquid passages 41 provided in 
the piston cover 39, holes 32" in the valve spring plate 32, and passages 
42 in the piston body. Since the support members38, which may be formed 
for example as balls or even pistons, are in this case of a diameter which 
is somewhat greater than the diameter of the liquid flow passages 31 
positioned below them, this ensures that there is no bending out of the 
valve spring plate 32 in the event of an outward movement of the damping 
piston 4, since the pressure in the reaction chamber 40 corresponds to the 
inflow pressure created in the passages 31. 
It is essential however that relief passages 43 branch off from the liquid 
supply passages 41, these relief passages leading to the other working 
chamber compartment, here the upper working chamber compartment 5, and 
having their mouths closed off by an auxiliary valve plate 45 which is 
mounted at its periphery on the piston cover 39, for example by means of 
connecting pins 44. This auxiliary valve plate 45 forms the armature of an 
electromagnet which has its coil winding 46 appropriately let into the 
piston cover 39 and whose current supply lead 47 is again here guided 
through the hollow piston rod 3 to the outside of the unit. As is 
indicated by the chain-dotted line 48, there is provided at the underside 
of the damping piston 4 a correspondingly constructed hydraulic 
compensating device offset by 90.degree. relative to the upper 
compensating device and equipped with electromagnetic drive means for the 
compression phase damping, with a current supply lead 47' for the 
electromagnetic drive means likewise being guided out of the unit through 
the piston rod 3. 
Upon the outward extension movement of the piston rod 3, i.e. with the 
corresponding downward movement of the damping piston 4, there is a 
build-up of pressure in the reaction chamber 40 through the supply 
passages 41,42, this build-up of pressure corresponding to the pressure in 
the lower working chamber compartment 6 and in the piston passages 31. 
This hydraulic pressure also acts on the very small diameter relief 
passages 43 and consequently also on the auxiliary valve plate 45 which is 
thereby raised to a greater or lesser extent, this leading to a 
corresponding pressure drop in the relief passages 43 and consequently 
also in the reaction chamber 40, whereby the valve spring plate 32 is 
raised from its seat on the upper surface of the piston by the action of 
the hydraulic pressure in the piston passages 31 and as a result the 
liquid flow passages 31 are opened. Since on the other hand however, by 
adjustment of the control current flowing through the coil winding 46 of 
the electromagnet, the auxiliary valve plate 45 which forms the 
electromagnet armature can be attracted back into its closed position by 
the application of a greater or lesser restoring force, in this way, by 
means of the relief passages 43, the hydraulic pressure in the reaction 
chamber 40 and consequently also the reaction pressure on the supporting 
balls 38 can be varied, with the result that the hydraulic displacement or 
bending force exerted through the piston passages 31 on the valve spring 
plate 32 is opposed, that is to say a corresponding adjustable restoring 
force is exerted on the valve spring plate 32. Thus, as has been 
demonstrated already in practice, the damping force can be adjusted 
extremely rapidly. For example, within a single movement phase, i.e. 
approximately during the extension movement of the piston rod in the 
expansion phase, damping force oscillations of surprisingly high amplitude 
and frequency can be achieved in the damping force-piston movement 
diagram. It follows from this that with such a damping piston and with the 
associated electrical control device it is possible without difficulty to 
obtain damping force diagrams of any desired characteristics, especially 
such diagrams with maximum energy dissipation. It should be understood 
that the same results can also be achieved during the relevant compression 
phase of the shock absorber by the corresponding electro-hydraulic 
compensating device 48 which is mounted on the underside of the damping 
piston 4 for this purpose. 
The shock absorber piston illustrated in FIGS. 10 and 11 is designed to 
have essentially the same character and mode of operation as the shock 
absorber shown in FIG. 9, but is of simpler construction. In this 
embodiment the liquid flow passages 31,31' which are alternately effective 
for the compression and expansion phases are closed off by tongues 50' of 
an annular valve spring plate 50 which is mounted between the piston body 
4" and a piston cover 39'. In the piston cover 39' are provided a 
plurality of circumferentially equispaced supply passages 51 which 
permanently connect the reaction chamber 40', which is here an annular 
chamber, with the lower working chamber compartment 6. In the annular 
reaction chamber 40' there is mounted an axially displaceable support ring 
53 which forms the support member, which is provided with a seal 52, and 
which engages against the rear side of the individual tongues 50' of the 
associated annular valve spring plate 50. On the other hand the support 
ring 53 leaves open or bridges over the entrances to the intermediate 
liquid flow passages 31 of the other passage group which is provided for 
the expansion phase damping. Relief passages 43' branch off from each of 
the feed passages 51. These relief passages 43' lead to the other working 
chamber compartment 5 and are closed off by an auxiliary valve plate 45' 
or alternatively by a number of suitably arranged separate valve elements. 
The coil winding 46 of the electromagnet is positioned between the piston 
body 4" which is made of ferromagnetic material and the piston cover 39'. 
Within an annular recess in the piston cover 39' is set, beneath the 
auxiliary valve spring plate 45' or the separate valve elements, a ring 54 
of non-magnetic material. This ensures that the magnetic flux is fully 
effective on the auxiliary valve plate 45', so that in consequence by 
suitable adjustment of the control current flowing through the coil 
winding 46 the auxiliary valve spring plate 45' is urged more or less 
strongly by the electromagnet into its closed position, whereby here 
again, just as in the embodiment shown in FIG. 9, the tongues 50' of the 
annular valve spring plate 50 can be controlled in a correspondingly 
sensitive manner by means of the correspondingly urged support ring 53, 
and thus here also the damping force properties can be controlled to an 
appropriately fine degree. 
The damping piston shown in FIG. 12 corresponds substantially in terms of 
its structural properties with the piston shown in FIGS. 10 and 11, and 
the corresponding elements are therefore given the same reference numbers, 
such as for example the piston body 4", the piston cover 39', the supply 
passages 51, the relief passages 43', the reaction chamber 40' and the 
sealed annular piston 53. In this embodiment however, as the 
electromagnetic drive means for the valve spring plate 45" which closes 
off the relief passages 43', there is provided a moving-coil winding 55 
which is mounted at the underside of the valve spring plate and which 
moves within an annular gap 56 of a permanent magnet circuit which lies 
between the two piston cover parts 39" and 39"'. The permanent magnet 
circuit comprises an annular permanent magnet 57, and the piston body 4" 
and the piston cover parts 39" and 39"', all of which are of ferromagnetic 
material. Between the piston body 4" and the permanent magnet ring 57 on 
the one hand and the piston rod 3 on the other hand, there is provided, 
for the magnetic screening of the permanent magnet, a sleeve 58 of 
non-magnetic material. 
As will be clearly apparent, here also, by a defined control of the 
electrical control current flowing through the annular coil winding 55, a 
suitably regulated restoring force can be exerted on the auxiliary valve 
spring plate 45", and thereby the mouths of the relief passages 43' can be 
freed to a greater or lesser extent, whereby, by means of the annular 
piston 53, a correspondingly adjustable counterpressure can be exerted on 
the annular valve plate 50, so that with this piston arrangement also it 
is possible to achieve a very sensitive, spontaneous control or adjustment 
of the damping force behaviour. 
Instead of the annular piston 53 which is provided in the embodiment shown 
in FIGS. 10 to 12, one can alternatively use some other supporting member 
as a support means for the valve plate 50, particularly for example 
hydraulically inflatable support members, such as for example tubes, metal 
bellows or membranes, all of which have the advantage that they can be 
made simply and above hydraulically inflatable support members are 
likewise connected with corresponding supply passages 51 and relief 
passages 43'. 
For all the embodiments described above it is a characteristic that with 
them the throttling member is on the one hand under the force influence 
produced by the hydraulic pressure difference, and on the other hand is 
under the influence of the magnetically produced and electrically 
controlled restoring force which opposes the opening of the throttling 
member and which is zero in its closed state or central rest position. 
Thus, all the embodiments described above can be operated not only with 
continuously adjustable control but also as simple displaceable shock 
absorbers whose damping force can be set or adjusted solely by means of a 
variable resistance. The adjustable control provided by the present 
invention makes it possible without difficulty to compensate for 
variations in the damping characteristic arising for example from 
manufacturing tolerances, temperature differences and the like. 
It will be appreciated that in all the embodiments in which only one 
electromagnetically controllable hydraulic compensating device for the 
driving of the throttling member is illustrated, a correspondingly 
constructed second electro-hydraulic compensating device can be provided 
on the damping piston for the other direction of movement of the piston 
and of the piston rod, so that the damping force behaviour can be 
appropriately controlled both in the compression phase and also in the 
expansion phase of the shock absorber. This control can be effected both 
manually and also, and especially, automatically in dependence upon the 
most varied influencing factors with a view to achieving maximum travel 
comfort and travel safety. 
In contrast to the embodiments described above, the damping piston which is 
illustrated in FIGS. 13 to 17 is equipped with only a single throttling 
valve member with reaction chamber and electromagnetically energizable 
control valve for both working directions. The damping piston which here 
again divides the cylindrical chamber containing a damping fluid, 
particularly damping oil, into two working chamber compartments A.sub.1 
and A.sub.2, comprises a damping piston body 104 connected to the piston 
rod by means of a screw thread connection 104'. As can be seen 
particularly clearly from the right-hand half of FIG. 13, the damping 
piston body 104 is provided with oil flow passages 131 arranged 
distributed at equal intervals around its circumference, these passages 
narrowing in a funnel-shaped manner towards the underside of the piston 
body and issuing into a recess 104" in the piston body. This piston body 
recess 104" is encircled by a closure rim 104"' which extends around it. 
A cup-shaped insert member 105 is secured in the piston body 104 by means 
of fastening screws 106 which extend through corresponding bores in the 
piston body 104. Within the insert member 105 there is located a permanent 
magnet ring member 107 which is retained in place by a pole piece plate 
108 which for its part is secured to the lower end of a valve sleeve 109 
which is supported in a central recess in the insert member 105 and which 
has an annular flange provided at its other end which engages over the 
insert member 105. At its lower end the insert member 105 is closed by a 
closure cover 110 which is set into it. A further valve sleeve 111 is set 
into a corresponding central bore in this closure cover 110. 
A valve needle 112 which forms part of a control valve S is guided axially 
through the valve sleeves 109 and 111. The valve needle 112 carries, at 
its two ends, respective control pistons 113 and 114 which are mounted 
displaceably in corresponding enlargements of the bores through the valve 
sleeves 111 and 109 respectively. The two control pistons 113,114 are each 
provided with an annular groove 113' and 114', as well as with an axially 
extending relief passage 113" and 114" which serves for pressure 
equalization on the two sides of each piston. The annular grooves 113' and 
114' work in conjunction with radial bores 111' and 109' and 111" and 109" 
which are provided in the valve sleeves 111 and 109 respectively. 
The first-mentioned radial bores 111' and 109' are in permanent 
communication by means of connecting passages 115 and 116 in the closure 
cover 110 as well as in the insert member 105 with an annular reaction 
chamber 140 which surrounds the insert member 105, while the radial bore 
111" is in communication with the working chamber compartment A.sub.2, and 
the radial bore 109" is in communication with the working chamber 
compartment A.sub.1 by way of a recess 104.sup.IV and a connecting passage 
104.sup.V. The annular grooves 113' and 114' provided in the control 
pistons 113,114, as shown in FIG. 14, are arranged offset inwardly 
relative to the corresponding radial bores 111', 111" and 109',109" in the 
valve sleeves, and indeed are offset by an amount corresponding 
approximately to half the diameter of the last-mentioned bores. 
A coil carrier 120 is mounted on the control valve needle 112 between its 
two control pistons 113,114. The coil carrier 120 projects into a chamber 
121 which lies between the closure cover 110 and the pole piece plate 108. 
The coil carrier 120 has an axially extending flange 120' which carries on 
it an electromagnetic moving-coil winding 122. This flange 120' surrounds 
the pole piece plate 108 and the permanent magnet 107. Between the 
permanent magnet 107 and the insert member 105 which is made of 
ferromagnetic material and the pole piece plate 108 there is a strong 
permanent magnetic field in which the moving-coil winding 122 can be 
axially displaced in one direction or the other in accordance with the 
flow of current controlled from externally, whereby a corresponding 
electromagnetic displacement or restoring force can be exerted by means of 
the coil carrier 120 on the valve needle 112 with its control pistons 113 
and 114. The true displacement of the valve needle 112 is effected by 
hydraulic means, and indeed in dependence upon the pressure difference 
which is present between the two working chamber compartments A.sub.1 and 
A.sub.2. 
An annular throttling valve member 150 is axially displaceably arranged and 
sealingly guided on the periphery of the insert member 105 and closes off 
the reaction chamber 140 as a capping member. This annular throttling 
member 150 is so designed and arranged that it has a total of three active 
surfaces which are subjected to the oil pressure. One of these is the 
surface F.sub.1 which faces towards the reaction chamber 140 and which is 
thus subject to the reaction chamber pressure. On its opposite side are 
the two concentric annular surfaces F.sub.2 and F.sub.3 which extend 
around it. The surface F.sub.2 is always subject to the hydraulic pressure 
created in the working chamber compartment A.sub.2 which immediately 
surrounds the throttling valve member 150, whereas the surface F.sub.3 
faces towards the oil flow passages 131 and therefore is permanently 
subjected to the pressure prevailing in the working chamber compartment 
A.sub.1. The size ratios of the three surfaces are so arranged that the 
surfaces F.sub.2 and F.sub.3 are of substantially the same area and the 
surface F.sub.1 corresponds in area substantially to the sum of the other 
two surfaces F.sub.2 and F.sub.3. Between the two reaction surfaces 
F.sub.2 and F.sub.3 the throttling valve member 150 is provided with an 
annular shoulder 151 which separates the two surfaces from each other. In 
the rest position this annular shoulder 151 engages against the closure 
rim 104"' of the damping piston body 104 and thereby closes off the 
through-flow passages 131. 
Two plate springs 160 and 170, shown in FIGS. 15 and 17, are provided on 
the underside of the insert member 105 and of its closure cover 110. Plate 
spring 160, which is effective during the expansion phase, has a cruciform 
shape. It is secured to the closure cover 110 by means of securing screws 
162 which extend through screw fastening holes 161, so that its outer ends 
163 rest against the lower edge 150' of the throttling valve member ring 
150. The plate spring 160 is also provided with internal resilient tongues 
164 produced by a suitable stamping operation and the inner ends 164' of 
which engage over the associated control piston 113 of the control valve 
S. The inner ends 164' of the spring tongues are therefore pressed more 
strongly against the control piston 113 the more strongly the opposing 
bending at the outer ends 163 is effected by the throttling valve member 
ring 150 in contact therewith in its opening movement. In contrast to the 
cruciform-shape plate spring 160, the plate spring 170 which is effective 
during the compression phase is of substantially rectangular shape. It has 
its outer ends 171 in contact with the lower edge 150' of the throttling 
valve member 150 and with the ends 163 of the plate spring 160, and spans 
the cruciform plate spring 163 in the manner as it were of a bridge. The 
plate spring 170 is likewise provided with internal spring tongues 172 
produced by an appropriate stamping operation and which have their inner 
ends engaging under an entraining collar 112' which sits on the adjacent 
outermost end of the valve needle 112. 
As will be appreciated most clearly from FIG. 14, in the extension movement 
of the piston rod, i.e. in the expansion phase of the shock absorber, by 
hydraulic pressurization the control valve needle 112 is displaced to the 
left, whereby the passage communication between. the control piston 114 
and the working chamber compartment A.sub.1 is more strongly throttled, 
while in contrast the fluid communication between control piston 113 and 
the working chamber compartment A.sub.2 is opened to a greater degree, so 
that there occurs a corresponding pressure drop in the reaction chamber 
140 and naturally also a correspondingly different pressure reaction is 
exerted on the surfaces F.sub.2 and F.sub.3 of the throttling valve member 
150 which as a result is moved to the left and the actual throttling 
position between the annular shoulder 151 and the closure rim 104"' is 
freed to a greater or lesser extent for the flow of fluid therethrough. 
Simultaneously however, by the displacement of the throttling valve member 
150, the cruciform-shape plate spring 160 is correspondingly bent outwards 
at its outer ends 163, which has the result that the inner ends 164' of 
its spring tongues 164 press ever more strongly against the control piston 
113 of the control valve needle 112 which thereby experiences a 
corresponding mechanical restoring force. Additionally, by adjustment of 
the current flowing in the moving-coil winding 122, a corresponding 
electromagnetic adjusting or restoring force can be exerted on the valve 
needle 112. When the piston rod again travels back into the damping 
cylinder in the compression phase, then the valve needle 112 is displaced 
to the right, whereby the reaction chamber 140 is connected more openly, 
i.e. in a less throttled manner, to the working chamber compartment 
A.sub.1, whereas in contrast the working chamber compartment A.sub.2 is 
more strongly throttled, so that again in this case the throttling valve 
body 150 performs a corresponding axial opening movement and the actual 
throttling gap between the annular shoulder 151 and the closure rim 104"' 
is freed to a greater or lesser extent. Then, by means of the plate spring 
170 and its spring tongue ends 172 a corresponding mechanical restoring 
force is exerted on the entraining collar 112' and consequently on the 
valve needle 112, and thus its corresponding hydraulic displacement is 
counterbalanced to a greater or lesser extent. It will be self-evident 
that in this case also, by the adjustment of the current flowing in the 
moving-coil winding 122, the valve needle 112 can be subjected 
additionally to magnetic forces in the one or other direction and 
consequently the damping force can be appropriately controlled and 
adjusted.