Shock absorber

A known shock absorber including a throttle cross section of a throttle passage which is electrically variable via a magnet, to adjust damping of fluid between separate work chambers. If the magnet has no current in the event of an electrical defect, then the throttle cross section of the throttle passage attains its minimum opening, and maximum damping is attained the shock absorber includes a different further throttle passage which is uncovered in the event of an electrical defect. As a result, in the event of an electrical defect an arbitrarily preselectable, preferably approximately average damping is brought about by the further throttle passage.

BACKGROUND OF THE INVENTION 
The invention is based on a shock absorber as defined hereinafter. Shock 
absorbers are already known to applicants in which a damping action is 
variable by means of an electromagnetic adjuster. The adjuster includes a 
magnet coil and a control slide, and the control position of the control 
slide determines the throttling of the pressure fluid being exchanged 
between the work chambers. 
In the version known to applicants, a throttle cross section in a throttle 
passage is opened to a variable extent depending a control position of a 
control slide. When there is maximum current to the magnet coil, the 
control slide is located in a terminal control position, in which a 
maximum-sized throttle cross section is uncovered in the throttle passage. 
The maximum throttle cross section means minimum damping by the shock 
absorber. Without current, the control slide is in another terminal 
control position, in which a minimum-sized throttle cross section is 
uncovered. The minimum cross section represents maximum damping by the 
shock absorber in the latter position. 
In the event of an electrical defect, such as if the magnet coil fails or 
if a supply lead to the magnet coil breaks, maximum damping of the shock 
absorber is obtained. Although maximum damping by the shock absorber is 
necessary in some extreme situations, still in the case of a defect it is 
not an optimal compromise. 
The adjuster may be provided either in the cylinder or outside the 
cylinder. 
OBJECT AND SUMMARY OF THE INVENTION 
By comparison, the shock absorber as defined hereinafter has a further 
throttle passage, with an advantage that in the event of a defect a 
preselectable, preferably approximately average damping of the shock 
absorber is established. This damping established in the event of a defect 
is independent of the maximum and minimum damping. 
Providing a further throttle passage with at least two openings, preferably 
uniformly distributed over a circumference of the control slide, 
advantageously minimizes a force crosswise to an adjusting direction of 
the control slide. 
Providing annular chambers on the control slide and on the valve body as 
components of a further throttle passage, so that the fluid under pressure 
can flow through these annular chambers in the event of an electrical 
defect, has an advantage, among others, that to attain the desired damping 
in the event of a defect only a short stroke of the control slide is 
necessary. Additionally and advantageously, an effective throttle area 
determining the damping may also be provided remote from the annular 
chambers, at any arbitrary point in the course of the further throttle 
passage. 
A particularly advantageous feature is that at least one valve may be 
provided in the further throttle passage. The valve may have any arbitrary 
structure. This assures that in the event the second throttle cross 
section is opened, for instance because of a defect, then any arbitrary 
desired damping characteristic is advantageously attainable. 
The invention will be better understood and further objects and advantages 
thereof will become more apparent from the ensuing detailed description of 
preferred embodiments taken in conjunction with the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows the first exemplary embodiment. A shock absorber 2 has a 
cylinder 4 with a jacket tube 6, shown in segments, having a first face 
end 8 and a second face end 10. A piston rod 12 protrudes from the first 
face end 8 of the jacket tube 6. Only the two ends of the piston rod 12 
are shown. The piston rod 12 is connected by one end to a stepped damper 
piston 14 and by its other end it is pivotably connected to a first mass 
16, represented by dot-dash lines. In other words, the damper piston 14 is 
connected to the first mass 16 via the piston rod 12. The second face end 
10 of the cylinder 4 is connected to a second mass 18, again shown in 
dot-dash lines. The first mass 16 is a vehicle body, for example, while 
the second mass 18 is for example a vehicle axle. The damper piston 14 may 
slide axially on an inner jacket face 22 of the jacket tube 6, via an 
interposed guide ring seal 20. An interior of the cylinder 4 is divided by 
the damper piston 14 and the guide ring seal 20 into a first work chamber 
24 and a second work chamber 26. In the drawing, the first work chamber 24 
is above the damper piston 14 and guide ring seal 20, and the second work 
chamber 26 is below them. The work chambers 24, 26 are at least partly 
filled with a pressure fluid. 
The two work chambers 24, 26 communicate with one another via a throttle 
passage 30. The throttle passage 30 includes a variable throttle cross 
section. The damper piston 14 includes the throttle passage 30, a magnet 
coil 32, a control slide 34, a restoring spring 36, and if desired a 
transducer 38. 
The piston rod 12 is hollow and receives a first electrical supply line 40 
to which the magnet coil 32 is connected. A second electrical supply line 
42 likewise leads through the hollow piston rod 12 and is connected to the 
transducer 38. The magnet coil 32 is located inside a valve body 44, which 
forms part of the damper piston 14. On the inside of the magnet coil 32, 
the valve body 44 forms an annular first pole 46. 
A second, likewise annular pole 48, which is connected to the valve body 
44, extends axially in the direction toward the first pole 46, maintaining 
a certain distance from it to form a spacing therebetween. The first pole 
46, provided with a coaxial bore 50, into which a portion of, an armature 
52 of the tubular control slide 34 protrudes at least part way. Depending 
on the control position of the control slide 34 in the bore 50, the 
armature 52 not only extends along the second pole 48 in the axial 
direction but also more or less extends along the first pole 46. The air 
gaps that are definitive for a magnet force acting upon the armature 52 
are located between a cylindrical outer jacket 54 of the armature 52 and 
the bore 50 forming the radial pole faces of the poles 46, 48, on the one 
hand, and between an axial step 56 of the first pole 46, which is set back 
in the manner of a blind bore, and a face end 57 of the armature 52 
oriented toward the step 56. 
An axial through bore 58 is located in the control slide 34, into which the 
piston rod 12 is inserted, making the control slide 34 axially slidingly 
displaceable on the piston rod. By means of the restoring spring 36 
surrounding the piston rod 12, the control slide 34 is subjected to a 
restoring force acting in the axial direction, which tends to urge the 
control slide 34 away from the first pole 46. Correspondingly, the 
armature 52 and with it the control slide 34 are moved counter to the 
restoring force of the restoring spring 36 in the direction of an 
increased overlap between the cylindrical outer jacket 54 of the armature 
52 and the first pole 46 when the magnet coil 32 is electrically excited. 
In other words, when excited, the electromagnet draws the armature toward 
the electromagent. 
Remote from the restoring spring 36, the armature 52 merges, via an 
enlargement in the form of an annular disk 60, with a tubular control part 
62 of the control slide 34, the diameter of the control part 62 in the 
exemplary embodiment shown being advantageously larger than the diameter 
of the armature 52. The control part 62, along with the armature 52, can 
either be an integral part of one component, that is, the control slide 
34, as shown in the drawing, or else it may comprise two components joined 
together. 
The tubular control part 62 of the control slide 34 is slidable with a 
fine-machined inner jacket face 64 on a likewise fine-machined jacket face 
66 of the valve body 44. 
An encompassing annular chamber 68 is machined into the jacket face 66 of 
the valve body 44. One or more axially eccentrically extending recesses 70 
provides an opportunity for a fluid flow between the annular chamber 68 
and the first work chamber 24. At least one flow opening 72 is machined 
radially around the annular chamber 68 and outside the control slide 34 in 
the valve body 44; this provides an opportunity for a flow between a 
control chamber 74 receiving the control slide 34 and the second work 
chamber 26 via an annular passage between the value body 44 and the inner 
surface 22 of the cylinder. 
The length of the control slide 34 is dimensioned such that depending on 
the axial control position of the control slide 34, the control slide 
covers the annular chamber 68 to a greater or lesser degree in the axial 
direction. A face end 76 remote from the magnet coil 32 is located on the 
control part 62 of the control slide 34. The edge between the inner jacket 
face 64 and the face end 76 of the control slide 34 is embodied as a slide 
control edge 78, which in cooperation with a control edge 80 defining the 
annular chamber 68 determines the size of the variable throttle cross 
section of the first throttle passage 30. The recess 70, the annular 
chamber 68, the variable throttle cross section, the control chamber 74 
and the flow opening 72 are components of the throttle passage 30 that 
connects the two work chambers 24, 26 during regular operation. 
The transducer 38 is secured to the valve body 44 in the vicinity of the 
control slide 34 and serves to detect the control position of the control 
slide 34 relative to the valve body 44. The transducer 38, which for 
instance makes inductive or capacitive measurements, emits a measurement 
signal via the second supply line 42 to an electronic control unit 81, 
which via a set-point/actual-value comparison operator generates a control 
signal that is delivered to the magnet coil 32 via the first supply lead 
40. This forms a control circuit, and the control slide 34 can be 
positioned substantially more accurately, and more independently of 
tolerances, than would be possible without feedback of the actual position 
of the control slide 34. Depending on the manner in which the transducer 
38 functions, it is necessary or at least practical for a suitable marking 
material 82 to be provided on the control slide 34, an example being a 
permanent magnet or a copper ring, so that the transducer 38 can 
satisfactorily detect the control position of the control slide 34. 
The slide control edge 78 and/or the control edge 80 may be provided with a 
tooth profile having axially extending raised and depressed areas, as is 
known from U.S. Pat. No. 4,905,798. 
The control slide 34 may be embodied such that no static hydraulic forces 
and no axial flow forces, or practically no axial flow forces, act upon 
the control slide 34. One of the provisions for this may be to embody the 
control slide 34 approximately as a sharp cutting edge in the vicinity of 
the face end 76, with relief connections 83 and 84 and/or a play between 
the control slide 34 and the valve body 44 or piston rod 12 assuring a 
pressure equilibrium. Further provisions for reducing the static forces 
and flow forces acting on the control slide 34 are disclosed in German 
Offenlegungsschrift 38 00 865. What is said of the shock absorber in U.S. 
Pat. 4,905,798 applies equally to the shock absorber of the present 
application. 
Depending on the current to the magnet coil 32, the control slide 34 is 
actuated counter to the restoring force of the restoring spring 36. The 
control position of the control slide 34 is defined when the armature 52 
of the control slide 34 comes to rest on the step 56, or the annular slide 
60 comes to rest on another step 86 of the valve body 44, depending on the 
clearances among the components. With decreasing magnet force of the 
magnet coil 32, the restoring force of the restoring spring 32 actuates 
the control slide 34 in the opposite direction, until the annular disk 60 
of the control slide 34 comes to rest on a further step 88 of the valve 
body 44. The annular disk 60 of the control slide 34 comes to rest on the 
step 88 whenever the magnet coil 32 has a relatively weak current or has 
no current running through it. 
If there is a strong current through the magnet coil 32, then the slide 
control edge 78 moves far away from the control edge 80, and the variable 
throttle cross section of the throttle passage 30 is large; that is, the 
damping of the shock absorber is slight. If there is a weak current 
through the magnet coil 32, then the slide control edge 78 is flush with 
the control edge 80, or the slide control edge 78 covers the control edge 
80 completely or partly, depending on the structural design, and the 
variable throttle cross section of the throttle passage 30 is small, so 
that the damping of the shock absorber is great. If there is no current 
through the magnet coil 32, for instance because of some electrical defect 
or other, then the annular disk 60 of the control slide 34 rests on the 
step 88, and the variable throttle cross section of the throttle passage 
30 attains its minimum opening, or depending on the structural design is 
completely closed. 
To assure that the maximum damping of the shock absorber will not ensue if 
there is some defect, such as an electrical failure, the control part 62 
of the control slide 34 is provided with at least one radial opening 91. 
As a result, depending on the control position of the control slide 34, a 
further throttle passage 90 can be uncovered. The recess 70, the annular 
chamber 68, the opening or openings 91, the control chamber 74 and the 
flow opening 72 are components of the further throttle passage 90 
connecting the two work chambers 24, 26 in the event of a defect. As shown 
in the drawing, the course of the flow of the throttle passage 30 and of 
the further throttle passage 90 may coincide intermittently, or they may 
have completely separate courses. 
The opening 91 includes a countersunk portion 92, by way of example. The 
countersunk portion 92 extends from an outer jacket 94 of the control part 
62 of the control slide 34 in the direction toward the jacket face 64; 
shortly before it reaches the jacket face 64, the countersunk portion 92 
merges with a slit 96. The opening 91 comprises the countersunk portion 92 
and the slit 96. This is particularly advantageous from a manufacturing 
standpoint. The slit 96 is preferably rectangular, but it may also be 
round, as an example. To make for the shortest possible structure of the 
shock absorber, it is favorable to make the slit 96 narrow and to align it 
in the circumferential direction. However, it is also possible to embody 
the opening 91 without any graduation, or in other words in the form of a 
simple through bore. If the slide control edge 78 is provided with at 
least one raised portion and one depression, then it is possible for the 
depression to merge, at a narrow point, with the opening 91 of the further 
throttle passage 90. 
The annular chamber 68 is defined toward the jacket 66 of the valve body 44 
by the control edge 80 and on the other side by a further edge 97. If the 
annular disk 60 of the control slide 34 is resting on the step 88 of the 
valve body 44, then the opening 91 of the further throttle passage 90 
between the annular chamber 68 and the control chamber 74 is at least 
partly opened. The slit 96 of the throttle passage 90 may be disposed such 
that if the annular disk 60 of the control slide 34 rests on the step 88 
of the valve body 44, the slit 96 is completely opened; alternatively the 
slit 96 may be disposed such that as shown in FIG. 1, it is partly covered 
by the edge 97 in this control position of the control slide 34. 
To avoid radial forces on the control slide 34, or at least to keep such 
forces as small as possible, it is favorable to include a plurality of 
openings 91. It is particularly practical for the openings 91 to be 
disposed as uniformly as possible, that is, at equal intervals in the 
circumference of the control slide 34. If the further throttle passage 90 
has two openings 91, then the openings should be provided diagonally 
opposite one another on the control slide 34. If there are at least two 
openings 91, it is practical to dispose them in the same way in the axial 
direction. 
In the drawing, the control slide 34 is shown in the position when the 
magnet coil 32 has no current through it. The slide control edge 78 of the 
control slide 34 has a profile with axially extending raised portions and 
depressions. For FIG. 1, a longitudinal section through the shock absorber 
was selected in which the left-hand part of the drawing shows the control 
slide 34 in section in the vicinity of a raised portion, while the 
right-hand part of the drawing shows it in section in the vicinity of a 
depression. In the shock absorber shown as an example in FIG. 1, a minimal 
portion of the throttle passage 30 having the variable throttle cross 
section is still open even when the magnet coil 32 has no current through 
it. However, it is also possible to design the control slide 34 such that 
when there is no current through the magnet coil 32 the variable throttle 
cross section is completely closed. In the shock absorber 2 shown, the 
raised portions of the control slide 34 cover the control edge 80, and so 
the variable throttle cross section of the throttle passage 30 is formed 
only in the vicinity of the depressions, and comprises a plurality of 
variable throttle cross sections, depending on the number of raised and 
depressed portions. The section through the shock absorber 2 is selected 
such that in the left-hand part of the drawing it extends through an 
opening 91 of the second throttle passage 90. 
In the regular operating state, that is, when the magnet coil 32 has 
current through it as intended, the control slide 34 is actuated counter 
to the restoring spring 36, far enough that the slit 96 of the opening 91 
of the further throttle passage 90 is completed covered by the edge 97 of 
the valve body 44. Thus, during regular operation of the shock absorber 
the further throttle passage 90 is completely closed and thus is not in 
operation. In the regular operating state of the shock absorber 2, the 
pressure fluid can flow only through the throttle passage 30 having the 
variable throttle cross section. The shock absorber may be structurally 
designed such that in the regular operating state the throttle cross 
section of the throttle passage 30 is variable between a very small 
minimum and a very large maximum. In this way, in the regular operating 
state any desired damping of the shock absorber is attainable, and the 
shock absorber is able to rise to any situation that may occur and can 
satisfy any customer wishes. 
If the magnet coil 32 loses current, however, or in some other way becomes 
inoperative because of some defect, then the restoring force of the 
restoring spring 36 actuates the control slide 34 counter to the step 88 
of the valve body 44, and the throttle passage 30 is closed to an extent 
greater than normal. At the same time, however, if the control slide 34 is 
actuated farther than normal toward the step 88, the further throttle 
passage 90 opens. 
Any throttling of the pressure fluid flowing through the further throttle 
passage 90 is substantially determined by a narrowest point of the further 
throttle passage 90. A hydraulically effective area 98 of this narrowest 
point will hereinafter be called the effective throttle area 98 of the 
further throttle passage 90. If the slit 96 is completely opened in the 
event of a defect, then the cross-sectional area of the slit 96 forms the 
effective throttle area 98 in a first approximation. However, if part of 
the slit 96 is covered by the edge 97 in the event of a defect, then the 
still-open part of the slit 96 roughly forms the effective throttle area 
98. The effective throttle area 98 can be made up of a plurality of 
individual effective throttle areas of a plurality of slits 96 or openings 
91. 
The throttle area 98 of the further throttle passage 90 that is effective 
in the event of a defect can be selected to be arbitrarily large. This 
makes it possible to design the shock absorber such that in the event of a 
defect any arbitrarily selectable but preferably average damping is 
established, and extreme situations are avoided even if a defect should 
arise. 
A valve 99 shown in dashed lines in the drawing may also be built into the 
opening 91, or into a plurality of openings 91, and thus into the further 
throttle passage 90. By way of example, the valve 99 may be a pressure 
limiting valve, in particular a plate valve or shutter valve, throttle 
valve, check valve, or a combination of these valves. Depending on the 
version of the valve 99, any arbitrary, desired damping characteristic can 
be provided for the shock absorber in the event of a defect, or in other 
words when the second throttle cross section 90 is uncovered. Here the 
effective throttle area 98 is formed inside the valve 99. A plurality of 
valves 99 could also be built into the further throttle passage 90; in 
that case, one of the valves 99 is for instance responsible for the 
damping when the pressure fluid flows out of the first work chamber 24 
into the second work chamber 26, and another valve 99 is responsible for 
the damping when the flow is in the opposite direction, in which case the 
valve 99 not involved at a given time is closed. 
It is also possible to control the shock absorber such that the further 
throttle passage 90 is uncovered not only in the event of a defect but 
also whenever the damping characteristic of the valve 99 is for instance 
desired. 
It is also possible to provide, instead of the annular chamber 68, only 
individual radial openings through the valve body 44, similarly to the 
openings 91 through the control slide 34. However, the annular chamber 68 
can also be shifted into the control slide 34, and the openings 91 and the 
valve 99 can be shifted into the valve body 44. Since these are simple 
construction variants, they need not be shown in the drawing. 
To assure that a sufficiently large effective throttle area 98 is available 
in the event of a defect, the slit 96 must be large enough. To enable 
limiting the stroke of the control slide 34 to a reasonable amount, the 
slit 96 must not extend too far in the stroke direction; that is, it 
should be narrow in the direction of reciprocation. In that case, however, 
it must extend relatively far in the circumferential direction. It is not 
exactly easy to produce very narrow, long slits, from a manufacturing 
standpoint. An annular chamber 100 is therefore provided on the control 
slide 34 in the second exemplary embodiment of FIG. 2. 
In all the drawing figures, elements that are the same or function the same 
are provided with the same reference numerals. 
In the exemplary embodiment of FIG. 2, the further throttle passage 90 
additionally includes the annular chamber 100. The annular chamber 100 
interrupts the jacket face 64 of the control slide 34. The annular chamber 
100 is a radial plunge cut on the jacket face 64 of the control slide 34. 
The opening 91 joins the annular chamber 100 to the outer jacket 94 remote 
from the annular chamber 100; that is, the opening 91 connects the annular 
chamber 100 to the second work chamber 26. 
The annular chamber 100 is disposed on the jacket face 64 of the control 
slide 34 in such a way that there is no communication between the annular 
chamber 100 and the annular chamber 68 during regular operation of the 
shock absorber 2. In the case of a defect, or in other words if the 
restoring spring 36 actuates the control slide 34 counter to the step 88 
of the valve body 44, then the annular chamber 100 moves at least part way 
beyond the stationary edge 97 of the valve body 44. In the case of a 
defect, the control slide 34 and annular chamber 100 are in a position in 
which a virtually unthrottling communication exists between the stationary 
annular chamber 68 and the annular chamber 100. Since the annular chamber 
68 advantageously extends over the entire jacket face 66 of the valve body 
44, and the annular chamber 100 extends over the entire circumference of 
the jacket face 64 of the control slide 34, in order to obtain a 
nontrottling communication between the annular chamber 68 and the annular 
chamber 100, an advantageously small overlap between the annular chamber 
68 and the annular chamber 100 that creates the communication is 
sufficient. The actual throttling of the pressure fluid flowing through 
the further throttling passage advantageously takes place substantially at 
the effective throttle area 98 of the opening or openings 91. The opening 
91 can be arbitrarily embodied in the second embodiment of FIG. 2. It is 
particularly practical to make the opening 91 round. If needed, a shutter 
103 can be disposed in or on the opening 91. The shutter 103 has a hole, 
which subtantially determines the effective throttle area 98 of the 
further passage 90. To obtain throttling of the flowing pressure fluid 
that is largely independent of its viscosity, it is suitable to make the 
hole passing through the shutter 103 as short as possible. The shutter 103 
can also be advantageously replaced later on. If no shutter 103 is used, 
then the opening 91 itself can determine the effective throttle area 98. 
In FIG. 2, the control slide 34 is shown in the position it assumes in the 
event of a defect. In this position, the further throttle passage 90 is 
opened. In the second exemplary embodiment, the control slide 34 is 
embodied such that in the event of a defect the throttle passage 30 having 
the variable throttle cross section is closed. 
For the sake of simplicity, the valve body 44 is shown in the drawing as if 
it were made in one piece. However, to enable mounting of the magnet coil 
32, the restoring spring 36 and control slide 34, for example, it is 
necessary to make the valve body 44 in a plurality of pieces and to join 
them later, which is familiar to anyone skilled in the art. 
Besides the throttle passage 30 and the further throttle passage 90, the 
damper piston 14 may also be provided with at least one further flow 
connection 107. A variable or constant throttle or shutter 108 may for 
instance be located in this further flow connection 107. 
In the exemplary embodiments shown, the throttle passage 30, the further 
throttle passage 90 and the flow connection 107 are disposed in the damper 
piston 14. However, it is also possible to dispose the throttle passages 
30, 90 and/or the further flow connection 107 and/or further flow 
connections outside the damper piston 14, for instance on an outside 
surface of the jacket tube 6 of the cylinder 4, or on some partition, not 
shown, inside the cylinder 4. 
When the piston rod 12 is driven into the cylinder 4, some of the pressure 
fluid is positively displaced out of the cylinder 4, as a function of the 
cross section of the piston rod. When the piston rod 12 is retracted from 
the cylinder 4, pressure medium should be capable of flowing back into the 
cylinder 4. For this purpose, the second work chamber 26 communicates with 
a compensation chamber 110. To enable generating a relatively high 
pressure in the second work chamber 26 and hence a relatively strong 
damping even when the pressure in the compensation chamber 110 is 
relatively low, a throttle 112 is installed between the compensation 
chamber 110 and the second work chamber 26. When the pressure fluid flows 
back out of the compensation chamber 110 into the second work chamber 26, 
the throttle 112 is unnecessary, and for this reason a check valve 114 is 
disposed parallel to this throttle 112. The check valve 114 is installed 
such that the pressure medium can flow through the check valve 114 only 
when the flow direction is out of the compensation chamber 110 into the 
work chamber 26. The compensation chamber 110 may for instance be a 
gas-filled pressure reservoir. Naturally, the compensation chamber 110 
could also be integrated with the cylinder 4 in a known manner. 
Depending on the desired damping and on the initial pressure of the gas in 
the compensation chamber 110, it may be possible to dispense with the 
throttle 112 and check valve 114. 
To assure that the volume of pressure fluid positively displaced in one of 
the work chambers 24, 26 is equal to the volume flowing into the other 
work chamber when there is a relative motion between the damper piston 14 
and the jacket tube 6, a double piston rod 12 may be used that protrudes 
from both ends of the damper piston 14, out of the face ends 8, 10 of the 
cylinder 4. It is particularly favorable if both ends of the double piston 
rod 12 have approximately the same diameter. 
A single-tube shock absorber has been selected as an exemplary embodiment 
of the shock absorber according to the invention. This is merely an 
example, however. The shock absorber could equally well be a so-called 
double-tube shock absorber. 
As already mentioned above, during regular operation the throttle passage 
30 with its variable throttle cross section substantially determines the 
damping of the shock absorber; in the case of a defect, the further 
throttle passage 90 with the effective throttle area 98 primarily 
determines the damping of the shock absorber 2. As anyone skilled in the 
art knows, the damping of the shock absorber is dependent not only on a 
throttle cross section or area, but instead, the relative speed between 
the damper piston 14 and the jacket tube 6 naturally plays a role as well. 
During regular operation the size of the variable throttle cross section of 
the throttle passage 30 can be set by a transducer 116, via the control 
unit 81. The transducer 116 may for instance be a sensor and/or a manual 
lever. If the shock absorber is provided with the further throttle passage 
90 in accordance with the invention, then the variable throttle cross 
section of the throttle passage 30 can advantageously be designed to be 
variable within very wide limits, without any need to fear an undesirable 
or even dangerous extreme damping in the event of a defect. 
In the exemplary embodiments shown in the drawing, the control part 62 of 
the control slide 34, viewed in the radial direction, surrounds the valve 
body 44 in the vicinity of the jacket faces 64, 66. However, a reverse 
arrangement is also possible, so that viewed in the radial direction, at 
least in the vicinity of the jacket faces 64, 66, the inside of the 
control slide 34 would merge directly with the valve body 44. In other 
words, at least in the vicinity of the pressure fluid transition between 
the valve body 44 and the control slide 34, the valve body 44 would 
surround the control slide 34. Since this is simply the reverse of the 
arrangement shown and is easily constructed, this variant embodiment is 
not shown in the drawing. 
The foregoing relates to a preferred exemplary embodiment of the invention, 
it being understood that other variants and embodiments thereof are 
possible within the spirit and scope of the invention, the latter being 
defined by the appended claims.