Patent Publication Number: US-5833037-A

Title: Vibration damper or shock absorber having apparatus for damping spring-mounted wheel suspension systems

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an apparatus for damping spring-mounted wheel suspension systems, which apparatus comprises a cylinder filled with damping medium, a piston, and two work chambers, whereby the two work chambers are connected to one another by means of damping valves. 
     2. Background Information 
     Such a device is disclosed, for example, by German Laid Open Patent Application No. 38 27 538 A1. This apparatus uses two valve devices in a series arrangement which can be switched separately. The special arrangement of the rotary disc of the valve device requires individual parts which must be manufactured to very precise tolerances, to keep the leakage of the individual rotary disks at an acceptable level. An additional problem is that the flow volumes which can be achieved by the valve device may be totally insufficient in actual practice. 
     Alternatively, EPS 0 405 123 B1 discloses a two-way solenoid valve with bypass control, in which an actuatable valve disc, in connection with a number of non-return valves, closes or opens a bypass channel. For the two directions of flow there are two bypass channels which have a common control chamber, the inflow of which is controlled by the valve disc. Apart from the necessary bypass channels, the design and construction of which can be problematic, significant damping force fluctuations occur even with relatively low tolerances in the area of the control edges of the valve discs. With regard to this valve device, it should also be noted that only two switching stages are possible, and when the valve disc is closed, the maximum damping force is generated by the throttle bodies. 
     OBJECT OF THE INVENTION 
     The object of the present invention is to create an apparatus, the construction of which is significantly simpler, which apparatus controls the necessary flow volumes and is less sensitive to tolerances with regard to the damping force characteristics which should be maintained. 
     SUMMARY OF THE INVENTION 
     The present invention teaches that this object can be achieved by means of an apparatus comprising a cylinder filled with damping medium, a piston, and two work chambers, whereby the two work chambers can be connected to one another by means of damping valves. The apparatus further comprises at least one fluid connection and an actuator for control of the damping valves. The total design and construction of the valve device, in particular of the fluid channel, can essentially be simplified to a major extent, since there can be a functional connection or interaction between the non-return valves and the valve device which can control the throttling. 
     The overall design and construction of the valve device, in particular of the fluid channel, can therefore be simplified to a major extent by the combination and functional connection or interaction between the actuator and the valves. The valves, which valves are dependent on the direction of flow, can be provided with resistance, which valves can in turn be actively connected to the damping valves. 
     The present invention also teaches that the fluid connection can have two non-return valves which can preferably be coupled by means of the actuator. The coupling can be accomplished by means of a rigid connection between the respective non-return valve and the armature. For the purpose of such a rigid connection, the non-return valves can preferably be designed simply as disc valves. 
     Additionally, for the purpose of rigidly connecting the non-return valves, the non-return valves can be designed as disc valves, which disc valves are essentially provided with a greater or lesser degree of resistance. The non-return valves can be optionally placed in their active positions axially and/or rotationally. 
     In one variant embodiment, the non-return valve can be operationally connected to two valve seat surfaces, and the operation can be switched arbitrarily between the two valve seat surfaces, as necessary. The non-return valve represents a quasi-double valve, which can thus be kept particularly short. 
     Alternatively, the non-return valves can be mounted in a floating manner relative to the actuator, so that a valve movement into an open or closed position occurs independently of the actuator force, e.g. by means of a closing spring. 
     In accordance with an additional advantageous feature, the present invention teaches that the damping medium can travel the same flow distance for both directions of flow. The fluid connection can preferably be simplified and shortened. The throughput of the flow volume can also be increased while maintaining essentially the same size of the component. 
     With reference to an additional advantageous embodiment, the present invention teaches that the regulating distance of travel of the actuator is essentially greater than the valve distance of travel from the open position into the closed position of the non-return valves. Thus, the prestress of the disc valves can be increased, and at least to some extent, a continuously-adjustable damping force characteristic can be achieved, whereby in the maximum position of the actuator, a hard damping force characteristic is possible for both directions. 
     Alternatively, the prestress of the disc valves can be increased, and at least to some extent, a continuously-adjustable damping force characteristic can be achieved, whereby in the limit positions of the actuator, an increased damping force setting is possible in one direction. 
     The present invention further teaches that the flow connection can advantageously be provided with a damping valve. For example, the damping valve can be realized as a constant throttle. It is thereby appropriate, to reduce the actuation forces, if the valve which can be moved into its operating position by the actuator is piloted or controlled by a pilot valve. 
     The entire valve device is essentially sufficiently compact such that the fluid connection to the valve device can be located inside the piston. The present invention teaches that the general problem in similar known devices is noise which is generated during switching processes in valve devices, in particular when there is a change from a hard setting to a soft setting. This problem of noise can be solved by making it possible to switch the actuator if the pressure on the inflow side in the closed non-return valve drops below a defined level. As an additional measure to control the flow volume between the two work chambers, the fluid connection can be realized in the form of a central channel. 
     One aspect of the present invention resides broadly in a shock absorber for a motor vehicle, which shock absorber comprises a cylinder and an outer surface; the cylinder comprising a substantial portion of the outer surface of the shock absorber; the cylinder comprising a first apparatus for attaching the cylinder to one of: a wheel suspension and a support structure of the motor vehicle; the cylinder defining a chamber therein, the chamber containing a damping fluid; a piston rod; the piston rod for sealingly projecting into the cylinder and being axially displaceable with respect to the cylinder; the piston rod having a longitudinal axis defining an axial direction parallel to the longitudinal axis of the piston rod; the piston rod having a first end and a second end; the first end of the piston rod being disposed substantially adjacent one of: the wheel suspension and the support structure of the motor vehicle; a piston body; the piston body being attached to the second end of the piston rod; the piston body being slidably disposed within the cylinder to sealingly divide the chamber into first and second chambers; the piston body having a first side and a second side; the first side of the piston body facing toward the piston rod; the second side of the piston body facing opposite the first side; the first side of the piston body being adjacent the first chamber; the second side of the piston body being adjacent the second chamber; an apparatus for permitting flow of damping fluid between the first chamber and the second chamber; the apparatus for permitting flow of fluid between the first and second chambers comprising a flow channel comprising valves; the valves comprising at least one valve; the at least one valve having a flow resistance being dependent on the direction of flow of damping fluid through the at least one valve, the dependence on the direction of flow comprising a first flow resistance of the at least one valve in a first flow direction and a second flow resistance in a second flow direction of the at least one valve; the first flow resistance in the first flow direction of at least one valve being substantially different from the second flow resistance in the second flow direction of the at least one valve; and a device for modifying the flow resistance of the at least one valve to modify at least one of: the first flow resistance in the first flow direction of the at least one valve and the second flow resistance in the second flow direction of the at least one valve. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention is explained in greater detail below with reference to the embodiments illustrated in the accompanying figures, in which: 
     FIG. 1 shows a valve device with a rigid coupling of the non-return valves; 
     FIG. 2 shows a valve device with a non-return valve between two valve seat surfaces; 
     FIG. 3 shows a valve device with non-return valves mounted in a floating manner; 
     FIG. 4 shows a valve device with a rigid coupling of the non-return valves and axial actuator function; 
     FIG. 5 shows a valve device with a rigid coupling of the non-return valves and rotational actuator function; 
     FIGS. 5A, 5B, and 5C show details of the valve device as shown in FIG. 5; 
     FIG. 6 shows a valve device with a non-return valve between two valve seat surfaces; and 
     FIG. 7 shows a valve device with non-return valves mounted in a floating manner. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIG. 1 shows an apparatus 1 for damping spring-mounted wheel suspension systems, for example, in the form of a single-tube vibration damper. The apparatus 1 comprises a cylinder 3 filled with damping medium, which cylinder 3 can be divided into an upper work chamber 9 and a lower work chamber 11 by a piston 5 on a piston rod 7. The two work chambers 9, 11 can be connected by means of damping valves 13, 15 for the decompression and compression direction of the apparatus 1. The piston 5 can also have a fluid connection 17, which fluid connection 17 can connect the two work chambers 9, 11, by means of an actuator 19. The actuator 19 can be actuated by a magnet coil 21 in connection with valves 23, 25. The valves 23, 25 can act as a function of the direction of flow and can preferably be parallel to the damping valves 13, 15. 
     The fluid connection 17 can preferably be formed by a central channel inside the piston 5 or inside the piston rod 7, whereby the identical flow distance can be used for both directions of flow. There can preferably be a connection 17a for the fluid connection on the end surface of the piston 5, while a second connection can preferably be formed by radial borings 17b in the piston rod 7. 
     In accordance with an embodiment of the present invention, therefore, the fluid connection 17 can comprise a channel located in either the piston 5 or in the piston rod 7, or the fluid connection 17 can be located and extend through at least a portion of both the piston 5 and the piston rod 7. Because the fluid connection 17 can be used for both directions of flow, the flow distance can be identical for both compression and decompression. Damping fluid from work chamber 9 can flow through radial borings or holes 17b and thereby into fluid connection 17 and through the disc valve 25. Similarly, damping fluid from work chamber 11 can flow through connection 17a and thereby into fluid connection 17 and then out of the radial holes 17b. 
     The disc valve 23 inside the preferably hollow piston rod 7 can have a valve seat surface 23a, which valve seat surface 23a can be formed by a friction-set, pressed-in, or inserted tube body 27. The other disc valve 25 can be in contact with a closing head 7a, which closing head 7a can be shaped on the piston rod 7. In accordance with an embodiment, the closing head 7a can preferably serve to fasten the piston 5 to the piston rod 7. A compression spring 29 can apply a prestress to the actuator 19. 
     In addition, in a preferred embodiment of the present invention, there can be stops or pins which can support the disc valve 23 and thereby essentially prevent the disc valve 23 from moving beyond its valve seat surface 23a into fluid connection 17. 
     In accordance with an embodiment of the present invention, therefore, an upper portion of the inserted tube body 27 can preferably form the valve seat surface 23a for disc valve 23. Likewise, the closing head 7a of the piston rod can form a contact or valve seat surface for the disc valve 25. 
     When there is a piston rod stroke during which the piston rod 7 is essentially inserted into the cylinder 3, the damping medium can essentially flow through the damping valve 13 independently, regardless of the actuator position. The volume of fluid in lower chamber 11 due to the insertion of the piston rod 7 can be compensated for by a gas-filled equalization chamber 31. When the magnet coil 21 is energized, the actuator 19 can be essentially moved into the illustrated position, as shown in FIG. 1. The actuator 19 has thereby essentially travelled the distance of portion &#34;a&#34; of the regulating distance of travel. A harder characteristic can preferably be set for the compression direction, since only the damping valve 13 is active. When the piston rod 7 moves in the opposite direction, i.e. out of the cylinder 3, the damping medium can essentially flow through the radial holes 17b, then, by means of the open disc valve 23, into the central channel of the fluid connection 17, and the damping medium can encounter the only lightly prestressed disc valve 25. Together with the damping medium which flows through the damping valve 15, a softer characteristic can be set in the decompression direction. 
     As shown in FIG. 1, therefore, in accordance with a preferred embodiment of the present invention, during compression, the damping medium can flow essentially only through damping valve 13. The compression direction can, in at least some embodiments, therefore, have a harder damping characteristic because essentially only the damping valve 13 can be in the active or open position during compression. During decompression, however, the damping medium can flow through damping valve 15 as well as through radial holes 17b, and therethrough, into the channel of fluid connection 17 due to an open position of the disc valve 23. During decompression, therefore, there can be a softer damping characteristic because of the combination of damping flow through damping valve 15, as well as through disc valve 25. 
     As illustrated in FIG. 1, there is still a portion &#34;s&#34; of the valve regulating distance available which, by means of the previous closed position of the valve 25, makes possible an additional prestress of the disc valve 25, so that the valve disc 25 can assume a throttle function which can be superimposed on, and can reinforce the damping valve 15. For the decompression direction, a damping force can therefore be set which essentially appropriately equals the damping force setting in the compression direction. 
     To summarize, in accordance with a preferred embodiment of the present invention, when the magnet coil 21 is fully energized, the actuator 19 can travel through the portion &#34;s&#34;, as shown in FIG. 1. As a result, there can be an additional prestress of the disc valve 25, over and above the prestress present in the position of disc valve 25, as shown in FIG. 1. The disc valve 25, thereby, can function as a reinforcing damping function, in addition to the damping function of the damping valve 15. Therefore, because of the additional prestress of disc valve 25, during the decompression direction, the damping medium can flow essentially only through damping valve 15, except at very high pressures. Such a configuration can provide essentially similar damping characteristics for both the decompression and compression directions because, during compression, the damping medium can flow only through damping valve 13. And, similarly, during decompression, preferably as a result of the additional prestress of disc valve 25, the damping fluid can essentially flow only through damping valve 15. 
     The elements as described with reference to FIG. 1 may be considered as elements that are interchangeable with the elements as described below with reference to FIGS. 2 and 3. Such elements, although not specifically mentioned with reference to FIGS. 2 and 3, may be assumed with reference to FIGS. 2 and 3. Such elements include, for example, radial holes 17b, the first fluid connection 17a, work chambers 9, 11, and tube body 27. 
     FIG. 2 illustrates a variant of FIG. 1, in which the two non-return valves (23, 25 in FIG. 1) can preferably be combined in the same space. The disc valve 23, 25 can be operationally connected between two valve seat surfaces 23a, 25a, with which the non-return valve 23, 25 comes into contact alternately, and assumes a closed position in the one direction and an open position for the other direction. However, an intermediate valve position is also possible in which there is a softer damping force setting for both flow directions of the fluid connection 17. The actuator 19 can thus be made particularly short and lightweight. It should be apparent that, in accordance with the preferred embodiment of the present invention, as shown in FIG. 2, the regulating distance &#34;s&#34;, as shown in FIG. 1, of the actuator 19 is substantially greater than the valve distance &#34;a&#34;, as shown in FIG. 1. 
     In accordance with a preferred embodiment of the present invention, in summary, the actuator 19 can essentially move the combined disc valves 23, 25 into their active or open positions. The actuator 19, as shown in FIG. 2, can open disc valve 23 by essentially pulling the disc valve 23 away from its valve seat surface 23a. Accordingly, the actuator 19 can open disc valve 25 by essentially pulling the disc valve 25 away from its valve seat surface 25a. Furthermore, the combined disc valves 23, 25, as shown in FIG. 2, can also be placed in an intermediate position whereby the combined disc valves 23, 25 can be located essentially between the valve seat surfaces 23a, 25a. In this intermediate position, a softer damping characteristic is essentially possible for both the decompression and compression directions because when the disc valves 23, 25 are in the intermediate position, the disc valves 23, 25 can essentially provide less resistance to the flow of damping medium into fluid connection 17. In the intermediate position of the disc valves 23, 25, therefore, the portion &#34;s&#34;, as shown in FIG. 1, i.e. the valve regulating distance of the actuator 19, is essentially greater than the portion &#34;a&#34;, also shown in FIG. 1, i.e. the distance travelled by disc valve 23, 25. 
     As an additional alternative, FIG. 3 illustrates a variant of the present invention in which the closing force of the check valves 23, 25 can preferably be independent of the actuator force. The actuator 19 essentially only opens the respective valve 23, 25, while the closing is performed by separate closing springs 29, 31. The non-return valves 23, 25 can be mounted so that they can float in relation to the actuator 19, and can be moved by means of contact surfaces 19a, 19b of the actuator 19. 
     In accordance with a preferred embodiment of the present invention, therefore, the actuator 19 can control the positions of contact surface 19a for check valve 23. Similarly, the actuator 19 can control the positions of contact surface 19b for the check valve 25. Accordingly, each of the disc or check valves 23, 25 can be slideably moveable with respect to the actuator 19, which actuator 19 can thereby individually control the disc valves 23, 25 into their open positions. However, the closing of the disc valves 23, 25 can preferably be controlled by their respective closing springs 29, 31. 
     When the magnet coil 21 is not energized, the spring 29 can essentially push the disc valve 23 with the maximum spring force into the closed position. A harder damping force setting can be assumed in this switched position in the decompression direction as well as in the compression direction. When the magnet coil 21 is energized, the prestress or bias of the spring 29 on the disc valve 23 is essentially eliminated, so that the disc valve 23 can act as an essentially pure non-return valve. 
     A setting of the actuator 19 is also possible in which, when the actuator 19 assumes an intermediate position, so that both disc valves 23, 25 are lifted off their seat surfaces 23a, 25a, so that there is a rather hard damping force setting for both flow directions when the distance between the contact surfaces 19a, 19b is less than or equal to the distance between the support surfaces 23a, 25a. If the distance between the contact surfaces 19a, 19b of the actuator 19 is greater than the distance between the support surfaces 23a, 25a, there is a softer damping force characteristic in an intermediate position of the actuator 19, since in that case, both non-return valves are preferably open. 
     In an embodiment of the present invention, as shown in FIG. 3, the actuator 19 can include contact surfaces 19a, 19b, which contact surfaces 19a, 19b can be located in between and in contact with disc valves 23, 25, respectively. When the actuator 19 is energized, the actuator 19 can lift the disc valve 23 off its contact surface 19a or the actuator 19 can lift the disc valve 25 off its contact surface 19b. By adjusting the contact surfaces 19a, 19b, the actuator 19 can thereby provide either a softer or a harder damping characteristic for both flow directions. 
     FIG. 4 shows an apparatus 1&#39; for damping spring-mounted wheel suspension systems, for example in the form of a single-tube vibration damper. The apparatus 1&#39; generally includes a cylinder 3&#39; filled with damping medium, which cylinder 3&#39; can be divided into an upper work chamber 9&#39; and lower work chamber 11&#39; by a piston 5&#39; on a piston rod 7&#39;. The two work chambers 9&#39;, 11&#39; can be connected by means of damping valves 13&#39;, 15&#39; for the decompression and compression direction of the apparatus 1&#39;. The piston 5&#39; can also preferably have a fluid connection 17&#39;, which fluid connection 17&#39; can connect the two work chambers 9&#39;, 11&#39;, by means of an actuator 19&#39;. The actuator 19&#39; can be actuated by a magnet coil 21&#39; in connection with valves 23&#39;, 25&#39;. The valves 23&#39;, 25&#39; can act as a function of the direction of flow and can preferably be parallel to the damping valves 13&#39;, 15&#39;. 
     The fluid connection 17&#39; can be formed by a central channel inside the piston 5&#39; or inside the piston rod 7&#39;, whereby the identical flow distance can be used for both directions of flow. There can be a connection 17a&#39; for the fluid connection on the end surface of the piston 5&#39;, while a second connection 17b&#39; can be formed by radial borings 17b&#39; in the piston rod 7&#39;. 
     The disc valves 23&#39; and 25&#39; inside the hollow piston rod 7&#39; can have valve seat surfaces 23a&#39;, 25a&#39; which can be formed by a friction-set, pressed-in, or inserted tube body 27&#39;. A compression spring 29&#39; can essentially apply a prestress to the actuator 19&#39;. 
     When there is a piston rod stroke during which the piston rod 7&#39; is essentially inserted into the cylinder 3&#39;, the damping medium can flow through the damping valve 13&#39; independently, regardless of the actuator position. The volume of the fluid in chamber 11&#39; due to the insertion of the piston rod 7&#39; can be compensated for by a gas-filled equalization chamber 31&#39;. When the magnet coil 21&#39; is energized, the actuator 19&#39; can be moved into the illustrated position. The actuator 19&#39; has essentially thereby travelled the portion &#34;a&#39;&#34; of the regulating distance. A high characteristic can be set for the compression direction, which high characteristic can essentially be determined by the damping valve 13&#39;. When the piston rod 7&#39; moves in the opposite direction, i.e. in the decompression direction, the damping medium can flow through the radial holes 17b&#39; by means of the open disc valve 23&#39; into the central channel of the fluid connection 17&#39;, and the damping medium can encounter the disc valve 25&#39;. Simultaneously with the damping medium which flows through the damping valve 15&#39;, a lower characteristic can be set in the decompression direction. 
     As illustrated in FIG. 4, there is still a portion &#34;s&#39;&#34; of the valve regulating distance available, which portion &#34;s&#39;&#34;, by means of the previous or current closed position of the valve 25&#39;, can make possible an additional prestress of the disc valve 25&#39;, so that disc valve 25&#39; can have an increased throttle function which can act in parallel to the damping valve 15&#39;. When the magnet coil 21&#39; is de-energized, there can be a reverse function of the actuator/valve unit. 
     Therefore, in a preferred embodiment of the present invention, the actuator 19&#39; can essentially travel the portion &#34;s&#39;&#34;, or the available valve regulating distance, as illustrated in FIG. 4. When the actuator 19&#39; has essentially travelled through the portion &#34;s&#39;&#34;, there can be an additional prestress of the disc valve 25&#39;, over and above the prestress present in the position of disc valve 25&#39;, as shown in FIG. 4. The disc valve 25&#39; can thereby essentially reinforce damping valve 15&#39; and superimpose a throttle function on damping valve 15&#39;. The actuator 19&#39; can also perform essentially the reverse function of the disc valve 25&#39; when the magnet coil 21&#39; is de-energized. 
     FIG. 5 illustrates a variant of FIG. 4, in which the coupled disc non-return valves (23&#39;, 25&#39; in FIG. 4) can be provided with passage cross sections 32&#39;, 33&#39;, which coupled disc non-return valves 23&#39;, 25&#39; can be set by means of a rotationally symmetrical actuating function of the actuator 19&#39; in different hydraulically active positions. For this purpose, the non-return valves 23&#39;, 25&#39; can preferably be connected in fluidic inversion to the fluid connections 17&#39;, 18&#39;. The non-return valves 23&#39;, 25&#39; can thereby be oriented with their passage cross sections 32&#39;, 33&#39; in relation to one another so that several different active positions can be realized. 
     FIGS. 5A, 5B, and 5C, for example, illustrate the disc non-return valves 23&#39;, 25&#39; each with 4 passage cross sections 32&#39;, 33&#39; in combination with the fluid connections 17&#39;, 18&#39;. Illustrated by way of example is the resistance-less active position of non-return valve 23&#39; in connection with the closing function (piston rod insertion direction) or opening function (piston rod expulsion position) of the non-return valve 25&#39;. With the non-return valve configuration coupled in this manner, 4 different hydraulic active positions are essentially possible, which can be actuated, for example, by using a stepper motor drive system. 
     Therefore, in accordance with a preferred embodiment of the present invention, as shown in FIGS. 5A-5C, the disc valve 23&#39; can preferably comprise passage cross sections 32&#39;. Similarly, the disc valve 25&#39; can preferably comprise passage cross sections 33&#39;. The passage cross sections 32&#39; of the disc valve 23&#39; essentially make possible a flow of fluid from disc valve 23&#39; to fluid connections 17&#39;, 18&#39;. The passage cross sections 32&#39; of the disc valve 23&#39; and the passage cross sections 33&#39; of the disc valve 25&#39; can be configured to be essentially in an inverse relationship with one another with respect to fluid connections 17&#39;, 18&#39;. Each of the passage cross sections 32&#39;, 33&#39; can also be essentially variably adjusted whereby the passage cross sections 32&#39;, 33&#39; can be set at partially open positions. 
     In accordance with a preferred embodiment of the present invention, further regarding FIGS. 5A-5C, the actuator 19&#39; can preferably rotate symmetrically. Upon the rotation of the actuator 19&#39;, the disc valves 23&#39;, 25&#39; can thereby rotate in relation to one another. The passage cross sections 32&#39;, 33&#39; of each of the disc valves 23&#39;, 25&#39; thereby make possible at least four different positions for the flow of fluid through the channel or fluid connections 17&#39;, 18&#39;. As shown by example in FIG. 5A, the disc valve 23&#39; is essentially in its active or open function, as such, the disc valve 23&#39; provides essentially no resistance to the flow of damping fluid. 
     FIG. 6 illustrates an additional variant of FIG. 4, in which the two non-return valves (23&#39;, 25&#39; in FIG. 4) are combined in the same space. The coupled disc valve is operationally connected between two valve seat surfaces 23a&#39;, 25a&#39;, with which the non-return valve comes into contact alternately, and assumes a closed position in the one direction and an open position in the other direction. However, any desired intermediate valve position is also possible in which there is a lower damping force setting for both flow directions of the fluid connection 17&#39;. The actuator 19&#39; can thus be made particularly short and lightweight. Of course, the regulating distance &#34;s&#39;&#34; of the actuator 19&#39; is greater than the valve distance &#34;a&#39;&#34;. 
     As shown in FIG. 7, the variant of the object of the present invention is illustrated wherein the closing force of the check valves 23&#39;, 25&#39; is independent of the actuator force. The actuator 19&#39; can essentially open only the respective valve, while the closing can be performed by separate closing springs 29&#39;, 30&#39;. The non-return valves 23&#39;, 25&#39; can be mounted so that they float in relation to the actuator 19&#39; and are moved by means of contact surfaces 19a&#39;, 19b&#39; of the actuator 19&#39;. 
     When the magnet coil 21&#39; is not energized, the spring 29&#39; preferably pushes the disc valve 23&#39; into the closed position. In this setting, there is a high damping force setting in the decompression direction and a low damping force setting in the compression direction. When the magnet coil 21&#39; is energized, the closing force of the spring 29&#39; on the disc valve 23&#39; can be essentially eliminated, so that the disc valve 23&#39; can act as a non-return valve with low resistance. 
     A setting of the actuator 19&#39; is also possible in which the actuator 19&#39; assumes an intermediate position, so that both disc valves 23&#39;, 25&#39; are lifted off their seat surfaces 23a&#39;, 25a&#39;. In this case, in which the distance between the contact surfaces 19a&#39;, 19b&#39; of the actuator 19&#39; is greater than the distance between the support surfaces 23a&#39;, 25a&#39;, in an intermediate position of the actuator 19&#39; there is a soft damping force characteristic in both directions of flow, since in that case, both non-return valves are open. 
     One feature of the invention resides broadly in the apparatus for damping spring-mounted wheel suspension systems, comprising a cylinder filled with damping medium and divided by a piston on a piston rod into two work chambers, whereby the two work chambers are connected to one another by means of damping valves, at least one additional fluid connection provided with a non-return valve between the two work chambers, which has an actuator which can be switched as desired inside a valve device with a damping force adjustment which acts in opposite directions for the two directions of flow, characterized by the fact that at least one non-return valve 23, 25 is moved into its operating position by the actuator 19. 
     Another feature of the present invention resides broadly in the apparatus characterized by the fact that at least one valve 23, 25 which is dependent on the direction of flow and is provided with resistance, is moved into its operating position by the actuator 19. 
     Still another feature of the invention resides broadly in the apparatus characterized by the fact that the coupled disc valves can be placed in their active positions optionally axially and/or rotationally by the actuator. 
     A further feature of the invention resides broadly in the apparatus characterized by the fact that the non-return valve is in an operational connection with two valve seat surfaces, between which the operation can be switched as desired. 
     Another feature of the invention resides broadly in the apparatus characterized by the fact that the fluid connection 17 is provided with a damping valve. 
     Another feature of the invention resides broadly in the apparatus characterized by the fact that the fluid connection 17 has two non-return valves 23, 25 which are coupled by means of the actuator 19. 
     Yet another feature of the invention resides broadly in the apparatus characterized by the fact that the non-return valves 23, 25 are designed as disc valves. 
     Still another feature of the invention resides broadly in the apparatus characterized by the fact that the non-return valve is in an operational connection with two valve seat surfaces, between which the operation can be switched as desired. 
     A further feature of the invention resides broadly in the apparatus characterized by the fact that the non-return valves 23, 25 are mounted in a floating manner relative to the actuator 19, so that a valve movement into an open or closed position takes place independently of the actuator force. 
     Another feature of the invention resides broadly in the apparatus characterized by the fact that the damping medium travels the same flow distance in the fluid connection 17 for both directions of flow. 
     Yet another feature of the invention resides broadly in the apparatus characterized by the fact that the regulating distance a+s of the actuator 19 is longer than the valve distance a from the open position into the closed position of the non-return valves 23, 25. 
     Still another feature of the invention resides broadly in the apparatus characterized by the fact that the fluid connection 17 is located with the valve device 17, 23, 25 inside the piston 5. 
     A further feature of the invention resides broadly in the apparatus characterized by the fact that the actuator 19 can be switched when the pressure on the inflow side of the closed non-return valve 23, 25 drops below a defined level. 
     Another feature of the invention resides broadly in the apparatus characterized by the fact that the fluid connection 17 is designed as a central channel. 
     Examples of stepper motor drive systems which may be utilized in accordance with the present invention may be disclosed in the following U.S. Pat. Nos.: No. 5,182,685 entitled &#34;Stepper Motor Torque Variance Compensation Using Varied Applied Voltage&#34; to Seagate Technology; No. 5,206,571 entitled &#34;Stepper Motor Controllers&#34; to Motorola; No. 5,225,756 entitled &#34;Stepper Motor Driver Circuit&#34; to Coutu; and No. 5,256,943 entitled &#34;Zero Adjustment Shaft Encoder Control for Stepping Motors&#34; to NCR Corporation. 
     Examples of linear solenoids which may be utilized in accordance with the present invention may be disclosed in the following U.S. Pat. Nos.: No. 5,178,053 entitled &#34;Electronic Pilot Positioner&#34; to Johnson; No. 5,186,204 entitled &#34;Linear Solenoid Valve Apparatus&#34; to Aisin; No. 5,202,658 entitled &#34;Linear Proportional Solenoid&#34; to South Bend Controls, Inc.; No. 5,247,965 entitled &#34;Linear Solenoid Valve Apparatus&#34; to Aisin; and No. 5,138,291 entitled &#34;Proportional Solenoid Actuator&#34; to AIL Corporation. 
     Examples of rotational valve devices which may be utilized in accordance with the present invention may be disclosed in the following U.S. Pat. Nos.: No. 5,238,022 entitled &#34;Internal Rotary Valve Actuator System&#34; to Montana Co.; No. 5,259,589 entitled &#34;Stop for Rotational Actuators&#34; to Posner; No. 5,283,495 entitled &#34;Rotary Actuator for Determining a Flow Cross Section of a By-pass Line around a Valve&#34; to Bosch; and No. 5,348,271 entitled &#34;Locking Device&#34; to Bettis Corporation. 
     Examples of shock absorber assemblies and components associated therewith which may be utilized with the embodiments of the present invention may be disclosed in the following U.S. Pat. Nos.: No. 4,650,042 entitled &#34;Hydraulic Adjustable Shock Absorber&#34; to Knecht et al.; No. 4,723,640 entitled &#34;Adjustable Hydraulic Vibration Damper&#34; to Beck; No. 4,749,069 entitled &#34;Vibration Damper for Motor Vehicles Having an Arrangement for Varying Damping Thereof&#34; to Knecht et al.; No. 5,301,776 entitled &#34;Hydraulic Adjustable Vibration Damper&#34; to Beck; and No. 4,986,393 which issued to Preukschat et al. on Jan. 22, 1991. 
     The appended drawings in their entirety, including all dimensions, proportions and/or shapes in at least one embodiment of the invention, are accurate and are hereby included by reference into this specification. 
     All, or substantially all, of the components and methods of the various embodiments may be used with at least one embodiment or all of the embodiments, if more than one embodiment is described herein. 
     All of the patents, patent applications and publications recited herein are hereby incorporated by reference as if set forth in their entirety herein. 
     The corresponding foreign patent publication applications, namely, Federal Republic of Germany Patent Application No. P 44 21 908.3, filed on Jun. 24, 1994, having inventor Alfred Preukschat, and DE-OS P 44 21 908.3 and DE-PS P 44 21 908.3, are hereby incorporated by reference as if set forth in their entirety herein. 
     The invention as described hereinabove in the context of the preferred embodiments is not to be taken as limited to all of the provided details thereof, since modifications and variations thereof may be made without departing from the spirit and scope of the invention.