METHOD FOR OPERATING A CONTROLLABLE SHOCK ABSORBER FOR MOTOR VEHICLES

Abstract

A method for operating a controllable shock absorber may involve damping movement of a valve body by loading the valve body with a back pressure on an outflow side. Further, the controllable shock absorber may include a cylinder tube, a piston within the cylinder tube that divides the cylinder tube into two working spaces and includes a couple fluid leadthroughs connecting the working spaces, and first and second valve assemblies for damping piston movement in first and second actuating directions that are disposed on the leadthroughs. Each valve assembly may have a pilot control chamber and a valve plate that is either seated on or spaced apart from a valve seat in closed and open valve positions. Each valve plate can be prestressed closed by pressure loading the pilot control chamber. The pressures of the pilot control chambers can be set by a pilot control valve that comprises a movable valve body. As a result, an outflow cross section between the pilot control chambers and the working spaces can be set. The valve body may be loaded on an outflow side with a back pressure, as a result of which movement of the valve body is damped.”

Claims

1.-9. (canceled)

10. A method for operating a controllable shock absorber, wherein the shock absorber comprises: a cylinder tube that contains a hydraulic fluid in a sealed manner; a piston that is movable axially along a cylinder tube axis within the cylinder tube, the piston dividing the cylinder tube into a first working space and a second working space, wherein the piston comprises a first fluid leadthrough and a second fluid leadthrough by way of which the first and second working spaces are connected; a piston rod disposed parallel to the cylinder tube axis and connected to the piston; a first valve assembly for damping piston movement in a first actuating direction disposed on the first fluid leadthrough; a second valve assembly for damping piston movement in a second actuating direction disposed on the second fluid leadthrough, wherein each of the first and second valve assemblies comprises: a pilot control chamber, and a valve plate that is seated on a valve seat in a closed valve position and that is spaced apart from the valve seat in an open valve position, wherein the valve plate can be prestressed into the closed valve position by pressure loading the pilot control chamber; and a pilot control valve configured to set pressures in the pilot control chambers, the pilot control valve comprising a valve body that is movable between a closed position and an open position, as a result of which an outflow cross-section between the pilot control chambers and the working spaces can be set, wherein the method comprises damping movement of the valve body by loading the valve body with a back pressure on an outflow side.

11. A controllable shock absorber comprising: a cylinder tube that contains a hydraulic fluid in a sealed manner; a piston that is movable axially along a cylinder tube axis within the cylinder tube, the piston dividing the cylinder tube into a first working space and a second working space, wherein the piston comprises a first fluid leadthrough and a second fluid leadthrough by way of which the first and second working spaces are connected; a piston rod disposed parallel to the cylinder tube axis and connected to the piston; a first valve assembly for damping piston movement in a first actuating direction disposed on the first fluid leadthrough; a second valve assembly for damping piston movement in a second actuating direction disposed on the second fluid leadthrough, wherein each of the first and second valve assemblies comprises: a pilot control chamber, and a valve plate that is seated on a valve seat in a closed valve position and that is spaced apart from the valve seat in an open valve position, wherein the valve plate can be prestressed into the closed valve position by pressure loading the pilot control chamber; and a pilot control valve configured to set pressures in the pilot control chambers, the pilot control valve comprising a valve body that is movable between a closed position and an open position, as a result of which an outflow cross-section between the pilot control chamber and the working spaces can be set, wherein the valve body is assigned an outflow valve on an outflow side by way of which a back pressure that acts on the valve body can be built up on the outflow side.

12. The controllable shock absorber of claim 11 wherein the outflow valve is connected on the outflow side to the pilot control chambers of the first and second valve assemblies.

13. The controllable shock absorber of claim 11 wherein the valve body is adjoined on the outflow side by a first outflow path and a second outflow path, wherein the first outflow path is closed by way of the valve body when an actuator for actuating a position of the valve body is inactive.

14. The controllable shock absorber of claim 13 wherein the outflow valve is connected on the outflow side to the first outflow path and to the second outflow path.

15. The controllable shock absorber of claim 13 further comprising a check valve disposed between the valve body and the outflow valve, wherein the check valve prevents a return flow of the hydraulic fluid from the first outflow path in a direction of the valve body through the second outflow path.

16. The controllable shock absorber of claim 15 wherein the outflow valve and the check valve comprise disks disposed on a common journal so as to be axially adjacent to one another.

17. The controllable shock absorber of claim 16 wherein the valve body is disposed in a radially inner recess of the common journal.

18. The controllable shock absorber of claim 11 wherein the valve body is disposed in a radially inner recess of a common journal.

19. The controllable shock absorber of claim 11 wherein loading the valve body with the back pressure on the outflow side dampens movement of the valve body.

Description

PREFERRED EXEMPLARY EMBODIMENTS OF THE INVENTION

[0019] Further measures which develop the invention will be shown in greater detail in the following text together with the description of preferred exemplary embodiments of the invention, using the figures, in which:

[0020] FIG. 1 shows a conventional shock absorber with a valve assembly in cross section,

[0021] FIG. 2 shows the cross section through a pilot control valve of a shock absorber according to the invention in a first operating state,

[0022] FIG. 3 shows the cross section through a pilot control valve of a shock absorber according to the invention in a second operating state, and

[0023] FIG. 4 shows the damping force profile of a conventional shock absorber.

[0024] FIG. 1 shows the section of a conventional shock absorber 1.

[0025] The shock absorber 1 comprises a cylinder tube 10, in which a piston 2 is held such that it can be displaced along a cylinder tube axis A. The piston 2 has an annular seal or a piston band 28 on its outer circumference, with the result that the piston 2 divides the cylinder tube 10 sealingly into a first working space 11 (remote from the piston rod) and into a second (piston rod-side) working space 21. The piston 2 is fastened to a fastening pin 42 which in turn is connected fixedly to a piston rod 3. Upon actuation of the piston rod 3 in a first actuating direction R1 toward the first working space 11 (also called “compression direction”), the pressure increases in the first working space 11. Fluid which is present in the first working space 11 then flows through a first fluid leadthrough 12 in the piston 2 into the second working space 21. Here, the fluid flows through the first fluid leadthrough 12 and through a first valve assembly 13 with a pressure limiting valve 14. The pressure limiting valve 14 can be formed, for example, from one or more flexible valve plates 14. When a minimum pressure of the fluid is reached in the first working space 11, the first pressure limiting valve 14 which is seated with prestress on a first valve seat 15 is released at least partially from the first valve seat 15. The valve plate 14 is thus transferred from the closed position into the open position, in which it is lifted up from the valve seat. A hydraulic connection is thus established between the first working space 11 and the second working space 21. Here, the first pressure limiting valve 14 generates the damping force in interaction with the first valve seat 15.

[0026] The pressure limiting valve 14 is loaded in the direction of the valve seat 15 by way of a pressure (“pilot control pressure” in the following text) which prevails in a first pilot control chamber 16. Said pilot control pressure in the first pilot control chamber 16 can be set in a defined manner during operation. It can be seen that the opening pressure of the pressure limiting valve 14 is higher, the higher the pilot control pressure is in the first pilot control chamber 16. Therefore, the pilot control pressure influences the characteristic curve profile of the damping force in the p-v diagram.

[0027] Furthermore, the shock absorber 1 comprises a second valve assembly 23 which is of analogous configuration to the first valve assembly 13. The second valve assembly is provided for the purpose of braking the flow of the fluid when the piston 2 is moved in a second actuating direction R2 (also called “rebound direction”). In this case, the fluid flows from the second working space 21 via a second fluid leadthrough 22 into the first working space 11. The second valve plate 24 is loaded in the direction of the valve seat 25 by way of a pilot control pressure which prevails in a second pilot control chamber 26. The second valve plate 24 and a second valve seat 25 are configured analogously with respect to the corresponding components of the first valve assembly 13.

[0028] The two pilot control chambers 16, 26 are connected to one another hydraulically via a connecting leadthrough 9. The connecting leadthrough 9 comprises an axial bore in the fastening pin 42 and two radial connecting bores in the fastening pin 42, which radial connecting bores connect the axial bore in each case to one of the pilot control chambers 16, 26. The same pressure always prevails substantially in both pilot control chambers 16, 26. If the piston 2 is then moved in the first actuating direction R1, the pressure increases in the first working space 11 and the damping fluid flows through a fluid leadthrough 27 between the first working space 11 and the second pilot control chamber 26 out of the first working space 11 into the second pilot control chamber 26, as a result of which the pilot control pressure in the second pilot control chamber 26 is increased. The pilot control pressure which is built up in the second pilot control chamber 26 also propagates into the first pilot control chamber 16 through the connecting leadthrough 9. As a result, the pilot control pressure is generated in the first pilot control chamber 16, by way of which pilot control pressure the damping behavior of the first valve assembly 13 is influenced. The same applies to the actuation in the second actuating direction R2. In this case, the fluid flows from the second working space 21 by way of a fluid leadthrough 17 between the second working space 21 and the first pilot control chamber 16 into the first pilot control chamber 16. The pilot control pressure which is generated in this way in the first pilot control chamber 16 in turn propagates by way of the connecting leadthrough 9 into the second pilot control chamber 26. In order that the fluid cannot flow by way of the fluid leadthroughs 17, 27 from the first pilot control chamber 16 directly into the second working space 21 or from the second pilot control chamber 26 into the first working space 11, a one-way valve 20 is attached in each case in the fluid leadthroughs 17, 27, which one-way valves 20 are configured, for example, as check valves.

[0029] The pilot control pressure in the two pilot control chambers 16 and 26 can be regulated. To this end, a pilot control valve 31 is provided which has a valve body 32. The valve body is held such that it can be moved along the cylinder tube axis A, and can be seated on a stationary (in relation to the fastening pin) valve seat 33. When the valve body 32 is seated on the valve seat 33, an outflow of fluid by way of the pilot control valve 31 is largely prevented. During a phase of this type, the pilot control pressure can be built up or held. If the valve body 32 is released from the valve seat 33, fluid can flow out of the connecting leadthrough 9 by way of the pilot control valve 31; in this phase, the pilot control pressure can be reduced. Here, the valve body 32 is loaded in the first actuating direction R1 by means of a magnetic actuator 40. In addition, a spring can be provided which loads the valve body 32. The valve body 32 is loaded in the second actuating direction R2 by way of the pilot control pressure. Depending on the force conditions, due to the magnetic actuator 40 and the pilot control pressure, the result is then the position of the valve body 32 with respect to the valve seat 33.

[0030] The fluid which flows out by way of the pilot control valve 31 flows by way of a second outflow passage 34 to the second working space 21 upon actuation of the piston rod in a direction R1 (increased pressure in the first working space 11). A one-way valve 36 is arranged in the second outflow passage 34. In this case, the one-way valve 36 prevents it being possible for fluid to pass out of the second working space 21 by way of the pilot control valve 31 in the direction of the pilot control chambers 16, 26.

[0031] Upon actuation of the piston rod 3 in the direction R2 (increased pressure in the second working space 21), the fluid which flows out by way of the pilot control valve 31 flows by way of a first outflow passage 38 to the first working space 11. The first outflow passage 38 is formed by way of an axial bore in the fastening pin 42. A one-way valve 36 in the outflow passage 38 prevents fluid from passing out of the second working space 21 by way of the pilot control valve 31 in the direction of the pilot control chambers 16, 26.

[0032] An arrangement as will be described in the following text using FIGS. 2 and 3 is then introduced according to the invention into a shock absorber of this type.

[0033] FIGS. 2 and 3 show a pilot control valve 31 of a shock absorber according to the invention which is of largely analogous configuration with respect to the embodiment in accordance with FIG. 1. The differences result from the following description.

[0034] Said pilot control valve 31 is in communication with the two pilot control chambers 16, 26 via the connecting leadthrough 9, in an analogous manner to the embodiment in accordance with FIG. 1. The connecting leadthrough 9 opens into a chamber 44, in which the valve body 32 is arranged. The latter can be moved parallel to the cylinder axis A and is loaded on one side by a spiral spring 30 and on the other side by way of the magnetic actuator 40 parallel to the cylinder axis A. In a first operating state, the regular operating state, the valve body 32 is held between an open and closed position by way of the magnetic force which can vary fundamentally between 0 and a maximum magnetic force F.sub.M max. If the valve body 32 is spaced apart from the valve seat 33, fluid can flow out by way of a first outflow path 18 via the outflow passages 38, 34 into the working spaces 11 and 21, in a manner which corresponds to the embodiment in accordance with FIG. 1. If the valve body 32 lies on the valve seat 33, the valve body 32 is situated in the closed position; otherwise, the valve body 32 is situated in one of a plurality of possible open positions. In the closed position, the valve body 32 can lie on the valve seat 33 in a completely sealing manner, but it does not have to lie on the valve seat 33 in a completely sealing manner.

[0035] An outflow valve 7 in the form of a disk valve is provided in said first outflow path 18. The outflow valve 7 throttles the outflow via the first outflow path 18 and thus generates a back pressure p which in turn acts on the valve body 32 on the outflow side. As a result, the movement of the valve body 32 is clamped hydraulically between the pressure in the connecting leadthrough 9 and the back pressure p in the first outflow path 18, and the movement of said valve body 32 is damped. An outflow valve 7 of this type can fundamentally have a progressive, linear and/or degressive characteristic and can be adapted to the specific intended purpose of the shock absorber. The stability of the overall system is improved by way of the damping of the movement of the valve body 32.

[0036] Furthermore, the pilot control valve 31 has a failsafe function as a second operating state, which will be explained using FIG. 3. In the case of a defect of the magnetic actuator 40, the magnetic force F.sub.M is canceled. In this case, the spring 30 loads the valve body away from the valve seat 33. The valve body 32 then blocks an inlet opening 41 of the first outflow path 18. The outflow of the hydraulic fluid then takes place exclusively via a second outflow path 19, at the end of which a disk valve 8 is arranged. The disk valve 8 has both the function of a throttle and the function of a one-way valve. The failsafe behavior, that is to say the damping behavior which the shock absorber is to configure in the case of a power failure at the actuator, can be set in a defined manner in advance by way of the dimensioning of the disk valve 8. Here, the disk valve 8 generates a back pressure, as a result of which a certain pilot control pressure is maintained in the pilot control chambers in a manner which is dependent on the flow velocity of the fluid, even if the pilot control valve fails.

[0037] The result of the arrangement which is shown in FIGS. 2 and 3 is a very small installation space for the outflow valve and the failsafe arrangement which is additionally required for the second outflow path 19 and the disk valve 8. Here, both the outflow valve 7 and the disk valve 8 are formed by way of disk packets which are arranged axially adjacently with respect to one another and are centered by way of a common journal 35. A spacer sleeve 37 is arranged in between, which spacer sleeve 37 provides space for deflecting the valve plate 8 as a consequence of the pressure loading. A further saving of space requirements results from the fact that both the outflow valve 7 and the disk valve 8 are provided for the failsafe operation for both stages (compression stage and the rebound stage), that is to say for the outflow of the hydraulic fluid from both pilot control chambers. In addition, the valve body 32 is arranged in a space-saving manner in the chamber 44 which configures a radially inner recess of the journal 35. According to the invention, the valve body 32 is then braked by the back pressure which prevails on the outflow side, as a result of which the oscillations of said valve body 32 are damped.

[0038] FIG. 4 shows an enlarged detail from FIG. 2 in the region of the plates of the outflow valve 7 and the disk valve 8. Here, the disk valve 8 is formed from a prestressing disk 8.sub.1, a throttle plate 8.sub.2 which adjoins it in the outflow direction, and a covering plate 8.sub.3 which loads it in the closing direction. This is adjoined by the sleeve 37 as a compensation washer. The outflow valve 7 comprises an outflow throttle plate 7.sub.1 and a covering plate 7.sub.2 which loads the outflow throttle plate 7.sub.1 into the closed position.

[0039] The throttle plate 8.sub.2 provides a constant opening cross section up to a certain pressure; above an opening pressure which can be set by way of the selection of the covering plate 8.sub.3, the throttle plate 8.sub.2 lifts up from the valve seat and the opening cross section is enlarged. This also applies correspondingly to the outflow valve 7. The outflow throttle plate 7.sub.1 provides a constant opening cross section up to a certain pressure; from an opening pressure which can be set by way of the selection of the covering plate 7.sub.2, the outflow throttle plate 7.sub.1 lifts up from a valve seat and the opening cross section is enlarged.

[0040] The outflow-side region is fundamentally understood to be that side of a component in the hydraulic path between the pilot control chamber 16, 26 and the working spaces 11, 21, which side faces away from the pilot control chamber 16, 26 and faces the working space 11, 21. The hydraulic fluid flows along the outflow direction from the pilot control chamber 16, 26 via the fluid leadthrough 9 to the valve body 32, and subsequently by way of one of the outflow paths 18, 19 to the outflow valve 7. It subsequently opens into one of the working spaces 11, 21.

LIST OF DESIGNATIONS

[0041] 1 Shock absorber

[0042] 2 Piston

[0043] 3 Piston rod

[0044] 6 Dimensionally stable movable cover

[0045] 7 Outflow valve

[0046] 7.sub.1 Outflow throttle plate

[0047] 7.sub.2 Covering plate

[0048] 8 Disk valve

[0049] 8.sub.1 Prestressing disk

[0050] 8.sub.2 Throttle plate

[0051] 8.sub.3 Covering plate

[0052] 9 Connecting leadthrough between the two pilot control chambers

[0053] 10 Cylinder tube

[0054] 11 First working space

[0055] 12 First fluid leadthrough

[0056] 13 First valve assembly

[0057] 14 First valve plate

[0058] 15 First valve seat

[0059] 16 First pilot control chamber

[0060] 17 Connecting leadthrough between the second working space 21 and the first pilot control chamber 16

[0061] 18 First outflow path

[0062] 19 Second outflow path

[0063] 20 One-way valve

[0064] 21 Second working space

[0065] 22 Second fluid leadthrough

[0066] 23 Second valve assembly

[0067] 24 Second valve plate

[0068] 25 Second valve seat

[0069] 26 Second pilot control chamber

[0070] 27 Fluid leadthrough between the first working space 11 and the second pilot control chamber 26

[0071] 28 Annular seal

[0072] 29 Nut

[0073] 30 Spring

[0074] 31 Pilot control valve

[0075] 32 Valve body

[0076] 33 Valve seat

[0077] 34 Second outflow passage to the second working space

[0078] 35 Journal

[0079] 36 One-way valve

[0080] 37 Spacer sleeve

[0081] 38 First outflow passage to the first working space

[0082] 39 One-way valve

[0083] 40 Magnetic actuator

[0084] 41 Inlet opening of the first outflow path

[0085] 42 Fastening pin

[0086] 43 Valve seat

[0087] 44 Chamber

[0088] A Cylinder tube axis

[0089] R Actuating direction

[0090] p Back pressure