DE29518973U1 - Vibration damper - Google Patents

Description

Reg. No. 13 803 DE1 \. ^:: .. ^: " .:..:.* .*! ^: ... ^: 28.11.95

Fichtel & Sachs AG - Schweinfurt

Utility model application

Description

The invention relates to a vibration damper according to the preamble of claim 1.

Such a vibration damper is known, for example, from DE-PS 33 03 293. The vibration damper includes, among other things, a pressure pipe in which a piston with a piston rod is arranged so that it can move axially, and the pressure pipe is divided into an upper and a lower working chamber. The upper working chamber is connected to an oil sump of a compensation chamber via a fluid connection. Damping valves for both flow directions are arranged inside the piston. Between a connection opening in the upper working chamber and the oil sump, the fluid connection has a controlled passage valve. The passage valve has two switching positions and is opened by the pressure in the lower working chamber in the retraction direction of the piston and connects the upper working chamber with the oil sump. In the pulling direction, the passage valve is brought into the closed position by a spring. The passage valve is arranged at the bottom of the vibration damper. The entire volume flow must flow through the piston in the pulling direction and in the pushing direction. Correspondingly large flow cross-sections must be designed in the piston, which inevitably results in relatively small webs on the piston or piston body cross-sections, which have a negative effect on the strength of the piston body, especially in the case of damping force peaks. Another disadvantage is the special design of the pass valve. It consists of a valve slide that moves axially between a passage and a blocking position due to the pressure conditions in the lower working chamber. The axial movement in connection with the

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The mass of the valve slide inevitably leads to rattling noises that are practically impossible to control.

The object of the present invention is to be able to design the ratio of damping force of the pulling direction/the pushing direction as desired, whereby cavitation in the upper working space in the pushing direction is to be avoided.

According to the invention, the object is achieved in that at least one damping valve is additionally designed for the piston valve(s) and in the retraction direction damping from the damping valve is used, which takes place depending on the volume flow distribution due to the flow resistance in the valves, so that a superimposed pressure damping of the valves results, whereby the maximum displaced volume of the lower working chamber and the minimum displaced volume of the piston rod flows through the damping valve and the flow resistance within the fluid connection in the flow direction from the oil sump into the upper working chamber is lower than in the opposite flow direction due to a direction-dependent effective passage valve.

Advantageously, the damping force in the compression direction can be designed very variably, since the bottom valve can, in extreme cases, take over the pressure damping and the piston valve the tension damping. Under this condition, the piston can even be designed as a displacer, so that the entire volume of the lower working chamber is displaced by the bottom valve for the pressure damping. Consequently, each of the damping valves only has to be dimensioned for one flow direction in terms of the flow cross-sections. The direction-dependent passage valve prevents cavitation from occurring in the upper working chamber. Of course, one can also deviate from this strict separation and allow any proportion of the volume of the lower working chamber to flow through the piston valves into the upper working chamber. In conventional vibration dampers, the lower limit of the damping medium flow through the piston during pressure damping is determined by the cavitation, whereby the cavitation is caused by the upper working chamber

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Reg. No. 13 803 DE1 *..·'..' .:..:. ..'...' 28.11.95

the retraction movement of the piston into the pressure pipe and no subsequent flow of damping medium takes place to fill this increase in volume.

Furthermore, it is advantageously provided that the fluid connection, starting from the connection opening, ends directly in the oil sump, bypassing the pressure pipe. A considerable cross-section is available at the bottom valve for the damping valve in the pressure direction.

In one embodiment, the fluid connection is formed by the concentric arrangement of the pressure pipe and an intermediate pipe enclosing the pressure pipe, with the direction-dependent passage valve being arranged within the annular fluid connection. Alternatively, the fluid connection is formed by a pipe body that runs essentially parallel to the vibration damper's longitudinal axis. For cost reasons, it is advisable for the pipe body to be formed by a flexible hose. An advantage of this solution is that relatively little volume is required for the fluid connection and, particularly in the case of a two-pipe damper, the oil volume in the compensation chamber is favorable for the same vibration damper dimensions.

Different variants can also be implemented with the direction-dependent passage valve. It has proven to be effective if the direction-dependent passage valve is formed by a slotted ring that is attached to the inner diameter of the pressure pipe.

However, it can also be provided that the direction-dependent passage valve is formed by a spring washer that at least partially covers a channel in the piston rod guide. For example, the spring washer can be clamped between the pressure pipe and the piston rod guide. So that the spring washer can be securely mounted and assumes a defined starting position, the spring washer is centered on a radial guide of the piston rod guide.

Reg. No. 13 803DE1 ·· ·· ····* 28.11.95

In an advantageous design, the direction-dependent passage valve consists of a constriction in the fluid connection with an axially movable valve body. The body forming the fluid connection also has the additional function of being a component of the direction-dependent passage valve. In a consistent further development, the constriction extends over the essential length of the fluid connection to the connection opening. The advantage of this feature is that the operating pressure within the fluid connection exerts a hydraulic support force on the body forming the fluid connection, whereby the hydraulic support force results from the product of the operating pressure and the projected area of the constriction.

Due to the fact that the vibration damper comprises a bottom valve with a bottom valve body, this advantageously extends radially from the pressure pipe into the fluid connection and is part of the direction-dependent passage valve.

Given that vibration dampers must be increasingly standardized, the bottom valve body in the fluid connection has an axial support surface on which a separate valve ring rests as part of the direction-dependent pass-through valve. Optionally, the direction-dependent pass-through valve can be used for any vibration damper or can be omitted, whereby the same bottom valve body is used in each case.

In conjunction with a constriction of the fluid connection, the intermediate tube is axially floating and is supported on the piston rod guide. In another type, the intermediate tube is fixed between the piston rod and a clamping ring at the bottom of the vibration damper.

For driving comfort, the damper behavior at damper speeds close to 0 is of great importance. In order to achieve a smooth run-in of the damping force-speed characteristic, passage openings are selected that

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Registration number. 13 803 DE1 \.. ^: \. ^: " .!..I. ,.'...* 28.11.95

however, they usually vary in the tension and compression directions. In the present design, it is advisable to integrate this passage opening for the tension direction into the direction-dependent passage valve. The passage opening for the characteristic curve in the compression direction is best placed in the bottom valve. This means that the piston is advantageously free of passage openings for the characteristic curve inlet, which are arranged on the piston and always act in the tension and compression directions without additional effort.

However, if no special passage opening is required for the characteristic curve inlet in the pulling direction, the direction-dependent passage valve can also be designed as a check valve.

To ensure a strict separation between the damping in the compression and tension directions, the direction-dependent passage valve is also designed as a check valve.

In addition, it can be provided that the valves in the piston and/or bottom valve body are adjustable.

The invention will be described in more detail using the following description of the figures.

It shows.

Fig. 1 Schematic diagram of the vibration damper according to the cited state of the art

Fig. 2 Schematic diagram of the vibration damper according to the invention

Fig. 3-4 Detailed views of the vibration damper

For a better understanding of the invention, the functionality of the vibration sensor known from the prior art in the introduction to the description is briefly described.

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damper is described. Figure 1 shows a vibration damper 1 in general with a pressure pipe 3 in which a piston 5 is arranged so as to be axially movable on a piston rod 7 with a cross section A _KS and the pressure pipe is divided into an upper and a lower working chamber 9; 11. The upper working chamber 9 with a cross section A _R is connected to an oil sump 15 of a compensation chamber 17 via a fluid connection 13. Furthermore, the two working chambers are connected to one another via at least one damping valve 19 for the tension and compression directions in the piston 5. The lower end of the lower working chamber 11 with a cross section A _K is formed by a bottom valve body 21 with a check valve 27 which connects the compensation chamber to the lower working chamber 11 when the piston moves in the tension direction. The fluid connection 13 is also equipped with a passage valve 28. This valve is a 3/2-way valve controlled by the pressure in the working chamber 11, which in the retraction or pressure direction is brought into the closed position by the pressure within the working chamber 11 and into the open position by a spring 30.

When the piston moves in the pulling direction, a pressure gradient inevitably arises between the upper and lower working chambers. The relatively low pressure in the lower working chamber 11 in conjunction with the spring 30 moves the passage valve 28 into the closed position with the effect that the fluid connection 13 is separated from the working chambers. The entire volume flow V _R as the product of the cross section A _R of the upper working chamber and the piston speed v must flow through the piston valves 19. The volume of the lower working chamber is inevitably larger than the volume of the upper working chamber by the piston rod volume remaining in the upper working chamber. Consequently, a volume flow Ql ₂ I corresponding to the extending piston rod cross section A _KS multiplied by the piston speed must flow through the check valve 27 from the oil sump 15 into the lower working chamber.

In the pressure or retraction direction of the piston rod, a pressure builds up in the lower working chamber, which opens the passage valve 28 via a control line 32. The upper working chamber 9 is thus connected to the oil via the fluid connection 13.

Registration number. 13 803 DE1 V.**..' .:..:. ..'...* 28.11.95

sump 15. At the same time, the check valve 27 closes. The entire volume flow Q _K {A _K * v) is displaced by the valves 19 into the upper working chamber 9, which is smaller than the lower working chamber by the current piston rod volume. Consequently, a volume flow Q ₁₃ corresponding to the product A _KS of the retracting piston rod and the piston speed v flows through the open passage valve 28 via the fluid connection 13. This results in the need for larger flow cross-sections to be provided, particularly for pressure damping, in order to be able to implement lower damping forces. Furthermore, the pressure control of the passage valve gives rise to the problem that the passage cross-section is always dependent on the pressure in the lower working chamber, with the result that the afterflow volume is also pressure-dependent.

In accordance with the prior art, Figure 2 shows in general a vibration damper 1 with the pressure pipe 3, in which the piston 5 is arranged axially movable on the piston rod 7 with the cross section A _KS and the pressure pipe is divided into the upper and lower working chambers 9; 11. The upper working chamber 9 with cross section A _R is connected to the oil sump 15 of a compensation chamber 17 via the fluid connection 13. Furthermore, the two working chambers are connected to one another via at least one damping valve 19 at least for the pulling direction, but preferably for the pulling and pushing directions in the piston 5. The lower end of the lower working chamber 11 with the cross section A _K is formed by a bottom valve body 21 with an additional damping valve 25 and the check valve 27, the latter connecting the compensation chamber to the lower working chamber 11 during a piston movement in the pulling direction. The fluid connection 13 is also connected to a passage valve 29, wherein the passage valve can optionally be designed as a general direction-dependent passage valve with two different passage cross-sections or as a check valve.

In a first consideration, it is assumed that the passage valve 29 is designed as a check valve. When the piston rod moves in

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In the opposite direction, the entire displaced volume flows from the upper working chamber 9 as Q _AR through the piston valves 19, since the check valve is closed. The oil sump is separated from the upper working chamber 11, so that there is no possibility of the displaced volume draining away by bypassing the piston valves. At the same time, the volume of the extended piston rod volume flows into the lower working chamber 11 via the check valve 27 in the bottom valve body.

Deviating from the prior art shown, the volume to be displaced (A _K * v) is divided in the pressure direction into a volume flow Q ₂₅ of the damping valve 25 and a volume flow Q ₁₉ through the piston valve 19 into the upper working chamber 11.

A _K *v = Q ₁₉ + Q ₂₅ (I)

The upper working chamber 11 with the cross section A _R , which increases with the speed v of the piston, is filled through the opened passage valve 29 with the volume flow Q ₂ g via the fluid connection 13 from the oil sump 15.

A _R * ν =Q ₁₉ + Q ₂₉ (II)
It is known that

^a ks *v + A _R *v = A _K *v (III)

From equations (I) and (II) inserted into equation (Ml) it follows that through the damping valve 25 the volume flow

Q-25 = A _KS * ν + Q ₂₉ (IV)

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flows. This determines the design of the bottom valve, because if, conversely, the bottom valve allows less than the amount calculated in equation (IV) to pass through, the overflow of damping medium in the upper working chamber into the fluid connection closes the passage valve 29, whereby the absolute limiting case is

Q ₂ S = A _KS * &ngr;
lies.

Due to the volume ratios between the upper and lower working chambers, at least the volume of the retracting piston rod must be displaced by the damping valve 25.

This principle is not limited to two-pipe dampers, but can also be used with single-pipe dampers in conjunction with a bottom valve for the compensation chamber. The compensation chamber does not have to be located directly on the vibration damper. With regard to the fluid connection, tubular bodies in rigid or flexible form, for example as a hose, can be used. It is important that the fluid connection bypasses the bottom valve so that only the check valve 27 and the damping valve 25 need to be arranged in the bottom valve.

The direction-dependent flow valve 29 does not necessarily have to be designed as a check valve. It is also sensible to use no throttling in the retraction direction of the piston and a significant throttling in the retraction direction within the direction-dependent flow valve 29. This creates a series circuit comprising the piston valves 19 and the flow valve 29. In the case of adjustable piston valves in particular, the result of equation (IV) means that the volume flow Q ₂ 5 can be reduced by a very small throttling cross-section or, in the other extreme case, when Q ₁₉ is zero, i.e. a hydraulically sealed piston, a very large variability in the setting of the pressure damping without the risk of cavitation, which is caused by the pre-

Registration number. 13 803 DE1 \. ^:s .. ^: ".:,.:." ü ^: ..." 28.11.95

lumen flow Q ₂₉ from the oil sump into the upper working chamber is controlled. In summary:

A _KS * &ngr;< Q ₂₅ ^ A _K * &ngr;

If one assumes a conventional vibration damper without damping force adjustment, the limiting case A _KS * v is not interesting, since no cavitation can occur.

Figure 3a is limited to the closure of the upper working chamber 9, which is formed by a piston rod guide 31. In this embodiment, the vibration damper 1 is shown as a two-tube damper. Concentrically to the pressure pipe 3, an intermediate pipe 33 is arranged which envelops the pressure pipe and, together with the pressure pipe, forms the fluid connection 13 to the compensation chamber 17. The fluid connection begins at a connection opening 35, which is optionally designed as a channel within the piston rod guide and/or in combination with openings in the pressure pipe. An essential requirement is that the connection opening has a cross-section which does not result in any throttling effects. Therefore, several connection openings can also be used.

Fig. 3b shows the end of the fluid connection immediately before entering the oil sump 15. The intermediate pipe used contains a constriction 37 in the cross section, which serves as a support for a closing spring 39. The closing spring 39 preloads a valve disk 41 as a valve body onto a valve seat 43, which is part of a radial extension of the bottom valve body 21. In this embodiment, the constriction 37 extends over the essential length of the fluid connection 13 to the connection opening 35. The area of the projected cross section of the constriction 37 multiplied by the operating pressure within the fluid connection represents a hydraulic pressure force, which is supported on the bottom valve body 21 and presses the intermediate pipe in the direction of the piston rod guide 31. Consequently, the intermediate pipe can also be

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floating, whereby length tolerances of the intermediate pipe become significantly less important. A further advantage is that the valve disk 41 only requires a small preload from the closing spring. The operating pressure within the lower working chamber plays practically no role in the opening behavior of the passage valve.

Figure 3c shows a modification of Figure 3b. The structural difference is that the direction-dependent passage valve 29 has a valve ring 43 which rests on a support surface 45 formed by the base valve body 21.

Fig. 4a includes two variants for the direction-dependent passage valve 29. In the left section, a spring washer 47 is used, which is radially centered on a radial guide 49. The spring washer is axially clamped between the pressure pipe 3 and the piston rod guide 31. In the inflow direction from the fluid connection 13, the spring washer lifts off the piston rod guide 31 and exposes the connection opening 35 in its entire cross-section. In the opposite direction, depending on the design of the cross-section of the spring washer, for example by notches, the entire connection opening or part of it can be covered.

In the right half of the cut, a slotted ring 51 is used for the direction-dependent passage valve 29, which is attached to the inside of the pressure pipe 3 in any way. In order for the ring 51 to lift off relatively easily and still not leave its position below the piston rod guide, a fastening rivet (not shown) can also be used. In this case, the necessary rivet opening is made from the inside of the pressure pipe to the outside in order to prevent the inevitable chip from reaching the seat area of the ring 51. Since the intermediate pipe has no constriction and therefore no hydraulic holding force or cannot use it, the intermediate pipe 33 is clamped between the underside of the piston rod guide 31 and a clamping ring 53, with the clamping ring in turn being located on the bottom 55 of the

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vibration damper. During assembly, the clamping ring is inserted into the vibration damper. The intermediate pipe is then inserted and the intermediate pipe is pre-tensioned via the piston rod guide, whereby the clamping ring deforms and reliably holds the intermediate pipe.

Claims (17)

Protection claims 1. Vibration damper, comprising a pressure pipe in which a piston with a piston rod is arranged so as to be axially movable and the pressure pipe is divided into an upper and a lower working chamber, the upper working chamber being connected to an oil sump of a compensation chamber via a fluid connection, at least one damping valve at least for the flow direction from the upper to the lower working chamber in the piston, a passage valve between a connection opening in the upper working chamber and the oil sump, a check valve within a bottom valve body which connects the lower working chamber to the compensation chamber, characterized in that at least one damping valve (25) is additionally designed for the piston valve(s) (19) and in the retraction direction a damping from the damping valve (25) is used, which takes place depending on the volume flow distribution due to the flow resistances in the valves (19; 25), so that a superimposed pressure damping of the valves (19; 25) results, the maximum displaced volume being limited by the damping valve (25). of the lower working chamber (11) and minimally the displaced volume of the piston rod (5) flows and the flow resistance within the fluid connection (13) in the flow direction from the oil sump (15) into the upper working chamber (9) through a direction-dependent effective passage valve (29) is lower than in the opposite flow direction. 2. Vibration damper according to claim 1, characterized in that the fluid connection (13) starting from the connection opening(s) ends directly in the oil sump (15) while bypassing the pressure pipe (3). &bull; · · rf* ·· Reg. No. 13 803 DE1 \. ^:: .. ^: * .:..:. ..·...* 28.11.95 3. Vibration damper according to claim 2, characterized in that the fluid connection is formed by the concentric arrangement of the pressure pipe and an intermediate pipe (33) enveloping the pressure pipe, the direction-dependent passage valve (29) being arranged within the annular fluid connection. ........ 4. Vibration damper according to claim 2, characterized in that the fluid connection is formed by a tubular body which runs essentially parallel to the longitudinal axis of the vibration damper. 5. Vibration damper according to claim 4, characterized in that the tubular body is formed by a flexible hose. 6. Vibration damper according to claim 1, characterized in that the direction-dependent passage valve (29) is formed by a slotted ring (51) which is attached to the inner diameter of the pressure pipe. 7. Vibration damper according to claim 1, characterized in that the direction-dependent passage valve (29) is formed by a spring disk (47) which at least partially covers a channel in the piston rod guide (31). 8. Vibration damper according to claim 7, characterized in that the spring washer is clamped between the pressure tube and the piston rod guide. 9. Vibration damper according to claim 8, characterized in that the spring washer is centered on a radial guide (49) of the piston rod guide (31). 10. Vibration damper according to one of claims 1 to 7, characterized in that the direction-dependent passage valve (29) consists of an Reg. No. 13 803 DE1 \. ^: \. ^: * .:. .:. * *'. ^: ... ^: 28.11.95 lacing (37) in the fluid connection (13) with an axially movable valve body (41). 11. Vibration damper according to claim 10, characterized in that the constriction extends over the essential length of the fluid connection up to the connection opening (35). 12. Vibration damper according to claim 2, characterized in that the bottom valve body (21) extends radially from the pressure pipe (3) into the fluid connection (13) and is part of the direction-dependent φ of the passage valve (29). 13. Vibration damper according to claim 2, characterized in that the bottom valve body in the fluid connection has an axial support surface (45), on which a separate valve ring (43) is supported as a component of the direction-dependent pass valve (29). 14. Vibration damper according to claim 11, characterized in that the intermediate tube (33) is mounted in an axially floating manner and is supported on the piston rod guide (31). 15. Vibration damper according to claim 3, characterized in that the intermediate tube (33) is fixed between the piston rod guide (31) and a clamping ring (53) on the bottom (55) of the vibration damper (1). 16. Vibration damper according to claim 1, characterized in that the direction-dependent passage valve is designed as a check valve. 17. Vibration damper according to one of claims 1 to 16, characterized in that the valves in the piston (5) and/or bottom valve body (21) are adjustable.