Valve for a vibration damper, vibration damper, and motor vehicle

Abstract

Valve for a vibration damper having a valve housing and a valve slide movable in the valve housing to at least partially close at least one flow path of a fluid flowing through the valve. The valve has an input side and an output side. Pressure impingement surfaces of the valve slide are substantially equal for an opening pressure and for a closing pressure, and the valve slide has a restriction through which a pressure difference between opening pressure and closing pressure can be generated.

Claims

1. A valve for a vibration damper comprising: a valve housing; an input side of the valve; an output side of the valve; a valve slide arranged movably in the valve housing and configured to at least partially close at least one flow path of a fluid flowing through the valve; respective pressure impingement surfaces of the valve slide for an opening pressure and for a closing pressure that are substantially equal, and a restriction of the valve slide through which a pressure difference between opening pressure and closing pressure can be generated.

2. The valve according to claim 1, wherein the valve slide is pretensioned by a force accumulator.

3. The valve according to claim 1, wherein the restriction is a circular narrowing.

4. The valve according to claim 1, wherein the valve slide has a first flow area at the output side in a first operating position, and a second flow area in a second operating position, wherein the first flow area is greater than the second flow area.

5. The valve according to claim 4, wherein walls of the valve slide on the output side define at least one recess.

6. The valve according to claim 5, wherein the valve slide at least two symmetrically arranged recesses.

7. The valve according to claim 1, wherein a main flow path configured to be closed by the valve slide is fluidically connected as flow path with the output side of the valve.

8. The valve according to claim 1, wherein a bypass path which can be closed by the valve slide is fluidically connected as a flow path with the input side of the valve.

9. The valve according to claim 8, wherein at least one guide of the valve slide has at least one recess connecting the bypass path and a space in which the at least one guide can be raised and lowered simultaneous with the valve slide.

10. The valve according to claim 8, further comprising a pressure limiting valve is arranged in the bypass path.

11. The valve according to claim 10, wherein the pressure limiting valve is a check valve that is pretensioned in closing direction.

12. A vibration damper for a motor vehicle, comprising: a valve comprising: a valve housing; an input side of the valve; an output side of the valve; a valve slide arranged movably in the valve housing and configured to at least partially close at least one flow path of a fluid flowing through the valve; respective pressure impingement surfaces of the valve slide for an opening pressure and for a closing pressure that are substantially equal, and a restriction of the valve slide through which a pressure difference between opening pressure and closing pressure can be generated.

13. The vibration damper according to claim 12, wherein the vibration damper comprises: an inner tube element, a center tube element, and an outer tube element arranged one inside the other; and a displaceable piston arranged in the inner tube element, wherein the valve is arranged at or inside the inner tube element, wherein the center tube element separates a main flow path from a bypass path, wherein the main flow path and the bypass path are fluidically connected to the interior of the inner tube element.

14. The vibration damper according to claim 13, wherein a damping force generating device is arranged in the main flow path.

15. A motor vehicle comprising a vibration damper comprising: a valve comprising: a valve housing; an input side of the valve; an output side of the valve; a valve slide arranged movably in the valve housing and configured to at least partially close at least one flow path of a fluid flowing through the valve; respective pressure impingement surfaces of the valve slide for an opening pressure and for a closing pressure that are substantially equal, and a restriction of the valve slide through which a pressure difference between opening pressure and closing pressure can be generated.

16. The valve according to claim 2, wherein force accumulator is a spring.

17. The valve according to claim 4, wherein the first operating position is a normal operating position, and the second operating position is an overload position.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further embodiments, details and features are indicated in the embodiment examples and figures described in the following. The drawings show:

(2) FIG. 1 is a portion of a vibration damper in longitudinal section;

(3) FIG. 2 is a valve slide;

(4) FIG. 3 is a pressure limiting valve;

(5) FIG. 4 is a guide portion in cross section;

(6) FIG. 5 is a diagram showing the dimensions of a valve slide; and

(7) FIG. 6 is a hydraulic circuit diagram.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

(8) FIG. 1 shows a portion of a vibration damper 1 with an inner tube element 2, an outer tube element 3, a center tube element 4 arranged between the inner tube element 2 and outer tube element 3, and a valve 5. A bypass path 6 is located between the inner tube element 2 and center tube element 4, and a main flow path 7 is located between the center tube element 4 and outer tube element 3. A damping force generating device, e.g., a damper valve 8, which is to be protected against excessively large volume flows, is located in the main flow path 7 or in the fluidic connection to the main flow path 7. A piston 9, which either works as a simple displacer or which has a compression valve that opens under very high pressures, is provided in the inner tube element 2. The valve 5 substantially comprises a valve slide 10, a valve housing 12 comprising housing parts 14 and 16, a spring 18, a pressure limiting valve 20, and feet 22.

(9) FIG. 2 shows the valve slide 10 in more detail. The valve slide 10 has an input side 24 on the piston side and an output side 26 remote of the piston. The terms piston side and remote of the piston refer to the valve 5 in installed state in a vibration damper 1. In the following, the valve slide will be described from the input side 24 toward the output side 26. The top of the valve slide 10 is formed by surfaces 28, 30, and 32. Surface 28 is on a narrow annular projection that leads towards the outer side to a surface 30 which is likewise annular. Surface 28 is the valve surface of the valve 5 constructed as a seat valve. Toward the inside, surface 32 forms a conically narrowing funnel that opens into the side surface 34. Surface 38 follows the side surface 34 extending parallel to the outer side 36. Surface 38 has a greater slope relative to side surface 34 than surface 32; that is, surface 38 and side surface 34 form a smaller angle than that formed by surface 32 and side surface 34. In other words, the narrowing formed by the restriction 40 becomes wider again more quickly on the output side 26 than on the input side 24. In this way, the pressure difference between input side 24 and output side 26 can be controlled.

(10) On the output side 26, surface 38 is followed by side surface 34 and surface 44.

(11) FIG. 2 shows the following characteristics for pressure-balancing the valve 5.

(12) The inner edge 46 of the valve slide 10 lies in a (longitudinal) plane with the outer side 36. This is the same plane in which the valve slide 10 terminates outwardly on the output side 26. Accordingly, the surfaces impinged by the opening pressure p.sub.1 and the closing pressure p.sub.2 are the same size. The pressure impingement surfaces can be determined through a projection of the cross section on a plane perpendicular to the longitudinal axis or movement direction of the valve slide 10. In other words, as long as the inner diameter and outer diameter of the two pressure impingement surfaces are equal, they are impinged equally with the same opening pressure p.sub.1 and closing pressure p.sub.2 regardless of the slope of surfaces 32, 38 and 44. In this embodiment of the valve slide 10, however, a pressure difference is produced by the volume flow flowing through the valve slide 10. This results in the following manner:

(13) The resulting force on the slide F equals the difference between the opening pressure p.sub.1 and the closing pressure p.sub.2 which are multiplied, respectively, by the pressure-impinged surface. The pressure impingement surface a.sub.1 for the opening pressure p.sub.1 can be determined by the diameter of the valve slide 10 on one side at the height of surface 28 (diameter d.sub.sf) and at the height of side surface 34 (diameter d.sub.si). In other words, the diameters at the valve surface, in this case the outer diameter of surface 28, and at the restriction 40 are to be used to calculate area a.sub.1. Using simple geometric circle calculations, area a.sub.1 is accordingly equal to the difference between a larger-area circle at the height of surface 28 and a smaller circle at the height of side surface 34. Equal diameters are used in calculating pressure impingement surface a.sub.2 of closing pressure p.sub.2 so that areas a.sub.1 and a.sub.2 are equal. This results as follows: to calculate the pressure-impinged surface a.sub.2 during closing pressure p.sub.2, diameter d.sub.si at restriction 40 is used on the one hand as for the opening pressure p.sub.1, and the diameter defined by the outer edge 50 of surface 52 is used on the other hand. Owing to the fact that fluid and therefore pressure also impinges on surface 52, the diameter to be utilized is defined by the outer edge 50 of surface 52 and not by the inner edge 48, which is also possible in principle. Accordingly, however, diameters that are exactly equal to those used for calculating the pressure impingement surface a.sub.1 enter into the calculation of pressure impingement surface a.sub.2. Therefore, a pressure difference results only by reason of the volume flow of the moving fluid, and this pressure difference depends on the diameter or cross-sectional area a.sub.4 of the restriction 40.

(14) On the output side, the valve slide 10 has a plurality of recesses 53. These recesses 53 can be passages from the underside of the valve slide 10, as is shown here, but can also be arranged as a type of window at some distance from the underside so that the valve slide 10 is closed on the underside. Of course, the recesses 53 extend through the wall of the valve slide so that there is always a minimum volume flow even in the overload position. Valve slide 10 is arranged in the normal operating position in FIG. 1 and in FIG. 2. This preferred position results from the pretensioning by spring 18. In the embodiment according to FIGS. 1 and 2, the normal operating position is characterized in that the valve surface, i.e., surface 28, is pressed against the opposite surface, namely, the valve seat surface 29. The bypass path 6 is closed in this position.

(15) On the input side 24, the valve slide 10 has an annular guide 54 with a plurality of axially penetrating recesses 56. As a result of the recesses 56, the fluid in the bypass path 6 communicates with the annular space outside of the valve slide 10. There is also a certain hollow space resulting from the lift path of the guide 54 during the movement of the valve slide 10 also without the spring 18 being arranged below the guide 54. When the spring 18 is arranged between guide 54 and valve housing 12, this hollow space is larger on the outer side 36 of the valve slide. The connection of the bypass path 6 and the space on the outside of the valve slide 10 ensures a defined pressure in this space outside of the valve slide 10. This further improves the pressure balance of the valve 5. Further, the recesses 56 have a defined cross section for damping the movement of the valve slide 10 during greater changes in volume flow.

(16) FIG. 3 shows the pressure limiting valve 20 according to FIG. 1 in detail. The pressure limiting valve 20 is formed as a check valve which is pretensioned in closing direction. Pressure limiting valve 20 comprises at least one elastically deformable disk 58, two rings 60 and 62 and a disk package 4. The ring 60 is supported on the elastically deformable disk 58, and the disk package 64 is fixed between rings 60 and 62. The deviation point 66 of the ring 60 is located such that an opening pressure of several bar, preferably between 2 bar and 15 bar, must be overcome before the fluid flows through the bypass path 6, which prevents the pressure from dropping abruptly at the damping valve 8 in the main flow path 7 when the bypass path 6 opens.

(17) An oil reservoir 68 is provided below the elastically deformable disk 58.

(18) FIG. 4 shows the valve slide 10 in a top view. The guide 54, which is circular per se, with surface 30 is flattened on four sides so that recesses 56 are formed. These recesses 56 are located between the guide 54 and the valve housing 12 in which the valve slide 10 is movable along the guide 54.

(19) Of course, a quantity of recesses other than four can also be used; regardless of their quantity, the recesses 56 are arranged symmetrically to improve pressure balance.

(20) To illustrate the dimensions mentioned with reference to FIG. 2, FIG. 5 shows these dimensions separately from FIG. 2 for the sake of clarity. The indicated diameters have reference characters starting with a d, while areas are denoted by a. Of course, the surfaces extending perpendicular to the drawing plane are not depicted as such. The following dimensions are given proceeding from the input side 24:

(21) The vibration damper 1 in which the valve 5 can be installed presents an inlet diameter. The next diameter shown is the inner diameter d.sub.sf along the inner edge of surface 28. Both pressure impingement surface a.sub.1 and pressure impingement surface a.sub.2 can be calculated via this inner diameter d.sub.sf depending on inner diameter d.sub.si. Further, the inner diameter d.sub.si predetermines the cross-sectional area a.sub.4 of the restriction 40:

(22) $a_1=.Math.{\left(\frac{d_{\mathrm{sf}}}{2}\right)}^2-.Math.{\left(\frac{d_{\mathrm{si}}}{2}\right)}^2$$a_2=.Math.{\left(\frac{d_{\mathrm{sf}}}{2}\right)}^2-.Math.{\left(\frac{d_{\mathrm{si}}}{2}\right)}^2$$a_4=.Math.{\left(\frac{d_{\mathrm{si}}}{2}\right)}^2$

(23) It should be noted that the first part of the formulas for calculating a.sub.1 and a.sub.2 correspond because the diameter along the inner edge of surface 28 for calculating a.sub.1 and the diameter at the outer edge 50 of surface 52 for calculating a.sub.2 are equal because of the structural design of the valve slide 10.

(24) FIG. 5 further shows the outer diameter d.sub.da, the distance h.sub.b of surface 28 from valve seat surface 29, and the distance h.sub.d from surface 52 to the base of the main flow path 7. Distance h.sub.b represents the height of the opening of the bypass path 6 and distance h.sub.d shows the height of the outlet area a.sub.31.

(25) Outlet area a.sub.31 is an annular area which is the product of a circumference and a height. The circumference depends on the diameter d.sub.ik defined by the inner edge 48; the height is, as was described above, the distance h.sub.d from surface 52 to the base of the main flow path 7. In the overload position, distance h.sub.d is equal to zero, and it reaches its maximum value in the normal operating position. Accordingly, the outlet area a.sub.31 can also vary from zero to a maximum value:

(26) $a_{31}=2.Math..Math.\frac{d_{\mathrm{ik}}}{2}.Math.h_d.$

(27) Outlet area a.sub.32 designates the area defined by all of the recesses 53. Outlet area a.sub.32 is that area in the main flow path 7 that is always open for producing a minimum flow. The total cross-sectional area a.sub.3 is equal to the sum of areas a.sub.31 and a.sub.32.

(28) Outlet area a.sub.5 is also an annular area. The circumference which, must be determined, is equal to the inner diameter d.sub.sf and the height is equal to distance h.sub.b:

(29) $a_5=2.Math..Math.\frac{d_{\mathrm{sf}}}{2}.Math.h_b.$

(30) Like distance h.sub.d, distance h.sub.b can vary from zero to a maximum value and, of course, the value of distance h.sub.b can be smaller if distance h.sub.b is larger.
h.sub.b+h.sub.d=const.

(31) Of course, this only applies when the flow area at the output side 26 can be varied. On the other hand, in an embodiment in which only the bypass path 6 is opened and closed and the flow area of the main flow path 7 remains constant, the total cross-sectional area a.sub.3 is constant, in which case it need not be formed of a plurality of areas.

(32) Outer diameter d.sub.da is the outer diameter of the guide 54 at the locations with no recesses 56. This diameter is also shown in FIG. 4. The flow area ad to the lift space or lift/spring space is indicated at a recess 56 in FIG. 5; however, it is equal to the sum of all of the surface areas of the recesses 56.

(33) The cross-sectional area a.sub.6 of the pressure limiting valve 20 is shown in FIG. 3 rather than in FIG. 5. Like outlet areas a.sub.31 and a.sub.5, cross-sectional area a.sub.6 is an annular area. The height corresponds to the height of the gap opened by the disk package 64, which height can accordingly be varied between zero and a maximum value. The circumference for calculating cross-sectional area a.sub.6 is defined by support point 67. Support point 67 is, of course, only a point in cross section; in actuality, it is a support circle.

(34) FIG. 6 shows a hydraulic schematic diagram of the valve according to FIG. 1. The dimensions shown in the drawing correspond to the dimensions which were used in the previous description of the figures. Owing to a piston movement, a total volume flow Q.sub.ges is present on the input side 24 of valve 5. The restriction 40 with an area a.sub.4 lies between the opening pressure p.sub.1 and the closing pressure p.sub.2. Area a.sub.4 of restriction 40 is evident from inner diameter d.sub.si. Following the restriction 40 in the flow path is total cross-sectional area a.sub.3 which is given by outlet area a.sub.31 and outlet area a.sub.32 in the normal operating position and only by outlet area a.sub.32 in the overload position. In the overload position, outlet area a.sub.31 is closed by the valve slide 10. Instead, outlet area a.sub.5 which connects the input side 24 and the bypass path 6 is open. Accordingly, at the output side 26 the valve slide 10 has a larger flow area in a first operating position, namely, the normal operating position, and a smaller flow area in a second operating position, namely, the overload position.

(35) It further follows from FIG. 6 that the total volume flow Q.sub.ges comprises partial volume flows Q.sub.1 and Q.sub.2. Q.sub.1 is the volume flow flowing in the bypass path 6 and Q.sub.2 is the volume flow flowing in the main flow path 7. In the normal operating position, total volume flow Q.sub.ges and partial volume flow Q.sub.2 are identical, since the bypass path 6 is closed. Further, a compensation space 70 which is not shown in FIGS. 1 to 5 can be seen in FIG. 6. The compensation space 70 fluidically communicates with the interior volume of the inner tube element 2. This receives the fluid volume displaced by the piston rod. Oil is preferably used as fluid; however, the valve 5 may be operated with any incompressible fluid in principle.

(36) Thus, while there have shown and described and pointed out fundamental novel features of the invention as applied to a preferred embodiment thereof, it will be understood that various omissions and substitutions and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit of the invention. For example, it is expressly intended that all combinations of those elements and/or method steps which perform substantially the same function in substantially the same way to achieve the same results are within the scope of the invention. Moreover, it should be recognized that structures and/or elements and/or method steps shown and/or described in connection with any disclosed form or embodiment of the invention may be incorporated in any other disclosed or described or suggested form or embodiment as a general matter of design choice. It is the intention, therefore, to be limited only as indicated by the scope of the claims appended hereto.