VIBRATION DAMPER HAVING A PUMP ASSEMBLY

Abstract

A vibration damper comprising a working cylinder, which is subdivided by an axially movable piston on a piston rod into a first and a second working chamber filled with a damping medium is disclosed. The vibration damper has at least one compensating reservoir for receiving the damping medium displaced by the piston rod. There is a flow connection between the two working chambers, in which connection there is incorporated a pump assembly. The pump assembly has a fluctuation in the delivery volume with a constant power supply. At least one pulsation accumulator is arranged within the flow connection, wherein the volume and spring rate of the pulsation accumulator are matched to a frequency of a fluctuation of the delivery volume of the pump assembly.

Claims

1. A vibration damper comprising a working cylinder, which is subdivided by an axially movable piston on a piston rod into a first and a second working chamber filled with a damping medium, wherein the vibration damper has at least one compensating reservoir for receiving the damping medium displaced by the piston rod, wherein there is a flow connection between the first and second working chambers, in which connection there is incorporated a pump assembly, which has a fluctuation in a delivery volume with a constant power supply, wherein, in addition to the at least one compensating reservoir, at least one pulsation accumulator is arranged within the flow connection, the volume and spring rate of the pulsation accumulator being matched to the frequency of the fluctuation of the delivery volume of the pump assembly.

2. The vibration damper according to claim 1, wherein the vibration damper has a separate pulsation accumulator for each of the first and second working chambers.

3. The vibration damper according to claim 1, wherein the pulsation accumulator has two accumulator chambers that are separated from one another by a separating piston, and in each case one accumulator chamber is connected to in each case one of the first and second working chambers of the working cylinder.

4. The vibration damper according to claim 3, wherein the accumulator chamber is connected to a delivery side of the pump assembly and to a suction-side working chamber of the vibration damper.

5. The vibration damper according to claim 1 wherein the separating piston of the pulsation accumulator has a gap seal between the accumulator chamber and a rear chamber.

6. The vibration damper according to claim 1, wherein the separating piston of the pulsation accumulator has a stop, by which a maximum working volume of the accumulator chamber is determined.

7. The vibration damper according to claim 1, wherein the at least one pulsation accumulator is embodied in a housing of the pump assembly.

8. The vibration damper according to claim 7, wherein the pump assembly has one outlet chamber for each conveying direction, which outlet chambers are arranged next to one another in the housing, wherein the pulsation accumulator is arranged within the housing in a lateral region which is common to the outlet chambers.

9. The vibration damper according to claim 8, wherein the pulsation accumulator is aligned in a manner radially offset with respect to a principal axis of the housing.

10. The vibration damper according to claim 8, wherein the pump assembly has a pump chamber whose base area extends at right angles to a principal axis of the pump assembly, wherein the pulsation accumulator is arranged in a plane parallel to the base area.

11. The vibration damper according to any of claim 1 wherein at least one flow connection between the pulsation accumulator and the pump assembly is adjustable in its cross section by means of a valve.

12. The vibration damper of claim 2, wherein the pulsation accumulator has two accumulator chambers that are separated from one another by-a separating piston, and in each case one accumulator chamber is connected to in each case one of the first and second working chambers of the working cylinder.

13. The vibration damper according to claim 12, wherein the accumulator chamber is connected to a delivery side of the pump assembly and to a suction-side working chamber of the vibration damper.

14. The vibration damper according to claim 2, wherein the separating piston of the pulsation accumulator has a gap seal between the accumulator chamber and a rear chamber.

15. The vibration damper according to claim 2, wherein the separating piston of the pulsation accumulator has a stop, by which a maximum working volume of the accumulator chamber is determined.

16. The vibration damper according to claim 1, wherein the compensating reservoir is arranged functionally between two adjustable damping valves.

17. The vibration damper according to claim 16, further comprising a non-return valve connection hydraulically in parallel with each adjustable damping valve such that the adjustable damping valves generate a damping force only for one operation direction of the vibration damper.

18. The vibration damper according to claim 1, wherein the pulsation accumulator is connection hydraulically in parallel with a delivery chamber of a pump in a flow connection.

19. The vibration damper according to claim 3, wherein a return spring is claimed on both sides of the separating piston.

20. The vibration damper according to claim 1, wherein the pump assembly has two delivery directions to selectively fill both working chambers with additional damping medium volume.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0020] The disclosure will be explained in greater detail with reference to the following description of the figures, of which:

[0021] FIG. 1 shows an equivalent diagram of a vibration damper having a pump assembly;

[0022] FIG. 2 shows an alternative variant to FIG. 1;

[0023] FIG. 3 shows a pulsation accumulator according to FIG. 1 as an individual part;

[0024] FIGS. 4-7 show pulsation accumulators within a pump assembly; and

[0025] FIG. 8 shows an alternative variant based on FIG. 7.

DETAILED DESCRIPTION

[0026] FIG. 1 shows an equivalent diagram for a vibration damper 1 having a working cylinder 3, which is subdivided by an axially movable piston 5 on a piston rod 7 into a first and a second working chamber 9; 11 filled with a damping medium. It is irrelevant here whether this is a single-tube or double-tube vibration damper known per se. The vibration damper 1 has at least one compensating reservoir 13 for receiving the damping medium displaced by the piston rod 7. In this exemplary arrangement, the compensating reservoir 13 is arranged functionally between two adjustable damping valves 15;17, wherein, in an outflow direction from the adjustable damping valves 15; 17, the compensating reservoir 13 is connected to a flow connection 19 between the two working chambers 9; 11. By way of example, a non-return valve 21; 23 is connected hydraulically in parallel with each adjustable damping valve 15; 17, with the result that the adjustable damping valves 15; 17 generate a damping force only for one operating direction of the vibration damper 1. There is absolutely no need for the adjustable damping valves 15; 17 to be arranged in a manner spatially separate from the working cylinder 3.

[0027] Between the two working chambers 9; 11 there is a further flow connection 25, in which a pump assembly 27 comprising a pump 29 and a pump drive 31 is incorporated. The further flow connection 25 need not necessarily be set up in a manner completely spatially separate from the first flow connection 19 with the adjustable damping valves 15; 17.

[0028] The pump assembly 27 comprises an alternately conveying pump 29, in one exemplary arrangement, a gear pump. In many types of pumps, there is a fluctuation in the delivery volume despite a constant power supply. This fluctuation leads to noises, which can be transmitted to a vehicle body (not illustrated). In order to minimize these noises, at least one pulsation accumulator 33 is arranged within the further flow connection 25 in addition to the at least one compensating reservoir 13, the volume and spring rate of the pulsation accumulator being matched to the frequency of the fluctuation of the delivery volume of the pump assembly 27.

[0029] As can be seen from the equivalent diagram, the pump assembly 27 has two delivery directions in order to selectively fill both working chambers 9; 11 with additional damping medium volume or to maintain only an operating pressure. For this reason, the vibration damper 1 has a separate pulsation accumulator 33; 35 for each working chamber 9; 11. The pulsation accumulator 33; 35 is connected hydraulically in parallel with a delivery chamber 37; 39 of the pump 29 in a third flow connection 41. In this equivalent diagram, the pulsation accumulators 33; 35 have two accumulator chambers 43; 45, which are separated from one another by a separating piston 47. Thus, two pulsation accumulators 33; 35 are arranged in a common housing 49. One accumulator chamber 43; 45 each is connected to one working chamber 9; 11 of the working cylinder 3. A return spring 51; 53 is clamped on both sides of the separating piston 47. Thus, starting from the delivery chamber of the pump, a hydraulic pressure force acts on the separating piston 47, wherein this pressure force is based on a pressure level as in the connected working chamber 9; 11. However, the pulsation accumulator 33; 35 also has a connection via the flow connection to the suction chamber within the vibration damper 1, that is to say the chamber from which the pump assembly 27 delivers during instantaneous operation. Thus, in addition to the return spring 51; 53, the separating piston 47 is acted upon by a pressure force based on the pressure level of the suction chamber. Consequently, the return spring 51; 53 can be dimensioned to be significantly weaker than if the pressure force contribution of the suction chamber were omitted. The return springs 51; 53 are designed in such a way that the differential pressure which the pump 29 builds up is supported.

[0030] To optimize the response behaviour of the pulsation accumulator 33; 35, the separating piston 47 of the pulsation accumulators 33; 35 has a gap seal 55 between the accumulator chamber 43 and a rear chamber 57 in which the return spring 51; 53 is arranged. In the case of a combination of two pulsation accumulators 33; 35, each of the two chambers is an accumulator chamber or a rear chamber, depending on the operating direction. Furthermore, the separating piston 47 is made of plastic. With the associated reduction in mass, the natural frequency of the pulsation accumulators 33, 35 is to be raised to a speed or delivery range which is not reached by the pump in normal operation or is selectively not approached.

[0031] FIG. 2 shows that there is no need at all for the two pulsation accumulators 33; 35 to be spatially connected to one another. The choice between the two variants depends on the installation space conditions in the specific application. The advantage of this variant is that the return springs 51; 53 have no reciprocal dependency with respect to their spring forces.

[0032] FIG. 3 shows the pulsation accumulator according to FIG. 1 as an individual part. The separating piston 47 is mounted in an axially movable manner in the housing 49. The separating piston 47 has a T-shaped cross section, wherein end faces 59; 61 each define a stop for the maximum displacement travel of the separating piston 47 within the pulsation accumulators 33; 35 and thus also the maximum working volume of the accumulator chamber. The working volume is calculated from the outer annular space multiplied by the maximum displacement travel of the separating piston 47 starting from an initial position with an inactive pump assembly 27. Therefore, the total storage volume of the housing 49 can be significantly larger in order to still obtain installation space for the return spring 51; 53. The return spring 51; 53 is clamped in each working direction between a bottom 63; 65 of the housing 47 and a circumferential flange 67, which forms the separating piston 47.

[0033] It is advantageous to design the return springs in such a way that, in the central position, that is to say when the pump has not built up any differential pressure, they do not exert any preloading force on the separating piston. As a result, only the rigidity of a return spring is relevant for each pressure direction. A rigidity which is as low as possible improves the insulation behaviour of the device. In the case of mutually preloaded return springs, the total stiffness would be relevant and the insulating effect would be impaired.

[0034] At least two connections 69 for the flow connection 41 to the pump 29 are provided in the housing 47.

[0035] Viewing FIGS. 4 to 7 together shows a design example of a pump assembly 27 in which at least one pulsation accumulator 33; 35 is embodied in a housing 71 of the pump assembly 27. In FIGS. 4 and 5, the pump drive 31 has been omitted in order to simplify the illustration. The pump chamber 75 of the pump 29 is arranged in a housing end section 73 (FIG. 5). The bearing locations 77; 79 for one of the gears (not illustrated) of the pump designed as a gear pump can be seen. The suction chamber and the delivery chamber are to be regarded as the pump chamber 75.

[0036] In the plan view according to FIG. 7, the bearing location 77 of one of the gears used can be seen. The outer surface of the pump chamber 75 forms a bearing location for the other gear of the pump. A first transverse axis of the housing 71 extends vertically within the sectional plane through the bearing location 77. A second transverse axis 85 extends at right angles thereto through the bearing location 77. The two transverse axes 83; 85 separate four quadrants within the sectioned plane in FIG. 7. The pump assembly 27 has one outlet chamber 87; 89 for each delivery direction. A first outlet chamber 87 extends within the first and fourth quadrants Q1; Q4. A second outlet chamber is arranged mirror-inverted with respect to the second transverse axis 85 and extends within the second and the third quadrant Q2; Q3. Consequently, the two outlet chambers 87; 89 are arranged next to one another in the housing 71. The housing region for the pulsation accumulator, which is formed by the housing of the pump assembly, is arranged in a lateral region which is common to the outlet chambers, namely the first and the second quadrant Q1; Q2. The pulsation accumulators 33, 35 are thus aligned in a manner radially offset with respect to a principal axis 91 of the housing 71. The principal axis is formed by the longitudinal axis of the pump assembly 27, which in turn has the same alignment as the bearing locations 77; 79 for the gears of the pump. As can be clearly seen, the flow connection 41 between the pulsation accumulator 33; 35 and the outlet chambers 87; 89 is formed by very short straight channels which can be produced very easily. In addition, the pulsation accumulators 33; 35 are placed in a very stable cover region of the pump assembly 27, thus ensuring that no relevant vibrations of the housing walls can occur. Viewing FIGS. 4 and 7 together, it is clear that the pump chamber 75, which also comprises the two outlet chambers 87; 89, extends with its base surface at right angles to the drive axis or to the principal axis 91 of the pump assembly 27, wherein the pulsation accumulators 33; 35 are arranged in a plane parallel to the base surface of the pump chamber 75.

[0037] FIG. 8 is based on the illustration according to FIG. 7. In addition, the pump assembly 27 has a valve 93 for setting the cross section of the flow connection 41 between the pulsation accumulator 33 and the outlet chamber 87. In the case of a combined arrangement of the two pulsation accumulators 33; 35, a single valve 23 is sufficient. In this way, the inflow to the pulsation accumulator can be controlled for one delivery direction of the pump assembly 27 and the outflow from the pulsation accumulator can be controlled for the other delivery direction. The control can optionally be configured as an on/off valve or as a continuously adjustable valve. This enables the pulsation accumulator 33; 35 to be deactivated or its influence reduced when it is not required.