WO2010015647A1

WO2010015647A1 - Magnetorheological valve

Info

Publication number: WO2010015647A1
Application number: PCT/EP2009/060138
Authority: WO
Inventors: Christoffer Kieburg; Claus Gabriel; Günter OETTER; Jürgen PFISTER; Martin Laun
Original assignee: Basf Se
Priority date: 2008-08-06
Filing date: 2009-08-05
Publication date: 2010-02-11

Abstract

The invention relates to a valve through which a magnetorheological fluid can flow, comprising a valve channel (7) through which a magnetic field (25) can flow, wherein at least one magnet is surrounded by at least one yoke for generating the magnetic field (25) and wherein opposing surfaces of a gap in a split yoke or opposing surfaces of two yokes (3, 5) form opposing walls of the valve channel (7). The valve channel (7) comprises a change in cross sectional area in the direction of flow (15) of the magnetorheological liquid, wherein the ratio of the maximum cross sectional area of the valve channel (7) to the minimum cross sectional area is in the range of 1.5 to 200. The invention further relates to a damper comprising a cylinder (45) with a piston (43) that can move in the axial direction inside the cylinder (45), wherein two chambers (57, 59) are formed in the cylinder, said chambers being separated from one another by the piston (43). A magnetorheological liquid is contained in the chambers (57, 59). At least one valve (1) according to the invention is housed in the piston (43), the magnetorheological liquid being able to flow through said valve from one chamber (57, 59) to the other (57, 59).

Description

Magnetorheological valve

description

The invention relates to a valve which can be traversed by a magnetorheological fluid, comprising a channel, which can be traversed by a magnetic field, wherein at least one magnet with at least one yoke is included for generating the magnetic field, and opposite surfaces of a gap in a split yoke or form opposite surfaces of two yokes opposite walls of the channel.

Magnetorheological valves, that is to say valves which can be flowed through by a magnetorheological fluid, are used, for example, in dampers, such as those used, for example, for suspension damping in motor vehicles.

Such a magnetorheological valve conventionally comprises an equidistant channel formed between two opposed surfaces of a split yoke gap or between two yokes of a permanent magnet or electromagnet, or the combination of both. The magnet is used to generate a homogeneous magnetic field perpendicular to the yoke wall. Under the action of the magnetic field, a high yield point is built up in the magnetorheological fluid, so that when the throughput is set, there is an increased pressure drop along the magnetized channel. The ratio of pressure drop with and without magnetic field is called stroke.

For technical applications of magnetorheological valves, for example in controllable dampers, a high pressure drop combined with a large stroke with the smallest possible weight of the field generator is sought.

A magnetorheological valve used in a damper is known, for example, from US-B 7,051,849. The magnetorheological valve is formed in a piston of a damper. The piston contains a plurality of channels, which can be flowed through by a magnetorheological fluid from a first chamber of the damper in a second chamber of the damper. In the piston, a coil is arranged to form a magnetic field in the channels. As a magnetorheological valve, however, only a portion of the channel, which is traversed by the magnetic field generated by the coil acts.

Magnetorheological dampers in which channels with equidistant walls are formed in the piston and in the piston a coil for generating a magnetic field are also known, for example from US-B 6,786.31 1, US 6,158,470, US-B 6,874,603 or US-B 6,311,810.

As an alternative to the embodiment with channels formed in the piston, it is also known to form a gap between piston and cylinder wall, which can be flowed through by the magnetorheological fluid. In general, a coil is also accommodated in the piston in this case, with which a magnetic field can be generated in the gap. Corresponding dampers are known, for example, from US 5,277,281 or from US 5,284,330.

A damper for receiving an internal combustion engine in a vehicle is described in US 5,176,368. This comprises an inner and an outer cylinder, which are arranged concentrically. Inside an axially displaceable hub is arranged. Between the hub and the housing, a chamber is formed in which a magnetorheological fluid is contained. A second electromagnetic unit is attached to the outer cylinder. Between the cylinders and the electromagnetic units, a gap with a constant cross-sectional area is formed in each case. In the electromagnetic units coils are arranged, each of which abuts against the surface of the electromagnetic unit, but whose axis is rotated by 90 ° to the hub axle se.

Also, a damper having an annular gap containing a magnetorheological fluid is disclosed in US 5,344,129. Furthermore, an oscillating plate is included, which is located away from the chamber containing the magnetorheological fluid. The unit is used as a vibration damper, for example for mounting a motor.

Disadvantage of the damper units known from the prior art is that to move the piston of the damper too high a basic force without magnetic field is required. In order to achieve a displacement of the piston with little force without applied magnetic field, for example, additional gaps are provided which are not flowed through by a magnetic field, so-called bypasses. Such bypasses, in which no magnetic field acts or in which the magnetic field is significantly reduced, also serve to generate a special force-velocity characteristic.

The object of the present invention is to provide a valve, which can be traversed by a magnetorheological fluid, in which a smaller force is required to move the magnetorheological fluid through the channel when no magnetic field is applied. The object is achieved by a valve which can be traversed by a magnetorheological fluid, wherein the valve comprises a channel, which can be traversed by a magnetic field and for generating the magnetic field comprises at least one magnet with at least one yoke, and opposite surfaces of a gap in a split yoke or opposite surfaces of two yokes form opposite walls of the canal. The channel has a change in the cross-sectional area in the direction of flow of the magnetorheological fluid, the ratio of the maximum cross-sectional area of the channel to the minimum cross-sectional area being in the range of 1.5 to 200.

Because of the generally high intrinsic viscosities of magnetorheological fluids, it is necessary to provide a channel of large cross-sectional area so that it can be traversed by a small pressure drop from the magnetorheological fluid when no magnetic field is applied. However, a large channel cross-section with a constant cross-sectional area of the channel has the disadvantage that significantly higher magnetic fields must be generated in the gap and possibly an increased channel length is required to the required pressure drop under magnetic field and thus the necessary force for pushing through the magnetorheological fluid through to create the channel.

Surprisingly, it has been found that a change in the cross-sectional area of the channel in which the ratio of the maximum cross-sectional area to the minimum cross-sectional area is in the range of 1.5 to 200, preferably in the range of 1.8 to 200, more preferably in the range of 2 to 150 and in particular in the range of 3 to 100, both a passage of the channel with low pressure drop without magnetic field allowed as well as a high pressure drop allows for applied magnetic field. According to the pressure drop, the necessary force is required to move the magnetorheological fluid through the channel. This makes it possible to use a smaller yoke for a sufficient magnetic force that allows shutting off the channel compared to valves with other geometries not according to the invention.

Surprisingly, selected valve geometries according to the invention under a magnetic field even give a higher pressure drop than the conventional geometry with a constant channel cross section with the same valve length, the same minimum channel cross section and the same current of the field generator. The field generator remains unchanged except for the flow channel. The cross-sectional expansion of the channel according to the invention also leads to a reduction of the magnetic flux in the valve. Both effects make it possible to achieve high damping forces under magnetic field with a smaller field generator.

The valve according to the invention allows a high pressure drop at a given magnetic field combined with a large stroke at a comparatively small weight of the field generator. The small weight of the field generator can be achieved by a small volume of magnetic yoke and coil.

The stroke is the ratio of the pressure drop with and without magnetic field. Such a valve is used, which can be traversed by a magnetorheological fluid, for example, for magnetically controllable flow control, pressure drop control or damping control.

Compared to a known from the prior art valve with a predominantly parallel or uniformly conical gap, but which has only a small change in cross section, can be achieved with the inventively designed valve, a larger stroke at a smaller volume of magnetic yoke and coil.

The maximum cross-sectional area of the channel preferably corresponds to the cross-sectional area necessary to apply a predetermined minimum force to move the magnetorheological fluid through the channel. The minimum cross-section preferably corresponds to the cross-section of a parallel-walled channel, as known in the art, and is used for a corresponding application.

Because the force required to move the magnetorheological fluid through the channel increases with increasing length of the channel, and particularly with increasing length, of sections of the constant cross-sectional channel, it is preferred that the sections of the constant cross-section channel - Each surface have a maximum length of 40% of the total length of the channel. In this case, the channel can have sections with a continuously changing cross-sectional area and sections with a constant cross-sectional area or the channel has a plurality of sections with a constant cross-sectional area, wherein the cross-sectional area changes from section to section, for example in steps. In this case, the maximum length of each section with constant cross-sectional area is no more than 40% of the total length of the channel.

In particular, it is preferred that the portion or the portions of the channel with minimum cross-sectional area each have a maximum of 20% of the total length of the channel. 2 to 8% of the total length of the channel is preferred. It has shown, that even such a small length of the section with minimum cross-sectional area is sufficient to achieve a sufficiently large pressure drop for the operation of the valve. The magnetic field that is applied acts in particular in the section of the channel with a minimum cross-sectional area. As a result, the required field generator used to generate the magnetic field can be reduced to the extent that the magnetic field is generated predominantly in the region of the section of the channel with a minimum cross-sectional area.

In a first embodiment, the channel has a continuous transition from the minimum cross-sectional area to the maximum cross-sectional area. The transition can be configured linear, parabolic, hyperbolic, circular or in any other geometric shape. Preferably, however, the transition from the maximum cross-sectional area to the minimum cross-sectional area is linear.

In an alternative embodiment, the transition from the maximum cross-sectional area to the minimum cross-sectional area of the channel has at least one step. However, it is preferred if the transition has at least two stages.

The channel may have a substantially conical profile, wherein the cross-sectional area of the channel decreases or increases in the flow direction, so that either the inlet or the outlet have the maximum cross-sectional area and correspondingly at an inlet with maximum cross-sectional area, the outlet has the minimum cross-sectional area at a minimum cross-sectional area entrance, the exit has the maximum cross-sectional area. The transition from the minimum to the maximum cross-sectional area can, as already described above, be either continuous or step-shaped.

However, it is preferred that the channel has at least one region with decreasing cross-sectional area and a region with increasing cross-sectional area in the flow direction. Particularly preferably, the channel is symmetrical with respect to the average sectional plane transverse to the flow direction. As a result, the behavior of the magnetorheological valve is independent of the flow direction. In this case, it is possible, for example, for the channel initially to have an increasing cross-sectional area in the direction of flow until the maximum cross-sectional area has been reached and for the cross-sectional area in the flow direction to decrease again after the maximum cross-sectional area has been reached. Alternatively, it is also possible for the channel to initially have a decreasing cross-sectional area in the flow direction until the minimum cross-sectional area has been reached, and the cross-sectional area to increase again in the flow direction after the minimum cross-sectional area has been reached. Besides only one area each with decreasing and one area with increasing Furthermore, it is also possible for the channel to have a plurality of regions in each of which the cross-sectional area increases or decreases. Thus, the wall of the channel in the flow direction, for example, zigzag or wave-shaped.

Due to the geometry of the channel with changes in the cross-sectional area, the magnetic flux density changes such that maxima of the flux density occur in areas of minimum cross-sectional area. Compared to a channel with parallel walls, the average flux density of the magnetic field in the geometry according to the invention is lower for the same current of the field coil. Although the maxima of the flux density in the areas of minimum cross-sectional area are also partially lower than the mean flux density of the parallel-walled channel, high pressure drops are achieved. However, with the coil turned off, despite possible residual remanence of the yoke, which is usually on the order of less than 0.1 Tesla for soft magnetic steel, for example steel 1.0037, smaller pressure drops are obtained in the channel than in a channel with parallel walls. Thus, the inventive design of the valve allows a substantial increase in the stroke at the same channel length.

A further advantage is that the field generator can be downsized since, on the one hand, the flux density is reduced overall and, on the other hand, high flux densities are required only in areas of minimum cross-sectional area of the channel compared to a valve with a parallel wall known from the prior art. In addition, it is possible to reduce the length of the channel as a whole due to the overall increased pressure drop, for example due to an overall increased pressure drop in a design having a region of increasing cross-sectional area and a region of decreasing cross-sectional area in the flow direction. The possible reduction of the field generator is advantageous in reducing the weight of the valve and the magnetic energy stored when the coil is turned on. In addition, switching times for flux density changes can be shortened and switching energies reduced.

In one embodiment, a wall of the channel of the inventively constructed valve is movable relative to the opposite wall in the flow direction or against the flow direction of the magnetorheological fluid. Such a valve is used, for example, in a damper in which the valve is formed by a gap between the damper piston and the outer wall of the damper. The length of the wall, which is not moved, preferably corresponds to the movement distance of the damper piston. If a wall is movable relative to the opposite wall, it is preferred that at least the wegbare wall has at least one recess or a projection through which the change in the cross-sectional area of the channel is realized. The non-moving wall of the channel can be designed flat. However, it is particularly advantageous if the non-moving wall has at least one recess or at least one projection.

The channel in which a wall is movable relative to the opposite wall, for example, is formed as a gap between a cylinder wall and a displaceable in the cylinder in the axial direction piston.

The magnet which is used to build up the magnetic field in the gap is preferably a switchable electromagnet. As the material for the yoke of the magnet, for example, a magnetic steel such as steel 1.0037 can be used. Further suitable materials for the yoke are, for example, iron, soft-magnetic iron alloys, for example permalloy, cobalt alloys, nickel alloys and other alloys known to the person skilled in the art.

The design of the valve according to the invention makes it possible, for example, to use magnetorheological fluids having a higher intrinsic viscosity, without an increased pressure drop when the magnet is switched off compared with a conventional valve operated with a low-viscosity magnetorheological fluid. Using magnetorheological fluids with a higher intrinsic viscosity allows the use of a higher pigmentation of magnetizable particles and thus a higher yield point or the use of higher-viscosity base oils, in particular in the range of low temperatures. On the other hand, in piston systems in which the valve according to the invention is used, the use of more effective sealing systems is possible, since their increased frictional force can be compensated by the reduced flow resistance with the magnet switched off, so that the force required to move the piston out at - switched magnet is not increased overall.

The valve according to the invention is used, for example, in a damper which encloses a cylinder with a piston movable in the cylinder in the axial direction. In the cylinder, two chambers are generally formed, which are separated by the piston. The chambers contain a magnetorheological fluid. By the valve according to the invention, which is accommodated in the piston, the magnetorheological fluid can flow from one chamber to the other. A flow through the piston is required to move the piston in the cylinder, since the total volume of the cylinder remains constant and the volume of the chambers separated by the piston during a movement of the piston bens changes. With the magnet switched off and thus a low resistance to flow, only a small amount of force is required to move the piston. In contrast, the force needed to move the piston increases when a magnetic field is applied and thus the pressure drop in the channel greatly increases.

In some applications, it is desirable that the pressure drop across the magnetorheological valve remain high without power. This means, for example, that a high force is required to move the piston in the damper. Such a behavior can be achieved in that a part of the yoke, preferably a part of the yoke not lying directly on the channel, is made of a permanent magnet, for example of neodymium-iron-boron (NdFeB), or a magnetizable material with high remanence, for example hard magnetic Iron-nickel alloys or amorphous ferromagnetic materials such as Metglas 2605 (Fe80B20). The field generated by the electromagnet overlaps in the yoke and, depending on the polarity, can either amplify or partially or completely compensate the flux density generated by the permanent magnet. For materials with high remanence, it is also possible to reverse the polarity of the remanent field.

In a first embodiment, the damper is configured such that the valve comprises at least one channel formed in the piston. In an alternative embodiment, the valve comprises a channel formed as a gap between the cylinder wall and the piston. According to the invention, the channel of the valve, which can be acted upon by the magnetic flux density field generator, has a changing cross-sectional area.

The channel of the valve designed according to the invention preferably has a slit-shaped cross section. Alternatively, however, it is also possible that the channel has a circular or elliptical cross section. Moreover, the shape of the cross-sectional area along the valve channel may also change, for example, from a rectangular cross-sectional area to a square cross-sectional area or a cross-sectional area having a round shape. It is preferred if the channel has a rectangular cross-section or is formed as an annular gap. In a design as an annular gap forms a yoke of the magnet, the inner wall of the annular gap and a second yoke, the outer wall of the annular gap. In the case of a cross-sectionally rectangular cross-sectional area of the channel, it is preferable for the opposing surfaces of the gap in a split yoke or the first and second yokes to form the opposite longer sides of the rectangle. However, it is alternatively also possible that the opposite surfaces of the gap in a split yoke or the yokes form the opposite shorter sides of the rectangle. Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description.

Show it:

1 shows a section parallel to the median plane of the channel through a valve designed according to the invention in a first embodiment,

2 shows a section perpendicular to the median plane of the channel through a valve according to the invention designed according to FIG. 1, FIG.

FIG. 3 shows a double-piston measuring arrangement,

FIG. 4.1 shows a piston which can be moved in a cylinder and has valves designed according to the invention in a first embodiment,

FIG. 4.2 shows a piston according to FIG. 4.1, wherein a part of the yoke is replaced by an annular permanent magnet,

FIG. 5 shows a piston which can be moved in a cylinder and has valves designed according to the invention in a second embodiment,

FIG. 6 shows a piston which can be moved in a cylinder and has valves designed according to the invention in a third embodiment,

Figure 7.1,

7.2 two views of a valve designed according to the invention in a further embodiment,

FIGS. 8.1 to 8.8 different channel geometries for the valve,

Figure 9.1, 9.2 valves with a central yoke in the valve channel.

1 shows a section parallel to the median plane of the channel through a valve designed according to the invention in a first embodiment. A valve 1 designed according to the invention comprises a first yoke 3 and a second yoke 5. The first yoke 3 and the second yoke 5 delimit a channel 7, wherein a first surface 9 of the first yoke 3 and a second surface 11 of the second yoke 5 respectively form opposite walls of the channel 7. Alternatively, the first surface 9 and the second surface 11 may also be opposite surfaces of a gap in a split yoke.

The valve 1 may for example be accommodated in a channel 13 through which a magnetorheological fluid flows. The direction of flow of the magnetorheological fluid is shown by an arrow 15. In addition to the flow direction 15 shown here, however, it is possible in all embodiments shown here that the valve 1 is also flowed through in the opposite direction by the magnetorheological fluid.

In the embodiment shown in FIG. 1, the channel 7 of the valve 1 is formed on a liquid inlet 17 and on a liquid outlet 19, each with a minimal cross-sectional area 21. The minimum cross-sectional area results from the distance between the first yoke 3 and the second yoke 5 at the liquid inlet 17 and the width of the channel 7.

In the flow direction 15 of the magnetorheological fluid, the distance between the first yoke 3 and the second yoke 5 increases linearly in the embodiment shown in FIG. 1 until a maximum distance 23 and thus a constant cross-sectional area of the channel 7 are achieved. After reaching the maximum cross-sectional area, the distance between the first yoke 3 and the second yoke 5 again decreases linearly until the minimum cross-sectional area at the liquid outlet 19 is reached. The increase or decrease in the distance between the first yoke 3 and the second yoke 5 is achieved in the embodiment shown in Figure 1 in that the first yoke 3 and the second yoke 5 each at its the channel 7 bounding surface 9, 11 a have triangular groove.

At the liquid inlet 17 and at the liquid outlet 19, the yokes 3, 5 each protrude into the channel 13. As a result, the flow cross-section of the channel 13 is reduced to the minimum cross-sectional area 21.

Due to the geometric design of the surfaces 9, 1 1 of the first yoke 3 and the second yoke 5 results in a magnetic field applied, which is shown here by arrows 25, a changing flux density in the flow direction 15 of the magnetorheological fluid. In the places with minimum distance 21 between the first Yoke 3 and the second yoke 5, the flux density of the magnetic field is maximum and in the range of maximum distance 23, the flux density is minimal.

Compared to a valve channel with parallel walls, that is, with a constant cross-sectional area, the average flux density of the magnetic field 25 at a geometry of the valve channel 7, as shown here, is lower. Nevertheless, when the magnetic field 25 is applied, higher pressure drops are obtained compared to a parallel-walled valve port. If no magnetic field is applied, however, despite any residual remanence of the yoke 3, 5, which is usually of the order of less than 0.1 Tesla, substantially smaller pressure drops than on a parallel-walled valve passage are obtained. This results in a inventively designed valve 1, a substantial increase in the stroke compared to a valve with parallel walls of the valve channel.

FIG. 2 shows a section perpendicular to the flow direction through a valve according to FIG. 1 with a complete yoke.

The first yoke 3 and the second yoke 5 are connected to each other outside the valve 1 to a split yoke and enclosed by a coil 27. By applying a voltage to the coil 27, a magnetic field is generated in the valve channel 7.

So that the magnetic field generated by the coil 27 flows through the valve channel 7 and the magnetorheological fluid contained therein, the lateral boundary 29 of the valve channel 7 is made of a non-magnetizable material. As a material for the lateral boundary 29 are, for example, non-metallic materials and non-magnetic steel such as 1.4571, brass, aluminum or titanium as metallic materials.

FIG. 3 shows a section of a channel with a valve embodied therein in accordance with the invention.

With the arrangement shown in Figure 3, for example, the pressure drop at the valve 1 can be determined. The valve 1, which is constructed according to the valve shown in Figures 1 and 2, is positioned in a channel 13. The channel 13 is bounded on one side by a first pressure chamber 31 and at its other end by a second pressure chamber 33. The first pressure chamber 31 is closed by a first piston 35 and the second pressure chamber 33 by a second piston 37. The first piston 35 and the second piston 37 can each be displaced in the axial direction in the first pressure chamber 31 and the second pressure chamber 33, respectively. In order to determine the pressure drop in the channel 13, a first pressure sensor 39 is positioned on one side of the valve 1 and a second pressure sensor 41 is positioned in the channel 13 on the other side of the valve 1. In this way, regardless of the direction of flow of the magnetorheological fluid in each case the pressure in the channel 13 in front of and behind the valve 1 can be detected. For the magnetorheological fluid to flow in the direction shown by the arrow 15, for example, the first piston 35 is moved into the first pressure chamber 31. As a result, the pressure in the first pressure chamber 31 increases and the magnetorheological fluid moves in the direction of the second pressure chamber 33. Due to the increasing pressure in the second pressure chamber 33, the piston 37 moves out of the pressure chamber 33 and the volume in the second Pressure chamber 33 is increased. Accordingly, the flow direction of the magnetorheological fluid can be reversed by moving the second piston 37 into the second pressure chamber 33.

The pressure drop at the valve 1 results from the difference between the pressure measured at the first pressure sensor 39 and at the second pressure sensor 41.

FIG. 4.1 shows a piston movably received in a cylinder, wherein a fluid passage with a valve according to the invention received therein is formed in the piston.

A piston, as shown in Figure 4.1, is used, for example, in a damper. For this purpose, a piston 43 is movably received in a cylinder 45. So that the piston 43 can be moved in the cylinder 45, a sliding gap 47 is formed between the piston 43 and the cylinder 45. When used in a damper, a passage 49 is formed in the piston 43. The passage 49 may be designed, for example, as an annular gap. Alternatively, it is also possible that, for example, at least one channel with a circular, triangular, rectangular or any other cross section is formed in the piston 43. In the passage 49 formed in the piston 43, in the embodiment illustrated here, two respective valves 1 designed according to the invention, which are designed in accordance with the valve shown in FIG. 1, are positioned. In order to generate the necessary magnetic field, a coil 51 is received in the piston 43. By energizing the coil 51 via leads 44 in the shaft of the piston 43, a magnetic field is generated. This flows through the yoke 53, which surrounds the coil 51. The yoke 53 bounds each of the valves 1 on one side of the valve channel 7. The opposite boundary of the valve channel 7 forms, for example, a magnet 55. The magnet 55 may be, for example, a second yoke made of a magnetizable material or a permanent magnet. In order to generate a closed magnetic field, it is possible, for example, to magnetize the second yoke to form the magnet 55 with a second coil, which is not shown here. However, it is also possible to provide only a magnetizable material which is also magnetized by energizing the coil 51 and the magnetic field thus formed.

FIG. 4.2 shows a piston according to FIG. 4.1, in which a part of the inner yoke is replaced by an annular permanent magnet 56. Alternatively, instead of the permanent magnet 56, a magnetizable material with a high remanence can also be used. In this way, even without energization of the coil 51, a remanent flux density in the valve channel 7 can be generated. When the coil 51 is energized, the remanent flux density in the valve channel 7 can either be boosted or compensated to zero, depending on the polarity and the voltage.

The valve geometry according to the invention with a larger stroke is particularly advantageous in the combination of electromagnet and permanent magnet if, despite active field compensation in the yoke, the flux density zero is not achieved over the entire gap of the valve.

Upon movement of the piston 43 in the cylinder 45, magnetorheological fluid is moved from a first chamber 57 above the piston 43 into a second chamber 59. During a movement of the piston 43 in the opposite direction, the liquid flows through the passage 49 from the second chamber 59 into the first chamber 57. As long as the coil 51 is not energized and thus in purely soft magnetic yokes without permanent magnet no magnetic field is applied to the valves 1 , the pressure drop at the valve 1 is low and the piston can be moved with only a small force in the cylinder 45. For this, it is advantageous to make the cross-sectional area of the passage 49 outside the valves as large as possible and the total length of the passage 49 as short as possible in order to keep the pressure drop outside the actual valve 7 low. As soon as a voltage is applied to the coil 51 and a magnetic field is formed, the pressure drop across the valves 1 increases and a much larger force is required to move the piston 43 in the cylinder 45. In the case of high remanence of the entire yoke or a part thereof as well as a permanent magnet in the yoke, as shown for example in Figure 4.2, even in the currentless state of the coil 51, a high pressure drop is achieved at the valves. In this case, the coil 51 with appropriate polarity and amperage must actively compensate for the remanent flux density in the valve to realize the state of minimal force.

FIG. 5 shows a piston movable in a cylinder in a second embodiment. The illustrated in Figure 5, movable in a cylinder 45 piston 43 differs from that shown in Figure 4.1 in that the passage 49 is not formed in the piston 43 but as a gap 61 between the piston and the cylinder 45. To generate the magnetic field in the valve channel 7, which is formed in the embodiment shown in FIG. 5 on one side by the yoke 53 and on the other side by the wall 63 of the cylinder 45, the wall 63 of the cylinder 45 or at least the inner part of the wall 63 made of a magnetic material.

In order to avoid disadvantages in operation, which may result from wall sliding on the smooth wall 63 of the cylinder 45, and to use on both sides of the channel, the potential of the cross-sectional change, it is advantageous, even the wall 63 of the cylinder 45 with a corresponding profile to provide. This is shown in FIG. As shown in FIG. 6, the cross-sectional profile may be zigzag-shaped analogously to the inner yoke or else wave-shaped or provided with periodic tips. In order to avoid that a position-dependent change of the inlet cross-section occurs in the valves by the displacement of the piston 43, it is possible, for example, the profiling in the form of HeNx with a slope of L _s / 2πR _R or a multiple thereof shape. L _s stands for the distance of the tips 65 and R _R for the inner radius of the cylinder. A corresponding profiling, for example, has the form of an internal thread.

Another design of a valve 1 designed according to the invention is shown in FIGS. 7.1 and 7.2. In contrast to the embodiment shown in FIG. 1, in the embodiment shown in FIGS. 7.1 and 7.2 the width of the valve channel 7 initially decreases until the maximum distance 23 of the first yoke 3 and the second yoke 5 has been reached and after reaching the maximum Distance 23 to the liquid outlet 19 again.

In addition to the embodiments shown here, it is also possible, for example, for the valve channel 7 to have a minimum cross-sectional area at the liquid inlet 17 and a maximum cross-sectional area at the liquid outlet 19. Alternatively, it is also possible that the cross-sectional area at the liquid inlet is maximum and at the liquid outlet is minimal.

In a further alternative embodiment, the cross-sectional area at the liquid inlet and at the liquid outlet is in each case at a maximum and minimal between the liquid inlet and the liquid outlet. In this case, the cross-sectional area of the liquid inlet initially decreases until the minimum cross-sectional area is reached and from reaching the minimum cross-sectional area to the liquid outlet again to. Also, more than one or two bottlenecks in which the minimum cross-sectional area is achieved may be provided. For example, a zigzag or wavy design of the channel walls with at least three minimal cross-sectional areas is also conceivable.

In order to achieve the mechanical stability against abrasion or plastic deformation, it is possible, for example, to reinforce the first yoke 3 and the second yoke 5 at the liquid inlet 17 or liquid outlet 19 by a wedge of a non-magnetisable material. The tip of the wedge lies on the side facing the liquid inlet 17 or liquid outlet 19. In addition, the tips that are formed in the embodiments shown here may be rounded. Furthermore, it is also possible for the region of the valve channel 7 with minimum cross-sectional area to comprise a section with walls running parallel, this section occupying a maximum of 20% of the total length of the valve channel 7.

Other suitable geometries for the channel are shown, for example, in FIGS. 8.1 to 8.8.

In FIGS. 8.1 to 8.3, channel geometries are shown in which the cross-sectional area at the liquid inlet is at its maximum and at the liquid outlet is minimal or at the liquid inlet is minimal and at the liquid outlet is maximum.

The increase or decrease in the cross-sectional area can be carried out with decreasing, constant or increasing pitch. In Figure 8.1, a channel is shown with a decreasing slope. In this case, the pitch to the minimum cross-sectional area closely approximates to a parallel gap. The wall runs parabolic from the maximum cross section to the minimum cross section. Alternatively, however, for example, a course in the form of a quarter circle is conceivable.

Figure 8.2 shows a channel constriction with constant slope.

Figure 8.3 shows a channel with an increasing slope of the channel constriction. Here, the channel has a substantially parabolic narrowing. Alternatively, it is also possible that the channel has a substantially semicircular constriction with an opening in the semicircle.

In the figures 8.4 to 8.8 channel geometries are shown with narrowing and widening. The illustrated channel shapes are in each case symmetrical to a sectional plane transversely to the flow direction. FIG. 8.4 shows an alternative course with minimal cross-sectional area at the liquid inlet and liquid outlet and maximum cross-sectional area in the plane of symmetry. The widening or narrowing of the channel is essentially circular. Alternatively, for example, an elliptical shape is possible.

In contrast, in FIGS. 8.5 to 8.8, channel shapes are shown with maximum cross-sectional area at the liquid inlet and liquid outlet and minimum cross-sectional area in the plane of symmetry. The channel walls may be circular or triangular, for example as shown in FIGS. 8.5 and 8.6. Also, for example, a course with increasing slope of maximum cross-sectional area to minimum cross-sectional area is possible, as shown in Figure 8.7. As an alternative to a continuous constriction or expansion, as shown in FIGS. 8.1 to 8.7, however, for example, a simple diaphragm, as shown in FIG. 8.8, can also be accommodated in the channel. This is a step-shaped narrowing of the channel.

In addition to the lateral constriction of a rectangular valve channel 7 shown in FIG. 7.2, it is alternatively also possible to position any other non-magnetic obstacles in the valve channel 7. By installing the non-magnetic obstacles, the cross-sectional area of the valve channel 7 is reduced.

In addition to any non-magnetic obstacle in the valve channel 7, it is alternatively also possible, as shown in FIG. 9.1, to position a central yoke in the middle of the channel, for example in the case of a channel with a circular cross-section. As a result, the channel cross section changes from a circular cross section to an annular cross section. In addition, the coil 69 is enclosed by a rotationally symmetrical yoke 71 with a U-shape. In order to position the central yoke 67 in the channel, at least one mandrel holder is required, with which this is held in position. However, more than one mandrel holder, for example at least two mandrel holders, is preferred in order to obtain a stable attachment of the central yoke 67.

Notwithstanding the illustration in Figure 9.1, the cross section of the channel can be designed either elliptical, rectangular or with any other shape. The central yoke is then to be equipped, for example, in the shape of its cross section, similar to the channel. However, a cross-section of the central yoke 67, which generates a constant flux density at the valve inlet and valve outlet along the circumference, is advantageous.

As shown in Figure 9.2, the cross section of the central yoke 67 may also change along its length. In this way, for example, sharper transitions ge between the annular channel around the central yoke 67 and the channels at the entrance and exit of the valve can be achieved. With a small minimum cross section of the central yoke 67, this must be made of a magnetically highly permeable material to avoid saturation confinement of the flux density. It is also advantageous to make the opposing tips of the yoke 71 enclosing the channel wedge-shaped as in FIG. 9.2. This also allows a larger cross-section of the channels facing away from the valve, so that in the de-energized case, the flow resistance of the arrangement can be kept small. As an alternative to the linear taper of the tip, this can be done with increasing or decreasing slope. The same applies to the central yoke.

When using a central yoke 67 in the valve channel 7, which is surrounded by all sides, for example in a cylindrical central yoke 67 in a circular channel, so that an annular gap is formed around the central yoke 67, there is a first valve 1 on the The upstream side of the central yoke 67 and a second valve 1 at the downstream end of the central yoke 67, at which the annular gap ends and generally merges back into the original cross section. Alternatively, however, it is also possible that the central yoke 67 is connected, for example, on two opposite sides to the wall of the channel. In this case, in each case on the sides of the yoke, which are not connected to the wall of the channel, gaps are formed in which the cross-section of the channel narrows. In this case, each of the gaps forms a valve 1 both on the upstream side of the central yoke 67 and on the downstream side of the central yoke 67. The embodiment with a central yoke 67 connected to the wall of the duct is suitable, for example, for a duct with a rectangular Cross-section.

Examples

example 1

In a rectangular flow channel with a cross-sectional area of 10 mm x 5 mm, a valve designed according to the invention with a geometry, as shown in Figure 1, installed. The valve channel is delimited by a field-guiding yoke made of steel 1.0037. The width of the valve channel is also 10 mm, the distance between the walls formed by the yoke is at the liquid inlet and liquid outlet in each case 1 mm, the maximum distance of the walls is 5 mm. The magnetic field is generated by a coil with impressed current. As long as no magnetorheological fluid is contained in the valve channel, the resulting magnetic flux density B perpendicular to the flow direction in the middle of the valve channel using a 1 mm-thick Hall probe to be detected.

In each case, 13 mm in front of and behind the valve, pressure sensors are positioned in the rectangular flow channel. These allow both the detection of the pressure drop across the valve and of the hydrostatic pressure. The pressure drop is the difference between the pressure measured at the pressure transducers and the hydrostatic pressure is the average of the pressure measured at the pressure transducers. The rectangular flow channel opens at both Ends respectively in pressure chambers of circular cross-section containing hydraulically driven pistons. The pistons are to be controlled independently of each other. In this way, on the one hand, the volume flow rate of the magnetorheological fluid through the valve and the hydrostatic pressure in the magnetorheological fluid can be specified. The hydrostatic pressure is set so that, when the magnetic field is applied, both pressure transducers always display positive pressures, regardless of the impressed flow direction.

The magnetorheological fluid used contains 87% by weight of carbonyl iron powder dispersed in mineral oil. The magnetorheological fluid is further added 0.3 wt .-% of a thixotropic additive to prevent the sedimentation of the carbonyl iron powder. In addition, 0.3% by weight of a dispersant is included.

As a reference, a conventional valve with a parallel gap of constant width is used with a length of the valve channel of 5 mm and a 1 mm x 10 mm rectangular rectangular cross-section with otherwise identical construction of the test arrangement.

Table 1 shows the pressure drop and the stroke, ie the ratio of the pressure drop with applied magnetic field and without magnetic field, for the valve according to the invention and the reference valve. The measurement was carried out in each case with the same direction movement of the piston at a speed of 10 mm / s. That corresponds to one

Volume throughput of the magnetorheological fluid of 785 mm ³ / s. Table 1

In Table 1, double wedge respectively means the inventively designed valve and reference the reference valve with parallel walls.

It turns out that when the magnetic field is not applied, the pressure drop across the valve designed according to the invention is smaller by a factor of 4 than at a valve, as is known from the prior art, with parallel walls. Furthermore, it is found that when applied magnetic field at currents of more than 0.75 A, the pressure drop across the inventively designed valve by about 35 to 60% higher than the reference valve. As a result, the valve designed according to the invention has a higher stroke by a factor of 6.6 to 7.8.

With the same experimental design, an oscillating flow through the valve was applied via a sinusoidal movement of the pistons. The course of the differential pressure from the measured values of the two pressure transducers before and after the valve was recorded over time. The pressure amplitude was determined to be half the value of the difference between the maximum and the minimum of the periodic curve.

The measured pressure amplitude at oscillatory flow is shown in Table 2.

Table 2

In Table 2, frequency and amplitude mean the frequency and amplitude with which the pistons were moved.

It can be seen that the pressure amplitudes in the inventively designed valve by 25 to 35% are greater than that of a valve with a valve gap with parallel walls.

Example 2

The inventively designed valve with the geometry of Figure 1 was replaced by a valve with a geometry according to Figure 8.7. The minimum distance of the walls was also 1 mm, the maximum distance 5 mm, the length of the valve channel also 5 mm and the width of the channel 10 mm.

Table 3 shows the pressure drop and stroke for the valve as shown in Figure 8.7 and as a reference for a parallel gap valve with a 1 mm wall clearance.

Table 3

In Table 3, tip means the valve designed according to the invention and reference the valve with parallel walls.

It turns out that when the coil is not energized, the pressure drop across the valve designed according to the invention is smaller by more than a factor of 5 than in the case of a valve with parallel walls. In contrast, the pressure drop at currents of more than 0.75 A when inventively designed valve reaches about 90% of the value of a valve with parallel walls. At the valve with the geometry according to the invention, the stroke is higher by at least a factor of 4.

With the same experimental set-up, an oscillating flow through the valve was also created.

The measured pressure amplitude at oscillatory flow is shown in Table 4.

Table 4

In Table 4, frequencies and amplitude are respectively the frequency and the amplitude with which the pistons were moved.

It turns out that despite the small effective length of the channel under a magnetic field, the inventively designed valve under the operating conditions reached pressure amplitudes, which are on average only about 9 to 10% below that of the reference valve with parallel walls. Also advantageous is the larger stroke due to the lower pressure drop when not energized coil.

LIST OF REFERENCE NUMBERS

1 valve

3 first yoke

5 second yoke

7 valve channel

9 first surface

1 1 second surface

13 channel

15 Flow direction of the magnetorheological fluid

17 fluid inlet

19 Liquid outlet

21 minimum cross-sectional area

23 maximum distance

25 magnetic field

27 coil

29 lateral limit

31 first pressure chamber

33 second pressure chamber

35 first piston

37 second piston

39 first pressure sensor

41 second pressure sensor

43 pistons

44 supply line

45 cylinders

47 sliding gap

49 passage

51 coil

53 yoke

55 magnet

56 permanent magnet

57 first chamber

59 second chamber

61 gap

63 Wall of the cylinder 45

65 tip

67 central yoke

69 coil

71 U-shaped yoke

Claims

claims

1. valve, which can be traversed by a magnetorheological fluid, comprising a valve channel (7), which can be traversed by a magnetic field (25), wherein at least one magnet with at least one yoke is included for generating the magnetic field (25), and opposing surfaces of a gap in a split yoke or opposite surfaces of two yokes (3, 5) form opposite walls of the valve channel (7), characterized in that the valve channel (7) in the flow direction (15) of the magnetorheological fluid has a change in cross-sectional area wherein the ratio of the maximum cross-sectional area of the valve channel (7) to the minimum cross-sectional area is in the range of 1.5 to 200.

2. Valve according to claim 1, characterized in that the portion or the portions of the valve channel (7) with a minimum cross-sectional area in each case a maximum

20% of the total length of the channel.

3. Valve according to claim 1 or 2, characterized in that the valve channel (7) has a continuous transition from the maximum cross-sectional area to the minimum cross-sectional area.

4. Valve according to claim 1 or 2, characterized in that the transition from the maximum cross-sectional area to the minimum cross-sectional area of the valve channel (7) has at least one stage.

5. Valve according to one of claims 1 to 4, characterized in that the valve channel (7) in the flow direction (15) initially has an increasing cross-sectional area until reaching the maximum cross-sectional area and the cross-sectional area in the flow direction after reaching the maximum cross-sectional area decreases again.

6. Valve according to one of claims 1 to 4, characterized in that the valve channel (7) in the flow direction (15) initially has a decreasing cross-sectional area until reaching the minimum cross-sectional area and the cross-sectional area increases again in the flow direction after reaching the minimum cross-sectional area.

7. Valve according to one of claims 1 to 6, characterized in that a wall of the valve channel (7) relative to the opposite wall in Strö- mung direction (15) or against the flow direction of the magnetorheological fluid is movable.

8. Valve according to one of claims 1 to 7, characterized in that the valve channel (7) as a gap (61) between a cylinder wall (63) and one in the

Cylinder (45) in the axial direction displaceable piston (43) is formed.

9. Valve according to one of claims 1 to 8, characterized in that the magnet is a switchable electromagnet.

10. Valve according to one of claims 1 to 9, characterized in that the change in the cross-sectional area by use of a central yoke (67) or an obstacle in the valve channel (7) is formed.

1 1. Valve according to one of claims 1 to 10, characterized in that portions of the valve channel (7) having a constant cross-sectional area each have a maximum length of 40% of the total length of the valve channel (7).

12. damper, comprising a cylinder (45) with a in the cylinder (45) in the axial direction movable piston (43), wherein in the cylinder two chambers (57,

59) are formed, which are separated from each other by the piston (43), and in the chambers (57, 59) a magnetorheological fluid is contained, wherein in the piston (43) at least one valve (1) according to one of claims 1 to 1 1 is received, through which the magnetorheological fluid from one chamber (57, 59) in the other (57, 59) can flow.

13. A damper according to claim 12, characterized in that the valve (1) comprises at least one valve channel (7) which is formed in the piston (43).

14. A damper according to claim 12 or 13, characterized in that the valve (1) comprises a valve channel (7) which is formed as a gap (61) between the cylinder wall (63) and the piston (43).