Method for characterizing magnetorheological fluids

Abstract

The present invention relates to a method for evaluating the characteristics of a magnetorheological fluid, the method for evaluating the characteristics of a magnetorheological fluid according to the present invention is a method for evaluating the characteristics of a magnetorheological fluid containing a dispersion medium and magnetic particles, and is characterized by comprising the steps of (a) preparing a container filled with the magnetorheological fluid or a flow path through which the magnetorheological fluid flows, (b) arranging a coil unit so that the container or the flow path is located in a hollow region of the coil unit, and (c) measuring an impedance signal or an inductance signal for the magnetorheological fluid via the coil unit.

Description

[Technical field]

[0001] The present invention relates to a method for evaluating the properties of a magnetorheological fluid, and more particularly to a method for evaluating the properties of a magnetorheological fluid, such as the content, concentration, sedimentation degree, and dispersion uniformity of magnetic particles, by measuring an impedance signal or an inductance signal of the magnetorheological fluid. [Background technology]

[0002] Magneto-rheological fluid (MRF) is a suspension of micro-sized magnetic particles that are sensitive to magnetic fields mixed in a dispersion medium such as oil or water, and is one of the smart materials whose flow characteristics can be controlled in real time by applying an external magnetic field.

[0003] Such magnetorheological fluids exhibit the magnetorheological phenomenon, in which their rheological behavior and electrical, thermal, and mechanical properties change in response to an external magnetic field. In general, magnetorheological fluids have the properties of a Newtonian fluid when no external magnetic field is applied, but when an external magnetic field is applied, the magnetic particles inside the fluid form a chain structure in the direction of the applied magnetic field, providing resistance to shear forces and flow that impede the flow of the fluid, and the fluid takes on the properties of a Bingham fluid, which generates a certain yield stress even without a shear deformation rate.

[0004] Magnetorheological fluids have the properties of resistance to flow, fast response speed, and reversibility, making them highly applicable in various industrial fields, such as vibration control devices such as dampers, clutches and brakes in automobiles, and haptic devices.

[0005] For a magnetorheological fluid to be effective, it must possess a high yield stress, the viscosity of the fluid must be low enough so that it can quickly recover to its original state when a magnetic field is applied and then removed, and the magnetic particles therein must be uniformly distributed within the dispersion medium.

[0006] However, since the density of the magnetic particles constituting the magnetorheological fluid (e.g., the tap density of iron particles is 3.9-4.1 g / cm3) is much higher than the density of the dispersion medium (e.g., in the case of silicone oil, about 0.8-1.0 g / cm3 at room temperature), the magnetic particles settle in the dispersion medium due to gravity, which causes a problem of reducing the dispersion stability of the magnetorheological fluid. Therefore, when using the magnetorheological fluid, the user must inconveniently remix or redisperse the magnetic particles and dispersion medium that have settled and separated in the container, and the physical properties of the magnetorheological fluid may change during the remixing / redispersion process.

[0007] In addition, before using a magnetorheological fluid, users need to understand the properties of the magnetorheological fluid, such as the concentration of magnetic particles in a container and the degree of sedimentation. Conventionally, signals were measured using an LCR meter outside the magnetorheological fluid, but the signal measured using this method had limitations in that it was difficult to accurately evaluate the properties because the strength of the signal was low. If the magnetic particles and dispersion medium are remixed / redispersed without accurately evaluating the properties, an unnecessary additional process is performed, which is not economical, and there is a possibility that the physical properties of the magnetorheological fluid may change due to the additional process. Therefore, research that can accurately evaluate the properties of a magnetorheological fluid is required. Summary of the Invention [Problem to be solved by the invention]

[0008] Therefore, the present invention has been devised to solve the above-mentioned problems of the prior art, and has an object to provide a method for evaluating the properties of a magnetorheological fluid that can accurately evaluate the properties of a magnetorheological fluid.

[0009] Another object of the present invention is to provide a method for evaluating the properties of a magnetorheological fluid, which can easily measure the content, concentration, sedimentation degree, and dispersion uniformity of magnetic particles in a magnetorheological fluid.

[0010] Another object of the present invention is to provide a method for evaluating the properties of a magnetorheological fluid that allows the magnetorheological fluid to be used with minimal remixing / redispersion of the magnetorheological fluid in which magnetic particles have settled.

[0011] However, these challenges are exemplary and are not intended to limit the scope of the invention. [Means for solving the problem]

[0012] The above-mentioned object of the present invention is achieved by a method for evaluating the characteristics of a magnetorheological fluid containing a dispersion medium and magnetic particles, the method comprising the steps of: (a) preparing a container filled with magnetorheological fluid or a flow path through which the magnetorheological fluid flows; (b) positioning the coil section so that the container or the flow path is located in a hollow region of the coil section; and (c) measuring an impedance signal or an inductance signal for the magnetorheological fluid via the coil section.

[0013] The above-mentioned object of the present invention is achieved by a method for evaluating the characteristics of a magnetorheological fluid containing a dispersion medium and magnetic particles, the method comprising the steps of: (a) preparing a container filled with magnetorheological fluid or a flow path through which the magnetorheological fluid flows; (b) preparing a measuring unit having a coil unit disposed inside or connected to the outside; (c) immersing the coil unit in the magnetorheological fluid; and (d) measuring an impedance signal or inductance signal for the magnetorheological fluid via the coil unit.

[0014] According to an embodiment of the present invention, the vessel or the pipe in which the flow passage is formed may be made of a non-magnetic or non-conductive material.

[0015] According to an embodiment of the present invention, the case of the measuring unit may be made of a non-magnetic or non-conductive material.

[0016] Furthermore, according to one embodiment of the present invention, when the container or the flow path is located in the hollow region of the coil section, the magnitude of the impedance signal or inductance signal can be measured to be more than 10 times larger than when the container or the flow path is located in the outer circumferential region of the coil section.

[0017] Furthermore, according to one embodiment of the present invention, as the content of the magnetic particles in the magnetorheological fluid increases, the difference in the impedance signal or inductance signal may be greater when the container or flow path is located in the hollow region of the coil unit than when the container or flow path is located in the outer peripheral region of the coil unit.

[0018] Furthermore, according to one embodiment of the present invention, when the coil portion is immersed in the magnetorheological fluid, the magnitude of the impedance signal or the inductance signal can be measured to be more than 10 times larger than when the container or the flow path is located in the outer peripheral region of the coil portion.

[0019] Furthermore, according to one embodiment of the present invention, as the content of the magnetic particles in the magnetorheological fluid increases, the difference in the impedance signal or the inductance signal may be greater when the coil unit is immersed in the magnetorheological fluid than when the container or the flow path is located in the outer peripheral region of the coil unit.

[0020] According to an embodiment of the present invention, an impedance signal or an inductance signal for the magnetorheological fluid may be measured through the coil unit according to the height of a container filled with the magnetorheological fluid.

[0021] Furthermore, according to one embodiment of the present invention, the degree of settling of the magnetorheological fluid can be calculated from (1) the difference between a first impedance signal measured at a first position in the container and a second impedance signal measured at a second position higher than the first position, or (2) the difference between a first inductance signal measured at the first position and a second inductance signal measured at a second position higher than the first position.

[0022] Furthermore, according to an embodiment of the present invention, as time passes from a reference point in time, the difference between the first impedance signal and the second impedance signal or the difference between the first inductance signal and the second inductance signal may become larger.

[0023] Furthermore, according to one embodiment of the present invention, as time passes from a reference point, (1) the first impedance signal may become larger and the second impedance signal may become smaller, or (2) the first inductance signal may become larger and the second inductance signal may become smaller.

[0024] According to an embodiment of the present invention, the impedance signal or the inductance signal for the magnetorheological fluid is measured via the coil unit, and the concentration of magnetic particles in the magnetorheological fluid can be calculated.

[0025] Furthermore, according to one embodiment of the present invention, a plurality of the coil sections may be prepared spaced apart from each other along the vertical direction of the container, and the container may be disposed in the hollow regions of at least two of the coil sections.

[0026] Furthermore, according to one embodiment of the present invention, the measuring unit includes a plurality of the coil portions arranged at a distance from each other along the vertical direction of the container, and the measuring unit can be immersed in the magnetorheological fluid such that the height of at least two of the coil portions of the measuring unit is located lower than the uppermost end of the magnetorheological fluid.

[0027] According to one embodiment of the present invention, an impedance signal or an inductance signal for the magnetorheological fluid may be measured through the coil unit at at least two time points at a specific point in the container filled with the magnetorheological fluid. According to one embodiment of the present invention, the step of measuring the impedance signal or the inductance signal for the magnetorheological fluid through the coil unit may include the steps of: (1) measuring the impedance signal or the inductance signal at at least two points or at least two time points in the container or the flow path; and (2) determining whether a difference between the impedance signals or the inductance signals measured at the at least two points or at least two time points is greater than a set reference value.

[0028] Furthermore, according to one embodiment of the present invention, the step of measuring an impedance signal or an inductance signal for the magnetorheological fluid via the coil section may include the steps of: (1) measuring the impedance signal or the inductance signal at at least two points or at least two time points in the container or the flow path; and (2) determining whether the impedance signal or the inductance signal measured at the at least two points or at least two time points is within a range of a preset reference value.

[0029] Furthermore, according to one embodiment of the present invention, if the difference between the impedance signal or the inductance signal measured at the at least two points or at least two time points is greater than a set reference value, the magnetorheological fluid may be further dispersed.

[0030] Furthermore, according to one embodiment of the present invention, the magnetorheological fluid can be used under conditions where the difference between the impedance signal or the inductance signal measured at the at least two points or at least two time points is equal to or smaller than a set reference value.

[0031] Furthermore, according to one embodiment of the present invention, if the difference between the impedance signal or the inductance signal measured at the at least two points or at the at least two time points is outside a range of a preset reference value, respectively, dispersion of the magnetorheological fluid can be further performed.

[0032] Furthermore, according to one embodiment of the present invention, the magnetorheological fluid can be used if the difference between the impedance signal or the inductance signal measured at the at least two points or at least two time points is within a range of a preset reference value, respectively. Effect of the Invention

[0033] According to the present invention configured as described above, it is possible to accurately evaluate the characteristics of a magnetorheological fluid.

[0034] Furthermore, according to the present invention, the content, concentration, sedimentation degree, dispersion uniformity, etc. of magnetic particles in a magnetorheological fluid can be measured by a simple method.

[0035] Furthermore, according to the present invention, there is an advantage that the magnetorheological fluid in which the magnetic particles have settled can be used with only minimal remixing / redispersion.

[0036] Of course, the scope of the present invention is not limited to such effects. [Brief description of the drawings]

[0037] [Figure 1] FIG. 2 is a schematic diagram showing a method for evaluating the properties of a magnetorheological fluid according to one embodiment of the present invention. [Diagram 2] 2 is a graph showing impedance values ​​of samples obtained by the methods of (1) and (2) in FIG. [Diagram 3] FIG. 4 is a schematic diagram showing a method for evaluating the properties of a magnetorheological fluid according to another embodiment of the present invention. [Figure 4] 4 is a graph showing impedance values ​​of samples obtained by the methods of (3) and (4) in FIG. [Diagram 5] 2 is a graph showing impedance values ​​versus frequency change for samples obtained by the methods of (1) and (2) in FIG. [Figure 6] 1 is a graph comparing impedance and inductance values ​​with respect to changes in frequency for a sample according to an embodiment of the present invention. [Figure 7] FIG. 2 is a schematic diagram showing a measurement unit according to an embodiment of the present invention. [Figure 8] 1 is a graph showing impedance change versus measurement height for a sedimented sample according to one embodiment of the present invention. [Figure 9] 1 is a graph showing the change in impedance versus measurement height for sedimentation samples at 1 month, 2 months, and 24 months according to an embodiment of the present invention. [Figure 10] 4 is a graph showing impedance values ​​versus content of magnetic particles according to an embodiment of the present invention. [Figure 11] 4 is a graph showing saturation magnetization versus content of magnetic particles according to an embodiment of the present invention. [Figure 12] 1 is a graph showing impedance values ​​versus types of magnetic particles in a magnetorheological fluid according to an embodiment of the present invention. [Figure 13] 2 is a schematic diagram illustrating a process of determining the concentration of magnetic particles in a magnetorheological fluid according to one embodiment of the present invention. FIG. [Figure 14] 4 is a graph showing a process of determining the concentration of magnetic particles in a magnetorheological fluid according to an embodiment of the present invention. [Figure 15] FIG. 1 is a schematic diagram showing a process for determining the degree of uniformity of dispersion of a magnetorheological fluid according to one embodiment of the present invention, for use in determining when the manufacturing process is complete, for quality control of sedimentation or redispersibility, injection, etc. [Figure 16] 1 is a schematic diagram showing a method for evaluating the characteristics of a magnetorheological fluid in a flow channel through which the magnetorheological fluid flows according to one embodiment of the present invention. [Figure 17] 4 is a schematic diagram showing a process for evaluating the redispersibility of a magnetorheological fluid according to an embodiment of the present invention. FIG. [Figure 18] FIG. 1 is a schematic diagram illustrating a magnetorheological fluid damper according to one embodiment of the present invention. [Figure 19] 2 is a schematic diagram illustrating an operation process of a magnetorheological fluid system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] The following detailed description of the present invention refers to the accompanying drawings, which show, by way of example, specific embodiments in which the present invention may be practiced. These embodiments are described in detail to enable those skilled in the art to fully practice the present invention. It should be understood that the various embodiments of the present invention are different from one another, but are not necessarily mutually exclusive. For example, a specific shape, structure, and characteristic described herein may be embodied in another embodiment without departing from the spirit and scope of the present invention. It should also be understood that the location or arrangement of individual components within each disclosed embodiment may be changed without departing from the spirit and scope of the present invention. Therefore, the following detailed description is not intended to be taken in a limiting sense, and the scope of the present invention is limited only by the appended claims, with the full scope of equivalents that the claims, if properly described, are to be claimed. In the drawings, like reference numerals refer to the same or similar functions throughout the various aspects, and lengths, areas, thicknesses, and the like and shapes may be exaggerated for convenience.

[0039] As used herein, terms such as "comprise" or "have" are intended to specify the presence of stated features, numbers, steps, operations, components, parts, or combinations thereof, and should be understood as not precluding the presence or additional possibility of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0040] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings in order to enable those skilled in the art to easily carry out the present invention.

[0041] According to an embodiment of the present invention, a magnetorheological fluid can be transformed between a liquid phase and a solid phase by an external magnetic field, or can have a mixed phase of a liquid phase and a solid phase. Magnetic particles contained in the magnetorheological fluid can form chains by an external magnetic field, and thus can exhibit properties similar to those of a solid.

[0042] According to an embodiment of the present invention, the magnetorheological fluid may include a dispersion medium and magnetic particles dispersed in the dispersion medium, and may further include a thixotropic agent, additives, etc.

[0043] The dispersion medium is a substance in which the magnetic particles are dispersed to form a suspension and may be polar or non-polar in nature, and preferably has low viscosity for maximum magnetorheological effect.

[0044] As an example, the dispersion medium may be at least one selected from the group consisting of silicone oil, mineral oil, paraffin oil, corn oil, hydrocarbon oil, castor oil, vacuum oil, and natural oil. The dispersion medium may have a kinetic viscosity at 40°C in the range of about 5 to 300 mm2 / s. If the kinetic viscosity is lower than this range, there is a problem of reduced sedimentation, and if it is higher than this range, there is a problem of reduced fluidity, so it is preferable that the kinetic viscosity is within the above range.

[0045] The magnetic particles may be at least one selected from iron, carbonyl iron, iron alloys, iron oxide, iron nitride, iron carbide, low carbon steel, nickel, cobalt, and mixtures or alloys thereof. The average particle size of the magnetic particles may be about 1 to 100 μm. The magnetic particles may be uncoated magnetic particles or magnetic particles coated with an organic resin or an inorganic substance.

[0046] For example, the magnetic particles may be contained in the magnetorheological fluid at a content of about 65 to 85 wt %. If the magnetic particles are contained in a content lower than this range, a problem of reduced shear stress may occur, and if the magnetic particles are contained in a content higher than this range, a problem of fluidity may occur, so it is preferable that the magnetic particles are contained within this range.

[0047] As the thixotropic agent, any known thixotropic agent that can cause the magnetorheological fluid to exhibit thixotropy when mixed and dispersed in the magnetorheological fluid can be used.

[0048] In addition, the magnetorheological fluid may further contain, as conventional additives, dispersants, anti-friction agents, antioxidants, corrosion inhibitors, and the like.

[0049] Fig. 1 is a schematic diagram showing a method for evaluating the properties of a magnetorheological fluid according to an embodiment of the present invention, in which (1) shows an embodiment of the present invention, and (2) shows a method for evaluating the properties of a magnetorheological fluid according to a comparative example.

[0050] A method for evaluating the properties of a magnetorheological fluid according to one embodiment of the present invention may include the steps of (a) preparing a container 10 filled with a magnetorheological fluid 20, (b) positioning the coil section 30 so that the container 10 is located in a hollow region 35 of the coil section 30, and (c) measuring an impedance signal or inductance signal for the magnetorheological fluid via the coil section 30.

[0051] Referring to FIG. 1(1), first, a container 10 filled with a magnetorheological fluid 20 can be prepared. The container 10 can adopt a material and shape capable of accommodating a dispersion medium, magnetic particles, etc., constituting the magnetorheological fluid 20. For example, since the density of the magnetorheological fluid 20 is high, a material with high rigidity can be used to accommodate a large amount of the magnetorheological fluid 20, and preferably a non-magnetic, non-conductive material can be used. To accommodate a relatively small amount of the magnetorheological fluid 20, a material such as glass or plastic can be used. The container 10 can be tubular so that it can be positioned in the hollow region 35 of the coil unit 30, and preferably has a cylindrical shape. When the container 10 is cylindrical and arranged so as to be coaxial with the hollow region 35 of the coil unit 30, an electric signal such as a current applied by the coil unit 30 can act more uniformly on the container 10 filled with the magnetorheological fluid 20.

[0052] Next, the coil section 30 can be positioned so that the container 10 is located in the hollow region 35 of the coil section 30. This includes moving and positioning the coil section 30 into the container 10 in a fixed position, or vice versa. The shape of the hollow region 35 of the coil section 30 is preferably larger than or the same as the shape of the outer periphery of the container 10 so that the container 10 can be located within the hollow region 35.

[0053] The position of the hollow region 35 can correspond to the magnetorheological fluid 20 filled in the container 10. In other words, it is preferable that the hollow region 35 of the coil section 30 is located within the height range of the container 10 filled with the magnetorheological fluid 20 so that the coil section 30 can measure a larger impedance signal of the magnetorheological fluid 20.

[0054] Next, an impedance signal or an inductance signal for the magnetorheological fluid can be measured through the coil unit 30. The coil conductor of the coil unit 30 can substantially correspond to an RLC circuit. When an electric signal such as a current is applied to the coil unit 30, a change in the electric signal can occur due to an interaction with magnetic particles in the magnetorheological fluid 20 around the coil unit 30. This change in the electric signal can correspond to a change in impedance or inductance due to an interaction between the coil unit 30 and the magnetorheological fluid 20. The impedance signal or the inductance signal can be measured by connecting a signal measuring device (not shown) to both ends of the coil conductor of the coil unit 30.

[0055] The impedance signal or inductance signal may correspond to the amount of magnetic particles dispersed at a particular location in the magnetorheological fluid 20. Depending on where the coil unit 30 is placed in the magnetorheological fluid 20, the impedance signal or inductance signal may be shown differently. The present invention is characterized in that the amount of magnetic particles in the magnetorheological fluid 20 at a location adjacent to the coil unit 30 is predicted based on the impedance or inductance signal measured at the coil unit 30. In particular, the impedance signal or inductance signal according to the height of the magnetorheological fluid 20 in the container 10 can be used to calculate the amount of magnetic particles at that height, and by calculating the amount of magnetic particles at at least two points in the total height of the magnetorheological fluid 20, the degree of sedimentation of the magnetorheological fluid 20 in the container 10 can be determined. The sedimentation rate S can be expressed as S (vol%) = 100 - [(△S) / (h)] × 100, where △S is the height of the supernatant liquid (the upper layer when magnetic particles in the magnetorheological fluid are separated into layers by sedimentation) after a certain time has elapsed after filling a container with the magnetorheological fluid, and h is the initial height of the magnetorheological fluid when it is filled into the container.

[0056] Meanwhile, when disposing the container 10 in the hollow region 35 of the coil unit 30, it is preferable that the container 10 is made of a non-magnetic, non-conductive material. If the container 10 is made of a magnetic or conductive material, when the coil unit 30 interacts with the magnetorheological fluid 20 to measure an impedance signal or an inductance signal, noise due to interaction with the container 10 may be included in the measured value, and therefore, in order to eliminate this, a container 10 made of a non-magnetic, non-conductive material may be used.

[0057] 1(2), in the comparative example of the method for evaluating the properties of a magnetorheological fluid, the coil unit 30 is disposed outside the container 10. In other words, the container 10 is not located in the hollow region 35 of the coil unit 30.

[0058] FIG. 2 is a graph showing impedance values ​​of samples obtained by the methods of (1) and (2) of FIG.

[0059] In one embodiment, a 10 kHz electric signal was applied to the coil unit 30 to measure the change in impedance for samples A, B, and C. The change in impedance is the difference between the initial impedance value when there is no measurement target around the coil unit 30 (or when the measurement target is in the air) and the impedance value measured after placing the measurement target around the coil unit 30. Samples A, B, and C are magnetorheological fluids with magnetic particle contents of 72 wt%, 80 wt%, and 85 wt%, respectively. The coil unit 30 was continuously placed at the same height of the container 10, and the change in impedance was measured for the case where the container 10 was placed inside the coil unit 30 [or in the hollow region 35] as shown in FIG. 1 (1) and the case where the container 10 was placed outside the coil unit 30 [or in the outer peripheral region] as shown in FIG. 1 (2).

[0060] 2, it can be seen that the case of FIG. 1(1) in which the container 10 is disposed inside the coil unit 30 [or the hollow region 35] shows a significantly larger impedance change value. It can be seen that, regardless of the magnetic particle content, all samples show a significantly larger impedance change value in FIG. 1(1) than in FIG. 1(2). It can be seen that the magnitude of the impedance signal in FIG. 1(1) is measured to be 10 times larger than that in FIG. 1(2), and is approximately 25 to 80 times larger. The method of FIG. 1(2) not only shows a smaller impedance change value, but also has the problem that the value measured for sample C, which has the highest particle content, is smaller than samples A and B, which is likely to cause errors.

[0061] As described above, in the method for evaluating the characteristics of a magnetorheological fluid according to one embodiment of the present invention, when an impedance signal is measured with the magnetorheological fluid 20 placed in the hollow region 35 of the coil section 30, a significantly larger signal is measured, resulting in the effect of being able to evaluate the characteristics much more accurately and easily than conventional techniques.

[0062] Also, the greater the change in impedance is measured from sample A to sample C, i.e., the greater the content of magnetic particles in the magnetorheological fluid 20. It can also be seen that the greater the content of magnetic particles in the magnetorheological fluid 20, the greater the difference in impedance signal becomes in the case of Fig. 1(1) than in the case of Fig. 1(2). In other words, it can be seen that the greater the content of magnetic particles in the magnetorheological fluid 20, the greater the change in impedance becomes.

[0063] 3 is a schematic diagram showing a method for evaluating the properties of a magnetorheological fluid according to another embodiment of the present invention, where (3) in FIG. 3 shows a method for evaluating the properties of a magnetorheological fluid according to an embodiment of the present invention, and (4) in FIG. 3 shows a method for evaluating the properties of a magnetorheological fluid according to a comparative example.

[0064] A method for evaluating the properties of a magnetorheological fluid according to another embodiment of the present invention may include the steps of (a) preparing a container 10 filled with a magnetorheological fluid 20, (b) preparing a measuring unit 50 having a coil unit 30 disposed therein, (c) immersing the measuring unit 50 in the magnetorheological fluid 20, and (d) measuring an impedance signal or inductance signal for the magnetorheological fluid via the coil unit 30.

[0065] Referring to Fig. 3(3), first, a container 10 filled with a magnetorheological fluid 20 can be prepared. This is the same as that described in detail in Fig. 1(1).

[0066] Next, the measuring unit 50 in which the coil unit 30 is disposed can be prepared. The measuring unit 50 is configured to enter from the open top of the container 10 and be at least partially immersed in the magnetorheological fluid 20. The measuring unit 50 preferably has a length longer than the height of the container 10 or at least the same length. The measuring unit 50 may be tubular having an empty space therein so that the coil unit 30 can be disposed therein. When the measuring unit 50 is immersed in the magnetorheological fluid 20, the measuring unit 50 may have a form that seals the coil unit 30 so that the magnetic particles do not stick to or aggregate on the coil unit 30. Alternatively, the coil case 40 may have a form that surrounds and seals the coil unit 30 and is connected to the measuring unit 50.

[0067] Next, the measuring unit 50 can be immersed in the magnetorheological fluid 20. This includes immersing the measuring unit 50 so that the coil unit 30 included in the measuring unit 50 is located at least in the height region where the magnetorheological fluid 20 is contained in the container 10. In other words, the coil unit 30 must be located within the height range of the container 10 filled with the magnetorheological fluid 20 so that the coil unit 30 can measure the impedance signal or inductance signal of the magnetorheological fluid 20.

[0068] Next, an impedance signal or an inductance signal for the magnetorheological fluid can be measured via the coil unit 30. Both ends of the coil conductor of the coil unit 30 extend to the outside through the space in the measurement unit 50 and are connected to a signal measurement device (not shown), thereby making it possible to measure the impedance signal or the inductance signal.

[0069] The impedance signal or inductance signal can correspond to the amount of magnetic particles dispersed at a particular position in the magnetorheological fluid 20. The present invention is characterized in that the amount of magnetic particles in the magnetorheological fluid 20 at a position adjacent to the coil section 30 is predicted based on the impedance signal or inductance signal measured at the coil section 30. This is the same as that described in detail in FIG. 1 (1).

[0070] Meanwhile, when immersing the measuring unit 50 in the magnetorheological fluid, it is preferable that the measuring unit 50 (or the coil case 40) is made of a non-magnetic, non-conductive material. If the measuring unit 50 is made of a magnetic or conductive material, when the coil unit 30 interacts with the magnetorheological fluid 20 to measure an impedance signal or an inductance signal, the measured value may include noise due to interaction with the measuring unit 50. In order to eliminate this, a measuring unit 50 made of a non-magnetic, non-conductive material can be used.

[0071] FIG. 4 is a graph showing impedance values ​​of samples obtained by the methods of (3) and (4) in FIG.

[0072] According to one embodiment, a 1 kHz electric signal was applied to the coil unit 30 to measure the change in impedance for Samples 1, 2, and 3. Samples 1, 2, and 3 are magnetorheological fluids with magnetic particle contents of 30 wt%, 70 wt%, and 90 wt%, respectively. The coil unit 30 was continuously placed at the same height in the container 10, and the change in impedance was measured for the cases where the coil unit 30 was placed inside the container 10 [or inside the magnetorheological fluid 20] as shown in Fig. 3(3) and where the coil unit 30 was placed outside the container 10 [or outside the magnetorheological fluid 20] as shown in Fig. 3(4).

[0073] 4, it can be seen that the case of FIG. 3(3) in which the coil unit 30 is disposed inside the container 10 [or inside the magnetorheological fluid 20] shows a significantly larger change in impedance. It can be seen that the change in impedance in FIG. 3(3) is significantly larger than that in FIG. 3(4) for all samples, regardless of the magnetic particle content. In FIG. 3(4), the change in impedance is shown to be nearly 0. The method of FIG. 3(4) has the problem that the change in impedance is very small, making it difficult to measure and highly likely to cause errors even if it is measured.

[0074] As described above, the method for evaluating the properties of a magnetorheological fluid according to another embodiment of the present invention is performed by disposing the coil unit 30 inside the container 10. This has the effect that when the impedance signal is measured with the device in a position such that the signal is measured to be significantly larger, the characteristics of which can be evaluated much more accurately and easily.

[0075] FIG. 5 is a graph showing impedance values ​​versus frequency for samples obtained by the methods of FIGS. 1(1) and 1(2).

[0076] According to an embodiment, electrical signals of 0.1 kHz, 1 kHz, and 10 kHz were applied to the coil unit 30 of samples A, B, and C, respectively, to measure the change in impedance. Samples A, B, and C are magnetorheological fluids with magnetic particle contents of 72 wt%, 80 wt%, and 85 wt%, respectively. Referring to FIG. 5, it can be seen from the three graphs that the case of FIG. 1(1) in which the container 10 is disposed inside the coil unit 30 [or in the hollow region 35] shows a significantly large change in impedance. In addition, in the case of FIG. 1(1), it can be seen that the measured change in impedance increases from sample A to sample C, that is, as the magnetic particle content of the magnetorheological fluid 20 increases. In contrast, in the case of FIG. 1(2), the magnetic particle content of the magnetorheological fluid 20 and the magnitude of the change in impedance tended to differ depending on the frequency. It is believed that in the case of FIG. 1(2), the change in impedance is small, which causes a large error and the results do not show a consistent trend.

[0077] FIG. 6 is a graph comparing impedance and inductance values ​​with respect to changes in frequency for a sample according to an embodiment of the present invention.

[0078] According to an embodiment, electrical signals of 0.1 kHz, 1 kHz, and 10 kHz were applied to the coil unit 30 of samples A, B, and C, respectively, to measure the change in impedance and inductance. Referring to FIG. 6, it can be seen from the three graphs that the trends of the change in impedance and the change in inductance are similar or substantially the same regardless of the change in frequency. This may mean that the change in impedance corresponds to the change in inductance of the coil, without the involvement of other impedance elements (resistance, capacitance). In view of this, it can be understood that the change in impedance and the change in inductance are interchangeable in this specification.

[0079] FIG. 7 is a schematic diagram showing a measurement unit according to one embodiment of the present invention.

[0080] 7, the measuring unit 50 according to an embodiment of the present invention may be provided to include a coil unit 30. One or more of the coil units 30 may be provided to be connected to the measuring unit 50. The measuring unit 50 of FIG. 7 is provided such that three coil units 30 are arranged vertically spaced apart from each other, so that impedance signals or inductance signals of the magnetorheological fluid 20 can be measured simultaneously at three vertical heights. However, the number and positions of the coil units 30 are not limited thereto and may be changed depending on the position to be measured.

[0081] The measuring unit 50 includes a housing 51 forming a body, and the coil case 40 may be connected to the housing 51. As shown in FIG. 3, the coil case 40 may be included inside the housing 51. The coil cases 40 (40a, 40b, 40c) may be provided in a number corresponding to the coil unit 30. Each coil case 40 may include a receiving portion 41 in which the coil unit 30 is received, and a cover portion 45 that covers the receiving portion 41 and seals the internal space of the receiving portion 41. The coil case 40 is preferably made of a non-magnetic or insulating material to minimize an effect on an electrical signal measured by the coil unit 30.

[0082] The coil unit 30 may be inserted and fixed in the receiving portion 41. At this time, an opening may be formed in the receiving portion 41 so that the hollow region 35 of the coil unit 30 may be inserted into the receiving portion 41. An opening may also be formed in the cover portion 45. A molding made of a rubber material or the like may be further formed around the coil unit 30 inside the receiving portion 41 to fix the coil winding.

[0083] The coil conductors 52 (52a, 52b) of the coil section 30 are extended along the housing 51 of the measuring section 50 and are connected to a signal measuring device (not shown) to measure an impedance signal or an inductance signal.

[0084] The housing 51 is formed with a grip portion 53, which can be used as a handle for moving the measuring portion 50. The housing 51 is provided with a weight portion 55 at its lower end, which provides a sense of weight. When the measuring portion 50 [or the coil portion 30] is immersed in the magnetorheological fluid 20, the housing 51 can be prevented from moving due to the buoyancy of the magnetorheological fluid 20.

[0085] FIG. 8 is a graph showing change in impedance versus measurement height for a sedimented sample according to one embodiment of the present invention.

[0086] A plurality of coil units 30 may be arranged according to the height of the container 10. When (1) of FIG. 1 is applied, the container 10 may be arranged in the hollow region 35 of three coil units 30 spaced apart from one another in the vertical direction. When (3) of FIG. 3 is applied, three coil units 30 may be arranged in the measuring unit 50 spaced apart from one another in the vertical direction, and the measuring unit 50 may be immersed in the magnetorheological fluid 20. Alternatively, the measuring unit 50 of FIG. 7 may be immersed in the magnetorheological fluid 20, so that the coil units 30 are immersed in the magnetorheological fluid 20. The height of the coil units 30 may be arranged to correspond to the height of the magnetorheological fluid 20. That is, the coil units 30 may be arranged at a height between the lowest end and the highest end of the magnetorheological fluid 20.

[0087] As an example, the bottom of the magnetorheological fluid 20 was set as the 0 mm reference, and three coil units 30 were used to measure the change in impedance at each height. The coil units 30 were placed at heights of about 40 mm (first position), 180 mm (second position), and 320 mm (third position). The container 10 was filled with a magnetorheological fluid sample that had been allowed to settle for one month and a magnetorheological fluid sample that had been allowed to settle for 24 months, and the change in impedance was measured.

[0088] The sample that was left to settle for one month exhibited impedance changes of approximately 53, 49, and 34 Ω at positions 1, 2, and 3, respectively. The sample that was left to settle for 24 months exhibited impedance changes of approximately 105, 28, and 2 Ω at positions 1, 2, and 3, respectively.

[0089] When compared with the first position, which is the lowest position, the impedance change value of the sample that had been settling for 24 months was significantly larger than that of the sample that had been settling for one month. This means that as time passed, more magnetic particles settled to the bottom in the sample that had been settling for 24 months. When compared with the second and third positions, the impedance change value of the sample that had been settling for 24 months was significantly smaller than that of the sample that had been settling for one month. This means that in the sample that had been settling for 24 months, there were fewer magnetic particles present from the bottom to the top. In other words, this means that the thickness of the upper layer (supernatant) in the magnetorheological fluid, where the magnetic particles were separated by sedimentation, became thicker as time passed. In particular, it can be confirmed that the impedance change value of the sample that had been settling for 24 months at the third position was about 2 (Ω), which is a level at which almost no magnetic particles were present.

[0090] 9 is a graph showing the change in impedance versus measurement height for a subsidence sample after 1 month, 2 months, and 24 months according to an embodiment of the present invention. The subsidence period was further divided into smaller periods to examine the change in impedance versus measurement height.

[0091] At the lowest position, position 1, the impedance change value of the sample that had been settling for two months is greater than that of the sample that had been settling for one month. Conversely, at the highest position, position 3, the impedance change value of the sample that had been settling for two months is smaller than that of the sample that had been settling for one month. At position 2, there is almost no difference in the impedance change value. It can be seen that at position 1, the impedance change value increases in the direction of the right arrow, and at position 3, the impedance change value decreases in the direction of the left arrow. Referring to the graph on the right side of FIG. 9, it can be seen that the difference in the impedance change value between positions 1 and 3 increases as the settling period increases.

[0092] If no settling occurs and the magnetic particles are uniformly mixed in all parts of the magnetorheological fluid 20, the impedance change values ​​at the first, second, and third positions may be the same. That is, the slope of a graph connecting the impedance change values ​​at the first, second, and third positions may be vertical. Since the degree of sedimentation of the magnetic particles is not yet large in the sample that has been settling for one month, the slope of a graph connecting the impedance change values ​​at the first, second, and third positions may be closer to vertical than that of the sample that has been settling for 24 months. The longer the period of sedimentation for a sample, the more negative the slope of the graph connecting any two height points on the graph of the X-axis (impedance change value) and Y-axis (height) may be.

[0093] The present invention sets data on the settling period of a magnetorheological fluid sample as reference data, and can calculate the degree of settling of the magnetorheological fluid from the difference between impedance signals measured at each height. As one example, the degree of settling can be calculated from the difference between a first impedance signal measured at a first position and a second impedance signal measured at a second position higher than the first position. As another example, the degree of settling and the period of settling can be calculated by calculating the slope of a graph connecting the change in the first impedance measured at the first position and the change in the second impedance measured at the second position higher than the first position.

[0094] FIG. 10 is a graph showing impedance values ​​versus the content of magnetic particles according to an embodiment of the present invention.

[0095] According to one embodiment, the content of magnetic particles in the magnetorheological fluid was changed from 10 wt% to 90 wt%, and the change in impedance was measured. The content of carbonyl iron powder (CIP) was changed, and electrical signals of 0.1 kHz, 1 kHz, and 10 kHz were applied to the coil unit 30 to measure the change in impedance. Referring to FIG. 10, it can be seen that the three graphs show similar trends in the change in impedance relative to the content of magnetic particles, regardless of the change in frequency. Therefore, the content and concentration of magnetic particles in the magnetorheological fluid can be calculated by setting the data of the change in impedance relative to the content of magnetic particles as reference data and measuring the change in impedance.

[0096] 11 is a graph showing saturation magnetization value versus magnetic particle content according to an embodiment of the present invention. Referring to FIG. 11, it can be seen that the saturation magnetization value increases proportionally as the magnetic particle content increases. Therefore, by measuring the change in impedance, the content and concentration of magnetic particles in the magnetorheological fluid can be calculated, and the saturation magnetization value can also be easily calculated.

[0097] FIG. 12 is a graph showing impedance values ​​versus types of magnetic particles in a magnetorheological fluid according to an embodiment of the present invention.

[0098] In one embodiment, the change in impedance was measured while changing the type of magnetic particles in the magnetorheological fluid. Groups A, B, C, and D are magnetorheological fluid samples that contain particle groups α and β of the same material but with different particle fractions having different average particle sizes. The fractions (wt%) of particle group α and particle group β are as follows: Group A (75:25), Group B (100:0), Group C (0:100), and Group D (50:50). The average particle size of particle group α is about twice as large as that of particle group β.

[0099] 12, it can be seen that the impedance change values ​​of groups A, B, C, and D have similar trends in the three graphs regardless of the change in frequency. This can mean that the method for evaluating the properties of a magnetorheological fluid of the present invention is independent of the type and size of the magnetic particles, and only the content and concentration of the magnetic particles affect the impedance change values.

[0100] Fig. 13 is a schematic diagram showing a process of determining the concentration of magnetic particles in a magnetorheological fluid according to an embodiment of the present invention, and Fig. 14 is a graph showing a process of determining the concentration of magnetic particles in a magnetorheological fluid according to an embodiment of the present invention.

[0101] A method for evaluating characteristics of a magnetorheological fluid according to one embodiment of the present invention includes the steps of: <1> A step (S11) of measuring an impedance signal (a change in impedance) of the magnetorheological fluid; <2> and determining a concentration of magnetic particles corresponding to the change in impedance (S12). As described in FIG. 6, the change in impedance can be replaced with a change in inductance, so the method for evaluating the properties of a magnetorheological fluid according to another embodiment of the present invention is as follows: <1> A step (S11) of measuring an inductance signal (change in inductance) of the magnetorheological fluid; <2> and determining (S12) the concentration of magnetic particles corresponding to the change in inductance.

[0102] Step S11( <1> ), a container 10 may be placed in the hollow region 35 of the coil section 30, or a measuring section 50 including the coil section 30 may be immersed in the magnetorheological fluid 20. Alternatively, the magnetorheological fluid 20 may be made to flow through the hollow region of the coil section 30. An electric signal such as a current is applied to the coil section 30 to interact with the adjacent magnetorheological fluid, and an impedance signal or an inductance signal may be measured by a signal measuring device (not shown) connected to the outside from both ends of the coil conductor of the coil section 30.

[0103] Next, step S12( <2> 14, the concentration of magnetic particles can be determined from previously collected reference data. By matching the magnetic particle concentration values ​​corresponding to the measured impedance changes in the graph of FIG. 14, the concentration of magnetic particles in the portion of the magnetorheological fluid 20 where the coil section 30 is located can be determined.

[0104] Fig. 15 is a schematic diagram showing a process for determining the degree of uniformity of dispersion of the magnetorheological fluid according to one embodiment of the present invention, for use in determining the completion time of a manufacturing process, quality control of sedimentation or redispersibility, injection, etc. Fig. 16 is a schematic diagram showing a method for evaluating the characteristics of the magnetorheological fluid in a flow channel 10' through which the magnetorheological fluid 20 according to one embodiment of the present invention flows.

[0105] A method for evaluating the characteristics of a magnetorheological fluid according to one embodiment of the present invention includes (1) a step (S21) of measuring impedance signals or inductance signals at multiple positions in a container 10 or a flow path 10' or at least two time points at a specific point, and (2) a step (S22) of determining whether the difference between the impedance signals or inductance signals corresponds to a set reference value. If the difference is greater than the set reference value, further dispersion of the magnetorheological fluid 20 is performed (S23), and if the difference is the same as or smaller than the set reference value, the magnetorheological fluid 20 is used (S24).

[0106] In step S21, the impedance signal or inductance signal can be measured at at least two heights of the container 10. The hollow regions 35 of the coil section 30 can be positioned at the at least two heights of the container 10, or the measuring section 50 can be immersed in the magnetorheological fluid 20 to position the coil section 30 at the at least two heights. An electric signal such as a current is applied to each coil section 30 to interact with the adjacent magnetorheological fluid, and the impedance signal or inductance signal can be measured by a signal measuring device (not shown) connected externally to both ends of the coil conductor of each coil section 30.

[0107] Alternatively, impedance signals or inductance signals can be measured at at least two positions in the flow channel 10'. The tube providing the flow channel 10' is also preferably made of a non-magnetic, non-conductive material like the container 10. The hollow regions 35 of the coil unit 30 can be located at at least two positions in the flow channel 10', respectively, or the coil unit 30 can be immersed in the flow channel 10' and positioned at two positions, respectively.

[0108] Alternatively, the impedance or inductance signal may be measured at at least two points in time with respect to a specific point in the container 10 or the flow path 10'. As an example, the impedance or inductance signal may be measured from the coil unit 30 for a plurality of times such as t1, t2, etc.

[0109] Next, in step S22, it may be determined whether the difference between the impedance signal or the inductance signal, i.e., the difference between the change in impedance or inductance, corresponds to a set reference value. The set reference value may correspond to reference data previously collected from magnetorheological fluids having the same magnetic particle content. For example, the ratio of the change in impedance or inductance measured at the second position on the top to the change in impedance or inductance measured at the first position on the bottom of the magnetorheological fluid may be calculated and compared with the set reference ratio. As another example, the ratio of the change in impedance or inductance measured through the coil unit 30 at a specific position for multiple times such as t1 and t2 may be calculated and compared with the set reference ratio.

[0110] Next, if it is determined that the difference between the impedance signal or the inductance signal is greater than the set reference value, the magnetorheological fluid 20 can be further dispersed (step S23). If the difference between the impedance signal or the inductance signal is greater than the set reference value, it means that the sedimentation of the magnetic particles has progressed significantly, and the uniformity of the magnetic particles is reduced, so that it is considered difficult to use the magnetorheological fluid in processes and products. Therefore, the magnetorheological fluid can be stirred so that the magnetic particles are dispersed again in the dispersion medium. After the redispersion, the steps S21 and S22 can be performed again. For example, if the set reference value is determined as a ratio such as 97%, if the change in impedance measured at the second position is less than 97% relative to the change in impedance measured at the first position, the magnetorheological fluid can be further dispersed.

[0111] The set reference value may be set according to the application product to which the magnetorheological fluid is applied. For example, in a magnetorheological fluid damper or magnetorheological fluid brake product, the set reference value may be determined as a range smaller than the specification of the characteristic related to the shear stress exhibited by the magnetic particles in the magnetorheological fluid within the specification. For example, if the specification of the damping force, which is the characteristic related to the shear stress of the magnetorheological fluid in a magnetorheological fluid damper, is ±10%, the set reference value may be within ±10% to ±1%.

[0112] On the other hand, if it is determined that the difference in the impedance signals is smaller than or equal to the set reference value, the magnetorheological fluid 20 can be used in the process or product. For example, if the set reference value is defined as a ratio, such as 97%, and the change in impedance measured at the second position is 97% or more relative to the change in impedance measured at the first position, the magnetorheological fluid can be evaluated as usable because it does not undergo much settling and is uniformly dispersed.

[0113] The method for evaluating the properties of a magnetorheological fluid of the present invention may be used in the production step of the magnetorheological fluid, the quality control step, the incoming inspection step of the magnetorheological fluid user, the injection step of the magnetorheological fluid by the magnetorheological fluid user, etc.

[0114] In the production step, the content and concentration of magnetic particles can be easily measured in real time using the coil unit 30 in the magnetorheological fluid 20. The coil unit 30 is attached to or immersed in the production or injection equipment of the magnetorheological fluid, and the impedance or inductance signal can be monitored continuously or discontinuously over time, thereby determining the presence or absence of abnormalities in the progress of the production process and the end point. In addition, the impedance or inductance signals from the coil unit 30 attached to multiple positions in the production or injection equipment can be compared to evaluate the completeness of the blending of the magnetorheological fluid in the production equipment.

[0115] Also, in order to determine whether there is an abnormality in the components of the magnetorheological fluid during the production step, the magnetorheological fluid flowing continuously through the coil unit 30 can be measured. The magnetorheological fluid flowing around the coil unit 30 or into the hollow region 35 of the coil unit 30 can be measured. As an example, an impedance or inductance signal can be measured from the coil unit 30 for a number of times such as t1 and t2 to determine whether it corresponds to a set reference value. If it does not correspond to the set reference value, it can be determined that the content of magnetic particles contained in the magnetorheological fluid during the production process is low, and further dispersion or a process of correcting the components can be performed.

[0116] In a quality control step, the degree of settling and uniformity of dispersion can be assessed by measuring the impedance or inductance signal of the magnetorheological fluid 20 at multiple positions, as previously described with reference to FIG. 8 et seq.

[0117] FIG. 17 is a schematic diagram showing a process for evaluating the redispersibility of a magnetorheological fluid according to an embodiment of the present invention.

[0118] When evaluating the redispersibility of a magnetorheological fluid, a magnetorheological fluid in which at least some of the magnetic particles have settled is provided (S31), and an external force is applied to the magnetorheological fluid in which the settling has occurred to cause redispersion (S32). After the external force is applied, impedance or inductance signals can be measured at least at two heights in the vertical direction (S33). Then, by determining whether the impedance or inductance signals according to the heights are within set reference values, or whether the difference between the impedance or inductance signals according to the heights is within set reference values ​​(S34), it can be confirmed whether redispersion has occurred sufficiently.

[0119] Also, in the step of inspecting magnetorheological fluid by a user upon receipt, the content, concentration, sedimentation degree, etc. of magnetic particles are checked for magnetorheological fluid that has been manufactured a relatively long time ago, and if the content does not reach the set standard value, a redispersion process is further performed, thereby enabling the use of magnetorheological fluid with desired properties. This can be useful in the step of injecting magnetorheological fluid, for a user to check whether the magnetorheological fluid is sufficiently dispersed before injecting the magnetorheological fluid into a magnetorheological fluid system (MR system) such as a magnetorheological fluid damper (MR damper).

[0120] In the method for evaluating the properties of a magnetorheological fluid of the present invention, a measurement unit according to FIG. 7 may be used in the production step of the magnetorheological fluid, the quality control step, the incoming inspection step by the user of the magnetorheological fluid, and the injection step of the magnetorheological fluid by the user of the magnetorheological fluid.

[0121] FIG. 18 is a schematic diagram illustrating a magnetorheological fluid damper 60 according to one embodiment of the present invention.

[0122] 18, the magnetorheological fluid damper 60 can adjust the damping force by using a magnetorheological fluid 65. The magnetorheological fluid damper 60 can include a cylinder housing 61, piston portions 62 and 63, a coil portion 64, and the magnetorheological fluid 65.

[0123] The cylinder housing 61 has a sealed structure, and the sealed internal space can be filled with a magnetorheological fluid 65 .

[0124] The piston parts 62, 63 may include a piston rod 62 extending in the longitudinal direction within the cylinder housing 61, and a piston head 63 provided at the end of the piston rod 62. The piston rod 62 can move up and down due to external vibrations and shocks. The piston head 63 is formed with an outer diameter corresponding to the inner diameter of the cylinder housing 61, and divides the inside of the cylinder housing 61 into upper and lower spaces, allowing the magnetorheological fluid 65 to be disposed in each space. When the piston rod 62 moves up and down, the magnetorheological fluid 65 can flow at least through the gap of the piston head 63.

[0125] The piston portions 62 and 63 may be configured with electromagnets, and a coil portion 64 may be disposed inside or at least on the outer circumferential surface of the piston portions 62 and 63. The coil portion 64 may generate a magnetic field by applying an electric current from the outside. The generated magnetic field is applied to the magnetorheological fluid 65, so that the viscosity and yield stress of the magnetorheological fluid 65 can be adjusted. The coil portion 64 and the magnetorheological fluid 65 correspond to the coil portion 30 and the magnetorheological fluid 20 described above.

[0126] The magnetorheological fluid damper 60 is not necessarily limited to the above-mentioned configuration, and various configurations can be adopted as long as the purpose is to adjust the damping force by changing the viscosity of the magnetorheological fluid.

[0127] 19 is a schematic diagram showing the operation process of a magnetorheological fluid system according to an embodiment of the present invention. The operation process will be explained by taking a magnetorheological fluid damper 60 as an example, but it should be clear that this can be equally applied to magnetorheological fluid systems such as magnetorheological fluid brakes.

[0128] According to one embodiment of the present invention, in the process of operating the magnetorheological fluid damper 60, an electric signal can be applied to the coil unit 64 (S41). Then, an impedance or inductance signal of the magnetorheological fluid 65' flowing through the piston units 62 and 63 can be measured via the coil unit 64 (S42). This makes it possible to determine the concentration or content of magnetic particles in the magnetorheological fluid 65'.

[0129] If the signal measured in the magnetorheological fluid 65' is lower than the set reference value, for example if it is determined that the concentration or content of magnetic particles in the magnetorheological fluid 65' is low, the strength of the electric signal applied to the coil unit 64 is increased to generate a stronger magnetic field and increase the viscosity of the magnetorheological fluid 65', thereby controlling the damping force to match the target value. Alternatively, the concentration or content of magnetic particles can be adjusted to correspond to the set reference value by adding a movement of the piston units 62, 63, etc. to perform dispersion (S43).

[0130] Conversely, if the signal measured in the magnetorheological fluid 65' is higher than the set reference value, for example if it is determined that the concentration or content of magnetic particles in the magnetorheological fluid 65' is high, the strength of the electrical signal applied to the coil portion 64 can be weakened to generate an even smaller magnetic field and the viscosity of the magnetorheological fluid 65 can be reduced to control the damping force to match the target value.

[0131] As described above, the present invention has an effect of being able to accurately evaluate the properties of magnetic particles in a magnetorheological fluid, such as the content, concentration, and sedimentation degree, in a simple manner. Moreover, the present invention has an effect of being able to protect the physical properties of the magnetorheological fluid and improve the economic efficiency by only performing a minimum amount of remixing / redispersion on the magnetorheological fluid in which the magnetic particles have settled, thereby eliminating unnecessary processes.

[0132] Although the present invention has been illustrated and described with reference to the preferred embodiment as described above, the present invention is not limited to the above embodiment, and various modifications and alterations may be made by those skilled in the art to which the present invention pertains without departing from the spirit of the present invention. Such modifications and alterations must be recognized as falling within the scope of the present invention and the appended claims. [Explanation of symbols]

[0133] 10 containers 10' Channel 20 Magnetorheological fluids 30 Coil section 35 Hollow area 40 Coil case 50 Measuring part 60 Magnetorheological Fluid Damper

Claims

1. A method for evaluating the properties of a magnetorheological fluid containing magnetic particles, comprising: (a) preparing a container filled with a magnetorheological fluid or a channel through which the magnetorheological fluid flows; (b) positioning the coil section such that the vessel or the flow path is located in a hollow region of the coil section; (c) measuring an impedance signal or an inductance signal for the magnetorheological fluid via the coil portion.

2. A method for evaluating the properties of a magnetorheological fluid containing magnetic particles, comprising: (a) preparing a container filled with a magnetorheological fluid or a channel through which the magnetorheological fluid flows; (b) preparing a measuring unit having a coil unit disposed therein or connected thereto; (c) immersing the coil portion in the magnetorheological fluid; (d) measuring an impedance signal or an inductance signal for the magnetorheological fluid via the coil portion.

3. The method for evaluating the characteristics of a magnetorheological fluid according to claim 1 , wherein the container or the pipe in which the flow passage is formed is made of a non-magnetic or non-conductive material.

4. The method for evaluating the characteristics of a magnetorheological fluid according to claim 2 , wherein a case of the measurement unit is made of a non-magnetic or non-conductive material.

5. A method for evaluating the characteristics of a magnetorheological fluid as described in claim 1, wherein the magnitude of the impedance signal or the inductance signal is measured to be more than 10 times larger when the container or the flow path is located in the hollow region of the coil section than when the container or the flow path is located in the outer peripheral region of the coil section.

6. 6. The method for evaluating the characteristics of a magnetorheological fluid as described in claim 5, wherein the greater the content of the magnetic particles in the magnetorheological fluid, the greater the difference in the impedance signal or the inductance signal when the container or the flow path is located in the hollow region of the coil section than when the container or the flow path is located in the outer peripheral region of the coil section.

7. 3. A method for evaluating the characteristics of a magnetorheological fluid as described in claim 2, wherein when the coil portion is immersed in the magnetorheological fluid, the magnitude of the impedance signal or the inductance signal is measured to be more than 10 times larger than when the container or the flow path is located in the outer peripheral region of the coil portion.

8. The method for evaluating the characteristics of a magnetorheological fluid according to claim 7, wherein the greater the content of the magnetic particles in the magnetorheological fluid, the greater the difference in the impedance signal or the inductance signal when the coil portion is immersed in the magnetorheological fluid than when the container or the flow path is located in the outer peripheral region of the coil portion.

9. 3. The method for evaluating the characteristics of a magnetorheological fluid according to claim 1 or 2, further comprising measuring an impedance signal or an inductance signal for the magnetorheological fluid via the coil section for each height of a container filled with the magnetorheological fluid.

10. 10. The method for evaluating the characteristics of a magnetorheological fluid as described in claim 9, wherein the degree of sedimentation of the magnetorheological fluid is calculated from (1) the difference between a first impedance signal measured at a first position in the container and a second impedance signal measured at a second position higher than the first position, or (2) the difference between a first inductance signal measured at the first position and a second inductance signal measured at a second position higher than the first position.

11. The method for evaluating the characteristics of a magnetorheological fluid as described in claim 10, wherein the difference between the first impedance signal and the second impedance signal, or the difference between the first inductance signal and the second inductance signal, becomes larger as time passes from a reference point in time.

12. The method for evaluating the characteristics of a magnetorheological fluid as described in claim 10, wherein as time passes from a reference point in time, (1) the first impedance signal becomes larger and the second impedance signal becomes smaller, or (2) the first inductance signal becomes larger and the second inductance signal becomes smaller.

13. 3. The method for evaluating the characteristics of a magnetorheological fluid according to claim 1 or 2, further comprising measuring the impedance signal or the inductance signal for the magnetorheological fluid via the coil section, and calculating the concentration of magnetic particles in the magnetorheological fluid.

14. The method for evaluating the characteristics of a magnetorheological fluid as described in claim 1, further comprising providing a plurality of coil sections spaced apart from each other along the vertical direction of the container, and placing the container in the hollow region of at least two of the coil sections.

15. The measurement unit includes a plurality of the coil units arranged at a distance from each other along a vertical direction of the container, 3. The method for evaluating the characteristics of a magnetorheological fluid as described in claim 2, wherein the measuring unit is immersed in the magnetorheological fluid so that the height of at least two of the coil portions of the measuring unit is located lower than the uppermost end of the magnetorheological fluid.

16. A method for evaluating the characteristics of a magnetorheological fluid as described in claim 1 or 2, comprising measuring an impedance signal or an inductance signal for the magnetorheological fluid via the coil section at at least two points in time at a specific point in a container filled with the magnetorheological fluid.

17. The step of measuring an impedance signal or an inductance signal for the magnetorheological fluid via the coil unit includes: A method for evaluating the characteristics of a magnetorheological fluid as described in claim 1 or 2, comprising the steps of: (1) measuring the impedance signal or the inductance signal at at least two points or at least two time points in the container or the flow path; and (2) determining whether the difference between the impedance signal or the inductance signal measured at the at least two points or at least two time points is greater than a set reference value.

18. The step of measuring an impedance signal or an inductance signal for the magnetorheological fluid via the coil unit includes: A method for evaluating the characteristics of a magnetorheological fluid as described in claim 1 or 2, comprising the steps of: (1) measuring the impedance signal or the inductance signal at at least two points or at least two time points in the container or the flow path; and (2) determining whether the impedance signal or the inductance signal measured at the at least two points or at least two time points is within a range of a predetermined reference value, respectively.

19. The method for evaluating the properties of a magnetorheological fluid as described in claim 17, further comprising dispersing the magnetorheological fluid if the difference between the impedance signal or the inductance signal measured at the at least two points or at least two time points is greater than a set reference value.

20. A method for evaluating the properties of a magnetorheological fluid as described in claim 17, wherein the magnetorheological fluid is used under conditions where the difference between the impedance signal or the inductance signal measured at the at least two points or at least two time points is indicated to be the same as or smaller than a set reference value.

21. The method for evaluating the characteristics of a magnetorheological fluid as described in claim 18, further comprising dispersing the magnetorheological fluid if the difference between the impedance signal or the inductance signal measured at the at least two points or at least two time points is outside a range of preset reference values, respectively.

22. A method for evaluating the properties of a magnetorheological fluid as described in claim 18, wherein the magnetorheological fluid is used if the difference between the impedance signal or the inductance signal measured at the at least two points or at least two time points is within a range of a preset reference value, respectively.

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