JP6611352B2 - shock absorber - Google Patents

Description

  The present invention relates to a shock absorber.

  Generally, a shock absorber is mounted on a vehicle in order to attenuate vibration during traveling in a short time and improve riding comfort and traveling stability. Among such shock absorbers, there is known a shock absorber using an electrorheological fluid (electrorheological fluid composition) in order to control the damping force according to the road surface condition or the like (see Patent Document 1). .

  Patent Document 1 discloses an electrorheological fluid in which particles having an electrorheological effect are contained in an electrically insulating medium in an apparatus such as a shock absorber.

JP-A-8-127790

  However, the particle-dispersed electrorheological fluid containing particles has a high temperature dependence of viscosity because it is a suspension in which resin particles are dispersed. For this reason, when the temperature of the electrorheological fluid changes, the viscosity changes and the damping force changes, so that the riding comfort of the vehicle may deteriorate. Patent Document 1 discloses an electrorheological fluid in which particles and composite particles made of a plurality of types of materials are dispersed. However, a technique for improving the deterioration of the riding comfort of a vehicle due to the temperature dependence of the electrorheological fluid is disclosed. There is no disclosure.

A shock absorber according to an aspect of the present invention includes a piston rod, an inner cylinder into which the piston rod is inserted, an electrorheological fluid provided between the piston rod and the inner cylinder, and a voltage applied to the electrorheological fluid. In the shock absorber having a voltage application mechanism for applying a pressure, the electrorheological fluid includes base oil and a temperature represented by (viscosity of the electrorheological fluid at −30 ° C./viscosity of the electrorheological fluid at 23 ° C.) × 100. Temperature-expandable particles having an average linear expansion coefficient of 1.4 × 10 ⁻⁴ / ° C. or more so that the dependence value is 300% or less.

  ADVANTAGE OF THE INVENTION According to this invention, the change of the riding comfort of the vehicle resulting from the temperature change of an electrorheological fluid can be suppressed.

The longitudinal cross-sectional schematic diagram explaining the structure of a shock absorber. The schematic diagram which shows the state which disperse | distributed one type of particle | grains (temperature expansible particle | grains which function also as ER particle | grains) to base oil. The schematic diagram which shows the electrorheological fluid which disperse | distributed two types of particle | grains (ER particle | grains and temperature expansible particle | grains) to base oil. The figure which shows the relationship between the temperature dependence of the viscosity in a low temperature range, and an average linear expansion coefficient. The figure which shows the relationship between the change rate of the temperature dependence of the viscosity in a low temperature range, and particle concentration. The figure which shows the relationship between the lower limit of the average linear expansion coefficient which satisfies the temperature dependence standard I of the viscosity in a low temperature range, and particle concentration.

  An embodiment of a shock absorber will be described with reference to the drawings. FIG. 1 is a schematic longitudinal sectional view illustrating the structure of a shock absorber. Although not shown, one shock absorber 1 is provided for each wheel of the vehicle. The shock absorber 1 fixes the head of the piston rod 6 to the body side of the vehicle, and fixes the end of the base shell 2 into which the piston rod 6 is inserted on the axle side. Reduce vibration.

  As shown in FIG. 1, the shock absorber 1 has a piston 9 provided with a piston 9 at one end (lower end in the drawing) and a head provided at the other end (not shown), and a cylindrical shape that constitutes the outline of the shock absorber 1. The base shell 2, the cylindrical outer cylinder 3 and the inner cylinder 4 provided between the piston rod 6 and the base shell 2, and the voltage application mechanism 20 are provided. An electrorheological fluid 8 is sealed in the base shell 2. The voltage application mechanism 20 includes an electrode (hereinafter referred to as an outer electrode 3a) provided on the inner peripheral surface of the outer cylinder 3, and an electrode (hereinafter referred to as an inner electrode 4a) provided on the outer peripheral surface of the inner cylinder 4. And a control device 11 for applying a voltage between the outer electrode 3a and the inner electrode 4a.

  The outer electrode 3a and the inner electrode 4a are in direct contact with the electrorheological fluid 8. For this reason, it is desirable to employ a material that is unlikely to cause electrolytic corrosion or corrosion due to components contained in the electrorheological fluid 8 as the material of the outer electrode 3a and the inner electrode 4a. For example, stainless steel or titanium can be used as the material of the outer electrode 3a and the inner electrode 4a. In addition, an electrode material whose corrosion resistance is improved by coating a metal that is not easily corroded on the surface of a metal that is easily corroded by plating or the like may be employed.

  The piston rod 6 passes through the upper end plate 2 a of the base shell 2, and a piston 9 provided at the lower end of the piston rod 6 is disposed in the inner cylinder 4. An oil seal 7 for preventing the electrorheological fluid 8 sealed in the inner cylinder 4 from leaking is disposed on the upper end plate 2 a of the base shell 2.

  As the material of the oil seal 7, for example, a rubber material such as nitrile rubber or fluorine rubber can be adopted. The oil seal 7 is in direct contact with the electrorheological fluid 8. For this reason, the material of the oil seal 7 is made of a material having a hardness equal to or higher than the hardness of the contained particles so that the oil seal 7 is not damaged by the particles contained in the electrorheological fluid 8. It is desirable to adopt. In other words, it is preferable that the particles to be contained in the electrorheological fluid 8 employ a material having a hardness comparable to or lower than the hardness of the oil seal 7.

  A piston 9 is inserted into the inner cylinder 4 so as to be slidable in the vertical direction. The piston 9 divides the inner cylinder 4 into a piston lower chamber 9L and a piston upper chamber 9U. The piston 9 is provided with a plurality of through holes 9h penetrating in the vertical direction at equal intervals in the circumferential direction. The piston lower chamber 9L and the piston upper chamber 9U communicate with each other through a through hole 9h. A check valve (not shown) is mounted in the through hole 9h, and the electrorheological fluid 8 flows in one direction through the through hole 9h.

  An upper end portion of the inner cylinder 4 is closed by an upper end plate 2 a of the base shell 2 through an oil seal 7. A body 10 is provided at the lower end portion of the inner cylinder 4, and a through hole 10 h is provided in the body 10 in the same manner as the piston 9, and a piston chamber 9 </ b> L communicates with a flow path 24 described later via the through hole 10 h. Yes. In the vicinity of the upper end of the inner cylinder 4, a plurality of lateral holes 5 penetrating in the radial direction are arranged at equal intervals in the circumferential direction. The upper end portion of the outer cylinder 3 is closed by the upper end plate 2a of the base shell 2 via the oil seal 7, and the lower end portion of the outer cylinder 3 is opened. The diameter of the outer cylinder 3 is larger than the diameter of the inner cylinder 4. The inner cylinder 4 is disposed inside the outer cylinder 3. The piston rod 6, the inner cylinder 4, the outer cylinder 3 and the base shell 2 are arranged concentrically.

  The horizontal hole 5 includes a piston upper chamber 9U defined by the inner side of the inner cylinder 4 and the rod-shaped portion of the piston rod 6, and a flow path 22 defined by the inner side of the outer cylinder 3 and the outer side of the inner cylinder 4. Communicate. The flow path 22 communicates at the lower end with a flow path 23 defined by the inside of the base shell 2 and the outside of the outer cylinder 3 and a flow path 24 between the body 10 and the bottom plate of the base shell 2. . The base shell 2 is filled with an electrorheological fluid 8, and an upper portion between the inside of the base shell 2 and the outside of the outer cylinder 3 is filled with an inert gas 13.

  When the vehicle is traveling on an uneven traveling surface, the piston rod 6 expands and contracts in the vertical direction with respect to the inner cylinder 4 as the vehicle vibrates. When the piston rod 6 expands and contracts with respect to the inner cylinder 4, the volumes of the piston lower chamber 9L and the piston upper chamber 9U change.

  An acceleration sensor 25 is provided on the vehicle body (not shown). The acceleration sensor 25 detects the acceleration of the vehicle body and outputs the detected signal to the control device 11. The control device 11 determines a voltage to be applied to the electrorheological fluid 8 based on a signal from the acceleration sensor 25 and the like.

  The control device 11 calculates a voltage for generating a necessary damping force based on the detected acceleration, applies a voltage between the electrodes based on the calculation result, and develops an electrorheological effect. When a voltage is applied by the control device 11, the viscosity of the electrorheological fluid 8 changes according to the voltage. The control device 11 adjusts the voltage to be applied based on the acceleration, thereby controlling the damping force of the shock absorber 1 generated in the interelectrode flow path and improving the riding comfort of the vehicle.

  The electrorheological fluid 8 has a dispersed phase composed of insulating particles and a dispersion medium composed of insulating liquid (hereinafter referred to as base oil), and the insulating particles are dispersed in the base oil. It is a suspension.

The type of base oil is not particularly limited as long as it is a dispersion medium capable of dispersing insulating particles. Specifically, silicone oil and mineral oils such as paraffin oil and naphthenic oil can be used as the base oil. Since the viscosity of the base oil contributes to the viscosity of the electrorheological fluid 8 and the temperature dependence of the viscosity, the viscosity is preferably 50 mm ² / s or less, more preferably 10 mm ² / s or less.

[Electrorheology (ER) particles]
In the present specification, the electrorheological (hereinafter referred to as ER) particle refers to a particle having insulating properties and particularly excellent in the expression of the ER effect. By dispersing the ER particles in the base oil, a high ER effect can be expressed. Specific materials for ER particles include methacrylic resin, polyurethane resin, acrylic resin, ion exchange resin, organic particles such as high density polyethylene, high density polypropylene, polyimide, and polyamide, and conductivity such as silica, alumina, and titania. And metal oxides, ceramics, etc. that do not have. Further, examples of the ER particles include composite particles obtained by coating organic particles with metal, and composite particles obtained by coating metal particles or organic particles with an organic semiconductor. Moreover, hollow organic particles can also be employed as the ER particles.

  The average particle size of the ER particles is not particularly limited. As the ER particles, nanoparticles having an average particle diameter of 0.1 μm or less may be employed, or particles having an average particle diameter larger than 0.1 μm may be employed. Considering the responsiveness of the electrorheological effect and the magnitude of the effect, the average particle diameter is preferably in the range of 1 μm to 10 μm, more preferably in the range of 3 μm to 7 μm, from the viewpoint of ease of particle movement and increase in viscosity. . In addition, ER particle | grains are not specifically limited by the linear expansion coefficient.

[Temperature expandable particles]
The temperature-expandable particle refers to a particle made of a material having a large volume change rate with temperature. In particular, in the present specification, it refers to a particle having a linear expansion coefficient of 1.4 × 10 ⁻⁴ / ° C. or more, which is a lower limit value of a linear expansion coefficient for satisfying a criterion I described later. Specific examples of the material for the temperature-expandable particles include fluorine resin, silicone resin, polyester resin, rubber material, low density polyethylene, and low density polypropylene. Examples of the polyester resin include polyethylene terephthalate. Examples of the fluororesin include polytetrafluoroethylene (PTFE). Examples of the rubber material include ethylene propylene rubber, chloroprene rubber (CR), natural rubber, styrene butadiene rubber, butadiene rubber, polysulfide rubber, isoprene rubber, acrylonitrile butadiene rubber, silicon rubber, and fluorosilicone rubber.

A specific value of the linear expansion coefficient is at least 1.4 × 10 ⁻⁴ / ° C. or more, preferably 1.6 × 10 ⁻⁴ / ° C. or more, more preferably 2.2 × 10 ⁻⁴ / ° C. or more. Good. For example, the linear expansion coefficient of polyethylene is 1.6 × 10 ⁻⁴ / ° C., and the linear expansion coefficient of polytetrafluoroethylene is 2.2 × 10 ⁻⁴ / ° C. Note that particles formed of these materials have not only a large coefficient of linear expansion, but also particles that act as dielectrics exhibiting insulating properties and exhibit an ER effect. Therefore, a suspension in which one kind of particles that are temperature-expandable particles and also ER particles is dispersed in the base oil can be employed as the electrorheological fluid 8 of the present embodiment.

ここで、α（ｋ）［／℃］は、電気粘性流体８に含まれる第ｋ粒子の線膨張係数であり、φ（ｋ）［−］は、第ｋ粒子の含有比率、すなわち含有されている全粒子の重量を１としたときの第ｋ粒子の重量の比率である。ｋは１以上の整数であり、粒子の種類を特定する識別番号である。 In addition, when n types (n is an integer of 1 or more) of particles are dispersed in the base oil, the average linear expansion coefficient α of the particles is obtained by the following formula (1).

Here, α (k) [/ ° C.] is the linear expansion coefficient of the k-th particle contained in the electrorheological fluid 8, and φ (k) [−] is the content ratio of the k-th particle, that is, contained. This is the ratio of the weight of the kth particle when the weight of all the particles is 1. k is an integer of 1 or more, and is an identification number that identifies the type of particle.

  When the electrorheological fluid 8 contains only one type of particle, the linear expansion coefficient of the particle becomes the average linear expansion coefficient. In order to make the effect of reducing the temperature dependence of the viscosity of the electrorheological fluid 8 to be described later and the ER effect compatible with one type of particles, the amount of water in the system is controlled, or the ER is doped with an electrolyte. An effect can also be given or improved. Note that, when the base oil penetrates significantly into the temperature-expandable particles, the temperature-expandable particles are always swollen by the base oil, so that the effect of reducing the temperature dependence of the viscosity of the electrorheological fluid 8 described later is lowered. Therefore, from the viewpoint of minimizing the interaction with the dispersion medium, fluorine-based resins, silicone-based resins, fluorosilicone rubber, etc., which have a low surface tension and low wettability with many substances are particularly effective.

  When the temperature-expandable particles and the insulating dispersion medium are the same material, for example, when the fluorine-based resin particles as the temperature-expandable particles are dispersed in the fluorine-based oil as the insulating dispersion medium, the above wettability effect cannot be expected. For this reason, it is necessary to give the particles a sufficient cross-linking structure to suppress swelling due to the dispersion medium.

  The shape of the particles may be a specific shape such as a sphere, a rectangular parallelepiped, or a cube, or may be an irregular lump, and the shape is not particularly limited. In consideration of the influence on the constituent members of the shock absorber 1, such as the oil seal 7, it is desirable to adopt spherical particles without protrusions.

  The average particle diameter of the temperature-expandable particles is not particularly limited. As temperature-expandable particles, nanoparticles having an average particle size of 0.1 μm or less may be employed, or particles having an average particle size larger than 0.1 μm may be employed. When the temperature-expandable particles behave as ER particles, the average particle size is preferably 1 μm to 10 μm from the viewpoints of the ease of movement of the particles and the increase in viscosity considering the responsiveness of the electrorheological effect and the magnitude of the effect. More preferably, it is in the range of 3 μm to 7 μm.

  By the way, the viscosity of the base oil has temperature dependence, and the viscosity of the base oil increases as the temperature decreases. Here, if the linear expansion coefficient of the particles dispersed in the base oil is small, the influence of the particles on the viscosity of the electrorheological fluid 8 is small, and the viscosity of the electrorheological fluid 8 increases as the temperature decreases. As a result, the riding comfort of the vehicle may change between a high temperature state and a low temperature state. For example, the ride comfort of the vehicle may change between summer and winter. Even on the same day, the shock absorber 1 absorbs vibrations and shocks while traveling, and the temperature of the electrorheological fluid 8 rises. Therefore, after the start of riding and after a certain amount of running time, Ride comfort may change.

As a general standard for the shock absorber 1 used in a vehicle, it is required to satisfy the temperature dependence standard I in the damping force of the shock absorber 1 at a low temperature as shown below. Since the damping force and the viscosity are in a proportional relationship, it can be considered that both are equivalent.
[Standard I]
{(Damping force (viscosity) of electrorheological fluid at −30 ° C.) / (Damping force (viscosity) of electrorheological fluid at 23 ° C.)}} 100 of “temperature dependence of viscosity in low temperature range” The value is 300% or less

  The present inventors have found that the above-mentioned standard I is satisfied by dispersing temperature-expandable particles having a large linear expansion coefficient in the base oil. FIG. 2 is a schematic view showing a state in which one kind of particles (temperature-expandable particles that also function as ER particles) is dispersed in the base oil. FIG. 3 is a schematic diagram showing an electrorheological fluid in which two types of particles (ER particles and temperature-expandable particles) are dispersed in base oil. Note that the ER particles 15 shown as an example in FIG. 3 have a linear expansion coefficient smaller than that of the temperature-expandable particles 12 and will be described as having less influence on the viscosity of the electrorheological fluid 8 due to temperature change.

  2A and 3A show a state where the temperature is high, and FIGS. 2B and 3B show a state where the temperature is low. As shown in FIG. 2A and FIG. 3A, when the temperature of the electrorheological fluid 8 is high, the temperature-expandable particles 12 are expanded as compared with the case where the temperature is low. For this reason, when the shock absorber 1 operates, the temperature-expandable particles 12 have a great resistance to the flow of the base oil 14. That is, when the temperature of the electrorheological fluid 8 rises, the volume change (expansion) of the temperature-expandable particles 12 acts in the direction of increasing the viscosity of the electrorheological fluid 8.

  On the other hand, as shown in FIG. 2B and FIG. 3B, when the temperature of the electrorheological fluid 8 is low, the temperature-expandable particles 12 are in a contracted state as compared with the case where the temperature is high. . That is, the volume fraction of particles in the electrorheological fluid is reduced as compared with the case where the temperature is high. For this reason, during the operation of the shock absorber 1, the resistance of the temperature-expandable particles 12 with respect to the flow of the base oil 14 is reduced as compared with the case where the temperature is high. That is, when the temperature of the electrorheological fluid 8 decreases, the volume change (shrinkage) of the temperature-expandable particles 12 acts in the direction of decreasing the viscosity of the electrorheological fluid 8.

The viscosity of the suspension, such as the electrorheological fluid 8, is, for example, as shown in the following Brinkman equation (2): the viscosity of the base oil that is the insulating dispersion medium, and the volume fraction of particles contained in the suspension Determined by.
Viscosity of electrorheological fluid = (viscosity of base oil) / (1-particle volume fraction) ^2.5
... (2)

  As represented by Expression (2), when particles having a large volume change due to temperature are contained, the influence on the viscosity of the electrorheological fluid 8 is greater than when particles having a small volume change due to temperature are contained.

  Therefore, in the present embodiment, the temperature-expandable particles 12 that have a large linear expansion coefficient and contract greatly when the temperature decreases are dispersed in the base oil 14, thereby increasing the viscosity of the electrorheological fluid 8 as the temperature decreases. Suppress. In the present embodiment, the temperature-expandable particles 12 that have a large linear expansion coefficient and expand greatly when the temperature rises are dispersed in the base oil 14, thereby reducing the viscosity of the electrorheological fluid 8 as the temperature rises. Suppress.

  Thus, the change in the volume of the temperature-expandable particle 12 accompanying a change in temperature depends on the linear expansion coefficient of the material forming the particle. For this reason, if the temperature-expandable particles 12 are made of a material having a high linear expansion coefficient, the increase in the viscosity of the electrorheological fluid 8 due to the increase in the viscosity of the base oil 14 due to the temperature decrease can be effectively reduced. The temperature dependence of the viscosity of the electrorheological fluid 8 can be reduced. The ability to reduce the temperature dependence of the viscosity of the electrorheological fluid 8 means that the temperature dependence of the damping force in the shock absorber 1 can be reduced.

  FIG. 4 is a diagram showing the relationship between the temperature dependence of the viscosity in the low temperature range and the average linear expansion coefficient. The horizontal axis represents the average linear expansion coefficient α of all particles dispersed in the base oil 14, and the vertical axis represents the temperature dependence (reference I) of the viscosity in the low temperature range. Each straight line shown in FIG. 4 plots the temperature dependence value using the average linear expansion coefficient α as a variable when the particle concentration φ is 50 wt%, 33 wt%, or 15 wt%, and linear approximation by the least square method or the like. It is obtained by doing. Here, the particle concentration φ represents the ratio of the weight of the particles to the total weight of the electrorheological fluid (φ = the weight of the particles / the weight of the electrorheological fluid). As described above, the temperature dependence value can be obtained by {(viscosity fluid at −30 ° C.) / (Viscosity fluid at 23 ° C.)} × 100. The viscosity of the electrorheological fluid at 23 ° C. and the viscosity of the electrorheological fluid at −30 ° C. were obtained by a rotary viscometer method.

  As shown in FIG. 4, the temperature dependence of the viscosity decreases as the average linear expansion coefficient α increases at each particle concentration φ. The higher the particle concentration φ, the greater the rate of decrease in temperature dependence due to the increase in the average linear expansion coefficient α. As shown in FIG. 4, for each particle concentration φ, a lower limit value (value indicated by x) for extracting the average linear expansion coefficient α for the temperature dependence value of the viscosity in the low temperature range to be 300% or less is extracted. .

  FIG. 5 is a graph showing the relationship between the change rate of the temperature dependence of the viscosity in the low temperature range and the particle concentration. The horizontal axis represents the particle concentration φ, and the vertical axis represents the rate of change of the temperature dependence of the viscosity in the low temperature range with respect to the average linear expansion coefficient α. The curve shown in FIG. 5 is obtained by plotting, for each particle concentration, the slope of each straight line shown in FIG. 4, that is, the change rate of the temperature dependence of the viscosity in the low temperature range with respect to the average linear expansion coefficient α, and is obtained by the least square method or the like. It is an approximate curve.

  It means that the smaller the rate of change of the temperature dependency of the viscosity in the low temperature range, that is, the larger the negative absolute value, the greater the effect of decreasing the temperature dependency by increasing the average linear expansion coefficient α. The lower the particle concentration φ, the smaller the temperature-dependent reduction effect due to the increase in the average linear expansion coefficient α. For example, the effect of decreasing the temperature dependence due to the increase in the average linear expansion coefficient α when the particle concentration φ is 15 wt% shown in FIG. 4 is smaller than when the particle concentration φ is 50 wt%. That is, when the particle concentration φ is low, even if the average linear expansion coefficient α is slightly increased, the effect of decreasing the temperature dependency is hardly exhibited.

  As shown in FIG. 5, the higher the particle concentration φ, the larger the interaction between particles, and the greater the influence of particle expansion and contraction on the viscosity. Therefore, as shown by the broken line in FIG. 5 in particular, when the particle concentration φ is 13 wt% or more, compared to the case where the particle concentration φ is less than 13%, the influence on the temperature dependency, that is, the viscosity change of the electrorheological fluid 8 is changed. It was found that the inhibitory effect appears remarkably. In other words, as shown in FIG. 5, the temperature-dependent change rate is extremely small when the particle concentration φ is less than 13%, and the absolute value of the temperature-dependent change rate increases as the particle concentration φ increases from 13 wt%. To increase. That is, 13 wt% is a boundary value of the particle concentration at which the temperature-dependent change rate changes. Since the interaction between particles starts to increase and the influence on the temperature dependency starts to appear suddenly, the particle concentration φ is 13%. Therefore, by setting the particle concentration φ to 13% or more, the temperature dependence of the electrorheological fluid 8 is effectively increased. Can be reduced. If the weight ratio of particles when the base oil is set to 1 instead of the particle concentration φ (particle weight / base oil weight) is explained, when the weight ratio is 0.2 or more, the influence on the temperature dependency is remarkable. It is effective because it appears in

  FIG. 6 is a graph showing the relationship between the lower limit value of the average linear expansion coefficient that satisfies the temperature dependence standard I of the viscosity in the low temperature range and the particle concentration. The horizontal axis represents the particle concentration φ, and the vertical axis represents the lower limit value of the average linear expansion coefficient α that satisfies the standard I. The straight line shown in FIG. 6 plots the lower limit value (value indicated by x) of the average linear expansion coefficient α for satisfying the standard I at each particle concentration φ shown in FIG. It is obtained by doing.

In order to satisfy the above-mentioned criterion I, the average linear expansion coefficient α and particle concentration φ of all particles contained in the electrorheological fluid 8 must satisfy the relationship of the following formula (3). They found out. Equation (3) indicates that the average linear expansion coefficient α needs to be larger than the straight line shown in FIG.

In the equation (3), the average linear expansion coefficient of the ER particles is a (/ ° C.), the average linear expansion coefficient of the temperature expandable particles is b (/ ° C.), the particle concentration, that is, the temperature expandable particles in the electrorheological fluid 8 and When the weight ratio representing the total amount of ER particles is φ and the weight ratio of the ER particles to the temperature-expandable particles is x, Equation (3) is transformed to obtain the following Equation (4). When the temperature-expandable particles and the ER particles are dispersed in the base oil 14, the criterion I can be satisfied by satisfying the formula (4).

As shown in FIG. 6, the lower limit value of the average linear expansion coefficient α for satisfying the above-mentioned criterion I is 1.4 × 10 ⁻⁴ / ° C. Therefore, when the average linear expansion coefficient α of the ER particles dispersed in the electrorheological fluid 8 is lower than 1.4 × 10 ⁻⁴ / ° C. and the above-mentioned criterion I cannot be satisfied, the temperature expansion having a high linear expansion coefficient is performed. Add functional particles. Thereby, average linear expansion coefficient (alpha) can be increased so that average linear expansion coefficient (alpha) may be 1.4 * 10 < ^-4 > / degreeC or more.

When the ER effect is expressed with one kind of particles and the above-mentioned criterion I is to be satisfied, the linear expansion coefficient of the ER particles can be increased as follows. In polyurethane, for example, a polyurethane having a high linear expansion coefficient can be obtained by changing the chemical structure between urethane bonds to a dimethyl silicone skeleton or a perfluoro skeleton. In polyurethane, for example, a polyurethane having a high linear expansion coefficient can be obtained by reducing the density of urethane bonds (crosslinking density) and increasing the molecular weight of the polyol which is a monomer component. Thus obtained polyurethane having a linear expansion coefficient α of 1.4 × 10 ⁻⁴ / ° C. or more has a function as ER particles and a function as temperature-expandable particles.

  As described above, when the particle concentration φ is less than 13 wt%, it is difficult to satisfy the standard I. As shown in FIG. 6, the particle concentration φ is 13% or more to satisfy the standard I. There is a need to. Furthermore, in order to disperse the ER particles 15 in the base oil 14 and to appropriately develop the ER effect, the particle concentration of the ER particles (weight of ER particles / weight of electrorheological fluid) is preferably 10% or more.

For example, non-patent literature: Jin-Yong Hong, Eunbyul Kwon and Jyongsik Jang, "Fabrication of silica / polythiophene core / shell nanospheresand their electrorheological fluid application", Soft Matter, 2009, 5, 951-953, 5-30 vol% It is described that the ER effect increases. The particle diameter of silica as a core material described in non-patent literature is 26 nm, and the thickness of the polythiophene layer as a shell material is 2 nm. The density of silica (silicon dioxide) is 2.2 g / cm ³ and the density of polythiophene is 1.1 g / cm ³ . For this reason, the particle density becomes 1.9 g / cm ³ , and when converted to 5 vol% in weight ratio, it becomes 9.5 wt%. That is, the non-patent literature describes that the ER effect appears at about 10 wt% or more.

  Hereinafter, although an example and a comparative example are shown and explained concretely, the present invention is not limited to the following examples at all.

[Example 1]
[Base oil]
Silicone oil was adopted as the base oil 14.
[particle]
Polyurethane particles using polyethylene glycol and toluene diisocyanate as ER particles are dispersed in the base oil 14, and as the temperature-expandable particles 12, Fluon (registered trademark) of polytetrafluoroethylene (PTFE) made of Asahi Glass Co., Ltd. is used. (Trademark) was dispersed in the base oil 14. The linear expansion coefficient of the polyurethane particles is 1.5 × 10 ⁻⁴ / ° C., and the linear expansion coefficient of the fluorine particles is 2.2 × 10 ⁻⁴ / ° C.

[Average linear expansion coefficient]
The particle concentration φ, which is the weight ratio of the total particles of the polyurethane particles and the fluorine particles to the electrorheological fluid, is 50 wt%. That is, the weight ratio of all particles to the base oil 1 (particle / base oil) is 1. The weight ratio of polyurethane-based particles to fluorine-based particles (ER particles / temperature-expandable particles) is 2.3. At this time, the average linear expansion coefficient α of the prepared electrorheological fluid 8 is 1.71 × 10 ⁻⁴ / ° C. from the equation (1).

[Comparative Example 1]
An electrorheological fluid 8 that does not contain fluorine-based particles as temperature-expandable particles is used as a comparative example 1, and the shock absorber 1 including the electrorheological fluid 8 according to the first embodiment and the electrorheological fluid 8 according to the first embodiment is used. On the other hand, the following verification was performed.

[Verification 1 (viscosity measurement)]
The temperature dependence of the viscosity in the electrorheological fluid 8 was measured by a rotational viscometer method using a rheometer (manufactured by Anton paar, MCR502). Using a flat plate having a diameter of 25 mm, the measurement was performed in the atmosphere under conditions of a shear rate of 200 s ⁻¹ , a measurement temperature range of −40 to 60 ° C., and a temperature increase rate of 10 ° C./min. In this rheometer, the shear rate is 2/3 × (ω × R) / H, and the shear stress is 4/3 × M / (π × R ³ ). Is the angular velocity, R is the plate radius, H is the distance between the plates, and M is the motor torque.

  As a result of measuring the viscosity, the electrorheological fluid 8 according to Example 1 containing fluorine-based particles has an increased viscosity in a low temperature range as compared with the electrorheological fluid 8 according to Comparative Example 1 not including fluorine-based particles. It was confirmed that the temperature dependence of the viscosity decreased.

  When the temperature dependence of the viscosity in the low temperature range is expressed as a percentage of the −30 ° C. viscosity with respect to the 23 ° C. viscosity of the electrorheological fluid 8 (see criterion I), in Comparative Example 1, the temperature dependence was 388%. On the other hand, in Example 1 to which the above-described temperature-expandable particles 12 were added, the temperature dependency was 238%. That is, in Example 1, temperature dependence decreased compared with the comparative example, and the reference | standard I was able to be satisfied.

[Verification 2 (Excitation test)]
An electrorheological fluid 8 was sealed in the shock absorber 1 and a vibration test was performed. The test conditions were a piston amplitude of 50 mm, a piston speed of 0.3 m / s, a temperature of 23 ° C., and a temperature of −30 ° C. As a result of the vibration test, the damping force of the shock absorber 1 using the electrorheological fluid 8 according to Example 1 containing fluorine-based particles was determined using the electrorheological fluid 8 according to Comparative Example 1 not including fluorine-based particles. Compared with the shock absorber 1, the temperature dependency of the viscosity in the low temperature region was reduced, and the value was 238%.

  As described above, according to Example 1, by adding the fluorine-based particles, which are the temperature-expandable particles 12 having a large linear expansion coefficient, to the electrorheological fluid 8, the shock that encloses the viscosity of the electrorheological fluid 8 and thus the electrorheological fluid 8 is included. It was found that the temperature dependence of the damping force of the absorber 1 can be improved. In particular, in the low temperature range, the absolute value of the viscosity is large, and it has been found that the effect of improving the temperature dependency is greatly exhibited.

  Examples 2 to 25 and Comparative Examples 2 to 6 will be described with reference to Tables 1 to 5. In the following, in each Example and each Comparative Example in which two kinds of particles are dispersed in the base oil 14, one of the two kinds of particles having a high linear expansion coefficient is referred to as a temperature-expandable particle 12. Of the two types of particles, the other particle having a high ER effect is called an ER particle. Further, the embodiment in which one type or three types of particles are dispersed in the base oil 14 is described so as to be consistent with the other embodiments in which two types of particles are dispersed in the base oil 14. In the following Examples and Comparative Examples, the viscosity is measured by the same method as in Example 1 described above, and the test results (temperature dependency values) are summarized in each table.

  Table 1 shows the presence / absence of the temperature-expandable particles 12 and the linear expansion of the temperature-expandable particles 12 for Examples 2 to 12 and Comparative Examples 2 and 3 in addition to Example 1 and Comparative Example 1 described above. Coefficient [/ ° C.], presence or absence of ER particles 15, linear expansion coefficient [/ ° C.] of ER particles 15, weight ratio [−] of ER particles 15 and temperature expandable particles 12, average linear expansion coefficient α [/ ° C.], It is a table | surface shown about the kind of base oil 14, the weight ratio [-] of particle | grains and the base oil 14, and the value of the temperature dependence of the viscosity in a low temperature range.

[Comparative Example 2]
Example 1 except that the weight ratio of the polyurethane particles as the ER particles 15 and the fluorine particles as the temperature expandable particles 12 is 9, and the average linear expansion coefficient α is 1.57 × 10 ⁻⁴ / ° C. It is the same. In this case, the temperature dependency of the viscosity in the low temperature range was 349%.

[Example 2]
Example 1 except that the weight ratio of the polyurethane particles as the ER particles 15 and the fluorine particles as the temperature-expandable particles 12 is 1, and the average linear expansion coefficient α is 1.85 × 10 ⁻⁴ / ° C. It is the same. In this case, the temperature dependency of the viscosity in the low temperature range was 230%.

[Example 3]
Example 1 is the same as Example 1 except that the ER particles 15 are not included. When only the fluorine-based particles that are the temperature-expandable particles 12 are dispersed in the base oil 14, the average linear expansion coefficient α of the particles is 2.2 × 10 ⁻⁴ / ° C. that is the linear expansion coefficient of the fluorine-based particles. In this case, the temperature dependency of the viscosity in the low temperature range was 226%.

[Comparative Example 3]
The same as Comparative Example 1 except that the weight ratio of all particles to the base oil 1 contained in the electrorheological fluid 8 is 0.5. In this case, the temperature dependency of the viscosity in the low temperature region was 320%.

[Example 4]
The same as Comparative Example 2 except that the weight ratio of all particles to the base oil 1 contained in the electrorheological fluid 8 is 0.5. In this case, the temperature dependency of the viscosity in the low temperature range was 296%.

[Example 5]
Example 1 is the same as Example 1 except that the weight ratio of all particles to the base oil 1 contained in the electrorheological fluid 8 is 0.5. In this case, the temperature dependency of the viscosity in the low temperature range was 270%.

[Example 6]
Example 2 is the same as Example 2 except that the weight ratio of all particles to the base oil 1 contained in the electrorheological fluid 8 is 0.5. In this case, the temperature dependency of the viscosity in the low temperature range was 240%.

[Example 7]
Example 3 is the same as Example 3 except that the weight ratio of all particles to the base oil 1 contained in the electrorheological fluid 8 is 0.5. In this case, the temperature dependency of the viscosity in the low temperature range was 206%.
[Example 8]
The same as Comparative Example 1 and Comparative Example 3, except that the weight ratio of all particles to the base oil 1 contained in the electrorheological fluid 8 is 0.2. When only the polyurethane-based particles that are the ER particles 15 are dispersed in the base oil 14, the average linear expansion coefficient α of the particles is 1.5 × 10 ⁻⁴ / ° C. that is the linear expansion coefficient of the polyurethane-based particles. The polyurethane-based particles according to this example employ a particle having a linear expansion coefficient of 1.5 × 10 ⁻⁴ / ° C., and function as the temperature-expandable particles 12. When the weight ratio of the polyurethane particles to the base oil 1 is 0.2, the temperature dependence of the viscosity in the low temperature range can be 296%. That is, even when only the polyurethane-based particles are dispersed in the base oil 14, the temperature dependency of the viscosity in the low temperature range can be set to 300% or less. That is, in Example 8, the particles contained in the electrorheological fluid 8 are only polyurethane-based particles, but can satisfy the standard I.

[Example 9]
The same as Comparative Example 2 and Example 4 except that the weight ratio of all particles to the base oil 1 contained in the electrorheological fluid 8 is 0.2. In this case, the temperature dependency of the viscosity in the low temperature range was 287%.

[Example 10]
The same as Example 1 and Example 5 except that the weight ratio of all particles to the base oil 1 contained in the electrorheological fluid 8 is 0.2. In this case, the temperature dependency of the viscosity in the low temperature range was 272%.

[Example 11]
The same as Example 2 and Example 6 except that the weight ratio of all particles to the base oil 1 contained in the electrorheological fluid 8 is 0.2. In this case, the temperature dependency of the viscosity in the low temperature range was 230%.

[Example 12]
Example 3 and Example 7 except that the weight ratio of all particles to the base oil 1 contained in the electrorheological fluid 8 is 0.2. In this case, the temperature dependency of the viscosity in the low temperature range was 190%.

  As shown in Comparative Example 1, Comparative Example 2, and Examples 1 to 3, the weight ratio of the ER particles 15 (ER particles / temperature expandable particles) when the weight of the temperature expandable particles 12 is 1. It was found that the smaller the temperature, the lower the temperature dependence of the viscosity in the low temperature range. In Comparative Example 1, only the ER particles 15 are dispersed in the base oil 14, so that the temperature dependency value is the largest. In Example 3, only the temperature expandable particles 12 are dispersed in the base oil 14, so that the temperature dependency is highest. The value is small. Focusing on the average linear expansion coefficient α, it was found that the temperature dependence of the viscosity in the low temperature region can be reduced as the average linear expansion coefficient α is larger. The same tendency can be confirmed by comparing Comparative Example 3 and Examples 4 to 7. Furthermore, it can also be confirmed by comparing Example 8 to Example 12.

  The temperature dependence values in Comparative Example 1 and Comparative Example 2 and Examples 1 to 3 are in the range of 226% to 388% (see the upper part of Table 1). Comparative Example 3 and Examples 4 to Example The temperature dependence value at 7 is in the range of 206 to 320% (see the middle of Table 1), and the temperature dependence value in Examples 8 to 12 is in the range of 190 to 296% (see Table 1). 1)). Therefore, it can be confirmed that as the weight ratio of the particles to the base oil 1 is smaller, the temperature dependency of the viscosity in the low temperature range tends to be reduced.

Table 2 shows the presence or absence of the temperature-expandable particles 12, the linear expansion coefficient of the temperature-expandable particles 12 [/ ° C.], the presence or absence of the ER particles 15, and the linear expansion coefficient of the ER particles 15 regarding Examples 13 to 19. [° C.], the weight ratio [−] of the ER particles 15 and the temperature expandable particles 12, the average linear expansion coefficient α [/ ° C.], the type of the base oil 14, the weight ratio [−] of the particles to the base oil 14, and the viscosity in the low temperature range. It is a table | surface shown about the value of the temperature dependence of.

[Example 13]
Example 2 is the same as Example 1 except that low-density polyethylene having a linear expansion coefficient of 1.8 × 10 ⁻⁴ / ° C. is used for the temperature-expandable particles 12. In this case, the temperature dependency of the viscosity in the low temperature range was 279%.

[Example 14]
Example 3 is the same as Example 3 except that low-density polyethylene having a linear expansion coefficient of 1.8 × 10 ⁻⁴ / ° C. is used for the temperature-expandable particles 12. In this case, the temperature dependence of the viscosity in the low temperature range was 251%.

[Example 15]
The same as Example 1 and Example 13 except that natural rubber having a linear expansion coefficient of 2.3 × 10 ⁻⁴ / ° C. was used for the temperature-expandable particles 12. In this case, the temperature dependency of the viscosity in the low temperature range was 278%.

[Example 16]
The same as Example 3 and Example 14 except that natural rubber having a linear expansion coefficient of 2.3 × 10 ⁻⁴ / ° C. was used for the temperature-expandable particles 12. In this case, the temperature dependency of the viscosity in the low temperature range was 260%.

[Example 17]
Except that chloroprene rubber (CR) having a linear expansion coefficient of 2.0 × 10 ⁻⁴ / ° C. was used for the temperature-expandable particles 12, it was the same as Example 1, Example 13, and Example 15. In this case, the temperature dependency of the viscosity in the low temperature range was 273%.

[Example 18]
Except that chloroprene rubber (CR) having a linear expansion coefficient of 2.0 × 10 ⁻⁴ / ° C. was used for the temperature-expandable particles 12, it was the same as Example 3, Example 14, and Example 16. In this case, the temperature dependency of the viscosity in the low temperature range was 226%.

[Example 19]
Example 2 is the same as Example 1, Example 13, Example 15, and Example 17 except that two kinds of particles made of fluororesin and particles made of natural rubber are used as the temperature-expandable particles 12. The ratio of the weight of the fluorine resin particles to the weight of the natural rubber particles is 1: 1. That is, the average expansion coefficient of the two types of temperature-expandable particles 12 is 2.25 × 10 ⁻⁴ / ° C., and the average linear expansion coefficient of the three types including polyurethane-based particles, that is, all types of particles, is 1.73 × 10. ^-4 / ° C. In this case, the temperature dependency of the viscosity in the low temperature range was 220%.

  As shown in Examples 13 to 19, by adopting particles having a large linear expansion coefficient as the temperature-expandable particles 12, even when particles made of various materials are employed. It was confirmed that the average linear expansion coefficient α could be increased and the temperature dependence of the viscosity in the low temperature range could be further reduced.

  Table 3 shows the presence or absence of the temperature-expandable particles 12, the linear expansion coefficient [/ ° C.] of the temperature-expandable particles 12, the presence or absence of the ER particles 15, the linear expansion coefficient of the ER particles 15 regarding Example 20 and Example 21 [/ [° C.], the weight ratio [−] of the ER particles 15 and the temperature expandable particles 12, the average linear expansion coefficient α [/ ° C.], the type of the base oil 14, the weight ratio [−] of the particles to the base oil 14, and the viscosity in the low temperature range. It is a table | surface shown about the value of the temperature dependence of.

[Example 20]
Example 1 is the same as Example 1 except that paraffin oil is used as the base oil 14. In this case, the temperature dependency of the viscosity in the low temperature range was 264%.

[Example 21]
Example 1 is the same as Example 1 except that naphthenic oil is used as the base oil 14. In this case, the temperature dependency of the viscosity in the low temperature range was 276%.

  As shown in Example 20 and Example 21, even when mineral oil such as paraffin oil and naphthenic oil is used for the base oil 14, the temperature-expandable particles 12 are formed in the same manner as when silicone oil is used for the base oil 14. It was found that the temperature dependence of the viscosity of the electrorheological fluid 8 can be reduced by the inclusion.

  Table 4 shows the presence or absence of the temperature-expandable particles 12, the linear expansion coefficient of the temperature-expandable particles 12 [/ ° C.], the presence or absence of the ER particles 15, and the linear expansion coefficient of the ER particles 15 regarding Example 22 and Example 23 [/ [° C.], the weight ratio [−] of the ER particles 15 and the temperature expandable particles 12, the average linear expansion coefficient α [/ ° C.], the type of the base oil 14, the weight ratio [−] of the particles to the base oil 14, and the viscosity in the low temperature range. It is a table | surface shown about the value of the temperature dependence of.

[Example 22]
Similar to Comparative Example 2, except that silicone rubber is used for the temperature-expandable particles 12 and paraffin oil is used for the base oil 14. In this case, the temperature dependency of the viscosity in the low temperature range was 286%.

[Example 23]
Example 3 is the same as Example 3 except that silicone rubber is used for the temperature-expandable particles 12 and paraffin oil is used for the base oil 14. In this case, the temperature dependency of the viscosity in the low temperature range was 133%.

  By comparing Example 22 and Example 23, it was found that even when the base oil 14 is paraffin oil, the temperature dependence of the viscosity in the low temperature range can be reduced when the average linear expansion coefficient α is larger.

  Table 5 shows the presence or absence of the temperature-expandable particles 12, the linear expansion coefficient [/ ° C.] of the temperature-expandable particles 12, and the ER particles 15 regarding Comparative Example 4 and Comparative Example 5, Example 24, Comparative Example 6 and Example 25. Presence / absence, linear expansion coefficient [/ ° C.] of ER particles 15, weight ratio [−] of ER particles 15 and temperature expandable particles 12, average linear expansion coefficient α [/ ° C.], type of base oil 14, particles and base oil 14 It is a table | surface shown about the value of the temperature dependence of the viscosity ratio in a low temperature range [-] and a low temperature range.

[Comparative Example 4]
The same as Example 9 except that acrylic particles having a linear expansion coefficient of 0.7 × 10 ⁻⁴ / ° C. were used for the ER particles 15. In this case, the temperature dependency of the viscosity in the low temperature range was 431%.

[Comparative Example 5]
The same as Example 10 except that acrylic particles having a linear expansion coefficient of 0.7 × 10 ⁻⁴ / ° C. were used for the ER particles 15. In this case, the temperature dependency of the viscosity in the low temperature range was 314%.

[Example 24]
The same as Example 11 except that acrylic particles having a linear expansion coefficient of 0.7 × 10 ⁻⁴ / ° C. were used for the ER particles 15. In this case, the temperature dependency of the viscosity in the low temperature range was 293%.

[Comparative Example 6]
The same as Example 9 and Comparative Example 4 except that ion exchange resin particles having a linear expansion coefficient of 1.0 × 10 ⁻⁴ / ° C. were used for the ER particles 15. In this case, the temperature dependency of the viscosity in the low temperature range was 392%.

[Example 25]
The same as Example 11 and Example 24 except that ion exchange resin particles having a linear expansion coefficient of 1.0 × 10 ⁻⁴ / ° C. were used for the ER particles 15. In this case, the temperature dependency of the viscosity in the low temperature range was 282%.

  As shown in Example 9, Comparative Example 4 and Comparative Example 6, by adopting ER particles 15 having a large linear expansion coefficient, the average linear expansion coefficient α can be increased, and the viscosity in a low temperature range can be increased. It was found that the temperature dependence can be further reduced. A similar tendency can be confirmed by comparing Example 10 and Comparative Example 5. Furthermore, the same tendency can be confirmed by comparing Example 11, Example 24, and Example 25.

  As shown in Comparative Example 4, Comparative Example 5 and Example 24, even when acrylic particles are used for the ER particles 15, the higher the average linear expansion coefficient α, the lower the temperature dependence of the viscosity in the low temperature range. I knew it was possible. A similar tendency can also be confirmed by comparing Comparative Example 6 and Example 25 when ion exchange resin particles are used for the ER particles 15.

According to the embodiment described above, the following operational effects can be obtained.
(1) The shock absorber 1 includes a piston rod 6, an inner cylinder 4 into which the piston rod 6 is inserted, an electrorheological fluid 8 provided between the piston rod 6 and the inner cylinder 4, and an electrorheological fluid 8. A voltage application mechanism 20 for applying a voltage is provided. The electrorheological fluid 8 has a temperature dependence value represented by base oil 14 and (viscosity fluid 8 viscosity at −30 ° C./viscosity fluid 8 viscosity at 23 ° C.) × 100 is 300% or less. And the temperature-expandable particles 12 having an average linear expansion coefficient α of 1.4 × 10 ⁻⁴ / ° C. or more. Thereby, since the change of the viscosity resulting from the temperature change of the electrorheological fluid 8, that is, the change of the damping force can be suppressed, the change in the riding comfort of the vehicle caused by the temperature change of the electrorheological fluid 8 can be suppressed. Thus, according to the present embodiment, a shock absorber with high practicality in which the ride comfort of the vehicle is improved even when no voltage is applied between the electrodes by the voltage application mechanism 20, that is, even in the absence of an electric field. 1 can be provided.

(2) The electrorheological fluid 8 has ER particles 15 different from the temperature-expandable particles 12, and the average linear expansion coefficient α of the temperature-expandable particles 12 and the ER particles 15 is 1.4 × 10 ⁻⁴ / ° C. or more. In this case, the change in the riding comfort of the vehicle due to the temperature change of the electrorheological fluid 8 can be suppressed as in (1) above. When one kind of particle is dispersed in the base oil 14, the particle needs to be the ER particle 15 having insulating properties and the temperature-expandable particle 12 having a linear expansion coefficient of 1.4 × 10 ⁻⁴ / ° C. or more. There is. On the other hand, when two types of particles of the ER particle 15 and the temperature-expandable particle 12 are provided, the ER particle 15 may have a linear expansion coefficient lower than 1.4 × 10 ⁻⁴ / ° C. It is effective by adding the temperature-expandable particles 12 having a large linear expansion coefficient to the base oil 14 and setting the average linear expansion coefficient α of the ER particles 15 and the temperature-expandable particles 12 to 1.4 × 10 ⁻⁴ / ° C. or more. In addition, the temperature dependence of the viscosity of the electrorheological fluid 8 can be reduced. For this reason, when two or more types of particles are contained in the electrorheological fluid 8, the degree of freedom in selecting the material of the ER particles 15 is improved.

(3) The temperature-expandable particles 12 include at least one of a fluororesin material, a silicone resin material, a polyester material, and a low density polyethylene material. As the temperature-expandable particles 12, one type of particle may be dispersed in the base oil 14, or a plurality of types may be dispersed in the base oil 14. By adjusting the weight of these temperature-expandable particles 12, it is possible to adjust the viscosity change characteristics and temperature dependency values due to temperature changes.

(4) The ER particles 15 include at least one of a polyurethane resin material, an acrylic resin material, an ion exchange resin, silica, alumina, and titania. As the ER particles 15, one type of particle may be dispersed in the base oil 14, or a plurality of types may be dispersed in the base oil 14. By adjusting the weight of these ER particles 15, the viscosity of the electrorheological fluid 8 when a voltage is applied and the value of temperature dependence can be adjusted.

(5) Since the electrorheological fluid 8 has 13 wt% or more of temperature-expandable particles, the rate of change in temperature dependence of the viscosity of the electrorheological fluid 8 is reduced, that is, the negative absolute value is increased, so the average linear expansion The effect of reducing the temperature dependence of the viscosity of the electrorheological fluid 8 by increasing the coefficient α can be made remarkable. When the temperature-expandable particles 12 and the ER particles 15 are dispersed in the base oil 1, the electrorheological fluid 8 has an average linear expansion coefficient of 13 wt% or more of all particles including the temperature-expandable particles 12 and the ER particles 15. The effect of reducing the temperature dependence of the viscosity of the electrorheological fluid 8 by increasing α can be made remarkable.

(6) As in (5) above, the weight ratio of the temperature-expandable particles 12 to the base oil 1 contained in the electrorheological fluid 8 is 0.2 or more, so that the electricity due to the increase in the average linear expansion coefficient α. The effect of reducing the temperature dependence of the viscosity of the viscous fluid 8 can be made remarkable.

(7) The base oil 14 includes any one of silicone oil and mineral oil (for example, paraffin oil and naphthenic oil). Since the effect of reducing the temperature dependence of the viscosity of the electrorheological fluid 8 can be adjusted by appropriately selecting the base oil 14, the degree of freedom in designing the shock absorber 1 can be improved.

(8) The electrorheological fluid 8 can satisfy the reference I by satisfying the above-described formula (4). By determining the types of the temperature-expandable particles 12 and the ER particles 15 and the particle concentration φ so as to satisfy the formula (4), the shock absorber 1 in which the temperature dependence of the damping force is easily reduced is provided. be able to.

The following modifications are also within the scope of the present invention, and one or a plurality of modifications can be combined with the above-described embodiment.
(Modification 1)
The structure and each component of the shock absorber 1 are not limited to those described above. A piston rod 6, an inner cylinder 4 into which the piston rod 6 is inserted, an electrorheological fluid 8 provided between the piston rod 6 and the inner cylinder 4, and a voltage applying mechanism 20 that applies a voltage to the electrorheological fluid 8 The present invention can be applied to various shock absorbers 1.

(Modification 2)
The material of the outer electrode 3a and the inner electrode 4a and the material of the oil seal 7 are not limited to the materials described above. Various materials can be adopted in consideration of the components of the electrorheological fluid 8 and the like.

(Modification 3)
A temperature sensor for detecting the temperature of the electrorheological fluid 8 may be provided, and the voltage applied between the electrodes by the control device 11 may be determined based on the temperature of the electrorheological fluid 8 detected by the temperature sensor. Thereby, the damping force according to the vibration from the road surface can be generated more appropriately.

(Modification 4)
The material of the temperature expandable particle 12 and the material of the ER particle 15 are not limited to the above-described examples. The particles dispersed in the base oil 14 are not limited to one type, two types, or three types, and four or more types of particles may be dispersed in the base oil 14 to form the electrorheological fluid 8.

  Although various embodiments and modifications have been described above, the present invention is not limited to these contents. Other embodiments conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention.

1 Shock absorber, 2 Base shell, 2a Top plate, 3 Outer cylinder, 3a Outer electrode, 4 Inner cylinder, 4a Inner electrode, 5 Side hole, 6 Piston rod, 7 Oil seal, 8 Electroviscous fluid, 9 Piston, 9L Below piston Chamber, 9U piston upper chamber, 9h through-hole, 10 body, 11 control device, 12 temperature-expandable particles, 13 inert gas, 14 base oil, 15 ER particles, 20 voltage application mechanism, 22 flow paths, 23 flow paths, 24 Flow path, 25 acceleration sensor

Claims (9)

A shock absorber having a piston rod, an inner cylinder into which the piston rod is inserted, an electrorheological fluid provided between the piston rod and the inner cylinder, and a voltage application mechanism for applying a voltage to the electrorheological fluid In
The electrorheological fluid has a temperature dependence value represented by base oil and (viscosity of the electrorheological fluid at −30 ° C./viscosity fluid at 23 ° C.) × 100 is 300% or less. A shock absorber having a temperature-expandable particle having an average linear expansion coefficient of 1.4 × 10 ⁻⁴ / ° C. or more. The shock absorber according to claim 1,
The electrorheological fluid has ER particles different from the temperature-expandable particles;
A shock absorber in which an average linear expansion coefficient of the temperature-expandable particles and the ER particles is 1.4 × 10 ⁻⁴ / ° C. or more. The shock absorber according to claim 2,
The temperature-expandable particles are shock absorbers including at least one of a fluororesin material, a silicone resin material, a polyester material, and a low density polyethylene material. The shock absorber according to claim 3,
The ER particle is a shock absorber including at least one of a polyurethane resin material, an acrylic resin material, an ion exchange resin, silica, alumina, and titania. The shock absorber according to claim 1,
The electrorheological fluid is a shock absorber having 13 wt% or more of the temperature-expandable particles. The shock absorber according to claim 1,
For the base oil contained in the electro-rheological fluid, the shock absorber weight ratio is 0.2 or more of the temperature expandable particles. The shock absorber according to claim 6,
The base oil is a shock absorber containing either silicone oil or mineral oil. The shock absorber according to claim 2,
The electrorheological fluid is a shock absorber that satisfies the following equation.

(A is the average linear expansion coefficient (/ ° C.) of the ER particles, b is the average linear expansion coefficient (/ ° C.) of the temperature-expandable particles, φ is the temperature-expandable particles and ER particles of the electrorheological fluid (Total amount (wt%), x is the weight ratio of the ER particles to the temperature-expandable particles) The shock absorber according to claim 8,
The electrorheological fluid is a shock absorber having 13 wt% or more of all particles including the temperature-expandable particles and the ER particles.

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