Compositions – Heat-exchange – low-freezing or pour point – or high boiling... – Organic components
Reexamination Certificate
1999-06-02
2002-03-05
Gupta, Yogendra N. (Department: 1751)
Compositions
Heat-exchange, low-freezing or pour point, or high boiling...
Organic components
C252S073000, C252S071000
Reexamination Certificate
active
06352651
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrorheological fluid which can be used by high performance electrorheological (ER) devices, such as a damper, a clutch or the like used in cars, a large-size apparatus, guns or the like and which has a high electrorheological effect (yield stress).
2. Description of the Related Art
Electrorheological fluids are those of which viscoelasticity characteristics can be changed significantly and reversibly under electric control. The phenomenon that an apparent viscosity of the fluid greatly changes due to application of an electric field has been long known as the Winslow effect and the application of this effect for electrically controlling devices or parts, for example, clutches, valves, engine mounts, actuators, and robot arms, has been discussed. However, initially, electrorheological fluids were obtained by dispersing powder particles such as starch in mineral oil or in lubricating oil, and therefore, although these fluids can provide electrorheological effects, they each have drawbacks of poor recoverability.
It should be noted that herein the term “recoverability” means an ability to recover the original state (viscosity) after experiencing a change in viscosity due to application of an electric field.
For this reason, there have been made many proposals mainly on powder particles used as a dispersoid for the purpose of obtaining a fluid having a high electrorheological effect and good recoverability. For example, Japanese Patent Application Laid-Open (JP-A) No. 53-93186 discloses a highly water-absorbent resin having an acidic group such as polyacrylic acid. Japanese Patent Publication (JP-B) No. 60-31211 discloses an ion exchange resin, and Japanese Patent Application Laid-Open (JP-A) No. 62-95397 discloses aluminosilicate. These substances are hydrophilic solid particles. They are made to soak up water and dispersed in an insulating oily medium. It is said that, when a high voltage is applied from the outside, polarization occurs in the particles forming the powder particles due to the action of water, and the viscosity increases due to the crosslinking in the direction of an electric field generated between the particles by the polarization.
However, the above-described water-containing type electrorheological fluids using water-containing powder particles have many problems such as inability to produce a sufficient electrorheological effect in a wide range of temperatures, restrictions on a working temperature set to prevent occurrence of evaporation or freezing of water, increase in the quantity of electric current consumed due to the temperature rising, instability caused by transfer of water, corrosion of electrode metal during the application of high voltage, and the like. As a result, putting these fluids to practical use has been difficult.
In order to solve the above-described problems, there have been proposed un-hydrous electrorhelogical fluids without water-containing powder particles. For example, Japanese Patent Application Laid-Open (JP-A) No. 61-216202 discloses organic semiconductor particles such as polyacene quinone. Japanese Patent Application Laid-Open (JP-A) Nos. 63-97694 and 1-164823 each disclose dielectric particles obtained by applying an electroconductive thin film on the surface of organic or inorganic solid particles and further applying an electrically insulating thin film thereon (that is, each disclose thin film-coated type composite particles which necessarily include thin coating films having electrically conducting/insulating characteristics). Further, there have been known, as dispersoid particles of which electric characteristics are controlled, surface-treated metallic particles, metal-coated inorganic powder particles, and the like. However, all of these non-aqueous electrorheological fluids using powder particles cannot obtain a sufficient electroviscous effect at a low electric power consumption and also have various problems such as difficulty in industrial production, limited functional effectivity achieved only in an alternating electric field, and the like. Accordingly, these non-aqueous electroviscous fluids have not yet been put to practical use.
In order to further improve the electrorheological effects in non-aqueous electrorheological fluids at a low electric power consumption, it is necessary to increase the adding ratio of dispersoid powder. However, the initial viscosity of the fluid increases when raising the adding ratio of the powder, thereby resulting in the poorer electrorheological effect during the application of electric current.
In order to solve this problem, an electrorheological fluid using carbonaceous particles having a spherical structure has been proposed in Japanese Patent Application Laid-Open (JP-A) No. 7-90287. As described therein, it is advantageous to use carbonaceous particles having a homogeneous and spherical structure as the powder for the electrorheological fluid. However, when the electrorheological fluid is applied to each of a damper, a clutch, and the like, the particles are destroyed due to vibration or load of shearing stress and viscosity when an electric field is not applied thereby increases. Namely, insufficient durability resulting from the strength of the particles was a problem.
The present inventors have diligently researched to eliminate the above-described drawbacks and have already found an electrorheological fluid using carbonaceous particles having a spherical structure (which may hereinafter referred to merely as “spherical carbonaceous particles”) which are obtained substantially from a solvent and a condensation product made by a methylene type bonding of an aromatic sulfonic acid or of a salt thereof (see Japanese Patent Application Laid-Open (JP-A) No. 10-81889).
This electrorheological fluid shows a high electrorheological effect at a low electric power consumption in a wide range of temperatures and under application of voltage, has high strength so as to make it difficult for powder particles to be destroyed due to a load of stress, and also has excellent durability.
However, when an electrorheological fluid is applied to high performance electrorheological (ER) devices such as a shock absorber used in a damper, a clutch or the like used in cars, a large-size apparatus, guns or the like, it is always necessary that the above-described spherical carbonaceous particles show a higher electrorheological effect under application of voltage than that currently observed. In other words, when ordinary silicone oil is used as a dispersion medium for the above-described electrorheological fluid, a sufficient electrorheological effect (yield stress) cannot be obtained under application of voltage.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an electrorheological fluid which has a higher electrorheological effect (yield stress) under the application of voltage and which can be used stably (that is, dielectric breakdown strength thereof is maintained at a high value).
In order to solve the above-described problems, the present invention has the following aspects.
According to a first aspect of the present invention, there is provided an electrorheological fluid which comprises: carbonaceous particles of a spherical form, obtained substantially from a solvent and a condensation product formed by a methylene type bonding of an aromatic sulfonic acid or a salt of the aromatic sulfonic acid as materials; and an electric insulating oil whose relative dielectric constant is 3 or more.
According to a second aspect of the present invention, the spherical form has a deviation of the maximum diameter and a deviation of the minimum diameter of the carbonaceous particles each within 30% of the average diameter, and the average particle size of the carbonaceous particles is of 0.1 to 20 &mgr;m.
According to a third aspect of the present invention, the electric insulating oil whose relative dielectric constant is 3 or more is any one of fluorosilicone oil and a mixture
Endo Shigeki
Wada Hiroaki
Bridgestone Corporation
Gupta Yogendra N.
Hamlin D.
Oliff & Berridg,e PLC
LandOfFree
Electrorheological fluid does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrorheological fluid, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrorheological fluid will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2840178