The invention relates generally to the field of Electro-Rheological (ER) and Magneto-Rheological (MR) fluids and powders, specifically methods of using ER and MR fluids and powders in mechanical and electrical devices.
ER and MR fluids and powders are substances that rely on a magnetic capable media compounded in a way that allows the substance to change form from a liquid or powder state to a rigid, solid state. These materials are formed from micron-sized, magnetizable particles called fines, suspended in oil or other media. ER and MR powders consist solely of magnetizable particles.
ER and MR fluids are very similar in their operation. The main difference is that ER fluids are responsive to an electric field and MR fluids are reactive to a magnetic field. However, MR fluids do have many advantages over ER fluids, and these will be discussed later.
ER and MR fluids are typically made up of three components: the magnetic particles, a carrier fluid, and a dispersant of some sort. The magnetic particles in ER and MR fluids are called magnetic fines. These fines are normally very small iron particles, on the order of 1-10 xcexcm. The size of the particles may vary, but it is known that while larger particles can give the ER or MR fluid a higher yield strength and therefore a greater binding capacity, larger particles also tend to settle out from the fluid quite easily. Smaller particles do not have as much of a settling out problem, but they are more temperature sensitive and tend to xe2x80x9ccake upxe2x80x9d more easily, which affects the fluidity of the substance. This problem of particles settling out and caking up has been addressed in a number of patents. For example, U.S. Pat. No. 5,645,752 discloses an MR fluid utilizing a thixotropic network to stabilize the particles and prevent some settling out. Methods as shown in the ""752 patent allow for the use of larger particles in the fluid and thus allow for a greater yield strength. However, the need for greater yield strength is always growing, and particle size can only be increased to a certain level. A new method for increasing the strength of both ER and MR fluid is still needed.
Carrier fluids are the fluids in which the magnetic fines are suspended. In the case of an ER or MR powder, there is no fluid; the particles themselves make up the entire substance. In ER and MR fluids, the carrier fluid is normally an inexpensive, temperature stable, non-reactive substance, preferably with a high boiling point. Commonly used carrier fluids are silicone or hydrocarbon oil. The most important features of a carrier fluid are its resistance to temperature changes and the fact that it should not cause sealing problems in the mechanism in which the ER or MR fluid is used.
The last component in most ER and MR fluids is a dispersant. The dispersant prevents some settling out and caking up of the magnetic particles. Normally, structured silica, fibrous carbon, or a number of various polymers are used to perform this function.
In their liquid form, ER and MR fluids have a consistency much like common motor oil. However, when an electric charge or magnetic field is applied, the fluids change form, becoming rigid and able to bond surfaces together. This rigid bonding mechanism results from a dipole moment introduced on the magnetic particles in the fluid from the electric charge or magnetic field. The particles form chains, aligning parallel to the electric charge or magnetic field. The strength of the bonding mechanism depends on the strength of the charge or field applied to the fluid and the size of the particles. The change in viscosity of the fluid takes place in a few milliseconds. ER and MR powders operate in the same manner, changing from a powder to a rigid form. MR fluids typically exhibit much stronger yield strengths than do ER fluids. MR fluids are also more resistant to temperature changes and have a high tolerance to impurities such as water. MR fluids can also be activated using a much lower voltage power supply. ER fluids require high voltage (near 5,000 volts) to operate, and this need can cause design and safety problems. For purposes of the present disclosure, discussion herein of the terms xe2x80x9cER and/or MR fluidsxe2x80x9d is also meant to refer to equivalent ER or MR substances, such as powders.
Extensive research has been performed for many years to find applications for ER and MR fluids in linear and rotating actuated mechanisms. For example, use of such materials as a rigid bonding material for such applications would provide a unique and effective solution to braking, power generation and other mechanical systems. U.S. Pat. Nos. 2,575,360, 2,661,825, and 2,886,151 disclose examples of devices using ER or MR substances to control such functions. One hindrance in such developments has been that the amount of electrical power required for the fluid to achieve its desired functionality as a binding material has been too great for practical use. As mentioned above it is possible to achieve stronger yield strengths by using ER and MR fluids with larger particles, but this results in the need to control the settling out of these larger particles. Using dispersants can accomplish this, but this increases the cost of the fluids and makes manufacturing them more complicated. As a result, the potential of ER and MR fluids as a rigid bonding mechanism in hydraulic and mechanical applications has been limited and there is a need to increase the functionality of these fluids without increasing their cost or complexity.
The impregnation of porous parts with oil has been a common practice in forming self-lubricating bearings and other parts. Since 1965, Chrysler has used a method to pull oil lubricant into porous bronze parts in order to maintain lubricity. However, the oil did not have the characteristics of ER and MR fluids in that it could only be used as lubrication, not as a holding mechanism. In later years, a similar method was used to mold a Teflon layer to a porous bronze layer. Again, Teflon acts as a good lubricant, but it has no shear strength, and cannot be used to hold parts in place.
The present invention may be embodied in a method for modifying a porous mechanical component by using an ER or MR substance. Preferably, the ER or MR substance is a fluid, but alternatively, it is possible to perform the method using an ER or MR powder.
In a first embodiment of the invention, a method for modifying a porous mechanical component using an MR substance is provided. The method includes the steps of providing at least one porous component having a porosity sufficient to receive the MR substance within a plurality of pores and impregnating the component with the MR substance.
In a second embodiment of the invention, a method for associating an amount of MR substance with at least two porous mechanical components is provided. The method includes the steps of providing at least one porous component having a porosity sufficient to receive the MR substance within a plurality of pores and impregnating the component with the MR substance.
In a third embodiment of the invention, a method for using an MR substance to releasably bind at least two porous mechanical components is provided. The method includes the steps of providing at least two porous components having a porosity sufficient to receive the MR substance within a plurality of pores and impregnating the components with the MR substance. The components are then placed such that the impregnated surfaces are in contact with each other and a magnetic field is applied to the components and the MR substance.
In a fourth embodiment of the invention, a method for using an MR substance to releasably bind at least two porous mechanical components is provided. The method includes the steps of providing at least two porous components having a porosity sufficient to receive the MR substance within a plurality of pores and impregnating the components with the MR substance. The components are then placed such that the impregnated surfaces are in contact with each other and a magnetic field is applied to the components and the MR substance. The magnetic field is then removed from the components and the MR substance.
In a fifth embodiment of the invention, a method for modifying a porous mechanical component using an ER substance is provided. The method includes the steps of providing at least one porous component having a porosity sufficient to receive the ER substance within a plurality of pores and impregnating the component with the ER substance.
In a sixth embodiment of the invention, a method for associating an amount of ER substance with at least two porous mechanical components is provided. The method includes the steps of providing at least two porous components having a porosity sufficient to receive the ER substance within a plurality of pores and impregnating the components with the ER substance.
In a seventh embodiment of the invention, a method for using an ER substance to releasably bind at least two porous mechanical components is provided. The method includes the steps of providing at least two porous components having a porosity sufficient to receive the ER substance within a plurality of pores and impregnating the components with the ER substance. The components are then placed such that the impregnated surfaces are in contact with each other and an electric charge is applied to the components and the ER substance.
In an eighth embodiment of the invention, a method for using an ER substance to releasably bind at least two porous mechanical components is provided. The method includes the steps of providing at least two porous components having a porosity sufficient to receive the ER substance within a plurality of pores and impregnating the components with the ER substance. The components are then placed such that the impregnated surfaces are in contact with each other and an electric charge is applied to the components and the ER substance. The electric charge is then removed from the components and the ER substance.
The present invention provides a number of advantages over the prior art. By using this method, an ER or MR fluid may be used to bind mechanical parts together without necessitating large amounts of electricity needed to activate the fluid. In the past, in order to get ER or MR fluid to adequately hold two components together, the electric charge or magnetic field had to be very strong. Using this method, the ER or MR fluid is allowed to interact with the internal structure of the mechanical components, forming a three-dimensional structure that is much stronger than the ER or MR fluid alone.
Another advantage to the present invention is that the method allows the use of less of the ER or MR fluid to get the same amount of binding strength. The efficiency of the ER or MR fluid""s binding feature is greatly improved using this method.
It is to be understood that both the preceding summary and the following detailed description are intended to be exemplary and are intended to provide a further explanation of the invention claimed. The invention will best be understood by reference to the following detailed description read in conjunction with the accompanying drawings.