Abstract:
A method for modifying a porous mechanical component by using an ER or MR substance including 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.

Description:
FIELD OF THE INVENTION 
     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. 
     BACKGROUND OF THE INVENTION 
     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 μm. 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 “cake up” 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 &#39;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 “ER and/or MR fluids” 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. 
     BRIEF SUMMARY OF THE INVENTION 
     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&#39;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. 
    
    
     BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
     FIG. 1 shows an enlarged view of the interaction of the particles in an ER or MR fluid without an electric charge or magnetic field applied and then with an electric charge or magnetic field applied; 
     FIG. 2 shows an enlarged view of a cross-section of the structure of a porous component that may be utilized in accordance with the present invention; 
     FIG. 3 shows a cross-section of the present method of two porous components impregnated with ER or MR fluid and a layer of ER or MR fluid between them in an inactivated state that may be utilized in accordance with the present invention; 
     FIG. 4 is the same as FIG. 3, but with a low-level electric charge or magnetic field applied, showing the interaction of the particles with the pores of the components; and 
     FIG. 5 is a schematic example of the connection of an electric circuit to the components from FIGS. 3 and 4 with an electric charge or magnetic field applied. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, the general mechanism of an ER or MR fluid is shown. The fluid  10  is located between a first  12  and a second  14  electrode. These electrodes  12 ,  14  may be any type of conducting material. The fluid  10  is made up of a medium  16  and a plurality of particles  18 , which are reactive to either an electric charge or a magnetic field. In the off position A. the particles  18  are evenly dispersed throughout the medium  16  in a substantially random manner. In the off position A, the fluid  10  acts like a liquid, and flows freely between the electrodes  12 ,  14 . 
     When the circuit is turned to the on position B, a dipole moment is introduced to the particles  18 , causing them to align in the direction of the electric charge or magnetic field. An arrow  20  in FIG. 1 shows the direction of alignment. The lines  22  of particles  18  cause the fluid  10  to approach solid form and develop a thick consistency. When the electric charge or magnetic field is removed, the particles  18  return to their random arrangement and the fluid  10  becomes a liquid once again. This characteristic of ER and MR fluids allows them to be used in many mechanisms where bonding or friction is needed. However, the binding strength of the solid formed by the fluids may not be strong enough to adequately bind two surfaces together unless very large particles  18  or a very high-energy source are used. 
     Referring to FIG. 2, this invention is first embodied as a method of using porous components  24 ,  26  along with ER or MR fluid to boost the binding strength of the fluid  10  without enlarging the particles  18  or increasing the amount of power used. The ER or MR fluid  10  is provided with porous components  24 ,  26 , preferably made of powder metal substrates with which to interact. As is well known in the art, the process of forming powder metal components  24 ,  26  is performed by grinding up metal into a fine powder and then pressure molding the powder back into a solid component substrate. This process results in components  24 ,  26  having a multitude of pores  28  in their structure and surface  30 . These pores  28  provide spaces for the ER or MR fluid  10  to be retained within the substrates of the components  24 ,  26 . 
     Referring to FIG. 3, the invention may be embodied in a method of having ER or MR fluid interact with the pores  28  of powder metal components  24 ,  26 . The fluid  10  may be impregnated into the components  24 ,  26  by a number of different methods. The fluid  10  could be impregnated by being pulled into the pores  28  of the components  24 ,  26  using a vacuum or a magnetic field. Alternatively, the fluid  10  could be impregnated into the components  24 ,  26  by being mechanically squeezed into the pores  28  or hydraulically ingested. When the effect of any singular or combination of the above methods is removed from the fluid  10  and the components  24 ,  26 , the fluid  10  and the particles  18  become lodged therein. A layer  32  of the ER or MR fluid may also be added between the components  24 ,  26 . 
     Referring in combination to FIGS. 3,  4  and  5 , the mechanism of FIG. 1 is shown along with the preferred embodiment of the present invention. Preferably, powder metal components  24 ,  26  are impregnated with ER or MR fluid  10  such that the fluid  10  and the particles  18  are embedded within the pores  28  of the components  24 ,  26 . In FIG. 3, the fluid  10  is in its liquid form. FIG. 4 shows the preferred embodiment of the method without a circuit present while FIG. 5 shows a schematic of a circuit attached to the components  24 ,  26 . It is important to note that ER fluid requires an electric charge to change forms while MR fluid requires a magnetic field. The proper charge or field should be used depending on the substance impregnated within the components  24 ,  26 . The mechanism of each type of fluid is the same when the appropriate charge or field is applied. 
     When the electric charge or magnetic field is applied to the components  24 ,  26  as shown in FIG. 5, the particles  18  in the fluid  10  align in the direction of the electric charge or magnetic field. An arrow  20  shows the direction of alignment. This causes the ER or MR fluid  10  to act as a solid, shown by the shaded areas  34  in FIGS. 4 and 5. FIG. 4 actually shows the fluid  10  with a low-level electric charge or magnetic field applied to it such that the main layer  32  has not yet begun to change form. Only the fluid  10  and the particles  18  on the surface  30  have become solid. The fact that the fluid  10  and particles  18  have been impregnated into the pores  28  of the components  24 ,  26  allows the fluid  10  to take advantage of the structure of the components  24 ,  26  and increase its binding strength. Instead of relying only on the shear strength of the fluid  10  itself, the fluid  10  forms a three-dimensional interface with the porous interior  36  of the components  24 ,  26 . This greatly increases the bonding strength of the fluid  10  and allows for the use of smaller particles  18 , less fluid  10 , less dispersant, and a lower voltage electric charge or magnetic field. 
     An advantage of the present invention is the fact that since less power and fluid may be used to produce the same level of binding strength, the costs of using these types of mechanisms is reduced. Another advantage is that the higher binding strength allows mechanisms that were not possible in the past to be performed. The voltage needed is lowered, making safer and smaller mechanisms possible and lowering the cost of running these mechanisms. Additionally, it will now be possible to use less fluid  10  to perform the same functions as in the past. 
     It should be noted that there could be a wide range of changes to the claimed method. For instance, ER or MR powder could be used instead of fluid  10 . Also, any size particles  18  could be used, and the size of the pores  28  in the components  24 ,  26  would have to be adequately adjusted. Any material could be used for the porous components  24 ,  26 , not necessarily only powder metal. The circuits shown in FIGS. 1 and 5 are meant to be illustrative, the actual circuit could have any arrangement, so long as an electric charge or magnetic field is applied to the ER or MR fluid  10 . Any number of parts could be used with the method. Additionally, the circuit could be reversed such that when the circuit is turned off, the fluid reverts to its solid form rather than its liquid form. Thus, it is intended that the foregoing detailed description be regarded as illustrative rather than limiting and that it be understood that it is the following claims, including all equivalents, which are intended to define the scope of the invention.