The present invention relates to shock absorbers and damping apparatuses, and more particularly, to a magneto-rheological damping apparatus for use in an automotive suspension system.
Automobiles and other vehicles utilize shock absorbers to dissipate shock forces sustained by the vehicle wheels. Similar damping apparatuses, such as body dampers, cab dampers, engine dampers and steering dampers are used in other parts of the vehicle. Conventional linear style shock absorbers include a pair of telescoping cylindrical sleeves oriented generally vertically in the vehicle. A piston associated with one of the sleeves travels in a fluid filled cylinder associated with the sleeve. One end of the shock absorber is coupled to a wheel support structure and the other end is fixed to the body, or frame of the vehicle. When a shock force displaces one of the vehicle wheels upwardly, the force drives the piston along the cylinder, thereby driving fluid through an orifice in the piston, which resists such motion with a force proportional to the shock force.
Monotube type dampers typically include a hollow cylinder, a rod guide positioned at one end of the cylinder, a piston rod extending through the rod guide and into the cylinder, a piston positioned on the piston rod within the cylinder, and a gas cup between the piston and the other end of the cylinder. The piston assembly separates a compression chamber from a rebound chamber within the cylinder. The rebound chamber and the compression chamber are normally filled with a hydraulic fluid, and the piston assembly typically includes a rebound stroke valve and compression stroke valve for controlling the flow of fluid between the rebound chamber and the compression chamber.
The gas cup separates a gas chamber at the end of the cylinder from the hydraulic fluid. The gas chamber compensates for internal volume changes due to rod stroking and thermal expansion, and is pressurized to prevent cavitation of the hydraulic fluid during stroking.
Recently, monotube damper assemblies have been developed that utilize magnetic theological components to control the viscosity of the hydraulic fluids passing through the passages in the piston. In such an apparatus, the piston is formed of a ferrous material having a solenoid positioned therein to produce a magnetic flux around the piston, where the magnetic rheological fluid passing through the passages of the piston will be affected by the magnetic flux created by the solenoid. Therefore, by controlling the current in the solenoid, the viscosity of the MR fluid passing though the piston valves can be controlled so as to, in turn, control the damping force of the damping assembly.
A disadvantage with such monotube-type dampers is that, because the piston rod is only supported by a single rod guide positioned at one end of the damping cylinder, the piston may contact and abrade against the interior of the damping cylinder if sufficient transverse force is applied to the piston rod. This may eventually cause the performance of the damping apparatus to degrade. Furthermore, with an internally pressurized design in which inward rod stroking increases the volume to which pressure is applied, the installed damper will always exert a force in such a manner as to extend the rod out of the damper.
Another disadvantage with conventional MR dampers is that the positioning of the solenoid within the piston requires complicated electrical connections, as well as complicated fluid channels, valves and associated seals within the piston. Furthermore, if any of these internal seals should fail, the MR fluid may contact the solenoid and cause shorts therein.
Therefore, a need exist for a monotube-type damping assembly in which the contact between the piston and the interior surfaces of the damping cylinder is substantially eliminated. There is also a need for a monotube-type damping assembly in which the available volume within the damping cylinder remains substantially constant. Finally, there is a need for an MR damping assembly having substantially reduced complexity, where the solenoid is isolated from the MR fluid.
The present invention provides a magneto-rheological controlled damping assembly that substantially eliminates contact between the piston and the damping cylinder and that maintains a constant volume for the magneto-rheological fluid within the damping cylinder, therefore substantially reducing abrasion and wear to the damping apparatus components and increasing the performance and the life of the damping apparatus. while the damping assembly is preferably used as a vehicle shock absorber, body damper, cab damper, engine damper, steering damper and the like; it is within the scope of the invention to utilize the damping assembly in non-vehicle applications as well.
In one aspect of the present invention a magneto-rheological damping apparatus includes a hollow cylinder having an MR fluid chamber portion containing a magneto-rheological fluid. A piston rod extends concentrically within the MR chamber portion of the cylinder; and a piston is mounted on the piston rod and positioned within the MR fluid chamber portion of the cylinder, where a radial gap is formed between the piston and the MR chamber portion of the cylinder so as to provide a flow path for the magneto-rheological fluid. A solenoid, operatively coupled to a current supply, is mounted around the cylinder outside the MR fluid chamber portion thereof for generating a magnetic flux in the radial gap and thereby controlling the viscosity of the magneto-rheological fluid in the flow path. Because the solenoid is positioned outside the damping cylinder, the solenoid is isolated from the magneto-rheological fluid; and this eliminates any chance that the metal particles entrained in the MR fluid will contact the solenoid and thus cause shorts to the solenoid. Furthermore, because the solenoid is positioned outside the damping cylinder, electrical connections to the solenoid are relatively simplified.
In one embodiment, the apparatus includes a pair of rod guides positioned on opposite ends of the MR fluid portion of the cylinder so that the piston rod extends through and is supported by both rod guides. Therefore, the piston will be prevented from contacting the inner surface of the damping cylinder. In another embodiment, the apparatus includes a single rod guide, positioned on a first end of the cylinder, slidably supporting the piston rod thereon, and includes a secondary rod extending axially into the MR fluid chamber from the opposite end of the cylinder, where the piston includes an axial channel that receives the secondary rod therein. In either of these embodiments, the volume for the MR fluid within the damping cylinder will remain substantially constant.
In another aspect of the present invention a magneto-rheological damping apparatus includes a cylinder having an MR fluid chamber portion containing a magneto-rheological fluid. A piston rod extends concentrically within the MR fluid chamber portion of the cylinder and is axially slidable with respect to the cylinder. A piston is mounted on the piston rod and positioned within the MR fluid chamber portion of the cylinder; and a radial gap is formed between the piston and the MR fluid chamber portion of the cylinder so as to provide a flow path for the magneto-rheological fluids. A pair of rod guides are positioned on opposite ends of the MR fluid portion of the cylinder; and the piston rod extends through and is supported by both rod guides. A solenoid is operatively coupled to a current supply for generating a magnetic flux in the radial gap and thereby controlling the viscosity of the magneto-rheological fluid in the flow path.
Because the piston rod extends completely through the MR fluid chamber portion of the damping cylinder, the volume for the MR fluid within the damping cylinder remains substantially constant, thereby substantially reducing the forces exerted by the piston rod during operation. In addition, because the piston rod is supported by rod guides on both ends of the damping cylinder, the piston will be substantially prevented from contacting the inner surface of the damping cylinder so as to prevent abrasions and degradation of the damping apparatus components. Furthermore, because the solenoid is positioned outside the damping cylinder, electrical connections to the solenoid are simplified, complex valves and seals within the piston are no longer needed, and the solenoid is isolated from the MR fluid.
In yet another aspect of the present invention, a magneto-rheological damping apparatus includes: a cylinder with an MR fluid chamber portion containing a magneto-rheological fluid. A piston rod extends concentrically within the MR fluid chamber portion of the cylinder and is axially slidable with respect to the cylinder. A piston is mounted on the piston rod and positioned within the MR fluid chamber portion of the cylinder, and a radial gap is formed between the piston and the MR fluid chamber portion of the cylinder so as to provide a flow path for the magneto-rheological fluids. A rod guide positioned on a first end of the cylinder slidably supports the piston rod; and a secondary rod extends axially into the MR fluid chamber portion of the cylinder from a second end of the cylinder and is slidably received in an axial channel of the piston. A solenoid is operatively coupled to a current supply for generating a magnetic flux in the radial gap and thereby controlling the viscosity of the magneto-rheological fluid in the flow path.
The piston slides back and forth over the secondary rod as the piston and piston rod move back and forth in the MR fluid chamber in response to vibrations experienced by the damping apparatus. The axial extent of piston movement over the secondary rod will equal the additional length of the piston rod extending into the MR fluid chamber. Therefore, the volume of the MR chamber taken up by the secondary rod and piston rod (if provided with the same diameters) will remain constant. In turn, the volume for the MR fluid within the damping cylinder will remain substantially constant, thereby substantially reducing the forces exerted by the piston rod during operation. Furthermore, because the solenoid is positioned outside the damping cylinder, electrical connections to the solenoid are simplified, complex valves and seals within the piston are no longer needed, and the solenoid is isolated from the MR fluid.
While the above-described embodiments employ the use of MR fluid and solenoids, it is within the scope of the present invention to utilize the through-rod or secondary rod configurations of the present invention with more standard damping arrangements. Thus, it is within the scope of the present invention to provide a damping apparatus that includes a substantially hollow cylinder having a fluid chamber portion containing a damping fluid, a piston rod extending concentrically within the fluid chamber portion of the cylinder and axially slidable with respect to the cylinder, a piston mounted on the piston rod and positioned within the fluid chamber portion of the cylinder, and a pair of rod guides positioned on opposite ends of the fluid portion of the cylinder, where the piston rod extends through, and is supported by, both rod guides.
Likewise, it is within the scope of the present invention to provide a damping apparatus that includes a substantially hollow cylinder having a fluid chamber portion containing a damping fluid, a piston rod extending concentrically within the fluid chamber portion of the cylinder and axially slidable with respect to the cylinder, a piston mounted on the piston rod and positioned within the fluid chamber portion of the cylinder, a rod guide positioned on a first end of the fluid chamber portion of the cylinder so as to support the piston rod extending therethrough, and a secondary rod extending concentrically within the fluid chamber portion of the cylinder from a second end of the cylinder and including an axial channel slidably receiving the secondary rod.
In view of the above, it will be apparent that another aspect of the present invention is to provide a method for reducing forces exerted by the primary piston rod of the monotube damping apparatus comprising the steps of: (a) providing a secondary body within the fluid chamber portion of the cylinder, where the secondary body has a volume that takes up a portion of the volume for the damping fluid in the cylinder; and (b) as the piston moves within damping fluid chamber, decreasing the volume of the secondary body within the damping fluid chamber as the primary piston rod moves into the damping fluid chamber and increasing the volume of the secondary body within the damping fluid chamber as the primary piston rod moves out from the fluid chamber portion of the cylinder. In the first embodiment, as described above, this method is accomplished by supporting the piston rod on a pair of rod guides, where the piston is mounted on the piston rod (in the damping fluid chamber) between the rod guides. If the portion of the piston rod extending from a first axial side of the piston is referred to as the primary rod and if the portion of the piston rod extending from the opposite axial side of the piston is referred to as the secondary body, then the volume of this secondary body in the damping fluid will decrease as the primary piston rod lengthens into the damping fluid. In the second embodiment, as described above, this method is accomplished by supporting the piston rod on a single rod guide on one end of the cylinder and providing a secondary rod extending from the other end of the cylinder, where the secondary rod is slidingly received concentrically within the piston. Accordingly, as the piston rod extends into the damping fluid chamber, the piston will slide over the secondary rod to an equal extent, thus decreasing the volume that the secondary rod takes up in the damping fluid chamber to the same extend that the volume of the piston rod within the damping fluid chamber is increasing.
Accordingly, it is an object of the present invention to provide a monotube-type damping assembly that substantially eliminates the contact between the piston and the interior surfaces of the damping cylinder. It is also an object of the present invention to provide a monotube-type damping assembly in which the available volume within the damping cylinder remains substantially constant. It is also an object of the present invention to provide an MR damping assembly that simplifies the electrical connections with the solenoid, that reduces the need for complex valves and seals within the piston, and that isolates the solenoid from the MR fluid. These and other objects and advantages of the present invention will be apparent from the following description, the attached drawings and the appended claims.
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