Bi-fold Valve Magnetorheological Damper for Tunable Automotive Damping
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Solution Overview
Problem
Magnetorheological energy absorption (MREA) devices are inadequate for automotive applications due to their large size and limited tunability of stroking force over a range of velocities, making them unsuitable for effective impact energy management and deceleration control.
Innovation Solution
A compact bi-fold valve-type MREA device with a damper assembly, concentric tubes, and magnetic end structure assemblies that create bi-fold valves, using MR fluid with coated magnetic particles and electrical coils to control damping force tunability over a wide range of piston velocities, and a pneumatic chamber to prevent cavitation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional MREA devices are used, then energy absorption capability is provided, but the device size becomes large and tunability of damping force is limited
Solution Approach 1:
The device is segmented into distinct functional zones: an inner chamber with a piston for high-velocity flow control, an outer chamber for additional flow management, and bi-fold valve-type cavities that create flow-reversing paths. This segmentation allows each zone to contribute to damping force generation, enabling tunability across a wider velocity range without proportionally increasing device volume.
Solution Approach 2:
The inner tube and inner chamber are nested within the outer tube and outer chamber, creating a compact concentric configuration. The bi-fold valve cavities are integrated into the end structure assemblies that surround the inner tube. This nested arrangement maximizes the use of internal space, allowing multiple flow paths and control mechanisms to coexist in a compact footprint.
2Adaptability or versatility
If conventional MREA devices are used, then impact energy absorption is provided, but the tunability ratio over velocity range is insufficient
Solution Approach 1:
The device employs dynamic flow control through the bi-fold valve cavities that reverse flow direction, creating variable resistance based on piston velocity. The magnetic field application to the MR fluid dynamically adjusts yield strength in real-time. This dynamic behavior enables the damping force to adapt across a broad velocity range, achieving the desired 2:1 tunability ratio.
Solution Approach 2:
The device changes the physical state and properties of the MR fluid by applying magnetic fields that alter yield strength. The bi-fold valve geometry changes flow parameters including direction and velocity distribution. These parameter changes enable continuous adjustment of damping force from minimum to maximum levels across the operating velocity range.
3Force
If MR fluid with high magnetic particle content is used, then yield strength and damping force increase, but viscosity and off-state yield stress increase
Solution Approach 1:
The magnetic particles are concentrated in the MR fluid that flows through the bi-fold valve cavities where magnetic fields are applied, rather than uniformly throughout the entire device. The coated particles provide the necessary yield strength enhancement locally in the flow paths while minimizing overall fluid viscosity. This localized concentration approach maximizes damping force generation without excessive energy loss to viscosity.
Solution Approach 2:
The MR fluid is formulated as a composite material with magnetic particles (40-60% by volume) suspended in a carrier fluid, with particles coated to control inter-particle interactions. This composite structure enables high yield strength when magnetic fields are applied while maintaining manageable viscosity levels, resolving the trade-off between force generation and energy loss.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The device achieves a tunable damping force ratio of up to 2:1 over a range of piston velocities, ensuring effective impact energy management and deceleration control in automotive applications while maintaining a compact size.
Implementation Method 1
Magnetorheological (MR) fluids belong to a class of controllable fluids. The essential characteristic of these fluids is their ability to change from a free-flowing, linear, viscous liquid to a semi-solid with controllable yield strength in milliseconds when exposed to a magnetic field.
Implementation Method 2
Electrical coils are fixed adjacent to the magnetic end structure assemblies, preferably concentric with the inner and outer tubes and are energizable to create a magnetic field that acts on the MR fluid to vary the damping force of the damper assembly.
Implementation Method 3
A piston is moveable within the inner tube and divides the inner chamber. The damper assembly is configured to form bi-fold valves (also referred to as bi-fold valve-type cavities) to operatively connect the inner chamber with the outer chamber. This is accomplished preferably by magnetic end structure assemblies positioned at opposing ends of the inner tube each of which, at least partially, defines a cavity with openings at both the inner and the outer chamber and a looped portion therebetween that establishes a flow-reversing path between the cavity openings.
Implementation Method 4
The MR fluid preferably contains 10-60 percent by volume magnetic particles, and preferably greater than 20 percent by volume magnetic particles. Preferably, the particles are coated, such as with a silicate coating, that causes the viscosity and the off-state yield stress of the MR fluid to decrease.
Data Source
AI summary
An energy absorbing device is provided that includes a damper assembly having inner and outer concentric tubes and a piston movable within the inner tube. The damper assembly is configured to form bi-fold valve-type cavities to operatively connect an inner chamber of the inner tube with an outer chamber formed between the inner and outer tubes. A magnetorheological fluid fills the chambers and the bi-fold valve-type cavities. The magnetorheological fluid preferably contains coated magnetic particles at about 10 to 60 percent by volume. Electrical coils adjacent the bi-fold valves are selectively energizable to such that the energy absorbing device provides a tunable damping force, preferably over the entire range of velocities of the piston, especially in automotive applications.