Adjustable spring rate suspension is designed to achieve a good balance between suspension performance and comfort, allowing users to adjust the spring strain rate according to specific conditions when using it. According to foreign media reports, a patent application recently published by the US Patent and Trademark Office (USPTO) shows that General Motors (GM) is developing an adaptive suspension system that can change the spring rate at any time, including a magnetorheological spring design.
The patent application is called “Variable Suspension Spring Rates Using Magnetorheological Fluid” and is assigned a serial number of US 2024/0367473 A1. The application was originally filed on May 5, 2023 and published on November 7, 2024.
General Motors is trying to apply adaptive damper technology to the springs of its future suspension systems. The company is a pioneer in magnetorheological damper devices, which use magnetic fluids to quickly change the hardness of the damper.
Magnetorheology works by using magnets to adjust viscosity, which occurs when metal particles in the fluid react to a magnetic field.
The patent application describes a suspension system that includes 2 independent springs with a central valve seat in between. The inner spring core is surrounded by a sealed spring seat filled with magnetorheological fluid. The valve seat contains an outer sleeve of magnetorheological fluid, as well as an electromagnet. When the magnet is energized, the fluid thickens and inhibits spring movement. The non-energized electromagnet supports more spring movement, thereby increasing suspension travel.
If the system works as expected, it will send a signal to the suspension control module to change the resistance or rate of the spring during vehicle operation. This will activate the electromagnet and change the viscosity of the magnetorheological fluid, instantly changing the rate of the suspension spring without the need for mechanical adjustment.
These adaptive suspension springs use technology already used in shock absorbers, which uses silicone oil to suspend metal particles in the suspension fluid. In addition, this includes a new function to adjust the spring travel through the control device in the vehicle, changing the balance between performance and comfort in real time as driving conditions change. Energizing the fluid makes the suspension firmer, while reducing or turning off the electromagnetic energy relaxes the spring.