The patented suspension system is designed to replace conventional suspension systems  (steel or air), with shock absorbers, and stabilizer bars by utilizing a compressible liquid. - LiquidSpring

The patented suspension system is designed to replace conventional suspension systems  (steel or air), with shock absorbers, and stabilizer bars by utilizing a compressible liquid.

LiquidSpring

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With hopes of finding a better ride on its cutaway buses, Española, N.M.’s North Central Regional Transit District (NCRTD) partnered with LiquidSpring to test its Compressible Liquid Adaptive Suspension System (CLASS).

The patented suspension system is designed to replace conventional suspension systems  (steel or air), with shock absorbers, and stabilizer bars by utilizing a compressible liquid. The compressible liquid provides the spring and damping. CLASS connects a first liquid volume (strut/damper) and a second volume (liquid only) with a hydraulic line and valve. The volumes are filled with a compressible liquid and pressurized, which serves as the spring. When the secondary volumes rate valve is open, all the liquid is available to compress, providing the lowest spring stiffness; when the rate valve is closed, only the liquid in the first volume (strut/damper) is available to compress, thereby providing the highest spring stiffness.

When the valve is Pulse Width Modulated (PWM), there is a seamless spring stiffness change. This configuration enables CLASS to change the spring rate and damping at each wheel independently, reducing harshness while increasing roll and pitch control.

Operationally, the system works by monitoring the vehicle’s steering, speed, braking, and the tide height at each wheel. This information is processed by an on-board microprocessor using its preprogrammed eight-degree-of-freedom vehicle and non-linear fluid models. The microprocessor instructs the corner valve for each strut/damper module to adjust the effective liquid volume, thus changing the stiffness and damping as required to minimize transmitted power and resonant vibrations from the suspension to the chassis, which cause a harsh ride.

CLASS includes a leveling system that maintains a pre-set “proper” ride height, regardless of load, or as the passenger load on the vehicle changes.

“[Our system] is unique [because] we can instantaneously change the suspension spring rate on a vehicle to go from super soft to super firm in fractions of a second,” explains Travis Ward, national sales at LiquidSpring. “All of our suspensions work the same, but as the GAWR changes per vehicle so does the perceived softness.”

In addition to a noticeable improved ride quality and handling, NCRTD has seen a decrease in suspension-related expenses when comparing two identical buses — E-450 cutaways — with the only difference being its previous suspension system on one bus and the CLASS system on the other bus, says David Funck Sr., fleet/facilities maintenance manager at NCRTD.

With the LiquidSpring-equipped bus, the agency is running about .031 cents per mile in suspension-related expenses, compared to its old suspension system where they were running .067 cents per mile. From increased tire life to a reduction in tightening of screws, nuts, and bolts on the chassis/body, the vibration reduction provided by CLASS is proving to be a cost savings in addition to improving rider/driver experience.

NCRTD currently has the CLASS suspension system on the rear axle of about 16 of its buses and hopes to install it on both the front and rear of its buses in the future.

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