LVDT Use in Automotive Suspension

Trans-Tek, Inc. LVDT Application 800-828-3964

For OEM applications, AC-AC LVDT�s from the Series 270-280-290 provide cost-effective solutions for accurate positionfeedback. To fully support these transducers, only basicelectronics are required, including one of several commerciallyavailable Integrated Chips or I/C�s. Combining an AC-ACLVDT with the necessary electrical components will result ina relatively low-cost system with high-end performance.

AimRite Holdings Corporation is a pioneer in the field ofcomputer controlled suspension technology for the automotiveindustry. Targeting mainly sports utility vehicles (SUV),trucks, buses and RV�s, AimRite�s trademark product - theCOAST system - uses the Model 0283-0000 AC-AC LVDTfor continuous position feedback. This advanced suspensiondesign offers numerous benefits including: luxury car ridewith sports car performance, on-road and off-road application,replacement of sway bars and shock absorbers, simultaneouscontrol of all vehicle dynamics, compatibility with conventionalor air springs, reliability and flexibility at a minimal cost, androbust construction.

The COAST system consists of four electronically adjustablehydraulic control units for a standard automobile or SUV, allconnected to a computer controller. Six units are required fora truck, bus or RV. Each control unit contains its own LVDTwhich reports the exact position of each wheel in hundreths ofan inch to the controller 200 times per second. The controllerthen determines the optimum force needed for every wheeland sends this compensation factor to each unit, also at a rateof 200 times a second. Each control unit in turn generates the

proper force, ranging from over ±1000 pounds for a standardautomobile or SUV to over ±2500 pounds for a truck, bus orRV.

The COAST constant force approach differs from conventionaldamping in that it uses pressure regulators rather than orificesto control fluid flow. The LVDT measures the fluid levelthrough the position of a float inside a valve. Housed in eachhydraulic control unit, the valve reacts to the up and downmotion of the wheel and the LVDT takes a precise reading ofthat movement. This design gives COAST a key technicaladvantage. An orifice must be constantly and very rapidlyadjusted as the wheel moves, whereas the COAST systemsupplies a signal representing the appropriate force based onthe fluid level change. The force value is largely independentof any movement at that instance of time.

The COAST systemis totally automatic:continuously moni-toring and controllingthe vehicle�s ride per-formance to providesoft and stable ridecharacteristics. Itsparameters can beconfigured to anyspecific land surfacetransportation ve-hicle. COAST ad-justs and controls upto nine dynamic areasof a vehicle�s suspen-sion through its unique and patented adaptive suspension tech-nology. The position feedback signal from the LVDT is acritical source of data, processed by the computer controllerto obtain independent control responses for each degree of mo-tion.

AC-AC LVDTs provide a cost effective solution to OEMapplications requiring a rugged sensor with accurate andreliable position feedback capabilities.

Vehicle Speed

Power

Position Signal

Compression &Rebound Signals

Controller