SAE 840069Objective Evaluation of On-Center Handling Performance中间位置操纵性评价目标ABSTRACTA test was developed to quantify automobile handling characteristics for the performanee region encountered in freeway driving. Steering wheel angle and torque ,vehicle speed and yaw rate are recorded dur ing a low freque ncy sinu soidal steer man euver. The data is reduced to steeri ng hysteresis, on-cen ter and off-ce nter steeri ng sensiti vities and torque gradie nts ,and a steeri ng work parameter.This paper describes the test procedure and parameters. Test results are presented comparing the general attributes of foreign versus domestic cars,manual versus power steeri ng ,and rear versus front wheel drive.The study of driver automobile interaction during steering maneuvers has been widely addressed in the technical literature. However, it remains an area of vehicle han dli ng where there is much to be lear ned. The “road feel” of automobiles in the low lateral acceleration or on-center” region is of particular interest in evaluating handling for highway driving.Optimization of steering characteristics for easier controllability and driving comfort was studied at least as early as 1964 when Segel examined the effect of varying steering torque gradient -) on drivers perception of the ease and precision of driving (1)*. He founddrivers preferred a steering torque gradient of 23N.m/g to steering torque gradients of 6.4 or 41N.m/g in lane change and 0.2g steadystate turning tasks. In his paper,Segel explained that driving situations demanding precise path control require the driver to be more attentive to vehicle response. This attentiveness is the gain of the response-feedback loop in Segels driver-vehicle control system block diagram.*Numbers in parentheses designate references at end of paperThe more attention needed, the tighter the loop. When less attention is needed, the driving strategy tends toward open-loop control. Segel postulated that a driver relies more on steering wheel force cues than steering wheel angle as driving strategy tends toward open-loop control. The highway driving task is primarily carried out at low levels of lateral acceleration and is predominantly low stress, open-loop driving as described by Segel. Therefore, a test to measure on-center handling performance must include the measurement of steering wheel force or torque as well as steering wheel angle.Later research by Jaksch of Volvo proposed steering torque gradient as well as steering angle gradient (d6/dAy) determines drivers perception of steering sensitivity (2). He termed the inverse of the product of these gradients steering sensitivity. Forty drivers evaluated a car with five different combinations of front and rear tire pressures. The car was driven through a series of lane changes and turns and rated for handling performance. Jaksch concluded from his study that there is an optimum value for steering sensitivity.Recent papers continue to stress the importance of providing good road feel through attention to steering gear and steering system design (3,4). One of these, authored by H. Kurachi, et al, measured the frequency response of steering stiffness (dT/dAy) to a pulse steer input. This test was used to evaluate the effect of steering gear design changes on overall steering system stiffness while driving.It is obvious from the studies referenced that a test to measure on-center performance would be valuable. They also show such a test has unique requirements. Tests designed to measure automobile steering response or stability in the linear range dont necessarily give adequate information for on-center handling evaluation. A step steer test measures vehicle responses to discrete increments of step steer inputs. Measurements are not continuous on-center, so they lack essential information for quantifying on-center performance. Likewise, constant radius, constant speed, and constant steer angle understeer tests do not give a continuous on-center measurement of vehicle characteristics.A random steer input test measures response to a pseudo-white noise steer input. With random or impulse steer tests, lateral acceleration, yaw rate and roll gains, and time lags are found as a function of steer frequency. The underlying theory however, presumes a linear system. Automobiles exhibit significant non-linearity at low levels of lateral acceleration due to such sources as static friction, nonlinear bushing compliances, steering system lash, and power steering boost characteristics. Therefore, tests designed to measure frequency response characteristics may not yield good coherence for on-center handling evaluations.The on-center handling test described here is intended for analyzing on-center handling performance under ideal conditions. No attempt is made to observe automobile responses to wind gusts or road disturbances. The test is run only if these are at a minimum. A test for measu