SAE 840069 中间位置操纵评价4444444.doc

SAE 840069 Objective 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 performance region encountered in freeway driving. Steering wheel angle and torque ,vehicle speed and yaw rate are recorded during a low frequency sinusoidal steer maneuver. The data is reduced to steering hysteresis, on-center and off-center steering sensitivities and torque gradients ,and a steering 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 steering ,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 handling where there is much to be learned. 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(dTdAy) on drivers perception of the ease and precision of driving (1)*. He found drivers 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 steady state 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 (d/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 measuring vehicle responses to wind was proposed by D. Schaffer (5). This test, if modified somewhat, may be a useful tool for studying on-center wind gust sensitivity.TEST PURPOSE试验目的This test is concerned with driver initiated automobile behavior and not wind or road disturbance effects. Its purpose is to measure handling characteristics observed by a driver during normal highway driving. This low lateral 横的，侧面的acceleration region of vehicle handling is termed on-center handling. Steering wheel torque转矩，扭矩，扭力, steering wheel angle, yaw rate and speed are measured since they are essential on-center cues to a driver. The test is run at a nominal 名义上的，象征性的，公称highway speed of 100 km/h.该试验与驾驶者启动汽车的行为有关，与风或路的干扰效果无关。其目的在于测量驾驶者在正常高速公路驾驶中观察到的操纵特性。车辆操纵的低横向加速度区被称为“中间位置操纵”。转向盘的扭矩，转向盘角度，车体转向角度和车速度都被测量，因为它们对驾驶者来说是必不可少的中间位置信号。该试验规定驾驶者以100公里小时的速度在高速公路上行驶。Sinusoid-like steering, whether for path correction or lane changing, is a typical driver on-center input. Steer angle amplitude for the on-center handling test depends on the test vehicles steering sensitivity (dAy/d). The amplitude is sufficient to give 0.2 g lateral acceleration peaks, so the entire on-center region is included. Steer angle frequency is approximately 0.2 Hz. This steer input is applied without a mechanical steer controller. With some experience, test drivers can generate this frequency and amplitude with good consistency. However, since this steer frequency is lower than the typical automobile steering sensitivity bandwidth at the test speed of 100 km/h, some steering frequency variation is allowable without greatly increasing vehicle gain variation. This frequency and amplitude combination require a minimum roadway width of two lanes. Greater amplitudes or lower frequency of steering inputs would require a wider roadway.正弦曲线状转向，无论改道或变道，都是典型的驾驶者的中间位置输入。中间位置操纵测试的转向角振幅取决于测试车辆的转向灵敏性(dAy/d)。振幅足够产生0.2g的横向加速度峰值，因此包含了整个中间位置区域。转向角频率约0.2Hz。此转向输入在没有机械转向控制器的情况下被应用。积累了一些经验，测试的驾驶者可以用良好的一致性来制造这种频率和幅度。然而，在测试速度为100公里/小时时，由于这一转向频率低于典型的汽车转向灵敏度的带宽，无需大大增加车辆增益变化，一些转向频率的变化是允许的。此频率和幅度组合要求的最小车道宽度为2车道。更大幅度或更低频率的转向输入将需要一个更广宽阔的道路。Further credence 信任，相信to this frequency selection comes from experiments McLean and Hoffmann conducted on a 1.2 km long and 3 m wide straight lane at speeds of 30 to 80 km/h (6). They found drivers generally exhibited peaks in their steering frequency spectra in the range 0.1 to 0.3 Hz. They also noted steering activity of this frequency content seemed to be associated with controlling the vehicles heading angle.对这一频率的选择的进一步信任是来自于试验，麦克莱恩和霍夫曼在一个长1.2公里、宽3米的直道上以30到80公里/小时的速度（6）进行测试。他们发现“驾驶者通常在驾驶频率在0.1到0.3Hz的频率范围内出现峰值。”他们还指出，这一频率内容的转向活动似乎与控制车辆的航向角有关。TEST PROCEDURE试验过程The on-center handling test begins after accelerating the test vehicle to 100 km/h. The driver then inputs a sinusoidal steer to the best of his ability. Steer frequency is one cycle every five seconds. The steer angle inputs are large enough to result in approximately 0.2 g lateral acceleration peaks. After about two full steer cycles the driver initiates sampling of steering wheel angle, steering wheel torque, vehicle speed and yaw rate. Storage capacity for the digital data acquisition system used limits a test segment to about 24 seconds. Eight to ten test segments of data are recorded during successive test runs. The data is recorded at a 40 sample/second rate. Because it is important to minimize external disturbances, testing is done on a smooth, level stretch of roadway. Wind speeds above 5 mph are avoided for testing. More severe wind conditions increase the variation and reduce the statistical confidence of the test results.在加速测试车辆100公里/小时后，中间位置操纵测试开始了。该驾驶者继而输入一个正弦转向到他能力的最大范围。驾驶频率是五秒一个周期。转向角输入到足够大导致出现约0.2克横向加速度的峰值。在约2个全转向周期时，该驾驶者启动抽样调查方向盘角，转向盘转矩，车辆速度和横摆率。用于数字数据采集系统的存储容量限制了测试段到大约24秒。八至十个测试段的数据在连续测试运行中被记录。数据以40样本/秒率被记录。因为尽量减少外部干扰是很重要的，测试是在一个光滑的，水平的巷道上完成的。风速超过5英里每小时避免测试。更严重的风况加速了变化，并降低了测试结果的统计信心。Lateral acceleration is calculated as the product of vehicle speed and yaw rate. The two are not equivalent for the sinusoidal maneuver used, but it is convenient to refer to the response variable in terms of gs. The major reason for measuring yaw rate instead of lateral acceleration is that lateral acceleration requires roll correction of an accelerometer signal. The roll gyro used to perform this function requires correction for drift and frequent operator attention to maintain a zero setting. A rate gyro, in contrast, is more desirable since it needs no corrections or operator attention.横向加速度被作为车辆速度和横摆率的输出来计算。两者并不等同于使用的正弦动力，但很方便响应变量中的“克”。测量车体转向角度而不是横向加速度的主要原因是横向加速度需要的加速度计信号的滚动校正。用于执行此功能的滚动陀螺仪需要校正流动和频繁的操作员的注意来维持一个零设置。相比之下，一个速率陀螺仪更为可取，因为它不需要更正或者操作员的关注。TEST DATA PROCESSING测试数据处理The data processing program first filters the recorded test data with a 3 Hz low pass digital filter. This eliminates noise without introducing a phase阶段，时期，相位周期 shift into the data. Since the frequency content of the steering input and vehicle responses is well below the filters cutoff frequency, no information is lost by filtering. Offsets in the data caused by electronic signal offsets are also corrected using zero speed calibration segments recorded before and after each test. Steer angle offsets are then corrected so the average of the steer angles is zero at zero yaw rate.数据处理程序首先用一个3Hz的低通数字滤波器过滤记录测试数据。没有引入一个相位转移到数据中来消除噪声。由于转向输入和车辆响应的频率内容远低于该滤波器的截止频率，在过滤过程中没有信息丢失。在由电子信号抵消所造成的数据中的偏移量也在每次测试之前和之后记录的零速校准段校正。转向角度偏移量继而被纠正，在零车体转向角下转向角平均为零。After converting the filtered data to engineering units the program computes the test parameter values described later. The test parameters are computed twice for each steer cycle, once for clockwise turning and once for counterclockwise turning of the steering wheel. Approximately forty clockwise and forty counterclockwise observations are computed for each parameter. Statistical methods are used to eliminate outlying parameter values caused by wind gusts, road disturbances, or driver error. Clockwise means, counterclockwise means, overall means and confidence intervals are computed from the remaining parameter values. Only the overall means will be discussed in this paper. The printout also lists the mean steering frequency during the test and flags any segment where the frequency is not within the range of 0.18 to 0.22 Hz.TEST PARAMETERSThe test parameters computed by the data processing program are selected characteristics from four cross plots. The four plots include: steering wheel angle versus lateral acceleration, steering wheel torque versus lateral acceleration, steering wheel torque versus steering wheel angle, and steering work gradient (dW/dAy) versus lateral acceleration. Typical time traces of steering wheel angle, steering wheel torque, and yaw rate are shown in Figure 1.图1STEERING WHEEL ANGLE VERSUS LATERAL ACCELERATION CHARACTERISTICS - There are four parameters used to characterize the cross plot of steering wheel angle versus lateral acceleration. Minimum steering sensitivity, steering sensitivity at 0.1 g, and steering hysteresis are shown in Figure 2.Steering sensitivity is calculated from the slope of the plot at 0.1 g. The slope is a linear fit of adjacent data points over a 0.01 g span of the plot. Slopes for other parameters are calculated similarly. The slope found is inverted and multiplied by 100 to give steering sensitivity in g/100 deg units. This measure of steering sensitivity is typically higher than that calculated from steady state handling test data. Steering sensitivity for a steady state handling test is found from measurements of nearly constant yaw rate or lateral acceleration at discrete increments of steering wheel angle. The sinusoidal steer of the on-center test results in a phase lag between steer angle and yaw rate. The influence of this lag on the steer angle versus lateral acceleration (ur) Lissajous plot is to reduce the slope at 0.1 g (7). This produces a higher value for steering sensitivity. Since lateral acceleration has a greater phase lag with steer than does yaw rate, lateral acceleration gain at 0.1 g would be higher than the yaw rate gain (steering sensitivity at 0.1 g test parameter) currently calculated from the on-center handling test.图2Minimum steering sensitivity is calculated from the maximum slope between plus and minus 0.1 g on the steer angle versus lateral acceleration plot. This sensitivity is usually much lower than that calculated at 0.1 g. This is primarily caused by nonlinear steering compliance. High on-center steering system compliance and lash reduce minimum steering sensitivity. Minimum steering sensitivity also varies somewhat proportionately with steering sensitivity at 0.1 g. Because of this, the ratio of these sensitivities is compared in an attempt to isolate the steering compliance effect.Steering hysteresis is calculated from the area inside the curve between plus and minus 0.1 g. The area is found by first calculating the area between each clockwise and counterclockwise steer direction curve and the abscissa. (The curve ascends to the right for a clockwise rotation of the steering wheel). The difference between the average clockwise area and the average counterclockwise area is taken to calculate the area inside the curve. This area is divided by 0.2 g to give hysteresis in units of degrees.Steering hysteresis is related to the lag of yaw rate with steer input since the greater the phase lag, the greater the hysteresis in a Lissajous plot. The parameter yaw rate lag time is the delay in seconds between the steering wheel angle passing through zero and yaw rate passing through zero.STEERING WHEEL TORQUE VERSUS LATERAL ACCELERATION CHARACTERISTICS - The plot of steering wheel torque versus lateral acceleration is characterized by five parameters: Lateral acceleration at 0 Nm, steering wheel torque at 0 g, steering torque gradient at 0 g, steering wheel torque at 0.1 g, and steering torque gradient at 0.1 g. These parameters are shown in Figure 3, which shows typical test results for a power steering car. The reduction in steering torque gradient with increasing lateral acceleration is a characteristic trait of power steering vehicles.图3Lateral acceleration at 0 Nm is an indication of returnability. To illustrate this, imagine negotiating a lane change. As the steering wheel is allowed to return to straight-ahead, There is a point at which the wheel, if released, would stick (i.e. steering wheel torque = 0 Nm). The lateral acceleration at this point is a measure of returnability. The on-center parameter calculated is similar, but it is also influenced by viscous damping and vehicle response lag. It is not a true measure of returnability. All parameters reflect the sign convention of the clockwise steer direction, hence the negative sign on lateral acceleration at 0 Nm.Steering wheel torque at 0 g is an indication of coulomb friction in the steering system. This parameter is also influenced by viscous damping and vehicle response lag.Steering torque gradient at 0 g is the change in steering wheel torque for a resulting change in lateral acceleration. This parameter is related to the terms road feel and directional sense. It is greatly influenced by kingpin axis torque gradient and overall steering ratio. In a power steering automobile, steering gear valve torsion bar rate, valve design, and steering system friction also affect the value measured.Steering wheel torque at 0.1 g is a measure of steering effort. Steering torque gradient at 0.1 g is a measure of road feel just off of straight ahead. Both torque and torgue gradient at 0.1 g are significantly reduced from manual steering with typical domestic power steering systems.STEERING WHEEL TORQUE VERSUS STEERING WHEEL ANGLE CHARACTERISTICS - Two parameters are used to characterize the cross plot of steering wheel torque versus steering wheel angle shown in Figure 4. These are the steering wheel torque at 0 deg and steering torque gradient at 0 deg, commonly referred to as steering stiffness.