PERCEPTION OF RIDE
The final assessment of ride vibrations must deal with the issue of how ride is perceived. For that purpose, one must first attempt to define ride. Ride is asubjective perception, normally associated with the level of comfort experienced when traveling in a vehicle. Therefore, in its broadest sense ,the perceived ride is the cumulative product of many factors. The tactile vibrations transmitted to the passenger’s body through the seat, and at the hands and feet, are the factors most commonly associated with ride. Yet it is often difficult to separate the influences of acoustic vibrations(noise)in the perception of ride, especially since noise types and levels are usually highly correlated with other vehicle vibrations. Additionally, the general comfort level can be influenced by seat design and its fit to the passenger, temperature, ventilation, interior space, hand holds, and many other factors. These factors many all contribute to what might be termed the “ride quality” of a vehicle.
Some of the above factors, such as vibrations, can be measured objectively, while others, such as seat comfort are still heavily dependent on subjective evaluation methods. To further complicate matters, the interactions between factors are not well established. For example, it is the author’s experience that tolerance for vibration in a truck often can be drastically reduced if the passenger space provisions do not allow room for body movement without contacting hard points on the vehicle interior.
Tolerance to Sest Vibrations
The judgment of ride vibration in a vehicle is still an area of controversy in the
automotive community. As a starting point it is instructive to look at research findings from the scientific community relating to human tolerance for vibration. A brief state-of-the-art review of vibration limits for human comfort covering work back to the 1920s is presented in the SAE Ride and Vibration Data Manual[26] published in 1965. Major works by Lee and Pradko , the International Organization for Standardzation , Oborne , Miwa, Parsons, Fothergill,
Leatherwood and others, have mase substantial contributions to the data base of information
related to vibration tolerance. These studies, in general, tend to tolerance as it relates to
discomfort in a seated position in an effort to sort out the frequency sensitivity of the human body. Pure sinusoidal inputs are often used in attempts to establish quantified levels of
discomfort or equal levels of sensation, as a function of frequency. Yet no universally accepted standard exists for judgment of ride vibrations due variables such as :
. seaing position
. influence of hand and foot vibration input
. single-versus multiple-frequency input
. multi-direction input
. comfort scaling
. duration of exposure
. sound and visual vibration inputs
Despite the controversy, certain common denominators can be seen in the results from much of the recent work. When examining tolerance for vertical and fore/aft vibration on seated passengers, the researchers usually observe comparable sensitivity curves.
Figure 1 shows lines of constant comfort as determined by a number of researchers.
Because of
Fig. 1
the different interpretations of comfort in each study, the nominal level of one curve is not comparable to the others, nor is it especially meaningful. Nevertheless, note that the majority show a minimum tolerance (maximum sensitivity) of the human body to vertical vibration in the frequency range between 4 and 8 Hz.This scnsitivity is well recognized as the result of vertical resonances of the abdominal cavity. At frequencies above and below this rang the tolerance increases in proportion to frequency. The actual shape of the boundaries will often show small inflections in the 10 to 20Hz range due to other organ resonances, especially head resonance near 10 Hz.
As indicated by the plots of the ISO curves in the figure, the duration of the vibration exposure also affects the maximum tolerable level. Hence, two boundaries are shown, one for one minute of exposure, and the second for one hour of exposure. General rules for determining boundaries appropriate to arbitrary exposure levels are available in the ISO Standard , and in the work of Lee and Pradko.
Very interesting findings were obtained by NASA in research on comfort in mass
transport vehicles, notably airplanes. The constant comfort lines for vertical vibration taken from that work are shown in Figure 2. The significant point observed is that the sensitivity as a function of frequency is dependent on the acceleration level. At high levels of vibration, the tolerance curves generally match those other researcher. But at low amplitudes the horizontal nature of the curves implies that discomfort is rather independent of frequency. Therefore, low levels of vibration are equal objectionable regardless of their frequency over the indicated
indicated range.
Human sensitivity to fore/aft vibration is somewhat different from that of the vertical. Figure 3 shows tolerance limits for for/aft vibration as determined form a number of sources. Again the nominal level of each curve is not especially meaningful but similar sensitivities are
indicated.
Fig.2
Fig.3
The most remarkable difference seen is that the region of maximum sensitivity occurs in the 1 to 2 Hz range. This sensitivity is generally recognized to result from the for/aft resonance of the upper torso. Note also that when the vertical and fore/ aft boundaries from individual researchers are compared, the minimum tolerance is observed in the fore/aft direction.
The tolerance curves shown in the figures are generally derived from pure sinusoidal inputs to the subject, whereas the ride environment in a motor vehicle contains all frequencies over a broad spectrum. Thus to apply this information to objective measurements of ride vibration on the seat of a car or truck ,it is necessary to resolve this incompatibility. One method commonly used is to filter the acceleration data in inverse proportion to the amplitude of the selected tolerance curve. The inverse filtering then allows the resultant acceleration spectrum to be viewed as if all frequencies were equally important.. With this method the vertical and fore/aft vibrations must be evaluated separately. To overcome this problem, the weighted root-mean-square(rms) accelerations in each direction are then sometimes combined by various formulas to obtain an overall rms value.
A more fundamental method for combining vertical and fore/aft vibrations emerged from the work of Lee and Pradko .The level of discomfort was related to the level of vibration power being dissipated in the subject’s body, whether from vertical, fore/aft ,or lateral inputs. By this method the tolerance curves could be used to weigh accelerations so as to arrive at an absorbed power for each direction, and the power quantities are simply added.
The ISO tolerance curves are one of the popular weighting functions used to assess the significance of an acceleration spectrum. However, in should be recognized that the proper in one-third octave and critique the vibration bases on the worst-case band in the spectrum.
When all is said and done , the tolerance curves determined by researchers are instructive to the ride engineer as background in evaluating the vibrations that are imposed on a passenger through the seat. Yet it has been found by many engineers that measurements of these vibrations, even weighted in accordance with selected tolerance curves, bear little correlation to the subjective ratings that will be obtained by o jury in road tests. For example, Healey
concluded that a simple measure of rms acceleration in a passenger car is as closely correlated
to subjective ratings as any combination of weighted accelerations he could devise.
Fig.4
Whether or not a frequency weighting function is used to adjust the relative importance of specific vibration frequencies, there are formats in which the acceleration specific can be presented that are more meaningful fir ride purpose. In the science of dynamics, it is common practice to present frequency domain information in log-log format as shown at the top of Figure 4. In this format, the modal response of a system asymptotically approaches straight lines ,and the behavior of complex systems (with multiple modes) can be combined as shown in the bottom of the figure. Thus it has great utility in analysis of dynamic systems. For ride purposes, however, this greatly distorts the relative importance of vibrations at the various frequencies. Presentation of area under the plot is indicative of mean-square or root-mean-square accelerations, depending on the units used on the ordinate axis. (Units of
acceleration /Herz correspond to mean-square values, whereas its square root corresponds to
the root-mean-square value.)
Fig.5
Figure 5 contrasts these two means of data presentation. Although the log-log format provides more information for understanding the dynamic system involved, the linear-linesr format allows the engineer to see the relative importance of vibrations in any frequency range by the involved. Log-log format creates the impression that vibrations are generally equally important across the entire spectrum. Yet in the linear-linear format it becomes clear that the major portion of the mean-square vibration in this case is concentrated in the low-frequency rang of 5Hz and below.
Other Vibration Forms
One reason why seat vibration measurements are inadequate as objective measure of ride is that the driver’s judgment of the vibration in the vehicle includes far more than what comes though the seat. The point was well demonstrated in studies of the influence of influence of wheel nonuniformities on the ride perception on a highway tractor, in which a jury of ten industry engineers rated the ride acceptability of the tractor under varying conditions of tire nonunifomity excitation. The ten-interval rating scale was used for rating seat vertical, seat
fore/aft, seat lateral, steering wheel, and cab shake vibrations. Sample results form these tests
for left front nonuniformity inputs are shown in Fifure 6.
A significant point observed in the results was the tendency to degrade the ride due to steering-wheel and cab-shake vibrations. Note that the ratings of seat vibrations showed little sensitivity to nonuniformity input; yet the ratings for cab shake and steering wheel were profoundly affected, especially for the second and third harmonics. The steering –wheel rating reflects vibration inputs to the hands of the drivers, while the cab-shake category represents inputs at the feet, as well as visual effects from shake of the A-pillar, rear view mirrors, sun visors, etc.
Note that in the these tests the jury was asked to rate the acceptability of the vehicle. Consequently, the ratings reflect the judgment of industry engineers with regard to the acceptability of this vehicle as a product. There is significance in the statement of the question
used for a rating experiment, example, highway engineers, in studies to rate roads for their roughness condition, have observed that question “How is the rode ?” versus “How is the ride ?” elicits a much different response from juries. The question “How is ride?” produce ratings that are dependent-higher ratings when the jury is transport the jury during a rating experiment-higher ratings when the jury is transported in a luxury car, and lower ratings when transported in an economy car. Whereas the question “How is the road?” prompt the jury to look beyond the vehicle and judge the road, with the result that the rating process is unaffected by the choice of the vehicle used in the rating study. The ride development engineer should be sensitive to this issue, and is advised to formulate the instructive question carefully before executing ride rating experiments.
CONCLUSION
As a final note, one might hypothesize that ride engineer’s goal should generally be to eliminate all vibrations in a vehicle. Even though this will never be possible in a motor vehicle, it dose give direction to development effort. Yet there are two contrary phenomena that must be dealt with. First, the elimination of one vibration will always expose another lesser annoyance. This has been illustrated in past stories of making cars ride so well that the sound of the clock became annoying. Second, in the limit, elimination of all vibration is also undesirable, inasmuch as vibrations are the source of road feel considered to be essential feedback to the driver of a motor vehicle.
对车的感悟车的感悟
最后评估振动必须处理的问题是如何感知车的感觉。为此目的，一个人必须首先尝试定义车。车是个人主观感知，通常与之相关联的是车在旅行时的舒适程度。在它最广泛的含义上，可以认为车是一些因素积累的结果。通过椅子传递到乘客身体上的触觉振动，在手上和脚上，通常产生的因素大多数与车有关。然而在感觉上很难分开美声（噪音）对心灵的影响，尤其是由于噪音的品种和层次通常要比其他与车相关的交通工具心灵感应高。另外，一般的舒适程度可以被对乘客座位的设计和安装所影响，温度，通风，内部空间，扶手，和一些其他的因素。那些因素可以促成一辆车的品质的条件。
上述的一些因素，像振动，可以客观的判断、测量：当其他的时候，像座位的舒适性严重的依靠在主观评价方法上。更为复杂的问题是，因素之间的相互作用并不确定。例如，如果乘客的空间规定不允许身体运动碰到上汽车内部的硬点，可以大幅度减少在卡车中的振动范围。
车振动的耐疲劳性车振动的耐疲劳性
在汽车的领域内评判车的振动仍然是一个共有的争议。从科学界与有关人类耐振动的研究结果作为起点是有非常教育意义的。覆盖工作回到上世纪20年代的人体舒适振动限值简短的现状综述主办的SAE ，1965年颁布的振动数据手册【26】。Lee 和Pradko 做的主要工作，标准化的国际组织, Oborne , Miwa, Parsons, Fothergill, Leatherwood以及其他人，给出了坚实的激射微波资料做振动公差的基础。这些研究，一般来说，它趋向于一个不方便的固定位置来挑选出的人体所能承受的频率。由于频率的作用，纯正弦投入通常用于在尝试建立不合适的量化等级或者感觉相等的等级。现在仍然没有存在公认的标准来判断车的振动变量，例如
座椅位置
振动对肢体的影响
单与多频率输入
多方向的输入
舒适度
暴露时间
振动视觉与听觉的输入
尽管有争论，可以在近来的大量工作结果中看到共同的命名者确定，研究人员通常观察可比灵敏度曲线来检验在前部（尾部）直立就座乘客所能忍受的振动。
一个研究人员确定了图像1展示的舒适衡量曲线，因为在每一个研究舒适的人员都有不同的解释，在名义上一条曲线的等级是比不上其他曲线的，也不是特别有意义。
图像1
然而，短文大多数展示了人体垂直时忍受最小（最大）频率在4HZ 到8HZ 之间。
此灵敏度公认为腹腔垂直共振1次的结果。在频率上下容忍量以频率的比例的形式增加，实际上在10HZ 到20HZ 共振时其他原件的接线变化很小，尤其是顶点接近10HZ 时。
图像中作为国际安全组织划分的曲线，揭露了持续振动的时间也达到了可容忍的最大限度。因此：两个边界都显示，一个用于一分钟的接触：和第二个一小时的暴露。在Lee 和Pradko 的工作中，在ISO 标准中一般可用于规则决定适当的曝光时间。
非常有意思的是美国航空局对大多数运输工具的研究，对飞机舒适度的研究获得结果。图2中的恒定舒适线与工作中的振动相垂直，观察到很重要的一点是灵敏度作为一个功能依靠在加速级别。那些振动，公差通常与其他研究员的相匹配。但是低于水平线1的振幅曲线暗示着频率是不舒适的。因此，低水平的振动与超过指示器指示行列引起的厌倦频率相等。
人类研究到前部的（后部的）与垂直的稍微有点儿不同。图像3展示的前部的（后部的）公差限值是从一个来源获取的。在此敏感问题表明了每条曲线时没有特别意义的。
图像2
图像3
最明显的不同看起来是敏感性最高的地方出现在1到2HZ 范围内。通常这种名感性被认为是前部（后部）上面未完成的部分产生了共鸣，笔记记载当研究人员个人的前部的（后部的）和垂直的边界相比较：在前部的（后部的）方向可观测到最小的公差。
一般公差曲线数值展示的是在这个题目上的纯正弦投入值，然而机动车乘驾环境包含的所有频率在一个广阔的光谱中。因此要在平顺的汽车或卡车座位上客观测量此信息，就必须解决这种不兼容性。常用的方法一般是把加速度资料反比例的通过滤波器。这个倒转过滤后的加速度光谱被认为与所有频率是同等重要的。这种方法被个别的用在处理车身振动上。为了解决这个问题，这个指向每个方向的均方根被各种公式处理得到一个有利用的均方根。
在Lee 和 Pradko 工作中发现另一个综合测量车身振动的方法。无论是从垂直，前部（后部），或者是外侧投入的不舒适振动能量在题目中被消散。只要每个方向都全神贯注的投入大量简单的附加力量就通过这种方法可以用公差曲线来测量加速度。国际标准化组织的规定曲线是用来评定加速度光谱的。然而，光谱边缘的振动是被批评的，八个一组中的三分之一是被公认是正确的。所有的都是说和做，研究人员决定的忍耐度曲线对汽车工程师在后台评价旅客通过座位所受的振动是有益的。尽管它已经被一些测量振动的工程师所发现，然而小幅度的修改容忍曲线是有利的，评判委员会在道路上测试的结果与个别的额定值有关。例如，Healey 在旅客车上客观单独测量的一个与额定值相接近的加速度均方根有利于与他设计的加速度相结合。
图像4
不论是否利用其他功能来调节与频率相关的重要细节，都有一些其它形式的加速度来提供给汽车的平顺性。在动力学中，它就像图像4顶部所展示的那样以日志格式实践给频率领域信息的。这种格式中，一个系统以这种形式反映接近真实值，系统（多重模式）复杂的反映就像图像底部所展示的那样。因而，它对分析动力学系统很有效用。然而，对于车的用途来说，这大大的扭曲了在不同频率振动的相对重要性。在这小块图形下面介绍的区域所显示的加速度均方或者均方根，取决于纵坐标轴上的单位（加速度的单位或者Herz 符合均方值，然而它的平方根符合有效值）。
图像5
图像5对应的资料显示两个意思。尽管日志格式提供了更多了解动力系统的信息，线性格式让工程师看到了在任何频率范围振动的重要性。日志格式给出的感觉是振动是同等重要的横跨在整个光谱。然而，线性格式清晰的显示出在这个例子中一部分重要的均方振动集中在5Hz 下面的低频率范围内。
其他形式的振动
测量汽车振动一个不充分的理由是司机判断来源于汽车的振动远远超过了来源于座位的那些。这一点表现在公路的不均匀对汽车车轮的影响，一个由10个产业工程师组成的评审委员会规定了在疲劳的条件下轮胎的寿命。这10个产业确定了用来生产座位的规定，座位前部或者后部，座位的侧部，操纵轮，驾驶室摇摆的振动。样品测试的结果显示在图像6。
图像6
在结果中可以观察到有重大意义的一点是方向盘和小室振动有退化的趋势。笔记上座位振动的额定值显示投入值有一点儿小小的不均匀，影响到方向盘和小室振动的额定值，尤其是第二次和第三次谐波。方向盘将振动传送到司机的手里，小室振动代表着脚上的输入，以视觉效果为摇柱，后视镜，遮阳板等等。
评判委员会的这些测试考虑到了车辆速度的可接受性。因此，这个额定值反映了产业工程师对此交通工具作为一个产品的可接受性的判断。它的意义在于陈述评级试验的问题所在，例如，公路工程师在研究道路的不平整度时，可以观察到一个问题“这条路怎么样？”，与之相对的是评审委员会对“这条路怎么样？”给出了一个不同的答案。“车怎么样？”这个问题在评审委员会依赖于更高的评级试验所产生的额定值，其额定值的
高低在于他们是坐在豪华车内还是经济车内。然而“路怎么样？”这个问题提示评判委员会来看要超越的车辆和路，在选择评级车辆的方法上是真实的。在车的发展这个问题上工程师是敏感的，在执行评级试验之前认真的考虑问题的表达方式是有益的。
结论
最后，车辆工程师把排除车辆上所有的振动作为一个假设。尽管对于一个发动机来说是不可能的，但是它能给出发展方向。然而有两个相反的现象必须着手处理。首先，消除一个振动会揭露另一个较小的烦恼，汽车里程计令人烦恼的声音已成为过去制造汽车的一个插图。第二，在汽车界中，排除所有振动是不受欢迎的，因为作为振动的来源，路的感觉是汽车发动机本质的反馈。
PERCEPTION OF RIDE
The final assessment of ride vibrations must deal with the issue of how ride is perceived. For that purpose, one must first attempt to define ride. Ride is asubjective perception, normally associated with the level of comfort experienced when traveling in a vehicle. Therefore, in its broadest sense ,the perceived ride is the cumulative product of many factors. The tactile vibrations transmitted to the passenger’s body through the seat, and at the hands and feet, are the factors most commonly associated with ride. Yet it is often difficult to separate the influences of acoustic vibrations(noise)in the perception of ride, especially since noise types and levels are usually highly correlated with other vehicle vibrations. Additionally, the general comfort level can be influenced by seat design and its fit to the passenger, temperature, ventilation, interior space, hand holds, and many other factors. These factors many all contribute to what might be termed the “ride quality” of a vehicle.
Some of the above factors, such as vibrations, can be measured objectively, while others, such as seat comfort are still heavily dependent on subjective evaluation methods. To further complicate matters, the interactions between factors are not well established. For example, it is the author’s experience that tolerance for vibration in a truck often can be drastically reduced if the passenger space provisions do not allow room for body movement without contacting hard points on the vehicle interior.
Tolerance to Sest Vibrations
The judgment of ride vibration in a vehicle is still an area of controversy in the
automotive community. As a starting point it is instructive to look at research findings from the scientific community relating to human tolerance for vibration. A brief state-of-the-art review of vibration limits for human comfort covering work back to the 1920s is presented in the SAE Ride and Vibration Data Manual[26] published in 1965. Major works by Lee and Pradko , the International Organization for Standardzation , Oborne , Miwa, Parsons, Fothergill,
Leatherwood and others, have mase substantial contributions to the data base of information
related to vibration tolerance. These studies, in general, tend to tolerance as it relates to
discomfort in a seated position in an effort to sort out the frequency sensitivity of the human body. Pure sinusoidal inputs are often used in attempts to establish quantified levels of
discomfort or equal levels of sensation, as a function of frequency. Yet no universally accepted standard exists for judgment of ride vibrations due variables such as :
. seaing position
. influence of hand and foot vibration input
. single-versus multiple-frequency input
. multi-direction input
. comfort scaling
. duration of exposure
. sound and visual vibration inputs
Despite the controversy, certain common denominators can be seen in the results from much of the recent work. When examining tolerance for vertical and fore/aft vibration on seated passengers, the researchers usually observe comparable sensitivity curves.
Figure 1 shows lines of constant comfort as determined by a number of researchers.
Because of
Fig. 1
the different interpretations of comfort in each study, the nominal level of one curve is not comparable to the others, nor is it especially meaningful. Nevertheless, note that the majority show a minimum tolerance (maximum sensitivity) of the human body to vertical vibration in the frequency range between 4 and 8 Hz.This scnsitivity is well recognized as the result of vertical resonances of the abdominal cavity. At frequencies above and below this rang the tolerance increases in proportion to frequency. The actual shape of the boundaries will often show small inflections in the 10 to 20Hz range due to other organ resonances, especially head resonance near 10 Hz.
As indicated by the plots of the ISO curves in the figure, the duration of the vibration exposure also affects the maximum tolerable level. Hence, two boundaries are shown, one for one minute of exposure, and the second for one hour of exposure. General rules for determining boundaries appropriate to arbitrary exposure levels are available in the ISO Standard , and in the work of Lee and Pradko.
Very interesting findings were obtained by NASA in research on comfort in mass
transport vehicles, notably airplanes. The constant comfort lines for vertical vibration taken from that work are shown in Figure 2. The significant point observed is that the sensitivity as a function of frequency is dependent on the acceleration level. At high levels of vibration, the tolerance curves generally match those other researcher. But at low amplitudes the horizontal nature of the curves implies that discomfort is rather independent of frequency. Therefore, low levels of vibration are equal objectionable regardless of their frequency over the indicated
indicated range.
Human sensitivity to fore/aft vibration is somewhat different from that of the vertical. Figure 3 shows tolerance limits for for/aft vibration as determined form a number of sources. Again the nominal level of each curve is not especially meaningful but similar sensitivities are
indicated.
Fig.2
Fig.3
The most remarkable difference seen is that the region of maximum sensitivity occurs in the 1 to 2 Hz range. This sensitivity is generally recognized to result from the for/aft resonance of the upper torso. Note also that when the vertical and fore/ aft boundaries from individual researchers are compared, the minimum tolerance is observed in the fore/aft direction.
The tolerance curves shown in the figures are generally derived from pure sinusoidal inputs to the subject, whereas the ride environment in a motor vehicle contains all frequencies over a broad spectrum. Thus to apply this information to objective measurements of ride vibration on the seat of a car or truck ,it is necessary to resolve this incompatibility. One method commonly used is to filter the acceleration data in inverse proportion to the amplitude of the selected tolerance curve. The inverse filtering then allows the resultant acceleration spectrum to be viewed as if all frequencies were equally important.. With this method the vertical and fore/aft vibrations must be evaluated separately. To overcome this problem, the weighted root-mean-square(rms) accelerations in each direction are then sometimes combined by various formulas to obtain an overall rms value.
A more fundamental method for combining vertical and fore/aft vibrations emerged from the work of Lee and Pradko .The level of discomfort was related to the level of vibration power being dissipated in the subject’s body, whether from vertical, fore/aft ,or lateral inputs. By this method the tolerance curves could be used to weigh accelerations so as to arrive at an absorbed power for each direction, and the power quantities are simply added.
The ISO tolerance curves are one of the popular weighting functions used to assess the significance of an acceleration spectrum. However, in should be recognized that the proper in one-third octave and critique the vibration bases on the worst-case band in the spectrum.
When all is said and done , the tolerance curves determined by researchers are instructive to the ride engineer as background in evaluating the vibrations that are imposed on a passenger through the seat. Yet it has been found by many engineers that measurements of these vibrations, even weighted in accordance with selected tolerance curves, bear little correlation to the subjective ratings that will be obtained by o jury in road tests. For example, Healey
concluded that a simple measure of rms acceleration in a passenger car is as closely correlated
to subjective ratings as any combination of weighted accelerations he could devise.
Fig.4
Whether or not a frequency weighting function is used to adjust the relative importance of specific vibration frequencies, there are formats in which the acceleration specific can be presented that are more meaningful fir ride purpose. In the science of dynamics, it is common practice to present frequency domain information in log-log format as shown at the top of Figure 4. In this format, the modal response of a system asymptotically approaches straight lines ,and the behavior of complex systems (with multiple modes) can be combined as shown in the bottom of the figure. Thus it has great utility in analysis of dynamic systems. For ride purposes, however, this greatly distorts the relative importance of vibrations at the various frequencies. Presentation of area under the plot is indicative of mean-square or root-mean-square accelerations, depending on the units used on the ordinate axis. (Units of
acceleration /Herz correspond to mean-square values, whereas its square root corresponds to
the root-mean-square value.)
Fig.5
Figure 5 contrasts these two means of data presentation. Although the log-log format provides more information for understanding the dynamic system involved, the linear-linesr format allows the engineer to see the relative importance of vibrations in any frequency range by the involved. Log-log format creates the impression that vibrations are generally equally important across the entire spectrum. Yet in the linear-linear format it becomes clear that the major portion of the mean-square vibration in this case is concentrated in the low-frequency rang of 5Hz and below.
Other Vibration Forms
One reason why seat vibration measurements are inadequate as objective measure of ride is that the driver’s judgment of the vibration in the vehicle includes far more than what comes though the seat. The point was well demonstrated in studies of the influence of influence of wheel nonuniformities on the ride perception on a highway tractor, in which a jury of ten industry engineers rated the ride acceptability of the tractor under varying conditions of tire nonunifomity excitation. The ten-interval rating scale was used for rating seat vertical, seat
fore/aft, seat lateral, steering wheel, and cab shake vibrations. Sample results form these tests
for left front nonuniformity inputs are shown in Fifure 6.
A significant point observed in the results was the tendency to degrade the ride due to steering-wheel and cab-shake vibrations. Note that the ratings of seat vibrations showed little sensitivity to nonuniformity input; yet the ratings for cab shake and steering wheel were profoundly affected, especially for the second and third harmonics. The steering –wheel rating reflects vibration inputs to the hands of the drivers, while the cab-shake category represents inputs at the feet, as well as visual effects from shake of the A-pillar, rear view mirrors, sun visors, etc.
Note that in the these tests the jury was asked to rate the acceptability of the vehicle. Consequently, the ratings reflect the judgment of industry engineers with regard to the acceptability of this vehicle as a product. There is significance in the statement of the question
used for a rating experiment, example, highway engineers, in studies to rate roads for their roughness condition, have observed that question “How is the rode ?” versus “How is the ride ?” elicits a much different response from juries. The question “How is ride?” produce ratings that are dependent-higher ratings when the jury is transport the jury during a rating experiment-higher ratings when the jury is transported in a luxury car, and lower ratings when transported in an economy car. Whereas the question “How is the road?” prompt the jury to look beyond the vehicle and judge the road, with the result that the rating process is unaffected by the choice of the vehicle used in the rating study. The ride development engineer should be sensitive to this issue, and is advised to formulate the instructive question carefully before executing ride rating experiments.
CONCLUSION
As a final note, one might hypothesize that ride engineer’s goal should generally be to eliminate all vibrations in a vehicle. Even though this will never be possible in a motor vehicle, it dose give direction to development effort. Yet there are two contrary phenomena that must be dealt with. First, the elimination of one vibration will always expose another lesser annoyance. This has been illustrated in past stories of making cars ride so well that the sound of the clock became annoying. Second, in the limit, elimination of all vibration is also undesirable, inasmuch as vibrations are the source of road feel considered to be essential feedback to the driver of a motor vehicle.
对车的感悟车的感悟
最后评估振动必须处理的问题是如何感知车的感觉。为此目的，一个人必须首先尝试定义车。车是个人主观感知，通常与之相关联的是车在旅行时的舒适程度。在它最广泛的含义上，可以认为车是一些因素积累的结果。通过椅子传递到乘客身体上的触觉振动，在手上和脚上，通常产生的因素大多数与车有关。然而在感觉上很难分开美声（噪音）对心灵的影响，尤其是由于噪音的品种和层次通常要比其他与车相关的交通工具心灵感应高。另外，一般的舒适程度可以被对乘客座位的设计和安装所影响，温度，通风，内部空间，扶手，和一些其他的因素。那些因素可以促成一辆车的品质的条件。
上述的一些因素，像振动，可以客观的判断、测量：当其他的时候，像座位的舒适性严重的依靠在主观评价方法上。更为复杂的问题是，因素之间的相互作用并不确定。例如，如果乘客的空间规定不允许身体运动碰到上汽车内部的硬点，可以大幅度减少在卡车中的振动范围。
车振动的耐疲劳性车振动的耐疲劳性
在汽车的领域内评判车的振动仍然是一个共有的争议。从科学界与有关人类耐振动的研究结果作为起点是有非常教育意义的。覆盖工作回到上世纪20年代的人体舒适振动限值简短的现状综述主办的SAE ，1965年颁布的振动数据手册【26】。Lee 和Pradko 做的主要工作，标准化的国际组织, Oborne , Miwa, Parsons, Fothergill, Leatherwood以及其他人，给出了坚实的激射微波资料做振动公差的基础。这些研究，一般来说，它趋向于一个不方便的固定位置来挑选出的人体所能承受的频率。由于频率的作用，纯正弦投入通常用于在尝试建立不合适的量化等级或者感觉相等的等级。现在仍然没有存在公认的标准来判断车的振动变量，例如
座椅位置
振动对肢体的影响
单与多频率输入
多方向的输入
舒适度
暴露时间
振动视觉与听觉的输入
尽管有争论，可以在近来的大量工作结果中看到共同的命名者确定，研究人员通常观察可比灵敏度曲线来检验在前部（尾部）直立就座乘客所能忍受的振动。
一个研究人员确定了图像1展示的舒适衡量曲线，因为在每一个研究舒适的人员都有不同的解释，在名义上一条曲线的等级是比不上其他曲线的，也不是特别有意义。
图像1
然而，短文大多数展示了人体垂直时忍受最小（最大）频率在4HZ 到8HZ 之间。
此灵敏度公认为腹腔垂直共振1次的结果。在频率上下容忍量以频率的比例的形式增加，实际上在10HZ 到20HZ 共振时其他原件的接线变化很小，尤其是顶点接近10HZ 时。
图像中作为国际安全组织划分的曲线，揭露了持续振动的时间也达到了可容忍的最大限度。因此：两个边界都显示，一个用于一分钟的接触：和第二个一小时的暴露。在Lee 和Pradko 的工作中，在ISO 标准中一般可用于规则决定适当的曝光时间。
非常有意思的是美国航空局对大多数运输工具的研究，对飞机舒适度的研究获得结果。图2中的恒定舒适线与工作中的振动相垂直，观察到很重要的一点是灵敏度作为一个功能依靠在加速级别。那些振动，公差通常与其他研究员的相匹配。但是低于水平线1的振幅曲线暗示着频率是不舒适的。因此，低水平的振动与超过指示器指示行列引起的厌倦频率相等。
人类研究到前部的（后部的）与垂直的稍微有点儿不同。图像3展示的前部的（后部的）公差限值是从一个来源获取的。在此敏感问题表明了每条曲线时没有特别意义的。
图像2
图像3
最明显的不同看起来是敏感性最高的地方出现在1到2HZ 范围内。通常这种名感性被认为是前部（后部）上面未完成的部分产生了共鸣，笔记记载当研究人员个人的前部的（后部的）和垂直的边界相比较：在前部的（后部的）方向可观测到最小的公差。
一般公差曲线数值展示的是在这个题目上的纯正弦投入值，然而机动车乘驾环境包含的所有频率在一个广阔的光谱中。因此要在平顺的汽车或卡车座位上客观测量此信息，就必须解决这种不兼容性。常用的方法一般是把加速度资料反比例的通过滤波器。这个倒转过滤后的加速度光谱被认为与所有频率是同等重要的。这种方法被个别的用在处理车身振动上。为了解决这个问题，这个指向每个方向的均方根被各种公式处理得到一个有利用的均方根。
在Lee 和 Pradko 工作中发现另一个综合测量车身振动的方法。无论是从垂直，前部（后部），或者是外侧投入的不舒适振动能量在题目中被消散。只要每个方向都全神贯注的投入大量简单的附加力量就通过这种方法可以用公差曲线来测量加速度。国际标准化组织的规定曲线是用来评定加速度光谱的。然而，光谱边缘的振动是被批评的，八个一组中的三分之一是被公认是正确的。所有的都是说和做，研究人员决定的忍耐度曲线对汽车工程师在后台评价旅客通过座位所受的振动是有益的。尽管它已经被一些测量振动的工程师所发现，然而小幅度的修改容忍曲线是有利的，评判委员会在道路上测试的结果与个别的额定值有关。例如，Healey 在旅客车上客观单独测量的一个与额定值相接近的加速度均方根有利于与他设计的加速度相结合。
图像4
不论是否利用其他功能来调节与频率相关的重要细节，都有一些其它形式的加速度来提供给汽车的平顺性。在动力学中，它就像图像4顶部所展示的那样以日志格式实践给频率领域信息的。这种格式中，一个系统以这种形式反映接近真实值，系统（多重模式）复杂的反映就像图像底部所展示的那样。因而，它对分析动力学系统很有效用。然而，对于车的用途来说，这大大的扭曲了在不同频率振动的相对重要性。在这小块图形下面介绍的区域所显示的加速度均方或者均方根，取决于纵坐标轴上的单位（加速度的单位或者Herz 符合均方值，然而它的平方根符合有效值）。
图像5
图像5对应的资料显示两个意思。尽管日志格式提供了更多了解动力系统的信息，线性格式让工程师看到了在任何频率范围振动的重要性。日志格式给出的感觉是振动是同等重要的横跨在整个光谱。然而，线性格式清晰的显示出在这个例子中一部分重要的均方振动集中在5Hz 下面的低频率范围内。
其他形式的振动
测量汽车振动一个不充分的理由是司机判断来源于汽车的振动远远超过了来源于座位的那些。这一点表现在公路的不均匀对汽车车轮的影响，一个由10个产业工程师组成的评审委员会规定了在疲劳的条件下轮胎的寿命。这10个产业确定了用来生产座位的规定，座位前部或者后部，座位的侧部，操纵轮，驾驶室摇摆的振动。样品测试的结果显示在图像6。
图像6
在结果中可以观察到有重大意义的一点是方向盘和小室振动有退化的趋势。笔记上座位振动的额定值显示投入值有一点儿小小的不均匀，影响到方向盘和小室振动的额定值，尤其是第二次和第三次谐波。方向盘将振动传送到司机的手里，小室振动代表着脚上的输入，以视觉效果为摇柱，后视镜，遮阳板等等。
评判委员会的这些测试考虑到了车辆速度的可接受性。因此，这个额定值反映了产业工程师对此交通工具作为一个产品的可接受性的判断。它的意义在于陈述评级试验的问题所在，例如，公路工程师在研究道路的不平整度时，可以观察到一个问题“这条路怎么样？”，与之相对的是评审委员会对“这条路怎么样？”给出了一个不同的答案。“车怎么样？”这个问题在评审委员会依赖于更高的评级试验所产生的额定值，其额定值的
高低在于他们是坐在豪华车内还是经济车内。然而“路怎么样？”这个问题提示评判委员会来看要超越的车辆和路，在选择评级车辆的方法上是真实的。在车的发展这个问题上工程师是敏感的，在执行评级试验之前认真的考虑问题的表达方式是有益的。
结论
最后，车辆工程师把排除车辆上所有的振动作为一个假设。尽管对于一个发动机来说是不可能的，但是它能给出发展方向。然而有两个相反的现象必须着手处理。首先，消除一个振动会揭露另一个较小的烦恼，汽车里程计令人烦恼的声音已成为过去制造汽车的一个插图。第二，在汽车界中，排除所有振动是不受欢迎的，因为作为振动的来源，路的感觉是汽车发动机本质的反馈。