SAE J1490-1999 Measurement and Presentation of Truck Ride Vibrations.pdf

SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.” SAE reviews each technical report at least every five years at which time it may be reaffirmed, revised, or cancelled. SAE invites your written comments and suggestions. TO PLACE A DOCUMENT ORDER: (724) 776-4970 FAX: (724) 776-0790 SAE WEB ADDRESS http:/www.sae.org Copyright 1999 Society of Automotive Engineers, Inc. All rights reserved.Printed in U.S.A. SURFACE VEHICLE 400 Commonwealth Drive, Warrendale, PA 15096-0001 RECOMMENDED PRACTICE Submitted for recognition as an American National Standard J1490 REAF. SEP1999 Issued1987-01 Reaffirmed1999-09 Superseding J1490 JAN1987 Measurement and Presentation of Truck Ride Vibrations ForewordThis Document has not changed other than to put it into the new SAE Technical standards Board Format. TABLE OF CONTENTS 1.Scope . 3 1.1Purpose 3 2.References. 3 3.Definitions. 4 3.1Vibration Measurement Axis Reference. 4 3.2Terminology 4 3.2.1Overlap Processing 4 3.2.2PSD 4 3.2.3Ride Vibrations. 4 3.2.4RMS . 4 3.2.5Seat Pad. 4 3.2.6Signal-to-Noise Ratio 4 3.2.7Spectrum 4 3.2.8Test Section . 4 3.2.9Transverse Sensitivity 4 3.2.10Windowing 4 3.3Letter Symbols . 4 4.General Test Design 4 5.Test Preparation And Documentation 5 5.1Vehicle 5 5.2Test Site . 5 5.3Operator . 5 5.4Operating Conditions 5 6.Subjective Ride Evaluations. 5 SAE J1490 Reaffirmed SEP1999 -2- 7.Instrumented Ride Vibration Measurements 5 7.1Measurement Instrumentation6 7.1.1Accelerometers and Signal Conditioning6 7.1.2Acceleration Data Recording6 7.1.3Instrumentation Data Sheet6 7.2Accelerometer Location7 7.3Data Analysis7 7.3.1Stationarity of Data .7 7.3.2Acceleration Measures .7 7.3.2.1g(rms) .7 7.3.2.2Weighted g(rms) .7 7.3.2.31/3 Octave Peak g(rms)7 7.3.2.4ISO 1/3 Octave Peak7 7.3.2.5Exceedance7 7.3.2.6Absorbed Power .8 7.3.3Data Analysis Parameters 8 7.3.3.1Data Duration8 7.3.3.2Preprocessing Filters8 7.3.3.3Sampling Frequency.8 7.3.3.4Sampling Accuracy.8 7.3.3.5Sampling Window.8 7.3.3.6Frequency Resolution.8 7.3.3.7Overlap Percentage8 7.3.3.8Precision of Spectral Estimates8 8.Data Presentation.9 8.1Graphic Presentation9 8.1.1Power Spectral Density 9 8.1.2Square Root of Power Spectral Density .9 8.1.3Time Domain Histogram.9 8.2Ride Measures Presentation 9 TABLE INDEX 1Acronyms for Ride Vibration Measures 10 2J1013 Spectrum Weighting Factors10 31/3 Octave Bands and ISO Factors to be Applied11 4Absorbed Power Constraints11 FIGURE INDEX 1Measurement Axes.12 2Test Vehicle Description Sheet 113 3Test Vehicle Description Sheet 214 4A to 4CTest Vehicle Description Sheets 3A to 3C15 5Test Vehicle Description Sheet 418 6A to 6CSample Subjective Evaluation Forms.19 7Instrumentation Data Sheet21 8Data Anlysis Data Sheet.22 9Vertical SAE J1013 Weighting Curve (Z) to be applied to RMS Acceleration 23 10Fore/Aft SAE J1013 Weighting Curve (X or Y) to be applied to RMS Acceleration24 11Vertical Absorbed Power Weighting Function (Z), Ci25 12Fore/Aft Absorbed Power Weighting Function (X), Ci.26 13PSD Display (Example) 27 14Square Root of PSD Display (Example).28 15Time Domain Histogram Display (Example).29 SAE J1490 Reaffirmed SEP1999 -3- 1.ScopeThere are two ways to assess the characteristics of ride vibrations of a vehicle during its operation. Subjective evaluation and objective measurement. Subjective assessments of the ride vibrations experienced by drivers during ride evaluations are generally performed by a panel of drivers and/or passengers who are instructed to operate or ride a group of vehicles in a predetermined manner in order to subjectively assess the levels and characteristics of ride vibrations. Figures 6A through 6C show examples of subjective evaluation forms presently in use. The disadvantages of the subjective method include need for careful experimental design, need for statistically unbiased samples, complexity of human perceptions of vibrations, and difficulty in comparing qualitative data of vehicles evaluated at different times and/or by different groups of people. Often ride characterization is not an easy task using only qualitative or descriptive terms. Therefore, it is necessary and desirable to develop objective techniques to enable ride engineers and others to measure ride vibrations during ride assessment in a quantitative manner. This recommendation details a uniform method for the measurement of ride vibrations of all Class 7 and 8 commercial vehicles, including both combination vehicles and straight trucks. Vibrations are to be measured utilizing cab and seat-pad mounted accelerometers in vertical (z axis) and fore/aft (x axis) directions. The measurement in lateral direction (y axis) is optional as these vibrations from a ride assessment standpoint are seldom significant in commercial vehicles. Several currently utilized methods of displaying, analyzing, and combining the measured accelerations are presented. This recommendation does not make any statements concerning how well any of the objective ride measures will correlate to subjective evaluations of ride, nor does it deal with any limits or establish any desirable values for acceptable ride. It is recognized that objective ride evaluation methods have some disadvantages due to the complexities of these measures, sophistication of instrumentation and analysis techniques, etc. Therefore, it is recommended that technically trained personnel conduct the objective tests and analyze the data. 1.1PurposeThis SAE Recommended Practice establishes the test procedure, environment, instrumentation, and methods for the measurement, analysis, and presentation of the ride-related vibrations to which seated occupants of Class 7 and 8 commercial vehicles are exposed during actual or simulated vehicle operation. It is intended that this recommendation will provide a degree of uniformity sufficient to allow characterization of ride needed for industry-wide communication of ride testing. Also presented are objective ride measures which have been suggested as having some degree of correlation to subjective ride evaluations. It is further intended that the use of this document will eventually result in objective ride measures being established as a generally accepted quantifier of subjective ride evaluations. 2.References 2.1Applicable PublicationsThe following publications form a part of this specification to the extent specified herein. Unless otherwise indicated, the latest version of SAE publications shall apply. 2.1.1SAE PUBLICATIONSAvailable from SAE, 400 Commonwealth Drive, Warrendale, PA 15096-0001. SAE J1013Measurement of Whole Body Vibration of the Seated Operator of Off-Highway Work Machines SAE J1060Subjective Rating Scale for Evaluation of Noise and Ride Comfort Characteristics Related to Motor Vehicle Tires SAE 680091“Analytical Analysis of Human Vibration,” F. Pradko and R. A. Lee, 1968. 2.1.2ISO PUBLICATIONAvailable from ANSI, 11 West 42nd Street, New York, NY 10036-8002. “Guide for Evaluation of Human Exposure to Whole Body Vibration,” ISO 2631, 1974 and 1978. SAE J1490 Reaffirmed SEP1999 -4- 2.1.3OTHER PUBLICATIONS Bendat and Piersol, Random Data: Analysis and Measurement Procedures, Wiley Interscience, 1971. 3.Definitions 3.1Vibration Measurement Axis ReferenceThe axis references will follow the convention established in Figure 1 where positive x is forward, positive y is right and positive z is down, all relative to the seated driver. 3.2Terminology 3.2.1OVERLAP PROCESSINGOverlapping of time domain data blocks to which a window has been applied. Overlap processing is necessary to achieve a precise spectral representation of short time records of data which have been windowed. The optimum overlap percentage is dependent on the type of window used (see 3.2.10). 3.2.2PSDPower Spectral DensityAcceleration spectrum normalized by filter bandwidth and scaled in g2/Hz, such that integration by frequency yields the mean squared acceleration. The square root of the PSD (g Hz1/2) can also be displayed for ride work. 3.2.3RIDE VIBRATIONSMechanical vibrations expressed in terms of accelerations in the 1 to 25 Hz bandwidth measured at the specified locations in the cab interior. 3.2.4RMSRoot mean square magnitude of a signal. 3.2.5SEAT PADMolded rubber pad that encapsulates the accelerometer that the occupant sits on.' The specifications of the pad are outlined in SAE J1013. 3.2.6SIGNAL-TO-NOISE RATIOThe ratio of the value of a recorded signal channel to that of a simultaneously- recorded shorted channel. 3.2.7SPECTRUMMagnitude versus frequency display. 3.2.8TEST SECTIONA well-defined section of road surface that exhibits uniform surface characteristics upon which ride tests are performed. 3.2.9TRANSVERSE SENSITIVITYFraction of accelerometer sensitivity which will apply to acceleration orthogonal to its principle axis. Also referred to as cross axis sensitivity. 3.2.10 WINDOWINGThe process equivalent to weighting a time domain acceleration record prior to transformation to the frequency domain. 3.3Letter Symbols 3.3.1Hz = Hertz, unit of frequency, cycles per second 3.3.2fi = frequency in Hz of the ith spectral line 3.3.3P = absorbed power in watts 3.3.4Ai = g2/Hz spectral magnitude at frequency fi 3.3.5Wi = angular frequency in sec-1, 2 fi 3.3.6g = acceleration of gravity, 9.8 m sec-2 SAE J1490 Reaffirmed SEP1999 -5- 4.General Test DesignA typical ride test consists of running vehicle(s) over selected well-defined sections of road at constant speed(s), while measuring cab and seat pad accelerations. A subjective evaluation of the ride by the driver may be simultaneously performed. Each acceleration should be displayed in one of the manners in 8.1 and further analyzed and presented as numerical measure(s) of the ride vibrations of 8.2. Ride vibration magnitudes can be sensitive to road speed, so generally each road section should be tested at several speeds. The validity of the comparison of objective ride vibration measurements is increased by averaging the independent measurements from several repeat tests at each speed. The validity of subjective ride evaluations is increased as the number of evaluators is increased since body weight, build, age, and many other factors affect a person's perception of ride vibrations. The inherent variability of subjective evaluations makes it advisable to always make simultaneous objective measurements. 5.Test Preparation and DocumentationThe usefulness of any data will be enhanced by a thorough test preparation and documentation using the following format. Photographs of the vehicle, driver, accelerometers in their mounted positions and test site should be taken to supplement the written documentation. 5.1VehicleThe test vehicle should be described by recording the information contained in the test vehicle description sheets shown in Figures 2 through 5. The drawings can be altered as needed to match a particular vehicle configuration, but all the information should be included. Fuel tank level should be noted when measuring the center of gravity and maintained as close as possible to this level throughout the test. Actual accelerometer positions should be noted on Figure 4C. 5.2Test SiteDocumentation should include written descriptions and photographs of exact site location with landmarks, description of the road surface types of test section, expansion joint (if any) spacing, and posted speed limit. For future comparisons, it is recommended that the profile of the test surface(s) be documented. 5.3OperatorThe height, seated height (floor to ear), sex, chest circumference, waist circumference, hip circumference, and weight of the operator who is sitting on the seat pad accelerometers should be documented. A photograph is suggested. The seat, if adjustable, should be properly adjusted per manufacturer's specifications, and the driver's posture should be consistent from test to test. 5.4Operating ConditionsThe weather and vehicle operation factors should be documented to the extent that they affect the vehicle ride. Some possible factors are: test date, time of day, personnel, ambient temperature, presence of rain or snow, wind velocity, and direction relative to vehicle direction and velocity of vehicle during test. 6.Subjective Ride EvaluationsSubjective ride evaluations are often conducted in conjunction with objective ride measurements. The subjective evaluations are generally conducted by having a jury of several members rate different aspects of ride using scales such as those illustrated in Figures 6A through 6C. The different categories for which individual rating values may be requested include: ride comfort (an overall rating), seat vertical vibrations, seat fore/aft vibrations, seat lateral vibrations, steering wheel vibrations, and cab shake. The rating tests are conducted over a selected test section(s) of road surface at constant speed(s). The means of the ratings among evaluators or among ride categories are used to compare vehicles under the same test conditions. The validity of the comparison may be established by statistical tests, but will generally improve with the size of the rating jury. 7.Instrumented Ride Vibration MeasurementsRide vibration measurements are obtained by measuring accelerations on the vehicle cab and on a “seat pad” placed between the driver and the seat. The output of each acceleration transducer is analyzed and the results are utilized to produce one or more numerical measures of ride vibration magnitude. SAE J1490 Reaffirmed SEP1999 -6- This document provides only guidelines for the measurement and analysis of ride vibrations. To avoid potential errors, only technically trained personnel current in the latest techniques of vibration measurement and analysis should select the instrumentation used and supervise equipment installation, calibration, operation, and data analysis. 7.1Measurement Instrumentation 7.1.1ACCELEROMETERS AND SIGNAL CONDITIONINGRide vibration shall be measured using accelerometers capable of withstanding instantaneous acceleration as great as 100 m/s2 without damage and transverse sensitivity of no greater than 7%. To assure that engine and other high frequency vibrations will not be amplified, accelerometers with sufficiently high natural frequency and appropriate internal damping shall be used. The accelerometers are mounted as described in 7.2. The accelerometers, together with their associated signal conditioning, shall be capable of measuring rms accelerations in the 1.0 to 25 Hz bandwidth ranging in amplitude from 0.1 m/s2 to 10 m/s2 with a crest factor as great as 3. Acceleration amplitudes within the previous ranges shall be measured with at least ±5% accuracy. If time domain