SAE J1574-2-2018
Steel@ Corrosion-Resistant@ Bars@ Wire@ Forgings@ Mechanical Tubing@ and Rings 16Cr - 4.0Ni - 0.30Cb (Nb) - 4.0Cu Solution Heat Treated@ Precipitation Hardenable

Standard No.

SAE J1574-2-2018

Release Date

2018

Published By

SAE - SAE International

Latest

SAE J1574-2-2018

Scope

This SAE Information Report presents the background and rationale for SAE J1574-1. The motor vehicle industry is working toward a more complete understanding of the factors affecting the motions of vehicles on the roadway@ by using a variety of techniques that predict responses to road and operator inputs. The capability to predict responses is desirable so that vehicles can be designed for optimum safety and utility. In addition to the force and moment properties of the pneumatic tires@ a number of vehicle and suspension parameters affect the response of the vehicle; these include weight@ center-of-gravity location@ moments of inertia@ suspension ride and roll rates@ suspension kinematic and compliance properties@ and shock absorber characteristics. These parameters must be quantified in order to predict vehicle responses. Measurement of most of these parameters will be limited to determining their values in the linear range for use in directional control simulations. The limitation to linear range characteristics primarily reflects current measurement practice@ to which SAE J1574-1 is directed. In the case of mass and inertia properties@ this limitation clearly does not apply. For those to which it does apply@ it is not felt to be a serious limitation since most of the measurement techniques can be extended beyond the linear range through appropriate increases in steering or suspension displacement or loading. Use of the measured parameters in simulations is assumed as the most frequent use. However@ this does not seem to limit their use to simulations. Vehicle and suspension characteristics appropriate for simulation can equally well be used for vehicle and suspension characterization and comparison@ suspension development and optimization@ and processing of road test data. As noted in SAE J1574-1@ vehicles addressed will be limited to passenger cars@ light trucks@ and on-highway recreational and commercial vehicles with two or more axles of approximately the same wheel track. This excludes bicycles@ motorcycles@ tricycles@ and vehicles intended primarily for off-highway use. This limitation is largely a recognition of the types of vehicles historically measured for ride and directional control simulation@ since SAE J1574-1 has been written to document the current state-of-the-art rather than to expand it. Additionally@ inclusion of these other vehicles might well require measurement of other chassis characteristics to properly simulate their dynamic characteristics. The measurement of these additional characteristics may not be supported by widespread experimental practice. Assumptions and Limitations The focus of SAE J1574-1 is consolidation and documentation of the best existing technology. The intent is to avoid introducing unproven and unestablished practices. The assumptions related to the methods of suspension characterization (static characteristics@ phenomenological descriptions@ characterization for linear range maneuvers@ and use of superposition) stem largely from established practice@ with established validity. All of these suspension characterization methods are widely@ though not exclusively@ used and have given valid simulated responses of steady-state and dynamic vehicle characteristics. This is not to say that other approaches are not also valid. The limitations associated with types of simulations addressed also stem primarily from the limitations of existing practice@ which has generally focused on the simulation of fixed control directional control properties in the linear range. While simulation of free control vehicle responses is not uncommon in the automotive industry@ its inclusion in SAE J1574-1 would require the measurement of steering system component masses and inertias. Such measurements are not common practice. The limitations associated with vehicle characteristics addressed deserve brief discussion. Suspension side view kinematic properties are not addressed since they are not required for constant speed directional control simulation. This is also true of rotational inertias of wheels@ tires@ brakes@ and driveline components as well as steer and camber compliances resulting from longitudinal force. The measurement of steer and camber compliances resulting from overturning and rolling resistance moment is omitted since these compliances normally have small effects on vehicle directional control characteristics. (Rolling resistance moment generally has negligible effects on steer and camber deflections.) Finally@ the measurement of the remaining variables (kingpin and caster offsets@ ride and roll damping@ and fifth wheel characteristics) is omitted due to the absence of standard industry practice. Ride and roll damping are usually calculated from shock absorber damping constants and suspension kinematic characteristics. These calculations will be discussed in Section 10. Characteristics Measured No discussion in addition to that of SAE J1574-1. Nature of Measurements SAE J1574-1 gives an overview of the types of measurements required for each class of variable measured. This discussion will generally be repeated in much more detail in the first two paragraphs of each section. This more detailed discussion will include minimum accuracy requirements@ based on simulation requirements or the capabilities of current experimental practice. In some cases@ simulation requirements are not particularly stringent and accuracy requirements may more realistically be indicated by experimental practice. With this in mind@ a brief@ general discussion of accuracy requirements may be helpful here@ with a more specific discussion for each variable given in this Information Report for each section. In those cases where the data are used solely for vehicle subjective development@ the measurements may normally be made to 5% accuracy@ especially if chassis parameter changes significantly larger than this are being made. This assumes that just noticeable subjective differences in response characteristics are about 10%@ thus necessitating chassis parameter changes of at least 10%@ preferably more. Vehicle and suspension parameter data may also be used as inputs for mathematical models that calculate vehicle responses. The sensitivity of the response to errors in the input data varies with the vehicle being simulated@ with its tire characteristics@ and the characteristic in question@ thus making it difficult to generalize about accuracy requirements. With regard to stability and control calculations@ it may be observed that the understeer gradient is the summation of numerous effects@ such as weight distribution@ roll camber@ roll steer@ lateral force deflection steer@ and aligning torque deflection steer. A 1% error in measurement of any one quantity is likely to alter the understeer gradient by 1% or less. Only when inaccuracies accumulate in the same direction is it possible for a significant error in the simulated response to result. Transient properties@ such as lateral acceleration response time or yaw velocity response time@ can be expected to have sensitivities similar to those for the understeer gradient. Accuracy requirements for simulation thus depend on the desired accuracy of the simulation and on whether one assumes that errors will accumulate in one direction or not. As a final note on the nature of the measurements@ the measurement of suspension kinematic and elastic characteristics with tires mounted should be briefly discussed. As noted in SAE J1574-1 for this section@ common practice is to leave wheels and tires mounted during all measurements. While this may introduce small errors in some measurements@ it is treated here as the primary mode of measurement@ because of its widespread use and relatively small effect on accuracy. However@ other methods@ which might omit or bypass the tire are not excluded if the additional accuracy is desired. Paragraph 9.2.2 of this document covers this subject in more depth. Use of Recommended Practice and Information Report No discussion in addition to that of SAE J1574-1.

SAE J1574-2-2018 history

• 2018 SAE J1574-2-2018 Steel@ Corrosion-Resistant@ Bars@ Wire@ Forgings@ Mechanical Tubing@ and Rings 16Cr - 4.0Ni - 0.30Cb (Nb) - 4.0Cu Solution Heat Treated@ Precipitation Hardenable
• 2012 SAE J1574-2-2012 Measurement of Vehicle and Suspension Parameters for Directional Control Studies--Rationale
• 2005 SAE J1574-2-2005 Measurement of Vehicle and Suspension Parameters for Directional Control Studies--Rationale
• 2000 SAE J1574-2-2000 Measurement of Vehicle and Suspension Parameters for Directional Control Studies - Rationale