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Chassis Lab Measurement Methodologies
Inertial Measurements
Vehicle is locked to baseplate Frame. For CG measurements Frame is mounted on knife edges, and is cycled through tilt angles by a vertical linear actuator, equipped with a load cell and mounted on a torque arm. CG is normally measured at several ride heights, to permit CG estimation under different loadings. For roll and pitch inertia Frame is mounted on knife edges and linear springs. For yaw inertia Frame sits on "yaw cradle", which is attached to the floor through a large-diameter ball bearing with torsion bar spring restraint. Separation of sprung and unsprung masses by measurement of total vehicle CG height at several different ride heights is theoretically simple. However, because of body beaming deflection and the compliance of engine/suspension subframe rubber mounts, the results have been so far insufficiently accurate. Development of the methodology is continuing.
Chassis Compliance
Vehicle sprung mass is locked to the Frame, with tires on ball-bearing low-friction tables mounted on platform scales. Hydraulic servo cylinders equipped with load cells apply forces and moments at the tire contact patches. Compliances are measured from a transducer plate mounted on lugnut extensions to a ball-slide follower mechanism attached to the sprung mass, or from the tire contact surface to the Frame.
Ride/Roll Spring Rates and Kinematics
Vehicle rests on scales and ball bearing tables. Sprung mass is restrained laterally and fore/aft by vertical posts in linear ball bearings. Four hydraulic servo cylinders apply ride and roll forces. Vertical posts are unrestrained vertically for ride motions. For roll motions they can be left unrestrained so vehicle "finds its own" roll center; or they can be locked to define roll centers at ground level or at any level from 4 inches below ground to 3.5 inches below the sprung mass bottom of body. Deflections are measured from a transducer plate mounted on lugnut extensions to a ball-slide follower mechanism attached to the sprung mass, or from the tire contact surface to the Frame.
Steering
Vehicle rests on scales with ball bearing tables, restrained by unlocked vertical posts. The steering wheel is cycled slowly by hand or by geared electric motor through full lock. Measurements of displacements of reference point on the spin axis are made from a transducer plate mounted on lugnut extensions to a four-axis ball slide assembly (X,Y,Z, steer angle) attached to the sprung mass. Caster and steering axis inclination are computed from camber and caster changes.
Standard Conditions
All tests are run at, or referenced to, curb trim height. All kinematics tests are run with engine stopped. Steering system tests are run with engine running and with engine stopped. Only handwheel torque is plotted for the engine stopped condition, as explained in the Notes below. Front lateral force and aligning torque compliances with forces or torques adding are run with engine running; and with forces and torques opposing the engine is stopped; as explained in the Notes below. Front longitudinal force compliance tests are run with engine running. All rear compliance tests are run with engine stopped.
Equations Fitted to Plotted Data
Third-order least-squares polynomial equations are fitted to most data plots. Where dictated by the character of the data, three-element linear plots (thru-center, and positive and negative extremes) are used instead. Examples of the latter are steer tests, where roadwheel steer angle vs aligning torque usually shows a distinct difference between on-center and off-center slopes; and wheel loads in ride and roll, where rates change as bump or rebound stops are engaged.
Choice of Data to Be Plotted
Raw data (vs time) required for all plots will be supplied on floppy disks for all tests, and will be included in the test charge. All of the plots in the following listing can be generated from the floppy disk format. Since many of the data plots in the listing are useful only in some simulation models, and the quotation for Data Processing includes a separate charge for each plot, costs will be minimized by circling only those plots actually intended for use, or those for which fitted equations are desired.
Vehicle is locked to baseplate Frame. For CG measurements Frame is mounted on knife edges, and is cycled through tilt angles by a vertical linear actuator, equipped with a load cell and mounted on a torque arm. CG is normally measured at several ride heights, to permit CG estimation under different loadings. For roll and pitch inertia Frame is mounted on knife edges and linear springs. For yaw inertia Frame sits on "yaw cradle", which is attached to the floor through a large-diameter ball bearing with torsion bar spring restraint. Separation of sprung and unsprung masses by measurement of total vehicle CG height at several different ride heights is theoretically simple. However, because of body beaming deflection and the compliance of engine/suspension subframe rubber mounts, the results have been so far insufficiently accurate. Development of the methodology is continuing.
Chassis Compliance
Vehicle sprung mass is locked to the Frame, with tires on ball-bearing low-friction tables mounted on platform scales. Hydraulic servo cylinders equipped with load cells apply forces and moments at the tire contact patches. Compliances are measured from a transducer plate mounted on lugnut extensions to a ball-slide follower mechanism attached to the sprung mass, or from the tire contact surface to the Frame.
Ride/Roll Spring Rates and Kinematics
Vehicle rests on scales and ball bearing tables. Sprung mass is restrained laterally and fore/aft by vertical posts in linear ball bearings. Four hydraulic servo cylinders apply ride and roll forces. Vertical posts are unrestrained vertically for ride motions. For roll motions they can be left unrestrained so vehicle "finds its own" roll center; or they can be locked to define roll centers at ground level or at any level from 4 inches below ground to 3.5 inches below the sprung mass bottom of body. Deflections are measured from a transducer plate mounted on lugnut extensions to a ball-slide follower mechanism attached to the sprung mass, or from the tire contact surface to the Frame.
Steering
Vehicle rests on scales with ball bearing tables, restrained by unlocked vertical posts. The steering wheel is cycled slowly by hand or by geared electric motor through full lock. Measurements of displacements of reference point on the spin axis are made from a transducer plate mounted on lugnut extensions to a four-axis ball slide assembly (X,Y,Z, steer angle) attached to the sprung mass. Caster and steering axis inclination are computed from camber and caster changes.
Standard Conditions
All tests are run at, or referenced to, curb trim height. All kinematics tests are run with engine stopped. Steering system tests are run with engine running and with engine stopped. Only handwheel torque is plotted for the engine stopped condition, as explained in the Notes below. Front lateral force and aligning torque compliances with forces or torques adding are run with engine running; and with forces and torques opposing the engine is stopped; as explained in the Notes below. Front longitudinal force compliance tests are run with engine running. All rear compliance tests are run with engine stopped.
Equations Fitted to Plotted Data
Third-order least-squares polynomial equations are fitted to most data plots. Where dictated by the character of the data, three-element linear plots (thru-center, and positive and negative extremes) are used instead. Examples of the latter are steer tests, where roadwheel steer angle vs aligning torque usually shows a distinct difference between on-center and off-center slopes; and wheel loads in ride and roll, where rates change as bump or rebound stops are engaged.
Choice of Data to Be Plotted
Raw data (vs time) required for all plots will be supplied on floppy disks for all tests, and will be included in the test charge. All of the plots in the following listing can be generated from the floppy disk format. Since many of the data plots in the listing are useful only in some simulation models, and the quotation for Data Processing includes a separate charge for each plot, costs will be minimized by circling only those plots actually intended for use, or those for which fitted equations are desired.
