3. Chassis Lab Services offered by ATI
3.0 "Topsy" - The Chassis Parameter Measurement Facility
Topsy is a modular system designed for measurement of all composite inertial,
kinematic, and compliance parameters that appear in today's sophisticated
mathematical simulation models. The emphasis in its design is not "production-line"
testing, but research: the operator can observe the vehicle's reaction
to developing forces; and as insights develop he can modify the test program
as he goes along. Test errors are minimized by running all tests under
servo control with continuous display of all data and recording of all
known error sources, while the operators closely monitor the test and the
developing data. The test facility is organized around an "infrastructure"
consisting of baseplates; vehicle locating fixtures; scales; hydraulic
and pneumatic power sources; interchangeable valve assemblies and actuators;
and transducers. These are organized along with specialized devices into
the several forms required for the different tests.
Topsy's development, test methodologies, equipment, and procedures are
described in SAE Paper 971056 "Topsy - A Modular Chassis Parameter Measurement
System", which was presented at the SAE International Congress in February
1997. An updated description based on that paper is available for download (http://www.atiheitz.com/download.htm).
All measurements made on Topsy are in accord with SAE J 1574/1 "Measurement
of Vehicle suspension Parameters for Directional Control Studies - Rationale,
Test Equipment, and Procedures", wherever that standard is applicable.
In general, measurements on Topsy are extended to higher force levels than
those suggested in J1574; and a number of parameters are measured in addition
to those covered by that standard.
Topsy uses the ATI/Heitz proprietary data acquisition system, which
allows close monitoring of a test in progress, and useful review of completed
test programs. All testing is videotaped, with raw transducer data recorded
in serial binary form on one or more lines at the top of the picture. Voice,
noises, and transducer outputs are recorded in synchronism continuously
during the entire test on two-hour tapes, so that anomalies that might
occur during or between test runs can later be investigated. Throughout
the test, data is displayed as columns of numerics, twelve channels to
a column, overlayed on the video picture, for visual monitoring. All processed
data is referenced to hours, minutes, and seconds of tape time, so that
final plotted data can be looked at while watching a replay of the test
The system is designed to use a maximum of nine "data lines" with 12
channels per line, for a total of 108 10-Hz data channels sampled at 60
Hz. However, it is also possible to devote some data lines to "high-speed"
use, with two data channels sampled at 480 Hz or one data channel sampled
at 960 Hz. A typical test program requires 24 to 36 "low-speed" 10 Hz channels.
3.1 Measurement Services Currently Offered
3.1.1 Inertial Measurements
Whole vehicle center of gravity
Whole vehicle moments of inertia: Roll, Pitch, Yaw
Whole vehicle roll/yaw product
CG of sprung and unsprung masses separated
Driveline rotational inertia
3.1.2 Chassis Compliances
Measurements with forces and moments in parallel (aiding) and opposing
Force and moment levels to wheel slip.
Lateral force compliance steer
Lateral force compliance camber
Lateral force compliance deflection (X, Y, Z at reference point on spin
Lateral force y-deflection at tire contact
Aligning moment compliance steer
Aligning moment tire twist
Aligning moment compliance camber
Roll center height by equilibrium jacking force method
Forces in parallel, forces opposing, forces applied to single wheel.
Steering Effort Reaction
Longitudinal force compliance steer
Longitudinal force compliance camber
Longitudinal force caster change
Longitudinal force compliance deflection (X, Y, Z at reference point on
Anti-dive angles by equilibrium jacking force method
To aligning moment
To side force
To balanced thrust/braking
To unbalanced thrust/braking
3.1.3 Ride/Roll Spring Rates & Kinematics
Measurements from compressed stops to wheel-off
Roll centers can be unrestrained, or fixed at ground or at any height
to 3.5 inches below bottom of body.
Normal forces at wheels
Ride spring rates
Ride coulomb friction
Roll spring rates
Roll coulomb friction
Tire spring rates
Roll stiffness distribution
Swing arm lengths
X,Y,Z displacements of reference point on spin axis
X,Y displacements of tire contact
Roll center heights by displacement method
Shock absorber travel
3.1.4 Steering System
Measured Lock-to Lock
Wheel steer vs handwheel angle
Overall steering ratio vs handwheel angle
Steering axis inclination angle
X,Y,Z displacements of reference point on spin axis
3.2 Measurement Methodologies
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
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.
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.
of Kinematics and Compliance Tests
3.3.1 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
3.3.2 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.
3.3.3 Choice of Data to
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.
3.3.4 Organization of Data
Data plots are organized into four groups:
Test type and configuration
Non-standard test conditions if present
Examples of non-standard test conditions are engine running or stopped,
non-curb ride heights, etc. For example, a front compliance test at 30
mm jounce instead of curb height would be coded as FC-30J-SFA, etc.
In front steering and compliance tests, side forces adding and aligning
torques adding include steering column compliance, which can be significant
with power steering inoperative because the engine is stopped. With power
steering in operation the steering column is affected only by steering
wheel effort. Forces and moments opposing will tend to balance at the steering
gear, and so do not load the steering column.
The self-centering effect of front end geometry is best evaluated with
power steering inoperative.
Quotations are based upon the following components of cost:
Whole-car CG and Moments of Inertia
Incoming vehicle inspection: listing of vehicle specifications, departures
from manufacturer's specifications, dimensional measurements, topping up
or draining gas tank, cleaning of underside of accumulated dirt, preliminary
vehicle wheel weights, etc.
Mounting and centering of vehicle on test fixture.
Ballasting of vehicle, if necessary.
Installation of vehicle clamping devices, or of Ride/Roll actuators and
Setting and recording installed ride height per test specification.
Calibration of equipment and instrumentation.
Installation of special equipment and instrumentation appropriate to each
Performance of the test.
Plotting of data.
Preparation of report.
Removal and restoration of the test vehicle to as-received condition.
Post-test calibration checks and restocking of instrumentation. and equipment.
Whole-car center of gravity and moments of inertia are all measured
with a single vehicle setup on the testing Frame. The principal cost items
are 1 through 7 above. Current (March 1996) approximate quotations are:
$2000 for CG height at specified trim and two additional trim heights or
loading conditions; $500 each for roll, pitch, and yaw moments of inertia.
For litigation-involved projects, we can provide as an extra-cost option,
an on-camera, stepwise multipoint calibration of each measuring system,
with computed linearity, measuring tolerance, and confidence limits for
the particular test.
Kinematics and Compliance Testing
Compliance tests done alone might be done with hydraulic, electric
or manual actuators in the vehicle positioning system, with hydraulic servoactuators
used to generate tire side forces and aligning torques. Kinematics testing
requires hydraulic servoactuators for body jounce, pitch, and roll motions.
When Kinematics and Compliance tests are both to be run, the same setup
of hydraulic actuators in the Ride/Roll crossmember fixtures is used for
both tests, with useful cost savings. Items to be measured are selected
from the list of identification codes. Of these, items to be plotted and
those to be curve-fitted are selected, and a quotation is made based on
all of these considerations.
As noted under "Specification of Kinematics and Compliance Tests", raw
data for all items measured are supplied on floppy disks. Some costs can
be saved by plotting only items certain to be needed: others can be plotted
by the Customer or by HCL at any time later.
Time & Material Quotes
For exploratory "cut & try" tests with a customer's engineer present,
a quotation can be prepared with a fixed price covering defined items,
with time & materials for "messing around" negotiated separately.
3.5 Rates and Charges
Fixed Price Services
When the testing services required or the character of the final work
product are sufficiently defined, ATI prefers to provide such services
at an agreed-upon quoted price, on a "not to exceed" basis.
The use of equipment owned by HCL, including test facilities, instrumentation,
data acquisition, video, and computation equipment, is included in the
rates quoted above, or in fixed-price quotes.
Other Project Expenses
Project expenses that are included in time & material charges
as line items, at HCL's cost, include (but are not necessarily limited
to) subcontracted work, special printing and reproduction, and shipping
3.8 Terms and Conditions
last modified 05/11/2006