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Rollover accidents are of special concern for commercial vehicle safety. The relatively low roll stability of the commercial truck promotes rollover and contributes to the number of truck accidents and injuries. This Research Report takes an in-depth look at the mechanics and contributing factors to rollover accidents and helps to identify prevention strategies.

The free-rolling cornering, straight-line braking, and pull force properties of a small sample of tire specifications is examined. This is done to examine potential differences between the specifications and the statistics of force and moment measurements. Two steer axle specifications, two drive axle specifications, and a trailer specification are considered, In addition, the evolution of properties for one drive axle specification is followed from new to naturally worn-out to retreaded. The summarized data is available from SAE Cooperative Research on electronic media.

The traction effects of water depth, speed, tread wear, inflation, and load on typical 295/75R22.5 truck tires have been examined in a set of designed experiments conducted on a single pavement. The results have been typified in terms of regression models of aligning moment and lateral force at 4 degrees slip angle plus peak longitudinal force and longitudinal force at slide during braking. The effects of the principal parameters are catalogued. An approximate idea of the effect of the operational and tread wear state parameters on the ability to control vehicle motion is provided within the discussion.

This study is to explore the application of electrorheology (ER) to the real-time control of damping forces that are transmitted through the nose landing gear for an F-106B aircraft. The main part of the landing gear is a strut that consists of a pneumatic spring and an ER controlled damper that is situated on the strut centerline and applies a force directly opposing the vertical displacement of the nose wheel. The damping element rotates in response to strut displacement, employing a co-axial arrangement of stator and rotor plates connected to the opposing electrodes in the control circuit. The vertical displacement is converted into rotation of the damper through a screw-nut mechanism. The ER fluid between the electrodes is thus engaged in shear along circumferential lines of action. This design results in a fast time response and a high ratio of strut forces achieved under ER- vs. zero-field control. Compact size and simplicity in fabrication are also attained.

Analysis of the dynamic modes of the single-track vehicle has been hampered by the general lack of facilities for gathering force and moment data on motorcycle tires under dynamic test conditions. The facility described was designed and constructed by UMTRI under the sponsorship of the HONDA Research and Development Company in order to alleviate this problem. Unlike conventional tire dynamometers, this new facility allows for testing under dynamic conditions and provides for non-zero path curvature. These particular capabilities hold promise for advancement in the state-of-the-art understanding of the dynamic operating modes of the single-track, pneumatic-tired vehicle. The facility is unique in its physical design in that it employs a small, light tire-mounting head which is controlled by a mechanically simple system of servo-controlled hydraulic cylinders.

A mobile dynamometer for measuring the longitudinal force acting at the fifth wheel connection between a tractor and a semitrailer has been developed. The use of this dynamometer for testing retarders installed in tractors is described and example results are presented. Computational methods for predicting total retardation of various vehicles equipped with retarders are discussed.

A new facility for the measurement of the compliance, kinematic and coulomb friction properties of heavy vehicle suspensions is described. The facility may test single or tandem and front or rear suspensions. Test procedures for measurement of vertical and roll rates, kinematic and compliant steer effects are presented. Qualitative findings are discussed and example data is appended.

This paper provides a method whereby vehicle stopping performance can be specified, measured, and compared independently of the test surface. The method provides for an independent measure of the prevailing friction potential of the test surface which is used to normalize the measured stopping performance of the test vehicle. The concept presented is tailored toward a safety argument and toward rulemaking as a potential adaptation to braking effectiveness requirements which currently exist. A new mobile tire dynamometer, developed for this program, is discussed, as are the results of a demonstration test program.

The large size of commercial highway vehicles can lead to significant problems in determining their inertial and suspension properties. New techniques and equipment used in the measurement of these properties have been developed and are discussed. Vertical spring deflection behavior, including coulomb friction, for the suspensions of a truck, tractor, and semitrailer are given.