Leonard Segel

Effect of Frame Compliance on the Lateral Dynamics of Motorcycles

SUMMARY The lateral dynamics of an uncontrolled motorcycle, running on a straight, level road surface, is investigated in this paper. The structural compliances in the front and the rear frames of the motorcycle are taken into account by introducing additional degrees of freedom in the analysis. The kinematics of the tires is represented by linear differential equations which are based on the taut-string model of pneumatic tires. The linear differential equations of motion are solved to yield the eigensolutions of the system. Numerical results, obtained for parameters corresponding to a Honda CB750 motorcycle, are presented and discussed.

THE INFLUENCE OF TIRE FACTORS ON THE STABILITY OF TRUCKS AND TRACTOR TRAILERS

SUMMARY The mechanical properties of tires and trucks are contrasted with comparable properties of the motor car to explain why the motor truck and the tractor-trailer can exhibit fixed-control instability at moderate levels of lateral acceleration. The (1) rearward bias in the distribution of roll stiffness, (2) large ratio of e.g. height to track, and (3) low torsional stiffness of the parallel-rail frame (as typically employed in heavy commercial vehicles) are found to be the major factors implicated in this phenomenon. Experimental and analytical evidence is provided to show how tire inflation pressure and mixes of (a) tire-carcass construction and (b) tread design also influence stability at moderate levels of lateral acceleration. Conclusions relating to the safety of commercial vehicle operations are drawn.

VEHICULAR ENERGY LOSSES ASSOCIATED WITH THE TRAVERSAL OF AN UNEVEN ROAD

SUMMARY The energy losses which derive from the vibratory phenomenon experienced by a motor vehicle when It traverses an Irregular road surface have been examined. The study has revealed that there are, at least, four “dynamic” energy-loss mechanisms contributing to vehicular rolling resistance. Specifically, it was determined that the energy losses associated with the dynamic deflection of the tire and the stroking of the suspension damper are predicted reasonably well by a linear mass-spring-damper model of a motor vehicle traversing an uneven road surface at constant speed. The energy losses attributable to impacts between tire and road become significant only when the speed is very high or the road is very rough. Finally, measurements have shown that the angular accelerations associated with time-varying radial deflections of the tire will cause an energy loss when the shear forces required to accelerate or decelerate the wheel become larger than can be sustained by the frictional coupling prevailing ...

REQUIREMENTS FOR DESCRIBING THE MECHANICS OF TIRES USED ON SINGLE-TRACK VEHICLES

The adequacy of Sharps analysis to predict the dynamic behavior of single-track vehicles is reviewed. A noteworthy feature of Sharps analysis is his inclusion of the lag between lateral force and lateral slip which is exhibited by a tire undergoing a time rate of change in lateral slip. In another study, Eaton has pointed out that every analysis of single-track vehicles published prior to 1960 failed to include external forces created by a sideslipping tire. The question is raised as to whether the nonstationary response to inclination is comparable to the nonstationary response to lateral slip or slip angle. The review of Sharps analysis and Eatons findings indicates that the attainment of better agreement between theory and experimentation will require that the motorcycle tire be described in greater detail, from both static and dynamic points of view. Transient measurements of lateral force resulting from inclination show that a small component of this force is in phase with inclination, whereas the remaining component lags the inclination angle. The component of force lagging the inclination angle appears to involve greater lag, i.e. larger relaxation length, than the force produced by lateral slip. The overturning moment caused by inclination also contains lagging and nonlagging components, although the lagging component is very small relative to the nonlagging component. It is concluded that lateral force and overturning moment due to inclination should be accurately described, statically and dynamically, to predict the dynamics of single-track vehicles. There is also a need to analyze the pneumatic tire with respect to lateral force and overturning moment produced by fixed and time-varying inclination.

Test Procedures for Studying Vehicle Dynamics in Lane-Change Maneuvers

The use of both closed- and open-loop test procedures for evaluating the performance of motor vehicles in lane-change maneuvers is reviewed. It is found that (a) variations in driver skill, (b) differences in the amount of information imparted to the driver by the layout of the test course, (c) the asymmetry in response between right and left lane-changes, and (d) the lack of understanding of the connection between open- and closed-loop performance present difficulties in evaluating lane-change performance. Further study is recommended using a particular form of evasive performance test to seek identifiable ergonomic and vehicle dynamics bounds on driver-vehicle system performance.

The influence of the steering system on the directional response to steering

SUMMARY Analysis and experiment both demonstrate that, in response to a sinusoidal displacement of the handwheel, the steer able roadwheels lead the motion of the handwheel at frequencies below 2 Hz. In addition, the roadwheel displacement, relative to its steady-state (i.e., zero-frequency) value, is amplified at frequencies below 2 Hz. By carefully examining the transfer function which relates the roadwheel response to handwheel displacement, it can be shown that the indicated phase lead and amplification phenomenon derives from two causes: (1) both the inertia and the damping of the roadwheel mass are essentially negligible with respect to the mass of the vehicle and other sources of damping moments; (2) the zeros of the applicable transfer function reflect the undamped natural frequency and damping ratio associated with the directional response to roadwheel displacement, whereas the poles reflect the higher undamped natural frequency and smaller damping ratio associated with the directional response o...

Traction Modifications Resulting from Test-Induced Treadwear

Measurements have shown that the traction performance of pneumatic tires can be profoundly influenced by wear which accrues during the testing process. These findings indicate that changes can occur in the shear forces generated at both high and low slip angles as a consequence of testing at high angular slip. These performance changes are capable of significantly altering a vehicles directional properties and thus suggest that data from tests involving high rates of test wear be interpreted with special caution. The paper reviews and expands upon the basic findings through presentation of data taken on laboratory and mobile tire traction dynamometers and from vehicle tests for both passenger car tires and truck tires.

THE INFLUENCE OF STEERING AND SUSPENSION SYSTEM DEGRADATION ON VEHICLE LIMIT PERFORMANCE

The influence of degraded steering and suspension components on open-loop vehicle performance at the limits of tire-road frictional coupling is examined in this paper. The major conclusion obtained is that, with the exception of the shock absorber in certain maneuvers, the range of limit performance exhibited by new cars, as derived from design differences, is much larger than the in-use changes in limit performance of individual vehicles deriving from degradation of steering and suspension system components.

Investigation of the Influence of Various Braking Regulations on Accident-Avoidance Performance

Passenger car braking regulations promulgated by the United States and various European countries are analyzed to determine the incompatibilities in brake proportioning that derive from the performance requirements of the regulations. Two vehicles, one produced in the U.S. and the other in Europe, with extreme loading conditions (as derive from option selection and vehicle loading) were considered. The analysis shows that the European regulations require a larger forward bias in brake proportioning than FMVSS 105-75. Computer simulations were used to predict the differences in braking performance which result from proportioning the example vehicles to comply with the different regulations. Conditions of straight-line braking, braking in a turn, and three surface friction levels were considered. In general, both vehicles were capable of achieving shorter stopping distances when proportioned to meet FMVSS 105-75 than when proportioned to comply with the European regulations, but the differences were small and could be considered trivial when a car is driven by an ordinary driver. When proportioned to meet FMVSS 105-75, the rear wheels of the two study cars sometimes locked up first, a result that the European regulations are designed to prevent. Braking-in-a-turn test procedures (which have been discussed both in the U.S. and abroad) were also studied through computer simulations and found to be relatively insensitive to the fore-aft proportioning of brake torques.