Active Dual Mode Tilt Control for Narrow Ground Vehicles

Small, narrow commuter vehicles have attracted considerable interest in recent years as a means to increase the utilization of existing freeways and parking facilities. However, conventional narrow track vehicles are likely to have reduced stability against overturning during hard cornering. A possible solution to this problem lies in vehicles which tilt toward the inside of a turn. Two different ways to achieve this tilt will be analyzed. For direct tilt control (DTC) an actuator forces the upper part of the vehicle to tilt. Steering tilt control (STC) uses steering to control the tilt as is done by motorcycle or bicycle riders. At low speeds, only the DTC system is effective while at high speeds the STC offers less lateral acceleration for the passenger during transient cornering and may seem more natural. The two methods of control will be studied separately and it will be shown that even though the same steady state tilt can be achieved with either system, the transient behavior of the systems is very different. It also will be shown that it is possible to switch from one system to the other at an arbitrarily chosen speed with virtually no transient effects even when the vehicle is not in a steady state. Regardless of which control system is active, the driver simply communicates his desire to follow the road by moving the steering wheel and the control systems take care of the tilting either by using the tilt actuator or by actively steering the road wheels. Thus the driver does not need to leam how to stabilize the tilt mode of the vehicle.     

Theoretical Limitations in Active Vehicle Suspensions

Vehicle suspensions in which forces are generated in response to feedback signals by active elements obviously offer increased design flexibility compared to conventional suspensions using passive elements such as springs and dampers. It is often assumed that if practical difficulties are neglected, active systems could in principle produce arbitrary ideal, behavior. It is shown, using a simple linear two degree-of-freedom suspension system, model that even using complete state feed back and in the case of in which the system is controllable in the control theory sense, there still are limitations to suspension performance in the fully active case. If the ideal suspension performance is defined based on low-pass filtering of roadway unevenness inputs, an active suspension may not offer much better performance than a partially active or adaptive passive suspension depending upon the values of certain vehicle parameters.     

Bond Graphs for Vehicle Dynamics

For the purposes of analyzing the stability and control properties of aircraft, automobiles, and ships, it is convenient to idealize the vehicle as a rigid body and to use a body-centered coordinate frame. A six-port bond graph is first developed which represents the nonlinear dynamics of a rigid body in a coordinate system rotating with the body. It is then shown how the graph simplifies if only lateral or longitudinal dynamics are studied. Finally, bond graphs for the type of stability studies in which the assumption of small perturbations permits linearization are shown for elementary models of automobiles and aircraft.     

Power Requirements for Traversing Uneven Roadways

Vehicles which travel on uneven roadways or rough surfaces require power beyond that associated with air drag, rolling resistance or other sources of friction even though kinetic and potential energy may be conserved on the average. This is true because damped relative motions within the vehicle dissipate energy, and, even for nearly rigid vehicles, energy is lost at impact with the ground whenever the vehicle loses contact with the ground surface due to the finite downward acceleration of gravity.

Using elementary vehicle models, the nature and magnitude of the component of propulsive force associated with these energy loss mechanisms is estimated. In certain speed ranges, this force is found to vary dramatically with speed for several types of periodic roadway profiles studied. While the force due to unevennesss may be small compared to other forces for high-speed vehicles operating on smooth surfaces, it can be the major source of required power for off-road vehicles operating on very rough terrain.     

Network economies in liner shipping: the role of home markets

This paper deals with the measurement of the network complexity of some selected shipping groups, also identifying the contribution of co-operative agreements among carriers. The empirical investigation is focused on: (i) the analysis of the distribution of the carrying capacity per range; and (ii) the comparison of that capacity with the throughput handled in the port facilities of the group. These variables are interpreted in the light of the impact that alliances have on the geographical wideness of the services supplied by each partner. This factor also allows to depict how the cultural and political origin of shipping lines affects the decision of joining an alliance and the outcomes deriving from such co-operation.     

On Inverse Equations for Vehicle Dynamics

Instead of writing equations which when solved yield the response of a vehicle to an input such as the front wheel steer angle, one can often invert the equations so that a response quantity is specified as an input and a new set of equations is solved yielding the steer angle required as an output. Using these equations one can discover the input steer angle a driver would need to impose in order to accomplish a specific maneuver for various vehicles.

It is shown that there are many possible inverse equation sets and that the eigenvalues of the inverse equations are hard to interpret since they may have little to do with the vehicle parameters. The linear single-input single-output case is studied first to fix ideas using a simple example. For the bicycle model vehicle, it is shown that any vehicle may have unstable inverse equations depending upon the response quantity used. Extensions to nonlinear and multiple-input multiple output systems are discussed.     

Active Suspensions Based on Fast Load Levelers

A class of active suspensions is presented which provides near optimum isolation of base motion as well as zero static deflection for force disturbances using a simple type of feedback. The load leveling effect is rapid with the system stabilized using isolated mass velocity feedback both for a semi-active damper and for the load leveler. The system can be made energy conservative and fail safe since the system reverts to a reasonable passive isolator if the load leveling effect and even if the active damping effect is switched off. The system could be incorporated in automotive vehicles with some extension of the feedback control to account for several aspects of body motion.     

Advanced Ground Vehicle Suspension Systems - A Classified Bibliography

This bibliographical list classifies the extensive literature related to the dynamic analysis and control design aspects of advanced ground vehicle suspension systems. It is restricted to the design of advanced suspensions for ride quality and safety. Brief generalized notices and definitions are presented.     

Development of a method for the identification and engineering design of endless fiber reinforced composites

The main objective of this paper is to introduce a novel method to develop a multi-material body-in-white concept with composite material or hybrid material system. A new method based on the work of Durst (2008) is presented, which works basically in three steps. In the first step, the anisotropy of the components is analyzed to pre-evaluate the potential of FRP-suitable parts. In the second step, the predominating orientation of every finite element is determined and clustered to get a first impression of an appropriate laminate architecture. In the last step, a suitable design with a preliminary stacking sequence is calculated. To prove the feasibility of this method, it has been applied to simple flat coupons and a body-in-white component to show that the method leads to reasonable results.