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A range of axle suspensions, comprising hydro-pneumatic struts and diverse linkage configurations, have evolved in recent years for large size mining trucks to achieve improved ride and higher operating speeds. This paper presents a comprehensive analysis of different independent front suspension linkages that have been implemented in various off-road vehicles, including a composite linkage (CL), a candle (CA), a trailing arm (TA), and a double Wishbone (DW) suspension applied to a 190 tons mining truck. Four different suspension linkages are modeled in MapleSim platform to evaluate their kinematic properties. The relative kinematic properties of the suspensions are evaluated in terms of variations in the kingpin inclination, caster, camber, toe-in and horizontal wheel center displacements considering the motion of a hydro-pneumatic strut. The results revealed the CL and DW suspensions yield superior kinematic response characteristics compared to the CA and TA suspensions.

Compared to the vehicles with conventional steering, the articulated frame steer vehicles (ASV) are known to exhibit lower directional and roll stability limits. Furthermore, the tire interactions with relatively rough terrains could adversely affect the directional and roll stability limits of an ASV due to terrain-induced variations in the vertical and lateral tire forces. It may thus be desirable to assess the dynamic safety of ASVs in terms of their directional control and stability limits while operating on different terrains. The effects of terrain roughness on the directional stability limits of an ASV are investigated through simulations of a comprehensive three-dimensional model of the vehicle with and without a rear axle suspension. The model incorporates a torsio-elastic rear axle suspension, a kineto-dynamic model of the frame steering struts and equivalent random profiles of different undeformable terrains together with coherence between the two tracks profiles.

A two-stage preview strategy is proposed to characterize steering control properties of commercial vehicle drivers. The strategy includes a near and a far preview points to describe the driver control of lateral path deviation and vehicle orientation. A human driver model comprising path error compensation and dynamic motions of the limb is subsequently formulated and integrated to a yaw-plane model of an articulated vehicle. The coupled driver-vehicle model is analyzed under an evasive steering maneuver to identify limiting values of the driver control parameters through minimization of a generalized performance index comprising driver's steering effort, path deviations and selected vehicle states. The performance index is further analyzed to identify relative contributions of different sensory feedbacks, which may provide important guidance for designs of driver-assist systems (DAS).

In this paper, a gain-scheduling optimal control approach is proposed to enhance yaw stability of articulated commercial vehicles through active braking of the proper wheel(s). For this purpose, an optimal feedback control is used to design a family of yaw moment controllers considering a broad range of vehicle velocities. The yaw moment controller is designed such that the instantaneous tractor yaw rate and articulation angle responses are forced to track the target values at each specific vehicle velocity. A gain scheduling mechanism is subsequently constructed via interpolations among the controllers. Furthermore, yaw moments derived from the proposed controller are realized by braking torque distribution among the appropriate wheels. The effectiveness of the proposed yaw stability control scheme is evaluated through software-in-the-loop (SIL) co-simulations involving Matlab/Simulink and TruckSim under lane change maneuvers.

Dynamic fluid slosh and its influence on the dynamic roll stability of a partially filled tank truck has been investigated through a field test program undertaken jointly by the CONCAVE Research Centre and Transportation Technology and Energy Branch of Ontario Ministry of Transportation. The paper describes the test methodology, instrumentation, data acquisition, fluid slosh behaviour, and its influence on the directional response of the tank truck. The data acquired during different directional maneuvers is analyzed to highlight the fluid slosh and its impact on the dynamic load transfer and roll stability of the vehicle. The magnitude of dynamic load transfer, derived from the video records of the dynamic fluid movement, is presented and discussed for various tank fill levels and directional maneuvers. The test results revealed that the magnitude of dynamic fluid slosh is strongly related to the vehicle speed, lateral and longitudinal acceleration, and the fill level.

A closed-loop articulated vehicle-driver model, incorporating the path errors, lateral accelerations of the two units and the rate of steering, is proposed to study the directional control behavior of the driver. The closed-loop driver-vehicle model is formulated upon integrating the yaw-plane model of a five-axle articulated vehicle and a comprehensive driver model. The driver model, incorporating the delays associated with the limb movement and muscle activities, is developed with an objective to minimize the lateral acceleration of vehicle, and the lateral position and orientation errors between the previewed and the actual path of the tractor. Various parameters required to describe the driver's contributions are identified through minimizing a weighted performance index subject to an array of limit constraints established from the reported data.

Optimal trailer design for tractor-trailer transportation depends on accurate and reliable estimates of typical lifetime loading duty cycles. On-the-road testing was done to measure the vertical acceleration response of three different trailers in forest logging conditions. The test conditions included various trailer axle and load configurations, weight transported, and road surfaces including both gravel and paved roads. It was concluded that the rigid trailer body bounce and pitch, the non-rigid body trailer bending, and the wheel hop are the primary components of the vertical response. These results establish approximately what types of operational amplitudes are to be expected for these operations and will provide the basis for the development of a more general trailer frame load prediction model.

Two different concepts in hydro-pneumatic suspension struts are formulated to conveniently realize either hydraulic or pneumatic interconnections between the struts within different wheel suspensions. The formulation employs a compact strut design that integrates a gas chamber and damping valves within the same unit, and provides considerably enhanced working area to appreciably reduce the operating pressure. A transverse interconnection between the hydro-pneumatic struts in the roll plane is analyzed to investigate its static and dynamic heave and roll properties, and relative potential benefits in enhancing the roll properties, while retaining the soft heave ride. Different hydraulically and pneumatically interconnected strut configurations are analyzed for a heavy vehicle, with appropriate considerations of the fluid compressibility, while the feedback effects associated with the interconnections are emphasized.

Low frequency terrain induced vibrations transmitted to the off-road vehicle operators are quite severe and exceed I.S.O specified “fatigue decreased proficiency” limits. In this paper, the ride improvement of an agricultural tractor is sought through effective designs of passive seat suspensions. The dynamic analysis of existing bounce suspension seats is carried out to establish its ride performance behaviour. Optimal bounce seat suspension parameters are selected with an objective to maintain the ride vibration levels within 4 hours exposure “fatigue decreased proficiency” limits. The roll and pitch ride vibrations, perceived by the operators, can be attenuated through a gimbal arrangement mounted to the bounce suspension seat. The optimal parameters of the combined seat isolator are selected using parametric optimization techniques. Also a horizontal isolator, attachable to the bounce or the combined seat isolator, is configured.

The unique difficulties associated with low frequency and large amplitude ride vibrations of off-road tractor are summarized. Concept of a cab suspension system for improving the ride quality of off-road tractors in the bounce, longitudinal, lateral, pitch and roll modes is explored. Influence of suspension parameters on the ride performance is presented followed by selection of optimal suspension parameters. It is shown that a cab suspension would provide improved performance in the longitudinal and pitch modes alone. Ride analysis of the cab suspension with a sprung seat reveals satisfactory bounce ride. Roll and lateral ride of the off-road tractor can be improved significantly through alterations in the cab geometry. The ride performance of the optimal suspensions is assessed with reference to ISO (International Standards Organization) specified “fatigue decreased proficiency” (FDP) boundaries.

The directional dynamics of partially filled articulated tank vehicles is investigated via computer simulation assuming constant forward velocity. The directional response characteristics of an articulated tank vehicle is investigated for various steering manoeuvres and compared to that of an equivalent rigid cargo vehicle to demonstrate the destabilizing effects of liquid load shift. It is concluded that during a steady steer input, the distribution of cornering forces caused by the liquid load shift yields considerable deviation of the path followed by the tank vehicle. The lateral load shift encountered in a partially filled tank vehicle during lane change and evasive type of highway manoeuvres gives rise to roll and lateral instabilities.

Ride quality of articulated vehicles is investigated via computer simulation in view of secondary suspension parameters. A tractor-semitrailer vehicle is modelled incorporating primary as well as secondary suspension. The ride vibration levels at the cab floor and at the driver-seat interface are evaluated using power spectral density approach. The effect of various vehicle parameters, such as secondary suspensions, primary suspensions, axle loads and tires on the vehicle ride quality is presented, and the significance of secondary vehicle suspension is specifically emphasized. A software package is developed to evaluate and assess the ride performance of articulated vehicles with suspended seat and cab. A limited validation of the computer ride model is achieved via field measurements.

Development of a micro-processor based early warning safety device that can detect and warn the drivers of impending dynamic instabilities is discussed to improve the operational safety of articulated freight vehicles. Directional dynamics of articulated freight vehicles are investigated to determine the key dynamic response parameters that can best describe the onset of rollover and jackknife instabilities. The feasibility of identified key response parameters is further investigated in view of various vehicle design and operating conditions, and ease of on-line acquisition and analyses. The study concludes that a general stability criteria can be established to identify impending roll and jackknife instabilities, and a safety monitor can be conceived to provide an early warning to the driver.

Vehicle jackknifing is generally associated with the loss of yaw stability, and is one of the most common cause of serious traffic accidents involving tractor-semitrailer combinations. In this paper, an active braking control strategy is proposed for jackknifing prevention of a tractor-semitrailer combination on a low friction road. The proposed control strategy is realized via upper-level and lower-level control structures considering braking of both the units. In the upper-level control, the required corrective yaw moments for tractor and semitrailer are generated using a PID controller aiming to reduce errors between the actual yaw rates of tractor-semitrailer and the target yaw rates deduced from a reference model. The corrective yaw moments are achieved through brake torque distribution among the tractor and semitrailer axle wheels in the lower-level control.

The articulated frame steering (AFS) systems are widely implemented in construction, forestry and mining vehicles to achieve enhanced maneuverability and traction performances. The kinematic and dynamic performances of articulated steered vehicles are strongly influenced by properties of the frame steering system. In this paper, a flow volume regulated frame steering system is described and analytically modelled. The analytical model of the steering system is formulated in conjunction with yaw-plane model of a 35 tonnes mining vehicle to investigate steady as well as transient responses of the steering system and the vehicle. A field test program was undertaken to measure responses of the steering system and the vehicle under nearly constant speed turning as well as path-change maneuvers.

The handling and braking responses of a heavy vehicle equipped with a cross-axle fluidically-coupled hydro-pneumatic suspension concept are investigated. The proposed fluidically-coupled suspension is conceived by diagonally interconnecting different hydraulic fluid chambers of the four suspension struts of the vehicle. The analytical formulations of suspension forces are derived based on fluid flows through the couplings and damping valves. A generalized full-vehicle model is developed and validated to evaluate the handling and braking responses to two critical vehicle maneuvers: (i) braking-in-a-turn; and (ii) split-μ straight-line braking. The responses of the vehicle model with the coupled suspension are compared with those of the uncoupled suspension under various inputs to demonstrate the potential benefits of the proposed cross-axle fluidic coupling of the suspension struts.