A Study of negative feedback damping property of roll-coupled hydro-pneumatic suspensions

The design of a vehicle suspension involves complex compromises due to conflicting ride comfort and handling requirements. High load capacity and high mass center commercial vehicles, especially, impose greater design challenges due to their relatively low rollover immunity. Road vehicles, invariably, employ auxiliary roll stiffeners such as antiroll bars to realize a better compromise among the roll dynamic and ride comfort performance. The anti-roll bars, however, add considerable weight, exhibit negligible damping and cause stronger coupling between the roll and vertical modes. Alternatively, roll-connected hydro-pneumatic suspensions offer superior anti-roll performance, while preserving the soft vertical ride characteristics. Reported studies have shown that such suspensions can provide anti-roll characteristics similar to an antiroll bar but with considerable roll damping and less weight. The feedback effects of the hydraulic couplings in such suspensions yield negative damping force in the vertical mode, which have not yet been explored. This thesis research presents a systematic study of negative damping features of the roll-coupled hydro-pneumatic suspensions and its significance for realizing variable damping properties. Three different configurations of hydro-pneumatic struts were conceived for realizing hydraulic couplings in the roll plane. Analytical models of the roll-coupled suspensions were formulated considering ideal gas law, turbulent flows through orifices and damping valves, laminar flows through interconnections, floating piston dynamics and fluid compressibility. The analytical formulations were used to describe the negative damping feature attributed to the flow feedbacks. The vertical and roll mode damping and stiffness properties of the proposed configurations were derived via analytical relations, which showed that hydraulic couplings yield high roll stiffness and damping with only minimal effect on the vertical mode properties. The simulation results demonstrated two negative damping force components of a strut attributed to flows through the interconnecting pipes and flows through orifices in the connected strut. These negative damping force components, however, contributed to only positive roll damping moment. A methodology to enhance negative damping force of the connected struts was proposed for realizing variable damping properties similar to those of the conventional damping valves. Deployments of small size multiple interconnections or the flow-control valves across the struts resulted in comprehensive magnitudes of negative damping force components. Simulation results were obtained under lateral acceleration excitation idealizing the centrifugal force encountered during a steady-turn maneuver, a road bump, and in-phase and out-of-phase harmonic road excitations. The results were obtained for unconnected and connected struts with and without the damping valves and interconnection flow valves. Comparisons of the results revealed that interconnection valves can provide variable damping properties similar to the damping valves. The interconnection valves, however, offer greater design/tuning flexibility since these are mounted externally. The results suggested that further efforts in parameterization of the coupling flows will be worthy for realizing optimal damping properties of the roll-coupled hydro-pneumatic suspensions

Handling Analyses Of A Vehicle Fitted With A Roll-Resistant Hydraulically Interconnected Suspension

Transient handling analyses of a sport utility vehicle (SUV) fitted with a roll-resistant hydraulically interconnected suspension is presented in this paper. SUVs have a greater likelihood to rollover due to higher center of gravity, and hydraulically interconnected suspensions (HIS) have been proven as one practical means to effectively improve vehicle anti-roll ability. The modeling of a vehicle fitted with a HIS consists of a 9 degrees-of-freedom (DOF) full-car model and a 34 DOF HIS model, dynamically coupled together through boundary conditions. Steering angle taken from the tests is used as input to the simulations. In field tests, vehicles with different anti-roll systems are put under test by driving through a series of pylons at a constant speed. Acceleration, pressure and displacement transducers are used to measure and evaluate vehicles performance. From tests, HIS shows a superior performance over anti-roll bars in resisting vehicle rolls. The pressure response of the hydraulic suspension closely matches the simulation results, and discussions are provided afterwards

Dynamic impact of ageing dump truck suspension systems on whole-body vibrations in high-impact shovel loading operations

Surface mining operations typically deploy large shovels, with 100+ tons per pass capacity, to load dump trucks in a phenomenon described as high-impact shovel loading operations (HISLO). The HISLO phenomenon causes excessive shock and vibrations in the dump truck assembly resulting in whole body vibration (WBV) exposures to operators. The truck suspension system performance deteriorates with time; therefore their effectiveness in attenuating vibrations reduces. No research has been conducted to study the impact of ageing suspension mechanisms on the magnitudes of WBV in HISLO operations. This study is a pioneering effort to provide fundamental and applied knowledge for understanding the impact of ageing on the magnitudes of WBV exposures. The effects of underlying ageing processes on a suspension performance index are mathematically modeled. The effects of scheduled maintenance and corrective maintenance on improving the performance index (PI) are also modeled. Finally, the proposed mathematical ageing model is linked to the truck operator\u27s exposure to WBVs via a virtual prototype CAT 793D truck model in the MSC ADAMS environment. The effects of suspension system ageing in increasing the WBV levels are examined in the form of both the vertical and horizontal accelerations under HISLO conditions. This study shows that the hydro-pneumatic suspension strut ageing results in deteriorating stiffness-damping parameters. The deteriorating suspension performance (with time) introduces more severe and prolonged WBVs in HISLO operations. The RMS accelerations increase significantly with time (suspension ageing). The vertical RMS accelerations increase to severe magnitudes of over 3.45, 3.75, and 4.0 m/s2 after 3, 5, and 7 years, respectively. These acceleration magnitudes are well beyond the ISO limits for the human body\u27s exposure to WBVs. This pioneering research effort provides a frontier for further research to provide safe and healthy working environments for HISLO operations --Abstract, page iii

Theoretical analyses of roll- and pitch-coupled hydro-pneumatic strut suspensions

Vehicle suspension design and dynamics analysis play a key role in enhancement of automotive system performance. Despite extensive developments in actively-controlled suspensions, their commercial applications have been limited due to the associated high cost and weight. Alternative designs in either passive or semi-active suspensions are highly desirable to achieve competitive vehicle performance with relatively lower cost and greater reliability. This dissertation research proposes two hydro-pneumatic suspension strut designs, including a twin-gas-chamber strut, and systematically investigates various concepts in roll- and pitch-coupled suspensions employing hydraulic, pneumatic and hybrid fluidic interconnections between the wheel struts. The proposed strut designs, including single- and twin-gas-chamber struts, offer larger working area and thus lower operating pressure, and integrate damping valves. Nonlinear mathematical models of the strut forces due to various interconnected and unconnected suspension configurations are formulated incorporating fluid compressibility, floating piston dynamics, and variable symmetric and asymmetric damping valves, which clearly show the feedback damping effects of the interconnections between different wheel struts. The properties and dynamic responses of the proposed concepts in roll- and pitch-coupled suspension struts are evaluated in conjunction with in-plane and three-dimensional nonlinear vehicle models. The validity of the vehicle models is demonstrated by comparing their responses with the available measured data. The analyses of the proposed coupled suspensions are performed to derive their bounce-mode, anti-roll, anti-pitch and warp-mode properties, and vehicle dynamic responses to external excitations. These include road roughness, steering and braking, and crosswinds. The results suggest that the fluidically-coupled passive suspension could yield considerable benefits in enhancing vehicle ride and handing performance. Furthermore these offer superior design flexibility. The suspension struts offer a large number of coupling possibilities in the three-dimensions, some of which however would not be feasible, particularly for commercial vehicles where suspension loads may vary considerably. A generalized analytical model for a range of interconnected suspensions is thus developed, and a performance criterion is formulated to assess the feasibility of a particular interconnection in a highly efficient manner. The handling and directional responses of a three-dimensional vehicle model employing X-coupled hydro-pneumatic suspension are evaluated under split-o straight-line braking and braking-in-a-turn maneuvers. The results clearly show that the X-coupled suspension offers enhanced anti-roll and anti-pitch properties while retaining the soft vertical ride and warp properties. Fundamental pitch and vertical dynamics of a road vehicle are also considered to derive a set of essential design rules for suspension design and tuning for realizing desirable pitch performanc

Untripped manoeuvre induced rollover prevention for sport utility vehicles

Rollover accidents account for a high number of serious injuries and fatalities and thus it is greatly important to reduce the number of occurrences. Although a large number of rollovers result from factors external to the vehicle design such as environmental obstacles there is a significant portion of rollover accidents which are preventable. On-road untripped rollovers are directly related to the vehicle design. It is possible to do work in this area to improve vehicle-related safety factors. During rollover, lateral acceleration acts on the centre of gravity of the vehicle over turning it about the outer wheels. Thus the method to reduce or prevent rollover of this study stemmed from decreasing the overturning moment by reducing the movement arm though which the lateral acceleration acts. This is achieved by lower the ride height of the test vehicle using slow active suspension control of the test vehicle (Land Rover Defender 110) fitted with a hydro-pneumatic suspension system. An experimental validated mathematical model representing the test vehicle is created to develop a rollover prevention control system that reduces the vehicle’s ride height and reduces the propensity to rollover. The control system applies one of three discrete suspension settings depending on the severity of the manoeuvre as well as lowering the ride height. The model is used to simulate the Fishhook 1B and the ISO 3888 Double Lane Change manoeuvres to evaluate the roll prevention system. The rollover prevention control system improved the two wheel lift off speed of the vehicle through a Fishhook 1 B manoeuvre by 64%, the body roll angle of the vehicle through the Double Lane Change manoeuvre by 13% and the body roll rate by 25.7%. The control system significantly improved the vehicle’s response with regard to smooth flat on-road untripped rollover. Further improvements are possible with the use of the proposed control system in conjunction with a fully active suspension system to allow for faster corrective action.Oorrol ongelukke is verantwoordelik vir ‘n hoe aantal van ernstige beseerings en dodelike ongelukke en dus is dit van groot belang om die hoeveelheid ongelukke te verminder. Alhoewel meeste oorrol ongelukke is as gevolg van faktore anders as die voortuig se ontwerp, soos byvoorbeeld omgewingshindernisse, is daar ‘n groot percentasie van oorrol ongelukke wat vermybaar is. On-pad onbelemmerde rollovers is direk verwant aan die voertuigontwerp. Dit is moontlik om werk in hierdie area te doen om voertuigverwante veiligheidsfaktore te verbeter. Tydens rolloverwerking tree laterale versnelling op die swaartepunt van die voertuig oor en draai dit om die buitenste wiele. Dus die metodiek in hierdie studie om oorrol te verminder of te verhoed, stem uit vermindering van die omkeer oomblik afgeneem, deur om die bewegingsarm waardeur die laterale versnelling werk, te verminder. Dit word behaal deur die rithoogte van die toetsvoertuig te verlaag deur gebruik te maak van 'n stadig aktiewe opskortingsbeheer van die toetsvoertuig (Land Rover Defender 110) wat met 'n hidro-pneumatiese suspensie stelsel toegerus is. 'N eksperimentele gevalideerde wiskundige model wat die toetsvoertuig verteenwoordig, word geskep om 'n rollover-voorkomingsbeheerstelsel te ontwikkel wat die voertuig se rithoogte verminder en die geneigdheid om oor te skakel, verminder. Die beheerstelsel pas een van drie diskrete skorsingsinstellings toe, afhangende van die erns van die maneuver asook die verlaging van die rithoogte. Die model word gebruik om die Fishhook 1B en die ISO 3888 Double Lane Change maneuvers te simuleer om die rolvoorkomingsisteem te evalueer. Die rollover-voorkomings-beheerstelsel het die twee-wiel oplig-snelheid van die voertuig verbeter deur 'n Fishhook 1 B-maneuver met 64%, die liggaamsrolhoek van die voertuig deur die Double Lane Change-maneuver met 13% en die liggaamsrolkoers met 25.7% te verbeter. Die beheersingsstelsel het die voertuig se reaksie aansienlik verbeter met betrekking tot gladde plat op-pad onbelemmerde oorrol. Verdere verbeterings is moontlik met die gebruik van die voorgestelde kontrolesisteem in samewerking met 'n ten volle aktiewe suspensie om vinniger regstellende aksie toe te laat.Dissertation (MEng)--University of Pretoria, 2018.Mechanical and Aeronautical EngineeringMEngUnrestricte

Narrow Urban Vehicles with an Integrated Suspension Tilting System: Design, Modeling, and Control

Narrow urban vehicles are proposed to alleviate urban transportation challenges like congestion, parking, fuel consumption, and pollution. They are designed to seat one or two people in tandem, which saves space in road infrastructures as well as improves the fuel efficiency. However, to overcome the high rollover tendency which comes as a consequence of reduced track-width ratio, tilting systems for vehicle roll motion control are suggested. Existing tilting solutions, which mechanically connect the wheel modules on both sides for motion synchronization, are not space-friendly for the narrow vehicle footprint. The mechanical linkages also add extra weight to those urban vehicles initially designed to be light-weighted. A novel integrated suspension tilting system (ISTS) is proposed in this thesis, which replaces rigid mechanical linkages with flexible hydraulic pipes and cylinders. In addition, combining the suspension and tilting into an integrated system will result in even more compact, light-weighted, and spacious urban vehicles. The concept is examined, and the suspension mechanism for the tilting application is proposed after examining various mechanisms for their complexity and space requirements. Kinematic and dynamic properties of the tilting vehicle under large suspension strokes are analyzed to optimize the mechanism design. Control of the active tilting systems for vehicle roll stability improvement is then discussed. Rather than tilting the vehicle to entirely eliminate the lateral load transfer during cornering, an integrated envelope approach considering both lateral and roll motion is proposed to improve the energy efficiency while maintaining the vehicle stability. A re-configurable integrated control structure is also developed for various vehicle configurations as well as enhancing the system robustness against actuator failures. The model predictive control (MPC) scheme is adopted considering the non-minimum phase nature of active tilting systems. The predictive feature along with the proposed roll envelope formulation provides a framework to balance the transient and steady-state performances using the tilting actuators. The suggested controller is firstly demonstrated on a vehicle roll model, and then applied to high-fidelity full vehicle models in CarSim including a four-wheeled SUV as well as a three-wheeled narrow urban vehicle. The SUV simulation results indicate the potential of using the developed envelope controller on conventional vehicles with active suspensions, while the narrow urban vehicle simulations demonstrate the feasibility of using the suggested ISTS on narrow tilting vehicles. By adopting the integrated envelope control approach, actuation effort is reduced and the vehicle handling, along with the stability in both lateral and roll, can be further improved

Improving off-road vehicle handling using an active anti-roll bar

This thesis investigates the use of an active anti-roll bar as a means of improving the handling of an off-road vehicle. The active anti-roll bar consists of a stiff anti-roll bar and a hydraulic actuator at the one end between the anti-roll bar and the rear axle of the vehicle. The system is designed so that the anti-roll bar can be preloaded in both directions by the actuator. The displacement of the hydraulic actuator is close loop controlled to be a function of the lateral acceleration of the vehicle, which is measured by an accelerometer. For this study, full vehicle simulations were done in ADAMS/View to predict the response of the proposed solutions. A Land Rover Defender 110 was used as the test vehicle to verify the results of the simulations. Constant radius tests and the severe double-lane-change manoeuvre, which are standard handling tests, were used to determine the vehicle’s handling performance. Handling performance was quantified by measuring the body roll angle during the manoeuvre and noting the maximum roll angle. The effect of the active anti-roll bar on ride comfort was measured by driving over Belgian paving at a constant speed. The results show that the proposed system reduces the body roll angle to zero up to a lateral acceleration of 0.4 g during steady state handling and provided a 74% improvement in maximum body roll angle during a double-lane-change-manoeuvre at 70 km/h. The system has no detrimental effect on the ride comfort of the vehicle.Dissertation (MEng)--University of Pretoria, 2008.Mechanical and Aeronautical Engineeringunrestricte

Ride and directional dynamic analysis of articulated frame steer vehicles

ABSTRACT Pazooki Alireza, Ph.D. Concordia University, 2012 Articulated frame steer vehicles (ASVs), widely employed in different off-road sectors, are generally unsuspended vehicles. Owning to their complex operating environment, high mass center, relatively soft and large diameter tires, wide load variations and load distribution, and kineto-dynamics of the frame steering mechanism, these vehicles transmit higher magnitudes of low frequency whole-body vibration (WBV) to the operators and also exhibit lower roll and directional stability limits. While the superior performance potentials of axle suspension in limiting the WBV exposure have been clearly demonstrated, the implementations in ASVs have been limited due to the complex design challenges associated with conflicting requirements posed by the ride and roll/directional stability requirements. Growing concerns on human driver comfort and safety, and increasing demands for higher speed ASVs such as articulated dump trucks, however, call for alternate suspension designs for realizing an improved compromise between the ride and stability performance. This dissertation research is aimed at analysis of a torsio-elastic axle suspension concept for achieving improve ride, while preserving the directional stability limits of the ASV. For this purpose a comprehensive three-dimensional model of the articulated frame steer vehicles is developed for design and analysis of the proposed axle suspension concept. The model is formulated considering a three-dimensional tire model, tire lag, coherent right- and left-terrain track roughness, and kinematics and dynamics of the steering struts. Field measurements were performed to characterize the ride properties of a conventional forestry skidder and that of a skidder retrofitted with the rear-axle torsio-elastic suspension under different load conditions. The measured data were analyzed to assess the ride performance potential of the suspension and to examine validity of the simulation model. Both the field measured and simulation results revealed that the proposed suspension could yield significant reductions in the magnitudes of vibration transmitted to the operator location, irrespective of the load and speed conditions. A simple yaw-plane model of the vehicle is also formulated to study the role of steering system design including the steering valve flows, kineto-dynamics of the steering struts and leakage flows on the snaking stability limits of the ASV. The results showed that the critical speeds are strongly dependent upon the kineto-dynamics of the articulated steering system. The comprehensive three-dimensional model subsequently used for analysis of integrated ride and roll/directional stability limits of the vehicle and the axle suspension designs. The stability performance measures are defined to assess the vehicle stability limits under steady as well as transient directional maneuvers. The results show that the proposed rear-axle suspension deteriorates the stability performance only slightly, irrespective of the load condition. It is concluded that the proposed suspension concept could yield a very good compromise in ride and stability performance. The proposed model could serve as an effective and efficient tool for integrated ride and handling analysis and to seek primary suspension designs for an improved compromise between the ride and stability performance of ASVs

Slow active suspension control for rollover prevention

Rollover prevention in Sports Utility Vehicles (SUV‟s) offers a great challenge in vehicle safety. By reducing the body roll angle of the vehicle the load transfer will increase and thus decrease the lateral force that can be generated by the tires. This decrease in the lateral force can cause the vehicle to slide rather than to roll over. This study presents the possibility of using slow active suspension control to reduce the body roll and thus reduce the rollover propensity of a vehicle fitted with a hydro-pneumatic suspension system. The slow active control is obtained by pumping oil into and draining oil out of each hydro-pneumatic suspension unit individually. A real gas model for the suspension units as well as for the accumulator that supplies the oil is incorporated in a validated full vehicle Adams model. This model is then used to simulate a double lane change manoeuvre performed by a SUV at 60 km/h and it is shown that a significant improvement in body roll can be obtained with relatively low energy requirements. The proposed control is successfully implemented on a Land Rover Defender test vehicle. A Proportional-Derivative (PD) controller is used to control on-off solenoid operated valves and the flow is adjusted using the lateral acceleration as a parameter. Experimental results confirm that a significant improvement in body roll is possible. AFRIKAANS : Omrolvoorkoming in Sportnutsvoertuie bied geweldige uitdagings in terme van voertuigveiligheid. Deur die rolhoek van die voertuig te verminder word die laterale lasoordrag verhoog en word die laterale krag wat die bande kan genereer minder. As die laterale krag genoeg verminder sal die voertuig eerder gly as omrol. Die studie ondersoek die moontlikheid om stadig-aktiewe suspensiebeheer op 'n voertuig met 'n hidropneumatiese suspensie te gebruik om bakrol te verminder en dus die omrolgeneigdheid van die voertuig te verlaag. Die beheer word toegepas deur olie in elke hidropneumaties suspensie-eenheid individueel in te pomp of te dreineer. 'n Werklike gas model word gebruik om die supensie-eenhede asook die akkumulator, wat die olie aan die suspensie voorsien, te modeleer. Hierdie modelle word in 'n gevalideerde volvoertuig ADAMS model geïnkorporeer en 'n dubbel laanverwisseling word gesimuleer teen 60 km/h. Die resultate toon dat 'n beduidende verbetering in die rolhoek moontlik is met relatiewe lae energievereistes. Die voorgestelde beheer is suksesvol op 'n Land Rover Defender geïmplimenteer en 'n Proportioneele-Differensiaal (PD) beheerder word gebruik om die aan-af solenoїde kleppe te beheer terwyl die vloei aangepas word na gelang van die laterale versnelling. Eksperimentele resultate bevestig dat 'n beduidende verbetering in bakrol moontlik is.Dissertation (MEng)--University of Pretoria, 2012.Mechanical and Aeronautical Engineeringunrestricte