This study is focused on modifying an existing solenoid valve based semi-active hydropneumatic spring-damper system using Magneto-Rheological (MR) fluid. The MR fluid's effective viscosity can be altered by application of a magnetic field. Therefore, using a magnetic/ MR valve makes it possible to change the state of the system by simply changing the applied magnetic field. A prototype MR valve was developed to determine whether a unit small enough for installation was possible. This prototype valve was designed from first principles and properties such as pressure drop over the valve (damping) and flow blocking (for switching between spring characteristics) were measured. The measured pressure drop over the valve was higher than what was design for which was due to an incorrect assumption for the viscosity of the thixotropic MR Fluid. The flow blocking ability of the valve was determined by constant force tests. Results showed that the valve could virtually block the flow of fluid for approximately a quarter of the vehicles weight. With the second prototype, the valve design and magnetic circuit design were improved. Two valves were constructed and implemented on a prototype suspension system. The damping characteristics of the system were lower than expected, however they can be improved by changing the valve geometry. The base spring characteristics are acceptable, however the higher spring characteristics fail when a high force is exerted on the strut that exceeds the valves flow blocking capability. The response time of the valve is not yet sufficient to make the system viable for real world implementation, especially under extreme conditions that can change more rapidly than the current valves. / Dissertation (MEng)--University of Pretoria, 2015. / Mechanical and Aeronautical Engineering / MEng / Unrestricted

The compromise between ride comfort and handling for a passive suspension system is a well-known and often researched problem. Semi-active suspension systems offer significant improvements to this compromise. One example of a semi-active system, that can change both spring and damper characteristics between two discrete values is the 4-state semi-active hydro-pneumatic suspension system. This system can switch between a ”ride comfort mode” (soft spring and low damping) and a ”handling mode” (stiff spring and high damping) within 100ms, improving both ride comfort and handling. The discrete 4S4 could be improved upon further by adding continuous variable damping. Work on this topic showed great promise but also posed its challenges in achieving this in a safe and controllable manner. In order to make continuous variable damping a reality a new configuration for the 4S4 is proposed. This new configuration incorporates a blow-off damper in parallel with a proportional flow control valve. The system ensures that, in the highly non-linear closing region of the proportional flow control valve, adequate damping for handling is maintained and uncontrollable peak pressure differences are avoided. Experimental work conducted showed that the system was capable of achieving the required spring and variable damping characteristics in a safe and controllable manner. The experimental data was used for parametrizing and validating a physics based mathematical model of the suspension system. The mathematical model incorporates the: pressure drop vs: flow characteristics for both the blow-off and proportional valves, response time for the on-off valves as well as the gas pressure vs: flow characteristic incorporating the compressibility of the oil and thermal properties of the gas. This model can be used to make informed decisions on further prototype development or in full vehicle simulations. The system makes continuous variable damping possible ranging from the optimal damping characteristic for handling to the low damping characteristic required for ride comfort. The system also shows a significant reduction in friction. / Dissertation (MEng)--University of Pretoria, 2020. / VDG / University of Pretoria / Mechanical and Aeronautical Engineering / MEng / Unrestricted

Mine haul road maintenance is traditionally done at scheduled intervals or after regular inspection. Both these methods can lead to unwarranted expenditure, either through over-maintaining the road, or failure to recognise significant deterioration, resulting in an increase in vehicle operating costs. Predictive maintenance management models for unpaved roads have been developed in recent years. These methods work well in a trivial environment where variables such as traffic volume can be predicted. However, many mining systems are too complex for such models to be effective. This work investigates the possibility of using haul truck response to aid haul road maintenance management. The approach adopted for the study was twofold: Firstly, can truck response data be used to recognise specific road defects, in terms of location, type and size? This is important since different defect types require different road maintenance strategies. Secondly, can road roughness be measured on a qualitative basis? With the emphasis on road defect reconstruction, a mathematical modelling approach was adopted. The truck was characterised in terms of its suspension and tyre properties. Dynamic truck response data was acquired during field measurements in which the vehicle was driven over defects of known dimensions. With these data sets available, mathematical modelling and simulation was possible. Quarter vehicle and seven degree of freedom vehicle models played a vital role in this work by laying a foundation in the use of haul truck response for the purpose of road defect reconstruction. A modelling methodology that is based on dynamic equilibrium of an independent front unsprung mass of the truck is proposed in which the vertical dynamic tyre force and eventually the road geometry is calculated. It is shown that defects can be reconstructed from measured truck response data with an accuracy sufficient to fulfil the requirements of defect recognition for road maintenance management purposes. Secondly, a preliminary investigation into the qualitative assessment of road condition via truck response measurements was conducted. The inherent response properties of the truck pertaining to road roughness measurement were studied and some correlation between measured suspension motion and road roughness measured with a high speed profilometer was found. / Dissertation (MEng (Mechanical))--University of Pretoria, 2005. / Mechanical and Aeronautical Engineering / MEng / Unrestricted

Electric buses often have batteries installed on the roof structure to have a better space utilization. This increases the height of the centre of gravity of the vehicle, affecting its roll stability. The existing vehicle setup uses an anti-roll bar to provide the roll stiffness. However, increasing the roll stiffness of the anti-roll bar for providing the required roll stability of an electric bus is limited due to the increase in weight of the anti-roll bar, its material properties and the design constraints. An alternate for the air suspension system is identified through a literature study. The identified system, an interconnected hydro-pneumatic suspension, is modelled analytically and compared to the air spring system. Multi-body simulations are performed to understand the roll performance.\par The thesis work also estimates the system's energy efficiency, and the feasibility of packaging the system within the existing vehicle architecture is studied in CAD software. The roll gradient of the vehicle is shown to improve compared to the existing air-spring system. The study also find that implementation of hydraulic-interconnected system can result in reduction of the unsprung mass of the vehicle. / Elektriska bussar har ofta batterier installerade på takkonstruktionen för att få ett bättre utrymmesutnyttjande. Detta ökar fordonets tyngdpunktshöjd och påverkar dess krängstabilitet. Den befintliga fordonskonfigurationen använder en krängningshämmaren tillsammans med luftfjädrar för att ge den krängsstabilitet som krävs. Men att öka krängstyvheten hos krängningshämmaren för att ge den nödvändiga krängstabilitet hos en elektrisk buss är begränsad på grund av ökningen av vikten av krängningshämmaren, dess materialegenskaper och konstruktionsbegränsningar. Ett alternativ till luftfjädringssystemet identifieras genom en litteraturstudie. Det identifierade systemet, ett sammanlänkat hydro-pneumatiskt fjädringssystem, modelleras analytiskt och jämförs med luftfjädringssystemet. Multibody-simuleringar utförs för att förstå fordonets krängprestanda. par Avhandlingsarbetet uppskattar också systemets energieffektivitet och möjl-igheten att paketera systemet inom den befintliga fordonsarkitekturen studeras i CAD-programvara. Fordonets krängningsgradient har visat sig förbättras jämfört med det befintliga luftfjädringssystemet. I studien konstateras också att införandet av hydrauliskt sammankopplade system kan leda till en minskning av fordonets ofjädrade massa.