University of Macau / Faculty of Science and Technology. / Department of Electromechanical Engineering

Suspensions play a crucial role in vehicle comfort and stability. Different types of suspensions have been proposed to fulfill the essential characteristics of vehicle suspensions. A semi-active suspension with adjustable damper improves the performance of a suspension in different conditions and it is better than a passive suspension in terms of ride comfort and handling. Furthermore, it is not as expensive and complicated as an active suspension. Semi-active suspensions rely on adjustable damping coefficient. A new type of air suspension with independent ride height and stiffness tuning has been developed recently. By using two air chambers in the suspension system, ride height of vehicle and stiffness of suspension can be adjusted independently and simultaneously. The conventional air suspension systems use compressor to pump the air into a single flexible rubber airbag and by inflating the air, the chassis will be raised from the axle (ride height control). In this type of suspensions, the stiffness of spring is not under control. In the new air suspension system, by controlling the air pressure on both chambers, one can tune the suspension stiffness and the ride height of the vehicle at the same time for different driving conditions. The air suspension is also able to maintain the vehicle body at the same height and natural frequency for different load or number of passengers. This thesis discusses about the design analysis of an air suspension with ride height and stiffness tuning. The analytical formulation is developed for the optimum design of the new air suspension system. In this thesis, the interconnection between the pressurized chambers of the new air suspension with ride height and stiffness tuning is studied to further improve the performance. Proper interconnection of air springs can help the suspension system to distribute the load between tires more evenly on rough roads or uneven surfaces. Different configurations in air spring interconnection have different impact on the handling and tire load distribution. To study the effect of air spring interconnection configurations on tires load distribution and vehicle handling, a general mathematical model is developed. This model is used to compare various configurations in detail. Results show that interconnection could improve tire load distributions greatly. It is also shown that improving tire load distribution will deteriorate roll stiffness that in turn deteriorate vehicle handling at higher speeds. Since on rough roads, vehicle’s speed is necessarily low, interconnection will not have adverse effects on vehicle handling when activated.

A heavy-duty vehicle can benefit from the height control of the chassis that anair suspension provides. For example, to retain a pitch angle parallel to the road,regardless of what load it carries. For the purpose of developing a controller,a model of the air suspension provides evaluation and testing opportunities aswell as it gives the option for more advanced model based controller algorithms.Furthermore, a model can provide with an accurate axle weight estimation. Inthis thesis, both physical and statistical models are developed and parametersare estimated by solving minimization problems. They are then evaluated usingdata collected from a Scania truck, comparing normalized mean-root error valuesas well as residual analysis of each model.

This research provides a thorough flow characterization study to compare the functionality of two types of load-leveling valves that are commonly used for air suspension systems of commercial trucks. The first valve features a simple disk/slot design and is relatively compact for installation. The second type is larger and has a sophisticated, chambered design, which allows for considerably quicker fill and exhaust response times in the transient region. A new approach is introduced to estimate the transient mass flow rate of a load-leveling valve under different suspension pressures, without requiring a mass flow meter. An extensive series of dynamic tests are conducted to characterize and compare the two load-leveling valves. A generic heavy-truck pneumatic suspension, consisting of load-leveling valves, airspring, air tank, and air-hose fittings, is configured for testing. The test setup is used to evaluate the transient performance of each type of load-leveling valve in a typical truck suspension. The flow behavior of the system is validated by the force/pressure responses of the air spring due to various displacement excitations. The experimental results describe the detailed flow behavior of both valves. The flow characterization results can be incorporated as one of the most critical parameters for future model development of pneumatic systems. The tests indicate that the leveling valve with chambered design has a far faster transient flow response than the disk valve, although it is more complicated in its mechanical design and therefore costs more. To take advantage of the design simplicity of the disk valve, while also enabling it to have a faster transient response (compared with the chambered design), it is re-designed with larger flow openings and other elements to match the performance of the chambered valve for transient flow. A comparison of the experimental results and simulations validates that the re-designed rotary disk valve performs nearly the same as the chambered valve, but is simpler and costs less. The study's results are directly applicable to improving the transient dynamics of heavy truck air suspensions by providing a better understanding of how load-leveling valves can be used not only to provide ride-height control, but also to influence the roll and pitch dynamics of heavy trucks. / Master of Science / Heavy trucks are balanced using air suspension systems. These pneumatic controls provide stability when a truck undergoes a turn or other change in movement, including roll and pitch. As a truck experiences these changes, air is supplied or purged from the system to balance the truck. Load leveling valves control this flow of air that provides stability and are considered crucial elements in the overall design of a heavy truck. This study evaluates many different types of valves, namely a "chambered" valve and a "disk" valve. The chambered valve is large and has many parts, resulting in a heavy expense but high performance. The disk valve is a simpler design, making it much cheaper but at the expense of performance. The quality of performance that is evaluated here is the time it takes to fill or purge the air suspension, which is related to the mass flow. These characteristics were experimentally obtained and compared. The results showed the disk valve taking more time and having a lower flow rate, making its performance lower when compared to the chambered valve. The next aspect of this study is the modification of this disk valve design that is commercially available to make its performance comparable to the chambered valve. After a series of experiments, the modified design was verified to perform as well as the chambered valve. Overall, these results are important for the future design of heavy truck load leveling valves and clarify important characteristics to consider when designing them. The results from this study can lead to lower costs for heavy truck companies and a better ride for truck drivers.

<p>Knowledge about the current road slope can improve several applications in a heavy-duty vehicle such as predictive cruise control and automated gearbox control. In this thesis the possibility of estimating the road slope based on signals from a vehicles air suspension system has been studied. More specifically, the measurement consists of a pressure signal measuring the axle load, and a vertical distance sensor.</p><p>A variety of suspension systems can be mounted on a Scania truck. During this thesis, two discrete-time models based on two different rear axle air suspension systems have been proposed. The models use the effect of alternating axle load during a change in the road slope and the estimates are computed using an extended Kalman filter.</p><p>The first model is based on a rear axle suspension known as the 2-bellow system. This type of suspension is strongly affected by the driveshaft torque, which results in a behaviour where the rear end is pushed upwards and thus decreasing the rear axle load during uphill driving. A model was developed in order to compensate for this behaviour. Unfortunately, the estimates showed less promising results and all attempts to determine the error was unsuccessful.</p><p>The latter model is based on the 4-bellow system. This suspension system is not affected by the driveshaft torque and a less complex model could be derived. The experimental results indicated that road slope estimation was possible and with a fairly accurate result. However, more work is needed since the estimate is affected by road surface irregularities and since the algorithm requires knowledge about the vehicles mass and the location of the centre of gravity.</p><p>All the presented results have been estimated based on real data from a test track at Scania Technical Centre in Södertälje.</p>

Knowledge about the current road slope can improve several applications in a heavy-duty vehicle such as predictive cruise control and automated gearbox control. In this thesis the possibility of estimating the road slope based on signals from a vehicles air suspension system has been studied. More specifically, the measurement consists of a pressure signal measuring the axle load, and a vertical distance sensor. A variety of suspension systems can be mounted on a Scania truck. During this thesis, two discrete-time models based on two different rear axle air suspension systems have been proposed. The models use the effect of alternating axle load during a change in the road slope and the estimates are computed using an extended Kalman filter. The first model is based on a rear axle suspension known as the 2-bellow system. This type of suspension is strongly affected by the driveshaft torque, which results in a behaviour where the rear end is pushed upwards and thus decreasing the rear axle load during uphill driving. A model was developed in order to compensate for this behaviour. Unfortunately, the estimates showed less promising results and all attempts to determine the error was unsuccessful. The latter model is based on the 4-bellow system. This suspension system is not affected by the driveshaft torque and a less complex model could be derived. The experimental results indicated that road slope estimation was possible and with a fairly accurate result. However, more work is needed since the estimate is affected by road surface irregularities and since the algorithm requires knowledge about the vehicles mass and the location of the centre of gravity. All the presented results have been estimated based on real data from a test track at Scania Technical Centre in Södertälje.

Investigation and testing of hydropneumatic suspension systems has previously been done at Scania between the year 1992 and 2000. Interest has aroused at Scania CV AB to further test a hydropneumatic suspension. The reason being the new ventures of decarbonised, clean, electrified, automatized and digitalised vehicles. If electrified trucks are to be adopted in the market as an alternative to trucks with combustion engines, solutions for this type of vehicle’s capacity need to be presented. The vehicle’s weight needs to be reduced; the effectiveness of the components needs to be increased and alternatives to increase battery storage needs to arise if it’s going match the traveling distance of a combustion engine. The mission of the project is to present an installation solution of a hydropneumatic suspension that retains the performance of the current air suspension. The presented material will contain CAD-models of all the brackets that will be designed to fit the suspension, as well as the placement in the vehicle assembly for said brackets. The results show that as for the front suspension the best solution is a placement of the hydraulic cylinders in front of the vehicles front axle. Furthermore the rear suspension is best suited for a placement of the hydraulic cylinders behind the vehicles rear axle. However it was concluded that the rear suspension will not be able to retain the current stroke of the vehicle without sacrificing its ground clearance. Parts of the suspension could however be terminated when the air suspension system was replaced by the hydropneumatic system namely: The front suspension anti-roll bar, shock absorbers, air springs and their coexisting brackets.

Currently, Scania is not offering full air suspended AWD trucks, which it seems to be a demand for. This study acts as a first step to fulfill this demand. Including, a benchmarking of what competitors offer as well as an investigation and an evaluation of Scania’s current suspension system. Moreover, a requirement specification and a concept generation for a front air suspension system on AWD trucks have been presented. Eight concept were generated, where two were chosen for further study of design, force analysis and roll gradient analysis. It was concluded that there is a market for this configuration, however, implementing it would require extensive design work. / I nuläget erbjuder inte Scania luftfjädring för samtliga hjulaxlar på AWD lastbilar, vilket det tycks finnas ett kundbehov av. Denna studie agerar som ett initialt steg till att uppfylla detta kundbehov. Studien inkluderar inledningsvis en analys av vad konkurrenter erbjuder samt en undersökning och utvärdering av Scanias nuvarande fjädringssystem. Utöver det, har en kravspecifikation och en konceptgenerering för främre luftfjädring på AWD lastbilar presenterats. Åtta stycken koncept genererades, varav två stycken valdes för vidare studie av design, kraftanalys samt krängstyvhetsanalys. Slutsatserna var att det finns en marknad för denna typ av konfiguration, dock skulle det behövas omfattande designarbete för att implementera det.

Os modelos simplificados de veículos são importantes em fases iniciais do projeto de um veículo, quando muitas características geométricas ainda não estão definidas. No caso de ônibus com sistema de suspensão a ar, os modelos encontrados na literatura não levam em conta efeitos da válvula niveladora de altura. Dois modelos de um ônibus foram desenvolvidos: um modelo não linear de veículo com três graus de liberdade e um modelo em sistema multicorpos com 109 graus de liberdade. Os dois modelos possuem sistema de suspensão a ar com a modelagem termodinâmica do bolsão com a válvula niveladora de altura. As equações do modelo não linear de três graus de liberdade foram construídas utilizando o conceito de derivativos de estabilidade. Para a validação dos modelos, foram realizados ensaios experimentais com o veículo e as seguintes grandezas foram medidas: aceleração lateral, velocidade em guinada, velocidade lateral, ângulo de escorregamento do veículo e ângulo de rolamento. Os resultados obtidos com os modelos foram validados experimentalmente. O comportamento do ângulo de rolamento do veículo devido ao sistema de suspensão a ar foi reproduzido nos dois modelos. Foi desenvolvida uma interface gráfica dentro do ambiente ADAMS para a geração automática de modelos simplificados. Os dados do veículo são inseridos através de uma interface gráfica com caixas de diálogo. Modelos simplificados de veículos são utilizados no controle da dinâmica do veículo. Neste tipo de aplicação, as equações do modelo não linear de três graus de liberdade são resolvidas em tempo real e podem servir como um modelo de referência para sistemas adaptativos de controle. / Simplified vehicle models are very important at the initial stages of vehicle development when all geometric data are not yet available. In the case of a bus with an air suspension system, the models you find in the literature does not taken into account the control leveling valve effects. Two bus models were developed: a nonlinear three degrees of freedom model and a multibody model with 109 degrees of freedom. Both models have thermodynamic air suspension system model with control leveling valve. The three degrees of freedom equations were built using the stability derivative concept. In order to validate the models, experimental tests were carried out and the following variables were measured: lateral acceleration, yaw velocity, sideslip angle and roll angle. The model results were validated against actual data. The roll angle behavior due to air suspension system was reproduced in both models. A graphic user interface for developing simplified vehicle model, based on the nonlinear three degrees of freedom model equations, was built using the ADAMS interface. All the data necessary for the model are introduced via dialog boxes. Simplified vehicle models can be used in vehicle dynamics control. In this kind of application, the three degrees of freedom equations can be solved in real time simulation and can be used as a reference model in adaptive control system, for instance.

Os modelos simplificados de veículos são importantes em fases iniciais do projeto de um veículo, quando muitas características geométricas ainda não estão definidas. No caso de ônibus com sistema de suspensão a ar, os modelos encontrados na literatura não levam em conta efeitos da válvula niveladora de altura. Dois modelos de um ônibus foram desenvolvidos: um modelo não linear de veículo com três graus de liberdade e um modelo em sistema multicorpos com 109 graus de liberdade. Os dois modelos possuem sistema de suspensão a ar com a modelagem termodinâmica do bolsão com a válvula niveladora de altura. As equações do modelo não linear de três graus de liberdade foram construídas utilizando o conceito de derivativos de estabilidade. Para a validação dos modelos, foram realizados ensaios experimentais com o veículo e as seguintes grandezas foram medidas: aceleração lateral, velocidade em guinada, velocidade lateral, ângulo de escorregamento do veículo e ângulo de rolamento. Os resultados obtidos com os modelos foram validados experimentalmente. O comportamento do ângulo de rolamento do veículo devido ao sistema de suspensão a ar foi reproduzido nos dois modelos. Foi desenvolvida uma interface gráfica dentro do ambiente ADAMS para a geração automática de modelos simplificados. Os dados do veículo são inseridos através de uma interface gráfica com caixas de diálogo. Modelos simplificados de veículos são utilizados no controle da dinâmica do veículo. Neste tipo de aplicação, as equações do modelo não linear de três graus de liberdade são resolvidas em tempo real e podem servir como um modelo de referência para sistemas adaptativos de controle. / Simplified vehicle models are very important at the initial stages of vehicle development when all geometric data are not yet available. In the case of a bus with an air suspension system, the models you find in the literature does not taken into account the control leveling valve effects. Two bus models were developed: a nonlinear three degrees of freedom model and a multibody model with 109 degrees of freedom. Both models have thermodynamic air suspension system model with control leveling valve. The three degrees of freedom equations were built using the stability derivative concept. In order to validate the models, experimental tests were carried out and the following variables were measured: lateral acceleration, yaw velocity, sideslip angle and roll angle. The model results were validated against actual data. The roll angle behavior due to air suspension system was reproduced in both models. A graphic user interface for developing simplified vehicle model, based on the nonlinear three degrees of freedom model equations, was built using the ADAMS interface. All the data necessary for the model are introduced via dialog boxes. Simplified vehicle models can be used in vehicle dynamics control. In this kind of application, the three degrees of freedom equations can be solved in real time simulation and can be used as a reference model in adaptive control system, for instance.