| 1. |
- Carbonne, Louis, et al.
(författare)
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Use of Full Coupling of Aerodynamics and Vehicle Dynamics for Numerical Simulation of the Crosswind Stability of Ground Vehicles
- 2016
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Ingår i: SAE International Journal of Commercial Vehicles. - : SAE International.. - 1946-391X .- 1946-3928. ; 9:2, s. 359-370
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Tidskriftsartikel (refereegranskat)abstract
- The prediction in the design phase of the stability of ground vehicles subject to transient crosswinds become of increased concern with drag reduced shapes, lighter vehicles as well as platooning. The objective of this work is to assess the order of model complexity needed in numerical simulations to capture the behavior of a ground vehicle passing through a transient crosswind. The performance of a full-dynamic coupling between aerodynamic and vehicle dynamic simulations, including a driver model, is evaluated. In the simulations a feedback from the vehicle dynamics into the aerodynamic simulation is performed in every time step. In the work, both the vehicle dynamic response and the aerodynamic forces and moments are studied. The results are compared to a static coupling approach on a set of different vehicle geometries. Five car-type geometries and one simplified bus geometry are evaluated. The aerodynamic loads and moments are obtained using Detached Eddy Simulation (DES) where the motion of the vehicle is enabled using an overset mesh technique. This motion is calculated with a single-track model, including a driver model and handling two degrees of freedom, namely lateral translation and yaw motion.The results show that for vehicles undertaking large yaw moments and therefore large yaw motions, like the bus-type geometry, the full dynamic coupling is beneficial. In this case, a static coupling overestimates the aerodynamic loads and in turn the vehicle motion. On less crosswind sensitive vehicles, like the car-type geometries, the full-coupling approach does not modify the results in a significant way compared to a static coupling.
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| 2. |
- Ekman, Petter, et al.
(författare)
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Aerodynamics of an Unloaded Timber Truck - A CFD Investigation
- 2016
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Ingår i: SAE International Journal of Commercial Vehicles. - : SAE INT. - 1946-391X .- 1946-3928. ; 9:2, s. 217-223
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Tidskriftsartikel (refereegranskat)abstract
- Reducing energy consumption and emissions are ongoing challenges for the transport sector. The increased number of goods transports emphasize these challenges even more, as greenhouse gas emissions from these vehicles increased by 20 % between 1990 and 2013, in Sweden. One special case of goods transports is the transport of timber. Today in Sweden, around 2000 timber trucks transport around six billion ton kilometers every year. For every ton kilometer these vehicles use around 0.025 liter diesel, and there should exist large possibilities to reduce the fuel consumption and the emissions for these vehicles. Timber trucks spend most of their operation time travelling in speeds of around 80 km/h. At this speed aerodynamic drag contributes to around 30 % of the total vehicle resistance, which makes the aerodynamic drag a significant part of the energy consumption. One of the big challenges with timber trucks is that they travel unloaded half of the time. This put higher demands on possible drag reduction modifications, as they need to function and be practical for both when the timber truck is loaded and unloaded. In this study an unloaded timber truck has been investigated by use of computational fluid dynamics. The recently released Stress Blended Eddy Simulation model has been used for simulating the flow over a timber truck at a Reynolds number of 1.1 million, based on the square root of its frontal area. From the results it could be seen that 52.8 % of the drag is generated by the cab. By investigating a drag reduction device that covered the gap between the bulkhead and the first stake pair, a drag reduction up to 6.7 % was possible, which shows potential for simple modifications that not influence the daily usage.
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| 3. |
- Lee, Chih Feng, et al.
(författare)
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Active Brake Judder Compensation Using an Electro-Hydraulic Brake System
- 2015
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Ingår i: SAE International Journal of Commercial Vehicles. - Warrendale : S A E Inc.. - 1946-391X .- 1946-3928. ; 8:1
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Tidskriftsartikel (refereegranskat)abstract
- Geometric imperfections on brake rotor surface are well-known for causing periodic variations in brake torque during braking. This leads to brake judder, where vibrations are felt in the brake pedal, vehicle floor and/or steering wheel. Existing solutions to address judder often involve multiple phases of component design, extensive testing and improvement of manufacturing procedures, leading to the increase in development cost. To address this issue, active brake torque variation (BTV) compensation has been proposed for an electromechanical brake (EMB). The proposed compensator takes advantage of the EMB’s powerful actuator, reasonably rigid transmission unit and high bandwidth tracking performance in achieving judder reduction. In a similar vein, recent advancements in hydraulic system design and control have improved the performance of hydraulic brakes on a par with the EMB, therefore invoking the possibility of incorporating the BTV compensation feature of the EMB within hydraulic brake hardware. In this paper, the typical characteristics of electromechanical and electro-hydraulic brake systems are presented. Based on the experimental results, the feasibility of active BTV compensation on the electro-hydraulic brake (EHB) systems is discussed. Furthermore, a BTV compensation algorithm designed for the EMB is presented and is shown to be applicable to the EHB. Using an experimentally validated model of BTV, the compensation was performed on a hardware in-the-loop EHB test rig. The preliminary results demonstrate the potential of using an EHB to compensate for brake judder.
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| 4. |
- Lindgärde, O., et al.
(författare)
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Optimal Vehicle Control for Fuel Efficiency
- 2015
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Ingår i: SAE International Journal of Commercial Vehicles. - : SAE International. - 1946-391X .- 1946-3928. ; 8:2, s. 682-694
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Tidskriftsartikel (refereegranskat)abstract
- CONVENIENT is a project where prediction and integrated control are applied on several subsystems with electrified actuators. The technologies developed in this project are applied to a long-haul tractor and semi-trailer combination. A Volvo truck meeting the Eu6 emission standard is rebuilt with a number of controllable electrified actuators. An e-Horizon system collects information about future road topography and speed limits. Controllable aerodynamic wind deflectors reduce the wind drag. The tractor is also equipped with a full digital cluster for human machine interface development. A primary project goal is to develop a model-based optimal controller that uses predictive information from the e-Horizon system in order to minimize fuel consumption. Several energy buffers are controlled in an integrated and optimal way using model predictive control. Several buffers are considered, such as the cooling system, the battery, and the vehicle kinetic energy. This paper presents details on the model predictive controller of the battery system and of the cooling system. Another project goal is to reduce fuel consumption by using adaptive aerodynamics. Controllers are developed that automatically sets an optimal roof deflector angle and the optimal side deflector angle. The results presented in this paper are encouraging. A third focus is the human machine interface and especially the communication between the driver and the control system during driving. This project develops a driver interface that encourages the driver to use the adaptive cruise controller when appropriate. The CONVENIENT project will be finalized this year. This paper presents the main project findings.
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| 5. |
- Lundahl, Kristoffer, 1984-, et al.
(författare)
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Analyzing Rollover Indices for Critical Truck Maneuvers
- 2015
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Ingår i: SAE International Journal of Commercial Vehicles. - : SAE International. - 1946-391X .- 1946-3928. ; 8:1, s. 189-196
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Tidskriftsartikel (refereegranskat)abstract
- Rollover has for long been a major safety concern for trucks, and will be even more so as automated driving is envisaged to becoming a key element of future mobility. A natural way to address rollover is to extend the capabilities of current active-safety systems with a system that intervenes by steering or braking actuation when there is a risk of rollover. Assessing and predicting the rollover is usually performed using rollover indices calculated either from lateral acceleration or lateral load transfer. Since these indices are evaluated based on different physical observations it is not obvious how they can be compared or how well they reflect rollover events in different situations.In this paper we investigate the implication of the above mentioned rollover indices in different critical maneuvers for a heavy 8×4 twin-steer truck. The analysis is based on optimal control applied to a five degrees of freedom chassis model with individual wheel dynamics and high-fidelity tire-force modeling. Driving scenarios prone to rollover accidents are considered, with a circular-shaped turn and a slalom maneuver being studied in-depth. The optimization objective for the considered maneuvers are formulated as minimum-time and maximum entry-speed problems, both triggering critical maneuvers and forcing the vehicle to operate on the limit of its physical capabilities. The implication of the rollover indices on the optimal trajectories is investigated by constraining the optimal maneuvers with different rollover indices, thus limiting the vehicle's maneuvering envelope with respect to each rollover index. The resulting optimal trajectories constrained by different rollover indices are compared and analyzed in detail. Additionally, the conservativeness of the indices for assessing the risk of rollovers are discussed.
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| 6. |
- Martini, Helena, 1984, et al.
(författare)
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Aerodynamic Analysis of Cooling Airflow for Different Front-End Designs of a Heavy-Duty Cab-Over-Engine Truck
- 2018
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Ingår i: SAE International Journal of Commercial Vehicles. - : SAE International. - 1946-3928 .- 1946-391X. ; 11:1, s. 31-44
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Tidskriftsartikel (refereegranskat)abstract
- Improving the aerodynamics of heavy trucks is an important consideration in the strive for more energy-efficient vehicles. Cooling drag is one part of the total aerodynamic resistance acting on a vehicle, which arises as a consequence of air flowing through the grille area, the heat exchangers, and the irregular under-hood area. Today cooling packages of heavy trucks are dimensioned for a critical cooling case, typically when the vehicle is driving fully laden, at low speed up a steep hill. However, for long-haul trucks, mostly operating at highway speeds on mostly level roads, it may not be necessary to have all the cooling airflow from an open-grille configuration. It can therefore be desirable for fuel consumption purposes, to shut off the entire cooling airflow, or a portion of it, under certain driving conditions dictated by the cooling demands. In Europe, most trucks operating on the roads are of cab-over-engine type, as a consequence of the length legislations present. However, there are new directions from the European Union, which would permit slightly longer vehicles to improve aerodynamics and also to allow for a safer, more environmentally friendly vehicle. The truck design, where a cab-over-engine cab has an elongated front, is often referred to as a Soft Nose, where, as the name implies, the nose should be “soft” to improve the safety for pedestrians and also for car occupants in the event of a collision. This paper deals with the analysis of cooling airflow for two different front-end designs of a heavy truck. The first design is a cab-over-engine cab; the second is a Soft Nose cab, which in this case is basically an elongation of the grille area of the cab-over-engine cab to obtain a smoother shape of the cab. The Soft Nose model used in this investigation was extended 200 mm from the cab-over-engine front. Computational Fluid Dynamics was used as the tool for examining the aerodynamic properties of the vehicle models. A steady RANS-based approach was conducted, based on the method evaluated in previous work performed by the authors. The cab-over-engine and Soft Nose models were evaluated in an open-road environment. The configurations were evaluated both with inactive and active heat exchangers, in order to examine the effect of heating the air on the drag co-efficient and also to determine the cooling capacity of the different models. A sub- study was performed where different opening percentages of the grille area was investigated to determine the minimum percentage opening that would be needed to achieve a radiator Top Tank Temperature value below a target limit of 100 °C. The results show that there was potential for drag reductions for the Soft Nose model used. The cooling airflow was different for the cab-over-engine and Soft Nose models; as a consequence of the longer distance between the grille and cooling package, less air entered the cooling module for the Soft Nose model. A large portion of the airflow entering the grille leaked around the cooling module for the Soft Nose model. Also, following on from the reduced airflow through the cooling package, the radiator Top Tank Temperature values were considerably increased with the Soft Nose model. It was also shown that for the specific driving condition simulated here, an opening of 17.5% of the grille area was required to ensure sufficient cooling capacity. An interesting continuation of the cooling airflow analysis of the Soft Nose model would be to add ducts, guiding the air from the grille to the cooling module, to investigate if leakage could be reduced and cooling capacity increased.
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| 7. |
- Risseh, Arash, 1980-, et al.
(författare)
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Design of a Thermoelectric Generator for Waste Heat Recovery Application on a Drivable Heavy Duty Vehicle
- 2017
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Ingår i: SAE International Journal of Commercial Vehicles. - : SAE International. - 1946-391X .- 1946-3928. ; 10:1, s. 26-44
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Tidskriftsartikel (refereegranskat)abstract
- The European Union’s 2020 target aims to be producing 20 % of its energy from renewable sources by 2020, to achieve a 20 % reduction in greenhouse gas emissions and a 20 % improvement in energy efficiency compared to 1990 levels. To reach these goals, the energy consumption has to decrease which results in reduction of the emissions. The transport sector is the second largest energy consumer in the EU, responsible for 25 % of the emissions of greenhouse gases caused by the low efficiency (<40 %) of combustion engines. Much work has been done to improve that efficiency but there is still a large amount of fuel energy that converts to heat and escapes to the ambient atmosphere through the exhaust system. Taking advantage of thermoelectricity, the heat can be recovered, improving the fuel economy. A thermoelectric generator (TEG) consists of a number of thermoelectric elements, which advantageously can be built into modules, arranged thermally and electrically, in a way such that the highest possible thermal power can be converted into electrical power. In a unique waste heat recovery (WHR) project, five international companies and research institutes cooperated and equipped a fully drivable Scania prototype truck with two TEGs. The entire system, from the heat transfer in the exchangers to the electrical power system, was simulated, built and evaluated. The primary experimental results showed that approximately 1 kW electrical power could be generated from the heat energy. In this paper the entire system from design to experimental results is presented.
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| 8. |
- Sert, Emre, et al.
(författare)
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Enhancement of Vehicle Handling Based on Rear Suspension Geometry Using Taguchi Method
- 2016
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Ingår i: SAE International Journal of Commercial Vehicles. - : SAE International. - 1946-3928 .- 1946-391X. ; 9:1, s. 1-13
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Tidskriftsartikel (refereegranskat)abstract
- Studies have shown that the number of road accidents caused by rollover both in Europe and in Turkey is increasing [1]. Therefore, rollover related accidents became the new target of the studies in the field of vehicle dynamics research aiming for both active and passive safety systems. This paper presents a method for optimizing the rear suspension geometry using design of experiment and multibody simulation in order to reduce the risk of rollover. One of the major differences of this study from previous work is that it includes statistical Taguchi method in order to increase the safety margin. Other difference of this study from literature is that it includes all design tools such as model validation, optimization and full vehicle handling and ride comfort tests. Rollover angle of the vehicle was selected as the cost function in the optimization algorithm that also contains roll stiffness and height of the roll center. In order to form the cost function, five different geometrical factors have been selected as design variables. The ultimate aim is to minimize the cost function by increasing the roll center height and suspension roll stiffness. To run the optimization routine, a rigid rear suspension mechanism used on the 7 m bus has been modeled using Adams/Car software program. Opposite wheel travel analysis has been performed as an optimization test method in order to simulate the vehicle passing over the bump. Then, in order to reach the minimum value of the cost function, statistical Taguchi method was used to perform design of experiments (DOE). In total, 27 experiments have been performed according to the selected design variables. Therefore, in each different experiment, the roll center height and the roll stiffness were measured. Then, the cost function was calculated and recorded to compare with the future iterations. The attachment points giving minimum cost function value are expected to be the optimal coordinates for installing the suspension mechanism.
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