Purpose
This article presents a proposal for an operating cycle format for describing transport missions of road vehicles, for example a logging truck fetching its cargo. The primary application is ...in dynamic simulation models for evaluation of energy consumption and other costs of transportation. When applied to product development, the objective is an ensemble of components and functions optimised for specific tasks and environments. When applied to selection of vehicle configuration, the objective is a vehicle specification tailored for its task.
Method
The proposal is presented and its four main parts: road, weather, traffic and mission, are thoroughly explained. Furthermore, we implement the proposal in an example of a dynamic forward simulation model.
Results
The example model is used for two case studies: a synthetic example of a complex transport mission (a logging truck fetching its cargo) that shows some advanced format features, and an example from a real vehicle log file (cargo transport) that seeks to compare the resulting simulated speed profile to the measured one.
Conclusion
The results show that the proposed format works in practice. It can represent complex transport missions and it can be used to reproduce the main features of a logged speed profile even when combined with simple driver and vehicle models.
•A novel road description using stochastic models in a hierarchical structure.•A method for how to generate data possible to simulate in a dynamic model.•Hilliness and stop intensity are the most ...prominent properties in the chosen range.•The statistical method is compared with real log data and the results match well.•Ideas discussed on how to make realistic predictions of CO2 emissions from vehicles.
We propose a novel statistical description of the physical properties of road transport operations by using stochastic models arranged in a hierarchical structure. The description includes speed signs, stops, speed bumps, curvature, topography, road roughness and ground type, with a road type introduced at the top of the hierarchy to group characteristics that are often connected. Methods are described how to generate data on a form (the operating cycle format) that can be used in dynamic simulations to estimate energy usage and CO2 emissions. To showcase the behaviour of the description, two examples are presented using a modular vehicle model for a heavy-duty truck: a sensitivity study on impacts from changes in the environment, and a comparison study on a real goods transport operation with respect to energy usage. It is found that the stop intensity and topography amplitude have the greatest impact in the sensitivity study (8.3% and 9.5% respectively), and the comparison study implies that the statistical description is capable of capturing properties of the road that are significant for vehicular energy usage. Moreover, it is discussed how the statistical description can be used in a vehicle design process, and how the mean CO2 emissions and its variation can be estimated for a vehicle specification.
An engine model developed earlier is validated through comparison between measurements and simulations of transient situations. In particular boost pressure build up is studied. The engine model is ...intended for use in computer simulation of transient behavior in drivetrain and vehicle systems. The model studied is semi-empiric. Some of the model properties are empiric: engine data in steady state operation and mappings of compressor and turbine performance. Others are physical properties, e.g. displacement and compression ratio. The measurements have been carried out in a transient engine test bed. In the measurements the delivered fuel amount is measured, as opposed to pedal position, and thus the engine control system and fuel injection system are not included in the comparisons. The time constants of the measured and the simulated boost pressure buildups are compared for eleven different step changes in pedal position. All step changes go from lower to higher pedal position. The engine speed is held approximately constant. Despite the simplifications in the model studied, it shows good agreement with the measurements. It is concluded that the agreement can be improved further by introducing a time delay in the model.
An engine model for use in computer simulation of transient behavior in drivetrain and vehicle systems is presented. Two elements, important for deviation (e.g. turbo-lag) from steady state ...characteristics, are the inertia of the supercharging unit (turbo shaft) and the fuel injection control system. No extensive combustion calculations are carried out within the model. Instead it uses condensed results from existing combustion models and measurements. The model is semi-empirical. Some of the engine specific properties needed for simulation are (e.g. for a turbocharged diesel): engine data in steady state operation, mappings of compressor and turbine performance, inertia of the engine components condensed to the crankshaft, turbo shaft inertia, displacement, compression ratio and the essentials of the fuel injection control strategy. Input parameters to the computer program based on the model are accelerator pedal position and external torque acting on the flywheel. Output properties from the program are engine torque, speeds, temperatures, pressures and emissions. In a typical downshift operation the delivered torque can instantly deviate by 30% as compared with steady state operation. It can be concluded that this model might be a useful tool for heavy vehicle drivetrain simulation.
The objective of this paper is to demonstrate a possibility of optimizing the fixed gear ratios of an automatic transmission by using a special modeling and simulation technique. It is a problem to ...design the set of ratios in general, and especially for transient driving situations. Sometimes there is a lack of systematic methods to optimize dynamic systems, and particularly vehicle powertrain systems, which is the focus of this paper. The techniques used involve a dynamic engine model and a refined gearbox model. To give each set of ratios a fair judgement, the gearbox control system is calibrated for each new set. The influence of a set of ratios on the vehicle acceleration performance and fuel economy in a given driving cycle is evaluated against an optimization criterion. Calibration of the gearbox control system is performed with stationary analysis. This is the most suitable way with respect to the input signals of gearbox control systems of today. On the other hand, the driving cycle simulation is dynamic, to achieve the desired accuracy. Traditionally, the set of ratios is designed considering only stationary analysis. The proposed method using dynamic analysis gives better gearbox optimization, for the desired transportation task. Design recommendations can be made by following the procedure presented.
Our aims were to estimate 1) the costs of hospital treatment and 2) the value of lost production due to early death associated with overweight and obese patients, and then to extrapolate the findings ...to national costs.
We use regression models to analyze survival, expected number of days in hospital treatment for patients with different body mass index (BMI), and costs with data obtained from screening of 33,196 middle-aged subjects living in Malmö, Sweden, and collected during a 15-year follow-up period. We subsequently scale up costs to national aggregate level using the BMI prevalence data from the screening project to the national population.
The total excess hospital (somatic, psychiatric) care cost (Swedish krona or SEK) for the national health-care budget, excess as compared to normal weight patients for obese (BMI > 30) and overweight (25 ≤ BMI < 30) was estimated to SEK2155 million per annum (US$269 million, assuming US$1 = SEK8), or about 2.3% of total hospital care costs in Sweden. The corresponding indirect costs due to early death were estimated to SEK2935 million (US$367 million). For males at age 55, the potential hospital costs saving, excluding costs of the intervention that could be gained by an intervention that successfully and safely could alter the weight of an obese individual to become normal weight, was estimated on average to SEK4434 (US$554) per annum.
Hospital treatment costs are found to be higher for obese and overweight patients than for normal weight patients indicating potential cost savings especially on indirect costs by effective, safe and low cost weight-loss intervention.
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