Urban and extra-urban hybrid vehicles: a technological review

Pollution derived from transportation systems is a worldwide, timelier issue than ever. The abatement actions of harmful substances in the air are on the agenda and they are necessary today to safeguard our welfare and that of the planet. Environmental pollution in large cities is approximately 20% due to the transportation system. In addition, private traffic contributes greatly to city pollution. Further, “vehicle operating life” is most often exceeded and vehicle emissions do not comply with European antipollution standards. It becomes mandatory to find a solution that respects the environment and, realize an appropriate transportation service to the customers. New technologies related to hybrid –electric engines are making great strides in reducing emissions, and the funds allocated by public authorities should be addressed. In addition, the use (implementation) of new technologies is also convenient from an economic point of view. In fact, by implementing the use of hybrid vehicles, fuel consumption can be reduced. The different hybrid configurations presented refer to such a series architecture, developed by the researchers and Research and Development groups. Regarding energy flows, different strategy logic or vehicle management units have been illustrated. Various configurations and vehicles were studied by simulating different driving cycles, both European approval and homologation and customer ones (typically municipal and university). The simulations have provided guidance on the optimal proposed configuration and information on the component to be used

An investigation into hybrid power trains for vehicles with regenerative braking

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A Study on the Integration of a High-Speed Flywheel as an Energy Storage Device in Hybrid Vehicles

The last couple of decades have seen the rise of the hybrid electric vehicle as a compromise between the outstanding specific energy of petrol fuels and its low-cost technology, and the zero tail-gate emissions of the electric vehicle. Despite this, considerable reductions in cost and further increases in fuel economy are needed for their widespread adoption. An alternative low-cost energy storage technology for vehicles is the high-speed flywheel. The flywheel has important limitations that exclude it from being used as a primary energy source for vehicles, but its power characteristics and low-cost materials make it a powerful complement to a vehicle's primary propulsion system. This thesis presents an analysis on the integration of a high-speed flywheel for use as a secondary energy storage device in hybrid vehicles. Unlike other energy storage technologies, the energy content of the flywheel has a direct impact on the velocity of transmission. This presents an important challenge, as it means that the flywheel must be able to rotate at a speed independent of the vehicle's velocity and therefore it must be coupled via a variable speed transmission. This thesis presents some practical ways in which to accomplish this in conventional road vehicles, namely with the use of a variator, a planetary gear set or with the use of a power-split continuously variable transmission. Fundamental analyses on the kinematic behaviour of these transmissions particularly as they pertain to flywheel powertrains are presented. Computer simulations were carried out to compare the performance of various transmissions, and the models developed are presented as well. Finally the thesis also contains an investigation on the driving and road conditions that have the most beneficial effect on hybrid vehicle performance, with a particular emphasis on the effect that the road topography has on fuel economy and the significance of this

Charging ahead on the transition to electric vehicles with standard 120 v wall outlets

Electrification of transportation is needed soon and at significant scale to meet climate goals, but electric vehicle adoption has been slow and there has been little systematic analysis to show that today's electric vehicles meet the needs of drivers. We apply detailed physics-based models of electric vehicles with data on how drivers use their cars on a daily basis. We show that the energy storage limits of today's electric vehicles are outweighed by their high efficiency and the fact that driving in the United States seldom exceeds 100 km of daily travel. When accounting for these factors, we show that the normal daily travel of 85-89% of drivers in the United States can be satisfied with electric vehicles charging with standard 120 V wall outlets at home only. Further, we show that 77-79% of drivers on their normal daily driving will have over 60 km of buffer range for unexpected trips. We quantify the sensitivities to terrain, high ancillary power draw, and battery degradation and show that an extreme case with all trips on a 3% uphill grade still shows the daily travel of 70% of drivers being satisfied with electric vehicles. These findings show that today's electric vehicles can satisfy the daily driving needs of a significant majority of drivers using only 120 V wall outlets that are already the standard across the United States

Hybrid vehicle assessment. Phase 1: Petroleum savings analysis

The results of a comprehensive analysis of near term electric hybrid vehicles are presented, with emphasis on their potential to save significant amounts of petroleum on a national scale in the 1990s. Performance requirements and expected annual usage patterns of these vehicles are first modeled. The projected U.S. fleet composition is estimated, and conceptual hybrid vehicle designs are conceived and analyzed for petroleum use when driven in the expected annual patterns. These petroleum consumption estimates are then compared to similar estimates for projected 1990 conventional vehicles having the same performance and driven in the same patterns. Results are presented in the form of three utility functions and comparisons of sevral conceptual designs are made. The Hybrid Vehicle (HV) design and assessment techniques are discussed and a general method is explained for selecting the optimum energy management strategy for any vehicle mission battery combination. Conclusions and recommendations are presented, and development recommendations are identified

Kinetic energy storage using a dual braking system for unmanned parallel hybrid electric vehicle

In this paper a novel regenerative dual braking strategy is proposed for utility/goods delivery unmanned vehicles in public roads, which improves the regenerative energy capturing ability and consequently improves the fuel use of parallel hybrid power train configurations for land unmanned vehicles where the priority is not comfort but extending the range. Furthermore, the analysis takes into account the power handling ability of the electric motor and the power converters. In previous research a plethora of regenerative braking strategies is shown, for this paper the key contribution is that the vehicle electric regeneration is related to a fixed braking distance in relation to the energy storage capabilities specifically for unmanned utility type land vehicles where passenger comfort is not a concern but pedestrian safety is of critical importance. Furthermore, the vehicle’s power converter capabilities facilitate the process of extending the braking time via introducing a variable deceleration profile. The proposed approach has therefore resulted in a regenerative algorithm which improves the vehicle’s energy storage capability without considering comfort since this analysis is applicable to unmanned vehicles. The algorithm considers the distance as the key parameter, which is associated to safety, therefore it allows the braking time period to be extended thus favouring the electric motor generation process while sustaining safety. This method allows the vehicle to brake for longer periods rather than short bursts hence resulting in a more effective regeneration with reduced use of the dual (i.e. caliper/stepper motor brake system). The regeneration method and analysis is addressed in the following paper sections. The simulation results show that the proposed regenerative braking strategy has improved significantly the energy recapturing ability of the hybrid power train configuration. The paper is also supported with experimental data that verify the theoretical development and the simulation results. The two strategies developed and implemented are Constant Braking Torque (CBT) and Constant Braking Power (CBP). Both methods were limited to a fixed safety-based distance. Overall the results demonstrate that the CBT method results in better energy-based savings

System and Thermal Modeling of Hydraulic Hybrids: Thermal Characteristics Analysis

Hybrid vehicles have become a popular alternative to conventional powertrain architectures by offering improved fuel efficiency along with various other environmental benefits. Among them, hydraulic hybrid vehicles (HHVs) have several benefits, which make it the superior technology for certain applications over other types of hybrid vehicles, such as lower component costs, more environmentally friendly construction materials, higher power densities, and more regenerative energy available from braking. There have been various studies on HHVs, such as energy management optimization, control strategies for various system configurations, the effect of system parameters on the hybrid system, and proposals for novel hybrid architectures. One area not been thoroughly covered in the past is a detailed modeling and examination of the thermal characteristics for HHVs due to a difficulty of describing the rapid thermal transients in the unsteady state systems. In this dissertation, a comprehensive system and thermal modeling has been studied for hydraulic hybrid transmissions (HHTs). The main motivation behind developing a thermal model of HHTs is to gain a deeper understanding of the system’s thermal performance, and key influencing factors, without relying on experimental data. This will enable HHVs to be designed more efficiently by identifying and addressing potential issues with transmission’s thermal performance prior to hardware testing. Since there exists no thermal study on HHVs in the past, a thermal modeling method has been introduced, which can be applicable to hydraulic hybrid architectures. A thermal modeling methodology based on a novel numerical scheme and accurate theoretical description has been developed in order to capture the rapid thermal transient in the hydraulic system under unsteady state conditions. The model has been applied to a series HHT and validated with measured data from the hardware-in-the-loop (HIL) test rig with a standard driving cycle, FTP-72. In addition, the proposed thermal modeling methodology has been used to analyze and optimize the cooling system of a novel HHV architecture, which is implemented in a sport utility vehicle (SUV) in Maha Fluid Power Research Center. The modeling results have been compared with the measured data while driving the vehicle. In both studies, the simulation results have shown a good correlation with the experimental data in terms of the overall trends and variation ranges. The goal of the developed model is the application to the system and thermal issues in HHVs, such as thermal stability analysis, management of the cooling system, packaging and hydraulic component optimization, and evaluation of thermal characteristics of different architectures. As an advanced topic of this research, thermal management of an open and a closed circuit hydraulic hybrid systems has been studied by simulation. The comparison results show a potential to a better thermal management for the open circuit systems with smaller heat exchangers, as well as less power consumption with incorporation of smaller charge pumps compared to the closed circuit systems. In the future, the developed comprehensive system and thermal modeling method can be applied to different advanced topics, such as analysis of performance and thermal characteristics, systems and components optimization, and systems evaluation with different external conditions, for different hydraulic hybrid systems

Hybrid vehicles: a temporary step

The presented paper discusses the diffusion of hybrid electric technology in vehicles. It is put into question whether the current strong acceptance of the technology especially by US consumers is of sustainable nature. Therefore, different variables influencing the diffusion of the technology are presented and their influence on the market analyzed. It is found that non-financial criteria drive consumers' buying decisions significantly.The article also presents an overview of company strategies in the field of OEMs and suppliers of hybrid electric components. It is found that most companies integrate hybrid electric vehicles in their technology portfolio. It is concluded that even though hybrid electric technology can not yet being applied profitably yet it seems to be a key technology to the industry due to its current positive perception in the US. However, diesel technology and the intelligent use of cost efficient measures to reduce fuel consumption provide sustainable alternatives.automobile; hybrid technology; innovation; strategy

The architecture of pneumatic regenerative systems for the diesel engine

For vehicles whose duty cycle is dominated by start-stop operation, fuel consumption may be significantly improved by better management of the start-stop process. Pneumatic hybrid technology represents one technology pathway to realise this goal. Vehicle kinetic energy is converted to pneumatic energy by compressing air into air tank(s) during the braking. The recovered air is reused to supply an air starter, or supply energy to the air path in order to reduce turbo-lag. This research aims to explore the concept and control of a novel pneumatic hybrid powertrain for a city bus application to identify the potential for improvements in fuel economy and drivability. In order to support the investigation of energy management, system architecture and control methodologies, two kinds of simulation models are created. Backward-facing simulation models have been built using Simulink. Forward-facing models have been developed in the GT-POWER and Simulink co-simulation. After comparison, the fully controllable hybrid braking system is chosen to realize the regenerative braking function. A number of architectures for managing a rapid energy transfer into the powertrain to reduce turbo-lag have been investigated. A city bus energy control strategy has been proposed to realize the Stop-Start Function, Boost Function, and Regenerative Braking Function as well as the normal operations. An optimisation study is conducted to identify the relationships between operating parameters and respectively fuel consumption, performance and energy usage. In conclusion, pneumatic hybrid technology can improve the city bus fuel economy by at least 6% in a typical bus driving cycle, and reduce the engine brake torque response and vehicle acceleration. Based on the findings, it can be learned that the pneumatic hybrid technology offers a clear and low-cost alternative to the electric hybrid technology in improving fuel economy and vehicle drivability

Kinetic energy recovery and power management for hybrid electric vehicles

The major contribution of the work presented in this thesis is a thorough investigation of the constraints on regenerative braking and kinetic energy recovery enhancement for electric/hybrid electric vehicles during braking. Regenerative braking systems provide an opportunity to recycle the braking energy, which is otherwise dissipated as heat in the brake pads. However, braking energy harnessing is a relatively new concept in the automotive sector which still requires further research and development. Due to the operating constraints of the drivetrain architecture and the varying nature of the braking conditions, it is unlikely that all the stored kinetic energy of the vehicle can be recovered during braking.The research work in this thesis addresses the effect of braking conditions on kinetic energy recovery enhancement of the vehicle. The challenge in kinetic energy recovery enhancement lies in braking conditions, power/torque handling ability of the electric propulsion system, managing the dual braking systems, employed energy conversion techniques, and energy storage capacity. In this work a novel braking strategy is introduced to increase the involvement of the regenerative braking system, so as to increase the kinetic energy recovery while achieving the braking performance requirements. Initially mathematical modelling and simulation based analysis are presented to demonstrate the effects of braking power variation with respect to braking requirements. A novel braking strategy is proposed to increase the kinetic energy recovery during heavy braking events. The effectiveness of this braking strategy is analyzed using a simulation model developed in matlab- simulink environment. Anexperimental rig is developed to test various braking scenarios and their effects on kinetic energy recovery. A variety of braking scenarios are tested and results are presented with the analysis. At the end, suggestions are made to further continue this research in the future