A state-of-the-art review on torque distribution strategies aimed at enhancing energy efficiency for fully electric vehicles with independently actuated drivetrains

© 2019, Levrotto and Bella. All rights reserved. Electric vehicles are the future of private passenger transportation. However, there are still several technological barriers that hinder the large scale adoption of electric vehicles. In particular, their limited autonomy motivates studies on methods for improving the energy efficiency of electric vehicles so as to make them more attractive to the market. This paper provides a concise review on the current state-of-the-art of torque distribution strategies aimed at enhancing energy efficiency for fully electric vehicles with independently actuated drivetrains (FEVIADs). Starting from the operating principles, which include the "control allocation" problem, the peculiarities of each proposed solution are illustrated. All the existing techniques are categorized based on a selection of parameters deemed relevant to provide a comprehensive overview and understanding of the topic. Finally, future concerns and research perspectives for FEVIAD are discussed

Campus Mobility for the Future: The Electric Bicycle

Sustainable and practical personal mobility solutions for campus environments have traditionally revolved around the use of bicycles, or provision of pedestrian facilities. However many campus environments also experience traffic congestion, parking difficulties and pollution from fossil-fuelled vehicles. It appears that pedal power alone has not been sufficient to supplant the use of petrol and diesel vehicles to date, and therefore it is opportune to investigate both the reasons behind the continual use of environmentally unfriendly transport, and consider potential solutions. This paper presents the results from a year-long study into electric bicycle effectiveness for a large tropical campus, identifying barriers to bicycle use that can be overcome through the availability of public use electric bicycles

Torque vectoring based drive assistance system for turning an electric narrow tilting vehicle

The increasing number of cars leads to traffic congestion and limits parking issue in urban area. The narrow tilting vehicles therefore can potentially become the next generation of city cars due to its narrow width. However, due to the difficulty in leaning a narrow tilting vehicle, a drive assistance strategy is required to maintain its roll stability during a turn. This article presents an effective approach using torque vectoring method to assist the rider in balancing the narrow tilting vehicles, thus reducing the counter-steering requirements. The proposed approach is designed as the combination of two torque controllers: steer angle–based torque vectoring controller and tilting compensator–based torque vectoring controller. The steer angle–based torque vectoring controller reduces the counter-steering process via adjusting the vectoring torque based on the steering angle from the rider. Meanwhile, the tilting compensator–based torque vectoring controller develops the steer angle–based torque vectoring with an additional tilting compensator to help balancing the leaning behaviour of narrow tilting vehicles. Numerical simulations with a number of case studies have been carried out to verify the performance of designed controllers. The results imply that the counter-steering process can be eliminated and the roll stability performance can be improved with the usage of the presented approach

Stability of an electric vehicle with permanent-magnet in-wheel motors during electrical faults

This paper presents an analysis of the stability of an electric vehicle equipped with in-wheel motors ofpermanent-magnet type during a class of electrical faults. Due to the constant excitation from the permanentmagnets, the output torque from a faulted wheel cannot easily be removed if an inverter shuts down, which directlyaffects the vehicle stability. In this paper, the impact of an electrical fault during two driving scenarios isinvestigated by simulations; using parameters from a 30 kW in-wheel motor and experimentally obtained tire data.It is shown that the electrical fault risks to seriously degrading the vehicle stability if the correct counteraction isnot taken quickly. However, it is also demonstrated that vehicle stability during an electrical fault can be maintainedwith only minor lateral displacements when a closed-loop path controller and a simple method to allocate theindividual tire forces are used. This inherent capacity to handle an important class of electrical faults is attractive;especially since no additional fault-handling strategy or hardware is needed

All wheel drive electric motorcycle modelling and control.

Conventional motorcycles are powered through a chain or shaft linking the engine to the rear wheel. However, motorcycle riders are now facing riding conditions and obstacles where having only rear wheel drive can lead to vehicle damage, loss of control and an unstable front wheel during cornering and off-road riding in general. Traction and climbing ability are severely limited in extreme mountain conditions by only having the rear wheel to provide power. Accordingly, there is a need in the industry for a two-wheel drive motorcycle that efficiently and safely transfers power from the motor to the front wheel, because it provides the rider with increased ability to safely negotiate rough terrain. In this background, the design of an optimal torque distribution strategy implemented by two separate electric motors in an all-wheel-drive electric motorcycle has many potentialities not fully explored and deeply understood for two wheel vehicles, that makes this study interesting from a scientific point of view. With this in mind, the research project aims to design control systems for improving rider’s safety and vehicle performance at low as well as high speeds, especially in critical situations and rough terrains, taking into account the presence of the front wheel torque generated by a hub-mounted electric motor. At low speed the research investigates whether and how the front wheel torque helps the stabilization of the vehicle around the upright position, without any rider action required. The study is developed by deriving a simplified analytical model of the vehicle, which captures its lateral motion and a model-based control system, employing the sliding mode control technique. As further requirement, the motorcycle should be balanced in a small bounded area, by means of Multi Input control system. At medium and high speeds the study explores how and how much the traction torque repartition can improve continuously the vehicle performances in combined longitudinal and lateral acceleration situations, such as the exit of a curve, especially in those conditions where a traditional motorcycle falls down because it overcomes tyre adherence limits. Last purpose is achieved deriving a dynamical optimal traction strategy which does not require the a priori knowledge of the friction coefficient. Steady state analysis indicates outperformances of the all wheel drive motorcycle over the classical rear wheel drive one. Then, dynamical simulations of selected manoeuvres, in both flat and uneven road, corroborate the result

Electric Hybrid Powertrain for Armored Vehicles

The performance of modern, new generation-armored vehicles would greatly benefit from overall engineering, optimization, and integration techniques of advanced diesel engines-electrified transmissions. Modern axial flux electric motors and controllers are perfectly able to replace the classical automatic gearbox and complex steering system of traditional Main Battle Tanks. This study shows a possible design of a serial hybrid electric power pack for very heavy tanks with a weight well over 50 tons. The result is a hybrid power system that improves the overall performance of armored vehicles off-road and on-road, improving the acceleration and the smoothness of the ride. In addition, fuel consumption will be reduced because the internal combustion engine operates at fixed rpm. The electric motors will outperform the traditional engines due to their very high torque output even at “zero speed”. The weight of a hybrid system has also been calculated. In fact, in many cases, it is possible to use all off-the-shelf components. The on-board diagnosis of the subsystems in the hybrid powertrain makes it possible to achieve a Time Between Overhaul (TBO) of 4500 h with a failure probability inferior to one in 10,000

On Advanced Mobility Concepts for Intelligent Planetary Surface Exploration

Surface exploration by wheeled rovers on Earth's Moon (the two Lunokhods) and Mars (Nasa's Sojourner and the two MERs) have been followed since many years already very suc-cessfully, specifically concerning operations over long time. However, despite of this success, the explored surface area was very small, having in mind a total driving distance of about 8 km (Spirit) and 21 km (Opportunity) over 6 years of operation. Moreover, ESA will send its ExoMars rover in 2018 to Mars, and NASA its MSL rover probably this year. However, all these rovers are lacking sufficient on-board intelligence in order to overcome longer dis-tances, driving much faster and deciding autonomously on path planning for the best trajec-tory to follow. In order to increase the scientific output of a rover mission it seems very nec-essary to explore much larger surface areas reliably in much less time. This is the main driver for a robotics institute to combine mechatronics functionalities to develop an intelligent mo-bile wheeled rover with four or six wheels, and having specific kinematics and locomotion suspension depending on the operational terrain of the rover to operate. DLR's Robotics and Mechatronics Center has a long tradition in developing advanced components in the field of light-weight motion actuation, intelligent and soft manipulation and skilled hands and tools, perception and cognition, and in increasing the autonomy of any kind of mechatronic systems. The whole design is supported and is based upon detailed modeling, optimization, and simula-tion tasks. We have developed efficient software tools to simulate the rover driveability per-formance on various terrain characteristics such as soft sandy and hard rocky terrains as well as on inclined planes, where wheel and grouser geometry plays a dominant role. Moreover, rover optimization is performed to support the best engineering intuitions, that will optimize structural and geometric parameters, compare various kinematics suspension concepts, and make use of realistic cost functions like mass and consumed energy minimization, static sta-bility, and more. For self-localization and safe navigation through unknown terrain we make use of fast 3D stereo algorithms that were successfully used e.g. in unmanned air vehicle ap-plications and on terrestrial mobile systems. The advanced rover design approach is applica-ble for lunar as well as Martian surface exploration purposes. A first mobility concept ap-proach for a lunar vehicle will be presented

Multi-objective optimisation for battery electric vehicle powertrain topologies

Electric vehicles are becoming more popular in the market. To be competitive, manufacturers need to produce vehicles with a low energy consumption, a good range and an acceptable driving performance. These are dependent on the choice of components and the topology in which they are used. In a conventional gasoline vehicle, the powertrain topology is constrained to a few well-understood layouts; these typically consist of a single engine driving one axle or both axles through a multi-ratio gearbox. With electric vehicles, there is more flexibility, and the design space is relatively unexplored. In this paper, we evaluate several different topologies as follows: a traditional topology using a single electric motor driving a single axle with a fixed gear ratio; a topology using separate motors for the front axle and the rear axle, each with its own fixed gear ratio; a topology using in-wheel motors on a single axle; a four-wheel-drive topology using in-wheel motors on both axes. Multi-objective optimisation techniques are used to find the optimal component sizing for a given requirement set and to investigate the trade-offs between the energy consumption, the powertrain cost and the acceleration performance. The paper concludes with a discussion of the relative merits of the different topologies and their applicability to real-world passenger cars