Improving Traction and Control in Electric Vehicles
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Engineering and Technology ︱ Professor Guoqing Xu Actual Torque Desired Traction Torque Traction Motor Unknown Electric Vehicles Tyre-Road Driving Unit Adhesion Driver Fast Measurements Slow Measurements Improving traction and Operation Traction/Brake with Low Precision with Low Precision Control Unit (Adhesion stability control) Current Voltage Force Transfer Slip Ratio control in electric vehicles Factor Estimation Stable/Unstable Adhesion State Wheel Speed Adhesion Stability Friction Speed Vehicle Electric vehicles look set s humanity begins to ramp an innovative range of new technologies Determination Estimation to increasingly dominate up its battle against the critical for realising these improvements. This our roads in the coming years, issues of climate change and progress is a result of four key studies Optimal Slip Ratio Reference A Optimal Slip Ratio Optimal but many remain unconvinced air pollution, electric vehicles will likely published between 2012 and 2016. Operation Point Traditional measured signals for tyre- Maximum Available Traction Torque Search of their advantages over their become an important part of a more Maximum Adhesion road adhesion detection and control. more traditional, fossil fuel- environmentally sustainable society. A THEORY FOR Novel detection and control using fast A schematic of one possible set-up Tyre-Road Adhesion Detection motor signals with high-precision. burning counterparts. In his Recently, countries including Norway, IMPROVING ADHESION to improve traction and control. recent research, Professor Sweden, and Denmark have set end- In their first study, carried out in 2012, Guoqing Xu at Shanghai dates for sales of vehicles which run Professor Xu’s team developed a vehicle- physical experiments demonstrating IMPROVING VEHICLE STABILITY a new detection model using electrical University has proposed new on fossil fuels, and in the coming integrated scheme for controlling traction its capabilities. Building on this work, Professor Xu parameters of motors were proposed, ways in which electric vehicles years, other developed nations will between tyres and the road, avoiding and colleagues next worked towards as well as a unified criterion for vehicle can be improved beyond be likely to follow. However, with many loss of control on surfaces like ice or mud DETECTING WHEEL SLIPPING developing systems which could stability. The force transfer factor can the capabilities of fossil fuel nations dragging their feet on their where friction is greatly reduced. Their Following on from this earlier work, automatically prevent slipping on low- be obtained by electrical parameters burners. Through innovations commitments to sustainability, it appears research aimed to discover how this Professor Xu’s team showed that friction surfaces. The team noted that such as current and voltage of the drive relating to both tyre adhesion that electric vehicles may need to offer friction – named the ‘adhesion force’, electric vehicles could be able to although traction can be gained when motor.” On a road surface with unknown stability and the recycling of more incentives to consumers before can be controlled by the vehicle itself automatically detect rates of slipping a vehicle’s wheels are spinning at just friction, the system could, therefore, braking energy, Professor Xu more traditional vehicles can be phased no matter the surface it is driving on. in their tyres when driving across low- the right speed, road surfaces have determine the most stable wheel rotation believes electric vehicles can out on global scales. “This study proposed a new structure friction surfaces. Slipping occurs when widely varying amounts of friction in speed, which would optimise wheel grip realistically become safe and for vehicle adhesion control, in which a vehicle’s wheels are rotating either too reality, making it extremely difficult for by transferring the most energy to the reliable features of our transport networks in the near future. In a series of studies carried out feedback including the adhesion stability quickly or too slowly to gain full traction drivers to manually maintain an optimal ground. Again, the researchers carried out over a six-year period, Professor Xu state and the maximum adhesion force, with a low-friction surface, resulting rotation. In the 2016 study, Professor Xu’s both experiments and simulations to show in a reduction in its speed. From the team aimed to gain new insights into the that this could be achieved simply using results of a study published in 2013, determination of the ‘Force transfer factor’ data from an electric vehicle’s drive motor. The research includes an improvement the researchers patented a system – a value which “directly determines of the energy efficiency… for electrically- for detecting slipping rates, simply the adhesion stability between the tyre RECYCLING BRAKING ENERGY using data gathered by the vehicle’s and road,” as Professor Xu explains. In addition to these areas relating to slip driven vehicles, and enhancement drive motor. “These studies proposed prevention, Professor Xu’s team have of the adhesion stability. a real-time detection method of vehicle “This study revealed a new detection also studied how the braking energy adhesion parameters for the first time, mechanism of tyre-road adhesion,” of electric vehicles can be recycled. and his colleagues at Shanghai University can be calculated with the electrical including the friction coefficient and Professor Xu continues. “A novel As they slow down, vehicles convert their and Shenzhen Institutes of Advanced parameters of the drive motor,” wheel slip-ratio, using only the motor’s concept of force transfer factor and kinetic energy into heat in their brakes. Technology, Chinese Academy of Professor Xu explains. voltage and current,” says Professor Xu. Sciences, have identified several areas where electric vehicles offer In the closed-loop feedback system In the patented system, data from improvements in safety, control, Professor Xu describes, data from devices which detect the voltage and energy efficiency over the vehicle’s motor is fed into an onboard and current of the vehicle’s motor polluting vehicles; computer, which calculates how the are fed into a processing unit and paying particular torque of the motor needs to adjust compared with the speed of the attention to to increase the adhesion force, before vehicle, allowing the computer maximising their sending its instructions back to the motor. to calculate the rate at which wheel performance on Tests using computer simulations revealed slipping is occurring. Through both slippery road surfaces. that this integrated control scheme could simulations and, for the first time, Through both realistically improve an electric vehicle’s physical experiments, Professor Xu’s simulations and real driving and braking force, as well as its team showed that slipping could experiments, the adhesion stability, even when a driver be successfully calculated, even researchers have has lost control of the vehicle. The team’s when the design of the vehicle’s motor designed and simulations proved that the technology is varied. This detection mechanism rigorously is entirely possible with electric would become an important basis The relationship between the speed of the wheel, the vehicle’s speed, brake torque and the tyre force tested vehicles, and paved the way for later for the team’s future studies. or vehicle brake force is a crucial calculation. www.researchfeatures.com Behind the Research Professor Guoqing Xu E: [email protected] T: +(86)13671588619 W: www.shu.edu.cn W: my.shu.edu.cn/en/10010264 Research Objectives References Two of the possible vehicle set-ups. Professor Xu’s research interests include electric vehicle Xu G, Xu K, Li W (2013). Novel estimation of tyre-road friction control, energy processing, and automotive electronics. coefficient and slip ratio using electrical parameters of traction In previous studies, researchers have motor for electric vehicles. International Journal of Vehicle proposed that electric vehicles could The research has made a breakthrough Autonomous Systems, 11(2-3), 261-278. convert this energy back into electricity, allowing for longer journeys without compared with the traditional vehicle Detail Xu G, Xu K, Zheng C, Zahid T (2016). Optimal operation point a need for frequent recharging. Such dynamics control method. Professor Guoqing Xu detection based on force transmitting behavior for wheel slip a system would make vehicles highly Room 617 No 9, Lane 333 prevention of electric vehicles. IEEE Transactions on Intelligent Transportation Systems, 17(2), 481-490. safe and energy efficient, but presents adhesion based on a knowledge-based be used to minimise slipping in its Nanchen Rd significant challenges in ensuring that methodology in a hierarchical control brakes. In a successful conclusion to Baoshan District Xu G, Xu K, Zheng C, Zhang X, Zahid T (2016). Fully electrified as much of a vehicle’s braking energy structure, and a technique for achieving their series of studies, the researchers Shanghai regenerative braking control for deep energy recovery and is fed back to its onboard energy the deep energy recovery of electrified demonstrated that a stable, high- P.R . C hi na maintaining safety of electric vehicles. IEEE Transactions on storage system as possible. vehicles with the maximum adhesion performance energy recycling system Vehicular Technology, 65(3), 1186-1198. control,” Professor Xu explains. “Results can be integrated