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 into electric vehicles, Bio Chen J, Xu G, Xu K, Li W (2012, June). Traction control for In another 2016 study, Professor show that the energy recovery improves even in unknown road conditions. Professor Xu received his PhD in electrical engineering from electric vehicles: A novel control scheme. In 2012 IEEE Xu and colleagues approached the the driving range by more than 25%.” Zhejiang University before joining Tongji University, where International Conference on Information and Automation, problem by again considering how the PROMISING POTENTIAL he was awarded his Professorship in 2000. He was Research 367-372. IEEE. transfer of force can be maximised, Again, using both simulations and FOR ELECTRIC VEHICLES Professor at The Chinese University of Hong Kong, Director this time between the wheels and experiments, Professor Xu’s team Through these four areas of study, of the CAS/CUHK SZ Institute of Advanced Integration the brakes. “This study proposed a proved that onboard processing using Professor Xu and his colleagues have Technology, Shenzhen, China, until 2015. He has been method for estimating the maximum data from a vehicle’s drive motor can shown that electric vehicles could a Professor at Shanghai University since 2016. realistically allow for greatly improved Personal Response braking systems and traction control Funding when compared with traditional Delt Environment & Educational Development Foundation vehicles. “The significance of the Your research has made important strides towards research includes an improvement Collaborators the improvement of energy-saving and safety of of the energy efficiency via braking • Dr Xu Kun, Associate Professor, Shenzhen Institutes electric-driven vehicles. What’s next for your research? energy recovery for electrically-driven of Advanced Technology (SIAT), Chinese Academy We will promote the application of research results vehicles, and the enhancement of of Sciences in the automotive industry. As it touches on the existing the adhesion stability,” Professor Xu • Dr Yang Ying, Associate Professor, Shanghai University active safety system of automotive industry, choosing a summarises. “The research has made reasonable industrialisation route is very important, such as integrating the new technology in the existing TCS/ABS a breakthrough compared with the system, or developing a new electrified TCS/ABS system. traditional vehicle dynamics control Furthermore, we will consider promoting the applications method, which adjusts the driving of research results in electric-driven rail vehicles. braking force based on the mechanical braking force distribution.”

The significant experiments and simulations carried out in the team’s studies prove that these improvements can push the capabilities of electric vehicles beyond those of their fossil fuel-burning counterparts. With the assurance that electric vehicles can be safer, more reliable, and more energy efficient than traditional vehicles, a

Testing in different conditions, e.g. a road with low-grip wet iron plates, gives different optimal transition away from traditional cars operation points depending on the conditions. looks set to ramp up in the near future.