Pure Electric or Hybrid: Which Will Revolutionize Formula Student?
Is pure electric or hybrid the future? This has been a topic of debate in the industry. Today, we invite Hao Zheng, a technical officer from the China Society of Automotive Engineers and the Formula Student China, to share his insights on the design and simulation of hybrid electric cars for Formula Student competitions.
Hao Zheng (second from right in the above photo) graduated from Wuhan University of Technology. As a freshman, he joined the university’s formula student team and was responsible for designing the transmission and steering systems. For his undergraduate thesis, he researched energy management and vehicle power control strategies based on parallel hybrid systems, achieving excellent results at the university level. After graduation, he joined the China Society of Automotive Engineers as a technical officer for Formula Student China, responsible for team organization, technical document review, and international exchanges.
Table of Contents
Pure Electric or Hybrid?
The year 2024 is significant for China’s passenger cars. With advancements in electric drive technology, energy storage technology, and vehicle energy efficiency management, many automakers have launched new hybrid models and key technologies, marking a surge in hybrid technology development.
Some view hybrid vehicles as a “compromise” technology representing “backwardness,” while pure electric vehicles are seen as the “future” of clean energy. However, current pure electric technology still faces significant challenges, such as charging speed, urban electricity capacity, and usage scenarios under all conditions. China’s energy strategy requires a diversified energy structure while achieving carbon peaking and carbon neutrality. It’s foreseeable that internal combustion engine technology will not disappear for a long time. Making internal combustion engines great again involves sustainable power solutions like hybrid technology and zero-carbon internal combustion engines.
In various Formula Student competitions, hybrid rules have been gradually introduced:
- In April 2023, the organizing committees of the Formula Student Austria, Hungary, Czech Republic, and two other countries jointly released the technical rules for hybrid electric racing cars.
- In October 2024, the 2024 Formula Student Rules (FS Rules 2024), primarily authored by the German competition’s organizing committee, officially opened up to hybrid technology.
- In November 2024, the Formula Student China also adopted hybrid technology rules. To increase the proportion of electric drive power and reduce the complexity of hybrid technology, the Chinese competition rules set a maximum weight limit of 6kg for battery cells (compared to 3kg in European competitions). In the Formula Student China Combustion (FSCC), three teams utilized hybrid technology in 2024: Jilin University, Harbin Institute of Technology at Weihai, and Liaoning University of Technology, where Jilin University retained their championship of FSCC with an aerodynamically driven long-wheelbase configuration, and a 690cc single-cylinder engine with the hybrid technology.
Design and Simulation of Hybrid Formula Student Racing Cars
Hybrid electric systems are mainly divided into series, parallel, and combined configurations, with parallel further divided into P0, P1, etc., based on motor placement. Although the Formula Student rules do not restrict configuration structures, P4 is expected to be the mainstream configuration.
Compared to passenger car hybrid systems, Formula Student hybrid systems are much simpler. One reason is the relatively low maximum voltage of the drive system (the rules require it to be within 60V), reducing risk. Another reason is that the main challenges of hybrid systems lie in optimizing economic efficiency and comfort, while FS cars have lower economic considerations and do not need to address parking power generation or smooth shifting.
Here, we focus on the design process of the P4 configuration shown in the picture below. A common P4 configuration for FS cars involves the internal combustion engine driving the rear axle and the motor driving the front axle. The main advantage of this structure is its simplicity and ability to achieve all-wheel drive, which is a significant advantage in racing engineering for effectively utilizing tire adhesion. In 2024, three Chinese hybrid teams (Jilin University, Liaoning University of Technology, and Harbin Institute of Technology (Weihai)) adopted the P4 configuration.
Regardless of the configuration, the main design tasks for FSAE hybrid systems include transmission system design, drive control strategy design, battery box design, and vehicle electrics. Next, I’ll share some thoughts on the design and simulation of these components under the P4 configuration.
Electric Drive and Transmission Design
The transmission system design involves selecting transmission ratios, mechanical modeling, and simulation verification. Traditional FS car transmission ratio selection requires lap time optimization software for simulation, determining the transmission ratio of the main reducer based on lap times and acceleration times.
In hybrid systems, transmission ratio design is more complex than in single-power-source cars. Lap time simulations often directly relate to hybrid system control strategies, and most lap time optimization software cannot directly provide hybrid system lap time simulations. Transmission ratio design in hybrid systems can separate the internal combustion engine and motor for calculation. The internal combustion engine’s reduction ratio can still be calculated using lap time optimization software, treating it as a pure internal combustion engine car.
The motor drive’s initial transmission ratio selection should consider the required torque at maximum acceleration. Subtracting the output torque of the internal combustion engine gives the motor’s maximum output torque. The maximum transmission ratio can be obtained based on the motor’s external characteristics. The designed maximum car speed should be within the motor’s speed range, determining the minimum transmission ratio. After calculation, the motor transmission ratio needs verification to ensure that the common speed range in endurance races is within the constant torque zone. A simulation platform for control strategies can be introduced for further calculations.
Control Strategy Design and Simulation
The P4 configuration’s control strategy can be divided into power distribution between electric and combustion drives, front axle dual-motor torque distribution, regenerative braking strategy, etc. In fact, hybrid system control strategy design does not necessarily require modifications to the internal combustion engine part. The motor’s control strategy can match the internal combustion engine’s characteristics. Aaron, the team leader at Karlsruhe University of Applied Sciences, described it as: “Our internal combustion engine doesn’t know it’s part of a hybrid.”
The first step in power source power distribution is pedal power demand division. The main idea of pedal demand division is “peak shaving and valley filling,” meaning compensating motor power in the external characteristic curve to make power output almost linear. The power demand for different pedal openings can also be calculated.
The next step is power source power matching. The engine’s output power at the corresponding throttle opening is easily obtained. Based on the current conditions, the motor drive power demand can be calculated. It’s worth noting that power source distribution strategies need to consider changes in driving force distribution caused by vehicle pitch and aerodynamic load transfer.
After establishing a power source distribution strategy, a track model needs to be built for lap time simulation. Lap time simulation can use Simulink and other vehicle dynamics simulation tools for co-simulation.
MathWorks provides a simulation platform “Hybrid Electric Vehicle Model in Simscape”, which can be modified to for designing FSAE hybrid system: https://www.mathworks.com/matlabcentral/fileexchange/92820-hybrid-electric-vehicle-model-in-simscape
This Simulink-based hybrid EV simulation platform includes mathematical models of internal combustion engines, motors, transmissions, and vehicle dynamics.
Beside the simulation platform, a video tutorial series provided by MathWorks on hybrid vehicle development could also be very helpful: https://www.mathworks.com/videos/series/hybrid-electric-vehicles.html
Summary and Outlook
China’s automotive industry has entered a new development stage, and its future height depends on the current dream-pursuing students. Matching and controlling multiple power sources remain challenging in the passenger car industry. Compared to fuel and electric cars, hybrid racing cars demand higher simulation and control technology. Here I just introduce the initial technical route from fuel to hybrid technology. As more teams adopt hybrid technology, I believe they will explore more diverse design routes.
I hope students can continuously explore hybrid technology, moreover, can actively innovate and share, keeping improving the Formula Student community. As a judge of FSC said: “We hope Formula Student is a platform for comprehensive technical practice, not just a high-end version of mechanical workshops.” Finally, I want to conclude with the slogan on the rear wing of the Hunan University of Technology team in FSC: “Where the nation lags, is where we strive.”
- Category:
- Automotive
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