Abstract
In this paper, the tuning process of a regenerative braking system for a full electric Formula Student car is reported. Experimental results will be discussed and recovered energy will be measured. In order to obtain the best tuning some preliminary requirements have been decided: no-slip motion of traction wheels during braking phase, no over current and over voltage of Li-ion cells and the best feeling from the braking pedal for the driver. The main target of the regenerative braking system is to obtain the maximum recovered energy during the Endurance event in a typical Formula Student Competition (FS Germany, Hockenheim ring). First, an accurate estimation of the admissible braking torques with the tires used was carried out, starting from the magic formula of Pacejka of the tires. The maximum electric braking torque that the installed engine can provide at various speeds was then estimated, compatibly with the charging currents allowed by the storage system. Subsequently, a mechanical regulating device for regenerative braking was designed and described here, installed directly on the gear lever system that connects the brake pedal to the brake pumps. The proposed system is able to appropriately delay the entry into action of the hydraulic brake pumps and this delay is mechanically adjustable by acting on threaded pins. In this way, the interval of actuation of the brake pedal which activates only the electric braking can be adjusted and tuned. Finally, the overall project was tested on the track, in order to validate the hypotheses previously calculated and determine the setting capable of optimizing the energy recovered during a test equivalent to the Endurance event, compatibly with the constraints of the installed systems on board.
Highlights
In this paper, the tuning process of a regenerative braking system for a full electric Formula Student car is reported
The maximum electric braking torque that the installed engine can provide at various speeds was estimated, compatibly with the charging currents allowed by the storage system
Main target of this case study is to set the best configuration of the regenerative braking device in order to maximize the total recovered energy during braking phase in a typical Formula Student Endurance Event
Summary
The car covered by this paper responds entirely to the dictates of the Formula Student rules, both as SAE (society of automotive engineers) and FSG (Formula student Germany). The car is equipped with 6.3 kWh energy storage (Figure 2) in 90s3p configuration using li-po pouch cells, with 380 V of maximum voltage and capable of 150 A of burst charge current, to be considered in the regenerative braking system design. Main target of this case study is to set the best configuration of the regenerative braking device in order to maximize the total recovered energy during braking phase (without rear wheels locking) in a typical Formula Student Endurance Event. Considering all the system constrains [1]; it will be very important information in order to design the new storage system for Season 2021 car. In order to develop the project of a Formula Student energy storage system, information is needed but the most important one is the energy required to complete endurance event. It is needed to choose the right configuration of cells in series and parallel to comply with battery pack voltage (nominal and maximum) in the best matching possible with inverter voltage range
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