Leon, J., Garcia, J., Acero, M., Gonzalez, A. et al., "Case Study of an Electric-Hydraulic Hybrid Propulsion System for a Heavy Duty Electric Vehicle," SAE Technical Paper 2016-01-8112, 2016, doi:10.4271/2016-01-8112.
In order to improve efficiency and increase the operation of electric vehicles, assistive energy regeneration systems can be used. A hydraulic energy recovery system is modeled to be used as a regenerative system for supplementing energy storage for a pure electric articulated passenger bus. In this study a pump/motor machine is modeled to transform kinetic energy into hydraulic energy during braking, to move the hydraulic fluid from the low pressure reservoir to the hydraulic accumulator. The simulation of the proposed system was used to estimate battery savings. It was found that on average, approximately 39% of the battery charge can be saved when using a real bus driving cycle.