Abstract
Regenerative braking can significantly improve the energy efficiency of hybrid and electric vehicles, and many studies have been carried out in order to improve and optimize the energy recovery of the braking energy. In the paper, the optimization of regenerative braking by means of braking force modulation is analysed, with specific application to the case of cars converted into Through-the-road (TTR) hybrid vehicles, and an optimal modulation strategy is also proposed. Car hybridization is an emerging topic since it may be a feasible, low-cost, intermediate step toward the green transition of the transport system with a potential positive impact in third-world countries. In this case, the presence of two in-wheel-motors installed on the rear axle and of the original mechanical braking system mounted on the vehicle can result in limited braking energy recovery in the absence of proper braking management strategies. A vehicle longitudinal model has been integrated with an algorithm of non-linear constrained optimization to maximize the energy recovery for various starting speed and stopping time, also considering the efficiency map and power limitations of the electric components. In the best conditions, the recovery can reach about 40% of the vehicle energy, selecting the best deceleration at each speed and proper modulation, and with a realistic estimate of the grip coefficient.
Highlights
Considerable research effort has been spent by universities and the automotive industry on methodologies and control algorithms to enhance the effectiveness of regenerative braking [5,6,7,8]
The feasible braking region is limited by the green line, which slope is such that a sufficient pedal sensitivity to the driver is kept. This aspect is peculiar where braking occurs the without grip loss.ofOf course, the maximum energy recovery is for hybridized vehicles, and requires development specific techniques to maximize achieved when the rear braking force keeps close to the blue line, and the distance between the energy recovery
The best conditions correspond to a deceleration ranging from 2.7 to 3.7 km/h per second, as shown in Figure 18, while in Figure 19, the optimal braking distance for each starting speed is presented. This is useful for possible application in a real-time control framework in determining the best braking intensity for a given starting speed to achieve the maximum energy recovery
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. While many topics associated with regenerative braking have been largely studied, further research is needed to adapt this technique to vehicles with specific architectures, in which the general concepts are not fully applicable This is the case of the hybridized vehicles, obtained by conversion of traditional cars through the adoption of two-wheel motors in rear wheels that transform the car into a TTR (through-the-road) parallel hybrid vehicle [20]. In an HEV with that configuration, one axle of the vehicle axes (usually the front one) is driven by the thermal engine, while the other axle (usually the rear one) is driven by an electric propulsion system This architecture, currently adopted on various ranges of hybrid vehicles, is widely studied in the technical literature because it gives the possibility of being used for the conversion of conventional vehicles into hybrid vehicles [21,22]. Electric braking on rear wheels will occur with
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