Abstract
Hybrid electric vehicles (HEV) equipped with continuously variable transmission (CVT) adjust the motor operating point continuously to achieve the optimal motor operating efficiency during regenerative braking. Traditional control strategies consider the CVT efficiency as constant, while the CVT efficiency varies in different operating conditions. In order to reflect the transmission efficiency more accurately during regenerative braking, the CVT theoretical torque loss model is firstly established which then leads to the battery–front motor–CVT joint operating efficiency model. The joint operating efficiency model indicates that the system efficiency is influenced by input speed, input torque, CVT speed ratio, and battery SOC (state of charge). The compensatory strategy for the front motor barking force is proposed to make full use of its braking power and the CVT speed ratio control strategy is modified to maintain the optimal operating efficiency of the system. The simulations are performed under three typical braking conditions and UDDS, NYCC, US06 respectively, the results show that the modified control strategy increases the front motor braking power and improves the system operating efficiency.
Highlights
Hybrid electric vehicles (HEV) can improve fuel economy and reduce emissions significantly by regenerative braking [1,2].HEV equipped with continuously variable transmission (CVT) can further improve the vehicle energy recovery rate because a proper CVT ratio control strategy enables the regenerative braking system to operate in a more efficient region [3].At present, the research on CVT regenerative braking systems mainly focuses on the braking force distribution strategy and the regenerative braking system efficiency optimization
The research on CVT regenerative braking systems mainly focuses on the braking force distribution strategy and the regenerative braking system efficiency optimization
Considered the battery SOC and vehicle velocity as the weight factors to determine the regenerative torque and a CVT ratio control strategy is proposed for optimal motor operation [7]; Tao Deng et al Energies 2018, 11, 497; doi:10.3390/en11030497
Summary
HEV can improve fuel economy and reduce emissions significantly by regenerative braking [1,2]. HEV equipped with CVT can further improve the vehicle energy recovery rate because a proper CVT ratio control strategy enables the regenerative braking system to operate in a more efficient region [3]. Considered the battery SOC and vehicle velocity as the weight factors to determine the regenerative torque and a CVT ratio control strategy is proposed for optimal motor operation [7]; Tao Deng et al. Energies 2018, 11, x FOR PEER REVIEW force distribution strategy which took the required braking force, vehicle speed, battery SOC, and temperature as input [6]. Addition, a nonlinear sliding mode was designed to obtain actual hydraulic torquethe to cooperative achieve the control cooperative control of regenerative and hydraulic brake torquebrake to achieve of regenerative braking and braking hydraulic braking [9,10] In these studies above, they all considered the CVT efficiency as constant. Strategy, the more efficient recovery of braking energy is achieved
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