Study on performance parameters of retarder in mountain condition of hybrid electric vehicle

In mountain driving scenarios, the continuous braking demands of vehicles pose significant challenges to the performance and reliability of braking systems. Traditional fuel-powered vehicles primarily rely on friction brakes for deceleration, which face issues such as high thermal fade risks and severe brake wear. While pure electric vehicles can utilize motor energy recovery to provide braking force and recover energy, their braking capacity is limited by the maximum regenerative torque of the motor. Moreover, when the battery State of Charge (SOC) is high, the energy recovery function may be restricted or disabled to protect the battery, leading to a sharp reduction or complete loss of braking torque—a safety hazard. Range-extended hybrid vehicles combine the advantages of both engine and electric drive systems. During long downhill operations, their motors can also serve as priority decelerators for efficient energy recovery. However, similar to pure electric vehicles, their motor braking capacity has an upper limit. When the battery reaches full charge (SOC reaches its maximum), the motor can no longer provide braking torque, and single-motor regenerative braking cannot meet continuous braking requirements. Therefore, this study focuses on braking strategies for range-extended hybrid vehicles in mountain driving conditions, specifically investigating the supplementary braking torque required by decelerators to ensure driving safety when motor capacity is insufficient or functions fail. This study establishes a vehicle dynamics model using slope gradient and length as core input parameters. By analyzing total braking demands under various slope-length combinations and deducting the actual regenerative braking force available from the motor, it precisely calculates the minimum braking torque required by the retarder. The findings aim to provide theoretical foundations for optimizing braking system matching and safety control strategies in hybrid electric vehicles operating within complex mountainous environments.