Serial regenerative braking system with auxiliary pedal for hybrid converted trucks

Abstract

This study proposes implementing a regenerative braking system for parcel delivery hybrid trucks which were obsolete diesel one ton trucks and converted. Normal diesel one ton truck has no Brake Control Unit(BCU), and the brake pedal and brake pad are hydraulically directly connected. Therefore, a separate device is required to operate regenerative braking, and a method of installing an auxiliary pedal on an existing brake pedal is proposed. The Interior Permanent Magnet Synchronous Motor(IPMSM) used in hybrid trucks is analyzed and the operating area where regenerative braking is possible is set up.

A regenerative braking control function is proposed, which provides the corresponding regenerative braking force required by the driver by inputting the degree which the auxiliary pedal is pressed and the current rotor speed within available maximum regenerative braking torque. Since the transmission of diesel trucks is still used, the brake force on the wheels of hybrid trucks and IPMSM varies with the gear stage of diesel trucks, and maximum regenerative braking power is limited to prevent from damage caused by high power charging for battery. When regenerative braking, braking force is offered to only rear wheels because hybrid trucks are rear wheel drive vehicles. Therefore, vehicle stability problem is considered by drawing front-rear braking force distribution curve of hybrid trucks.

It was confirmed that proposed regenerative braking system improvs fuel efficiency, NOx and Particulate Matter(PM) emissions by simulation with Representative Driving Cycle of Delivery Truck(RDCDT), Urban Dynamometer Driving Schedule(UDDS) and Federal Test Procedure-75(FTP-75). Lastly, an auxiliary pedal was set up on the hybrid truck, and the regenerative braking system and ability to charge the battery was verified through experiments on the chassis dynamometer and road. In addition, recovered energy through regenerative braking was calculated. This study contributes to verifying the feasibility of implementing a serial regenerative braking system maintaining existing hydraulic braking lines and using the auxiliary pedal without BCU for rear-wheel drive hybrid converted trucks.