Study On Braking Performance Of Parallel Hybrid Electric Truck

The process that using brake devices makes the vehicle slow down or stop is called braking. As far as hybrid electric vehicles, the brake system consists of two kinds:the traditional mechanical and energy regenerative brake system. The torque generated by the former can be acted on wheels, directly; Torque generated by the latter is transmitted to wheels by transmission. During braking, how to distribute properly brake torque between the two devices is premise of stability of vehicle and also one of the important content of study for hybrid electric vehicle.In this paper, parallel hybrid electric trucks can be considered as the main object of the research. Consider the analysis of the regenerative brake mode as starting point, point to brake process with gear shifting, find shortage of preceding control scheme, make efforts to improve braking performance of hybrid electric trucks, analyze deeply the properties of brake devices, and present control schemes and strategies for the sub-ject. The research problems embody retrieving the kinetic energy of vehicle as much as possible satisfying vehicle safety and the comfort requirement of driver. The main research work is as follows:(1) According to requirements of brake control of hybrid electric truck, the pa-per will give the mathematical model of the conventional mechanical brake system, the regenerative brake system (electrical, super capacitors, inverters) driveline (motor re-ducer, automated manual mechanical gearbox, main gear, drive shaft) and wheels. This provides the basis for brake torque control and simulation for hybrid electric truck.(2) Based on the brake system model, the coordinated torque control scheme is p-resented between the conventional mechanical brake system and the regenerative brake system, and the stability of the closed system is proved. The braking process can be divided into brake with no gear shifting and brake with gear shifting. In the former stage, approximate proportional-integral feedback controller is designed and stability is proved under the condition of the measurable brake torque and unmeasurable brake torque. In the latter stage, the two strategies are presented:motor advanced compensa-tion strategy and motor-synchronizer gears pressure compensation strategy, which en-sures successful completion of gear shifting and reduces the vibration of brake torque.(3) Based on equivalent model of super-capacitor, observer to estimate voltage of real capacitor is presented. Under the condition of known model parameter, the actual capacitor voltage is estimated by using observer similar to Luenberger type, and the estimated results is analyzed on sensitivity of observer parameters and the model param-eters. Under the condition of unknown model parameter, the least squares identification method with forgetting factor is used to estimate the real model parameters, and then the estimated parameters can be used as parameters of above observer to estimate real capacitor terminal voltage. With the consideration of disturbance effect in real process, Gaussian white noise is considered as real state disturbance and output measurement disturbance. The extended Kalman filter is designed to estimate simultaneously mod-el parameters and real capacitor terminal voltage.