Torsional vibration analysis of planetary hybrid electric vehicle driveline

Abstract: Noise, Vibration, and Harshness (NVH) are important factors with which to evaluate a vehicle. The automotive industry pays more and more attention to NVH to meet the growing comfort expectation of customers. Therefore, the noise and vibration analysis of the hybrid electric vehicles (HEVs) is significantly meaningful. In order to investigate the torsional vibration behavior of a planetary power split hybrid electric vehicle (HEV), the MEEBS hybrid driveline was studied by the dynamic equation. The compound planetary gear set in this HEV consists of a ring, a carrier, a small sun gear 1, a big sun gear 2, three short planets, and three long planets. All the short and long planets are mounted on the carrier. The compound planetary gear set has two rows. The first planetary row is made up of sun gear 1, short planets, and the ring, while the second planetary row consists of sun gear 2, short planets, long planets, and the ring. The planetary rows share the carrier and the ring. The short planet and corresponding long planet engage with each other. The sun gear 1 and sun gear 2 are connected to electrical motors E1 and E2, respectively. Both motors are permanent magnetic synchronous machines. The carrier was connected to the engine through a torsional damper. All of the system output torque was exported to the ring, and then to the wheels through the reducer, differential, and halfshafts. Compared with the traditional Ravingneaux gear set, the power-split system can increase the lever efficiency of the second row to reduce the requirement power of E2, leading to decreased system cost. Compared with the traditional Ravingneaux gear set, the power-split system can increase the lever efficiency of the second row to reduce the requirement power of E2, leading to decreased system cost. In order to realize the optimizing control in electric-only mode and make the engine work in the optimum working zone, the power-split system also has two brakes to lock the carrier and S1, respectively. Numerical results for natural frequencies and corresponding modes of the hybrid driveline are produced. The forced torsional vibrations under different excitations and parameters were analyzed. The main factors that influence the torsional vibration of the driveline were found out. The results show that the low-order frequencies are focused on the vehicle and wheels, while the high-orders are concentrated on the differential, reducer, and planets. The results also show that the amplitude of the torsional vibration of the driveline is the lowest when the damping and stiffness of the torsional damper were 15 N·m·s/rad and 618 N·m/rad respectively and the rotational inertial of flywheel was0.42 kg·m2. The research can provide a reference to improve the vibration and noise levels of HEVs.