Investigation on the oscillation characteristics and performance prediction of a linear range extender: An analytical and numerical combined method

Linear range extender (LRE) system is directly coupled with free piston engine and linear motor and has great application potential in extended-range electric vehicles. In this paper, an analytical and numerical combined method was adopted to investigate the effect of key design parameters on the design and performance prediction of an LRE system. The results showed that the energy input and consumption reach a balance state, the LRE system maintains a stable steady vibration. Increasing the system load will reduce the piston operating stroke. The peak operating velocity of the piston, the average operating velocity of the piston gradually decrease, the operating frequency and the output power decreases as the load increases. When S/B is 0.8, the system output power reaches 4.5 kW, and when S/B is 1.2, the output power is only 2.2 kW. When the mover mass is 3.0 kg, the system output power reaches 3.8 kW, and when the mover mass is 8.0 kg, the output power is only 2.4 kW. When the excess air ratio increases from 0.8 to 1.2, the peak piston speed was reduced from 6.79 m/s to 6.03 m/s, the average piston operating speed was reduced from 5.30 m/s to 4.96 m/s, and the system operating frequency was reduced from 51.2 Hz to 47.96 Hz. If the LRE system wants to have stronger resistance to load fluctuations, it should choose a larger S/B ratio and a relatively larger mover mass during design. In order to pursue higher power output, the S/B and mover mass must be relatively small.