Chongbo Jing

On–off motion of a hydraulic free-piston engine

The current paper presents the on–off characteristics of a compression ignition single-piston hydraulic free-piston engine. A pilot control circuit and a control method for on–off control of the engine are introduced. Detailed piston motion under on–off control of the engine is investigated. The results indicate that the piston on–off motion of 1 cycle can be divided into a pilot phase and a wave phase. The piston motion in the pilot phase is determined by the flow capacity of the frequency control valve. The piston acceleration during the accelerated compression process peaks in the pilot phase. The wave phase consists of a rebound stage, a decaying stage and a creep stage. The rebound stage determines the initial conditions of the other two stages and affects the piston frequency control. The control method proposed is immune from the bottom-dead-centre cycle variation. A high piston frequency results in a better engine fuel economy.

Architecture of a Hydraulic Hybrid Vehicle with Pressure Cross-Feedback Control

A hydraulic hybrid vehicle equipped with the hydraulic transformer is proposed. The hybrid system features in rotary swash plate type hydraulic transformer and pressure cross-feedback control. The full numerical model has been built. Extensive simulated and tested results are given. The contributions of the hydraulic transformer dynamics to the hydraulic hybrid vehicle performance are investigated. The proposed hydraulic hybrid vehicle can achieve the ideal vehicle dynamic performance by adjusting the hydraulic transformer controlled angle. The switching between the driving and the regenerative breaking of the hydraulic hybrid vehicle is realized by the pressure cross-feedback control. The propulsion mode of the hydraulic hybrid vehicle can be changed automatically. The larger hydraulic transformer controlled angle realises a higher driving pressure while the smaller one achieves a higher driving flow. Due to the small inertia of the hydraulic transformer, the hybrid system is able to satisfy the speed requirement of the driver.