Research On Damping Characteristics And Semi-active Control Strategy Of Hydraulic-electromagnetic Energy Regenerative Suspension System

This dissertation proposed a novel suspension system named Hydraulic-electromagnetic Energy Regenerative Suspension(HERS), whose key component is a Hydraulic-electromagnetic Energy Regenerative Shock Absorber(HERSA). The principle of HERSA proposed in this dissertation is as follows: during the compression stroke, the oil in the upper section of cylinder was driven by the piston and flew through a check valve, and then flew to the inferior section of cylinder.During the extension stroke, the oil flew through the check valve to a hydraulic motor, which drove the electric motor and transferred the pressure energy of oil into electricity. The advantages of the HERSA are as follows: firstly, it could be matched with traditional vehicle suspension easily, so the HERS could be used as a traditional suspension; secondly, HERSA could harvest vibration energy; thirdly, it could work as a semi-active suspension by controlling the generator. This dissertation presents the theoretical studies the external characteristic and impact factors of HERSA, magnitude-frequencycharacteristic and key components matching method of HERS, regenerative characteristic of HERS, and semi-active control strategy of HERS. The main research works are as follows:A HERSA with a half hydraulic rectifier was proposed, and its external characteristic and impact factors were analyzed. Firstly, the mathematical model of damping force was derived. With the purpose to investigate the effects of the parameters of HERSA on external characteristic, the single parametric variation method was used, and at each simulation, the selected parameters are increased by 10% of the initial value, while other parameters kept constant. Then, the test bench was constructed, and the evaluation results showed that the model of HERSA was correct. Lastly, an integrated HERSA was trial-manufactured. The research results showed thatthe external characteristic curve of HERSA was close to the traditional absorber, which make the HERSA match with the traditional suspension easily.The magnitude-frequency characteristic of HERS and parameters matching of key parts in HERS were investigated.Selected body acceleration, suspension deflection and relative dynamic load as suspension performance indexes, the mathematical expressions of magnitude-frequency characteristicof suspension performance index were deduced based on the math equations of two degree of freedom(DOF) suspension model and math model of HERSA. The effects of hydraulic motor displacement, orifice area of check valve and inner diameter of hydraulic pipelines on the magnitude-frequencycharacteristic and time domain statistical characteristic were analyzed. On this basis, the matching method of rotation speed, torque of hydraulic motor and electric motor was proposed.A fourteen DOF vehicle dynamic model was constructed, the virtual road tests were carried out based on fourteen DOF vehicle model with HERS. The simulation work conditions which can reflect the vehicle roll, pitch, vertical vibration were selected. The effects of hydraulic motor displacement, orifice area of check valve and inner diameter of hydraulic pipelines on the vehicle body roll angle, roll angular velocity, pitch angle and so on were analyzed. The simulation works provided basis for HERS matching work.The math expression of suspension dissipation energy was deduced based on two DOF suspension model. Orthogonal experimental design method was used in simulations. In the simulation processing, the variation of relative damping factor, mass ratio and stiffness ratio were defined within reasonable range. The analysis results showed that the impact factors of dissipation energy ranked in a descending order were tire stiffness, unspring mass, spring mass, suspension stiffness, suspension damper. Meanwhile, the suspension dissipation energy increased with the rise of the tire stiffness, unspring mass, spring mass, and decreased with the expansion of suspension stiffness, suspension damper. The road tests were carried out for validating the simulation results. Then the energy harvest efficiency was analyzed through the bench test of the integration hydraulic-electromagnetic energy regenerative shock absorber.According to the system principle of HERS, the damping force during extension stroke could be controlled, but not in compression stroke. This characteristic was different from the traditional semi-active suspension system. So, the passive suspension model, traditional semi-active suspension model, HERS model were constructed based on two DOF model. And the skyhook control and LQG control were used in simulation tests. The simulation results showed that hydraulic-electromagnetic energy regenerative semi-active suspension could improve the main index parameters of suspension in certain extent, but because of the uncontrollable damping force during compression stroke, its controlling effect was worse than the traditional semi-active suspension for body acceleration, but better than traditional semi-active suspension for suspension deflection in high frequency band.