Research On The Potential Energy Regeneration System Based On The Hybrid Hydraulic Excavators

Following the "energy crisis", the demand for more environmental and fuel efficient construction machinery, especially for hydraulic excavator (HE), has been increased in response to growing concerns on the clean environment and saving energy. Most of the time, in a typical working cycle, the weight of the boom itself is much heavier than the load. When the load goes down it does not need energy, but energy losses rise up in breaking the load motion. The gravitational potential energy is dissipated into heat in the control valves of the hydraulic system. So it is required for us to make maximum use of regenerative energy for further improvement of fuel consumption and also to ensure higher system control performance equivalent to that of conventional control system. The successful application of hybrid system in construction machinery provides a new way for hydraulic excavator to achieve energy saving.The chapters of this dissertation are organized as follows.In Chapter 1, the the significance of the research on energy regeneration system (ERS) based on HEs is discussed, and some characteristics and shortcomings of kinds of ERS are analyzed. Then, the difference between the ERS based on the hybrid automobile vehicle and the ERS based on the hybrid hydraulic excavator (HHE) are reviewed. The development of ERS in construction machineries and HEs are introduced. Finally, the primary research contents of this dissertation are provided.In Chapter 2, Applying the ERS in HHE, the system has to be considered to fit its special working style, a 7-ton HE was tested and the data of the pressure of the cylinder raw chamber, the pressure of the cylinder rod chamber and so on. Then, we caculated the regenerated energy of the boom, the arm, the bucket and the swing. The typical working condition of Boom ERS based on HEs is analyzed based on the the measured working data. Then, we have proposed a Motor-generator ERS(MGERS), the mathematical model of MGERS is constructed. The effects and improvements of system dynamic response are analyzed. Secondly, united simulation of the MGERS with AMESim and MATLAB/simulink for the MGERS is carried out and the influence on the control performance of the the pipe length, the time constant of the generator and the rotary inertia of the motor and the generator is brought forward.In Chapter 3, when the boom goes down, the gravitational potential energy is converted into electric energy to be stored in the capacitor. And the motor, the generator, the capacitor is the key components. Hence, the efficiency mathematical model of the motor, the generator and the capacitor are constructed. As some parameter of the motor are unknown, we test a rig and propose a measure method to identify the unknown parameters. At last, the characteristics of efficiency of the key components in ERS are analyzed. The analyses provide rules for the control strategy applied in the two proposed ERSs which are shown in Chapter 4 and Chapter 5.In Chapter 4, In order to control the boom in quick and precise responses when the boom velocity is controlled by the motor and the generator in the ERS, a new ERS that used a proportional throttle valve to help the hydraulic motor contol the boom is proposed. here we call is JMGERS. The mathematical model of JMGERS is constructed. The effects of system dynamic response are analyzed.When the conventional boom control circuit is enabled, it works with two modes: 'Boom Up', and'Boom Down'including digging. On the contrary, the operation of the boom system with an ERS is divided into four modes:'Boom Up'with holding function, 'Boom Stop Down','Boom ER Down', and'Digging'. The working principle of the boom system is characterized by the status of the joystick and the pressure of the boom cylinder. Considering the bad control performance in the low rotational speed, the total-power loss, the efficiency of the motor and the generator, a dynamic-working-points of the generator and the motor is discussed. Then, as the displacement and the velocity sensors can not be assembled in HE, a compound control that consist of orifice control and volume control is presented. At last, a test rig is constructed, an estimated 35%-39%of the total potential energy could be regenerated at the lowering of the boom in the JMGERS and it is also shown that the JMGERS features better speed control of the boom and response characteristics than the MGERS. In Chapter 5, As the hydraulic accumulator systems have an order of magnitude advantage in terms of the power density over electric system and the energy storage density is severely limited relative to other competing technologies, an energy recovery system that combines the advantages of an electric and hydraulic accumulator is proposed, here we call is AMGERS. Then, the mathematical model of AMGERS is constructed. The effects of system dynamic response are analyzed.As the hydraulic accumulator plays a very important role in the AMGERS, it must be properly designed to offset the gap between the load power and the generator power input. The parameter matching for the AMGERS are discussed by considering economics, weight saving, installation and controllability. Then, the control strategy incuclude the working mode of the motor-generator, how to control the generator and the control valves at the lowering of the boom, how to improving the recovery effieciency when the boom stops to go down are presented.The main conclusions and achievements are summarized in Chapter 6, and the further research work is put forward.