Novel High Energy Efficiency Linear Drive And Control Technology And Its Application In Wheel Loader

Construction machinery is the collective name of all construction and building machines such as wheel loaders,excavators,forklifts,cranes,etc.It is widely used in construction,emergency rescue,disaster relief and other fields,and is an important symbol of a country’s industrial level.It is an important symbol to measure the industrial level of a country.After decades of development,China has become a major engineering machinery manufacturing,ownership and annual production are the world’s first,the industry has also become the most likely to take the lead in the ranks of the world’s most advanced industries.Construction machinery generally uses hydraulic system to distribute and transmit power,and its energy-efficient transmission and high-precision control of flow determines the quality and core competitiveness of construction machinery.The electrification of construction machinery can significantly improve the energy efficiency of the machine,but is still in its infancy,only using electric motors instead of internal combustion engines,although the elimination of emissions pollution,but the hydraulic system is still commonly used to centralize the power source supply,multi-way valve group distribution and transmission of power multi-actuator parallel drive program,making the hydraulic system energy efficiency is extremely low,the hydraulic pump output energy only about 20-30%really do work,the machine energy efficiency is limited.Taking the most widely used wheel loader in construction machinery as an example,in2021,China has 1.8 million loaders,consuming nearly 15 million tons of fuel annually and generating about 4.5 million tons of carbon emissions annually.If the hydraulic system energy efficiency is increased by 10%,it will reduce the fuel consumption of internal combustion engine driven loaders by 28.6%from the source and emit 13 million tons less CO₂,with significant double carbon benefits,and also break through the limitation of battery capacity on the promotion and application of all-electric drive loaders,with the same battery capacity host having more working hours.The hydraulic system of the loader mainly consists of steering,lifting and bucket turning systems.In addition to the serious energy loss generated by the hydraulic valve in the process of power distribution,the three systems with different power demands use the same centralized power source to supply energy,and when only the small power demand system is working,the power source and the load are not matched and work in low efficiency conditions;in the falling condition of the lifting system,a large amount of gravitational potential energy is converted into thermal energy by the throttling effect of the valve port.In the process of lifting and bucket system working together,the difference between the two actuator loads further increases the throttling loss of the valve port and reduces the energy efficiency of the system.Therefore,the energy-efficient linear drive system and control technology is innovatively proposed.The distributed closed pump-controlled steering,lifting and bucket turning system is adopted to drive the loader,to realize the decoupling of centralized power source,to eliminate the throttling loss in the system and the load difference between multiple actuators,and to recycle the gravitational potential energy of the lifting system.By combining two hydraulic cylinders,designing asymmetric hydraulic pumps and designing integrated hydraulic cylinders respectively,the flow balance of the closed pump-controlled single-outlet hydraulic cylinder system is realized;the gravitational potential energy of the system is recycled by hydraulic means;the potential energy storage and self-weight balancing chamber of the lifting system is added to improve the efficiency of gravitational potential energy recycling and expand the application range of linear actuators;electro-mechanical linear actuators are introduced to high-precision and high-efficiency control system movement,and promote the development process of loader electrification.Further application of the proposed system to other construction machinery with internal combustion engine drive or all-electric drive can reduce the energy consumption of construction machinery from the root,accelerate the pace of energy-efficient,green,electrification and intelligent development in the field of construction machinery in China,and help achieve the strategic goal of"double carbon"in China.The main innovative results of this paper,supported by the National Natural Science Foundation of China（NO.51875385）and the NSFC-Shanxi Coal-based Low Carbon Joint Fund（NO.U1910211）,on the research work of linear drive system and control technology for energy-efficient distributed power sources are as follows.（1）For low power requirements of energy-efficient linear drive systems,a closed pump control combination hydraulic cylinder drive steering system is innovatively proposed.The hydraulic valve of the original steering system was removed,and a hydraulic pump driven by a servo motor was used to supply oil directly to the single rod steering hydraulic cylinder,and a rod chamber of the hydraulic cylinder and another rodless chamber were connected in series to realize the flow balance of the closed pump-controlled single rod hydraulic cylinder system.The servo motor is controlled by an electronically controlled steering wheel in a closed-loop displacement mode,and different speed and steering ratio steering control strategies are designed to achieve arbitrary adjustment of steering ratio and automatic steering.Through theoretical analysis,simulation optimization and experimental testing,it can be seen that the proposed system can significantly reduce the pressure shock and fluctuation in the steering process,and by adjusting the steering ratio between the steering wheel and the steering angle,the steering efficiency of the steering system can be improved exponentially,and the energy consumption can be reduced by 46%compared with the original valve-controlled steering system under the same steering conditions.（2）For medium and high power requirements of energy-efficient linear drive systems,a closed asymmetric pump-controlled lifting and tilting system is innovatively proposed to achieve the flow balance of the closed pump-controlled single-rod hydraulic cylinder on the basis of which the gravitational potential energy of the lifting system can also be recycled.According to the effective area ratio of the two chambers of the single rod hydraulic cylinder,the area of two of the distribution ports is designed to achieve the flow balance of the closed pump-controlled single rod hydraulic cylinder,while the third distribution port is connected to the accumulator to recover the gravitational potential energy of the lifting device.The closed type asymmetric pump control system is used to drive the loader lift and bucket system respectively.The simulation analysis and experimental tests show that the proposed system can reduce the system energy consumption by 55%and the gravitational potential energy recovery efficiency is 42%.（3）Innovative proposed closed pump control integrated hydraulic cylinder drive lifting system to further improve the efficiency of gravitational potential energy recovery and output power of the lifting system.The plunger rod of the single rod hydraulic cylinder is changed into a hollow structure,and the area of the new hollow chamber is designed to be equal to that of the rod chamber,and the two chambers are connected to the inlet and outlet of the hydraulic pump respectively,so as to realize the flow balance between the hydraulic cylinder and the hydraulic pump on the basis of a closed pump control circuit.The original rodless chamber of the hydraulic cylinder is connected to the accumulator to form a liquid and gas energy storage unit,which directly recycles the gravitational potential energy of the lifting device.The simulation and test results show that with the proposed system,under different load,displacement and speed conditions,the actuator can quickly and accurately complete the corresponding action in accordance with the set curve,which improves the response speed and control accuracy of the lifting system;the gravitational potential energy recovery efficiency of the lifting device can reach 52%,which can reduce the system energy consumption by 58%compared with the original valve-controlled system.Energy consumption can be reduced by 58%compared with the original valve control system.（4）Innovative electric-hydraulic dual-power hybrid drive lifting system is proposed to further improve the energy efficiency and the motorization of the system.The electric cylinder drive as the main drive and hydraulic cylinder-accumulator as the supplementary dual-power hybrid drive scheme,making full use of the advantages of high energy efficiency of electro-mechanical drive and high power density of hydraulic drive,controlling the movement state of the lifting system by electric cylinder,using hydraulic cylinder-accumulator to balance the self-weight of the lifting system and recycling the gravitational potential energy of the system with high efficiency.Experimental tests show that compared with the original valve-controlled system,the electric-hydraulic dual-power hybrid drive system can reduce energy consumption by 63%,and the system gravitational potential energy recycling efficiency is 47%.