The Characteristics Research Of Independent Variable Speed Pump Control Steering System Of Wheel Loaders

The wheel loader,as a large ownership and commonly used construction machinery,are widely used to loading and transporting loose materials.In the country alone,there are nearly 2 million wheel loaders,which grow at the rate of about 20 thousand vehicles per year.In conventional wheel loader,an engine driving fixed displacement hydraulic pump is adopted to supply oil for both the hydraulic steering system and working device.When the hydraulic steering system is working,for its priority over the working device in power supply,the working device is stopped working.Due to the required power by the steering system is much smaller than that of working device,there is a large of relief and throttling loss during steering operation.Especially in the steering process with high running speed,the engine rotational speed is high,and the supplied oil by the hydraulic pump is large which make a great amount of oil flow back to the tank through the relief valve.That significantly increases the energy consumption.Therefore,reducing the relief loss and realizing on-demand oil supply of the steering system is essential to improve the energy efficiency of steering system of wheel loaders.Therefore,under the assistance of national natural science foundation of China(U1510206),a novel variable speed and displacement independent control principle is proposed to reduce these energy losses,in which a fixed displacement hydraulic pump driven by a servo motor is used to supply oil for steering system independently,and the supplied oil is fully consistent with the demanded flow for steering operation.The principle is applied to the redundant open circle pump controlled flow matching steering system.In the system,the rotational speed and angle of the servo motor are determined by the angular velocity and rotational angle of the steering wheel.Thus both steering speed and angle of the wheel loader can be controlled.To enhance the safety and reliability of the steering operation,the original steering system is still retained.When the oil supply unit of the new system is out of order,the original system is automatically switched on through a solenoid valve.Based on the simulation and experimental results,by using the proposed system,the energy consumption of the proposed steering system can be reduced by 16%as compared to the conventional steering system,owing to the reduction of throttling loss and elimination of relief loss.By working8 hours and turning 1000 times a day,and calculating 300 days per year,a machine can save about 83.6 L of fuel.In 2016,there are about 2 million wheel loaders in the Chinese market.If this novel steering system is adopted,the carbon emissions of 3.3*104 T will be reduced per year.In addition,the pressure fluctuation can be reduced from 1.2 MPa to 0.6 MPa as compared to the conventional system,indicating an improvement in the stability of the steering operation.Furthermore,the safety and reliability enhancement strategy is also verified experimentally.In order to further reduce these energy losses,an energy-saving closed circle pump controlled flow matching steering system is proposed.All the hydraulic valve of the original steering system are removed.So,the required flow of the hydraulic steering cylinder is supplied by the constant pump,independently and directly.The servo motor speed is set proportional to the steering speed of an independent electric controlled steering wheel.Thus the output flow and the output volume of the pump match with steering speed and the steering angular of the wheel loader,respectively.To verify the feasibility of the steering system,firstly,a co-simulation model of it is built in the SimulationX software.Then,in order to validate the dynamic characteristics of the steering system,the test prototype of it is established.Finally,energy consumption of new steering systems is analyzed.Based on the results,by using the energy-saving closed circle pump controlled flow matching steering system the throttling loss,the overflow loss and the median unloading loss of the steering process are eliminated,the energy consumption is reduced by 56%.A wheel loader can save about 83.6 L of fuel.If this energy-saving steering system is adopted to all wheel loaders in china,the carbon emissions of 3.3*10~4 T will be reduced per year.After adding the pressure accumulator,the pressure fluctuation can be reduced from 1.2 MPa to 0.3 MPa as compared to the conventional system during the steering process a,and the steering process is more stable and rapid.Moreover,the higher the initial pressure of the oil filling system,the faster the response of the closed circle pump control steering system.