Analysis on steering characteristics of wheel loader based on electric-hydraulic flow matching principle

Abstract: As one of the most commonly used construction project machines, wheel loader has the problems of high fuel consumption and serious emissions. On one hand, the hydraulic steering system which uses a fixed displacement pump, will produce large energy losses; on the other hand, the action of steering is frequent during working process. Therefore, reducing the energy consumption of steering system is becoming one of the key research directions. Currently, small wheel loader generally uses load sensing steering system. Although the pressure of the system can match the load, the flow of the fixed displacement pump is proportional to the engine speed and can't match the varied loads, which leads to energy losses. For this issue, a new steering control method of electro-hydraulic flow matching which adopts a servo motor to drive the fixed displacement pump independently is proposed. By this method, the ratio between cycle number of motor and angle of steering wheel changes to a certain value. The speed of motor will level off if there is no steering movement, so finally the system energy consumption can be reduced. Meanwhile, in case of motor fault, this system automatically switches into the primal system by adopting electromagnetic valve. In addition, an accumulator is also added to the new method to reduce the installation power of servo motor. The loader co-simulation model built by the software Simulation X is used to simulate and calculate the characteristics of the steering system under pivot steering condition. The models of steering gear and tire have been described specifically during the modeling. The relationship between flow area and relative angle of the steering gear's spool and sleeve is achieved by adopting the valve edge module in software Simulation X. Meanwhile, the testing system platform is built to test the accuracy of simulation model. Before the experiment, displacement transducers and pressure transducers are installed to avoid affecting the performance and structure of wheel loader. The accuracy of simulation model is verified by comparing the results of simulation and experiment. The difference between the 2 results is mainly due to the discontinuous input signal of steering wheel. In addition, the model established in this paper is simplified appropriately. At last, the simulation model is used in the electro-hydraulic flux matching steering system. By comparing the energy efficiency between load sensing system and electro-hydraulic flux matching system, the simulation results show that, the energy consumption under the no-load condition with low and high speed can be reduced by about 36% and 37% respectively when using this method. Moreover, the energy consumption under positive and unbalanced load with middle speed can be reduced by about 39% and 28% respectively. This is mainly due to that the electro-hydraulic flux matching steering system can avoid not only the overflow losses when high pressure appears, but also the median loss of unloading. Moreover, the accumulator can provide certain pressure to the suction port of pump during the steering process, which also can finally decrease the output energy of pump. The output power of servo motor and battery capacity are calculated in this paper finally. The electric-hydraulic flow matching method can adjust the flow of pump according to the need of steering hydraulic cylinders, and thus decrease the loss of oil flow. Therefore, this method can provide a reference to the design of other hydraulic systems in which the load frequently changes.