| The steering system in wheel loader determines the driving security, working efficiency,fuel consumption and the labor intensity of the driver. However, the traditional steeringsystem of wheel loader has no adjustable steering sensitivity. In order to tacklebetween higher working efficiency and the more stability at high speed, and provideappropriate road sense to the driver, this paper applies the Electro-HydraulicProportional Pressure Control technology to wheel loader's Steering System. Itreplaces the traditional mechanical or hydraulic connect by connecting and controllingall the component of steering system through micro-electronics technology, usingsensors to collect the data of steering, then transfer them to the micro computer on thevehicle. The computer processes these signals, makes decision and outputs actuatingsignals such as the steering degrees of vehicle. As there is no mechanical connectbetween the steering wheel and the turning wheel, the limitation of tradition steeringsystem is completely eliminated. Therefore the design and the assembly of the vehiclescan be simplified greatly and the design of force and angle transfer characteristicsbecomes freely.The wheel loader has the distinct characteristics under different operating modes.During the working mode, the vehicle's speed is low, but the steering angle variesgreatly and frequently. While in normal driving mode, the vehicle's speed is high. As faras these characteristics are considered, the Electro-Hydraulic Proportional PressureControl is state-of-the-art technology for the wheel loader: Under low speed workingmode, the high steering sensitivity mode is adopted to increase the work efficiency anddecrease operator's labor intensity because in this mode the steering wheel onlyrotates 180° for the full steering. While in the normal driving mode, in order to enhanceoperation security and the stability, the low steering sensitivity is set. Therefore thesteering wheel must rotate 900° for the full steering. At the same time the wheelloader's maximum speed is only about 30km/h, while that of the automobile is beyond100km/h, these features make the Electro-Hydraulic Proportional Pressure Controltechnology applied in the wheel loader other than in the automobile.The original steering system of wheel loader is replaced by a new Electro-HydraulicProportional Pressure Controls', which is suitable for the wheel loader's characteristic.It eliminates the traditional mechanical or hydraulic connection by connecting andcontrolling all the component of steering system through micro-electronics technology.This system integrates electro-hydraulic proportion control technology, computertechnology and automatic control technology etc. The switch between the two steeringsensitivity modes in the light of the wheel loader actual operation can be implemented.Also the proper road sense can be provided to the operator. This technology applied tothe wheel loader can bring our construction machinery's progress a great stride. Itsentire machine working performance and the mobile flexibility can be enhanced greatly,the enhancement international competitive ability will increase, and the operator's laborintensity will be decreased.This dissertation put up the studies of the steering system by Electro-HydraulicProportional Pressure Control technology on the articulated wheel loader as following:1. The project of controlling the flow amplifier valve by steering system of theElectro-Hydraulic Proportional Pressure Control is confirmed.2. The flow amplifier valve's mathematical model is established by the transfer function,On the basis of which the transfer functions for flow amplifier valve by proportionpressure reduce valve controlled has been deduced.3. Experiment was carried out aimed to the characteristic of the flow amplifier valve ontest bench, the test results have confirmed that the shortcoming of the flow amplifiervalve. Also the experiment was done for the steering system by Electro-HydraulicProportional Pressure Control, the test results indicated that the control performanceproposed by this article has been used by wheel loader on the steering system byElectro-Hydraulic Proportional Pressure Control and the control strategy is improvedgreatly.4. The shortcomings of CAT flow amplifier valve are presented:1) the pilot oil in spring cavity of flow divider valve has not been coupled with the wheelloader operating mode, which causes the hydraulic steering system pressure oiloverflow under high-pressure and the power loss increasing;2) The displacement of flow amplifier valve main valve spool is controlled by thepressure drop which the oil flow through the orifice located on the ends main valvespool, this will lead to the characteristic to be influenced by the processing precisionand the oil temperature. If the pressure directly controls the displacement of main valvespool, then the above factor can be avoided. |
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