2.1 calculation of steering resistance torque
In the matching design of hydraulic steering system, the steering resistance moment should be calculated first. Generally, the steering resistance moment is divided into in-situ steering resistance moment and driving steering resistance moment. Considering that the in-situ steering resistance moment is 2 ~ 3 times of the driving steering resistance moment, the steering system of the self loading mixer shall be designed to meet the requirements of in-situ steering torque. The factors that affect the steering resistance moment of automobile include the load of automobile front axle, the friction coefficient between tire and ground, tire pressure and so on. Currently commonly used empirical calculation formula:
Where: MR1 - steering resistance moment, n · m;
f ——輪胎與地面摩擦系數，取 0.7；
F - friction coefficient between tire and ground, taken as 0.7;
G1 -- axle load of vehicle steering axle, N;
P -- tire pressure of vehicle tire, kPa.
自上料攪拌車單軸軸荷 75000N，正常工作胎壓550kPa，代入數值可得 Mr1= 6462N·m。
Since the maximum single axle load of the charging mixer is 75000n and the normal working tire pressure is 550kpa, the value can be substituted to get MR1 = 6462n · M.
2.2 steering cylinder selection and verification
轉向系統設計需要考慮兩種情況，種情況，轉向油缸隨車橋確定，且受結構限制不能隨意改變，此刻應計算轉向橋載荷，通過調整整機質心，使轉向橋載荷在合適的范圍內，同時對轉向油缸進行校核計算。第二種情況，轉向橋所受載荷已確定，需要對轉向油缸進行選型設計，使之符合轉向要求。目前自上料攪拌車選用林德10t 車橋，油缸性能參數已經確定，先需要對油缸進行校核，參數見表 1。
Two situations need to be considered in the design of the steering system. In the first case, the steering cylinder is determined with the axle and cannot be changed arbitrarily due to structural constraints. At this time, the steering axle load should be calculated, the steering axle load should be within the appropriate range by adjusting the mass center of the whole machine, and the steering cylinder should be checked and calculated at the same time. In the second case, the load on the steering axle has been determined, and the steering cylinder needs to be selected and designed to meet the Steering requirements. At present, Linde 10t axle is selected for the self loading mixer, and the performance parameters of the oil cylinder have been determined. First, the oil cylinder needs to be checked, and the parameters are shown in Table 1.
The maximum thrust of steering cylinder is
By substituting the value, Fmax = 76302n can be obtained
自上料攪拌車車橋轉向油缸的轉向作用力臂隨轉向角的關系曲線如圖3 所示。車橋轉向角為 32°，由圖可知更小力臂 Rmin＝125mm。
The relationship curve between the steering action arm of the axle steering cylinder of the self loading mixer and the steering angle is shown in Fig. 3. The maximum steering angle of the axle is 32 °. It can be seen from the figure that the minimum force arm Rmin = 125mm.
根據轉矩公式：Fmax =Mr2 / (Rmin η)
According to the torque formula: Fmax = MR2 / (Rmin) η)
Where: Rmin - minimum force arm, mm;
η—— Steering mechanical efficiency, taken as 0.8;
MR2 -- steering torque, n · M.
By substituting the value, we can get MR2 = 7630.2n · M
According to the calculation results, MR2 ＞ MR1, it meets the use requirements.
2.3 determination of displacement of steering gear
When the steering wheel moves from one limit position to another, the number of turns n of the steering wheel should not only meet the driving conditions and prevent the poor stability of the vehicle body caused by excessive steering of the wheel, but also meet the requirements of less work cycles and improve the convenience of operation. In general design, n = 3 ~ 5 cycles.
Full stroke oil volume of steering cylinder: v = SA
Where: s -- piston stroke, mm;
A - oil pressure action area, mm2.
Substitute the value to obtain v = 858ml
先選取 n=4，則轉向器排量為V/n=858/4=214，對照轉向器廠家樣本，選用排量為 200mL/r 型號的轉向器。
If n = 4 is selected first, the displacement of the steering gear is v / N = 858 / 4 = 214. Compared with the sample of the steering gear manufacturer, the steering gear with a displacement of 200ml / R is selected.
2.4 determination of gear pump displacement
Steering system flow: q = QN
Where: Q -- displacement of steering gear, ml / R;
N -- steering wheel speed, taken as 0.8r/s.
Substitute the value to get q = 160ml / s
The displacement of the gear pump is analyzed according to the idle state of the engine
Where: Nd -- engine idle speed, taken as 750r / min;
η—— Steering pump efficiency, taken as 0.95.
Substitute the value to get QC = 13.5ml/r
The displacement of gear pump is 16ml / R, which meets the use requirements.
Full hydraulic four-wheel steering system has the characteristics of convenient layout and flexible steering. At present, it is widely used in wheel excavator. Starting from the principle of hydraulic steering, this paper introduces in detail the application of four-wheel hydraulic steering in self loading mixer truck, checks the strength and displacement of steering cylinder through calculation and analysis, and determines the displacement of steering gear and gear pump, so as to provide a reference for the design of hydraulic steering system.
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