Stability Analysis of Three-point Leveling Mechanism of Hilly Mountain Tractor
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摘要:
针对丘陵山地拖拉机作业环境复杂、底盘稳定性差及易翻覆等问题，设计一款具有三点式自动调平机构的丘陵山地拖拉机底盘。采用液压油缸自动控制车架平衡的三点调平方案，保证调平角度为−25°～25°，基于Simulink软件对调平机构进行了运动学仿真分析，并运用经典力学理论，分析了拖拉机坡面横向及纵向稳定性。结果表明，底盘上坡极限翻倾角为55.38°，下坡极限翻倾角为44.03°，上坡纵向滑移角为25.62°，下坡纵向滑移角为13.18°。调平油缸角度范围为63.9°～107.5°，角速度范围为−0.2061～−0.1535 rad/s，角加速度范围为−0.0035～0.0358 rad/s2，液压调平机构运行平稳。该丘陵山地拖拉机底盘可提高拖拉机山地适应性及驾驶员安全性，具有良好的稳定性。
Abstract:Aiming at problems of complex working environment, poor chassis stability and easy overturning of hilly tractors, a hilly tractor chassis with three-point automatic leveling mechanism was designed．A three-point leveling scheme with hydraulic cylinder automatically controlling frame balance was adopted to ensure leveling angle between −25° and 25°．Based on Simulink software, kinematics simulation analysis of leveling mechanism was carried out, and lateral and longitudinal stability of the tractor when driving and working on ramp was analyzed by using classical mechanics theory．Results showed that limit tilting angle of chassis was 55.38° in uphill, 44.03° in downhill, 25.62° in uphill and 13.18° in downhill．The oil cylinder angle ranged from 63.9° to 107.5°, angular velocity ranged from −0.2061 to −0.1535 rad/s, and angular acceleration ranged from −0.0035 to 0.0358 rad/s2．Hydraulic leveling system ran smoothly．The chassis of tractor in hilly areas could improve adaptability of tractor in mountainous areas and the safety of drivers, and has good stability．
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Keywords:
- hilly mountain tractor /
- chassis /
- three-point leveling mechanism /
- stability
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图 1 丘陵山地拖拉机底盘结构示意
1. 车架 2. 散热器 3. 快慢挡变速箱 4. 变速箱 5. 离合器 6. 后摇摆支撑臂 7. 后驱动轮 8、10. 万向节 9. 锥齿轮换向箱 11. 前摇摆支撑臂 12. 前驱动轮 13. 前转向驱动桥 14. 发动机机架 15. 发动机 16. 后转向驱动桥
Figure 1. Chassis structure of hilly mountain tractor
图 2 底盘调平机构机构示意
1. 左侧驱动轮 2. 前转向驱动桥 3. 车身 4. 调平油缸 5. 固定铰接支座 6. 摇摆支撑座 7. 机架固定支座 8. 右侧驱动轮
Figure 2. Structure of chassis leveling mechanism
图 5 底盘调平机构矢量分析
r1——前桥回转中心A与车架上的固定铰接支座C的距离，mm；r2——前桥的固定铰接支座B与车架上的固定铰接支座C的距离，mm；r3——前桥回转中心A与固定铰接支座B的距离，mm；θ1——前桥回转中心A与车架上的固定铰接支座C的连线AC与前桥夹角，（°）；θ2——液压油缸调平角度，（°）
Figure 5. Vector analysis of chassis leveling mechanism
图 6 底盘调平机构的Simulink仿真模型
Figure 6. Simulink simulation model of chassis leveling mechanism
图 11 山地拖拉机底盘上坡受力分析
h——底盘的质心与地面之间的垂直距离，mm；d——后驱动轮到质心距离，mm；δ1——底盘上坡翻倾角，（º）；δ2——底盘下坡翻倾角，（º）
Figure 11. Force analysis of mountainous tractor chassis uphill
图 13 拖拉机底盘在横向坡道上受力分析
${F_{Z1}}$——底盘上侧车轮所受地面支反力，N；${F_{Z2}}$——底盘下侧车轮所受地面支反力，N；${F_{Y1}}$——底盘上侧车轮侧向滑移阻力，N；${F_{Y2}}$——底盘下侧车轮侧向滑移阻力，N；$B$——底盘轮距，mm；H——底盘的重心与地面之间的垂直距离，mm；$\beta $——横向翻倾角，（º）
Figure 13. Force analysis of tractor chassis on transverse ramps
表 1 调平机构初始位置参数
Table 1. Parameters of initial position of leveling mechanism
项目 初始参数 项目 初始参数 r1/mm 677.5 θ3/（°） 180.00 r2/mm 526.0 w1/（rad·s−1） −0.1762 r3/mm 297.5 w2/（rad·s−1） −0.2061 θ1/（°） 132.21 a1/（rad·s−2） −0.0070 θ2/（°） 107.45 a2/（rad·s−2） −0.0174 
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