Study On Traction Ability For Driving Wheel Of The Lunar Rover

China lunar exploration program has been carried out since 2004 that is the third landmark in Chinese spaceflight and it is significant for politics, economy and military. There are three stages in China lunar exploration, which are moving around the moon, dropping on the moon and returning to the earth respective, and the lunar rover is important equipment for the second and third stage. The lunar rover is special vehicle with efficiency instrument for the lunar explore. It is a complicated systems engineering for developing the lunar rover, and it relates many techniques, thereinto the traffic ability is an important technique. Some academes and universities have developed different lunar rover in China, but the traffic ability research is beginning just now and the report about it is very few. So, it is very important to research the relationship between the lunar rover and the lunar soil at present.The authors are grateful for the financial supported by the Key Project of Chinese Ministry of Education (No. 107035) and the 985 Project of Jilin University. First, the research simulated the lunar soil for the lunar terramechanics test, developed the soil bin equipment and designed different wheels for lunar rover, and studied the traction ability of the lunar rover based on the soil bin test in laboratory. Secondly, the lunar soil characteristics measurement is divided into a vertical and a horizontal soil strength measurement, and modeling relationship between the lunar rover wheel and lunar soil. Finally, the research used the DEM (Discrete Element Method) software to simulate lunar soil particles change under a driving wheel and analyzed the relationship.The basic material of simulant lunar regolith is the eruption that was mined from Huinan district Jilin province of China, and some hematite is added into it as regulator. This research made five samples according to the different particle size distribution and hematite content. The sample 2 is been selected as the simulant lunar regolith after correlative tests and comparing with the parameters of lunar soil and JSC-1. The parameter of the sample 2 is closed to those of JSC-1 and ranges in the parameters of the lunar soil. The conclusions by analyzing qualitatively and quantitatively are as followed: water content is 1.9±0.9%, the specific gravity is 2.9 after 6 percent hematite were added as regulator, angle of internal friction is 32.75o , cohesion is 1.79kPa, the mean diameter is 134.703μm, the median diameter is 97.386 μm, the d10 (effective grain diameter) is 25μm, the d60 (manipulative grain diameter) is 129μm, the Cu (coefficient of unuiformity) is 5.16 and Cc (tortuosity coefficient) is 0.937, plentiful of feldspar and pyroxene are contained in it, the coefficient of compressibility is 0.19MPa-1 and the relative compaction is 0.66. The research has tested the axial deviatoric stress versus the axial strain and the negative volumetric strain versus the axial strain of stimulant lunar soil by triaxial test. The results of the triaxial test show that the yield stress is present to 6%~10% and compress process of samples is brevity. The Young's modulus is 68.8MPa and the Poisson's ratio is 0.34 from the triaxial tests by calculated. Finally, the hardness of stimulant lunar soil is tested by SC-900 penetrometer, and the results show that the hardness is increased with press and the hardness of surface increase more than the deep. These data indicate that the properties of simulant lunar soil is close to the real lunar soil, and can be used in the vehicle terramechanics test and other related engineering researches.The paper has taken the lead in researching the traction ability of lunar rover in China, and develops the soil bin test system based on the characteristic of lunar rover and structure of wheel. The soil bin test system is composed of soil bin, mechanism system and test system. The mechanism system is constructed with fixed soil bin and moving wheel, the test wheel is drove and controlled by the timing motor, the traction load is controlled by the EDC and servo D. C. motors. By the sensor, measuring instrument and software, the soil bin test system can test the DP, sinkage, velocity, torque, speed of rotation, et al ,and the test wheel can be replaced easy.The research has analyzed the shear failure of stimulant lunar soil. And the results show that the grouser-wheel and smooth-wheel have different track, which indicate the stimulant lunar soil with different shear failure after the test wheel passed. The track of the smooth-wheel is scale by crushed but the grouser-wheel is determined by the grousers, which explain the area and shape of the wheel have affinity with the lunar soil thrust. And the thrust of the driving wheel increases with the slip ratio. According to the indexes of the traction performance, we study the Influence of the lunar wheel configuration, load, velocity and mechanics of lunar soil on the traction ability. And the comparative indoor test was carried out on simulation lunar soil. The test results show that, the DP (drag bar pull) increases obviously when theλ(slip ratio) is between the 10% and 40%, and then the DP increases slowly whenλmore than 40%. Whenλless than 30%, the TE (traction efficiency) is is small, but increases very rapidly. Whenλcomes up to 30%, the TE reaches the max, and then it decreases untilλequals to 100%. DP and TE increase along with the wheel width and diameter increase. With the increase of the rug height, the DP increases, and the TE increases whenλis smaller then 2%, and then it reduces whenλis bigger than 20%. With the augment of the rug distributing density, the DP and TE rise at first, and then descend. The DP is increasing but the TE is descending when the load increases. The DP and TE are increasing with the velocity and hardness of stimulant lunar soil increase. The driving wheel DP is 6.7 times on the rocks as much as that on the stimulant lunar soil whenλis 10% and the others test condition is same. The traction ability is better when the test wheel passes the simulant regolith than it passes the sands, and the DP is 36.8N and 33.1N respectively when the slip ratio is 10%.Based on the tradition methods and theory of terra-mechanics, this paper separates the lunar surface's mechanics characteristic to the pressure-bearing characteristic, the cutting characteristic and the load-supporting characteristics, and gives the relevant model of the lunar soil under the driving wheel. As a result of this model approach the soil can be described by means of two different characteristics: pressure-sinkage relation and shear tension displacement relation. The rolling resistance caused by the lunar soil (external rolling resistance) is computed on bases of the lunar soil compaction work of the plastic soil deformation. The calculation of the tractive force is based on the local pressure and the local shear displacement in the contact patch. The push resistance may be calculated by the load model parameters. The DP and the TE is selected as criterion to evaluate the traction ability, and the software Matlab is used to develop the program to simulate interaction between rigid wheel and lunar soil. The lunar soil characteristics measurement can be divided into a vertical and a horizontal soil strength measurement. For the measurement of the vertical lunar soil strength the plate-sinkage-test is used, and the n (sinkage exponent) is 1.13, K (module of deformation) is 1056kN/mn+2 by calculated. The horizontal shear strength can be measured by means of a shear-test, and k (shearing strength displacement modulus) is 1.2cm by calculated. By comparing with the experiment data, the results show that the predicted values of the model conform to the test results that indicated the software is reasonable and fit to predict the lunar rover traction ability before an unknown lunar terrain. Finally, using the software Matlab to simulate the traction ability, the results show that the parameters below are very important to evaluate the interaction between automobile and terrain: b (wheel width), r (wheel radius), w (wheel load), grouser etc.The paper introduces the DEM to terra-mechanics at first time in China based on analyzing the FEM (Finite Element Method) and DEM (Discrete Element Method); and this research considers that the DEM is feasible and superior to the FEM in simulating the interaction between the wheel and the lunar soil. The model of the interaction between the rigid wheel and the lunar soil is setup. The system of soil bin is simulated by means of the software PFC2D. The linear contact-stiffness model is used as DEM contact model for lunar soil and biax-test is used to adjust particle's micro parameters. The plate-sinkage-test and the shear-test were simulated by the PFC2D. The parameters of terra-mechanics were calculated by calculated. The results showed that parameters of simulant lunar soil in this simulation are close to the parameters of the lunar soil after adjusting the micro parameters.According to the results of the soil-bin test, the lunar soil kinetics characteristics are studied by DEM software PFC2D. The paper studies the influence of the friction coefficient, porosity, rmax/rmin and gravity of the lunar soil. The results of the simulation test shows that the draw bar pull (DP) increases with the increase of the friction coefficient and the gravity acceleration, and reduces with the increase of the porosity. It increases with the increase of the rmax/rmin until the rmax/rmin is bigger than 5. Soil–wheel interaction especially soil deformation caused by the wheel motion was investigated by EDM simulation. Characteristics of lunar soil deformation were summarized focusing on the behavior of displacement and distribution of velocity. DEM were examined in order to describe the displacements loci of soil particles. The results show that the particles loci under smooth-wheel have three phases: pushed, pressed and ascended, and the particles loci under grouser-wheel have two kinds, one kind similar to smooth-wheel, another kind has three phases: pressed, heaved and dropped. Shapes of the velocity distribution in simulation have onwards flow area and back flow area which closely similar to those in experiment. The porosity of the lunar soil descends and then decline when the driving wheel passes. DEM can simulate the interaction of wheel and lunar soil, and it has advantage in simulating the dynamic behavior between discrete soil and the machine, and the simulation test would be help to design the wheel of the lunar rover.