Operating conveniences of steering wheels, hand and foot controls and meters installed on 34 tractors were investigated, in relation to the standard physique of Japanese adult male. (1) Steering wheel: Both diameters and inclinations are generally too large, especially in imported tractors. The large part of gripping points are longitudinally so distant and vertically so low, that few operators can keep their adequate carriages (angle of upper arm 0-25°, angle of elbow 90°, when sitting on seat) (Fig. 1). (2) Control levers: Reasonable correlations cannot be found between frequency of use and arrangement of levers. Because of inadequacy of positions of grips, operation of some controls often cause contact of operators' bodies with other controls and unnatural carriages (Fig. 2, 3). Especially, the Pto lever needs severe foreward inclination and bending of the upper body (Tab. 1). The starter lever and the main switch are almost too distant longitudinally, but low frequency of use may permit the existing circumstances. The size, shape and operating direction of grips should be standardized from the view-point of convenience, comfort and safety of work. (3) Control pedals: In general, positions of pedals are longitudinally so near from the tuber points of hackle bones of operators that operation, especially of differential locks, causes exessive bending of knees and stress of back muscles, and horizontally so distant that operation, especially of imported tractors, brings twisting of bodies (Fig. 4). In several domestic tractors, size of the pedal is too short horizontally to be under a half of standard width of foot (Tab. 2). Shortage of surface inclination often brings too large front angle of ankles and exessive tension of legs. The operating angle of pedals of domestic tractors is generally beyond adequate range (about 20°), except differential lock pedals. (4) Meter installation (Tab. 3): Considerations for human engineering are seemed to be insufficient in regard to arrangement, size and colour conditioning of meters.
The problems of the tractor sinkage on the soft soil are a matter of the floatation under the vertical direction. The performances of the tractor are not only disclosed by the floatation, but traction of them are more important factor. If the traction or drawbar pull on the various soil condtions will be able to predict easily as same sa the prediction of the sinkage by a cone or the other methods, we could know the tractor concept or mechanism to improve the traction, but this problem contains many difficult factors as revealed in many research papers. This test and analysis were aimed to find out the starting points to predict the traction by the tractor elements and soil conditions. Three soil conditions having the various internal friction angle and cohesion force shown in figure 1 were selected and five tractors which equipped pneumatic tire, half tracks, girdles and double tires were used. Tractor sinkage was proportional with the slippage of the running elements and contact surface increased with the sinkage and contact pressure decreased. Curves of traction on a unit ground contact surface area vs. contact pressure were shown in figure 4 and this curves did not cross the lines of the shearing resistances of soil which the tractor tested. Curves of traction on a unit ground contact surface area vs. slippage (deformation of soil) were quite similar with the curves of stress-strain curves at the soil shearing test. This clarified the soil under the running elements were sheared by them and the traction was the resultants of shear resistance of soil. Maximum drawbar pull on a unit contact area was proportional with maximum resistance of shearing soil as in figure 6 and had the linear relation with the contact pressure as in figure 7.
In order to find the relation of the soil hardness which is measured by the cone penetrometer to the tractor sinkage on the soft paddy field, the tests were repeated by the methods produced by the Waterways Experimental Station. Test fields were the low swampy ground scattered near the Lake Biwa which had been harvested the rice plants and located as the dots in Fig. 1. Thirteen test tractors were used and they had the various running elements, such as pneumatic single tires, dual tires, half tracks, strake type wheels, girdles and tracks and they had the dimensions as in Table 1. Vehicle cone index of each tractor on the same Table were calculated according to the WES methods. Abscissa of Fig. 3 shows the cone index calculated from the cone penetrating resistance and ordinate is the depth measured from the land surface. These diagrams are recorded by the self recording penetrating devices produced by the way of experiment in our laboratory and called TN-4. reported previously. Fig. 4 is the result of these tests and the abscissa of the coordinate is the actual measured sinkage of the tractors and the ordinate is the presumed sinkage from the cone diagrams and the vehicle cone index. Fig. 6 shows the increases of sinkage with the increases of slippage of the wheel or other running elements of the tractors on the test field having the cone diagrams as the upper part of the same figures. 1. Tractor sinkages presumed by the cone index and vehicle cone index are almost agreed with the actual sinkages except special examples, such as the large sinkage caused when the running elements excavate the soil surface at the time of 100 percent or large slippage. 2. On the surface we can get the cross point to the cone diagrams of the vertical line drawing to the scale corresponding to the vehicle cone index of the tractor which crosses on that surface, the depth of that cross point were agreed with the actual sinkage of the tractor having no load, however, when the tractors had the large drawbar pull and the hard layers of the surface of soil were excavated by the slippage of the running elements of that tractors, they sank to the second cross point we can get at the deeper layer. If we can not get the cross point at that layer, they can not cross on that surface. 3. On the surface having the hard cone diagrams, slip sinkage according to the excavation of the running elements were affected by the hardness of the soil. 4. Rotary tiller is not need to be treated as the drawbar load, it rather may be available as the means of increase of floatation. 5. As the combine harvester had generally less slippage and less excavation of soil, they can cross the surface which have the hard layer on the top of the surface, even if the deeper layer are extremely soft.
As a conclusion of the series of studies aiming the minimum tillage resistance, the following suggestions have been made. 1. The basic tillage methods: Straight, rotary and vibratory tillage were studied and compared each other from the view point of tillage resistance and energy. Considering the degree of soil pulverization, the vibratory method is, generally, the most favorable for minimum resistance and small energy. Straight cutting method is the second. 2. Blade shape and motion: The favorable factors relevant to blade shape are; small cutting angle, convex surface, discontinuity (like slat moldboard plow), certain types of cutting line and dimension of blade. Freedom of blade motion (like free rotating disc), low cutting velocity, cutting action towards free surface of the soil are preferable among motion factors. 3. Soil and tillage method: Each tillage method includes different amount of cutting, shearing and tensile action of soil failure, A favorable way of breaking soil is to be varied according to the soil properties. Consequently, there must be a favorable tillage method according to the soil type and conditions. For example, a tillage method including much cutting action is suitable for clay soil, whereas, shearing action is more important for sandy soil. 4. New tillage method: A factorial classification of existing tillage method shows that there are quite many lost links of the chain of tillage machines which might be more preferable for minimum tillage energy. By introducing favorable factors above mentioned into these lost links of chain, better tillage machines will be developed.
The result of the calculation of the plowing efficiency, which is an important factor for the plowing capacity on the one-way plowing, was previously given by the report No. 7. Through our recent experiments it has become evident that the value of the calculation agrees almost with the value obtained from the experiments. The tractor used in the experiments was YM-18A, the furrow width being 10 in. two furrow and the working speed 1m/sec. In the central portion of the experiment field we took the normal plowing and the furrowed plowing method, dividing the portion into section of which the short side was 10m, We consider this to be the most capable method for the field. In the peripherical portion of the field. we took the semi furrowed plowing method. The efficient curves getting from the experiments are shown in Fig. 2. It will be seen from the figure that the efficient curve of the furrowed plowing method is lower about 3% on an average than that of the normal plowing method. The result of the calculation on actual values of the turning time which was measured setting different types of plows onto tractors is shown in Fig. 3. In this figure, we can see a tendency of the narrower the plowing width the lower the plowing efficiency in the normal plowing, while in the furrowed plowing, the plowing efficiency does not depend on the plowing width but is always constant. If we set the forward speed of a tractor constant, the turning time varies by types of the tractor. The influence of these factors to the efficiency is shown in Fig. 4. In the normal plowing method on a small area, a type of the tractor of which the turning time is short is superior. However, if the field area is increased, the efficiency of large type tractors having a higher reversible speed will be superior. In the furrowed plowing method, the difference of the turning time shows directly differences of the efficiency. When the field area increases, however, we can see a tendency of these differences decrease gently. Lastly, the capacity curve, which was made from experimental efficiency values, is shown in Fig. 5. In considering plowing capacity, increases of the working speed and plowing width, besides the efficiency, are generally considered to be important. In the Fig. 5, however, we can see that the working speed is somewhat less effective to the plowing capacity than the plowing width. Consequently, it seems important to make wider the plowing width as much as possible according to the traction capacity of each tractor.
Importance of soil shear resistance to trafficabilities and performance of tractors, combines and other farming macshines, has been pointed out by several investigations in the past. And a few methods have been applied to determine the soil shearing force. In this study, as to compare the traditional measuring result by standard shear head, five other shear heads with different type were used. Examined soil type were sand, sandy loam, clay and other. The maximum shearing stress were calculated by using following formulas, in which the torque value was measured while the maximum soil resistance presented. S1=T4/2/3π(r13-r23)+2πH(r12+r22) S2=T3/2/3π(r13-r23) In comparing with value S1 and S2 to maximum shearing stress value of direct shear test, it was presented that value S2 was considered reasonable.