Parallel between the evolution of the tractor and that of means of ensuring tractor mobility

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for switching from suspension bound to rebound and vice versa. Frequency-response characteristics with an empty and fully loaded trailer for input frequencies from 1.3 to 15 cycles/s. revealed that, e.g.: (1) irrespective of the extent of trailer loading, body accelerations reached their maximum values under high-frequency-resonance conditions, (2) sprung-mass displacemerits with both an empty and a loaded trailer reached their maximum values under lowfrequency-resonance conditions, and (3) wbeel-displacement values for a loaded and an empty trailer were greatest under low- and high-frequency-resonance conditions respectively.** 32 M. L Pogeabekov. Opredelenie buksovaniya samokhodnykh selskokhozyaistvennykh mashin [Determination of wheelslip of self-propelled farm machinery]. * Vestn selkhoz. Nauki, 1964, 9 (6) 121-123; A theoretical analysis.* 33. M. G. Prigozlmya. Nekotorye dannye po dinamike povorota traktora DT-54 [Data on the dynamics of turning the DT-54 tractor]. Mekhaniz. Elektrif. sots. seL Khoz., 1958, 16 (2) 23-25; Torque on driving sprockets of a 54 h.p. tractor was measured for turns of 20, 16, 12, 8, 4 and 0 m radius on hard and soft ground with and without D.B.loading and mounted implements. The tangential force on the retarded track was negative and reached > 1000 kg.* 34. A . R . Reeee. Problems of Soil Vehicle Mechanics. Components Research and Development Laboratories, U.S. Army Tank-Automotive Center, Warren, Michigan, Report No. 8470, March 1964. A proposal is made that the approach to soil vehicle mechanics be modified so that all the curve-fitting equations used are based on theoretical analyses approximately valid for incompressible rigid soils. The equations would have to be chosen to include the effect of compressibility also, and they would therefore be partially empirical but each would have a definite theoretical basis. This concept has been applied to several outstanding problems and leads to new solutions. The importance of curve-fitting procedures is emphasized and a new non-statistical method proposed. It is shown that the current pressure sinkage equation p-~kz n should be replaced by one of the formp=f(z/b) and this is justified experimentally. It is concluded that the results from circular plates cannot in general be applied to vehicles, long rectangular plates being necessary. Considerations of plastic equilibrium lead to a new equation for the traction from the sides of a grousered track. A detailed analysis of excavating effect of lugs has been made and a new conclusion is reached. Some efforts were devoted to a study of surface shear devices for measuring shear strength and it was found that in frictional soils they give lower values of ~ than confined tests. Suggestions for their modified design and use are made. It is shown that current methods of determining soil deformation by superposition of the effects of horizontal and vertical loads taken separately, are wrong and can lead to serious overestimates of vehicle performance. The additional factor is called slip-sinkage and it was found to be important in sand but less in clay An analysis is made which explains this, gives some insight into the physical nature of the phenomenon and may provide the basis for a theoretical study of equilibrium sinkage under combined loads. A method is proposed whereby data from existing Bevameters may be used to predict slip sinkage. 35. J. Remus Parallel between the Evolution of the Tractor and that of Means of Ensuring Tractor Mobility. lngdnieurs de l'Auto., January, 1965, Vol. 38, No. 1, p. Trends distinguished by the author in the evolution of the agricultural tractor include trends towards higher power, reduced dead-weight/power ratio, generalisation of differential locking, extended use of power-assisted steering, higher road and working speeds, greater safety through use of disc brakes, and greater attention to driver comfort and simplification of working. The guiding principle is to save time and avoid fatigue. Tractor mobility is discussed in regard to tyres. The driving-wheel tyre is based directly on the truck tyres, the aim being to provide sufficient adhesion, casing flexibility, a large surface of contact with the soil, low inflation pressure to permit casing flexibility, and a patterned tread. Until recently, tread pattern was considered all-important. The latest trend is to provide tread bars of moderate height, spacing adequate to simplify cleaning, thickness adequate to maintain an acceptable wear surface and sufficient shoulder to offset tyre roundness. Wide tyres and largediameter tyres have certain advantages, but there are also drawbacks. U.S. systems favouring a wider rim or a small section height are noted. Recent research by tyre manufacturers and other interested parties have shown links between agricultural-tractor problems and problems of other off-the-road vehicles. A study by Professor W. Srhne in 1962 advises investigation of tyre pressures permissible over deformable soils and ways of adapating tyre pressure to diverse soil conditions. On the road, the radial belted tyre has given excellent results, and its wear resistance, flat tread and lateral flexibility have been successfully used in agricultural applications in Italy and

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France. Adhesion is ensured by the wide and lengthy contact section. Improved radial tyres are desirable. Meanwhile, a fiat, low-inflation-pressure, flexible tyre of more convantional construction has been developed. This Stabilarge tyre and radial tyes permit increases in durability and adhesion of 15-20 per cent.** 36. S. I. Rokns ( K a u n a u Polytech. Inst.). Determination of Fundamental Soil Parameters for Evaluating Vehicle Tractive-Adhesive Properties. Avtom. Prom., January, 1965, No. 1, p. 24-26; Factors affecting the cohm'ence C and anale of internal friction p of different soils are briefly discussed, and it is shown that, with a known or given specific ground pressure in the contact patch, the maximmn traction obtainable depends on the soil-shear-corve paramete~ C and p. Disadvantages of existing devices for measuring these parameters are pointed out, and infomuttion is presented on a device des/gned by the author to permit measurement of two mechanical soil characteristics, this time, specific resistance to deformation q and coherence C expremted in kg/cm2, much more quickly. Formulae for determining q and C are presented, together with some considerations regarding the r c s i s t a n c e - t ~ value ~ of various soils, z finally being equated to C. The value p, essential to determination of the resistance to shear of some soils, is difficult to obtain in practice and, therefore, it is proposed this be replaced by two other more easily determined parameters characte~sing soil dispenfion, viz., an~le of colummce ~ and angle of friction properties ~. The relationship between these parameters is eharacterlsed by the following: ~=45 ° - ~, and the method of determining ecwith the device designed by the author is descrihed. Relationships between the adhesion cocEacient ¢p and the type and state of soils were derived with the soil-evaluation method presented; also, the shear-limited adhesion force was determined, in field tests with a ZIL-157 vehicle, from the rolling resistance and the maximum tractive effort at the towing hook over various types of fresh ground. The method of conducting the vehicle tests, 12.00 x 18-in. tyrcs at pressures of 0.5, 1-5 and 3.0 atm being utilised, and obtaining the soil parameters q and z with the previously mentioned device is described. From the experimental results, the correlation relationships were derived between the rolling-resistance coefficient and the specific resistance to soil deformation and between the adhcsion coetf~ient and the soil coherence and angle of friction properties at the different tyre gn~,~,sures. Graphs are reproduced of the functions q~=~(~, ~) for tyre pressures, with 12-00× 18-in. tyres, of 3.0 and 0.5 atm, and the influence of the soil parameters ~ and ~ in promoting the same adhesion on different soils is discussed. Similarly, the effect of tyre pressure on the function ¢p~¥(~, ~) is explained. Further tests with a GAZ-63 vehicle produced similar adhesion-coeff~ent/soilparameter relationships and still better confirmation of the aptness of the function qp=V(z, f~).** 37. E . T . Small, Tractor Earth Blading at High Speeds--Now a Reality. S.A.E. Paper, Internat. Automot. Engng. Congr. January, 11-15, 1965; Large flotation front tyres, robust tractor design and powerful engines have improved construction-tractor performance considerably, but proper control of the blade remains a problem. The basic principles and sequence of movements necessary in the cycle of blade adjustments for smooth cutting with overhung blading equipment arc explained by reference to a bulldozer mounted on a tyred tractor. Each blade cycle (lowering or raising) comprises three reversing blade movements, each of which must conform to three requirements. These relate to: (1) amount of vertical blade movement, (2) timing of starting each blade readjustment, and (3) vertical blade speed necessary to end each blade movement at the required time. Results when a single requirement is unfulfilled, viz., when blade-raising speed is equal to blade-lowering speed instead of twice as great, are described. Modem tractors have not been fully exploited hitherto, because operators arc handicapped in controlling the blade. Blade sliding shoes provide no solution. However, automatic precision adjustment now makes high-speed blading possible. The hand-lever control comprises three electrical switches, one for blade lowering, one for blade raising, and one for manual operation. Manual control serves for blade raising at turn-around, blade resetting, digging out rocks, etc. The automatic process is described. For slope changes adjustments are made by the operator. The automatic system brings various benefits which include accurately controlled thickness of cut and spread, the production of a smooth, plane surface, and high-speed blading limited only by tractor-engine power. Smooth road surfaces reduce the rolling resistance of vehicles travelling on the haul road, allow faster travel and reduce vehicle maintenance. In military operations, the automatic cycle control allows the quick construction and maintenance of service roads for supplying troops. A remote-control feature brings further advantal~. In limited tests, bulldozing operations have been performed at travelling speeds of 5-12 m.p.h.** 38. J . J . Smimov; G. N. Dyachenko. Issledovanie geometrii i rezhimov raboty aktivno deistvuyushchikh lap kultivatorov na povyshennykh skorostyakh [Investigation of the geometry and the