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Engineering aspects of tyre testing
ABSTRACTS
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frequency of the sprung-mass oscillations, the latter change being a factor influencing the vertical-acceleration frequency components. In consideration of the pronounced influence of acceleration-frequency-spectrum changes on the individual, frequency ranges of the size of an octave have been recommended for the evaluation of ride smoothness, e.g. 1-2, 2 4 , 4-8, 8-16, 16-32 c/sec etc. where it is difficult to make an analysis with frequency intervals of 1/3 octave. (M.1.R.A.) 19.
J. A. Turley (Dunlop Ltd.). Engineering aspects of tyre testing. I. Mech. E. Auto. Div. Proc. 185, 1003-1014 (1970-1971). An introduction lists the functions of tyres in the control of wheeled vehicles and explains differences in construction between cross-ply, bias belted, and radial-ply tyres. Tyres vary in size, weight and construction according to the vehicles they are intended for, from cycles to earthmoving vehicles. Various testing machines, track facilities and instrumented vehicles are necessary to check the performance of the wide range of existing tyres and develop future tyres. While most tests are performed on machines, tread-wear tests are performed by a test fleet on public roads, handling tests on individual cars on proving-ground or other tracks, and noise tests on special provingground surfaces and on special laboratory equipment. Tyre-casing strength is determined, e.g. by means of hydraulic-probe-machines which force domed tools into the inflated tyre until it bursts. In fatigue tests, tyres are run at constant speed, either under-inflated or overloaded or both, until a certain mileage is attained or tyres fail. Tyre properties such as speed performance, cornering ability under wet or dry conditions and rolling resistance are examined on specially instrumented machines. Plate-glass facilities incorporating plates let into a road surface over which tyred vehicles are driven allow low-speed and high-speed photography, the larger plate serving for investigating water-clearance properties of tyres travelling at speeds up to 70 m.p.h. Special machines are used for testing earthmover tyres and aircraft tyres. Testing-machine requirements according to number of tyres for simultaneous testing, size of tyre and type of test are explained. A circulating power machine using hydraulic rams to load the tyre carriages which move on rollers against a vertical drum is described. Special properties of tyres and the testing of these properties are examined with reference to static tyre, rolling tyre, steered tyre and driven tyre, rolling resistance and tyre power-loss. In "chunking" tests, the circulating power machine is used to produce tread cracking and tearing at speeds below ripple by the application of torque such as may occur when high-speed vehicles use high acceleration forces. Tyre patterns can be designed to minimise chunking; an example is given. It is concluded that, while many measurements, tests and studies are necessarily made with tyres fitted on vehicles, it is also possible to examine basic features of the dynamic action of a tyre by means of drum machines and suitable measuring links. Accuracy in tyre testing has been promoted by the development of calibration methods. (M.I.R.A.)
20.
G. V. Vedenyapin and L. P. Zyuban. Effect of soil moisture, normal pressure and velocity on the coefficient of sliding friction for steel. Pochvovedenie, No. l l , 144-147 (1971) (Ru, en) Volgogradskil Sel'skokhozyaistvennyi Institut, Ministerstvo Sel'skogo Khozyaistva, USSR. Statistical treatment of the isolated and combined effect of these three factors on the coefficient of friction between soil and steel have a multi-linear regression equation for calculating the coefficient. Analysis of paired and partial correlation coefficient showed that soil moisture had the greatest effect. (Soils and Fertilizers.)
21.
J. O. Wendeborn (Daimler-Benz AG). The present state of development of the Unimog. A.T.Z. 74 (2), 69-76. (February 1972). The first Unimog, a multi-purpose vehicle for agricultural and forestry operations, was developed in the early post-war years. Despite many changes, improvements and additions, the basic design and the sphere of action for which it was intended have persisted to this day, the aim being to permit mechanization of all operations where the tool must be brought to the worksite, and this site shifts as the work progresses. Two parallel side U-members and five cross-members made up the basic frame. Engine block, clutch, gear-box and auxiliary gear-box were elastically suspended in this frame. Front and rear axles were formed as rigid universal shaft axles. With a cylindrical coil spring and a shock-absorber in parallel for each wheel, vibration characteristics permitted high vehicle speeds and, in conjunction with features such as good ground clearance, made for outstanding crosscountry mobility. The power unit was a water-cooled 25-h.p. Mercedes-Benz Diesel engine. The transmission allowed six forward and two rearward speeds; a special drive provided power-
71
frequency of the sprung-mass oscillations, the latter change being a factor influencing the vertical-acceleration frequency components. In consideration of the pronounced influence of acceleration-frequency-spectrum changes on the individual, frequency ranges of the size of an octave have been recommended for the evaluation of ride smoothness, e.g. 1-2, 2 4 , 4-8, 8-16, 16-32 c/sec etc. where it is difficult to make an analysis with frequency intervals of 1/3 octave. (M.1.R.A.) 19.
J. A. Turley (Dunlop Ltd.). Engineering aspects of tyre testing. I. Mech. E. Auto. Div. Proc. 185, 1003-1014 (1970-1971). An introduction lists the functions of tyres in the control of wheeled vehicles and explains differences in construction between cross-ply, bias belted, and radial-ply tyres. Tyres vary in size, weight and construction according to the vehicles they are intended for, from cycles to earthmoving vehicles. Various testing machines, track facilities and instrumented vehicles are necessary to check the performance of the wide range of existing tyres and develop future tyres. While most tests are performed on machines, tread-wear tests are performed by a test fleet on public roads, handling tests on individual cars on proving-ground or other tracks, and noise tests on special provingground surfaces and on special laboratory equipment. Tyre-casing strength is determined, e.g. by means of hydraulic-probe-machines which force domed tools into the inflated tyre until it bursts. In fatigue tests, tyres are run at constant speed, either under-inflated or overloaded or both, until a certain mileage is attained or tyres fail. Tyre properties such as speed performance, cornering ability under wet or dry conditions and rolling resistance are examined on specially instrumented machines. Plate-glass facilities incorporating plates let into a road surface over which tyred vehicles are driven allow low-speed and high-speed photography, the larger plate serving for investigating water-clearance properties of tyres travelling at speeds up to 70 m.p.h. Special machines are used for testing earthmover tyres and aircraft tyres. Testing-machine requirements according to number of tyres for simultaneous testing, size of tyre and type of test are explained. A circulating power machine using hydraulic rams to load the tyre carriages which move on rollers against a vertical drum is described. Special properties of tyres and the testing of these properties are examined with reference to static tyre, rolling tyre, steered tyre and driven tyre, rolling resistance and tyre power-loss. In "chunking" tests, the circulating power machine is used to produce tread cracking and tearing at speeds below ripple by the application of torque such as may occur when high-speed vehicles use high acceleration forces. Tyre patterns can be designed to minimise chunking; an example is given. It is concluded that, while many measurements, tests and studies are necessarily made with tyres fitted on vehicles, it is also possible to examine basic features of the dynamic action of a tyre by means of drum machines and suitable measuring links. Accuracy in tyre testing has been promoted by the development of calibration methods. (M.I.R.A.)
20.
G. V. Vedenyapin and L. P. Zyuban. Effect of soil moisture, normal pressure and velocity on the coefficient of sliding friction for steel. Pochvovedenie, No. l l , 144-147 (1971) (Ru, en) Volgogradskil Sel'skokhozyaistvennyi Institut, Ministerstvo Sel'skogo Khozyaistva, USSR. Statistical treatment of the isolated and combined effect of these three factors on the coefficient of friction between soil and steel have a multi-linear regression equation for calculating the coefficient. Analysis of paired and partial correlation coefficient showed that soil moisture had the greatest effect. (Soils and Fertilizers.)
21.
J. O. Wendeborn (Daimler-Benz AG). The present state of development of the Unimog. A.T.Z. 74 (2), 69-76. (February 1972). The first Unimog, a multi-purpose vehicle for agricultural and forestry operations, was developed in the early post-war years. Despite many changes, improvements and additions, the basic design and the sphere of action for which it was intended have persisted to this day, the aim being to permit mechanization of all operations where the tool must be brought to the worksite, and this site shifts as the work progresses. Two parallel side U-members and five cross-members made up the basic frame. Engine block, clutch, gear-box and auxiliary gear-box were elastically suspended in this frame. Front and rear axles were formed as rigid universal shaft axles. With a cylindrical coil spring and a shock-absorber in parallel for each wheel, vibration characteristics permitted high vehicle speeds and, in conjunction with features such as good ground clearance, made for outstanding crosscountry mobility. The power unit was a water-cooled 25-h.p. Mercedes-Benz Diesel engine. The transmission allowed six forward and two rearward speeds; a special drive provided power-