BACKGROUND: Trucks, as a rule, have a significate difference between the kerb and gross weights. Usual spring or leaf suspensions do not allow to have acceptable values of static running and suspension stiffness at different machine loading, and pneumatic elastic elements, despite their relative simplicity, are mainly implemented only on overseas technology samples, and designers do not pay attention to pneumatic elastic elements with counterpressure. One of determinants of truck users is the acceptable vibration loading of the drivers seat. Trucks with a carrying capacity comparable or even overestimated to their kerb weight, when they move without cargo on public roads, especially with a dirt surface, have significant levels of vibration acceleration at using the metal elastic. AIMS: The purpose of the present work is to reduce the vibration loading of the drivers seat due to rational choice of parameters of the cushioning system with pneumatic elastic elements with backpressure, that ensures the non-zero static travel and saticfactory stiffness of suspension in the kerb and loaded state. METHODS: Using the regorous mathematical tools of Mechanics, Pneumatics and Thermodinamics, scientific-based theoretical prerequisites as well confirm the validity and reliability of the presented dependencies for characteristics calculation, conclusions and recommendations. RESULTS: According to the method developed and proposed in this article, effective characteristics of the pneumatic elastic elements with a single-level stiffness and backpressure for a KAMAZ-53215 Selkhoznik truck were obtained. At the kerb weight, the static stroke of the front and rear suspensions is approximately 0.06 m; at a gross weight it is of 0.12 m and 0.24 m, respectively. The period of normal vertical vibrations decrease by 25% versus a gross vehicle weight and by 31% at absence of backpressure, however, it occurs in the allowable range. CONCLUSIONS: The proposed method allows to determine the base design parameters of the pneumatic elasticity of the suspension elements of wheeled vehicles, providing an acceptable periods for a normal vertical oscillations of the cushoining body with maintaining the non-zero static stroke to a large weight range.

BACKGROUND: The information about application of hydraulic springs in suspension systems of tanks and self-propelled artillery weapons may be found in domestic scientific and nonfiction literature. In addition, machines, which prototypes were equipped with this type of suspension, are known. For instance, possibility of hydraulic suspension implementation was proven on the T-34 tank prorotype, whereas application of this type of suspension with heavy tanks gave the most prospectivity. Complication of sealing build-up with sufficient life span, development of technologies of metal springs strengthening and shutdown of heavy tanks development did not allowed hydraulic suspensions to become widespread. At present, they are not used at all, whereas methods of analytical calculation are not in public access, despite of the interest of a group of scientists. AIMS: Development of the method of determination of main parameters of suspensions with hydraulic springs and analysis of properties of the T-34-76 Soviet middle tank prototype hydraulic suspension from the point of modern theory of nonlinear suspension systems. METHODS: Justification and confidence of given dependencies for properties calculation, conclusions and recommendations are confirmed with application of strict mathematical apparatus of mechanics, hydraulics and thermodynamics as well as scientifically justified theoretical backgrounds. RESULTS: Historic data on liquids compressibility researches, method of analytical determination of main properties of hydraulic springs with various design schemes, allowing restoring of properties of suspensions of existing tracked vehicles, synthesizing properties of other suspensions and, moreover, estimating reasonability of properties of suspension with hydraulic springs, are presented in the article. According to the method, proposed in the article, properties of the hydraulic spring from the T-34-76 Soviet middle tank prototype, equipped with hydraulic suspension, were restored and analyzed. In addition, suspension properties for the same vehicle were synthesized and used for a comparative analysis. CONCLUSIONS: The information, presented in the article, is helpful for research engineers, interested in study of elastic behavior of liquids in case of their application in suspension systems, whereas the proposed method, allowing synthesis of reasonable properties of hydraulic springs, gives an opportunity to study the ride comfort of tank propotypes, equipped with hydraulic suspension, with a good quality and, moreover, to synthesize hydraulic springs properties according to the demands, given to a design engineer.

BACKGROUND: The issues of choosing reasonable properties for suspension system of wheeled vehicles, including vehicles for agricultural purposes, still remain relevant, especially for the vehicles, which load capacity is comparable to their curb mass. Significant difference between static loads, acting in suspension under the curb and total masses of a vehicle, is a consequence of high load capacity. Two or three times difference is possible (depending on axles load distribution), whereas 70% to 80% of mass of trailing load is on rear axles. Use of convenient suspension systems with metal springs is not able to ensure demanded nonlinearity of properties, where non-zero static wheel travel under the curb mass is kept with reasonable value of period of vertical eigenmodes for curb-massed and total-massed vehicle as well as with dynamic factor value. Air springs with two pressure stages are more advanced solution, as they allow choosing stiffness for small and large wheel travel by means of operation of different pressure stages, which volumes are conditioned by differents stiffnesses in area of static displacement. AIMS: The aim of the study, which results are given in this paper, is to develop the method of determination of main design parameters and characteristics of air springs with two pressure stages (stiffnesses) and counterpressure, applicable for ensuring non-zero static wheel travel of curb-massed vehicles with keeping the given value of dynamic factor. METHODS: The analytical analysis methods are used. RESULTS: An example of implementation of the developed method for the KamAZ-53215 Selhoznik truck is given as the study result. CONCLUSIONS: The dependencies, presented in the paper, make possible to determine main design parameters of uncontrolled air suspensions with two pressure stages (and stiffnesses) and counterpressure for wheeled vehicles, which give an opportunity to ensure given values of static wheel travel and dynamic factor and, in addition, provide insignificant increase of stiffness in comparison to air suspensions without counterpressure.