Modern pneumohydraulic suspension systems for high-speed tracked vehicles have fairly typical versions of kinematic schemes, implying the installation of an elastic-damping element directly on the suspension housing (inside or outside). This solution is structurally relatively simple, and it is understood that it allows to reduce the values of unsprung masses. Other options, with placement of elastic and damping elements inside the guide elements (balancers), did not “take root” due to the greater structural complexity of both elastic or damping element and the suspension guide element. In addition to the structural complexity of implementation, such a solution increases the values of unsprung masses and, most importantly, complicates the organization of the cooling system. The protruding elements of the chassis are clogged with soil, snow (mud) when driving, which acts as a heat insulator. Nevertheless, with modern technological capabilities, these difficulties can be over-come to a certain extent, in whole or in part. However, despite the above disadvantages, this solution also has important advantages: the sus-pension does not take up space in the reserved volume, but is completely inside the tracked bypass, which allows using the housing volume more efficiently, and, in addition, providing the most suc-cessful bottom design for protection from mine detonation (in the case of a heavy tank “Object 279”, this also made it possible to significantly increase the cross-country ability). This article provides an overview of Soviet prototypes of heavy and rocket tanks, which suspen-sion system was implemented in the guide element. The article also presents a method for determin-ing the power and kinematic transfer functions for these suspension options, analyzes the design implementations and shows that the characteristics of the elastic elements of experimental vehicles meet modern requirements for the suspensions of high-speed tracked vehicles.

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.

When developing new suspensions for tracked and wheeled vehicles, as well as in the so-called reverse engineering of existing structures (including in the educational process of training person-nel), it is necessary to solve the problem of finding the elastic characteristics of the suspension. In the first case, it is necessary to ensure the fulfillment of the specified tactical and technical require-ments, in the second - to restore the form of characteristics according to a known design. Both of these tasks are greatly complicated in the absence of precise and universal analytical dependencies suitable for determining the characteristics of elastic suspension elements of various design imple-mentations. The experience of interaction with some factories shows that designers, not being able to qualitatively calculate the elastic characteristics, use the method of selection and analogy, when for a new vehicle they use the suspension as on the old one, scaling it in size in order to approxi-mately keep the values of working pressures. The numerous bench tests are carried out, which results are used for selecting required charging volume and pressure. Suspensions with backpressure cause particular difficulty, since not only the final characteristic, but also the performance of the entire unit depends on the combination of volumes and pressures of the two chambers, which work in antiphase: when one is loaded, the other is unloaded, and vice versa. Using analytical dependencies will reduce the time spent on design, to parameterize, to a certain extent, the suspension kinematics, to obtain the values of the equivalent suspension stiffness, and also to be able to develop the characteristics of the model range of pneumohydraulic springs for vehicles of various weight cate-gories. This article presents a technique for the analytical determination of the characteristics of pneu-mohydraulic springs of various designs. The options include both actually used in modern and his-torical technology (in particular, on BMD-1, 2, 3, 4; GM-352; Ural Typhoon; Object 775, etc.), and obtained by combining various structural elements, which implementation can be useful in the edu-cational process in training personnel. The dependences presented in the article make it possible to obtain static and dynamic elastic characteristics at various polytropic indices and are suitable for the design of suspensions for wheeled and tracked vehicles for various purposes.

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.