卷 83, 编号 12 (2016)

Depletion of oil fields and environmental deterioration demand the search of alternative sources of energy. Actuality of the article is driven by the need for increased use of alternative fuels in internal combustion engines. As advanced alternative fuels for diesel engines, the article considers fuels extracted from vegetable oils and animal fatty substances. These fuels are produced from renewable feedstocks and characterized by good environmental qualities. The advantages of use of vegetable origin fuels as motor fuel are shown. One of the problems of use of fuels based on vegetable oils is their increased viscosity. The viscosity characteristics of mixtures of petroleum diesel fuel and vegetable oils are investigated. Various vegetable oils, namely rapeseed oil, sunflower oil, soybean oil, corn oil, mustard oil, as well as oil extracted from the Pongamia Pinnata plant are considered. A method of approximation of viscosity characteristics of mixed biofuels in the form of algebraic polynomial is suggested. Experimental data on viscosity of these oils and their mixtures with petroleum diesel fuel are used in calculation researches. Approximating dependences of these experimental data with the use of the familiar logarithmic method and a suggested algebraic method are obtained. The analysis of approximation accuracy of experimental data on viscosity of biofuel is carried out with the use of mentioned methods. Parameters of the D-245.12S diesel engine operating on mixtures of rapeseed and sunflower oils with petroleum diesel fuel are presented. The effectiveness of the suggested method of approximation of viscosity characteristics of petroleum diesel fuel and vegetable oils mixtures is shown. The method is characterized by high accuracy and can be used for the approximation of viscosity characteristics of various fuel mixtures.

There are various ways to control the value of normal responses of surface under tractor movers. One of them is to regulate the height of hitch point and the angle of drawbar power. The advantage of this method is that the necessary conditions are created for the automatic control of position of the center of pressure, which ensures the optimization of technical and economic indices of machine-tractor unit operation. To verify this method, it is necessary to carry out the tests determining the parameters of tractor operation, including the traction coefficient of driving wheels. Two variants of its determination are proposed: the towing of tractor with locked driving wheels and the drawbar tests. In both cases, the tractive effort at drawbar is applied at an angle. As a result of drawbar tests, an experimental tractive characteristic of tractor will also be obtained. In preliminary calculations, the weight distribution along the axes is determined depending on the value and the angle of drawbar power. The weight change on the rear axle is more intense than on the front one. It is necessary to use ballast weights on the tractor rear to compensate its unloading. As for tractors and agricultural implements under design, it is necessary to choose the rational component layout and design taking into account the weight redistribution during aggregation. The pre-calculated verification confirms the possibility of use of tractor towing in reverse gear with locked wheels to determine the traction coefficient of driving wheels. The applying of drawbar power at an angle allows to increase or decrease the responses of bearing surface on tractor movers during a particular operation and therefore has an advantage over conventional ballasting at the front of tractor. In combination with the ability to change the back tipping moment, this allows to optimize the traction characteristics of tractors.

Screen separators are widely used in grain-cleaning machines. The separation occurs in the process of movement of grain over the surface of screen. The relative movement of grain is provided by different devices with various modes of motion. The most common is a vibrating sieve pan (screener), in which the grain is moved over screen by inertia. Screener has a high efficiency, but the alternating dynamic loads cause the metal fatigue and reduce machine reliability. The grain-cleaning separators with cylindrical screens operate without dynamic loads and have a simple design. They are less sensitive to grain moisture and impurity. But the separation process uses only 1/4-1/6 of the cylindrical screen surface. This problem reduces the throughput and limits the scope of application of cylindrical screens. The proportion of useful surface area can be increased by simultaneous use of two cylindrical screens. They are located one inside the other and rotate in opposite directions. The grain enters on the inner surface of the inner screen and forms a movable layer that moves in the axial direction. During the movement process, the grain passes through perforations, while the large impurities fall down from the screen. The grain having passed through the perforations of the inner screen reaches the section of the outer screen that is clear of movable grain layer. The rational conditions of simultaneous operation of screens are determined, under them the separation process on the outer screen starts immediately after the grain had passed through the perforations of the inner screen. Due to that the separation area is increased by 34-57%.

To ensure the operating efficiency of plowing unit it is required to comply with the specified speed regime of motion and optimal loading of tractor engine. Difference of tractive resistance of soil in different fields creates a situation where it is difficult to select the optimal loading of tractor engine providing constant speed. For example, for the fields with a specific resistance equal to 20 000 and 30 000 newton per square meter, tools with grasp width equal to 2.4 and 1.9 meters respectively are required. The aim of the paper is to find a design scheme of variable width tillage tool, which provides the necessary reliability and reduces the complexity of grasp width regulation. The main research method in achieving this goal is the rational use of condition of external force loading of working organs of tillage tool. The condition of external loading of working organs is investigated. The principal vector and principal moment are accepted as external load equivalents. The conditional center of external soil pressure on working organ is determined by finding the points of intersection of the axis of thrust-and-torque combination with the working surface of plow body. As a result of study, the design scheme of tillage tool that provides the necessary reliability and reduces the complexity of grasp width regulation is proposed. The value of external cutting forces in the obtained scheme is used as a sensor of specific resistance of soil in a specified field and provides the adjustment of grasp width of tool under optimal loading of tractor engine.

The unified system of tolerances and fits is a very important system that provides internationally the interchangeability of products, and is widely used in machine-building and instrument-making industries, in repair and maintenance of machinery and in other fields. The new standard 286-1:2010 of International Organization for Standardization provides an improved international system of tolerances on linear dimensions containing series of tolerances and deviations. It contains the clear indication that the system refers to the two types of dimensional features, namely a cylinder and two parallel planes. In the older version of the standard 286-1:88, to interpret the part feature dimension the rule of outer limits was applied a priori, however, in the international standard 14405-1:2010, the interpretation of dimension on the double-point measurement was established. It means that the accuracy of form deviation no longer depends on the dimension accuracy and the requirements to the form should be established separately. Now, in many cases, normalization only of the diameter tolerance is not enough to control the design and performance characteristics of the joint. Theoretically, as provided by geometrical product specifications, it is necessary to establish the requirements and determine the outer limit; as well as in some cases, it is necessary to normalize the requirements for tolerances of form, waviness and surface roughness. The article describes the changes in the terminology from the perspective of the theory of precision and interchangeability. It is concluded that all minor changes in the terms, concepts and regulations do not affect the overall construction of the unified system of tolerances and fits, but clarification of a number of old terms and introduction of new concepts take place. Most significant is the arising of new link between the standards on geometric characteristics of products based on the principle of the general construction of models of precision and common terminology. Of particular note is a bad translation of English version into Russian language. The scientists working in the theory of precision and interchangeability were not involved in the translation. Most of the newly introduced terms could be interpreted more technically-oriented and more understandable.