Influence of dynamic loads created by the weight of the power unit on the structural elements of buses.
Students Name: Karmazyn Andrii Myroslavovych
Qualification Level: magister
Speciality: Motor Vehicle Transport
Institute: Institute of Mechanical Engineering and Transport
Mode of Study: full
Academic Year: 2020-2021 н.р.
Language of Defence: ukrainian
Abstract: Karmazyn A.M. Influence of the dynamic loadings created by weight of the power unit on elements of a design of buses. // Master’s qualification work. - NU "Lviv Polytechnic", Department of "Operation and repair of automotive equipment". - Lviv, 2020. Examples of the layout of power units of buses and features of the layout of auxiliary units in the engine compartments of buses are given. When the auxiliary units are located on the frame, dynamic loads are applied to their shafts through the belt drive, caused by the movements of the power unit in the event of dynamic loads when moving road bumps, turns, structural oscillations of the body frame and so on. For the same reason, the loads on the shafts of auxiliary units installed outside the engine on the body frame are accompanied by significant vibration accelerations. The general problems of dynamic loadings are covered. Auxiliary units of cars are driven from a pulley of a cranked shaft of the engine. The example of the generator shows mathematical models of the kinematic connection of the power unit and auxiliary units. Mathematical models of oscillations of the power unit under the action of nonstationary loads are given. Calculation of the movement of the power unit under the action of non-stationary loads requires a large amount of initial data and time-consuming calculations for complex analytical dependencies. Therefore, in each case, it is advisable to have statistics on the movement of the power unit under the action of non-stationary loads. These statistics can only be obtained experimentally under appropriate operating conditions for a specific vehicle model. The tests were carried out on a medium-sized city bus (LAZ-1414 prototype). A generator mounted on the bus frame was adopted as an auxiliary unit. The movement of the power unit relative to the generator shaft was recorded using a recorder mounted on the engine near the crankshaft pulley. The recorder recorded the movement of the power unit relative to the body under the action of non-stationary forces. The marks of the recorder in the process of testing formed a plot of the distribution of displacements of the power unit. On the graph of movements of the power unit the maximum movement which is equal 8,5 mm in the cross direction, in the party opposite to the generator. The calculated amplitudes of the load change are: at a transverse movement of 3.5 mm, the shaft overload is 76 N; at the largest transverse displacement equal to 3.5 mm, the overload of the shaft is 174 N. The shaft of the generator, with two belts in the transmission, the initial load from the side of the belt transmission 342.8 N. Experimental studies of the generator shaft load during the bus movement were carried out. The largest amplitudes of the oscillating load are characteristic of the modes of acceleration, right turn and driving through road bumps. The maximum values of dynamic loads are: 90 N in rectilinear motion in acceleration on the rise; 135 N when turning; 175 N when moving through road bumps. These data correlate satisfactorily with the value of the maximum loads obtained by the calculation method, where the maximum value of dynamic loads is equal to 174 N. With elastic mounting, the amplitudes of the dynamic load are significantly reduced.