T. Matyja

Coil springs in passenger cars – general theoretical principles and structural requirements

The main role of the coil springs, as any kind of elastic elements is shock absorption caused by the movement of the so called unsprung masses (wheels, brakes, suspension components) on the uneven ground. This is to ensure not only driving comfort, but also protect the car from damage. The article presents the principles of strength calculations for coil springs used in the suspension of contemporary cars. Modern technological and structural solutions in contemporary cars are reflected also in the construction and manufacture of coil springs. A proper construction and the selection of parameters influence the strength properties, the weight, durability and reliability as well as the selection of an appropriate production method. An improper preparation of Finite Element Method calculation models consequently leads to wrong results. It is particularly difficult to interpret the results and to find an error if we do not have a comparative calculation base (such as results of fatigue tests, analytical strength calculations). Coil springs with linear and progressive characteristics were taken into consideration. In article was conducted a comprehensive calculation of these springs (analytically and FEM using) in order to show the differences and problems in the construction process. A proper selection of springs, that is also taking strength parameters into consideration, has a fundamental effect on correct functioning of the suspension of motor vehicles.

Simulation Studies of the Effect of Shaft's Nonlinear Flexural Stiffness Parameters for Critical States of Rotating Power Transmission Systems

The paper presents simulation studies, performed using Simulink, the impact of nonlinear flexural stiffness of shafts for critical speed range and amplitude of vibration. The tests were performed on the selected model of a rotating machine, consisting of a drive, two torsional vibration dampers, shaft with mounted on it two rigid rotors (discs), supported on a three self-aligning roller bearings and mechanical power receiver (brake). The machine startup and braking with crossing the critical states was simulated using specialized Simulink library, which was developed by authors for analysis of transient states in rotating machines and flexural-torsional couplings. In accordance with the concept of modeling adopted by the authors, rotating system is divided into inertial rigid elements (rotors, bearings, clutches, etc..) and compliance elements (parts of the shaft). The main component of the currently developed library is block modeling rigid rotor with 6 degrees of freedom and with the static and dynamic unbalance. By assumption the library is a modular, expandable and allows modeling the systems of any configuration. The goal of the simulation was to verify how nonlinear flexural stiffness of shaft influences the values of critical speeds and the level of flexural and torsional vibrations.