Research On Dynamic Characteristics Of Cutting Wheel System Of Trench Cutter

Trench cutter is a type of construction equipment dedicated for the underground diaphragm walls. The rapid development of underground engineering in China has resulted in a large market demand for trench cutters. However, at present, China is unable to develop and produce trench cutters with proprietary intellectual property rights. Therefore, the localization of trench cutter development has become an important issue desiderated to be solved.The working device of trench cutters, namely the cutting wheel system, is the most important module of the equipment. The dimension of the groove limits the design, which makes the transmission system unable to endure heavy loading and random and impactive external excitations produced by geotechnical sections in working conditions. Therefore, a vibration isolation system is necessary between cutters and transmission system to form a loading route from geotechnical sections to cutters, vibration isolation, transmission, and drive. In this route, the rubber vibration isolation system and the multistage planetary gear train are the two most important subsystems. Their dynamic characteristics have decisive influences on the realization of the cutting function and the equipment’s working performances such as reliability, stability, and life expectancy. Therefore, researching and improving the dynamic characteristics of the cutting wheel system under complex geotechnical boundary conditions is of great significance.Through theoretical modeling, numerical analysis, and experimental measurement, the dynamic characteristics of the cutting wheel system of trench cutters, including the rubber vibration isolation system and the multistage planetary gear train, are studied systematically and penetratingly in this thesis. The main contents and conclusions are as follows:1. The mechanical properties of isotropic natural rubber (NR60) and anisotropic short fiber-reinforced rubber (FR75), two kinds of rubber materials that can be used in the cutting wheel vibration isolation system of trench cutters are studied. Based on the calculation methods of static and dynamic mechanical properties for material NR60, the one-dimensional hyperelastic-viscoelastic-elastoplastic mechanical model of material FR75is built. By fitting experimental data, parameters of such two material models are identified, and the two models are verified, which provides the material parameters for analyzing the vibration and shock isolation properties of the cutting wheel vibration isolation system under its working conditions.2. The dynamic design process of the cutting wheel rubber vibration isolation system is planed. Following this process, the external excitations of the cutting wheel in its working conditions are analyzed. Considering the limitation of the groove and the transmission space, the design requirements, structure, and size boundary conditions of the vibration isolation system are identified. Subsequently, the finite elements model is established, the configurations of anisotropy and comprehensive mechanical properties of rubber materials are achieved, the dynamic responses of the system are solved and analyzed. Results show that both material NR60and FR75satisfy the damping requirement of the system. However, in heavy-loaded systems, material FR75is remarkably superior in strength, thus more suitable as the damping material. With the increase in rubber thickness, the circumferential damping coefficient decreases, and the shock attenuation time extends. Comparisons show that the overall performance of the system is optimal when the rubber thickness is15mm. Increasing rubber thickness axially is available for improving the stress status of the rubber material. Consequently, the dynamic design of the vibration isolation system meets the design requirements.3. The transmission scheme of the cutting wheel transmission system is carried out by analyzing design requirements and constraint conditions of the system. The purely torsional dynamic model for a multistage planetary gear train of the cutting wheel is established by lumped mass method, considering time-varying meshing stiffness, error excitations, as well as piece-wise backlash nonlinearities. The equations of motion in general coordinates for this model are deduced using the Lagrange equation. This model and equations of motion can be applied to multistage planetary gear train with diverse stages, number of planet gears, and power flows. This provides a theoretical model for exploring the nonlinear dynamic characteristics of the cutting wheel transmission system.4. Based on the purely torsional dynamic model of the cutting wheel transmission system, the nonlinear dynamic response is solved by using the Gill integration method. With the global bifurcation diagrams, the influence of excitation frequency, mesh damping coefficient, and backlash on system bifurcation and chaos property are analyzed. The ways of motion state changes into chaos are explored. Results show that the amplitude of vibration response in chaotic motion is considerably larger than that in stable periodic motion. To restrain chaos, the input speed of the first-stage planetary gear train should avoid the range255r/min-310r/min,380r/min-390r/min, and570r/min-615r/min. With the increase in mesh damping coefficient, the non-periodical motion and the amplitude of dynamic response decrease. Reduction of the backlash is beneficial to the improvement of system dynamic characteristics.5. Based on the purely torsional dynamic model of the cutting wheel transmission system, the translational-torsional coupled dynamic model is established by additionally considering the transverse vibration displacements of each central element. Based on this model, the dynamic load sharing factor of the system are solved, and the influence of floating component form, number of planet gears, and error type on the dynamic load sharing factor are analyzed. Results show that the increase in load and floating of one or more central elements can improve the load sharing performance. The load sharing performance is optimal when floating both the sun gear and the carrier for the cutting wheel transmission system. When the static strength requirements are satisfied, decreasing the number of planet gears can improve the load sharing performance. The manufacturing error has the greatest influence on the load sharing performance, compared with the assembling error and the tooth thickness deviation. The abovementioned results have been well validated in the practical design of prototype to improve the system’s load sharing performance.