Research on the rotational inertia of radial piston pump and the optimization method of the pump parameters
This paper aims to propose a method of optimizing the structure of radial piston pump from the aspect of reducing the rotational inertia. A modeling method based on basic dimensions and scale factors is developed. By using this method, three different types of radial piston pumps are studied. And the relative rotational inertia coefficient is adopted to evaluate the difference among them. Further study states that the relative rotational inertia coefficient changes along with the eccentricity ratio and the thickening factor. Finally a criterion is obtained, which could be used to optimize the structure and the dimensions of radial piston pumps.
Measurement of Time-varying Moment of Inertia Based on Hilbert Transform
In order to measure the time-varying moment of inertia,the measurement model based on torsion pendulum is established and the calculation method of moment of inertia based on Hilbert transform is proposed.According to the principle of analytical dynamics,the differential equation of the torsion pendulum is presented using the second Lagrange equation.The analytic signal is calculated by the Hilbert transform of the angular displacement signal.The instantaneous undamped natural frequency is computed by the instantaneous angular frequency and the envelope signal.The time-varying moment of inertia is calculated by the instantaneous undamped natural frequency of the torsion pendulum.The torsion pendulum system based on air-turntable is used to measure the time-varying moment of inertia of the test object.With the introduction of the air-turntable,the influence of friction force can be reduced.The experimental result shows that the relative measurement error of the time-varying moment of inertia is less than 0.5%,which indicates the validity of the measurement method.
Speed control of an overcentered variable-displacement hydraulic motor with a load-torque observer
Abstract This study deals with the speed control of an overcentered variable-displacement hydraulic motor on a constant pressure network, which is noted for its high system efficiency, fast dynamic response and energy recovery capability. To obtain robust speed control despite torque disturbances and variations in system parameters, the load torque is estimated by an observer based on a mathematical model and compensated for by a feedforward loop. It is shown by experiment that robust speed control may be obtained with the proposed controller, in spite of torque disturbances and variations in system parameters. The experimental data agree fairly well with the theoretical results. The frequency and time responses of a simplified first-order model for the regulating piston, driven by a servo valve, are in good agreement with those of an exact fifth-order model. It is also shown that the proposed controller gives better speed control and response characteristics than the conventional cascade PI controller.