Recently, HILS(Hardware in the Loop Simulation) has been investigated in the field of the multibody dynamics(MBD). The fast calculation is necessary for the HILS system in order to require the real time simulation. This paper presents a fast simulation technique using the domain decomposition method. The domain decomposition method is widely used in the dynamic simulation for the mechanical system involving the hydraulic control system. This method is, however, not absolutely stable as the numerical integration. Fujikawa proposed a numerical stable solution scheme by introducing the iteration calculation. This paper applies the method to actual simulations of flexible multibody system in which the flexible linkage system and the hydraulic drive system are coupled with each other, and examines the speedup by parallel computing with the common memory in the calculation time. It is shown that using the present method in a multi-degrees-of freedom model can shorten the computing time. The present method is effective for the speedup in the calculation time by applying the dynamic simulation of the actual digging works on the hydraulic excavator.
A characteristic improvement method for dynamic simulation of a stiff mechanical system by adding mass is presented. Hydraulic systems with check valves and control valves on construction machinery exhibit piecewise-linear characteristics for hydraulic flow rate and spool stroke. The proposed improvement method involves no time delay in determining the mass by considering both eigenvalue distortion of the system and time response. This paper shows a practical application to the boom derricking system of a rough terrain crane, and demonstrates that this method is useful for dynamic simulation of hydraulic system including stiff piecewise-linear elements.
The pace of globalization of vehicles has increased in recent years, along with new requirements for steering stability and durability in rough road conditions that had not been anticipated in Japan. Accordingly, the range of physical quantities such as acceleration and force needs more in-depth examination. The shock absorber is a component that particularly determines ride comfort. A shock absorber is composed of a piston and a cylinder. In general, when the piston speed is low, the damping force is generated by fluid passing through a fixed orifice. When the speed is higher, a valve opens in addition to the fixed orifice. This suppresses the damping force of the fluid flow, thus maintaining stability and improving ride comfort. Therefore, the damping characteristics of the shock absorber have a large non linearity. In addition, when the excitation frequency increases, hysteresis appears between the piston speed and the damping force. The parameters such as the loss factor and dynamic stiffness in the frequency domain can be used for steady-state response analysis. However for transient response analysis of bumps and rough road conditions that affect the ride comfort, those characteristics must be expressed in the time domain. Therefore, in this study, measurement results are used to build a physical model composed of frequency-independent elements as simple as possible. This allows a time domain analysis to be done for a shock absorber with non-linearities of complex structure and frequency dependence. The Maxwell model is used to take into account the non-linearity of damping force and represents the hysteresis and frequency dependence that can be found in the actual measurement results. Our model can provide a non-linearity in the damping characteristics of the dashpot of the Maxwell model. In addition, the effectiveness of the proposed method is verified by experimental analysis of the shock absorber only and the whole vehicle.
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