Modeling, simulation and analysis of a simple load sense system

摘要

Hydraulic load-sensing (LS) control systems have found increased applications in open circuit hydraulics work function systems for off-highway mobile equipment. Providing only the needed power requirements in a work function generates energy savings, thus increasing machine productivity and reducing cost of fuel. A conventional LS system is composed of a variable displacement pump with feedback control, other hydraulic components and the load. The feedback control strategy is realized by monitoring the pressure differential between the pump outlet and the LS signal. This regulates servo pressure to move the swash plate angle to the commanded position to provide only the required flow. However, it is well known in the mobile hydraulics industry that the nature of the dynamic response of a LS system is oscillatory. The degree of mismatch between the hydraulic power system and load could lead to instability. This instability causes intense oscillation of some components in the machine and is often accompanied by high frequency noise. This results in operator discomfort and, more importantly, is a safety concern. In a work function application, for example, a paving machine, there are reports of LS system instability. This paper investigates a generic open circuit hydraulics power system of a work function in a paver machine. This circuit was modeled and simulations were conducted using the Matlab Simhydraulics. The time series simulation of system pressure oscillation was reconstructed using the phase portrait [2] that showed a limit cycle oscillation. Fourier Transform analysis was conducted that showed a subharmonic frequency f1/3. The existence of a limit cycle and sub-harmonic frequency indicated a highly nonlinear dynamics of the system. Mathematical analysis based on a research finding that was reportedly recently [1] was applied. One solution is presented that attenuated the amplitude of the oscillation.