Influence of Novel Redirector with Bypass Damping on the Performance of Load-Sensing Steering System

Load-sensing steering systems for articulated loaders are prone to large pressure shocks and oscillations during steering operations,affecting the system stability.An optimized structure of the redirector with bypass damping is proposed to improve this phenomenon.In this structure,orifices and throttle grooves are added to the traditional redirector.To control the steering load and working conditions,the steering load of the loader is replaced by a pressure regulating valve.Simulation and experimental results reveal that the redirector with bypass damping has better load-sensing characteristics than the traditional redirector.The peak output pressure shock caused by the load unit step signal decreases from 6.50 to 5.64 MPa,which means the pressure oscillation of the hydraulic system is reduced by 13.4%.The pressure fluctuation time can be reduced from 2.09 to 1.6 s,with a decrease rate of 23.4%.The output pressure oscillation decays swiftly,and the smoothness of the steering operation is improved significantly.

Improving the Performance of an Electro-Hydraulic Load-Sensing Proportional Control Valve

The paper deals with the simulation and the experimental verification of the hydraulic behavior of an electro-hydraulic load-sensing proportional control valve. An innovative CAE （computer aided engineering） methodology, developed combining CFD （computational fluid dynamics） simulations with lumped and distributed numerical modeling, is firstly introduced and tailored by comparing the numerical results with measurements coming from an experimental campaign performed for a wide range of pressure loads and metered flow rates. Then, both the reliability and the limits of the numerical approach are highlighted through a detailed numerical vs. experimental comparison, involving the pressure of the main hydraulic lines, the flow rate through the first section and the local compensator displacement. Finally, the CAE methodology has been applied for assessing the internal ducts hydraulic permeability and the local compensator spring pre-load influence on the control valve metering curves. At the end of this analysis, an optimized design configuration, featuring a maximum controlled volumetric flow rate increased of more than 25%, has been proposed.

EXPERIMENTAL STUDY OF LOAD SENSING SYSTEM WITH LONG PIPES

A test platform is established as per the practical working condition ofelevating platform fire truck. The influences of pipes and load on dynamic characteristics ofload-sensing system are studied by series of step response experiments. Experimental results showthat the feedback pipe makes the most important influence on the dynamic response speed ofload-sensing system. Its internal diameter should be optimized for given length of pipe. On theother hand, the stability of load-sensing pump is improved as the length of input pipe increases ina certain range. The influence of input pipe on the dynamic response speed is caused mainly by thepressure-wave travel time in the input pipe.

Mechanical-Hydraulic Co-Simulation of Full Hydraulic Articulated Steering System

With the development and improvement of the hydraulic steering system,the articulated steering system became the research focus of numerous domestic and foreign scholars.The full hydraulic steering system with a compact structure and ease of operation,is widely used in articulated steering mode.Furthermore,its performance can directly impact the steering sensitivity and stability.This paper studies the working principle and actual structure of the priority valve and the steering control valve,which are very important.By setting up a mathematic model,the system’s load-sensing characteristics and the impact of steering control valve bypass throttle damping on steering stability can be analyzed.The Hydraulic Components Design(HCD)model was established for the hydraulic part of this system.It is proved that the model can reflect the system’s actual properties by comparing simulation and experimental results.The dynamic model is based on its actual prototype parameters by taking the tire and ground forces into account.The steering process’s dynamic characteristics are co-simulated in the 1D+3D system model by combining AMESim and Virtual.Lab Motion.The simulation results show that the system’s load-sensing characteristics ensure the sensitivity of the steering operation,and the bypass throttle damping has significantly improved the operation stability and lowered down the cylinder pressure fluctuations.This can improve the system performance by appropriate optimization.